Research: Class of 2006 (December)

Bailey, AM. "Protein Secretions of the Parotid Gland: A Comparison of Stimulated and Unstimulated Flow " Orthodontic Thesis for M.S. degree, Oregon Health & Science University, December 2006.


Introduction: A previous study at OHSU School of Dentistry investigated human whole saliva proteome using 2-DLC (2-Dimensional Liquid Chromatography; Wilmarth et al., 2004) and was able to identify most known salivary proteins, a large number of common serum proteins, and three previously undiscovered proteins. In contrast to whole saliva which contains a conglomeration of secretions from all salivary glands and contaminants from gingival fluid, bacteria, and food, parotid gland saliva can be readily isolated during collection. This ease in collecting uncontaminated saliva as well as the ability to drastically increase parotid flow rate upon stimulation make this gland a prime candidate for study using proteomic techniques to determine the parotid proteome, measure changes in protein composition, and potentially identify protein biomarkers. Previous investigations of the parotid proteome have used the 2-DE (2-Dimensional Electrophoresis) techniques. These studies identified 16 (Hardt et al., 2005) and 12 (Walz et al., 2006) proteins. A few of the parotid proteins (proline-rich proteins, histatin, and statherin) appeared to undergo extensive proteolytic processing (Hardt et al., 2005). The limited sensitivities of the 2-DE studies, however, did not allow for further characterization of the parotid proteome. 

Purpose: The purpose of this study was to analyze the protein composition of parotid gland secretions, under conditions of stimulated and unstimulated flow, using 2-DLC.  

Methods: Parotid gland saliva was collected using a Lashley cup from six Caucasian males (ages 28 to 34 years) first during unstimulated saliva flow and then during stimulated (citric acid) saliva flow. Each sample was digested with trypsin, and the peptides were separated using 2-DLC (strong cation exchange/reverse phase). A quadrapole ion trap mass spectrometer was used to perform tandem mass spectrometry to identify peptides and proteins. For positive identification, proteins were required to have least two distinct peptides, and be present in a minimum of two biological subjects. Counts of MS/MS spectra were used to provide relative protein abundance estimates and to compare the protein abundance in unstimulated flow compared to stimulated flow. 

Results: Using 2-DLC the number of identifiable parotid proteins was increased by a factor of 3 to 4 over that reported in previous 2-DE studies. Comparison of the relative abundances of 37 proteins under the two salivary flow conditions showed no statistically significant differences.  

Conclusions: This study established a parotid proteome for healthy, young males for future use in studies of parotid gland, for example with aging and dysfunction. The similar protein composition between unstimulated and stimulated flow implies that stimulated saliva flow can be used in future studies, greatly reducing the time necessary for collection of parotid saliva.   

Carter, BL . "The effect of curing light source on shear bond strength and degree of conversion over time of an orthodontic adhesive" Orthodontic Thesis for M.S. degree, Oregon Health & Science University, December 2006.


Purpose: The purpose of this study is to evaluate over time the shear bond strength (SBS) and degree of conversion (DC%) of an orthodontic resin-composite adhesive activated with a quartz-tungsten halogen and a high-intensity (second-generation) light-emitting diode (LED) light-curing unit (LCU) in order to determine the effect of light-source type on the SBS and DC% of the adhesive at various time points after light exposure and to determine whether there is a correlation between SBS and DC%.   

Methods: Brackets were bonded to permanent mandibular bovine incisors (N=138) with an orthodontic adhesive (Transbond XT, 3M Unitek, Monrovia, CA) and cured with either a second-generation LED light source (Ortholux LED, 3M Unitek) for 10 seconds or a quartz-tungsten halogen (Ortholux XT, 3M Unitek) for 20 seconds per manufacturer's instructions. SBS testing was done on a universal mechanical test instrument (Q Test, MTS Sintech, Research Triangle Park, NC) at 5 minutes, 60 minutes, and 24 hours after initial exposure. Immediately after bond failure, composite specimens were removed from the adhesive remaining on each tooth and were analyzed by Fourier Transform Infrared (FTIR) spectroscopy (DS-20/XAD, Analect Instruments, Irvine, CA) to determine the degree of conversion of carbon-carbon double bonds within the polymerized composite adhesive. Data were analyzed with two-way ANOVA and Bonferroni and Tukey post-hoc testing (p<0.05).   

Results: There was no significant effect of light source type on the SBS or DC% at each time interval after photopolymerization (p = 0.05). Time, however, was found to have a significant effect on the SBS of orthodontic brackets – SBS increased significantly with time up to 24 hours (p < 0.0001). DC%, however, did not change significantly over time (p = 0.05).   

Conclusions: In addition to its practical and operational advantages the Ortholux LED LCU offered similar bond strength in half the cure time than the Ortholux XT quartz-tungsten halogen. Although it is not fully understood why SBS increases with time up to 24 hours while DC% remains constant, crosslinking and polymer entanglement may be factors. Within the limitations of this study, the use of second-generation LED technology is well justified. 

Carter, C. "Differences in Periodontal Health Mesial to the Mandibular First Molar Following First vs. Second Premolar Extractions for Orthodontic Purposes" Orthodontic Thesis for M.S. degree, Oregon Health & Science University, December 2006.


Introduction: Following extractions of either first or second premolars and space closure of the extraction site, the anatomic form of the embrasure between the lower first molar and premolar will differ on account of the morphology of the distal contour of the second versus first premolars. 

Purpose: The purpose of this study was to investigate the impact on the periodontal health of the mandibular first premolar and the mandibular first molar in patients who had second premolars extracted for orthodontic therapy.   

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: Comparison showed that the group with second premolar extractions showed more adverse periodontal findings at the distolingual of the first premolar vs. the second premolar in all six measurements observed (p<0.05). With the contact between first molar and first premolar versus second premolar, there was a greater percentage of food impaction (55% vs. 17%), a higher percentage of loose and open contacts (19% vs. 0%), and a higher percentage of plaque accumulation (67% vs. 22%). Results also showed that the distolingual side of the first premolar had deeper probing depths (3.57 mm vs. 2.61 mm), increased clinical attachment loss (0.48 mm vs. 0 mm), and a higher percentage of bleeding on probing (10% vs. 0%).   

Conclusions: The results suggest that extracting mandibular second premolars and placing the mandibular first premolar in contact with the mandibular first molar may lead to periodontal breakdown of the tissue adjacent to the contact, particularly along the distal aspect of the first premolar. In contrast, all participants who had first premolars extracted were found to be periodontally healthy between the mandibular first molar and second premolar. Further long term studies are needed to access the long-term consequences of these periodontal findings.  

Nichols, LO. "A study model comparison of monozygotic twins, dizygotic twins and sibling pairs." Orthodontic Thesis for M.S. degree, Oregon Health & Science University, December 2006.


Objectives: During growth and development of individuals, the relative contribution of genetic versus environmental influences is of importance to orthodontics and the prognosis for modifications attempted during orthodontic therapy. This cross-sectional, retrospective study using monozygotic twin pairs, dizygotic twin pairs and sibling pairs was conducted to assess the extent to which genetic factors affect dental morphologic variation.  

Methods: The sample consisted of 96 adolescents with an age range of 12.0-16.3 years (mean:13.6 years). There were 24 monozygotic twin pairs, 6 same-sex dizygotic twin pairs, and 18 same-sex sibling pairs. Records analyzed included study models of the maxillary and mandibular dental arches. The intra-pair differences of the monozygotic twin pairs and the dizygotic twin and sibling pairs were analyzed by use of the t-test (significance set to p<0.05) for overjet, overbite, buccal segment relationship, intercanine width, intermolar width and dental irregularity. Co-pair correlation coefficients and heritability estimates were also calculated for all parameters studied. 

Results: There was a trend in monozygotic twins toward smaller mean intra-pair difference for all parameters studied. Mean intrapair differences for overbite, mandibular intermolar width and mandibular anterior dental irregularity were significantly less than those of dizygotic twins and sibling pairs. Co-pair correlation coefficients for monozygotic twins were generally higher than those for dizygotic twins and sibling pairs – specifically for overbite, overjet, mandibular intermolar width and mandibular anterior dental irregularity, which suggests a genetic influence.  

Conclusions: Results of this study suggest the etiology of malocclusion to be multifactorial. Significant heritability estimates were calculated for overbite, overjet, mandibular intermolar width and mandibular anterior dental irregularity. Further study with a larger sample is recommended to confirm these findings.