Research: Class of 2015

Darcy, K. Evaluation of in vitro models for assessment of resin infiltration treatment of artificial enamel white spot lesions. Thesis submitted in partial fulfillment of M.S. in Orthodontics, Oregon Health &Science University, December 2015


Introduction: Resin infiltration has been evaluated as a restorative technique for treatment of post-orthodontic smooth surface white spot lesions (WSLs) and outcomes of esthetic assessments have varied. The purpose of this in vitro study was to 1) to evaluate the effect of three different caries simulation models on penetration and esthetic outcomes of a commercially available resin infiltration system, and 2) assess the impact of two etch protocols on esthetic outcomes and tooth structure loss.

Materials and Methods: With 54 extracted bovine incisors, the facial enamel surface was cleaned and then abraded with a silicone diamond polishing bur to remove any irregularities. Except for of a 7 x 15mm window centered on the facial surface of the crown, tooth surfaces were sealed with acid-resistant nail varnish. The teeth were equally allocated into three treatment groups to create WSLs: (1) chemical demineralization, (2) pH cycling demineralization, or (3) microbiological demineralization, where each group was exposed to demineralization for 2 weeks. Following formation of the WSL in the exposed enamel window, a strip of varnish was painted across the center of each WSL to divide it into two windows and to preserve an area of WSL under the varnish stripe as a control. For each tooth, the lesions were treated with ICON®smooth surface resin infiltration system (DMG America, Englewood, NJ) according to the manufacturer's instructions, with each half of the WSL receiving either the minimum (2x) or maximum (4x) recommended etch protocols, and then resin application. For all teeth, an intraoral spectrophotometer (VITA Easyshade®Model #62011, Vident, Brea, CA) recorded baseline (T1) color values, analyzed using the CIE-L*a*b* (Commission Internationale L'Eclairage) color system. For microscopic evaluation of the WSLs and resin infiltration, samples of 4 teeth from each group were embedded in epoxy resin. Using a diamond saw, 1 mm thick sections were obtained across the center of the WSL lesion windows. Polished sections were photographed at 175x using a stereo microscope. Measurements of lesion thickness were made to determine the amount of tooth structure removed by the two etch protocols relative to the protected area of the WSLs. Another sample of 4 specimens per group was prepared for imaging with a scanning electron microscope (SEM;Quanta 200, FEI, Hillsboro, OR, USA). Lesion depths produced by the three demineralization techniques were compared by one-way analysis of variance (ANOVA) followed by Tukey's multiple comparison test at α ≤ 0.05. Measurements of color change and tooth structure loss were analyzed using a two-way ANOVA followed by Tukey's multiple comparison test at α ≤ 0.05.

Results: The microbiological demineralization method produced significantly deeper lesions (264.7 ± 18.8 µm) than either the chemical demineralizing solution alone (145.5 ± 27.7 µm) or the pH cycling method (124.013 ± 26.175 µm;p <0.001), whereas the depth of lesions produced by the chemical and pH cycling demineralization methods were not differ (p = 0.38). Color assessment data showed significant differences between the two etch protocols in both the bacteria and the pH cycling groups (p <0.001). The color change for the microbiological demineralization group and the pH cycling group was significantly different than that of the chemical demineralization group for 2x etch, but there was no difference between the microbiological and pH cycling methods. Within all three demineralization groups, the 4x etch protocol resulted in significantly more tooth structure loss than the 2x etch protocol (p <0.001), where removal of tooth structure was roughly proportional to the length of etching. For both etch protocols, the bacterial lesions demonstrated significantly more loss of tooth structure (p <0.001), whereas there was no difference in structure loss between the chemical and pH cycling demineralization methods.

Conclusions: Different methods for the creating artificial WSLs result in significant differences in tooth structure loss, with the microbiological approach creating the deepest lesions. The depth of the demineralization impacts the ability of resin infiltration to mask the lesion. With deeper lesions, the results suggest that longer etch times are needed to produce the maximum esthetic outcome, as only shallower lesions were capable of being fully penetrated by the resin. Although improvements in color matching were produced by the prolonged etch times for the deeper lesions, measurements of the color difference from the pre-lesion state indicate that the lesions would still be clinically perceptible.  

Pace, JA. The esthetic effects of camouflaging dentoskeletal discrepancies with facial hair. Thesis submitted in partial fulfillment of M.S. in Orthodontics, Oregon Health &Science University, December 2015


Introduction: The purpose of this study was to assess how well facial hair can camouflage dentoskeletal discrepancies. The specific aims were to see how two styles of facial hair affect the appearance of systematically altered profile views, and to determine the degree of concordance regarding facial hair and profile esthetics among three groups of assessors, laypeople, orthodontists, and oral surgeons, between males and females, and among age groups.

Materials and Methods: An online photographic survey was made using profile photographs of 3 adult males. Each model's photograph was altered to create 7 different profile types—ideal, mandibular retrognathic, mandibular prognathic, concave lips, convex lips, recessive chin, and prominent chin. For each of these profile types, three versions were created in Photoshop (Adobe, San Jose, CA): one clean-shaven, one bearded, and one mustached. The profiles were randomly assembled into the online survey, one per page with an 11-point Likert scale that was scored in 10 point increments from 0 to 100. Several profiles were randomly repeated throughout the survey to test intrarater reliability. Surveys were distributed until responses were received from 50 laypeople, 50 orthodontists, and 50 oral surgeons. Agreement within different rater groups was assessed with intraclass correlation coefficients (ICC). To determine differences in attractiveness preferences, factorial ANOVAs with repeated measures and Bonferroni multiple comparison tests were conducted with significance level set to p<0.05.

Results: Rater agreement within groups, as shown by ICC, varied among the 3 groups: 0.62 for laypeople, 0.73 for oral surgeons, 0.80 for orthodontists. Facial hair significantly affected the ratings of all profiles, where beards significantly improved each discrepancy profile, except the ideal profile. The profiles most improved with beards relative to the clean-shaven profiles were the recessive chin (+20.4 points, p<0.0001) convex lips (+10.2, p<0.0001), and mandibular retrognathia (+10.1, p<0.0001) profiles. Mustaches significantly worsened every profile. The 3 groups of evaluators followed these general trends and were mostly in agreement.

Conclusions: Survey results indicate that beards enhanced the appearance of individuals in profile view when antero-posterior mandibular, lip or chin discrepancies were created. These findings may assist clinicians in treatment planning and providing recommendations on facial hair options to male patients.  

Vo, AH. Morphological assessment of alveolar bone height changes with mandibular incisors after non-extraction orthodontic therapy. Thesis submitted in partial fulfillment of M.S. in Orthodontics, Oregon Health &Science University, December 2015


Introduction: The impact on alveolar bone height of changing the position of mandibular incisors during orthodontic treatment would be of value for orthodontic treatment planning. The aims of this study were to assess alveolar bone changes associated in patients treated with non-extraction orthodontic therapy using CBCT and to evaluate for potential correlations between changes in mandibular incisor inclination and alveolar bone height and thickness, as well as pre-treatment bone thickness to vertical bone changes. Lastly, this study explores a new best-fit superimposition method to measure incisor inclination changes and determine its accuracy compared to measurements of mandibular incisor to mandibular plane (IMPA) in growing patients.

Materials and Methods: Pre- and post-treatment CBCTs from 54 patients, with initial mean age of 12.8, (range 10.5 to 15.5) years, with a mean treatment duration of 1.5 years, were included. The sample encompassed 17 males and 37 females, including 33 Class I, 20 Class II, 1 Class III malocclusions. Based on standardized 2D slices of the CBCT scans, facial and lingual bone height and thickness, overjet, and IMPA were measured. Best fit mandibular structural superimpositions were used to measure changes in incisor inclination, and the results were compared changes in IMPA. Pearson Correlation Coefficients were used to assess the relationship between IMPA change versus changes in alveolar bone crest height and thickness, alveolar bone thickness changes versus alveolar bone crest height changes, IMPA change versus best-fit superimposition inclination changes, and IMPA change versus overjet change versus facial alveolar crestal height change. A paired-sample t-test was used to determine significant difference in facial and lingual alveolar crestal height and thickness between T0 and T1 measurements. P<0.05 was considered as statistical significance.

Results: The average facial and lingual alveolar bone height loss was 0.95 ± 1.89 mm and 1.30 ± 1.99 mm (p<0.001). The average facial and lingual alveolar bone thickness loss was -0.17 mm and -0.32 mm (p<0.05), while IMPA changes averaged 3.67 ± 5.45 degrees (p<0.001). There was no correlation between IMPA change and alveolar bone height or thickness changes. There was a positive correlation between best-fit superimposition angulation change and IMPA change (0.97;p<0.001). Pre-treatment facial alveolar bone thickness 3 mm apical to the CEJ had a positive correlation with increased facial alveolar bone height loss (0.48;p<0.05).

Conclusions: With non-extraction orthodontic therapy, there was a correlation with an increase in IMPA and generalized facial and lingual alveolar bone reduction where bone height loss averaged 1.0 to 1.5 mm. Changes in IMPA were not correlated with alveolar bone loss in height or thickness. Thicker facial pre-treatment cortical bone thickness at the level of the alveolar crest was correlated with greater facial vertical bone loss. With incisor mandibular plane angle serving as a guide, best-fit superimposition method is accurate in determining incisor inclination changes and can best serve as a visual aid for reviewing incisor tooth movement.  

Weber, L. Effects of brands and color on force decay and water absorption of elastomeric chains. Thesis submitted in partial fulfillment of M.S. in Orthodontics, Oregon Health &Science University, December 2015


Introduction: A common clinical observation in orthodontic patients is elastomeric chains show varying amounts of deformation after they have been in place for several weeks. The purpose of this study was to compare the force decay and water absorption of different manufacturers and colors of elastomeric chain after a simulated aging process, and to determine whether force decay and water absorption differences are correlated.

Materials and Methods: Four brands of elastomeric chain were studied: RMO Energy Chain (Denver, CO), 3M Unitek Bobbin Chain (Monrovia, CA), Ormco Power Chain (Orange, CA), and Ortho Technology Maximum Power Chain (Tampa, FL). Six colors from each manufacturer were included: clear, gray, purple, black, blue, and orange. Specimens were stretched to 72mm on a Universal Testing Machine to determine the initial force. All specimens were then stretched to a distance of approximately 72mm on a custom jig and stored in distilled water in a dry oven at 37°C. Force values for each specimen were obtained at time points: 24 hours, 2 weeks, 4 weeks, 6 weeks, and 8 weeks. An additional sample of specimens was created from the same manufacturers and colors to examine water absorption differences. Initial weight values were obtained for each specimen and then the specimens were placed individually in capped tubes filled with distilled water that were stored in an oven at 37°C. After 2 and 4 weeks, each specimen was dried and reweighed. Differences in percent force reduction as well as percent weight gain between brands and colors were determined using two-way ANOVA and Tukey post-hoc tests (α <0.05). Pearson correlation coefficients were determined relative to the percent force reduction and percent weight gain values.

Results: All chains lost a majority of their force within the first 24 hours. Force levels then remained consistent for the remaining 8 weeks. All colors of RMO Energy Chain as well as gray and clear Ormco Generation II chains retained higher force values over a period of 8 weeks than the other brands and colors investigated in this study (α <0.05). Within each brand, colors behaved similarly, except for the Ormco Generation II gray and clear chain, which had significantly less force reduction than the other Ormco colors. Statistically significant differences were found for percent weight gain values among brands and colors (α <0.05), but there was no correlation between percent force reduction and percent weight gain values.

Conclusions: RMO Energy Chain and Ormco Generation II chains had significantly less force reduction relative to other brands. Although there were statistically significant differences in water absorption among brands and colors, these differences were not correlated to percent force reduction. Therefore, water absorption cannot serve as an explanation for force decay differences among brands and colors of elastomeric chain.