Download IMPLANT-BONE INTERFACE OF MINISCREWS TREATED WITH SURFACE

IMPLANT-BONE INTERFACE OF MINISCREWS TREATED WITH SURFACE
LUBRICANTS USING A WATER SOLUBLE-POLYMER OR BONE WAX;
AN ANIMAL MODEL STUDY
Robert J. Marshall, D.D.S.
An Abstract Presented to the Faculty of the Graduate School
of Saint Louis University in Partial Fulfillment
of the Requirements for the Degree of
Master of Science in Dentistry
2010
Abstract
Purpose:
The purpose of this investigation was to evaluate
the change in insertion torque and the effects of the
implant-bone interface of miniscrew implants (MSIs) that
were treated with a surface lubricant of either bone wax or
Ostene®.
Methods:
MSIs coated with bone wax or Ostene®
were compared to control MSIs to determine the acute
difference in insertion torque when placed in synthetic
bone and pig femur.
The pullout strength was also
evaluated using the MSIs placed in the synthetic bone.
In
addition, MSIs coated with bone wax or Ostene® were
compared to control MSIs to determine the difference in
insertion torque in synthetic bone and pig spare ribs at
five second intervals from initial insertion until fully
seated using a custom insertion machine.
Histological
samples of Beagle dogs were evaluated for the cellular
response around the MSI controls, MSIs coated with bone
wax, and MSIs coated with Ostene® immediately after removal
and after two weeks of healing.
Results:
A significant
difference (p<.05) in insertion torque was found between
the MSI control group and both the bone wax and Ostene®
groups in synthetic bone with the control group requiring
the greatest insertion torque.
No significant differences
(p>.05) were found between any groups for insertion torque
1
when the MSIs were placed in a pig femur or for pullout
strength in the synthetic bone.
Additional testing showed
that at time points T1, T2, T3, and T4 (15, 30, 45, and 60
seconds respectively), the MSI control group required a
statistically significant (p<.05) greater torque to insert
the MSIs in synthetic bone than when treated with bone wax
or Ostene®.
No differences were shown when each group was
placed in pork spare ribs at any time point.
Conclusions:
Lubricating MSIs with bone wax or Ostene® reduces the
insertion torque in synthetic bone.
2
COMMITTEE IN CHARGE OF CANDIDACY:
Professor Rolf G. Behrents,
Chairperson and Advisor
Assistant Professor Ki Beom Kim
Associate Clinical Professor Donald R. Oliver
i
DEDICATION
I dedicate this project to my wife, Jamie, for her
support, patience, and constant love as we have and will
continue moving forward together.
I also what to express a special thanks to my parents
for their dedication to and sustaining influence on my
pursuit of education over all these years.
Finally, may this thesis take part by showing in a
very small way the great program that Dr. Ken Marshall
devoted so much of his life to creating.
ii
ACKNOWLEDGEMENTS
I would like to acknowledge the following individuals:
Dr. Rolf Behrents for guiding and providing direction
through this entire project.
Your answers to questions
that I could not answer provided needed insights and
results.
Dr. Donald Oliver for providing the technical support
and encouragement to finish a professional paper.
I
appreciate how approachable you are with questions.
Dr. Ki Beom Kim for serving on my thesis committee.
Your simple questions led to teaching moments.
Dr. John Long, Ms. Nancy Roth, and Mr. Frank Strebeck,
Jr. and everyone in the Comparative Medicine Department of
Saint Louis University for the humane and professional
manner in which the animals were handled.
This project
would not have been started or finished without your help.
3M Unitek and the Imtec Corporation for providing the
miniscrew implants and the drivers required to insert and
remove them.
Mr. Eric Perkins for providing the necessary equipment
to further this research.
Dr. Robert Spears for his time and knowledge devoted
to understanding the intricate cellular responses that must
be understood to further science.
iii
Drs. Ben Lough and Heidi Israel for guiding me through
the statistical analysis.
iv
TABLE OF CONTENTS
List of Tables ..........................................vii
List of Figures ........................................viii
CHAPTER 1: INTRODUCTION ...................................1
CHAPTER 2: REVIEW OF THE LITERATURE
Orthodontic Miniscrew Implants .......................4
Placement of MSIs ...............................5
Stability .......................................5
Pullout Strength ................................6
Influences on MSI Failure ............................8
Design of MSIs ..................................8
Bone and MSI Interface ..........................9
MSI Inflammation ...............................11
Insertion Torque ...............................13
MSI Fracture ...................................15
Friction ............................................16
Heat ...........................................16
Lubricants in Medicine .........................19
References ..........................................23
CHAPTER 3: JOURNAL ARTICLE
Abstract ............................................29
Introduction ........................................30
Methods and Materials ...............................34
Miniscrew Implants .............................34
Testing Methods ................................35
Synthetic Bone Model ......................35
Pig Femur .................................36
Mechanical Testing .............................36
Placement Torque ..........................36
Pullout Analysis ..........................38
Animals ........................................39
MSI Placement .............................39
MSI Lubricant Evaluation ..................41
Further Research ...............................42
Statistical Analysis ................................44
Results .............................................45
Standard Tests .................................45
Synthetic Bone Model Insertion Torque .....45
Synthetic Bone Model Pullout ..............45
Pig Femur Model ...........................46
Custom Insertion Machine Tests .................47
Synthetic Bone Model ......................47
v
Pig Spare Ribs ............................52
Discussion ..........................................57
Conclusions .........................................60
References ..........................................62
Appendix .................................................65
Vita Auctoris ............................................69
vi
LIST OF TABLES
Table 3.1:
Descriptive statistics for MSIs in synthetic
bone and pig femur............................45
Table 3.2:
Statistical comparison of original
measurements..................................45
Table 3.3:
Descriptive statistics of MSIs in Synthetic
Bone (T1, T2, T3, and T4 equal 15, 30, 45, and
60 seconds respectively)......................50
Table 3.4:
Statistical comparison of MSIs in Synthetic
Bone (T1, T2, T3, and T4 equal 15, 30, 45, and
60 seconds respectively)......................51
Table 3.5:
Descriptive statistics of MSIs in pork spare
ribs (T1, T2, T3, and T4 equal 15, 30, 45, and
60 seconds respectively)......................55
Table 3.6:
Statistical comparison of MSIs in pork spare
ribs (T1, T2, T3, and T4 equl 15,30, 45, and 60
seconds respectively).........................56
vii
LIST OF FIGURES
Figure 3.1:
MSIs used in this research A. Control MSI,
B. MSI coated with bone wax, C. MSI coated
with Ostene® ..............................33
Figure 3.2:
Custom jig securing synthetic bone block
with Mecmesin® instrument attached to driver
and MSI ...................................36
Figure 3.3:
Placement of MSIs (red dots) on dog’s right
side ......................................40
Figure 3.4:
Placement of MSIs (red dots) on dog’s left
side ......................................40
Figure 3.5:
Custom insertion torque machine from left
side ......................................42
Figure 3.6:
Custom torque machine from back showing
motor attached under drill press table ....43
Figure 3.7:
Individual control MSI’s insertion torque
over time in synthetic bone ...............47
Figure 3.8:
Individual bone wax coated MSI’s insertion
torque over time in synthetic bone ........48
Figure 3.9:
Individual Ostene® coated MSI’s insertion
torque over time in synthetic bone ........49
Figure 3.10:
Average of each group of MSIs’ insertion
torque over time in synthetic bone ........50
Figure 3.11:
Individual control MSI’s insertion torque
over time in pig spare ribs ...............52
Figure 3.12:
Individual bone wax coated MSI’s insertion
torque over time in pig spare ribs ........53
Figure 3.13:
Individual Ostene® coated MSI’s insertion
torque over time in pig spare ribs ........54
Figure 3.14:
Average of each group of MSIs’ insertion
torque over time in pig spare ribs ........55
viii
Figure A.1:
Individual bath soap coated MSI’s insertion
torque over time in synthetic bone ........65
Figure A.2:
Individual candle wax coated MSI’s insertion
torque over time in synthetic bone ........66
Figure A.3:
Individual control MSI’s insertion torque
over time in synthetic bone without the help
of the custom insertion machine ...........67
Figure A.4:
Averages of each group of MSIs’ insertion
torque over time in synthetic bone (n=5) ..68
ix
CHAPTER 1: INTRODUCTION
The necessity for anchorage has been a topic of
interest for as long as orthodontists have attempted to
move teeth.
A wide selection of strategies has been
employed in order to establish anchorage for numerous tooth
movements with varying levels of success.
Common methods
of establishing anchorage might include extraoral headgear,
differential forces, and intermaxillary elastics.
Starting in 1945, animal studies were conducted to
evaluate the possibility of using screws in bone to achieve
anchorage.1 Since that time, and particularly in the last
few years, the use of implants to establish anchorage has
become widespread. Their value is based on the fact that
miniscrew implants, although they do not always stay
perfectly immobile, are a stable anchorage unit.2 While
obviously valuable, problems exist and implants fail.
Some
of the reasons for failure include peri-implant
inflammation, site of placement, poor implant design, bone
necrosis due to heat generated during placement, and high
torque during placement.
An aspect of possible miniscrew implant (MSI)
improvement is reduction of insertion torque.
Increased
torque during placement of the MSI leads to decreased
1
mechanical strength and thus earlier failure.3 In an effort
to decrease the insertion torque, Lima et al. studied the
torque difference when the length, diameter, and shape of
the MSIs were altered.
They determined that torque was
affected most by the diameter, followed by the length, and
then the shape.4
Another way to decrease the insertion torque would be
to reduce the friction at the bone and MSI interface with
lubricants.
However, the author could not locate
literature that shows that surface lubricants have been
applied to MSIs in order to achieve this objective.
For
years lubricating surfaces has shown favorable results in
reducing friction.5 Both bone wax and a water solublepolymer, Ostene®, have been used in medicine for different
purposes, and will be used to lubricate the MSIs for this
study.
Bone wax has been used since the 1800s as a way to
achieve hemostasis during surgical procedures.6 Throughout
the years it has been widely used because it is inexpensive
and typically has few related complications.7 Ostene® is a
water soluble-polymer that has gained more acceptance as
studies have revealed that it has better biocompatibility
and less incidence of infection than bone wax.
It has also
been shown to increase bone healing at the surgery site.
2
Using 20 rabbits, Wellisz et al. compared the results when
placing Ostene® and bone wax on median sternotomies.
The
histological samples taken after six weeks identified
normal bone healing in the soluble-polymer group while the
bone wax group showed an absence of new bone formation.8
The long-term objective of this study is to determine
whether surface lubricants can reduce the insertion torque
of MSIs without affecting adversely the bone-implant
interface.
If this is the case, then surface lubricants
could be used to reduce the friction and heat generated at
the bone-MSI interface and possibly decrease the amount of
bone necrosis around the MSI.
As the amount of insertion
torque decreases, the number of MSIs fracturing upon
insertion should also decrease.
In addition to their
lubricating characteristics, the biological response will
be evaluated to determine whether there are untoward
problems associated with their use in orthodontics.
The following review of the literature will give a
better understanding of MSIs, their use in orthodontics,
some of the problems that are currently faced, and how
reducing the friction upon insertion might be beneficial.
3
CHAPTER 2: REVIEW OF THE LITERATURE
Orthodontic Miniscrew Implants
The correction of misaligned teeth in dentistry has
been sought after for more than a century.
One of the most
difficult tasks is to move teeth that are out of position
while preventing correctly aligned teeth from being
affected.
Throughout the years, many different types of
appliances have been used both intraorally and extraorally
to achieve anchorage.
One of the more recent ways of
attaining the objective of absolute anchorage is through
the use of MSIs.
These devices are relatively small, do
not require a complex surgical procedure to place, and aid
in achieving better orthodontic results.9
MSIs have many uses.
They can be used for the
correction of anteroposterior and vertical skeletal
discrepancies.
Even more commonly, they are being used to
effect various tooth movements including molar uprighting,
intrusion, or extrusion of single or multiple teeth, and
anteroposterior tooth movements.10 Essentially, MSIs have
become a very helpful and useful tool in orthodontics.
To
be useful, each MSI must be placed in the oral cavity in
order to perform its function, and inherent in this process
arise many variables that affect usefulness.
4
Placement of MSIs
The goal of MSI placement is to insert the MSI in bone
in such a way that forces can be applied between the MSI
and certain teeth with the result being optimal tooth
movement while the MSI remains immovable in bone.
There is a wide variety of MSIs currently in use.
Some of them are self-drilling and others are not.
Those
that are not self-drilling require a tissue punch and pilot
hole be placed prior to MSI insertion.11 The pilot hole is
normally 0.2 mm to 0.3 mm smaller in diameter than the
MSI.12 The self-drilling MSIs, on the other hand, do not
necessarily require a hole punch or pre-drilling and can be
inserted directly through the gingival tissues and into the
bone.
Both types of MSIs are typically placed using one of
the following instruments: torque wrench, hand driver,
finger/thumb driver, or motorized hand piece with limited
torque.10
Stability
The subject of stability can be broken down into two
different categories.
Primary stability, by definition, is
a mechanical locking of the bone and MSI upon placement
that is directly related to the quality and quantity of
5
local bone.
Secondary stability, however, is associated
with the changes that occur at the bone to implant
interface over time due to the remodeling of the tissues
and surrounding bone.13 Without good primary stability,
secondary stability generally will not occur.
Poor primary
stability leads to small movements of the MSI, which does
not allow for the necessary bone remodeling and thus
secondary stability is not achieved.14 As the implant is
moved back and forth due to poor primary stability, micro
fracturing occurs which is followed by necrosis.
Subsequently a fibrous connective tissue capsule slowly
thickens around the implant as bone resorption continues.
Eventually the implant may fail due to lack of bone to
implant contact.15,16 If primary and secondary stability are
achieved, the bone to implant interface becomes
osseointegrated, or mechanically locked.17
Pullout Strength
One of the more common ways to evaluate the stability
of MSIs is to perform a pullout test.
This measures the
holding power of a MSI.18 As discussed before, the bone to
MSI interface is very important in the stability of an
implant.
It has been shown that the amount of force
required to pull out a MSI is directly related to this bone
6
to implant contact.19 This is one of the reasons this test
is frequently used.
Typically the material that the screw is embedded in
is held firmly in a vice while a calibrated machine slowly
applies a force in the vertical direction, along the long
axis of the MSI, until it is dislodged.
The measure of the
highest force applied before the implant fails is recorded.
It has been found that the diameter and length, both of
which affect the amount of bone to MSI contact, are
important factors in determining the amount of force that
can be withstood on pullout.20-22 Another crucial variable is
the material in which the MSI is placed.
Huja et al.
placed 56 MSIs in four skeletally mature dogs.
Two of the
56 MSIs could not be tested because of the inability to
prepare the specimens.
For the remaining 54 MSIs, the
pullout strength was found to be most in the posterior
mandible and least in the anterior mandible.
There was a
significant difference in the data collected from an
average of 338.3 N down to 134.5 N.
Huja et al. then
concluded, “A correlation between cortical bone thickness
and pullout strength was obtained.
Other factors such as
bone density and quality possible play roles in determining
pullout strength.”19
7
In another study, Huja et al. evaluated the
biomechanical stability of MSIs immediately after placement
and also after six weeks of healing.
They determined that
there was no significant difference in pullout strength
between the two times.
These results indicate that the
holding strength of MSIs is highly dependent on the initial
interface between the cortical bone and the MSI.14
Influences on MSI Failure
Sometimes MSI failure is defined as loss of ability to
hold anchorage.23 However, other studies conclude failure
occurs when mobility has reached a predetermined amount.24-26
Such implants may still be functional, but are slightly
mobile.
There are many reasons for MSI failure and some of
them will be discussed in greater detail.
Design of MSIs
With so many different companies marketing MSIs and
each company creating a product that is physically a little
different, the options seem endless when choosing which
implant is best.
However, many studies have been done
comparing a few of the different MSI characteristics so
that failure is reduced.
MSIs has been studied.
First, the length and diameter of
Mortensen et al. showed recently
8
that immediately loaded 3 mm MSI success rates were
significantly lower than 6 mm MSIs in Beagle dogs.15
A different study where 59 MSIs were placed in 29
patients compared the stability of 6 and 8 mm lengths.
The
success rate was 72.2% for the 6 mm and 90.2% for the 8 mm
MSIs.23 Miyawaki et al. followed 134 MSIs of different
diameters in the posterior region of the mouth for one
year.
Among other findings, they concluded that a MSI with
a diameter of less than 1.0 mm was associated with
increased mobility and failure.26
As recently as 2008, Brinley et al. evaluated the
effects of pitch and fluting on primary stability in a
synthetic and cadaver bone model.
Their work resulted in
the findings that, within certain parameters, decreasing
MSI thread pitch increases the primary stability.
In
addition, they concluded that decreasing MSI fluting
increases primary stability.27
Bone and MSI Interface
As was explained previously, the MSI to bone interface
is very important because it directly affects the primary
stability of the anchorage unit.14,28 When a MSI is inserted
into bone, many events occur.
Brunski et al. described
some of the cellular responses. Interestingly enough, the
9
first process that takes place is the adsorption of
proteins that have come from the blood and tissue fluids.
This adsorption causes a small amount of corrosion byproduct that permeates into the tissues.
This surface
conditioning, or oxidation, plays an important role in the
host response that follows.29
Ideally, the host response leads to tissue healing
giving a close contact between the MSI and bone.
Beginning
with a blood clot and moving through an afibrillar
interfacial zone, proteins such as osteopontin and bone
sialoprotein aid in the process of cell adhesion and
mineral binding.
This interfacial zone grows in two
directions, from the MSI toward the bone and from the bone
toward the MSI.
Osteoblasts, osteoid, and mineralized
matrix are all observed in the interfacial zone as
osseointegration occurs.29
Looking at it from a more mechanical perspective, it
has been shown that microfractures develop as the implant
is placed.30,31 Often, these microfractures are a result of
the shear stress that is introduced along the long axis of
the MSI upon insertion.32 As the implant is placed farther
and farther into the bone, this stress is increased and is
partly responsible for the increase in friction and torque
that is noted.
When a bone is placed under this type of
10
stress and friction, necrosis often occurs at the bone to
MSI interface.33 Nkenke et al. showed this necrosis and the
fibrous encapsulation of the MSI that can result in seven
mini pigs.34 Their study showed that not all of the necrotic
bone breaks down at the same time, but is often removed
over an extended period of time.
They reasoned that if
this were not the true process, there would almost always
be a loosening and loss of the MSI.34 Nkenke et al.
concluded, among other things, that there was no difference
between immediately loaded and unloaded implants with
regards to the bone mineral apposition rate.34
MSI Inflammation
Perhaps one of the greatest predictors of MSI failure
is inflammation around the tissues of the implant, or periimplantitis.24 In a very large and thorough study, Park et
al. examined 18 different clinical variables in 87
consecutive patients in which a total of 227 MSIs were
placed.
They followed the patients for 15 months to
determine the success rate as determined by loosening,
which equated with failure. They reported that the overall
success rate was 91.6%. In their study, no statistically
significant difference in success rates were found in
diameter, length, occlusogingival positioning, angle of
11
placement, timing or type of force application, ligature
wire extension, amount of exposed screw head, or oral
hygiene.
Age and sex also did not show any statistically
significant difference.
However, the jaw in which the MSI
was placed, the side of placement, and inflammation around
the implant were all statistically significant reasons for
failure.24 Nevertheless, the MSI typically must be placed
near the site of the needed anchorage.
This makes it
difficult for a practitioner to place the MSI in a more
ideal location and still achieve the desired results.
Therefore it is of importance to note that Park et al.
concluded that in order to minimize the failure of MSIs,
inflammation must be controlled.24 Park et al. are not alone
in concluding that inflammation around the MSI site is a
risk factor for failure.
Roberts et al., Maino et al., and
Johansson and Albrektsson all arrived at similar
conclusions.35,36,37
Another study showed that MSIs placed in nonkeratinized tissues have a greater failure rate due to an
increased inflammatory response.38 It is safe to conclude
from the literature that MSI success rate is inversely
related to peri-implantitis.
12
Insertion Torque
The amount of torque required to fully insert the MSI
is another factor that must be evaluated to reduce failure.
In 2006, Motoyoshi et al. recorded the maximum torque on
insertion of 124 MSIs in 41 orthodontic patients.
The
recorded values were between 7.2 Ncm and 13.5 Ncm depending
upon the location within the mouth.
Although they had not
suspected it, it was discovered that the MSIs in the
mandible had a significantly higher failure rate than the
maxilla, which corresponded to a higher insertion torque in
the mandible.
They concluded that, “according to our
calculations of the risk ratio for failure, to raise the
success rate of a 1.6 mm diameter mini-implant, the
recommended implant placement torque is within the range
from 5 to 10 Ncm.”39 In explaining this finding, the authors
theorized the higher torque resulted in a higher stress,
which led to bone degeneration at the bone to implant
interface, and ultimately the bone turnover in the area was
reduced.39
In a follow up study, they placed another 87 implants
in 32 patients and set out to determine whether cortical
bone thickness and implant placement torque had an effect
on stability.
With an 87% success rate after six months,
13
they discovered that the cortical bone thickness was
significantly greater for the implants that were not mobile
than those that had failed.
The success group had a mean
of 1.42 mm of cortical bone and the failure group only had
a cortical thickness of 0.97 mm on average.
The success
group also had torque values between 8 and 10 Ncm, whereas
the failure group tended to fall outside of that range.40
A different study, however, did state that the most
stable MSIs are placed in the densest bone.41 This study was
performed with several different types of MSIs and in
various locations on cadaver bone.
After reaching the
aforementioned conclusion, the authors noted that there
could be a maximum limit after which the bone would be
damaged if the insertion torque were too great.41
These same findings were not duplicated by Weichmann
et al. and Cheng et al. who both reported higher success
rates in the maxilla than in the mandible where the
insertion torques were less.
It was then deduced that the
MSIs were overheating the bone in the thicker cortical
plate of the mandible and thus leading to greater failure
rates.25,38 As of yet, there does not seem to be a consensus
on the maximum or minimum limits to insertion torque
throughout the literature.
14
MSI Fracture
An obvious reason for MSIs to fail is when the implant
itself fractures.
While conducting a biomechanical
comparison of four different MSIs, Mischkowski et al.
discovered that MSIs fracture at different insertion
torques depending on the design of the implant itself.42 If
the design reveals a weaker portion, a pilot hole may be
necessary to minimize the danger of screw fracture.
MSIs are typically placed under three phases of
mechanical loading throughout their use.
Phase one and
three are torsional loading when the implant is placed and
removed, and phase two is flexural loading when the MSI is
loaded during function.43 If the MSI design is flawed,
premature mechanical weakening can occur as the insertion
torque increases which increases the risk of fracture.43 A
significant study by Jolley and Chung indicates that
factors that contribute to increased fractures “include the
insertion site, bone density, and whether a pilot hole is
drilled.”44 They also state that changing the insertion
angle during placement, or when placing a MSI into an
object with greater density, such as a root, increases the
possibility for fracture.44
Another potential characteristic of MSIs that can lead
to fracturing is the alloy of the implant itself.
15
Depending on the mixture of metals that are combined to
produce the alloy, the MSI can be weakened and thus more
prone to fracture at lower torque values.
Specifically,
MSIs can be more prone to fracture depending on whether
hard or soft titanium is used.44
Friction
When two or more independent objects are in contact,
the motion of moving one of the objects past the other is
resisted by friction.45,46 This action of rubbing one surface
against the other plays a very important role at the bone
to MSI interface.
Friction can be reduced or overcome by
using some sort of lubricant such as water, oil, or grease
between the two surfaces.
Types of lubricants used in
medicine will be discussed later in greater detail.
Heat
One definition of heat is “thermal energy transferred
between a system and its surroundings.”47 While inserting a
MSI, thermal energy is produced in two different ways.48
First, when the drill bit shears the surface layer of a
material, the intermolecular bonds are broken and heat is
released.
Second, as the MSI is inserted into the bone,
friction from the non-cutting surfaces of the implant, such
16
as the flank and shaft, all produce thermal energy.48 This
heat is dissipated through the blood, tissue fluid, bone,
and the bone chips that are removed.
Even with these
outlets for the heat, bone is a poor heat conductor and it
is common for the temperature to rise considerably.48
As early as 500 BC, Hippocrates had a rudimentary idea
that heat produced while drilling in the skull was damaging
to the bone and tissues.
To prevent this, he recommended
dipping the drill in cold water frequently.49
All of the negative effects of heat on bone are still
not completely understood, but there has been substantial
research into this area.
It is currently taught that as
heat increases, protoplasmic proteins are changed along
with the inactivation of enzymes, metabolic processes, and
alterations in protoplasmic lipids.47 If the temperature is
elevated too much, water is transformed into a vaporous
state resulting in several other detrimental occurrences
such as dehydration, desiccation, shrinkage, membrane
rupture and even carbonization.50 Even more specific are the
effects of heat on proteins with their wide variation in
thermal resistivity.
Lysyl-rRNA-synthetase, for example,
is vital for cellular functions and can be denatured at
temperatures as low as 45° C that last for five minutes or
more.
There are small amounts of lysyl-rRNA-synthetase
17
that are denatured at even lower temperatures, around 40°
C.51 More resistant proteins include collagen at 60° C and
bone alkaline phosphatase at 56° C.47,52
Much more recently, Karmani summarized the effects of
drilling on bone.
In recapping the literature, the author
determined that the drill speed, the condition of the
drill, and the use of coolants all had effects on the post
surgical reaction of the bone.47
Eriksson et al. recorded the maximum insertion
temperature at a distance of 0.5 mm from the periphery of
the drill hole.
Their study included five rabbits, two
dogs, and five humans.
Using a constant drill speed, it
was discovered that the mean temperatures were as great as
40° C in rabbits, 56° C in dogs, and 89° C in humans.
The
initial bone temperatures were reported at 32° C in both
rabbits and dogs, but was not reported for the human
subjects.
Eriksson et al. concluded that the difference in
temperature was due to the variation in cortical thickness
between the three subject groups.53 Because the cortical
bone in the mandible is typically thicker than the maxilla,
this study may help explain why the findings of others show
there is a greater failure rate of MSIs in the mandible.
While doing further research Eriksson and Albrektsson
determined that the critical threshold at which necrosis
18
occurs is 47° C for one minute in rabbits.54,55 This
temperature is under which bone should be kept in order to
promote increased stability and decreased bone necrosis.
Lubricants in Medicine
For many years, lubricants have been applied to
various surfaces to reduce friction.
Lubricants can be
applied either in a solid, mist, or liquid form.5 Wax in
particular is often used when either oil or grease is not
appropriate.5 The properties of wax have been shown to
reduce friction and have good wear resistance.56 As recently
as 2008, Quaglini et al. studied the ideal roughness of a
metal material with some of the more common lubricants in
reducing friction.
By applying six different polymer
lubricants to steel and measuring the sliding velocity
between the metal surfaces, the best lubricant and steel
surfaces were determined.
They discovered that the ideal
interaction for smoothly polished metal surfaces are
lubricants with low modulus of elasticity.56 Lubricants that
were wax based, although not the best, also showed good
friction reducing characteristics in this study.56
Tribology is defined as the “study of friction, wear,
lubrication mechanisms, and their interrelationships.”57
Since 1973, biotribology has become a branch of tribology
19
that focuses on friction and lubricants that are used in
the body, especially in joints.57 The human body naturally
produces various lubricants to reduce friction between
articulating surfaces.
Some examples of these lubricating
components that have shown to reduce friction include
synovial fluid, lubricin, hyaluronic acid, surface active
phospholipids, and chondroitin sulphate.58 When the body no
longer produces enough of these lubricating components,
commercially available supplements and replacements are
available.
Hyaluronic acid derivatives, peptides,
synthetic phospholipids, recombinant lubricin, low
molecular weight hyaluronate, and high molecular weight
hyaluronate have all been approved and marketed to be
placed in the human body to lubricate the appropriate
sites.59-61,58
Bone wax, essentially sterile bees wax, has been used
in medicine since the 1840s.6 Gupta and Prestigiacomo
summarized the use of bone wax over more than 100 years and
described some of its uses.
It has historically been used
as a way of controlling bleeding, especially in the
cranium.
Some of the properties that have made it so
desirable in applying it over an exposed bone that is
hemorrhaging include being soft, malleable, and nonbrittle.6
Bone wax is also inexpensive and readily available.7
20
Another form of a potential lubricant that is used in
medicine is a water-soluble polymer called Ostene®.
One of
the more significant studies using Ostene® and bone wax
involved 20 New Zealand White rabbits.
Median sternotomies
were performed and either bone wax or Ostene® was
sufficiently applied to result in hemostasis.
After a six-
week time frame, the healing was inspected using x-rays,
histology, and mechanical strength testing.
The results of
the inspections indicated in the Ostene® group normal bone
healing had occurred and that the strength was twice as
much as the bone wax group.
They also demonstrated that in
the bone wax group fibrotic scar tissue formed rather than
bone.62
One of the major disadvantages of bone wax is it does
not inhibit infection.
Wellisz et al. compared the
infection rates and healing in 24 rabbit tibias between
bone wax, Ostene®, and a control group.
Immediately after
the defects were made and treated according to the study,
they were inoculated with Staphylococcus aureaus.
After
four weeks, all of the bone defects treated with bone wax
were infected and osteomyelitis had developed.
observed that no bone healing had occurred.
It was also
However, in
the control and Ostene® groups there was a statistically
significant lower rate of osteomyelitis and higher rate of
21
healing.
This study shows that using a soluble-polymer
material, such as Ostene®, rather than bone wax can
decrease the rates of postoperative bone infections.8
As we can see, the literature demonstrates that there
are many factors influencing MSI failure.
Among them, high
insertion torque and heat generated by friction are two
that can be diminished by a surface lubricant.
Two popular
FDA approved substances, bone wax and Ostene®, are
currently being used in medicine to reduce hemostasis, but
potentially can reduce the effects of both high insertion
torque and the heat generated by friction on human bone.
This could lead to a MSI that provides better anchorage by
being more stable and failing less frequently, a type of
anchorage that is highly beneficial for the orthodontic
profession.
22
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32. Hughes AN, Jordan BA. The mechanical properties of
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42. Mischkowski R, Kneuertz P, Florvaag B, Lazar F, Koebke
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Ann Thorac Surg. 2008;85:1776-80.
28
CHAPTER 3: JOURNAL ARTICLE
Abstract
Purpose:
The purpose of this investigation was to evaluate
the change in insertion torque and the effects of the
implant-bone interface of miniscrew implants (MSIs) that
were treated with a surface lubricant of either bone wax or
Ostene®.
Methods:
MSIs coated with bone wax or Ostene®
were compared to control MSIs to determine the acute
difference in insertion torque when placed in synthetic
bone and pig femur.
The pullout strength was also
evaluated using the MSIs placed in the synthetic bone.
In
addition, MSIs coated with bone wax or Ostene® were
compared to control MSIs to determine the difference in
insertion torque in synthetic bone and pig spare ribs at
five second intervals from initial insertion until fully
seated using a custom insertion machine.
Histological
samples of Beagle dogs were evaluated for the cellular
response around the MSI controls, MSIs coated with bone
wax, and MSIs coated with Ostene® immediately after removal
and after two weeks of healing.
Results:
A significant
difference (p<.05) in insertion torque was found between
the MSI control group and both the bone wax and Ostene®
groups in synthetic bone with the control group requiring
29
the greatest insertion torque.
No significant differences
(p>.05) were found between any groups for insertion torque
when the MSIs were placed in a pig femur or for pullout
strength in the synthetic bone.
Additional testing showed
that at time points T1, T2, T3, and T4 (15, 30, 45, and 60
seconds respectively), the MSI control group required a
statistically significant (p<.05) greater torque to insert
the MSIs in synthetic bone than when treated with bone wax
or Ostene®.
No differences were shown when each group was
placed in pig spare ribs at any time point.
Conclusions:
Lubricating MSIs with bone wax or Ostene® reduces the
insertion torque in synthetic bone.
Introduction
Orthodontic miniscrew implants (MSIs) have been widely
accepted as a very useful tool in establishing and
maintaining nearly absolute anchorage in order to correct
various orthodontic problems.1,2 MSIs can be used in many
different parts of the oral cavity to establish either
direct or indirect anchorage; however, MSIs may come loose
and even have the potential to fail.
In order to have the greatest success when using MSIs,
each potential aspect of failure must be addressed.
Many
studies have focused on determining the reasons for MSI
30
failure.
It has been shown that inflammation around the
MSI site is risk factor for failure.3-6 Successful MSI
placement must be achieved without fracturing the implant.
Each MSI fractures at different torque values depending on
the design.7 The location of the insertion site, bone
density, insertion angle, potential barriers within the
bone and whether a pilot hole has been drilled are all
contributing risk factors that also affect MSI fracture.8
Another important aspect of MSI failure can be related
to high insertion torque, which leads to increased friction
that then produces heat and bone necrosis.
Karmani et al.
explained that drilling in bone produces heat by breaking
intermolecular bonds as each layer of material is sheared
off.
This often occurs in two ways.
First, the cutting
surface breaks the molecular bonds, which releases energy,
and second, the non-cutting surface of the screw produces
friction and heat.9 Thus, the denser the bone, the greater
the friction produced.
Because bone is a poor conductor of heat, the
temperature can rise significantly and damage can occur.
This increase in temperature can lead to bone necrosis and
later implant failure.
The temperature of vital bone in
rabbits is approximately 32°C.
However, rabbit bone can be
damaged if it reaches the threshold of 47ºC for as little
31
as one minute.10 In another study by the same authors, the
range for bone damage was determined to be even lower,
between 44ºC and 47ºC for one minute.11 Once necrosis has
occurred, for a MSI to be successfully stable, the damaged
bone from the placement must regenerate.11
Many MSIs are self-drilling, that is, they do not
require a pilot hole.
Whether a pilot hole is first
created, or a self-drilling implant is used, the bone
temperature surrounding the MSI can rise beyond the 44ºC47ºC limit and lead to bone necrosis and ultimately MSI
failure.
In addition, some orthodontists place MSIs
without irrigation and with greater speed than is
recommended.
Both of these technical errors may lead to an
increase in temperature as well.11
Biotribology, or the study of friction, wear, and
lubrication mechanisms relating to a biological
environment, has been researched since 1973.12 As joints in
the body lose the natural lubrication that they posses,
commercially available supplements such as hyaluronic acid
derivatives, peptides, synthetic phospholipids, recombinant
lubricin, low molecular weight hyaluronate and high
molecular weight hyaluronate all serve to lubricate and
reduce friction between bone and cartilage.13-16 This
32
artificial lubrication works to increase the longevity of
the original tissue.
Bone wax has been used in medicine since the 1800s as
a way to maintain hemostasis during surgical procedures.17
Throughout the years it has been widely used because it is
not very expensive and typically its use produces few
related complications.18
Ostene® is a water soluble-polymer that has gained more
acceptance as studies have shown that it has greater
biocompatibility and less incidence of infection is seen
when it is used.
It has also been shown to increase bone
healing at the surgery site. Using 20 rabbits, Wellisz et
al. compared the results when placing Ostene® and bone wax
on median sternotomies.
The samples taken after six weeks
identified normal bone healing in the soluble-polymer group
while the bone wax group showed an absence of new bone
formation.19
The purpose of this study was to compare MSIs that
were coated in either bone wax or Ostene® to MSIs without a
coating to determine whether the amount of friction
required to place the implants could be decreased and what
the effect on the implant-bone interface would be.
33
Materials and Methods
Miniscrew Implants
MSIs were randomly assigned to one of three groups:
control, surgical wax, or Ostene®.
All the MSIs were 3M
Unitek 6 mm long and 1.6 mm in diameter IMTEC implant.
Nothing was done to the control group and they were used
immediately after removal from the sterile package (Fig
3.1).
A. Control
B. Bone Wax
C. Ostene®
Figure 3.1 MSIs used in this research A. Control MSI, B. MSI coated
with bone wax, C. MSI coated with Ostene®
The wax group was dipped in surgical wax heated to
150°F. The MSIs were weighed before and after the coating
process to ensure a uniform amount of lubricant was placed.
The mean amount of bone wax applied to each MSI was 7.0 mg.
Each MSI with the coating cooled completely to room
temperature before being inserted.
34
The Ostene® group were dipped in Ostene® heated to
150°F.
The MSIs were weighed before and after the coating
process to ensure a uniform amount of lubricant was placed.
The mean amount of Ostene® applied to each MSI was 7.7 mg.
Each MSI with the coating cooled completely to room
temperature before being inserted.
Testing Methods
Two models were used to test the effects of lubricants
on MSIs.
First, each group of MSIs was inserted into a
synthetic bone material that was uniform in nature.
Second, each group of MSIs was placed in a pig femur that
resembles the density of human bone.
Synthetic Bone Model
A manufactured block of synthetic polyurethane
cancellous bone (Sawbones®, Vashon, WA) was employed to
determine the insertion torque and pullout strength of each
MSI.
Synthetic bone use has become more desired in implant
research because of the uniform material properties it
exhibits.20-22 The synthetic model had a density of 0.64g/cc,
a compressive strength of 31 MPa, a tensile strength of 19
MPa, a shear strength of 11 MPa, and a moduli of 759 MPa,
1000 MPa, and 130 MPa respectively.
35
Ten mm cubes of the
synthetic bone were cut from a larger block for testing.
30 MSIs from each of the three groups were tested.
Pig Femur
A fresh pig femur was used.
All remaining soft
tissues were removed and the femur was examined for overt
pathology.
Thirty MSIs of each of the three groups were
placed randomly in the articular head. With each MSI
insertion, the torque was carefully measured and recorded.
Mechanical Testing
The effect of the lubricants on the MSI was evaluated
by measuring the insertion torque and the pullout strength.
The insertion torque was chosen as a way to measure the
primary stability of the MSIs because it is a common
standard to evaluate stability and has been found to be a
good predictor of the bone to implant interface.23 The
pullout test was also conducted because it is often used to
test implant design on primary stability.24-26
Placement Torque
All measurements for insertion torque were recorded
using a Mecmesin® Advanced Force and Torque Indicator
36
(Mecmesin, Ltd, West Sussex, UK) and maximum insertion
torque (MIT) was recorded in Ncm.
The synthetic bone cubes were placed in a base and a
jig to secure and guide the placement of the MSIs was
attached over the base.
The jig allowed each MSI to be
placed in a vertical direction until one thread (360°)
remained exposed above the level of the synthetic bone.
At
this point, the Mecmesin® instrument was attached and the
torque was recorded for a one-half turn (180°), thus
leaving half of a thread exposed (Figure 3.2). This method
was used to avoid countersink friction, which is the
product of the head of the MSI contacting and compressing
the bone, leading to a dramatic spike in the insertion
torque.27,28
Mecmesin® torque
indicator
Custom jig
MSI and synthetic
bone block
Figure 3.2 Custom jig securing synthetic bone block with Mecmesin®
instrument attached to driver and MSI
37
The MSIs placed in the pig femur were also hand placed
into the specimens in a vertical direction until one thread
(360°) remained exposed. At this point, the Mecmesin®
instrument was attached and the torque was recorded for a
one-half turn (180°), thus leaving half of a thread
exposed.
Pullout Analysis
Following the recording of the insertion torques, all
of the MSIs that were placed in synthetic bone were also
evaluated to determine the amount of force required to pull
them out in a direction coincident with the long axis of
the MSI.
Each block with the MSI imbedded in it was placed
in a custom base with a lid to secure it while an adapter
was attached to the head of the implant.
The adapter was
then secured to an Instron Machine Model 1011 (Instron
Corp, Canton, MA).
A vertical force at the rate of 10
mm/min was exerted parallel to the long axis of the MSI
until failure occurred.
load failure in Newtons.
The Instron machine recorded peak
The pullout strength of a MSI is
established as the tensile force required to remove it from
a medium.25
38
Animals
The sample included two healthy male, 12 month old
beagle dogs (approximate weight 8kg).
They were obtained
from Marshall Bio-Resources (North Rose, NY) and were
immediately placed on a soft diet (Canidea® Lamb and Rice,
Canidea Corporation, San Louis Obispo, CA and 5006 Canine
Diet, PMI Nutrition International, LLC., Brentwood, MO) one
week prior to MSI placement.
The husbandry was conducted
by the Comparative Medicine Department of Saint Louis
University Medical School.
All procedures were pre-
approved by the Saint Louis University Animal Care
Committee (Authorization #2010).
MSI Placement
Both dogs were administered 25 mg/kg of Enrofloxacin
(Baytril, Bayer Health Care, LLC., Animal Health Division,
Shawnee Mission, KS) intravenously as a prophylactic
measure and again for two days post surgery.
Carprofen
(Rimadyl®, Pfizer Animal Health, Exton, PA) 4mg/kg was
administered subcutaneously for analgesia.
Induction was
obtained using propofol (Propofol®, ABBOTT Animal Heath,
Exton, PA) 7 mg/ml.
Maintenance for both dogs was achieved
using isoflurane (Aerrane, Baxter Healthcare Corporation,
Deerfield, IL) 2-3% and an IV drip of 0.9% sodium chloride
39
(Hospira, Inc., Lake Forest, IL) at a rate of 12 ml/kg/hr.
Pre-operative lateral head plate radiographs were taken to
determine where sufficient bone existed between the teeth
in order to place the MSIs.
The selected sites were
swabbed with 0.12% chlorhexidine gluconate (Acclean®, Henry
Schein, Inc., Melville, NY).
15 MSIs were then placed
through the soft tissues and into the mandible of each
beagle.
Five MSIs in each of the three groups, control,
bone wax, and Ostene® were randomly assigned to locations
in the mandible.
On the left side, two MSIs were placed
below the 3rd premolar furcation, between the 3rd premolar
and 1st molar, below the 1st molar furcation, and between the
1st and 2nd molars (Figure 3.3).
On the right side, each dog
received one MSI below the furcation of the 3rd premolar and
two MSIs between the 3rd premolar and 1st molar, below the
furcation of the 1st molar, and between the 1st and 2nd molar
(Fig 3.4).
No pre-drilling was done and the MSIs were
placed using a hand driver.
After all MSIs were inserted,
a follow-up lateral head plate radiograph was taken to
verify that none of the MSIs were touching the roots of any
teeth.
Both dogs were given 0.2 ml acepromazine maleate
(WEDCO, Inc., St. Joseph, MO) IV to calm post anesthetic
excitement.
40
Figure 3.3 Placement of MSIs (red dots) on dog’s right side
Figure 3.4 Placement of MSIs (red dots) on dog’s left side
MSI Lubricant Evaluation
Both dogs were allowed to heal for four weeks.
After
the healing time, the first dog’s MSIs were removed
following the same operative procedure used at insertion.
This dog was then allowed to heal for two more weeks before
it was sacrificed for histological evaluation of the MSI
sites.
The second dog, after the initial four-week healing
time period, was sacrificed with the MSIs still in place
and the mandible was sectioned for histological evaluation
as well.
The two dogs were sacrificed by giving 260 mg of
41
sodium pentobarbital (Fort Dodge Animal Health, Fort Dodge,
IA) intravenously.
The histological specimens of the two Beagle dogs will
be evaluated when they become available and placed in the
appendix.
Further Research
In order to reduce the amount of human error in the
project and produce more accurate results, a second series
of torque measurements were obtained on both synthetic bone
and pig spare ribs using a custom made device.
The same
type of synthetic bone that was previously used was again
tested.
A jig to hold the specimen was attached to a motor
with a constant rotational speed of nine revolutions per
minute (Figures 3.5 and 3.6).
Using a drill press that was
modified to secure the torque indicator in place, the MSI
was lowered by a constant weight (three pounds for the
synthetic bone and four pounds for the ribs) attached to
the arm of the drill press.
As this constant pressure
connected the MSI and the rotating specimen, a video camera
recorded the amount of torque at all time points for 70
seconds, the time needed to fully insert the MSI up to the
tip of the driver.
The videotape was then reviewed and the
42
insertion torque for each MSI was graphed at five-second
intervals.
Drill Press
Torque Indicator
Rotating Specimen
Constant Weight
Figure 3.5 Custom insertion torque machine from left side
43
Torque Indicator
Rotating Specimen
Motor with
Constant
Rotation
Figure 3.6 Custom torque machine from back showing motor attached under
drill press table
Statistical Analysis
Analyses of variance and post hoc tests were used to
determine whether significant differences (p<.05) were
present regarding the initial torque insertion of the
synthetic bone, pig femur, and pullout strength.
The
nonparametric Mann-Whitney test and independent t-test were
used to determine if there were significant differences
(p<.05) at T1, T2, T3, and T4 (15, 30, 45, and 60 seconds
respectively) between the groups tested with the custom
built insertion machine for the synthetic bone and the pig
44
spare ribs.
The statistical analysis was processed with
SPSS software. (SPSS for Windows, version 16.0, SPSS,
Chicago, Ill).
Results
Standard Tests
Synthetic bone model insertion torque
MSIs coated with bone wax or Ostene® showed a
significant (p<.05) difference for insertion torque when
compared to the control (Tables 3.1 and 3.2).
Post hoc
tests demonstrated that both the MSIs with an application
of bone wax or Ostene® resulted in a significantly lower
insertion torque than the MSIs without any coating.
There
was no significant difference (p>.05) found between the
MSIs coated with bone wax and Ostene®.
Synthetic bone model pullout
There was no significant (p>.05) difference between
the control, MSIs coated with bone wax, and MSIs coated
with Ostene® regarding the amount of force required to pull
the MSI out of the synthetic bone in a vertical direction
(Table 3.2).
45
Pig femur model
There was no significant (p>.05) difference between
the control, MSIs coated with bone wax, and MSIs coated
with Ostene® for the insertion torque of MSIs placed in a
pig femur (Table 3.2).
Table 3.1 Descriptive statistics for MSIs in synthetic bone and pig
femur
———————————————————————————————————————————————————————————
Control
Bone Wax
Ostene®
Measurements
(n=30)
(n=30)
(n=30)
———————————————————————————————————————————————————————————
Torque in
Synthetic Bone (Ncm)
Mean
13.0 ± 1.8
9.8 ± 1.9
9.5 ± 2.4
Torque in
Pig Femur (Ncm)
Mean
8.6 ± 1.7
8.5 ± 1.4
7.9 ± 1.5
Pull-out in
Synthetic Bone (N)
Mean
18.5 ± 1.9
17.9 ± 2.5
19.7 ± 3.0
———————————————————————————————————————————————————————————
Table 3.2 Statistical comparison of original measurements
———————————————————————————————————————————————————————————————————————
Diff. in
Measurements
means
p
———————————————————————————————————————————————————————————————————————
Torque in Synthetic Bone (Ncm)
Control-Bone Wax
2.97
<.001*
Control-Ostene®
3.25
<.001*
Bone Wax-Ostene®
.28
.837
Torque in Pig Femur (Ncm)
Control-Bone Wax
.16
.912
Control-Ostene®
.76
.122
Bone Wax-Ostene®
.60
.261
Pull-out in Synthetic Bone (N)
Control-Bone Wax
.52
.780
Control-Ostene®
-1.22
.257
Bone Wax-Ostene®
-1.74
.067
———————————————————————————————————————————————————————————————————————
* Equals significant difference at p<.05
46
Custom Insertion Machine Tests
Synthetic bone model
All MSIs in each group are shown in Figures 3.7, 3.8,
3.9.
3.10.
The average of each group is represented in Figure
At all time points T1, T2, T3, and T4 (15, 30, 45,
and 60 seconds respectively), there was a statistically
significant difference of insertion torque between the
control and bone wax groups (p<.05) tested in synthetic
bone with the bone wax coated MSIs requiring less insertion
torque (Tables 3.3 and 3.4).
This same finding of a
statistically significant difference (p<.05) was found
between the control and Ostene® groups where the Ostene®
group also required less insertion torque.
However, when
comparing the bone wax and Ostene® groups, there was a
statistically significant difference found at time points
T2 and T4 (p<.05), but not at T1 and T3 (p>.05).
For all
time points, Ostene® coated MSIs were shown to require less
insertion torque than the control group.
47
Control MSIs in Synthetic Bone
25
20
Screw 1
Screw 2
Screw 3
Screw 4
Screw 5
Torque (Ncm)
15
Screw 6
Screw 7
Screw 8
Screw 9
10
Screw 10
Screw 11
Screw 12
Screw 13
5
0
0
5
10
15
20
25
30
35
40
45
50
55
60
65
70
Time (Seconds)
Figure 3.7 Individual control MSI’s insertion torque over time in
synthetic bone
48
MSIs Coated with Bone Wax in Synthetic Bone
25
20
Screw 1
Screw 2
Screw 3
Screw 4
Screw 5
Torque (Ncm)
15
Screw 6
Screw 7
Screw 8
Screw 9
10
Screw 10
Screw 11
Screw 12
Screw 13
5
0
0
5
10
15
20
25
30
35
40
45
50
55
60
65
70
Time (Seconds)
Figure 3.8 Individual bone wax coated MSI’s insertion torque over time
in synthetic bone
49
MSIs Coated with Ostene® in Synthetic Bone
25
20
Screw 1
Screw 2
Screw 3
Screw 4
Screw 5
Torque (Ncm)
15
Screw 6
Screw 7
Screw 8
Screw 9
10
Screw 10
Screw 11
Screw 12
Screw 13
5
0
0
5
10
15
20
25
30
35
40
45
50
55
60
65
70
Time (Seconds)
Figure 3.9 Individual Ostene® coated MSI’s insertion torque over time
in synthetic bone
50
Figure 3.10 Average of each group of MSIs’ insertion torque over time
in synthetic bone
Table 3.3 Descriptive statistics of MSIs in Synthetic Bone (T1, T2,
T3, and T4 equal 15, 30, 45, and 60 seconds respectively)
———————————————————————————————————————————————————————————
Control
Bone Wax
Ostene®
Time
(n=13)
(n=13)
(n=13)
———————————————————————————————————————————————————————————
T1
Mean
2.07 ± 3.29
.66 ± .30
.46 ± .27
(Ncm)
T2
Mean
3.83 ± 1.03
2.77 ± .69
2.23 ± .44
(Ncm)
T3
Mean
9.67 ± 1.10
7.51 ± 1.55
6.52 ± 1.10
(Ncm)
T4
Mean
15.83 ± 1.27 13.64 ± 1.70
11.97 ± 1.06
(Ncm)
———————————————————————————————————————————————————————————
51
Table 3.4 Statistical comparison of MSIs in Synthetic Bone (T1, T2, T3,
and T4 equal 15, 30, 45, and 60 seconds respectively)
———————————————————————————————————————————————————————————————————————
Independent
Mann-Whitney U test
t-test(n=13)
(n=13)
———————————————————
————————————————————————————
t
p
Diff. in
p
Time
means
———————————————————————————————————————————————————————————————————————
T1
Control-Bone Wax
1.53
.138
10.38
<.001*
Control-Ostene®
1.75
.092
12.54
<.001*
Bone Wax-Ostene®
1.78
.089
5.38
.072
T2
Control-Bone Wax
3.08
.005*
8.92
.002*
Control-Ostene®
5.15
<.001*
11.00
<.001*
Bone Wax-Ostene®
2.36
.027*
6.54
.029*
T3
Control-Bone Wax
4.10
<.001*
9.76
.001*
Control-Ostene®
7.31
<.001*
12.70
<.001*
Bone Wax-Ostene®
1.89
.071
5.00
.101
T4
Control-Bone Wax
3.73
.001*
9.7
.001*
Control-Ostene®
8.39
<.001*
12.92
<.001*
Bone Wax-Ostene®
3.00
.006*
7.76
.009*
———————————————————————————————————————————————————————————————————————
* Equals significant difference at p<.05
Pig spare ribs
All MSIs in each group are shown in Figures 3.11,
3.12, 3.13.
The average of each group is represented in
Figure 3.14.
At all time points T1, T2, T3, and T4 (15,
30, 45, and 60 seconds respectively), there was no
statistically significant (p>.05) difference of insertion
torque between the control group, bone wax group, or
Ostene® group in pig spare ribs (Tables 3.5 and 3.6).
52
Figure 3.11 Individual control MSI’s insertion torque over time in pig
spare ribs
53
Figure 3.12 Individual bone wax coated MSI’s insertion torque over time
in pig spare ribs
54
Figure 3.13 Individual Ostene® coated MSI’s insertion torque over time
in pig spare ribs
55
Figure 3.14 Average of each group of MSIs’ insertion torque over time
in pig spare ribs
Table 3.5 Descriptive statistics of MSIs in pig spare ribs (T1, T2, T3,
and T4 equal 15, 30, 45, and 60 seconds respectively)
———————————————————————————————————————————————————————————
Control
Bone Wax
Ostene®
Time
(n=13)
(n=13)
(n=13)
———————————————————————————————————————————————————————————
T1
Mean
1.38 ± 1.72
.88 ± .94
1.06 ± .68
(Ncm)
T2
Mean
4.43 ± 2.11
3.91 ± 1.38
3.76 ± .82
(Ncm)
T3
Mean
8.01 ± 3.12
7.53 ± 2.73
7.33 ± 1.29
(Ncm)
T4
Mean
10.32 ± 3.91
9.34 ± 4.17
9.70 ± 2.31
(Ncm)
———————————————————————————————————————————————————————————
56
Table 3.6 Statistical comparison of MSIs in pig spare ribs (T1, T2, T3,
and T4 equal 15, 30, 45, and 60 seconds respectively)
———————————————————————————————————————————————————————————————————————
Independent
Mann-Whitney U test
t-test(n=13)
(n=13)
—————————————————————
——————————————————————————
t
p
Diff. in
p
Time
means
———————————————————————————————————————————————————————————————————————
T1
Control-Bone Wax
.919
.367
3.76
.223
Control-Ostene®
.629
.535
.38
.920
Bone Wax-Ostene®
-.505
.588
-3.38
.960
T2
Control-Bone Wax
.749
.461
2.16
.479
Control-Ostene®
1.070
.297
2.84
.362
Bone Wax-Ostene®
.329
.745
-.16
.960
T3
Control-Bone Wax
.415
.682
.92
.762
Control-Ostene®
.723
.477
1.30
.687
Bone Wax-Ostene®
.239
.813
.16
.960
T4
Control-Bone Wax
.616
.544
1.92
.545
Control-Ostene®
.489
.629
1.76
.579
Bone Wax-Ostene®
-.273
.787
-.84
.801
———————————————————————————————————————————————————————————————————————
* Equals significant difference p<.05
Discussion
The purpose of this study was to determine if coating
MSIs with bone wax or Ostene® would reduce the amount of
insertion torque and what histological responses would be
noted when these same lubricants were used.
During the initial experiments, although the synthetic
bone model testing showed that a significant reduction in
torque existed when the control group was compared to the
bone wax and Ostene® groups, human error and large amounts
of variability existed. It is of interest to note that even
though the pullout force was not statistically significant
57
when comparing the three groups, more force was required to
remove the Ostene® coated MSIs than the others.
Even though recording 180º of insertion torque on the
final thread has been used often in the past, there is room
for inaccuracy.
It is at times difficult to determine
precisely the final 180º before insertion is complete.
Even with jigs and other aids, this final half of a turn is
not always easily ascertained and varying even 90º can make
a difference.
In addition to this challenge, it is even
more difficult to keep the Mecmesin® machine from leaning
from one side to another and introducing even more torque
and variability.
Jigs have been used to reduce some of the
error when testing uniform pieces of synthetic bone, but
testing bones with different dimensions make using a
standard and firm jig less feasible.
The speed of the
final 180º turn can also affect the maximum torque
registered.
Another area where this particular method of
testing was limited is in the ability to know the insertion
torque at various points along the insertion path.
It is
possible the lubricant impacted the insertion torque only
at certain position along the way and not others, though
the author is unable to account for these differences in
this specific study.
With these variables and others that
are inherent in the system recognized, it was determined to
58
do a second set of experiments using a new custom designed
device with the goal of eliminating or greatly reducing the
inaccuracies.
The data collected from the new custom designed device
produced valuable information.
As is expected from Figure
3.10, at all time points T1, T2, T3, and T4 (15, 30, 45,
and 60 seconds respectively), there was a statistically
significant (p<.05) difference of insertion torque between
the control and both the bone wax and Ostene® groups in
synthetic bone with the bone wax coated MSIs and Ostene®
coated MSIs requiring less insertion torque than the
control MSIs.
When the MSIs were coated with bone wax, the
insertion torque was reduced by 68%, 28%, 22%, and 14% at
T1, T2, T3, and T4 respectively when compared to the
control group.
Likewise, the Ostene® coated MSIs reduced
the insertion torque by 78%, 28%, 33%, and 24% at T1, T2,
T3, and T4 respectively when compared to the control group.
This shows that upon insertion, and until the MSI is
completely seated in the synthetic bone, MSIs coated with
bone wax or Ostene® substantially reduce the amount of
torque required to place the MSI.
It is hypothesized that
this will then reduce the amount of heat generated and
therefore less bone damage would be expected.
59
This in turn
might produce better primary and secondary stability and
decreased MSI failure.
However, when comparing the bone wax and Ostene®
groups in the synthetic bone, there was a statistically
significant difference found at time points T2 and T4
(p<.05), but not at T1 and T3 (p>.05).
Time points T1 and
T3 were trending toward significance, nevertheless.
For
all time points, Ostene® coated MSIs were shown to require
less insertion torque.
Even with the custom insertion machine, the variation
within the same pig spare rib and between pig spare ribs
proved too much to accurately demonstrate the effects of
lubricants on MSIs.
There was no significant difference
(p>.05) between any of the groups.
Conclusions
-
MSIs coated with bone wax significantly decreases the
amount of torque required for insertion in synthetic bone.
-
MSIs coated with Ostene® significantly decreases the
amount of torque required for insertion in synthetic bone.
-
There is not a significant difference between the bone
wax and Ostene® groups at all time points when inserted in
synthetic bone.
60
-
No significant difference was found in the pullout
strength for MSIs coated with bone wax or Ostene® when
compared to the control group.
-
No significant difference was found in insertion torque
between the control, bone wax and Ostene® group when placed
in pig spare ribs.
61
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64
APPENDIX
Throughout this research, several other types of
lubricants were experimented with and the data is shown
below.
Figure A.1 Individual bath soap coated MSI’s insertion torque over time
in synthetic bone
65
Figure A.2 Individual candle wax coated MSI’s insertion torque over
time in synthetic bone
66
Figure A.3 Individual control MSI’s insertion torque over time in
synthetic bone without the help of the custom insertion machine
67
Figure A.4 Averages of each group of MSIs’ insertion torque over time
in synthetic bone (n=5)
68
VITA AUCTORIS
Robert Jay Marshall was born January 24, 1980, in
Bigfork, Montana to Jon and Jean Marshall.
He attended
Ricks College from September through December of 1998.
From 1999 to 2001, he lived in Peru while serving a mission
for The Church of Jesus Christ of Latter-day Saints.
Upon
his return he attended Brigham Young University-Idaho from
2001 to 2003.
Robert entered the University of Minnesota
School of Dentistry in 2003 and graduated with a Doctor of
Dental Surgery in 2007.
He continued is his education in
pursuit of a master’s degree from Saint Louis University’s
Center for Advanced Dental Education in 2007.
Upon
graduation in January 2010, Dr. Marshall and his family
will move to Great Falls, Montana, where he will practice
orthodontics.
69