Download AMOUNT OF TOOTH MOVEMENT GENERATED BY TWO

AMOUNT OF TOOTH MOVEMENT GENERATED BY TWO
DIFFERENT ORTHODONTIC FORCE APPLICATIONS
Nalinee Srianantanon1,*, Supatchai Boonpratham2,#, Suwannee
Luppanapornlarp3, Rudee Surarit4
1
Master of Science (Orthodontics), Department of Orthodontics, Faculty of Dentistry,
Mahidol University, Thailand
2,3
Department of Orthodontics, Faculty of Dentistry, Mahidol University, Thailand
4
Department of Oral Biology, Faculty of Dentistry, Mahidol University, Thailand
*e-mail: [email protected], #e-mail: [email protected]
Abstract
Background: Orthodontic tooth movement occurs as a result of bone and surrounding tissue
remodeling. Many researchers have been studied in animals and human to identify the
optimal magnitude or range of force for orthodontic tooth movement. Previous findings in
human showed the proper forces for tooth movement had range from 18 g force to 1515 g
force. The optimal force that can be recommended for clinical use is still controversy. This
study aimed to compare the effectiveness of 50g and 150g orthodontic forces by measuring
the amount of tooth movement after 2 months of canine retraction.
Materials and methods/ Study designs: Five female patients, aged 18-30 years old who had
four first bicuspid extraction were participated in this study. The upper canines were retracted
with continuous 50g and 150g forces using NiTi coil springs on segmented archwires using a
miniscrew implant as an anchorage. A cone beam computed topographic (CBCT) images
were taken before force application and 2 months after canine retraction. The two images
from cone beam computed tomography or CBCT were superimposed by using all posterior
teeth as reference points. The distance between distal most of the crown of the two
superimposed canines was used to determine the amount of tooth movement.
Results: A paired t-test was used for comparing the amount of canine movement between the
50g and 150g force. No significant difference in the amount of tooth movement was found
between two different magnitudes of force at two months (p < 0.05).
Conclusions: Both 50g and 150g forces could effectively induce tooth movement in a similar
manner.
Keywords: tooth movement, optimal force, CBCT
Introduction
Orthodontic tooth movement results from applying forces to teeth. This
stimulation induces cellular responses in dental and paradental tissues, including dental pulp,
periodontal ligament, alveolar bone, and gingiva (1). Orthodontic force moves teeth through
bone to obtain a more perfect dental occlusion. The proper force magnitude and knowledge
of tissue response can lead to the accurate and precise control of tooth movement.
Mechanical force alters the blood flow and localized electrochemical
environment leading to change of homeostatic environment of the periodontal ligament
space. An optimal magnitude of force is capable of evoking an inflammatory response in
paradental tissues, resulting in remodeling of tissues and efficient tooth movement into their
desired position.
There have been many studies in animals and human tried to find the optimal
magnitude or range of force for orthodontic tooth movement (2-9). The concept of optimal
force is based on the hypothesis that a force of a certain magnitude and temporal
characteristics (continuous vs. intermittent, constant vs. declining, etc.) would be capable of
producing a maximum rate of tooth movement without tissue damage and with maximum
patient comfort (3). The optimal force for orthodontic tooth movement may differ for each
tooth and for each individual patient (6).
Many studies have been performed to identify the optimal amount or range of
orthodontic force (9-12). Previous findings in human showed the proper forces for tooth
movement had range from 18 g force to 1515 g force (2,8,12). The exactly optimal force that
can be recommended for clinical use is still controversy (2).
This study aimed to compare the effectiveness of 50 g and 150 g orthodontic
forces in tooth movement after 2 months of canine retraction.
Methodology
Five female patients aged 18-30 years (mean age 21 ± 5.2 years) participated in
this study. All patients met the following criteria (13): good general health; requirement of
four 1st bicuspids extraction as parts of orthodontic treatment plan; all subjects are able to be
participated in every visit of this program.
The protocol was reviewed and approved by the Committee on Human Rights
Related to Human Experimentation of Mahidol University. Subsequently, the participants
were participated in the examination, diagnosis and treatment planning for orthodontic
treatment and were referred for a proper treatment such as filling, scaling, prophylaxis and
tooth extraction all first biscuspids according to treatment plan.
Experimental design
All subjects received an instruction about oral hygiene control one month before
tooth movement. After first bicuspid extractions, all patients started to rinse with
chlorhexidine mouthwash twice daily. This antibacterial rinse was used continuously
throughout the study period.
One week after extraction, two mini-screw implants were placed at both side of
alveolar bone between second bicuspid and first molar area. Brackets (0.022 inch slot, Ormco
Corp.) and segmented archwires (0.016 x 0.022 inch stainless steel wire) were placed on the
upper canines, second bicuspids and first molars.
The experimental canines were retracted with different continuous force
magnituge using nickel-titanium coil springs (Tomy®, Tokyo, Japan). Two retraction forces,
50 and 150 g. were used in this study. For each patient, the low (50g) and high forces (150g)
were randomly applied to the upper right and left canines. One end of the spring was placed
at mini-screw implant. The other end of the spring was placed at a hook of the canine bracket
as shown in Figure 1.
Figure 1. Canine retraction
Determination of the amount of canine movement
A cone beam computed topographic (CBCT) images were taken before force
application and 2 months of canine retraction. The two images from CBCT were
superimposed by using InVivoDental5.0® software (Anatomage Inc., California, USA)
(Figure 2). All posterior teeth were used as referent points. The distance between distal most
of the crown of the two superimposed canines was measured to represent the amount of tooth
movement. The amount of canine movement was re-measured by the same investigator after
1 week in order to avoid measurement error. A paired t-test showed no statistically significant
difference between the first and second measurement.
Figure 2. Superimposed cone beam image
Data analysis was performed using the Statistical Package for Social Sciences
version 18 (SPSS Inc., Chicago, Illinois, USA). A paired t-test was used to compare the
amount of canine movement between the 50 g and 150 g forces. The significance level was
set at p< 0.05.
Results
In this study, 5 female patients, mean age 21 ± 5.2 years, could participate until
the end of the experiment procedures. All patients maintained good oral hygiene throughout
the experimental period. There was no difference in demographical data in all the
participants.
When the experimental canines were retracted with the force of 50 g, average
distal tooth movement for 5 subjects over the 2 months period was 2.31 mm. (SD 0.71 mm.)
and 2.23 mm. (SD 0.97 mm.), for the force of 150 g. There was no significant difference
between these experimental groups, according to paired t-test analysis (t = 0.259, p> 0.05).
Table 1 and Figure 3 showed the total tooth movement achieved in each subject.
Table 1. Total tooth movement of each subject in two experimental canine applied different magnitude of
forces
Force (gram)
50
150
Case 1
2.45
3.19
Case 2
3.41
3.24
Total tooth movement (mm.)
Case 3
Case 4
Case 5
2.05
2.14
1.49
2.05
1.02
1.63
Mean (SD)
2.31 (0.71)
2.23 (0.97)
Distance (mm.)
Force
Figure 3.The mean amounts of canine retraction after 2 months of application of continuous orthodontic forces
of 50 and 150 g. No significant difference was found between the two experimental groups (p > 0.05).
Discussion and conclusion
Although many authors have expressed the similar opinion that an optimal force
is the force that can move teeth efficiently without causing discomfort or tissue damage to the
patient (14). Storey in 1973 suggested that some tissue damage is unavoidable. It is also
beneficial because it stimulate inflammatory cell (11). Schwarz defined the optimal force as a
force leading to a change in tissue pressure that approximated the capillary vessels’ blood
pressure, thus preventing their occlusion in the compressed periodontal ligament. He
recommended applying force not greater than 15-30 g/cm2 through root surface (3). However,
amount of force is impossible to exactly measure in general practice. Normally, the force
distribution in the periodontium is vary, resulting in area of great and little strain (15).
Orthodontic forces can be categorized as light and heavy. Light forces are
preferable to create adequate biological response in periodontium, because such forces can
evoke frontal bone resorption. In contrast, heavy forces often cause necrosis or hyalinization
of the PDL, undermining bone resorption, and root resorption (6,10,14). Many authors
recommended applying light forces for tooth movement because of cell-free compressed
areas in the PDL (4,10,16).
A meta-analysis of the literature concerning the optimal force or range of forces
for orthodontic tooth movement was performed by Ren et al. (2). This article reviewed
several studies on human maxillary canines with ranges of force from 18 to 450 g with
variation in several factors in each experiment.
In the present study, we measured the amount of tooth movement under different
magnitudes of orthodontic force (50 g and 150 g). Since Burstone et al. and Quinne and
Yoshikawa recommended 100-200 g force was suitable for canine retraction, we chose an
average force of 150 g as a higher force magnitude in this study. A lower magnitude of 50 g
was chosen for comparison because of its efficacy for tooth movement found in many studies
(9,12,17). These different magnitudes of force would expectantly result in different
mechanical stress loading to the PDL. Therefore, 50 g and 150 g forces might lead to
differences in biological responses. Segmental archwires and mini-implant anchorage were
used in this study in order to reduce the confounding factors.
In this study, the mean amount of canine movement between forces of 50 g and
150 g after 2 months showed no significant difference. This finding agrees with the results of
Luppanapornlarp et al. (13), who also reported that there was no significant difference in the
amount of canine movement between 50 g and 150 g forces at 2 months after force loading.
Iwasaki et al.(12,17) reported that continuous average forces of 18 g and 60 g could retract
canine effectively. This finding conformed to our study that 50 g force produces an effective
canine movement with similar rate of tooth movement to that of 150 g force.
Moreover, the pain associated with orthodontic force application is related to the
development of ischemic areas in the PDL. Pressure induces inflammation at the apex and the
mild pulpitis that usually appears soon after orthodontic force loading contributes to the pain.
There seems to be a relationship between the magnitude of force loading and the amount of
pain. Since greater force generates larger areas of ischemia, the greater force may produce
greater pain (6). Iwasaki et al.(12,17) stated that lower forces could produce tooth movement
with no lag phase. This can be implied that force of 50 g may produce less pain than that of
150 g force. Therefore, it may be suggested that a force of 50 g could be considered as an
optimum force for canine retraction.
From this study, the mean distances derived from tooth movement generated by
two different magnitudes of continuous forces (50 g and 150 g) were not significant
difference. Both 50 g and 150 g forces could effectively induce tooth movement similarly.
For orthodontic treatment, it could be suggested that 50 g loading continuously could produce
satisfactory tooth movement.
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