Research: Class of 2007

Aranda,G." Cephalometric Comparison of the Effects of Cervical and High-pull Headgear on High Mandibular Plane Angle Cases" Orthodontic Thesis for M.S. Oregon Health and Science University, December 2007 


Introduction: The purpose of this retrospective study was to compare the differences that occurred when high mandibular plane angle (MP-SN > 36°) Class II patients were treated with cervical vs. high-pull headgear.   

Methods: Records from 28 high-pull headgear (21 females, 7 males) and 34 cervical headgear (18 females, 16 males) patients that started treatment with high mandibular plane angles were obtained from 2 private practice orthodontic offices. The patients also received comprehensive orthodontic treatment with fixed appliances (.022"), using Class II elastics as needed. Pretreatment and post-treatment lateral cephalometric radiographs were analyzed using QuickCeph Studio 2007. Measurements from the 2 groups were compared using independent t-tests with a level of significance of p<.05.  

Results: Changes in the sagittal dimension were not found to be significantly different between the two groups. Vertically, the Y axis increased more in the cervical group (1.6º) than in the high-pull group (0.4º; p<.05). The occlusal plane angle increased in the cervical group (1.2 º) and decreased slightly in the high-pull group (0.5º, p<.05). Changes in the mandibular plane angle were not statistically different between groups. Linear dimensions showed a statistically significant difference in the lower facial height where the cervical headgear group exhibited an increase of 5.6 mm whereas the high-pull headgear group increased 3.9 mm (p<0.05). 

Conclusions: Although several of the angular and linear changes produced by the two different treatment protocols showed statistically significant differences, the clinical significance of the differences was questionable due to their small magnitude. Results of this study suggest that treatment with either type of headgear approach would be acceptable for patients with high mandibular plane angles.   

Carver, CD." Comparison of Protein Composition in Stimulated vs. Unstimulated Whole Human Saliva" Orthodontic Thesis for M.S. Oregon Health & Science University December 2007. 


Introduction: Saliva is an easily accessible biofluid with diagnostic potential. Essential to saliva-based diagnostics is a complete catalog of proteins in saliva, as well as an understanding of the effect of collection method on its composition. For example, little is known of the changes to the whole human salivary proteome caused by stimulation. The purpose of our study was to compare the proteome of stimulated vs. unstimulated whole human saliva.  

Methods: Two samples of whole saliva, one unstimulated, one stimulated with citric acid, were collected from five healthy male subjects age 27-32. Saliva samples were analyzed using highly sensitive 2-dimensional-liquid chromatography/mass spectrometry (2D-LC/MS) to identify both major and minor proteins present. Relative protein amounts were estimated from the 2D-LC/MS data utilizing spectral counting. Changes in protein relative abundance were compared using paired two-tailed Student's t-test with the level of significance set to p<.05.  

Results: The 2-DLC analysis was able to identify with high confidence 509 non-redundant proteins. 288 proteins found in at least 3 of 5 subjects were compared to detect changes in relative abundance. 36 proteins were found to change significantly (p<.05) following stimulation (14 increased, 22 decreased). 

Conclusions: Stimulation with citric acid alters the proteome of human whole saliva, inducing changes in protein relative abundance. Future biomarker and proteome studies of whole saliva will need to account for the effect of stimulation on protein composition when considering collection protocols.  

Masaki, KM." Retrospective evaluation of A Modified Bonded Lingual Retainer for the Maxillary Incisors" Orthodontic Thesis for M.S. Oregon Health and Science University December, 2007


Introduction: Prevention of relapse after orthodontic tooth alignment has been one of the greatest challenges within the field of orthodontics. The purpose of this study was to compare upper anterior tooth alignment after use of Hawley retainers vs. fixed retainers bonded to the upper central and lateral incisors, and to see if there were differences in periodontal indices between the two groups.    

Methods: Participants between the ages of 16 and 31 who were at least two years post debond were selected to participate if they had either mandibular first or second premolars extracted for orthodontic therapy. Participants were excluded from the study if they had periodontal disease, rampant caries, interproximal restorations at the contact between the remaining premolar and the molar, pregnancy or for a history of smoking. For the mandibular first molar and the adjacent premolar, recordings were made of clinical attachment loss, probing depth, bleeding on probing, plaque accumulation, and food impaction. Comparison of these factors between the two groups was made using paired t-tests with significance set to <0.05.   

Results: A random chart review was conducted from a private orthodontic practice and the Oregon Health & Science University orthodontic clinic to result in a sample of 25 participants for each retention group. Subjects had to have before and after treatment study models and to have been in retention for at least 7 months. At a recall exam an impression was made of their upper arch and periodontal measurements were made including probing depths, bleeding on probing, and gingival recession. Little's index of irregularity was used to calculate tooth irregularity from canine to canine. Differences in tooth alignment and periodontal recordings were compared between groups using t-tests. Regression analysis was applied to analyze the following relationships between: time in retention and amount of relapse, number of bleeding sites and probing depths; age and number of bleeding sites and probing depths; initial irregularity and relapse; bleeding sites around the canines and bleeding sites around the central and lateral incisors. The P-value was set at 0.05 for all tests.  Results: There was no statistical difference in initial irregularity between the two groups (mean: 9.0 mm) or time in retention (41.8 months). At retention recall, the Hawley group had significantly greater change in tooth alignment relative to the bonded group. For both groups, no significant relationship was found for the amount of time in retention and amount of relapse, or for the amount of initial irregularity and amount of relapse. There was no significant relationship for age and number of bleeding points or number of pockets, and the number of pockets and time in retention. A greater number of bleeding points was found in the Hawley retention group and there was a significant positive relationship for bleeding on the canines and bleeding on the central and lateral incisors in the Hawley group but not for the bonded group.   

Conclusions: The bonded maxillary retainer appears to be a reliable retainer for keeping upper incisors aligned for many years. No evidence was found indicating that the bonded maxillary retainer contributes to periodontal disease.   

Shimogaki, SK. "Position of the Lips and Facial Profile: Preferences of Orthodontists Versus Lay People" Orthodontic Thesis for M.S. Oregon Health and Science University December, 2007


Introduction: The purpose of this study was to assess and compare the esthetic lip preferences of orthodontists and the lay public in straight, retrognathic and prognathic Caucasian profiles. 

Methods: The profile images of 2 Caucasian subjects, male and female, having normal cephalometric values with straight profiles were altered digitally using Dolphin Imaging program. For both subjects the chin was moved to create retrognathic and prognathic profiles of varying severity. The position of the upper and lower lips were then horizontally protracted and retracted in 2 millimeter increments in each profile to a maximum distance of 6 millimeters. The profile images were assembled into a booklet and distributed to 50 orthodontists and 100 lay people who evaluated the attractiveness of the profiles by marking a Visual Analogue Scale (VAS). To assess reliability, a month later 13 orthodontists and 18 lay people repeated the survey. Factorial ANOVAs with repeated measures and Bonferroni multiple comparison tests were conducted to determine differences in attractiveness preferences. All tests were set at a significance level of p<.05).  

Results: Lay people and orthodontists did not differ significantly in their preferred lip positions for both the male (p=.058) and female profiles (p=.134). The straight profiles for both sexes had the highest overall ratings. Lip retrusion of 2 to 4 mm was preferred for the retrognathic profiles, while greater lip protrusion was preferred up to 4 mm for the prognathic profiles. Minimal lip retrusion was deemed more acceptable in the male profiles. Lay people and orthodontists had high reliability in their assessments of facial profile attractiveness  

Conclusions: Both rater groups were similar and tolerated changes in lip position between 2 and 4 millimeters from their original positions, where lip retrusion was favored with retrognathic profiles and lip protrusion was preferred with prognathic profiles.