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RELIABILITY AND VALIDITY OF MEASURING IMPLANT
STABILITY WITH RESONANCE FREQUENCY
ANALYSIS
Georgios Katsavrias
An Abstract Presented to the Faculty of the Graduate School
of Saint Louis University in Partial Fulfillment
of the Requirement for the Degree of
Master of Science in Dentistry
2009
Abstract
Purpose: To evaluate the reliability and validity of
resonance frequency as a method for measuring the
stability of miniscrew implants. Methods: One hundred and
twenty miniscrew implants were randomly allocated to
synthetic bone blocks of different densities: 40 low
[cortical part: 38.1pcf, cancelous part: 30.0pcf ]
density, 40 medium [cortical part: 40.6pcf, cancelous
part: 31.8pcf] density, and 40 high [cortical part:
50.1pcf, cancelous part: 31.8pcf] density. For each
implant insertion torque was measured using Mecmesin
Advanced Force and Torque Indicator©. Pullout strength was
measured using the Instron© Machine, Model 1011 and
applying a vertical force at 20mm/min until failure.
Resonance frequency was measured three times parallel and
three times perpendicular to the long axis of each bone
block. Results: Intraclass correlations based on multiple
measures of resonance frequency ranged from 0.953 to
0.992; single measure intraclass correlations ranged from
0.870 to 0.977. Analysis of variance showed significant
effects of bone density on resonance frequency; post-hoc
tests showed differences for high density only. Insertion
torque and pullout strength demonstrated statistically
significant differences between all three densities. The
two orientations showed no significant differences for
low and medium densities, the high density bone showed a
1
significant (p= .049) orientation effect. Independent of
bone density, correlations between resonance frequency,
insertion torque, and pullout strength were low and
showed no consistent pattern.
Conclusions: Resonance
frequency is a reliable measure. It is also a valid
measure that is related with bone density. As expected
for homogeneous synthetic bone, resonance frequency shows
little or no relationship with orientation, insertion
torque, or pullout strength.
2
RELIABILITY AND VALIDITY OF MEASURING IMPLANT
STABILITY WITH RESONANCE FREQUENCY
ANALYSIS
Georgios Katsavrias
A Thesis Presented to the Faculty of the Graduate School
of Saint Louis University in Partial Fulfillment
of the Requirement for the Degree of
Master of Science in Dentistry
2009
COMMITTEE IN CHARGE OF CANDIDACY:
Adjunct Professor Peter Buschang,
Advisor
Professor Rolf G. Behrents
Assistant Professor Ki Beom Kim
Assistant Professor Donald R. Oliver
i
DEDICATION
I would like to dedicate this study to my beloved
family for their constant support and encouragement
towards my goals.
To my mother, for devoting a huge amount of her
personal time to me at critical points in my carrier.
To my father, for encouraging me to try harder
throughout my education.
To my brothers Stamatis and Iasonas, for showing me
the need of persistence in life and teaching me about the
need for acceptance of diversity.
ii
ACKNOWLEDGEMENTS
Dr. Ana Claudia Melo for supporting me from the
beginning and throughout the whole study despite of all
the occurring difficulties. Without her support this
study would not be possible.
Dr. Buschang, for helping me substantially in the
design, the statistical analysis and the interpretation
of my results.
Dr. Behrents, for being available whenever I needed
his guidance and his support. For picking out for me all
the small details which would make a significant
difference in the end, encouraging me to work further.
Dr. Kim, for his time, interest and help in the
support of my thesis.
Dr. Oliver, for his insightful comments on my work,
keeping me on my toes throughout the duration of the
study and being sure that I have paid attention to every
single detail.
Dr. Araujo’s family for their substantial support
when this study was in jeopardy. Without their help this
project would surely be dropped.
Neodent for sponsoring me with their miniscrew
implants.
iii
Table of Contents
List of Tables.........................................vi
List of Figures.......................................vii
CHAPTER 1: INTRODUCTION.................................1
CHAPTER 2: LITERATURE REVIEW............................7
Miniscrew Implants in Orthodontics...........7
Uses and Importance of Miniscrew
Implants..................................7
Failure of Miniscrews.....................9
Primary and Secondary Stability..........13
Techniques to Measure Stability.............18
Invasive Methods.........................19
Histologic and Histomorphometric
Technique.............................19
Cutting Torque Resistance Analysis....22
Reverse/Removal Torque Value..........23
Insertion Torque Analysis.............24
Pullout Test..........................26
Non-Invasive.............................28
Radiographic Analysis.................28
Finite Element Analysis...............29
Percussion Test.......................32
Pulsed Oscillation Waveform...........33
Impact Hammer Method..................34
Resonance Frequency Analysis..........38
Summary.....................................49
Reference List..............................51
CHAPTER 3: JOURNAL ARTICLE.............................71
Abstract....................................71
Introduction................................72
Materials and Methods.......................76
Miniscrew Implants.......................76
Synthetic Bone...........................77
Insertion Torque.........................78
Resonance Frequency Analysis.............79
Pullout Strength.........................79
Statistical Analyses........................80
Results.....................................81
Reliability..............................81
Validity.................................82
Stabilization of Blocks..................84
Discussion..................................84
Conclusions.................................90
References..................................91
iv
Appendix I.............................................96
Appendix II...........................................102
Vita Auctoris.........................................106
v
List of Tables
Table 1: Comparison of resonance frequency (RF) of three
consecutive measurements [taken parallel (║) and
perpendicular (⊥)to the long side of the
rectangular synthetic bone block] for the high,
medium and low density bone blocks............97
Table 2: Reliabilities of resonance frequency (RF)
measures evaluated using intraclass correlations
for single measurements and Cronbach’s Alpha for
multiple measurements.........................98
Table 3: Comparison of resonance frequency (RF
measurement averages [taken parallel(║) and
perpendicular (⊥) to the long side of the
rectangular synthetic bone block] insertion
torque (IT) and the pullout strength (POS) for
the high, medium and low density bone blocks..99
Table 4: Correlations between resonance frequency (RF)
measurements [taken parallel(║) and
perpendicular (⊥)to the long side of the
rectangular synthetic bone block],insertion
torque (IT) and pullout strength (POS) for the
high, medium and low density synthetic bone
blocks.......................................100
Table 5: Comparison of resonance frequency (RF)
measurements [taken parallel (║) and
perpendicular (⊥)to the long side of the
rectangular synthetic bone block] with
the medium density block clamped and not
clamped......................................101
vi
LIST OF FIGURES
Figures 1: Miniscrew Implant and Custom PulloutBase...103
Figures 2: Synthetic bone.............................103
Figures 3: Miniscrew Implant Driver...................104
Figures 4: Resonance frequency analysis measurements..104
Figures 5: Comparisons of resonance frequencies of three
consecutive measurements...................105
Figures 6: Scatterplots...............................105
vii
Chapter 1: Introduction
One of the most important changes in the way
orthodontic treatment is executed occurred with the
introduction of miniscrew implants, by providing better
control of tooth movement. Their relative stability under
the application of substantial force makes it possible
for the orthodontist to diminish the negative
consequences of the force system being applied. Their
advantages plus their ease of use are the major reasons
that miniscrew implants have been quickly and extensively
accepted by the orthodontic community.
Their generalized usage has revealed that one of the
major problems connected with miniscrews is the degree to
which they fail.1 Research has suggested multiple factors
may be responsible for failures including mobility of the
miniscrew, overheating of the bone during drilling,
gingival inflammation, and placement in areas with nonkeratinized mucosa.
Great efforts have been made to reduce the number of
failures and increase the ability to predict the implants
most likely to fail. Very important in this regard is the
effort to increase our understanding of primary
stability. With adequate primary stability, the adjacent
bone can remodel and enhance secondary stability.
Poor
bone quality or random events like trauma can increase
1
the likelihood of necrosis, reducing effective stability
of the screw through the formation of woven bone around
the implant.2 Woven bone is poorly organised and its
structure does not provide adequate strength for
supporting loads,3 thus lowering the implants ability to
resist forces. A technique that can estimate the physical
properties of the peri-implant bone will allow us to time
loading accordingly and avoid loading when the quality of
the bone around the implant is not optimum.
One of the most established measures of stability
is insertion torque, which is the rotational force
required to insert a screw into bone. Insertion force is
transferred through the screw and becomes a compressive
force onto the adjacent bone. A minimal level of
insertion torque is required to achieve primary
stability. Excessive torque during placement can cause
damage to the adjacent bone and increases the likelyhood
of screw failure. According to Motoyoshi et al., there is
a range of acceptable insertion torques outside of which
the implants might be expected to fail.4
Another well established method for evaluating
stability is the pullout test. Pullout tests have been
used extensively to measure biomechanical holding power
and gauge the amount of stability that has been
attained.5-7
2
A relationship between insertion torque and pullout
strength has been observed and a connection with screw
stability has been established.8 Although insertion torque
has been found to correlate linearly with pullout
strength, there are some limits. Studies have shown that
excessive insertion torque can cause osseous damage and
lead to a decrease in pullout strength.9,10 As insertion
torque increases, pullout strength increases up to a
point, after which pullout strength decreases and the
likelyhood of failure increases. The decrease in pullout
strength occurs due to excessive compression that causes
trauma to the adjacent bone and increases the likelihood
of failure.11 Finally, extreme insertion torque could lead
to screw distortion or breakage and, ultimately,
failure.11 Failure is determined by the amount of movement
of the implant,12 establishing a way to measure implant
movement will offer us a way to predict failure.
Currently there is no technique available that
allows assessment of a miniscrew’s stability after
insertion and before removal. However, non-invasive
methods for measuring dental implant stability have been
available for almost a decade.13,14 The two methods most
commonly used are resonance frequency analysis (Osstell
Mentor, Göteborg, Sweden) and dampening capacity
assessment (Periotest, Modautal, Germany). A number of
studies have shown that resonance frequency analysis with
3
the Osstell device is the best method quantifying implant
stability.15,16 The Periotest instrument shows a greater
measurement error in clinical application (intraclass
correlation 0.88), thus making the Osstell a more
reliable option to be used clinically(intraclass
correlation 0.99).17
The Osstell Mentor device measures implant stability
based on the resonance frequency analysis technique. This
technique utilizes a bending test of the implant-bone
complex with a transducer applying an extremely small
bending force. A fixed lateral force is applied to the
implant and its displacement is measured, thus mimicking
the clinical loading condition, albeit of a much reduced
magnitude.18 The most recent version of the resonance
frequency analysis is wireless, where a metal rod (peg)
connected to the implant by a screw connection. The peg
has a small magnet attached to its top, which is excited
by magnetic pulses generated by a handheld computer. The
magnetic pulses, of known frequency, force the peg to
oscillate in the direction of the transducer.18 The peg
vibrates in two directions, which are approximately
perpendicular to each other. Vibration is measured in the
directions that produces the highest and lowest resonance
frequencies.18 Thus, two implant stability values are
provided, one high and one low. In this way,
4
circumferential estimation of the implants stability can
be made.18
This method has proven useful for dental implants in
research and clinical applications. The dental implant
literature has shown that Osstell measurements correlate
with bone-to-implant contact,19 bone density measured from
CT scans,20,21 and insertion torque.20,22 Osstell
measurements have also helped in establishing individual
healing curves of implants after load initiation.21,23-26
Sequential measurements have shown that the Osstell
device can be used to quantify ongoing osseointegration.27
Osstell measurements are most influenced by changes in
the stiffness of alveolar bone.28
Despite of the fact that the Osstell device has been
used extensively with dental implants, it has not yet
been used with miniscrew implants. Until recently, it was
not possible to mount a peg on miniscrews.
The purpose of this study is to investigate if the
resonance frequency analysis can be used to evaluate the
stability (primary and secondary) of orthodontic
implants. To validate the Osstell Mentor device, the
measurements will be correlated with insertion torque and
pullout strength (from mini implants that are placed in
synthetic bone with known and homogenous density). The
primary objective of this study is to establish the
reliability of the Osstell used with miniscrew implants,
5
by repeating the Osstell measurements multiple times, the
reliability of the technique will be tested. This novel,
non-invasive, measurement technique could prove useful in
helping orthodontists better understand the healing
procedures of bone around miniscrews.
6
Chapter 2:Literature Review
Miniscrew Implants in Orthodontics
Uses and Importance of Miniscrew Implants
Maintaining anchorage has been a challenge in
orthodontics. In fact, being able to achieve adequate
anchorage during treatment is an important determinant of
the treatment outcome.29 According to the third law of
Newton, teeth connected by an active appliance are
subjected to equal and opposite forces. It is, however,
not desirable in most cases to perform equal and opposite
tooth movements. Various methods have been introduced to
maintain anchorage. These methods include the application
of Tweed mechanics,30 segmented mechanics,31 bioprogressive
technique,32 bi-dimensional technique,33 archwires with
differential sizes and shapes, uprighting springs,34
intra-arch elastics and headgears with various vectors of
action.
The last two methods are the approaches most
commonly used, but they depend heavily on patient
compliance.35 In noncompliant patients, there may be
unpredictable tooth movements, which could lead to
unfavorable treatment results.
Miniscrew implants are becoming increasingly popular
in orthodontics,36,37 because they provide skeletal
7
anchorage for orthodontic tooth movements.38-42 The
possibility of moving miniscrews is minimal due to the
absence of a periodontal ligament. Animal and human
studies have provided the basis for clinical use.43-45
Creekmore and Eklund46 first suggested that such screws
could be used for orthodontic applications. The
biomechanical principles of this approach are very
similar to those applied in traditional anchorage, making
their utilization in treatment easier. However, the
possibility of using a stable anchorage point has
extended the treatment possibilities for orthodontic
patients. For example, miniscrews make treatment possible
when a significant number of teeth are missing, when
existing bone support is inadequate, and in adults or
some adolescent patients, who refuse to wear headgears.
In the past, when miniscrews were not available, if
the patient had simultaneous prosthetic implant
restorations dental implants would be utilized for
orthodontic purposes. When dental implants were used in
such a way a healing period was considered necessary.47-53
The time period for healing was based upon Branemark’s
suggestion that endosseous dental implants should remain
unloaded for three months in the mandible and for six
months in the maxilla in order for osseointegration to
occur.54 The same trend, of delayed loading, continued in
the first studies published for miniscrew impants. Those
8
older clinical studies using miniscrews applied forces
ranging from 30 gm-250 gm, with a delay in the
application of forces ranging from 4 to 36 weeks. The
authors believed that longer healing periods were
necessary to ensure longterm success.48,55,56 Later studies
showed that shorter healing periods did not compromise
implant stability.38,53,57,58 Presently, most miniscrew
implants are loaded immediately. According to Buchter et
al., miniscrew implants can be loaded immediately without
impairing their stability if moments of forces are
maintained below 900 cN·mm .59
Failure of Miniscrews
The number of miniscrew failures plays a significant
role in the orthodontists’ decision to utilize them in
everyday practice. The literature reports success rate
for miniscrews ranging from 83.9% to 91.6%.4,60,61
Due to the absence of studies about the influence of
systemic factors upon the failure rate of miniscrew
implants some conclusions can be made from the dental
implant literature. Research with dental implants have
shown that failures are due to a number of host factors
that can interfere with the healing process.62 These
factors include: osteoporosis, uncontrolled diabetes,
smoking, and parafunctional habits (this is more
9
problematic with dental implants that support crowns in
bruxist patients). Another group of factors that can
cause failures in miniscrew implants relate to the
surgical procedures or techniques used at the time of the
placement. For example, Kang et al. noted that the
failure rate for miniscrews that contacted the roots was
79.2%, compared to an 8.3% failure rate in alveolar
bone.63 In a recent survey by Buschang and coworkers it
was found that practitioners who experienced
significantly more failures in miniscrews did not measure
insertion torque nor the forces applied to the implants.64
Problems may also arise due to improper selection of the
implant site, based on the quality of bone. A dental
implant at a site of very low bone quality loaded with
orthodontic forces might be subject to movement during
the first few days of loading, and then either settle
into a fixed position after a few weeks or fail.49 In such
cases, failure has been related to microfracture or
microcracks of the peri-implant bone and bone remodeling
on the tension and compression sides of the miniscrew.49
Placement of the implant in very dense bone may also
reduce the chances of implant survival due to excessive
pressure on the surrounding bone, as expressed by
excessive insertion torque values.4 Also, premature loads
have been shown histologically to produce a layer of
fibrous tissue between the bone and implant.65,66 Increased
10
failure rates have also been related to the side into
which miniscrews have been inserted (with the left side
showing more failures than the right) and to the jaw
(with the mandible showing more failures than the
maxilla).67 Failure may also be the result of overheating
at the time of the implant placement. Bone overheating
during drilling may cause an inflammatory infiltration of
interposed soft tissue that has been correlated with
complete loosening or failure of the implant.
It has
been shown that temperatures above 47oC can cause bone
damage.68,69 Heat generation may be due to excessive
pressure of the drill on the bone surface, and to the use
of worn drills.70 Finally, pilot hole diameter has been
related to the survival of the implant. Pilot holes that
are too small increase the pressure to the surrounding
bone, leading to possible necrosis;71 pilot holes that are
too large will increase initial micro-motion and inhibit
the healing process, both of which could dramatically
decrease the holding power of the screw/bone system.72,73
Management factors, pertaining to the doctor and the
patient after the implant’s placement are also important.
These include poor home care, poor oral hygiene which may
lead to inflammation and infection, and excessive load
during the treatment (900 cN·mm).59 General oral hygiene
does not affect miniscrew success as much as hygiene
around the implant.61 Inefficient hygiene ultimately leads
11
to peri-implantitis which has been shown to be an
important risk factor in dental-implant failure.74 Local
inflammation can be exaggerated not only by oral hygiene
but also by non-keratinized soft tissue around the neck
of the implant. A recent study suggested that nonkeratinized mucosa was a risk factor for miniscrews.60
Park et al. showed that local inflammation can damage the
bone surrounding the neck of screw implants.61 With
progressive damage of the cortical bone, screw stability
can be compromised.74 Costa and coworkers also suggest
that a force system that generates a force in the
unscrewing direction causes implants to failure.38 Buchter
et al. reported loosening of implants subjected to forces
of 900 cN·mm (force 300 cN and 3mm lever arm).59 They
related implant failure to the tipping movements. None of
the implants that were tested moved through the bone, but
three of them showed slight tipping in the direction of
the applied force (an observation that agrees with the
observations of Liou et al.75). It is also worth
mentioning that their reference implants, which had no
forces applied to them, showed significantly higher
removal torque than loaded implants at the end of the
study. Along the same lines, Isidor found that all forces
may not be tolerated by the crestal bone.76 High strain
values, above 6700 μstrain, resulted in peri-implant bone
12
resorption and a negative balance between bone apposition
and resorption.76
The ability of an implant to withstand such negative
effects is not the same throughout its utilization.
Implants stability is related initially to mechanical
retention and ultimately to the amount of healing that
takes places around the implant.
Primary and Secondary Stability
The stability of an implant can be defined as the
implant’s capacity to withstand loading. Since loading
can be lateral, axial or rotational, stability can be
divided, mechanically, into at least three types.77
Biologically, stability can be categorized as primary,
mechanical, stability and secondary stability, associated
with bone remodeling around the implant.
The events that occur during a dental implant’s
osseointegration have been described by Scwartz and
Boyan.78 Right after implant placement, serum proteins
adhere to its surface. During the first three days,
mesenchymal cells attach to the implant and proliferate.
By day six osteoid is produced. After two weeks, matrix
calcification is complete and by three weeks remodeling
is well underway.
13
Similar stages have been reported by Berglundh and
coworkers, who used implants with a wound chamber, that
were placed in Labrador dog mandibles.79 After two hours
the wound chamber was occupied by a coagulum of
erythrocytes, neutrophils and macrophages in a fibrin
network. After four days, osteoclasts and mesenchymal
cells were observed along the implants surface; vascular
structures and densely packed connective tissue cells
were found within the wound chamber. By day seven new
woven bone started to appear on the implant surface,
along with vascular units. The trabeculae were lined with
osteoblasts and there was a provisional matrix, which had
collagen fibrils and vasculature. At two weeks, newly
formed bone appeared to be extending from the parent
bone. At four weeks, marked formation of woven bone and
lamellar bone was seen. After eight to twelve weeks there
were marked signs of remodeling within the wound chamber.
Fluorescent bone labels and microradiography have been
used to demonstrate that woven bone forms close to the
implant surface after approximately three days of
healing.80 Due to the inferior physical properties of
woven bone, in comparison to lamellar bone, loading of
the implant at this phase of healing has a greater risk
for the implant to fail.
The primary stability of screws used to enhance
orthodontic anchorage is largely determined by the
14
cortical plate; primary stability may be in the form of
monocortical or bicortical anchorage.81 The density of the
cortical bone greatly influences the distribution of
stress from the screw to the bone. Dense bone restricts
the stress in the cortical area, whereas less dense
cortical bone distributes the stress along the entire
length of the miniscrew.82,83 Relative motion between the
implant body and the surrounding bone during the early
phase of healing is considered to be an important risk
factor for early implant loss due to failure of
osseointegration.84,85 Primary stability is important
because micromotion at the implant-to-bone interface can
result in the formation of fibrous tissue, as
demonstrated with blade-type implants.65,66 It is important
to recognize that pluripotential bone cells can
differentiate into fibrous tissue, cartilage and bone.86
Fibrous tissue cannot be converted to bone; once the
fibrous tissue forms between the bone-to-implant
interface the osseointegration process is inhibited and
the implant is destined to fail.87
Following the placement of an endosseous implant
(dental or miniscrew implant), primary mechanical
stability (from the interlocking of the screw threads in
the peri-implant bone) gradually decreases and secondary
(biologic) stability gradually increases. The transition
from primary mechanical stability to secondary stability,
15
provided by newly formed osseointegrated bone, takes
place during early wound healing.88 To study healing
Morinaga et al. used Ti-coated plastic implants placed in
the tibiae of rats, which they followed for 28 days by
means of light microscopy, transmission electron
microscopy and micro computed tomography.88 The plastic
implants were free of threads, but they were the size of
commonly used orthodontic implants, with a diameter of
1.6 mm and a length of 7 mm. They noted that bone
formation started a small distance away from the implant
and after 28 days, covered the implant continuously.88
During the transition from primary (mechanical
interlocking of screw threads in peri-implant bone) to
secondary stability (from the newly formed bone around
the implant), there was a period of time during which
osteoclastic activity decreased stability,
because the
formation of new bone has not yet occurred.89 Luzi and
coworkers noted a decrease in bone-to-implant contact
between 1 week and 1 month for loaded miniscrew
implants.89 Due to remodeling, there is gradual
replacement of peri-implant bone, with new bone formation
near the implant surface.90 According to Frost, if the
load of the implant falls into the window of adaptation
of the surrounding bone, then the adjustment of
the
bone’s architecture will lead into an increase of
strength in that area.91 Jing et al. placed miniscrews in
16
rabbit tibiaes and found that placement removal torque
and pullout force increase significantly after four
weeks, histomorphometric analyses showed new bone around
the miniscrew.7 Prager and coworkers showed no significant
differences in bone-to-implant contact and mineral
apposition rate between pre-drilled and self drilling
miniscrew implants,90 which agrees with the findings of
Luzi and coworkers.89 While the bone remodeling and
loading occur simultaneously, the interaction of these
two factors seems to be critical for the survival of the
implant.
17
Techniques to Measure Stability
Stability, an indirect indication of osseointegration, is
a measure of implant’s resistance to movement.71
Quantification of implant stability at various time
points provides significant information about individual
healing times.92
The available methods for studying stability can be
categorized as invasive, which interfere with the
osseointegration process of the implant, and noninvasive, which do not. Invasive methods include
histologic and histomorphometric evaluations, cutting
torque resistance analysis, insertion torque and pullout
tests. Unlike all other methods, histologic and
histomorphometric evaluations evaluate osseointegration
directly. Thus, they provide the best methods for
establishing secondary stability. The reliability of
these methods, however, has not been evaluated. The same
applies for the other invasive methods. The non-invasive
methods include radiographic evaluations of the implant,
three dimensional finite element analysis, percussion
tests, pulsed oscillation waveforms, impact hammer tests
and resonance frequency analyses. With the exception of
the last two, the reliability of the noninvasive methods
has also not been tested. It has been suggested that
18
resonance frequency analysis is the most reliable method
for dental implants.17
Invasive Methods
Histologic and Histomorphometric Technique
The implant’s stability (i.e. its anchorage
potential) can be estimated indirectly by examining the
bone-implant interface. With a microscope the boneimplant interface can be studied, cell proliferation and
local bone morphology can be observed, and the implant’s
capability to resist movement can be estimated.
Histomorphometry is commonly used as a quantitative
method for establishing the percentage of bone to implant
contact from ground sections of implants.80,93,94 Typical
parameters measured include percentage of bone contact
and the bone area within the threads. In addition, the
number of osteocytes can be counted.
Histomorphometric studies of miniscrew implants have
also been conducted. Vannet showed that the amount of
osseointegration, estimated based on bone-to-implant
contact, was independent of loading time and location.95
His findings support previous animal studies in
evaluating miniscrew impants96-99 and dental implants.83-85
Melsen and Lang showed that there was a significant
19
increase in bone-to-implant contact and in bone density
after six months.96 The bone in close contact to the
miniscrew implant was characterized as woven. Melsen and
Costa studied, histologically, immediately loaded
implants placed into the infrazygomatic crest and the
mandibular symphysis of four adult male Macaca
Fascicularis monkeys.57 They observed no difference in the
amount of bone-to-implant contact between screws loaded
with 25 grams and those loaded with 50 grams. Bone-toimplant contact increased over time. After one month of
loading, 21% of the screw was in contact with bone; after
six months, the bone-to-implant contact increased to 60%.
Bone density also increased over time, from 8% in the
first month to 50% in the sixth month. The bone in close
contact to the mini implant was characterized as woven
and, was in most cases, distinguishable from the
surrounding lamellar bone. Melsen and Lang,96 who
evaluated the amount of bone turnover adjacent to
miniscrew implants, showed that bone density was
generally higher within 1 mm of the miniscrew implants
surface than at a distance of more than 1 mm. The bone
close to the screw was mostly woven. Similar observations
have been made by Deguchi et al., who reported continuous
turnover of bone in dental implants that were used as
anchor units for orthodontic treatment.53
20
Ultrastructural studies performed on decalcified
specimens that were sectioned for transmission electron
microscopy indicated that bone closely approximated the
surface of titanium implants (inserted in the rabbit
tibia for 12 months) but that it was never in a direct
contact with the implant.100 However, it is not possible
from decalcified sections to make observations about the
presence of mineralized tissue and its relation to the
surface of the implant.
While histologic and histomorphometric measurements
provide the most objective estimates of osseointegration,
they are of no use clinically. First, they require the
extraction of the implant with the surrounding bone,
which is unethical to perform clinically. Destruction of
the implant site also prevents sequential or longitudinal
measurements from being taken. Sequential measurements
are necessary to fully understand the healing process
associated with secondary stability. Finally, a
microscopic image does not provide any information about
the physical properties of bone, such as stiffness around
the implant, which also can affect the implants anchorage
potential.101
21
Cutting Torque Resistance Analysis
Cutting torque resistance analysis was originally
developed by Johansson and Strid102 and later improved by
Friberg et al.103,104 It is based on the energy (J/mm3)
required for an electric motor to cut off a unit volume
of bone during implant surgery. This energy has been
shown to be significantly correlated with bone density,
which has been suggested as one of the factors that
influences implant stability.105 Cutting torque resistance
analysis can be used to identify areas of low bone
density and to quantify bone hardness during the lowspeed insertion of implants. In orthodontics cutting
torque has also been used to improve the clinician’s
ability to detect root contact when placing mini
implants.106
The major limitation of cutting torque resistance
analysis is that it does not give any information on bone
quality until the osteotomy site has been prepared.
Furthermore, it does not allow longitudinal changes in
bone quality to be assessed. Its primary use, therefore,
lies in estimating primary stability indirectly, through
the quantification of bone hardness, before placement.
22
Reverse/Removal Torque Value
The reverse torque test was first proposed by
Roberts et al.3 and developed further by Johansson and
Albrektsson.93,107 It measures the critical torque
threshold when the bone-implant contact is broken.
Removal torque provides information on the degree of
bone-to-implant contact in a given implant.
Reverse torque values, in combination with
histologic evaluations, have shown that greater bone-toimplant contact can be achieved with longer healing
times.93 With surface treated (Hydroxyapatite coated)
miniscrew implants, the longer the period of time after
initial placement, the higher the torque.108 Okazaki et
al. used removal torque to evaluate the stability of
miniscrew implants placed in dog femurs. They inserted
1.2 mm diameter miniscrew implants using 1.0 mm and 1.2
mm pilot holes and showed that the removal torque values,
compared to initial insertion torque measurements,
increased for the implants placed in the 1.2 mm pilot
holes and decreased in the 1.0 mm pilot holes. As a
result the removal torque values 6, 9 and 12 weeks post
insertion were almost equal for the two pilot holes.109
Removal torque has been criticized as being
destructive. Branemark110 cautioned about the risk of
irreversible plastic deformation within peri-implant bone
23
and of implant failure when unnecessary load is applied
to an implant that is still undergoing osseointegration.
A lower threshold (i.e., the value under which an implant
is destined to fail) for removal torque has yet to be
supported scientifically. Subjecting implants placed in
bone of low quality, may result in a shearing of bone-toimplant contact and cause implants to irretrievably fail.
Insertion Torque Analysis
Insertion torque analysis quantifies the amount of
force that is applied to the implant as it is inserted.
Implant placement insertion torque is initially minimal,
and increases rapidly until the cortical layer is fully
engaged. As the implant is driven into the bone repeated
measurements are taken and a graph is often produced. The
maximum value is attained when the head of the screw
makes contact with the cortical plate. Countersink
friction between the head of the screw and the cortical
plate explains why insertion torque increases
dramatically at the end of implant placement.111 The
analysis consists of finding the maximum insertion torque
value when the screw head contacts the cortical plate.
Further insertion of the screw beyond that point leads to
fracture of the implant or stripping of the surrounding
24
bone; eventually, the screw spins freely in the hole with
its holding strength severely limited.112
This test has been generally well accepted and has
been used for evaluating various implant designs.113
Insertion torque has been found to correlate with bone
density,114 which has in turn been shown to be correlated
to implant stability.114 In other words, insertion torque
measurements allow assumptions to be made about the
quality of bone that supports the implant. Insertion
torque has been shown to increase as the thickness of the
cortical bone increases.115 In a study by Lim and
coworkers, insertion torque significantly increased with
increasing screw length and diameter.116 Values of
insertion torque less than 15 Ncm have been related to
failure of both machined and sandblasted miniscrew
implants.117 Extreme insertion torque values, either too
high or too low, have also been related to implant
failure.4
However, insertion torque has been shown to be
limited in certain applications. With self-drilling
miniscrews, insertion torque may not reflect differences
in the cortical bone thickness.115 Moreover, it is
impossible to estimate the quality of the bone until you
actually start implant insertion. As such, insertion
torque measurements cannot be used for the selection of
implant sites. Additionaly, insertion torque does not
25
offer the possibility of sequential measurements without
damaging the bone-to-implant interface; as such it cannot
be used to follow implant healing and osseointegration
procedures.
Pullout Test
A pullout test is another indirect test of an
implant’s anchorage potential. It usually measures the
tensional force, applied vertically to the surface of
bone into which an implant has been inserted, necessary
to pull the implant out of bone. The force is applied
parallel to the long-axis of the implant.
Pullout tests have been extensively used in other
medical fields, such as otolaryngology,118
orthopedics,119,120 as well as for the evaluation of dental
implants.121 Pullout strength has typically been used to
evaluate the design of implants and the mechanical
interface between bone and implants.122 Chapman and
colleagues showed that the pullout force of an implant is
proportional to the length of the thread engaged in the
bone, its major diameter and its thread depth and
inversely proportional to the thread pitch.123
In orthodontics, Huja et al. showed that pullout
measurements are significantly higher in the posterior
part of the mandible of dogs specimens than in the
26
anterior part.124 They also found a weak correlation
between pullout and cortical bone thickness. Salmoria et
al. found that pullout decreases over time, which they
related to the resorption of the cortical plate.125 Their
findings have been confirmed by others.126 Because they
could not establish a relationship between insertion
torque and cortical bone thickness, Salmoria et al.
concluded that pullout measurements are more efficient
(easier to show difference) than insertion torque.125
Miniscrew pullout tests have also been used to evaluate
different designs. Carano et al., who studied three
different designs of miniscrews of the same dimensions,
concluded that screws with asymmetric cut show higher
pullout values.127 Leung et al.128 found that cylindrical
2.0 mm miniscrews connected with mini-plates produced
significantly higher pullout forces than miniscrews of
lesser diameters.
Pullout tests suffer from the same limitations as
insertion torque. Since the procedure is invasive, the
implant site is destroyed after the test has been
performed, making it impossible to use pullout tests to
evaluate the implant-bone interface periodically. Because
it cannot be used in normal clinical situations, this
test is limited to laboratory experiments.
27
Non-Invasive
Radiographic Analysis
Radiographic analysis was one of the first methods
applied to evaluate implants after they had been placed.
The density, and therefore the physical properties of the
surrounding bone, can be indirectly estimated through
radiographs. This method is more commonly used and more
efficient with dental implants, due to their position
after placement. Dental implants are oriented with their
long axis parallel to the long axis of the surrounding
teeth, which makes them well suited for radiographic
analysis.
Bitewing radiographs are used to measure crestal
bone level, because it has been suggested as an important
indicator for implant success.129 However the resolution
of bitewing radiographs is not to evaluate either primary
or secondary stability. There is also the possibility of
distortion, if the central x-ray tube is not positioned
parallel to the structures of interest. Bone loss usually
starts from the facial and then extends to the
mesiodistal surfaces of the implant.130 Conventional
periapical and panoramic views do not provide information
about facial bone levels.
28
Regular radiographs cannot be used to quantify bone
quality nor density. They can be used to assess changes
in bone mineral only when there are decreases that exceed
40% of the initial mineralization.131 It may be that
computer assisted measurements of bone level change or
three dimensional estimations of radio-opacity will prove
to be the best ways to use radiographic information.132
Finite Element Analysis
Two and three dimensional finite element models
provide a computer simulated, theoretical analysis, based
on known material properties. Young’s Modulus, the
Poisson ratio and bone density are typically properties
used. By altering boundary conditions, such as the bone
level, finite element modeling can theoretically be used
to calculate the anticipated stresses and strains in
various simulated peri implant bone levels.133,134
Finite element modeling has been used to study the
stress and strain provided by miniscrew implants.82,83 A
study done by Dalstra and Melsen used the finite element
method for stress/strain analysis of complex bone-implant
interactions.83 They used two three-dimensional models,
one that was a geometrical representation of the actual
bone-miniscrew interface (from micro-computed tomography)
29
and one that was used to study the influence of cortical
bone and trabecular bone density on local strain
distributions. It was shown that the miniscrew was
displaced in a tipping mode, with the screw apex moving
in the opposite direction of the screw head. This
generates compressive stresses in the opposite direction
of the applied force. In general, the stress levels were
higher in the cortical bone than in the underlying
trabecular bone. The opposite was the case for the strain
values. Higher strains were observed in the trabecular
bone.
The same finite element study83 showed that the
miniscrew implants dimensions and geometry play a
significant role in the transfer of load from the implant
to the bone. The diameter and the length of the implant
were especially important. If the diameter is doubled,
the stresses in the screw, loaded under bending,
decreased by a factor of eight. On the other hand, the
strains in the surrounding bone decreased only by a
factor of two, and the effective surface area of bone-toimplant contact doubled. The overall deformation mode of
the screw remained the same. As far as the length is
concerned, the part of the miniscrew that was out of the
bone was deformed in a tipping mode. The further it
extended from bone, the higher the lever effect of the
applied force on the miniscrew implant. On the other
30
hand, the less the miniscrew implant extended out of the
bone, the lower the resistance of the surrounding
trabecular bone against deformation, leading to higher
bone strains. This could create a potential risk of
loosening.
Miyajima et al. performed another finite element
analysis using two different miniscrew implant models,
one was 1 mm in diameter and 5 mm long, and the other was
2 mm in diameter and 15 mm long.82 The miniscrews were
placed in virtual alveolar bone model that was 10 mm
wide, 10 mm deep, 30 mm tall, with the top 2 mm
consisting of cortical cone. The finite element analysis
revealed that the stress distributions and deflections
were similar for the two miniscrew models, although the
values were much larger for the smaller screw. The
maximum stress in the alveolar bone was again found to be
distributed in the cervical region, which approximates
the first two revolutions of the miniscrew threads. The
same study also showed that horizontal forces applied to
the miniscrew produces greater stress in both the
alveolar bone and the miniscrew,82 the vertical forces
applied to the miniscrew were distributed over a larger
area, and consequently produced less stress. Finally,
Miyajima et al. noted that the further away from the
surface of the bone that orthodontic forces are applied,
31
the higher the stress in both the alveolar bone and the
miniscrew.82
A serious limitation of finite element modeling is
that it is a theoretical approach, based on assumptions
derived from average bone properties. It is essentially a
static analysis that is difficult to apply in clinical
situations.
Percussion Test
A percussion test is one of the simplest methods
that can be used to estimate osseointegration. It is
based upon vibrational acoustic science and impact
response theory. A clinical judgement about
osseointegration is made based on the sound heard upon
percussion with a metallic instrument. A ringing sound
indicates successful osseointegration, whereas a “dull”
sound indicates no osseointegration. However, this method
heavily relies on the clinician’s experience level and it
is very subjective. It has not been used experimentally
and is difficult to standardize clinically.
32
Pulsed Oscillation Waveform
Kaneko et al. used a pulsed oscillation waveform to
analyze the mechanical vibrational characteristics of the
bone-to-implant interface using forced excitation of a
steady-state wave.135
Pulsed oscillation waveform is based on the
frequency and amplitude of the implant vibration induced
by a small pulsed force.135-138 This system consists of an
acoustoelectric driver, an acoustoelectric receiver, a
pulse generator and an oscilloscope. Both the
acoustoelectric driver and the acoustoelectric receiver
consist of a piezoelectric element and a puncture needle.
A multifrequency pulsed force of about 1 kHz is applied
to the implant by lightly touching it with two fine
needles connected to piezoelectric elements. Resonance
and vibration generated from the bone-implant interface
of an excited implant are picked up and displayed on an
oscilloscope. An in vitro study showed that the
sensitivity of the pulsed oscillation waveform test
depended on load directions and positions; sensitivity
was low for the assessment of implant rigidity.136
33
Impact Hammer Method
The impact hammer method is an improved version of
the percussion test. By enhancing the response detection
using various devices, such as a microphone, an
accelerometer, or a strain gauge, and by processing the
detected response with fast fourier transform, it becomes
possible to quantify and qualify the response wave in
terms of dislocation, speed, acceleration, stress,
distortion, sound and other physical properties.
The Dental Mobility Checker (Osaka, Japan) was
originally developed by Aoki and Hirakawa. It detected
the level of tooth mobility by converting the rigidity of
teeth and alveolar bone into acoustic signals. The dental
mobility checker uses a small impact hammer as an
excitation device and has been shown to provide quite
stable measurement for osseointegrated implants.139 The
two most common difficulties with the Dental Mobility
Checker are double tapping and the ability to attain
constant excitation.
The Periotest has been reported to be a reliable
method for determining implant stability.140-144 Periotest
uses an electromagnetically driven and electronically
controlled metallic tapping rod located in a handpiece.
The implant’s response to striking is measured by a small
accelerometer incorporated into the head of the device.
34
Contact time between the test object and tapping rod is
measured and then converted to the Periotest value. The
Periotest and Dental Mobility Checker are similar. They
both use a transient impulse as an excitation force, and
in both cases the analysis is conducted over time. Also,
they were both developed for measuring natural tooth
mobility.140
Reports using the Periotest for measuring dental
implant stability have noted a lack of sensitivity.142,145
Periotest permits a very wide dynamic range [ -8 to +50
(Periotest Values-PTV)] of possible responses, which is
necessary due to variation in natural tooth mobility.140,142
However, the dynamic range of implant mobility is very
limited (-5 to +5), which reduces the sensitivity of
these devices.140 Studies have indicated that Periotest
values of clinically stable implants fall within an even
narrower range(-4 to -2 or -4 to +2).146,147 Values measured
with Periotest are significantly influenced by excitation
conditions, such as position and direction; the device is
also sensitive to technical errors. As noted in the
Periotest user’s manual, “The Periotest measurement must
be made in the midbuccal direction” and “During
measurement the Periotest handpiece must always be held
perpendicular to the tooth axes”.148
Considering the intraoral environment, and the pengrip-shaped handpiece of the Periotest, it can be used
35
quite easily for the anterior region. However, its use in
the molar region is extremely difficult due to the
presence of buccal mucosa. Derhami et al. used a fixing
device to hold the handpiece at the correct angle.149 The
fixing device was used for in vitro measurements of a
cranial bone model. It has been shown that “in vitro”
Periotest measurements are reliable15 and can be used to
identify peri-implant bone loss in millimiter
increments.16 In addition to the previous studies, longterm term data have shown that the Periotest provides
objective clinical measurements of bone-implant
anchorage.150,151 Aparicio used the Periotest to measure
implant stability and found a direct correlation between
Periotest values and the degree of initial
osseointegration.152 Later studies have produced similar
findings.150,151 However, other researchers have concluded
that Periotest values cannot be used to identify an
implant that may or may not be adequately
osseointegrated.153
Despite these controversies, there has been interest
in using the Periotest for evaluating miniscrew
stability. For example, Orquin and colleagues used the
Periotest to show that neither the length nor the
diameter of miniscrew influence their primary
stability.154 The reliability (intraclass correlation) for
36
the Periotest was found to be 0.88 in a clinical17
and
0.86 in a laboratory environment.15
Periotest measurements are limited because they are
strongly dependent to the orientation of the excitation
source and the striking point. Periotest measurements
have been shown to increase 1.5 units for each millimeter
from the marginal bone in abutment or reference point
height.145 In vitro and in vivo experiments have
demonstrated that the influence of the striking point on
Periotest values is much greater than the effect of
increased implant length, due to marginal bone
resorption, or even other excitation conditions, such as
the angle of the handpiece or repercussion of a rod.145,149
Unfortunately, controlling these factors is extremely
difficult. Despite some positive claims for the
Periotest,142,152 the prognostic accuracy of the Periotest
for implant stability has been criticized for a lack of
resolution, poor sensitivity and susceptibility to
operator variables.155
37
Resonance Frequency Analysis
In resonance frequency analysis the implant, through
various ways (such as physical contact or excitation with
magnetic forces), is forced to oscillate. The frequency
that causes the implant to oscillate at maximum amplitude
is registered as the implant’s resonance frequency. A
physical system can have as many resonance frequencies as
it has degrees of freedom; each degree of freedom can
vibrate as a harmonic oscillator and have its own mode of
vibration. A mode of vibration is a characteristic
pattern or shape in which a mechanical system will
vibrate. Most systems have many modes of vibration, and
it is the task of the modal analysis to determine these
shapes. The actual vibration of a structure is always a
combination of all the vibration modes. But they need not
all be excited to the same degree. While resonance
frequency has shown to be of limited clinical value if
single readings are used to evaluate osseointegration,
they are useful if sequential measurements are taken.27
There are two commercially available devices used to
evaluate the resonance frequency of implants placed into
bone. Their main difference is in the way they excite the
implant.
The Implomates device (Taipei, Taiwan) has been
studied extensively by Huang et al.24,156-159 Huang et al.
38
conducted their first study in a laboratory
environment.158 They used an impulse hammer to excite the
implant, which was secured in a clamp stand, and recorded
the results with an acoustic sensor.158 The results showed
that the resonance frequency values correlated with the
height of the clamping level and the magnitude of the
clamping torque.158 In another study by Huang et al., the
resonance frequency was evaluated in vitro and also
theoretically, through the use of a finite model
analysis.24 The study showed that the resonance frequency
of the implant was affected by its marginal bone
characteristics, including type, density and level.24 It
was also shown that finite element analysis provides
reliable results for the analysis of the vibrational
characteristics of a dental implant.24 Their results were
repeated in another “in vitro” study by Huang et al.160
Chang et al.159 used the same type of device for
detecting resonance frequency of dental implants. Their
results showed that the device can be used for evaluating
bone union during osseointegration.159 They maintained the
orientation of the device when evaluating resonance
frequency in the buccolingual direction.159 The
frequencies increased as clamping torque and exposed
height of the implants increased.159 Their results also
correlated with the Osstell device.159 Results
substantiate the notion that higher initial resonance
39
frequency values are related to higher final resonance
frequency values taken 12 weeks after implant
placement.156
A major disadvantage of the Implomates technique is
that when a structure is excited transiently by tapping,
with a hammer for an example, it oscillates in all its
modes of vibration, with the strengths of the different
modes being dependent on the nature of the impulse.13 The
structural response is a function of natural frequencies
of all the modes of the system.13 It is very important to
restrict the oscillation in the first mode of resonance,
which is the mode that is a function of the length of the
beam and its stiffness(i.e., the two factors of greatest
clinical importance).13
The Osstell Mentor device also uses resonance
frequency for evaluating the stability of dental
implants.161,162 It excites the implant with a steady-state
sinusoidal method, which is the traditional method of
measuring the natural frequencies and the corresponding
damping factors of a structure.13 The Osstell device has
been found to be better than the Periotest device as a
mean of measuring dental implant stability in the
clinical (intraclass correlation coefficients for the
implant stability quotient based on Mentor was found 0.99
and 0.88 for the Periotest)17
and in a laboratory
environments (intraclass correlation coefficients for the
40
implant stability quotient was found to be 0.99, compared
to 0.86 for the Periotest).15
Current resonance frequency analysis systems are
battery driven and use third generation transducers that
are precalibrated by the manufacturer.18 The results are
presented as the implant stability quotient rather than
in hertz, as measured by the systems. The implant
stability quotient is based on the underlying resonance
frequency and ranges from 1 (lowest stability) to 100
(highest stability). This index is only valid for a
transducer calibrated for a specific type of implant.163
The first and second generation transducers had to be
calibrated in order for their measurements to be
comparable. Each transducer had its own fundamental
resonance frequency.18 Precalibrated transducers are
available for different implant systems, making resonance
frequency analysis measurements comparable, irrespective
of the type of implant measured. Without precalibration,
the Osstell transducer would not be suited for
quantitative comparison of the implant stability.164,165 If
the transducer is not precalibrated for a particular type
of implant, then the resonance frequency value should be
used instead.163
The third generation transducer is wireless, with a
metal rod (a peg) that is screwed into the implant. The
peg has a small magnet attached to its top which is
41
excited by magnetic pulses generated by a handheld
computer.
The peg vibrates in two directions, which are
approximately perpendicular to each other. The vibration
is measured in the direction that gives the highest
resonance frequency, as well as in the direction that
gives the lowest resonance frequency. Thus, two implant
stability quotient values are provided. It has been shown
that changes in dental implant stability measured with
the newer magnetic, third generation, device correlates
well with those of the electronic, second generation
device, even though the values cannot be directly
compared.166
It should be noted that the transducer’s orientation
influences the measurement. As such it is important to
standardize the orientation when taking sequential
measurements.18,163,167 Implant resonance frequency analysis
stability readings vary depending on which orientation
the measurements are made using the transducer. If the
orientation of the transducer is maintained, the
reliability has been shown to be excellent in the
clinical environment17 as well as in laboratory
situations15 (both studies found intraclass correlation
coefficients of 0.99). Recently, Brouwers and coworkers,
who studied the reliability for the second generation
transducer, reported intraclass correlations of 0.46 and
42
0.77 for intra-observer and inter-observer reliability
with this particular device.168
In an in vitro study Ito et al.169 used sets of three
screws to stabilize an implant at four different levels.
Resonance frequency decreased when the most coronal
screws were unscrewed. This suggests that the marginal
region is the most important for the implant stability.
These findings have been confirmed by Rodrigo et al., who
noted higher resonance frequency measurements in
specimens where the cortical bone had been maintained
than when it had been eliminated.170 Finite element
analysis by Deng et al. also showed that coronal
osseointegration models produce slightly higher resonance
frequencies than models that had other patterns of
osseointegration.171
There are a substantial number of studies that have
shown correlations between resonance frequency analysis
and various other measures of dental implant stability.
In a clinical study by Lopez et al., resonance frequency
analysis was found to be significantly correlated with
insertion torque (r=.284) implant diameter and negatively
related to implant length.172 Guncu et al. found negative
relations between the radiographic bone level and implant
stability for both immediately and conventionally loaded
dental implants.173 For conventionally loaded implants,
the relationship reached significant levels at 6
43
months.173 O’Sullivan et al. reported a statistically
significant difference in insertion torque and resonance
frequency for implants that were placed in type IV bone,
when compared with dental implants that were placed in
type II and III.174 Tozum et al. used the third generation
transducer to study the implant stability quotient,
insertion torque175 and vertical bone defects.176 They
found significant correlation between the first two
( r = .76) in laboratory conditions175 and a significant
negative correlation between the implant stability
quotient and vertical bone defects in clinical
environments (r = -.464).176 Turkyilmaz et al. showed
moderate correlations between resonance frequency
analysis and bone density (r= .557), as measured in
Hounsfield units from a CT scan and insertion
torque(highest was r=.853 and lowest r=.78).114,177,178,
179,180
Degidi reported significant positive correlations between
resonance frequency values and implant diameter, implant
length and the diameter of bur used to create the pilot
hole.181 Stenport et al. found a significant difference in
resonance frequency measurement in rabbits that were hGH
treated when compared to rabbits that were not.182
Finally, Wook and coworkers found a correlation between
resonance frequency and the density of the surrounding
bone(r= .829).183
44
The use of resonance frequency analysis as a means
of evaluating osseointegration has been theoretically
confirmed by finite element analyses, which show that
resonance frequency increases as the interfacial bone
stiffness increases.171,184 Wang and colleagues used finite
element analysis to show that bi-cortical anchorage
increases axial bending resonance frequency values.185
Pattijn et al. also conducted a finite element analysis
study, followed by some in vitro and in vivo measurements
with the second generation Osstell device. According to
their results
the adapted transducer does not always
measure the first bending mode of the system.163 Their
finite element analysis suggested that several resonance
frequencies lie within the measurement range of the
transducer.
Relationships between resonance frequency and
histomorphometric measurements have also been
established. Using resonance frequency analysis, Zhou et
al. were able to distinguish between sand blasted/acid
etched and machined implants.19 They also showed that
increased bone-to-implant contact during healing was
correlated with the implant stability quotient.19
Correlation between histomorphometric data and the
implant stability quotient was also observed by Scarano
et al. in a sample of 7 implants.186 Kim et al., who
compared different types of dental implants and surgical
45
placement techniques, found that the implant stability
quotient and the bone-to-implant contact increased
significantly between 0 to 8 weeks for all groups
tested.187 A long-term study by Gualini et al. found very
small changes in implant stability, as measured with
resonance frequency, over a five year observation
period.188
A number of researchers have been able to quantify a
loss of dental implant stability after
placement.79 Lopez
et al., who used resonance frequency to evaluate the
healing process with dental implants,189 noted a marked
decrease in stability during the fourth week, which was
followed by increases of resonance frequency through the
tenth week. A similar decrease in resonance frequency was
noted around the third week by Stadlinger et al. for
dental implants with various surface coatings.190 They
also noted increases thereafter. Also based on resonance
frequency, Strand et al. observed a decrease between the
1st and 9th week for machined implants,191 while Gleuser et
al. observed a decrease between the 1st and 8th week for
implants that had their surface processed.192 Becker and
colleagues noted that implants may have a high or low
value of resonance frequency initially.193 Those that
start with high values, later showed lower values; those
that started with low values showed an increase.193
46
A number of studies have focused on the potential of
using resonance frequency for making clinical decisions
about implants. Scarano and coworkers showed that implant
stability quotient values below 36 could be used to
identify irretrievably failed implants.194 West et al.
also found that resonance frequency analysis was useful
when deciding about the timing of loading after the
implant has been left unloaded for a period of time.195
They were able to identify reductions in stability
initially and delay implant loading until greater
stability has been attained.195 Seong et al., who measured
the resonance frequency of dental implants in different
anatomical regions of fresh human cadavers, found that
mandibular implants had significantly higher stability
than maxillary implants, with implants placed in the
posterior maxilla being the least stable.196
There have also been a number of studies that were
not able to estalish correlations between resonance
frequency and implant stability. Veltri and colleagues
observed a relationship between the implant stability
quotient and marginal bone levels, but the correlation
was not statistically significant.167 Cunha et al.
evaluated two dental implant systems using resonance
frequency analysis and cutting torque.197 They were not
able to identify a correlation between the two
measurements. Friberg and coworkers also failed to show
47
any correlation between cutting torque and implant
stability quotient.104 They did, however, note a
significant correlation between cutting torque and the
implant stability quotient in the upper/crestal third of
the implants (similar to the findings of Ito et al.28).
Rasmusson et al. were not able to establish relationship
between bone to implant contact and resonance
frequency.198 Balleri et al. examined 45 implants after
one year of loading and did not find any significant
correlations between implant length, marginal bone level
and resonance frequency.
199
An older study by Zix and
coworkers showed no significant differences in the
resonance frequency between immediately loaded and delay
loaded implants.200 There also was no statistical
difference in the implant stability quotient between the
anterior and posterior segments of the maxilla. Ostman et
al.201 also found no differences between immediately
loaded implants and delayed loaded implants. Ramakrisha
and Nayar reached the same conclusion based on a sample
of eight implants.202 Schliepake et al., who evaluated
resonance frequency, histomorphometric data, bone density
and insertion torque, did not find any correlations
between the aforementioned measurements.203 Ito et al.
were also not able to identify a correlation between
resonance frequency and histomorphometric data.28 Nawas et
al. concluded that neither insertion torque nor resonance
48
frequency were predictive of implant loss.204 Finally,
Huwiler and coworkers, who took weekly measurements of
resonance frequency, were not able to identify
significant changes over time.205 They did note that
measurements increased during the first week, then
decreased during the second and third week and finally
increased again during the fourth.
Summary
With their increased popularity, miniscrew implants
will soon be implemented extensively in everyday clinical
practice. Their possible failure will heavily influence
the outcome and efficiency of the treatment. As such, an
in vivo method to evaluate miniscrew implant stability
would hold great clinical implications. By quantifying
stability, it would be possible to follow the changes
that occur during the transition from primary to
secondary stability. Changes in stability due to
inflammation of the peri-implant tissues, overloading
etc. could also be evaluated. Resonance frequency has
been used to quantify implant stability in dental
implants for the last ten years. There is substantial
support for the method in the literature, especially when
compared to other available methods. Resonance frequency
analysis also holds great potential for quantifying the
49
stability of miniscrew implants. This project will test
the validity of this approach with miniscrew implants by
comparing resonance frequency with insertion torque and
pullout test values. Its reliability will be tested
through sequential measurements. All the tests will be
conducted in synthetic bone so that the variability of
the measurements can be controlled.
50
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69
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70
Chapter 3: Journal Article
Abstract
Purpose: To evaluate the reliability and validity of
resonance frequency as a method for measuring the
stability of miniscrew implants. Methods: One hundred and
twenty miniscrew implants were randomly allocated to
synthetic bone blocks of different densities: 40 low
[cortical part: 38.1pcf, cancelous part: 30.0pcf ]
density, 40 medium [cortical part: 40.6pcf, cancelous
part: 31.8pcf] density, and 40 high [cortical part:
50.1pcf, cancelous part: 31.8pcf] density. For each
implant insertion torque was measured using Mecmesin
Advanced Force and Torque Indicator©. Pullout strength was
measured using the Instron© Machine, Model 1011 and
applying a vertical force at 20mm/min until failure.
Resonance frequency was measured three times parallel and
three times perpendicular to the long axis of each bone
block. Results: Intraclass correlations based on multiple
measures of resonance frequency ranged from 0.953 to
0.992; single measure intraclass correlations ranged from
0.870 to 0.977. Analysis of variance showed significant
effects of bone density on resonance frequency; post-hoc
tests showed differences for high density only. Insertion
torque and pullout strength demonstrated statistically
71
significant differences between all three densities. The
two orientations showed no significant differences for
low and medium densities, the high density bone showed a
significant (p= .049) orientation effect. Independent of
bone density, correlations between resonance frequency,
insertion torque, and pullout strength were low and
showed no consistent pattern.
Conclusions: Resonance
frequency is a reliable measure. It is also a valid
measure that is related with bone density. As expected
for homogeneous synthetic bone, resonance frequency shows
little or no relationship with orientation, insertion
torque, or pullout strength.
Introduction
Because miniscrew implants provide skeletal
anchorage for tooth movements,1,2 they are becoming
increasingly popular in orthodontics.3,4 They can be
easily implemented for orthodontic tooth movement using
established biomechanic principles. Miniscrews hold the
potential for making treatment more efficient and
expanding the treatment possibilities.4
The literature reports success rates for miniscrews
ranging from 83.9% to 91.6%.5-7 Failures may be caused by
general factors, local factors or erroneous decisions at
the time of placement or during utilization.8 Stability is
72
ultimately related to the healing process that takes
place around the implant.9 Primary stability is also
important because micromotion at the implant-to-bone
interface can result in the formation of fibrous tissue,
which leads to implant failure.10,11 Relative motion
between the implant body and the surrounding bone during
the early phase of healing is considered to be an
important risk factor for early implant loss due to
failure of osseointegration.12,13
Various techniques and devices have been suggested
for evaluating of the stability of miniscrew implants.14
Some of the most commonly used methods used to evaluate
stability are insertion torque, removal torque and
pullout strength.6,15-17 Wu and coworkers, who evaluated
miniscrew implant stability from 0 to 8 weeks, noted that
removal torque and pullout strength increased over time,
with statistically significant increases in removal
torque after 4 weeks. Due to their invasive nature,
neither of these methods can be used to evaluate
stability longitudinally while the bone is healing. In
order to evaluate healing of miniscrews of individual
patients, a non-invasive technique that can be applied
clinically is needed.
The dental implant literature has shown that
resonance frequency analysis holds great potential for
evaluating stability in vivo.18-20 Resonance frequency
73
analysis has been found to be a reliable, with repeated
measures of dental implants showing intraclass
correlations of 0.99 in controlled laboratory settings21
and 0.99 in clinical situations.22 In living bone,
resonance frequencies have been shown to be correlated
with insertion torque (at least r= .78, p<.05)23 and bone
density (at least r=.79, p<.05).23 Resonance frequency
analysis is routinely used to make clinical decisions
about dental implants. For example, Scarano and coworkers
have provided a threshold value stability, below which
dental implants might be expected to fail.24 West and
coworkers used resonance frequencies to identify initial
reductions in stability and subsequent increases in
stability in order to determine the best time to load
dental implants of individual patients.25
One of the most commonly used devices to evaluate
resonance frequency is the Osstell Mentor. It uses a peg
that is screwed into the head of the implant to measure
resonance frequency. The peg holds a small magnet that is
excited by magnetic pulses. The signal is captured with a
transducer, processed with fast fourier transforms,
measured in hertz, and shown on the instrument as the
implant stability quotients.26 The implant stability
quotient is pre-calibrated for specific combinations of
implants and pegs. Because implants are often not been
pre-calibrated, it has been recommended that hertz rather
74
than the implant stability quotient should be used when
reporting resonance frequences.27 It has been shown that
resonance frequencies are influenced by the design of the
peg, the stiffness of the implant fixture and its
interface, and the effective length of the implant above
the marginal bone level.26
While resonance frequency analysis holds great
potential, its application with smaller implants remains
limited. Gedrange and coworkers used resonance frequency
analysis to show that there was no difference in
stability between 4 mm and 6 mm Straumann palatal
implants.28 Recently, Jackson and coworkers, who also used
resonance frequency analysis with palatal implants (3.3mm
diameter, 4-6mm length), showed that immediately loaded
implants were significantly less stable than implants
that remained unloaded for eight weeks.29 Resonance
frequency analysis has also been used to show that there
are no differences in stability between cylindrical and
conical miniscrew implants.30 Most recently, Veltri et al
used resonance frequency to show that there were no
significant differences between three commercially
available miniscrew implants.31 The reliability of
resonance frequencies of miniscrew implants has not been
investigated.
The purpose of this project was to determine the
reliability and the validity of using resonance frequency
75
analysis with miniscrew implants. The following working
hypotheses were tested:
1.
Multiple resonance frequency measures taken on
the same specimen are reliable and show no
systematic errors.
2.
There are differences in the resonance
frequency between synthetic bone of low,
medium and high density.
3.
There are no correlations between resonance
frequency analysis, insertion torque and
pullout test.
4.
There are no differences in resonance
frequencies associated with the orientation of
the device.
Materials and Methods
Mini Screw Implants
The miniscrews that were used for this study were
the Ancoragem Ortodontica made by Neodent© (Curitiba,
Brazil). They were 11 mm long, with an external diameter
of 1.6 mm, an internal diameter of 0.9 mm, and a 0.7 mm
pitch (Figure 1a, Appendix II). The implant has a conical
shape and was self drilling. The head had been modified
with an inner thread of maximum diameter of 1.1 mm
76
(Figure 1b, all figures in appendix II), for insertion of
the Osstell Mentor Smartpeg Type A3 (Figure 1c).
Synthetic Bone
The miniscrews were placed in synthetic bone blocks
made by Sawbones© (Vashon, Washington). The synthetic bone
blocks included three combinations of cortical and
cancellous bone of differing densities, including low
density [cortical part: 38.1pcf, cancellous part:
30.0pcf], medium density [cortical part: 40.6pcf,
cancellous part: 31.8pcf], and high density [cortical
part: 50.1pcf, cancellous part: 31.8pcf]. The cortical
bone was 2 mm thick and fixed to the cancellous bone with
40 pcf rigid polyurethane foam. The densities of the
synthetic bone selected for this study were chosen to
represent the human mandible, which has been reported to
be 41.2pcf (0.66 g/cc).32 Previous studies have shown that
synthetic bone is a good substitute for real bone.33 The
homogenous nature of synthetic bone is essential for
controling the variability of bone properties found in
natural bone.
Each block of synthetic bone (170 mm x 120 mm x 42
mm) was marked so that the surface delimited 20 squares
(30 mm x 30 mm). A miniscrew was inserted into the center
of each square (Figure 2a). There were two blocks per
77
density (high, medium, low), with a total of six blocks
and 120 miniscrews.
The synthetic bone blocks were embedded in plaster
stone to stabilize the blocks with two vices. The
compression forces of the vices were applied to the
plaster stone so as not to interfere with the resonance
frequency measurement (Figure 2b).
Insertion Torque
A guide for the miniscrew driver was placed over the
bone block to standardize miniscrew insertion. It ensured
that each screw was inserted in the same direction; it
also prevented wobble of the driver during insertion
(Figure 3a). Each miniscrew was inserted manually with
the hand driver until only one thread remained exposed
above the surface of the cortical bone. The hand drive
was then replaced by the Mecmesin Advanced Force and
Torque Indicator© (Mecmesin, Ltd, West Sussex, UK) (Figure
3b) and the miniscrew was inserted until the point right
before the head touched the synthetic bone. This was done
to prevent countersink friction. The maximum value of
insertion torque was measured in N/cm.
78
Resonance Frequency Analysis
After the miniscrews had been inserted into the
synthetic bone, the Osstell Smartpeg was fitted onto the
head of each miniscrew with finger pressure, according to
the manufacturer’s instructions. It has been previously
shown that tightening the transducer 10 Ncm or more has
no significant effect on resonance frequency of
implants.18 Once the Smartpeg was fitted, sequential
measurements of the resonance frequency were taken using
the Osstell Mentor© transducer (Göteborg, Sweden). Three
measurements were taken parallel to the long side of the
synthetic bone block and three more were taken parallel
to the short side of the synthetic bone block (Figure 4.
These two sets of measurements were perpendicular to each
other. All resonance frequency measures were reported in
hertz.
Pullout Strength
To measure pullout strength, each bone block was
sectioned into 20 smaller blocks (12mm x 12mm x 12mm),
with one implant in the center of each block. Each of the
smaller blocks was placed in a base specially designed to
secure the block and fit the Instron© Machine, Model 1011
(Instron Corp, Canton, MA). The base had a lid that
secured each block of bone during pullout testing (Figure
79
1d). The miniscrews was attached to the Instron using a
custom made grappling device designed to fit the head of
the miniscrew. A vertical force of 20mm/min was oriented
parallel to the long axis of the miniscrew and applied
until failure. Peak load at failure was obtained from the
readout and recorded in kilograms.
Statistical Analyses
Skewness and kurtosis statistics showed that the
variables were normally distributed. Repeated measures
analyses of variance were used to evaluate systematic
differences between the three measures of resonance
frequency. Cronbach’s Alpha was used to estimate the
reliability of the three measures taken on each
miniscrew; intraclass correlations were used to evaluate
the reliability of single measures of resonance
frequency.
Validity of the resonance frequency measures was
evaluated two ways. Assuming that valid measures are able
to identify differences that should exist (discriminant
validity), analyses of variance were used to evaluate
differences in resonance frequency associated with bone
density. Based on the fact that the synthetic bone is
homogeneous in its material properties, valid measures of
resonance frequency should not be related to other
80
measures of stability and should be independent of the
orientation from which the measure were taken (convergent
validity). To this end, paired t-tests were used to
compare differences in orientation and correlations were
used to evaluate associations between resonance
frequency, insertion torque and pullout force.
Results
Reliability
Analysis of variance showed no significant
differences between the three measurements taken parallel
and perpendicular to the long axis of the bone block
regardless of density (Table 1; Figure 5, Appendix I and
II).
Multiple measure intraclass correlations ranged from
0.953 to 0.992 and single measure reliabilities range
from 0.870 to 0.977(Table 2, all tables are to be found
in Appendix I). All of the intraclass correlations were
statistically highly significant (p< .001). The lowest
reliability (0.870) was found for single measurements in
the medium density synthetic bone block; the highest
reliability (0.992) was found for multiple measurements
in the low density synthetic bone block. The multiple
81
measurements were generally more reliable than the single
measurements in all instances.
Validity
Based on the mean values of the three resonance
frequency measurements, paired t-tests showed that there
was a statistically significant difference between the
parallel and perpendicular orientation for the medium
density bone (p=0.049). There was no statistically
significant (p>.05) difference due to the orientation of
the device for low and high density bone.
Analyses of variance demonstrated significant
difference in resonanance frequency between the three
bone densities. Post hoc tests showed differences for
high density only. There was no significant difference in
resonance frequency between the low and the medium
density bone (Table 3). Analyses of variance also showed
significant effects of bone density on insertion torque
and pullout strength, with significant differences
between all three densities (Table 3).
With the three bone densities combined (ie. not
controlling for density) there was a moderately high
correlation (r= 0.830) between insertion torque and
pullout strength (Table 4; Figure 6).
Insertion torque
was also significantly (p<.01) related with the parallel
82
resonance frequency measures (r= 0.471), as well as the
perpendicular resonance frequency measures (r= 0.337).
Pullout strength showed significant correlations with
both the parallel (r= 0.490) and perpendicular (r= 0.327)
resonance frequency measures.
Independent of bone density (i.e. with the three
densities evaluated separately), correlations between
resonance frequency, insertion torque and pullout
strength were limited and showed no consistent pattern
(Table 4). Only six of the fifteen possible correlations
were statistically significant (p<.05). The medium
density bone blocks showed low correlations between
resonance frequency and insertion torque (r=0.336 and
r=0.338 for the parallel and perpendicular orientations,
respectively). Resonance frequency was also related to
pullout strength in the medium density bone; the high
density bone showed significant correlations between
resonance frequency and pullout strength for the parallel
orientation only (r=.401). Insertion torque was
significantly related to pullout strength (r=.412) only
in the low density bone blocks.
83
Stabilization of Blocks
Regardless of orientation there were no statistically
significant differences in resonance frequency between
the miniscrew implants that had been stabilized and those
that had not been stabilized (Table 5).
Discussion
The results showed high level of reliability when
using the Osstell Mentor with miniscrew implants. The
lowest intraclass correlation was 0.953 for multiple
measurements and 0.870 for single measurements. As
multiple measurements were more reliable than single
measures, it may be preferable to measure resonance
frequency multiple times and average the measures in
order to obtain the most reliable estimates. While
reliability has not previously been established for
miniscrew implants, studies have shown similar or lower
levels of reliability for dental implants. In a clinical
study, Zix and coworkers reported an intraclass
correlation of 0.99 for the Mentor.22 Lachmann and
coworkers, in a laboratory study, also found an
intraclass correlation coefficient of 0.99.21 On the other
hand, Brouwers and coworkers, reported an intraclass
correlation of 0.46.34 However, Brouwers and coworkers
84
studied dental implants that had been placed in dry
edentulous mandibles that had not been stabilized, which
holds important implications for the clinical application
of resonance frequency measures. Based on the present
findings, the Osstell Mentor can reliably be used to
quantify the stability of miniscrew implants.
The resonance frequency recorded for miniscrew
implants in this study was substantially lower than
previously reported for miniscrews. Veltri and coworkers
reported resonance frequencies of 6000 hertz (compared
with the 2000 hertz found in this study) for three types
of miniscrew implants placed in rabbit femoral condyles.35
However, their miniscrews had an adapter for the Osstell
transducer soldered onto the miniscrew head, which could
have affected the resonance frequencies. They also used a
previous generation of the device, the frequencies of
which have been shown not to correlate with the newer
generation devices.36 Moreover, their miniscrews were
fully inserted while those in the present study were not,
which also could have produced different frequency
values.26
As expected, insertion torque, pullout strength and
resonance frequency were significantly related to bone
density. While these relationships have not been
previously demonstrated for miniscrews, it has been shown
that resonance frequencies of dental are correlated with
85
insertion torque,23,37,38 bone density.23,37,39 The
relationship between resonance frequency and pullout
strength has not been previously investigated. Pullout
strength has been found to correlate with bone density40
and insertion torque.41 The existence of relationships
between the measurements taken and bone density is
important because they make it possible to indirectly
estimate the process of mineralization around the
implant. Resonance frequencies were not significantly
different between the low and medium density bone. This
may be due to the fact that there was relatively little
difference in bone properties between low and medium
density bone. Low density was made from a cortical part
of 38.1 pcf and a cancellous part of 30.0 pcf, while
medium density was made from a cortical part of 40.6 pcf
and a cancellous part of 31.8 pcf. There was a total 4.3
pcf difference between the low and medium density bone,
while the high and the medium difference was 10.5 pcf. It
is also possible that the device may not be as sensitive
in the lower end of the frequency spectrum. The Osstell
Mentor measures resonance frequencies between 1000 and
10,000 hz, and the measurements taken were clearly at the
lower end of that spectrum.
Associations between resonance frequency, insertion
torque, and pullout strength and bone density have been
previously reported for dental implants. However, most
86
studies reporting correlations did not control for
variation in bone properties, and correlations that do
not control for extraneous sources are by definition
spurious.
In a cadaver study, Turkyilmaz and coworkers
found that resonance frequency was correlated both with
insertion torque (r= 0.78) and bone density (r= .853).23
When bone density was not controlled, the present study
also showed significant, albeit slightly lower,
correlations between resonance frequency and insertion
torque. Similarly, Song and coworkers found correlations
ranging from 0.72 to 0.81 between insertion torque and
pullout strength in Sawbones, but they included bone of
different cortical thicknesses.41 The present study showed
a correlation of .83 between insertion torque and pullout
strength when all three densities were included in the
calculations (i.e. did not control for density). The
present findings emphasize the importance of controlling
extraneous variation when evaluating associations between
stability measures.
When variation in density was controlled, there was
little or no association between resonance frequency,
insertion torque and pullout strength. Only six of the
fifteen possible correlations were statistically
significant (Table 4). Importantly, correlations should
not be expected in homogeneous bone. If the technical
aspects could be totally controlled without error, all of
87
the resonance frequencies should be identical. The weak
correlations identified simply indicate that the
procedures were not controlled and that there was error.
Most important, there was no pattern of association
evident and the associations identified were weak. Since
there was no distinct pattern of across the three density
groups, the correllations could have be due to lack of
technical control, especially in the medium density group
that should the greatest number of association. Moreover,
the lack of association between insertion torque and
pullout strength suggests that the correlations were not
due to variation in stability. Because the lack of
association in homogeneous bone is expected, the present
finding serve to validate resonance frequency
measurements with miniscrew implants.
Resonance frequencies have been previously shown to
differ in real bone, depending on the orientation of the
transducer at the time of the measurement.26,36,42-44
With
homogeneous bone, difference should not be expected. The
effect of orientation of the measurement has not been
previously evaluated with sawbone. While there were no
differences for low and medium density bone, the high
density bone showed a significant difference (p=.049).
However, after a Bonferroni adjustment for multiple
measurements, this difference was not statistically
significant. Because no differences were found and no
88
differences were expected, this further serves to further
validate the use of resonance frequency with miniscrew
implants.
While no significant effects were found in the
present study, it is important to stabilize specimens
when measuring resonance frequency. Lack of stability
interferes with the measurement and can lead to erroneous
results. Pattjin et al showed that the nearer the
clamping vice is to the implant the higher the
measurement that is measured.42 The present study
stabilized the bone blocks indirectly using plaster
stone, the weight of which was evidently sufficient to
stabilize the miniscrews.
Otherwise, there should have
been differences between the stabilized and not
stabilized resonance frequency measures.
89
Conclusions
1) Resonance frequencies of miniscrew implants are
reliable and show no systematic
errors.
2) Measures of resonance frequency are valid
- Frequencies of high density bone differ from low
and medium density bone, as expected
- No difference in synthetic bone due to
orientation, as expected
- After the effects of bone density have been
controlled, correlations between RF, IT, and POS
are small and inconsistent, as expected
90
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95
Appendix I: Tables
96
Table 1. Comparison of resonance frequency (RF) of three consecutive measurements [taken parallel (║) and perpendicular (⊥)to the long side
of the rectangular synthetic bone block] for the high, medium and low density bone blocks.
97
RF ║
(Hz)
RF ⊥
(Hz)
Low
Medium
High
Low
Medium
High
1st Measurement
Mean
SD
CV (%)
2nd Measurement
Mean
SD
CV (%)
3rd Measurement
Mean
SD
CV (%)
1888.4
1896.6
2015.0
1898.2
1906.1
1996.7
1878.0
1897.9
2028.6
1896.4
1894.6
1988.5
1886.0
1902.3
2024.6
1901.5
1896.1
1994.6
131.7
103.0
96.9
126.7
102.7
81.9
6.9
5.4
4.8
6.7
5.4
4.1
139.9
95.4
90.4
125.5
111.8
90.0
7.4
5.0
4.4
6.6
5.9
4.5
129.6
94.2
90.8
129.0
110.8
85.6
6.9
5.0
4.5
6.8
5.8
4.3
ANOVA
P Value
.529
.840
.068
.399
.131
.278
Table 2. Reliabilities of resonance frequency (RF) measures evaluated using intraclass correlations for single measurements and Cronbach’s
Alpha for multiple measurements.
RF ║
RF ⊥
98
Single
Multiple
Single
Multiple
Low Density
Estimated
P Value
.928
<.001
.975
<.001
.977
<.001
.992
<.001
Medium Density
Estimated
P Value
.870
<.001
.953
<.001
.947
<.001
.982
<.001
High Density
Estimated
.912
.969
.886
.959
P Value
<.001
<.001
<.001
<.001
Table 3. Comparison of resonance frequency (RF) measurement averages [taken parallel (║) and perpendicular (⊥) to the long side of the
rectangular synthetic bone block] insertion torque (IT) and the pullout strength (POS) for the high, medium and low density bone blocks.
99
Mean
RF ║ Average(Hz) 1884.5
RF ⊥ Average(Hz) 1898.7
IT (Ncm)
18.2
POS (Kg)
45.5
Low Density
SD
CV (%)
130.5
6.9
126.1
6.6
1.2
6.6
2.1
4.6
Medium Density
Mean
SD
1898.9
97.5
1898.9
108.4
21.0
1.4
54.5
1.8
CV (%)
5.1
5.7
6.5
3.4
Mean
2022.7
1993.3
24.5
61.2
High Density
SD
92.7
85.8
2.2
3.4
CV (%)
4.6
4.3
8.9
5.5
Difference
P Value
<.001
<.001
<.001
<.001
Table 4. Correlations between resonance frequency (RF) measurements [taken parallel (║) and perpendicular (⊥)to the long side of the
rectangular synthetic bone block],insertion torque (IT) and pullout strength (POS) for the high, medium and low density synthetic bone blocks
separately and combined.
100
RF ║ w/ IT
Low Density
r (prob)
.006 (.972)
Medium Density
r (prob)
.336 (.034)*
High Density
r (prob)
.194 (.231)
All Densities
r (prob)
.471 (<.001)*
RF ⊥ w/ IT
-.082 (.614)
.338 (.033)*
.057 (.726)
.337 (<.001)*
RF ║ w/ POS
.027 (.867)
.388 (.013)*
.401 (.010)*
.490 (<.001)*
RF ⊥ w/ POS
-.138 (.395)
.335 (.035)*
.134 (.409)
.327 (<.001)*
IT w/ POS
.412 (.008)*
.096 (.557)
.251 (.118)
.830 (<.001)*
Table 5. Comparison of resonance frequency (RF) measurements [taken parallel (║) and perpendicular (⊥)to the long side of the rectangular
synthetic bone block] with the medium density block clamped and not clamped.
st
101
RF║ 1
RF║ 2nd
RF║ 3rd
RF║ Average
RF ⊥ 1st
RF ⊥ 2nd
RF ⊥ 3rd
RF ⊥ Average
Mean
1875.8
1893.8
1893.8
1887.8
1916.4
1915.1
1907.0
1912.8
Not Clamped
SD
CV (%)
119.4
6.4
119.6
6.3
119.6
6.3
119.5
6.3
151.1
7.9
126.2
6.6
142.6
7.5
140.0
7.3
Mean
1945.9
1942.2
1932.7
1950.3
1936.4
1909.0
1927.9
1924.4
Clamped
SD
134.5
118.9
110.4
121.3
127.4
124.0
141.6
131.0
Difference
CV (%) P Value
6.9
.083
6.1
.108
5.7
.254
6.2
.101
6.6
.464
6.5
.802
7.3
.466
6.8
.627
Appendix II: Figures
102
a
b
c
d
Figures 1: Miniscrew Implant and Custom Pullout Base
a) Neodent miniscrew implant,
b) Head modified for the attachment of the Osstell peg,
c) Miniscrew implant with the Osstell peg,
d) Custom base to hold implants during pullout test.
a
b
Figures 2:Synthetic Bone
a)Synthetic bone marked for implant placement,
b)Synthetic bone block stabilized with two vices on
laboratory bench.
103
b
a
Figure 3: Miniscrew Implant Driver
a) Hand driver with customized placement device,
b)Insertion torque measuring device.
a
b
Figure 4: Resonance frequency analysis measurements
a) parralel and
b) b) perpendicular to the long side of the synthetic
bone block.
104
a
b
c
3rd
2100
2050
2000
1950
1900
1850
1800
1750
1700
2100
2050
2000
1950
1900
1850
1800
1750
1700
d
2nd
3rd
1st
Hz
1st
Hz
e
1st
2nd
3rd
1st
2nd
2nd
3rd
2100
2050
2000
1950
1900
1850
1800
1750
1700
f
3rd
Hz
2100
2050
2000
1950
1900
1850
1800
1750
1700
2nd
Hz
Hz
Hz
1st
2100
2050
2000
1950
1900
1850
1800
1750
1700
1st
2nd
3rd
2100
2050
2000
1950
1900
1850
1800
1750
1700
Figure 5. Comparisons of resonance frequencies of three
consecutive measurements [taken parallel (║ ) to the long side of
the synthetic bone block for the a) low, b) medium and c) high
density; comparison of resonance frequencies of three consecutive
measurements [taken perpendicular (⊥) to the long side of the
synthetic bone block for the d) low, e) medium and f) high
density
a
Low
Medium
b
High
Resonance Frequency
Pullout Strength
70
65
60
55
50
45
Low
Medium
High
2200
2000
1800
1600
1400
40
150
170
190
210
230
250
270
150
290
170
190
210
230
250
270
290
Insertion Torque
Insertion Torque
Resonance Frequency
c
Low
Medium
High
2200
2000
1800
1600
1400
40
45
50
55
60
65
70
Pullout Strength
Figure 6. Scatterplots of a) pullout strength with insertion
torque, b) resonance frequency with insertion torque, and c)
resonance frequency with pullout strength.
105
Vita Auctoris
Georgios Katsavrias was born in Marousi, Athens on
the 3rd of June 1979. He was raised in Chalandri, Athens.
He attended primary and secondary school in Chalandri,
Athens and high school in Penteli, Athens. He entered the
Dental School of the University of Athens in September,
1999 and graduated in 2005.
In June, 2006 he came to
Saint Louis, USA to attend the postgraduate orthodontic
program of Saint Louis University from which he graduated
in June, 2009.
106