Research: Class of 2011

Cook, VC. "Accuracy of alveolar bone measurements from cone beam computed tomography at multiple parameters." Thesis submitted in partial fulfillment of M.S. in Orthodontics, Oregon Health & Science University, December 2011


Introduction:Cone-beam computed tomography (CBCT) imaging has expanded the potential to analyze alveolar bone morphology in 3 dimensions, but accuracy of the technique has yet to be well defined. To investigate the accuracy and reliability of CBCT measurements, buccal alveolar bone height (BBH) and thickness (BBT) were assessed using 2 acquisition settings.

Materials and Methods: 12 embalmed human cadaver heads were scanned twice with an i-CAT® 17-19 unit (Imaging Sciences International, Hatfield, PA), once (long scan) using 0.2 mm voxel-size, 26.9 s scan, and 360º revolution, and again (short scan) using 0.3 mm, 4.8 s, and 180º. BBH and BBT measurements associated with 65 teeth were made at standardized locations in radiographic sections consistently oriented through use of a detailed protocol. Each measurement was repeated at 3 separate occasions and compared to direct measurements obtained through dissection. Measurements made from the 2 settings were compared by two tailed t tests (p ≤ 0.05), and agreement was assessed by concordance correlation coefficients (CCC).

Results: Mean absolute differences in measurements for long scan were BBH 0.17± 0.12 mm and BBT 0.10 ± 0.07 mm, and for short scan were BBH 0.41±0.32 mm and BBT 0.12±0.11 mm. Comparing the settings, t tests showed statistical similarity for all BBH or BBT measurements. Neither setting demonstrated an under- or over-estimation tendency.Agreement between the measurement methods compared to direct measurement was high, although agreement was higher for BBH than BBT as demonstrated by CCC (BBH: A=0.99, B=0.97 vs. BBT: A=0.94, B=0.88).

Conclusions: Using multiple voxel sizes and scan times, CBCT can be used to accurately and reliably assess BBH and BBT with repeated measurements. Compared to the longer scan times, the similarity in results with the reduced scan time and hence reduced effective radiation dose favors use of shorter scans, unless a purpose for higher resolution imaging can be defined.

Courtright, M. "Comparison of the effects of different mouthrinses on intraoral bacteria in orthodontic patients: a randomized clinical trial." Thesis submitted in partial fulfillment of M.S. in Orthodontics, Oregon Health & Science University, December 2011


Introduction: Increased plaque and enamel decalcification around fixed orthodontic appliances are common problems in orthodontics. The objective of this randomized clinical trial was to compare the amount of oral bacteria found in plaque around orthodontic brackets in 3 groups of orthodontic patients: one using a mouthrinse containing fluoride, xylitol and a pH neutralizing agent, a group using a standard over-the-counter fluoride mouthrinse, and a control group that was not provided a rinse.

Materials and Methods: Fifty-four adolescent patients undergoing comprehensive orthodontic treatment were randomly assigned to 3 groups. Group 1 was given a mouthrinse containing fluoride, xylitol and a pH neutralizing agent (CariFree®, Oral Biotech, Albany, Oregon). Group 2 was given an over-the-counter fluoride mouthrinse (ACTÒ, Chattem Inc., Chattanooga, TN). Group 3 was not provided with a mouthrinse.Plaque specimens were collected from the maxillary canines and assayed for the amount of oral bacteria using ATP-bioluminescence at pretreatment (T0), 6 weeks (T1) and 15 weeks (T2). Post-study surveys were given to study subjects to assess oral hygiene home care and compliance.For data analysis, intra- and inter-group bacterial counts were made using 2-way ANOVA with Tukey post-hoc comparisons.Pearson Correlation Coefficient and T-tests were used to analyze the survey data.

Results:Comparing bacterial counts within groups, Group 1 showed no significant changes between T0 to T1 and T1 to T2.Groups 2 and 3 showed significant increases between T0 and T1 (p<0.05), but no change T1 to T2.Comparison among groups showed no significant differences at T0, T1 or T2.There was no significant difference in compliance between groups.In Groups 1 and 2, there was no correlation with compliance and taste of the mouthrinses.

Conclusions: Results suggest that use of a mouthrinse containing fluoride, xylitol, and a pH neutralizing agent during fixed appliance orthodontic treatment helps prevent significant increases in oral bacterial counts after 6 and 15 weeks of treatment.However, no significant differences were found when comparing groups using an over-the-counter fluoride mouthrinse or when no mouthrinse was provided.

Fleischner, LN. "A novel biomimetic orthodontic bonding agent for prevention of white spot lesions: an in vitro study of surface microhardness changes adjacent to orthodontic brackets." Thesis submitted in partial fulfillment of M.S. in Orthodontics, Oregon Health & Science University, December 2011


Introduction: The objective of this study was to compare changes in enamel microhardness adjacent to orthodontic brackets after using bonding agents containing various compositions of bioactive glass compared to a traditional resin, and following a simulated caries challenge.

Materials and Methods:Extracted human third molars (n=10 per group) had orthodontic brackets bonded using one of four novel bioactive glass (BAG)-containing orthodontic bonding agents (BAG-Bonds) or commercially available Transbond XT.The four new adhesives consisted of BAG in varying percentages incorporated into a traditional resin monomer.The teeth were cycled through low-pH demineralizing and physiologic-pH remineralizing solutions over a period of 14 days.Microhardness was measured on longitudinal sections of the teeth 100, 200, and 300 µm from the adhesive edge and beneath the brackets, at depths of 25 to 200 µm from the enamel surface.Normalized hardness values were compared using three-way ANOVA.

Results: Significantly less reduction in enamel microhardness was found with the experimental adhesives at depths of 25 and 50 µm at all distances from the adhesive edge. In all groups there were no significant changes in enamel microhardness past 125 µm depth.Results varied with the different BAG-Bonds with 81BAG-Bond showing the smallest decrease in enamel microhardness.

Conclusions: The BAG-Bonds tested in this study showed a reduction in the amount of superficial enamel softening surrounding orthodontic brackets compared to a traditional bonding agent.The results suggest that clinically BAG-Bonds may aid in maintaining enamel surface hardness, therefore helping prevent white spot lesions adjacent to orthodontic brackets.

Werner, GR. "Atomic layer deposition coatings on orthodontic archwire and brackets: resistance to sliding, coefficient of friction, and mechanical testing." Thesis submitted in partial fulfillment of M.S. in Orthodontics, Oregon Health & Science University, December 2011


Introduction:The objective of this study was to measure the resistance to sliding, coefficient of friction and mechanical properties of atomic layer deposition (ALD) coatings on stainless steel archwires.

Materials and Methods:ALD-coated archwires and brackets were tested along with as-received archwires and brackets to make 4 different groups. A bracket was ligated and pulled parallel to the archwire and force measurements were made to test the resistance to sliding. Nanomechanical testing compared the coefficient of friction between as-received wires and the ALD-coated wires. A scratch test was performed to assess the adherence of the coating to stainless steel and look for signs of delamination. The elastic modulus and elastic limit were tested using a three-point flexure device. Data were analyzed using ANOVA and Student's T-test with p <0.05.

Results: The ALD-coated wire and bracket combination had the lowest resistance to sliding and the as-received wire and bracket combination had the highest. The coefficient of friction of the coating was significantly lower than the wire surface and coatings did not delaminate during scratch testing. The elastic modulus of the ALD-coated wire did not differ significantly from the as-received wire.

Conclusions:The ALD-coated wire had lower resistance to sliding and a lower coefficient of friction. The ALD-coating did not significantly alter the elastic modulus of the wire and did not delaminate during scratch testing.