Research: Class of 2002

Beg, Z. "Assessment of Straight Wire vs. Standard Edgewise Orthodotnic Treatment Using the PAR Index." Orthodontic Certificate Thesis, Oregon Health & Science University, June, 2002.


The purpose of this study was to compare the outcomes of Class I crowded cases treated with standard edgewise appliances versus straight-wire appliances. Twenty-five cases of each group (standard edgewise cases and straight-wire cases) were randomly selected from records in the graduate orthodontic clinic at the Oregon Health Sciences University. The PAR Index was used to score the pre- and post-treatment study models and the results were compared using the paired t-test, with p< 0.05. Results show that the pre-treatment PAR scores were not different between the straight-wire cases (mean score: 21.16 ± 8.7) and the standard edgewise cases (21.52 ± 11.1). The post-treatment PAR scores were also found not to be significantly different (straight-wire: 3.28 ± 2.5; standard edgewise: 4.36 ±3.99). The net PAR score reductions were nearly identical, with the straight-wire cases showing a reduction of 17.88 ± 8.7 and the standard edgewise cases showing a reduction of 17.16 ± 10.7. Although the straight-wire cases showed a greater percent PAR score reduction (82.6%) than did the standard edgewise cases (77.4%), the difference was not statistically significant. Similarly, the average treatment time for the two approaches did not differ statistically (straight-wire: 24.16 ± 7.2 months; standard edgewise: 21.56 ± 7.4 months). In conclusion, this study demonstrated that based on PAR scores and treatment time, equivalent orthodontic results were obtained using either the straight-wire or standard edgewise appliances.

Chamberlain, TH. "Comparison of Bond Strength and Degree of Conversion of a Metal, Polycrystalline and Monocrystalline Bracket by Use of Sheer Bond-strength Testing and Micro-FTIR." Orthodontic Certificate Thesis, Oregon Health & Science University, June, 2002.


Past studies have demonstrated higher bond strengths for ceramic orthodontic brackets relative to their metal counterparts, but there has been no definitive explanation for this difference. One hypothesis attributes the greater bond strength to increased degree of conversion (DC) of light cured adhesive under the translucent bracket. The purpose of this study was to compare the bond strength and DC associated with brackets made of 3 materials: stainless steel, polycrystalline ceramic and monocrystalline ceramic. Sixty extracted premolar teeth were prepared for either shear bond-strength or micro-Fourier transform infrared (FTIR) spectroscopy testing (10 for each test with the 3 bracket types). The teeth were cleaned with pumice, and for bond-strength samples, etched with 37% phosphoric acid, rinsed and dried. Samples for DC analysis were not etched in order to remove the bracket with the composite intact. Brackets were bonded to the teeth using light cured composite (Transbond XT, 3M-Unitek, Monrovia, CA). Debonding and DC data were compared using ANOVA and Tukey's multiple comparison tests (a= 0.05). Results showed that the shear bond strength of the metal brackets (mean: 8.12 MPa) was significantly less than that of the two ceramic brackets (polycrystalline: 13.57 MPa; monocrystalline: 13.38 MPa). Micro-FTIR spectroscopy showed no difference in the DC among the three bracket types. Thus, although the monocrystalline brackets were more transparent than the polycrystalline brackets, this did not affect the DC. During bond-strength testing three monocrystalline brackets had cohesive failures of the bracket itself, possibly due to increased crack propagation within the brittle single crystal bracket. In conclusion, although bonded metal brackets showed lower shear bond strength than ceramic brackets, micro-FTIR spectroscopy showed no difference in the DC of the composite among the bracket types. Another possibility to explain the difference in shear bond strength may relate to variations in the flexibility of metal vs. ceramic brackets. 

Crandell, EK."Cervical Skeletal Maturity Index (CSMI): A Predictor for Percentage Remaining Mandibular Growth." Orthodontic Certificate Thesis, Oregon Health & Science University, June 2002.


The purpose of the study was to test the usefulness of the Cervical Skeletal Maturity Index (CSMI) to predict the percentage of remaining mandibular growth in individuals that did not receive orthodontic treatment. In a previous study performed by Kim (OHSU Certificate Thesis, 2000), a ratio of the inter-vertebral disc space of C2-3 to the vertebral height of C3 (CSMI) was compared to chronological age and other skeletal indices to assess their ability to predict the amount of remaining facial growth. The sample in this study consisted of longitudinal cephalograms of 10 males and 10 females selected at random from the Child Study Clinic archives at Oregon Health Sciences University. The records had to meet specific inclusion criteria including having lateral cephalograms for ages 8, 12, 16, and 20, plus or minus 6 months and the mandible and cervical vertebrae (C2, C3) were clearly visible. CSMI at each time point was obtained. Correlation coefficients for males, females, and both sexes were calculated for CSMI and percent total growth remaining, and CSMI and chronological age. Results indicated that there was a high correlation between CSMI and percent remaining mandibular growth (male: 0.89; female: 0.81; combined: 0.87), which was greater than for CSMI and chronological age (male: 0.84; female: 0.77; combined: 0.81). A CSMI of approximately 1.0 indicated a high growth potential, while a CSMI closer to 0.3 indicated that growth was almost complete. In conclusion, results of this study suggest that the CSMI is a potentially useful method for clinicians to estimate a patient's percentage remaining mandibular growth. 

Kohrs, KJ."Survey of Practice Administration Training in Graduate Orthodontic Programs." Orthodontic Certificate Thesis, Oregon Health & Science University, June 2002


The purpose of this study was to assess the current level of practice administration training in graduate orthodontic programs in the United States, and to identify areas that recent graduates believe would make for a smoother transition to private practice. Using survey questionnaires, topics addressed included the amount and type of practice administration training included in graduate orthodontic programs, topics recommended for inclusion in practice administration training, and perceived reasons for practice administration training in graduate orthodontic programs. Two surveys were designed, one sent to graduate orthodontic program directors in the United States (n= 47) and another sent to recent graduates listed in the annual directory of the American Association of Orthodontists (n= 397). Response rates were 53% and 31% respectively. Results showed that both program directors and recent graduates strongly believe that practice administration training should be part of graduate orthodontic training. Nearly three-quarters of graduates felt unprepared for private practice, and the majority of graduates were seeking additional practice administration training after graduation. While all programs reported providing practice administration training, program directors were more likely to indicate that topics were adequately covered than did the recent graduates. These results suggest a need for program directors to reevaluate what topics are covered and to look for ways to confirm that knowledge is being effectively conveyed to residents. Respondents' comments indicated that the best practice management training for residents would include a formal approach (a structured course), designed and implemented by experienced private practitioners. 

Moses, JR. "Brackets to Adhesive Bond Strength Using Filled vs. Unfilled Resins." Orthodontic Certificate Thesis, Oregon Health & Science University, June 2002.


The purpose of this study was to determine which of 4 methods for applying composite resin to an orthodontic bracket and tooth resulted in the highest bond strength and to analyze where the resin remained attached following debonding. Extracted human central incisors and canines were prepared by flattening the facial surfaces with abrasive and randomly divided into 4 groups, 10 teeth in each. For group 1 (control), the bonding material (Transbond XT light cure; 3M-Unitek, Monrovia, CA) was handled according to the manufacturer's instructions. For group 2, the bonding material was handled according to the manufacturer's instructions except unfilled resin was painted into the pad of a foil mesh bracket base, thinned with compressed air and light cured prior to placing the filled resin. For group 3, the materials were handled as in group 2 except the unfilled resin applied to the bracket base was not cured before placing the filled resin. For group 4, the filled resin was pressed into the bracket base using a Gregg instrument and then bonded according to manufacturer's instructions. Each bracket was light cured for 20 seconds from gingival and 20 seconds from occlusal directions. The brackets were debonded using a shear force in an Instron (Instron Corp, Canton, MA) and the maximum force was recorded. The teeth and brackets were analyzed visually to determine where the resin remained attached. The groups were compared using one-way ANOVA and the Tukey Multiple Comparison tests, with a= 0.05. Results showed no difference in shear bond strength among the four groups (range: 15.14 MPa - 16.32 MPa). The two groups bonded with unfilled resin on the bracket base (groups 2, 3) showed a higher percentage of resin remained attached to the bracket bases after debond relative to the other two groups. In conclusion, the results do not support the need for applying unfilled resin to the bracket base, nor forcing the filled resin into the bracket pad mesh with a hand instrument for the purpose of increasing mean bond strength. 

Robinson, WL. "The Effectiveness of Invisalign Treatment as Assessed by the PAR Index and the American Board of Orthodontics' Standards." Orthodontic Certificate Thesis, Oregon Health & Science University, June, 2002.


Align Technology developed the Invisalign System in 1997, as an alternative to the traditional wire and bracket orthodontic therapy. Align is one of the first companies to use digital three-dimensional imaging of a patient's malocclusion in order to fabricate clear overlay aligners that facilitate tooth movement. These removable appliances must be worn full time and replaced every two weeks until the desired tooth movement is achieved. With such a new appliance, little research has been conducted to test the effectiveness of this appliance on treating malocclusions. The aim of this study was to assess the treatment improvement on selected cases treated solely with the Invisalign System. Also, the components of the malocclusion were analyzed to see where the System works most effectively. 25 patients with pre-and post-treatment final records were included in the sample. Treatment was carried out by five area private orthodontists. The PAR Index, which shows excellent intra- and inter-examiner reliability was used to assess treatment change. Also the American Board of Orthodontics grading criteria was used to detect minor occlusal discrepancies following treatment. It was found that the mean percentage PAR reduction was 46.03%. This was statistically significant and further indicates successful treatment as shown by Richmond's category of improvement. 72% of the cases finished with acceptable alignment. The pre-treatment alignment showed only 24% with acceptable alignment, further indicating successful treatment. The maxillary and mandibular anterior alignment were the only components to show statistically significant treatment change(p< 0.05). 28% of the cases passed the post-treatment ABO grading criteria ( 25 points). The occlusal contact score accounted for 27% of the post-treatment ABO score.