EFFECT OF ALIGNER MATERIAL, DURATION, AND FORCE LEVEL ON TOOTH MOVEMENT

By

NEHA D. PATEL

A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT

OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE

UNIVERSITY OF FLORIDA

2014

© 2014 Neha D. Patel

To my husband and family for helping me reach for the stars and to God for giving me the strength to reach that high

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ACKNOWLEDGMENTS

Thank you to my mentors, Dr. Timothy Wheeler, Dr. Susan P. McGorray, and Dr.

Madhu Nair, for your support and guidance through this process. Thank you to my

husband and family for their support throughout my entire residency. Thank you to my

instructors, Dr. Wellington Rody and Dr. Calogero Dolce for their pearls of wisdom and

patience these past three years.

5

TABLE OF CONTENTS page

ACKNOWLEDGMENTS.............................................................................................................. 4

LIST OF TABLES ......................................................................................................................... 6

LIST OF FIGURES....................................................................................................................... 7

ABSTRACT ................................................................................................................................... 8

CHAPTER

1 INTRODUCTION................................................................................................................... 9

2 MATERIALS AND METHODS ......................................................................................... 14

Study Design........................................................................................................................ 14 Enrollment and Study Participation .................................................................................. 14 Collection of Data ................................................................................................................ 16

Clinical Tooth Movement ............................................................................................ 16 Radiographic Measures .............................................................................................. 16

Statistical Considerations .................................................................................................. 17

3 RESULTS ............................................................................................................................. 22

4 DISCUSSION ...................................................................................................................... 28

5 CONCLUSIONS .................................................................................................................. 34

LIST OF REFERENCES ........................................................................................................... 35

BIOGRAPHICAL SKETCH ....................................................................................................... 40

6

LIST OF TABLES

Table page 2-1 Outline of inclusion and exclusion criteria. ................................................................. 19

2-2 Schedule of Study Events ............................................................................................. 20

3-1 Demographics of subjects............................................................................................. 24

3-2 Age of subjects ............................................................................................................... 24

3-3 Material differences in average percent of tooth movement at Day 14 (Pct14), Day 25 (Pct25), and time points in between (Diff3514). .......................................... 24

3-4 Material differences in average compliance on Day 14 and Day 25...................... 24

3-5 Average percent of tooth movement achieved between the materials and subject composition of movement groups. ................................................................. 25

3-6 Average percent of tooth movement achieved and average compliance scores for accompanying percentage groups............................................................ 25

3-7 Differences in average tooth movement achieved between genders.................... 25

3-8 Comparison of CBCT Measures and Tooth Movement at Day 14 (Pct 14) and Day 25 (Pct 25)............................................................................................................... 26

7

LIST OF FIGURES

Figure page 2-1 Overview of radiographic measurements of the target tooth. ................................. 21

3-1 Tooth movement (in mm) by material over the 25-day study period. .................... 26

3-2 Tooth movement by gender and material over 25 days. ......................................... 27

3-3 Overall tooth movement between previous UF studies and the current study by material. ...................................................................................................................... 27

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Abstract of Thesis Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Master of Science

EFFECT OF ALIGNER MATERIAL, DURATION, AND FORCE LEVEL ON TOOTH

MOVEMENT

By

Neha D. Patel

May 2014

Chair: Timothy T. Wheeler Major: Dental Sciences - Orthodontics

SmartTrackTM, created by Align Technologies®, has a lower initial insertion force

and a longer working range compared to the older EX30 material to aid orthodontic

tooth movement (OTM). To investigate the effect of SmartTrackTM on OTM in-vivo over

a 25-day period compared to the EX30 material. Aligners made of one of the two

materials and programmed for 0.25mm of buccal movement of a maxillary incisor were

used in 33 subjects (17 females and 16 males), 18-40 years old, for 22 hours/day for 25

days, in a randomized, blinded manner. Cone beam computed tomography (CBCT)

imaging was conducted prior to tooth movement. SmartTrackTM achieved significantly

higher mean OTM (73.1%) compared to EX30 (42.8%) by Day 14. No difference in

OTM occurred from Day 14-25. Mixed modeling revealed SmartTrackTM and compliance

separately provided 16% and 9% higher OTM. No difference between CBCT

measurements and tooth movement was noted. SmartTrackTM achieved a higher mean

OTM with a seemingly shorter lag phase compared to the EX30 material over a 25-day

period. A combination of SmartTrackTM effects and compliance play a collective role in

achievement optimal OTM.

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CHAPTER 1 INTRODUCTION

Clear orthodontic aligners are actively sought by the public through its thin and

easily adaptable nature 1, ideal aesthetic optical properties, ease of proper hygiene, and

comfort of wear2-4. Kusy defined ideal archwires as those with properties of high

strength, resilience, formability, are springy, biocompatible, have good springback, good

range, and are highly esthetic5. Similar ideals are held for orthodontic treatment utilizing

aligners. Although the advent of clear aligner therapy sparked interest within the public

to seek orthodontic treatment, initial case studies showed that treatment is successfully

achieved in minor to moderate crowding. It has been reported that those patients

exhibiting crossbites, a deep bite6, 7, an anterior open bite or shallow over bite, and

those with periodontal problems may all be treated with clear aligner therapy8.

Extraction spaces have been shown to be difficult to close with bodily tooth movement

since tipping occurs readily as orthodontic force is placed9-11. Newer treatment

strategies have been able to overcome the drawbacks of aligner therapy by being able

to treat complex maloccusions7, 12, 13, and integration of aligner therapy with fixed

treatment in orthognathic surgery cases and with functional appliances has been able to

achieve orthodontic success14-17.

The aligners tend to function optimally by producing tooth movements in an

anterior-posterior (AP) direction and improving transverse relationships generally by

tipping movements11, 18. More difficult movements, such as controlling root position and

tooth rotations have been aided with the advent of Power Ridges and attachments to

facilitate movement 2, 7, 19. Polyurethane is the main element in fabrication of the

aligners and can be affected by several variables, including heat and moisture. The

10

prescribed wear to allow for proper aligner prescription expression is at least a twenty

hour interval per day for two weeks2. The majority of tooth movement has been proven

to occur within the first week of aligner wear, but controversy still remains as to whether

the extra week of aligner usage will aid in fulfilling the prescription of the tray 10 20.

Vardimon et al found that the distortion energy, or von Mises strain, during maxillary

incisor retraction decreased over a fifteen day period, with the highest at day 1,

decreasing at day 2, and then maintaining levels from day 2 to day 15 with no complete

relapse to the original level21. Due to the decaying forces, it has been suggested to have

patients wear aligners for 24 hours for the first two days per aligner and then

intermittently up until day 1521. Baldwin et al. had reported of a clear aligner company

suggesting a wear pattern of three weeks for full expression of aligner prescription9.

Clinical studies previously conducted have shown labial expansion of incisors to

achieve only 38%-61.6% of the full aligner prescription expression20, 22-24. According to

Kravitz et al, retroclining maxillary incisors is two times more predictable in lingual

tipping as opposed to than proclination24.

Orthodontic tooth movement tends to occur in three general phases of initial, lag,

and postlag phases25. In rat models, Arias and Marquez-Orozco 26 had reported that the

first four days of OTM tended to be in the initial and lag phases. The transition to the

postlag phase may take as long as 20 days to complete27, which is after the two week

wear pattern for aligners. To facilitate OTM, the coupling of bone resorption and bone

regeneration are necessary in response to the high orthodontic force placed on teeth27-

29. Accomplishing tooth movement usually requires 20-150g of orthodontic force per

tooth 30. Light, continuous forces are generally preferred over heavy forces to prevent

11

hyalinization of the PDL and unstable bone resorption that may occur with heavy forces,

which tends to surpass a capillary blood pressure of 20-25 gm/cm2 of root surface.

Light forces allow for a proper biologic response and allow for stable bone resorption 27.

Alveolar bone height concurrent with root length also greatly influence tooth movement

and the position of the tooth center of resistance (CRes). Over time, alveolar bone

levels tend to decrease, thus displacing the CRes to a more apical level 31. Since CRes

affects how force applied at the coronal level, moments may be greater if alveolar bone

levels are decreased.

In 2005, a randomized and controlled clinical trial was conducted at UF to assess

the effects of recombinant human relaxin during OTM with clear aligners of a single

anterior incisor over an eight week period 23. Although the results of the study found no

significant variance between treatment and control groups, other effects were noted.

These effects include a higher rate of OTM during the first week compared to the

second week of continuous aligner wear during the two-week prescription cycle, the

absolute expression of the aligners was not achieved, the age of subjects had a positive

correlation with OTM, and OTM differed greatly between subjects, which also was

echoed in previous studies20.

Performance of aligner material influences tooth movement. Studies have shown

that a hard versus soft aligner material had no statistically significant difference in

outcome of extraction space closure9-11, but it has been shown that a combination of a

hard aligner material and a two-week interval allows for optimal tooth movement10. As

with any aligner, working range and initial insertion force are two of the vital traits in

performance of the aligner material. Initial insertion force is defined as the force

12

influencing the movement of the teeth according to the prescription expressed in the

aligner upon initial insertion. Patients tend to feel more elevated levels of discomfort

within the initial days after insertion of the appliance 3, 32. Working range of an appliance

is the difference between the full amount of force imparted by the appliance at initial

activation until deactivation. Larger working ranges are favorable due to its decreased

discomfort perceived by patients and the force influencing tooth movement is able to

work over a larger range of distance. An improved material, called SmartTrackTM,

developed for Invisalign® treatment compared to the existing EX30 material was shown

to be superior in both traits. MSDS information procured from Align Technologies

reports the material is made from multilayer aromatic thermoplastic polyurethane, and

suggests the material may show improved flexibility and a longer working range similar

to the properties reported of a multistranded archwire5. Multistranded stainless steel

wires tend to have high springback, moderately low stiffness33, high range, and

administer a lower force34, which are properties desired in an aligner35. The improved

material imparts a force of 4N, compared to the old material force of 4.5N, and also has

a working range of 0.20mm, compared to 0.15mm of the old material.

The purpose of this study is to investigate the effect of appliance activation force

over time on total tooth movement utilizing a human tooth movement model using the

standard material (Material S) and an experimental material (Material E). The benefit of

utilizing CBCT imaging will also aid in evaluating the alveolar bone relationship to tooth

movement. Since the lag phase may last longer than the 2 week prescribed wear

period, a longer investigational period from a two-week wear pattern to a four-week

wear pattern will be evaluated to determine if tray prescription expression can be

13

enhanced. Tooth movement curvatures will also be evaluated to investigate whether

Material E may allow for a more linear phase of tooth movement as opposed to the

three defined phases25.

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CHAPTER 2 MATERIALS AND METHODS

Study Design

The basis of the study design is echoed off of previous aligner research20, 23. IRB

approval had been obtained to conduct a single center clinical trial at the University of

Florida Graduate Orthodontic Clinic. Participating subjects were between and including

the ages of 18-40, had minor incisor misalignment, and would undergo orthodontic

treatment. Five groups of subjects with five to seven participants in each group were

randomized to a material (S or E) with a standard activation schedule of 0.250 mm over

a twenty-five day study period. Study clinicians were blinded to the aligner material and

an equal number of subjects were randomized to each material group.

Enrollment and Study Participation

Each subject was initially phone screened and then scheduled for the first of two

preliminary visits. The inclusion and exclusion criteria are outlined in Table 2-1. The first

visit is the Eligibility Visit, which is to distinguish potential study subjects with minor

maxillary incisor malalignment and to exclude those falling under the exclusion criteria.

The following procedures will be performed. The informed consent form, completed

medical history, and intraoral clinical examination were completed. Those who are

deemed eligible based on this preliminary visit were then allowed to proceed to the

Screening Visit. The goal of this visit was to determine if the subject is fully eligible for

completion of the study according to the Cadent iTero™ digital impression scans, which

were sent to Align Technology for fabrication of Invisalign® appliances, intraoral and

extraoral photographs, and a cone-beam computed tomography radiograph (CBCT). A

CBCT is standard protocol before orthodontic treatment at the University of Florida.

15

Women were required to undergo a urine pregnancy test to ensure a negative reading

before any imaging procedures. Those who are deemed eligible for completion of the

study had digital impression scans sent to Align Technology for Invisalign® appliance

fabrication, given a study number, and enrolled in the study. An outline of data collected

at each study visit is depicted in Table 2-2.

Once a participant was accepted into the study, one central incisor, the right or

left, was chosen for activation through the aligners and termed as the “target tooth”. The

target tooth had to follow proper criteria, such as no adjacent teeth to block tooth

movement and must have been able to move a 0.50mm in an AP direction. The maxilla

was the only arch receiving an aligner, which was fabricated using either Material S or

Material E and had an activation prescription in the antero-posterior (AP) direction of

0.250mm. Instead of utilizing polyvinyl siloxane (PVS) impressions as in previous

studies20, 23, digital scans were taken with an iTero™ optical scanner for each subject.

The iTero™ optical scanner is reliable in replication of the dentition and an alternative to

the conventional PVS impressions36. The single maxillary aligner was delivered on a

Monday, and scans were taken on days 1, 2, 3, 4, 7, 9, 11, 14, 16, 18, 21, 23, and 25.

The study terminated at day 25, and final data collection was taken.

A total of 33 subjects were enrolled in the study after initial screening. If a subject

missed more than 2 study visits, they were involuntarily dropped from the study. One

subject was dismissed midway through treatment due to the lack of follow-up with study

visits. Data was utilized from the terminated subject since the last study visit. Subjects

were required to wear the aligners full time except for brushing their teeth, drinking, and

eating. Compliance with aligner wear was documented through a daily diary distributed

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to study subjects at the initial delivery of aligners. A completed medical and dental

history was also taken at the initial visit and routinely checked along with the daily diary

at every visit to monitor any excessive medication intake.

At the end of data collection, study subjects were given the opportunity to be

treated at the University of Florida Graduate Orthodontic Clinic for routine orthodontic

treatment using the Invisalign® appliances.

Collection of Data

Clinical Tooth Movement

The measurement of the AP movement of the target tooth was done using

iTero™ digital impression scans and a Bite Matching algorithm, a proprietary software

developed by Align Technologies® to superimpose scans more efficiently and

effectively.

Radiographic Measures

Each cone beam radiograph was sliced with a 0.4mm and 3.6mm thickness to

include the full length of the target tooth for each subject with accompanying apical

bone, making sure to account for the incisive canal. Sliced images were then flattened

to an 8bit TIF image, minimizing any compression. ImageJ® software was used to

magnify the image without changing the innate properties of the initial file. A fractal

analysis (FA) was conducted to quantify bone by evaluating the organization and

complexity of bone structure using the TACT® workbench. This analysis was used to

qualitatively and quantitatively assess bone in the apical region of the tooth prescribed

for movement. A FA is advantageous compared to gray level analysis in that it is

independent of projection geometry or exposure parameters. Digital subtraction

techniques require multiple images with reproducible projection geometry to yield

17

meaningful results and is, thus, impractical in the clinical scenario. Independent of other

extraneous variables, FA utilizes the range of signal intensities, converts the intensities

into a frequency plot in order to plot the intensities to a 2D regression plot. All images

were normalized by utilizing a reference image and a 32 by 32 region of interest (ROI)

within the apical bone of the target tooth. The FA was conducted for each ROI using a

power spectrum method within the Tuned Aperture Computed Tomography (TACT)®

workbench. Following a 2D fast Fourier transformation (FFT), the log of the magnitude

was plotted against the log of frequencies created by the FFT. The slope of the

regression line generated the fractal dimension for each specific ROI 37.

Measurements of the target tooth mimic that of previous studies20 and are

summarized in Figure 2-1. All measurements were done using InVivo Anatomage®

Software, version 5, and included measurements of tooth length, root length, crown

length, crown to root ratio, the distance of the root apex to the buccal plate, and the

widest buccolingual dimension of the target tooth at the crest of the alveolus was done

at three different timepoints by one researcher (NDP) and averaged.

Statistical Considerations

Statistical assessments were able to utilize a parametric analysis due to the normal

distribution of the data. The outcomes of interest were to observe tooth movement from

baseline to Day 14 and to Day 25. Primary comparisons were done between treatment

groups and the outcomes as well as correlations of CBCT measures and the outcomes.

Additional variables such as age, gender, and compliance were also taken into

consideration. Analyses conducted included two-sample t-tests and Pearson correlation

coefficients with a p value less than 0.05 considered statistically significant. With the

addition of multiple data points in this study, we had the advantage of using mixed

18

modeling to test interactions between radiographic measures, material, compliance,

gender, age, and tooth movement.

19

Table 2-1. Outline of inclusion and exclusion criteria.

Inclusion criteria

1. Males or females between and including the ages of 18 and 40 years old, desiring correction of minor incisor malalignment using the Invisalign® appliance. Subjects may have had previous orthodontic treatment.

2. Adult dentition with all upper anterior teeth present.

3. At least one maxillary central incisor that has sufficient space between it and adjacent teeth to allow AP movement of 0.5mm (crown tipping only).

4. Normal pulp vitality and healthy periodontal tissues as determined by intraoral exam.

5. Good health as determined by medical history.

6. Willingness and ability to comply with study procedures, attend study visits, and complete the study.

7. The ability to understand and sign a written informed consent form, which must be signed prior to initiation of the study procedures.

Exclusion Criteria

1. Significant periodontal disease (>3mm pocket depth or >1mm of recession on maxillary anterior teeth).

2. Active dental disease not under care of either a dentist or periodontist.

3. Chronic daily use of any nonsteroidal anti-inflammatory medication, estrogen, calcitonin, or corticosteroids.

4. History of use or current use of any bisphosphonate medication or other medication for treatment of osteoporosis.

5. Current smoker (must not have smoked in the last six months).

6. Fibroblast function is necessary for proper conservation of periodontal structures. Nicotine has been shown to be destructive to periodontal elements such as periodontal ligament fibroblast growth in a dose dependent manner and can inhibit cell proliferation and diminish protein synthesis58. Tobacco products may also be a major factor in the development of periodontal disease.

7. Women must not be pregnant. Negative urine pregnancy tests prior to exposure to cone beam computed tomography (CBCT) imaging is require to verify pregnancy status. Dental x-ray exposure with pregnant women has been questioned in potential association to pituitary and thyroid disorders and low birth weight in infants59.

8. Any condition or use of medication which in the opinion of the investigator interferes with the biology of tooth movement.

9. Any condition which in opinion of the investigator results in increased risk to the subject.

20

Table 2-2. Schedule of Study Events

Event Prelim

1 Prelim

2 Day

0 Days

1, 2, 3, 4, 7, 9, 11, 14, 16, 18, 21, 23

Day 25

Informed Consent1 X Inclusion/Exclusion X X Medical History X Pregnancy Test X Intraoral Exam X X X X Maxillary occlusal and frontal photos X X X

Cadent iTero™ digital impression scan X X X

Intraoral photos (complete set) X Extraoral photos X Cone beam imaging2,3 X Dispense aligners and daily diary X

Collect aligners and daily diary X Begin planned orthodontic treatment X

1Informed consent must be given before any subject can progress further within the study. 2Cone beam imaging is a usual protocol for orthodontic treatment at the University of Florida. 3Women will be required to take urine pregnancy tests immediately prior to exposure to verify they are not pregnant.

21

Tooth Length -Measured from incisal tip to apex of the target tooth

Crown Length -Measured from incisal tip perpendicular to a line connecting the buccal and lingual cortical plates. Root Length -Measured from a line connecting the buccal and lingual cortical plates to the root apex. Crown to root ratio -The division of the crown length into the root length. Distance from apex to buccal cortical plate -The measurement of the perpendicular distance from the apex to the buccal cortical plate Widest buccolingual width of tooth at crest of alveolus -The measurement of the buccolingual thickness of the tooth at the alveolar crest.

Figure 2-1. Overview of radiographic measurements of the target tooth.

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CHAPTER 3 RESULTS

An outline of the subject demographic information is displayed in Table 3-1 and

Table 3-2. An equal number of males (48.48%) and females (51.52%) participated in

this study with an average age of 26.95 (± 5.31) years. Orthodontic tooth movement

between materials was statistically significant at Day 14 (p=0.02) and Day 25 (p=0.02),

and values are depicted in Table 3-3. Material E was able to achieve a higher average

percentage of tooth movement at Day 14 (73.06%) and Day 25 (77.38%) compared to

Material S (42.75% and 50.07%, respectively). A diagrammatic representation of the

average amount of tooth movement achieved at all time points between the materials is

displayed in Figure 3-1. The term Diff2514 is defined as the percentage of tooth

movement achieved at Day 14 subtracted from the percentage of tooth movement

achieved at Day 25 to evaluate tooth movement between the time points. No significant

difference was noted in tooth movement between the materials and over time from Day

14 to Day 25 (p=0.18).

In comparing a two-week aligner protocol versus a four-week aligner protocol, no

difference was noted (p=0.23) in tooth movement achieved between Day 14 and Day

25. Material S noted 9.73% of tooth movement from Day 14 to Day 25, as defined by

the Diff3514 variable, while Material E was -0.47%, thus showing that the majority of

tooth movement was achieved by Day 14 with Material E while Material S still allowed

for a residual amount tooth movement to occur past Day 14. Average percentage of

tooth movement in relation to age was not significant at Day 14 (r= -0.05, p=0.78), Day

25 (r= -0.03, p=0.86), or time points in between (r= -0.08, p=0.67).

23

Compliance between the materials at Day 14 and Day 25 showed no significant

differences in the average number of hours of reported aligner wear (p=0.65; p=0.61) as

shown in Table 3-4. Thus, compliance was similar between the materials with

accompanying similar maximum and minimum hours of wear. Table 3-5 shows 10

subjects had ≥80% of average tooth movement achieved at Day 14, and 9 out of those

10 subjects were assigned to Material E. Table 3-6 shows that of those 10 subjects, the

hours of compliance were slightly higher than the other percentage groups. Thus,

slightly higher compliance may point towards higher amounts of tooth movement.

Gender and tooth movement is depicted in Table 3-7. No significant relationship

can be seen in tooth movement between the genders at Day 14 (p=0.39), Day 25

(p=0.65), and time points in between (p=0.69). Females and males had higher average

percentages of tooth movement with Material E than Material S, as seen in Figure 3-2.

Males tended to have higher percentages of tooth movement than women at all time

points of average percentages of tooth movement.

Radiographic measures had no significant relationships to tooth movement as

displayed in Table 1-8. Marginal significance was noted with tooth length in relation to

tooth movement achieved at Day 14 (r=0.33, p=0.07) and Day 25 (r=0.31, p=0.09), and

root length had marginal significance at Day 14 (r=0.33, p=0.07). Mixed model analyses

between all variables noted significant interactions between tooth movement with

compliance (p=0.0001) and Material E (p=0.0017).

Overall average tooth movement in millimeters between the materials is

displayed in Figure 3-3. The average tooth movement achieved at Day 14 and Day 25

24

with Material S is similar to the previous studies done at the University of Florida20, 22, 23.

Material E outperformed the previous studies at each time point.

Table 3-1. Demographics of subjects

Variable N Material E Material S P-Value Total 33 17 16 p=0.87

(NS) Females 17 9 8 Males 16 8 8

Table 3-2. Age of subjects

N Mean (yrs) SD Min

(yrs) Max (yrs) P-Value

Total 33 26.95 5.31 20.06 40.07 p=0.74 (NS) Material E 17 26.65 5.44 22.05 40.07

Material S 16 27.72 5.32 20.06 38.08

Table 3-3. Material differences in average percent of tooth movement at Day 14

(Pct14), Day 25 (Pct25), and time points in between (Diff3514).

Variable N Mean SD Min Max P Value

Material E Pct 14 16 73.06% 37.98% -18.00% 133.00% Pct 14

p=0.02**

Pct 25 p=0.02**

Diff2514 p=0.18 (NS)

Pct 25 16 77.38% 30.36% 17.00% 130.00% Diff2514 15 -0.47% 19.96% -35.00% 39.00%

Material S Pct 14 16 42.75% 30.93% -31.00% 103.00% Pct 25 15 50.07% 31.06% 4.00% 120.00%

Diff2514 15 9.73% 20.62% -27.00% 42.00%

Table 3-4. Material differences in average compliance on Day 14 and Day 25. Variable Mean (hrs) SD (hrs) Min (hrs) Max (hrs) P-Value

Material E Meanwear 14 21.40 1.73 15.89 22.81 Meanwear

14 p=0.65 (NS)

Meanwear

25 p=0.61 (NS)

Meanwear 25 21.44 1.36 17.69 22.84

Material S Meanwear 14 21.17 0.87 19.39 22.42

Meanwear 25 21.21 0.99 18.74 22.63

25

Table 3-5. Average percent of tooth movement achieved between the materials and subject composition of movement groups.

Percentage of Tooth Movement Achieved at Day 14 Material E (N) Material S (N) Total (N)

≤35% 2 7 9 36-79% 5 8 13 ≥80% 9 1 10

Table 3-6. Average percent of tooth movement achieved and average compliance

scores for accompanying percentage groups.

Percentage of Tooth Movement Achieved at

Day 14

Mean (hrs) SD Min

(hrs) Max (hrs)

Mean Wear 14

≤35% 20.76 0.84 19.39 22.10 36-79% 20.90 1.68 15.89 22.42 ≥80% 22.21 0.63 20.89 22.81

Table 3-7. Differences in average tooth movement achieved between genders.

Variable Mean SD Min Max P Value

Females

Pct 14 52.1% 42.5% -31.0 119.0

Pct 14 p=0.39 (NS)

Pct 25

p=0.65 (NS)

Diff2514 p=0.69 (NS)

Pct 25 61.3% 36.7% 4.0% 108.0%

Diff2514 6.3% 21.6% -35.0% 39.0%

Males

Pct 14 63.7% 31.8% 20.0% 133.0%

Pct 25 66.9% 30.6% 9.0% 130.0%

Diff2514 3.2% 20.3% -35.0% 42.0%

26

Table 3-8. Comparison of CBCT Measures and Tooth Movement at Day 14 (Pct 14) and Day 25 (Pct 25).

Variable Mean SD Pct 14 P-Value

Pct 25 P-Value

Tooth Length 23.66mm 1.45mm 0.07 0.09

Crown Length 11.93mm 0.81mm 0.66 0.49

Root Length 11.35mm 2.38mm 0.07 0.12

Crown to Root Ratio 1.03 0.13 0.20 0.24

Fractal Analysis 1.83 0.32 0.78 0.80

Distance from apex to buccal cortical plate 2.40mm 1.19mm 0.21 0.16

Widest Buccolingual Width of Tooth at Crest of Alveolus 6.63mm 1.57mm 0.89 0.62

Figure 3-1. Tooth movement (in mm) by material over the 25-day study period.

Toot

h M

ovem

ent A

chie

ved

(mm

)

27

Figure 3-2. Tooth movement by gender and material over 25 days.

Figure 3-3. Overall tooth movement between previous UF studies and the current study

by material.

Toot

h M

ovem

ent A

chie

ved

(%)

Toot

h M

ovem

ent A

chie

ved

(%)

28

CHAPTER 4 DISCUSSION

Orthodontic tooth movement (OTM) is the product of intricate cellular

mechanisms. These delicate mechanisms are the foundation of which exogenous

pharmacologic influences, endogenous influences, and vitamin supplements tend to

affect the rate of OTM. Studies have shown that the exogenous use of estrogen,

bisphosphonates, corticosteroids, and nonsteroidal anti-inflammatory drugs can affect

the rate of OTM26, 38-40. As orthodontic treatment begins, discomfort may ensue,

resulting in patients reaching for pain relief medications. Miller et al.3 compared a fixed

appliance treatment group to an Invisalign treatment group and has shown that at every

time point over a 7-day period, Invisalign treatment was perceived as more comfortable

and manageable than fixed treatment. Although both treatment groups experienced a

decrease in quality of life at the beginning of treatment, the quality of life scores for

those undergoing fixed appliance treatment decreased as treatment progressed and

experienced decreases in various aspects of their daily lives. Analgesic usage was

highest among the fixed appliance subjects, but became insignificant after the third

day3. Shalish et al. compared a lingual fixed treatment group, buccal fixed treatment

group, and an Invisalign treatment group and reported 0% of analgesic usage among

Invisalign subjects by the 6th day of treatment32. The lingual and buccal fixed treatment

groups on average were not able to completely recover from initial declines in food

consumption until the 5th-10th day of treatment, while the Invisalign treatment subjects

had recovered by the 4th day at most32. Although this study did not specifically track

analgesic usage over the 25-day experimental period, the effects of an analgesic may

29

not have had a significant effect on tooth movement since the amount of tooth

movement achieved is similar to previous studies20, 22, 23.

Tooth movement with clear aligners over a 14-day period has been shown to

produce less than 100% of prescription expression20, 22-24. The results found in this

study tend to echo similar sentiments. As the data shows, tooth movement over a 14-

day period provides a similar amount of tooth movement as a 25-day period. This is the

first study to take such minute time points, which proved that tooth movement with clear

aligners still follows the three phases previously described25, but the SmartTrackTM

material possibly exhibits a short lag phase of 2-3 days and completes the majority of

tooth movement by the 14th-day of wear. The SmartTrackTM material also proved to

achieve a higher mean percentage of tooth movement at Day 14 and Day 25, which

was significantly higher than the standard EX30 material.

When aligners are worn, there are short-term and long-term forces involved.

Short-term forces are when an aligner is fitted initially in the mouth and long-term forces

are after initial fitting of aligner, forces are placed on teeth through the prescription in the

tray and occlusal loading35, 41. Modes of deformation pertinent to aligners are tension,

bending, and torsion. The elastic property of aligners allow the aligners to adapt to the

prescribed movement when strain occurs in the aligners, but the viscoelastic property of

aligners causes the fatigue of force over time. Long-term moisture exposure of 48 hours

may affect aligner performance after strain placement and tensile properties tend to

decrease35. Stress relaxation of the aligner decreases the ability of the material to

produce the appropriate amount of force for an appropriate amount of tooth

movement42. Mimicking of an intraoral environment in a water bath of 37.0oC and

30

placement of 5% strain upon thermoplastic material has shown to quicken the stress

relaxation of the material. Furthermore, only about 42.3-66.6% of the initial forces was

delivered after the immersion in the water bath42. As thermoplastic polyurethane

materials age, a process called plasticization occurs in which water is absorbed as the

material relaxes. The absorption of water may play a role in the breakup of Hydrogen

bonds present within the composition of the material, and the hygroscopic expansion of

the material may possibly accelerate further degradation43. A study by Ryokawa et al.

compared the Invisalign EX30 material to various other thermoplastic materials by

submerging the material in a distilled water bath at 37.0oC and reported the highest

water absorption by the Invisalign material after 24 hours and 336 hours of immersion44.

This may be due to the amorphous polymer composition, allowing for more free space

to be utilized by the water absorption. It is interesting to note that the Invisalign material

did not have the highest hygroscopic expansion rate when compared to other

thermoplastic materials after immersion in the water bath, possibly due to previous

water absorption and hygroscopic expansion at room temperature44. This combination

of water absorption and the temperature of the oral cavity may play a role in the

continued degradation of the aligner material43. The oral cavity exhibits a more

complicated nature and temperature differences and the intermittent pressures placed

on the teeth with aligner removal and reinsertion may also play an additive role in the

fatigue of force levels. As temperatures rise, the amount of water absorption also

increases43 and oxidation of methylene diphenylene units within the composition of the

thermoplastic polyurethane material can lead to degradation of the elastic properties45.

With a plastic device in the oral cavity, the use of Invisalign appliances has been shown

31

to be chemically stable46 and not induce any cytotoxic effects on human gingival

fibroblasts and lack any estrogenic effects of the material eluents47.

A noticeable amount of wear has been proven evident in the aligners after the

recommended two week interval. Calcification, distortion, cracking, and development of

biofilms within the aligner material have been shown46, 48, 49. Plaque accumulation may

interfere with the surface contour of the aligner50. Buccal aspects of worn appliances

have also shown an increase in hardness from mastication-induced cold working 49. A

randomized and controlled clinical trial performed at UF in 200920 studied the effects

and efficiency of OTM by inserting a fresh aligner after one week of wear, replacing the

worn aligner. The results showed that there is no added benefit of placing a fresh

aligner with the same prescription after one week of wear instead of utilizing the same

aligner for the two week period. This finding suggests that material fatigue and

deactivation is not the rate-limiting factor in the event of tooth movement.

In terms of force application, the SmartTrackTM material imparts an overall force

of 4.0N to the maxillary incisor, but studies have shown that even a 1.80N (183.5g)

force with a SentalloyTM wire for intrusion or extrusion of a single tooth may be too high

and may contribute to root resorption over a 4 week period51. Although there is no

scientific evidence of specific numeric force values necessary for tooth movement52, the

force levels of thermoplastic appliances with an activation of 0.50mm may range from

2.91N to 5.10N24, 53. A recent study showed that a lower aligner activation of 0.50mm

tended to impart a higher level of force than a 1.0mm activation, and thinner aligner

materials delivered lower forces overall than thicker materials53. The higher force level

of the lower activation may be due to possible slippage of the material from the tooth

32

due to a high activation distance. Invisalign utilizes a thin material of 0.30 inches, which

is easily adaptable in the mouth and cause minimal posterior intrusion1. The high forces

imparted upon the teeth from clear aligners may dissipate through stretching of the

aligner material from repeated removal and insertion thus reducing the high impact of

the overall force. Although Invisalign may use a higher force range than usual fixed

appliance therapy, root resorption is usually not a cause for concern for treatment with

Invisalign appliances54. Recent data shows that 100 consecutively treated Invisalign

patients had little to no root resorption. On the other hand, 10% of patients treated with

fixed appliances had root resorption of at least 3mm7.

Our findings have shown that a lower activation of 0.25mm with a low initial

insertion force and longer working range with the new SmartTrackTM material were able

to achieve a higher average percentage of tooth movement achieved than previous

studies with 0.50mm of activation per aligner after 14 days20, 23. Tipping within the

periodontal ligament (PDL) space was achieved during the initial phase since the PDL

space is generally 0.15-0.20mm55 from Day 0-Day 2, and the lag phase of tooth

movement seemed to be limited to Day 2 to Day 4. This finding suggests that the lower

millimeter activation coupled with a more adaptable material may have imparted a much

more operational force on the incisor compared to higher millimeter activation with the

standard material. Since proclination of maxillary incisors is a difficult movement

compared to retroclination24, overcorrection of maxillary buccal tipping movements may

aid in achieving the desired measurement1.

As previous studies have shown3, 20, 22, 23, 32, a larger percentage of female

subjects partook in Invisalign studies, but this study had an approximately equal

33

distribution of males and females. No difference in the average percent of tooth

movement achieved was noted between age groups or genders, compared to

In evaluating the data, some subjects were able to experience more than 100%

of tooth movement prescribed. Occlusal factors and lack of intra-arch contacts were

analyzed and found that even those patients with a proximal contact in place, tooth

movement may be affects by the opposing occlusion. Although it has been found that

intra- and inter-arch contacts may negatively affect tooth movement56, the opposite

situation may have been shown in this study with the added effect of the lower anterior

occlusion affecting the excessive positive outcome of the maxillary incisor AP

movement.

Future studies investigating tooth movement with clear aligners may include the

use of cyclical force devices, local delivery of exogenous molecules such as

inflammatory cytokine IL-1 for stimulation of osteoclasts, and low-level laser therapy57.

Animal studies conducted so far show promising results, but human clinical trials with

defined methods and durations are necessary to help implement a proper treatment

protocol to achieve exceptional tooth movement in an efficient and effective manner.

34

CHAPTER 5 CONCLUSIONS

The SmartTrackTM material with a lower initial insertion force and a longer working

range had an increased mean percentage of tooth movement compared to the standard

EX30 Invisalign® material. The SmartTrackTM material was more effective at tooth

movement over a 14-day span than the EX30 material, but the amount of average

residual tooth movement from Day 14 to Day 25 between the materials is not

statistically significant. A higher percentage of tooth movement was achieved over a 25-

day period compared to a 14-day period, but this difference is not statically significant.

Initial decrease of strain in the SmartTrackTM aligner may deliver a more physiologic

force on the maxillary incisor to allow for more optimal tooth movement. No statistical

difference was noted between tooth movement and gender, age, or CBCT

measurements. Our study echoed previous studies, showing that 100% of aligner

prescription was not achieved. The SmartTrackTM material had a higher mean

percentage of tooth movement at Day 14 and Day 25 compared to previous studies

done at UF. Orthodontic tooth movement still follows the three phases of tooth

movement, even with a decrease in initial insertion force and an increase in working

range.

35

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BIOGRAPHICAL SKETCH

Neha D. Patel was born in Chicago, Illinois to Doctors Dipak and Neela Shah.

Her father is an interventional radiologist and her mother is a retired pediatric dentist.

Neha has one sibling, Akash Shah, who is a dual fellowship trained radiologist. Neha’s

family moved from Chicago to Galesburg and finally to Moline, Illinois, where the rest of

her childhood was spent.

Upon graduation from Moline Senior High School, Neha attended the University

of Illinois at Urbana-Champaign and received a BS in psychology. After her

undergraduate training, Neha was awarded her DDS at the University of Michigan in

Ann Arbor, Michigan. Fresh from dental school, Neha applied for residency in

orthodontics and matched at the University of Florida. After her first year of residency,

Neha was married in Moline, Illinois to Pratik S. Patel. In May of 2014, Neha will

graduate from the University of Florida with a certificate in orthodontics and a Master of

Science. Neha and her husband will move to Indianapolis, Indiana in June of 2014 to

begin their lives together.

Neha is a member of the Omicron Kappa Upsilon dental honor fraternity, Delta

Sigma Delta dental fraternity, The National Scholars Honor Society, and Phi Kappa Phi.

During her dental training, she was given the International College of Dentists Award,

Comprehensive Care Award, and Russell W. Bunting Award in Periodontics. Neha has

published one article in the Journal of Public Health Dentistry, titled Pediatric patients'

orthodontic treatment need, quality of life, and smiling patterns–an analysis of patient,

parent, and provider responses.

Neha has many hobbies, including travelling, rock climbing, running, baking, and

Indian classical dancing.