Research: Class of 2013
Messenger, JM. “The effect of variation in orthodontic bracket pad design on bond strength, adhesive thickness, tooth adaptation, and curing light penetration.” Thesis submitted in partial fulfillment of M.S. in Orthodontics, Oregon Health & Science University, December 2012
Introduction: The shape and retentive features incorporated into the base of orthodontic brackets varies widely and may influence the bond strength and curing properties of composite adhesives. The purpose of this study was to investigate the effect of differences among bracket pad designs on the shear bond strength, adhesive thickness, bracket-tooth adaptation, and curing light penetration.
Materials and Methods: Three types of bracket pads were compared, a new bracket (NB) pad design (Ortho Classic Corporation, McMinnville, OR), a foil mesh (FM; Victory Series Low Profile, 3M Unitek, Monrovia, CA), and a milled mesh equivalent (MM; BioMimm, Ortho Classic Corporation, McMinnville, OR). The Transbond XT adhesive system and Ortholux LED curing unit were used to bond the brackets to teeth. Forty five brackets, bonded to extracted human maxillary and mandibular premolars, were subjected to a shear bond strength test using a universal testing machine (Qtest, MTS Systems Corporation, Cary, North Carolina). The bond strengths and mode of failure using the Adhesive Remnant Index (ARI) were compared between groups. Fifteen brackets were bonded to a single non-etched extracted human maxillary premolar utilizing a centering device and debonded with the adhesive left intact under the bracket. Brackets were cut in cross-sections and the thickness of the adhesive was measured in multiple locations. A mean overall thickness of adhesive was determined and compared between the three groups. Transmission Fourier-Transform Infrared Spectrometry (FTIR) was performed using an FTIR microscope in near-IR mode at the edge and center of the brackets on the sectioned samples. From the spectroscopy, the area under the carbon double bond (C=C) peaks was measured and compared within the three groups. A one-way analysis of variance (ANOVA) with follow up Tukey Post-hoc testing, a chi-squared test, t-test, and a paired t-test were performed to determine if there were any significant differences.
Results: The mean shear bond strength was 12.22 2.97 MPa for the NB, 14.74 4.24 for the FM, and 14.43 3.58 for the MM. A one-way ANOVA indicated no significant differences (p=0.129). The ARI comparisons indicated that all three pads had similar bracket failure modes and were not significantly different (x2=0.600, p=0.741). The mean overall adhesive thickness along the gingival and occlusal pad edges was significantly less in the FM group, 0.089mm, compared to the MM, 0.168mm, and NB, 0.138mm, groups (p<.001). The NB retentive features produced a significantly thicker layer of resin under the bracket pad, 0.434mm, compared to the other two groups and the NB and MM pad designs had retentive features that were significantly closer in proximity to the tooth, 0.014mm and 0.022mm, respectively, than the FM bracket, 0.072mm (P<0.001). All three groups were adapted evenly to the tooth in the mesial-distal direction along the occlusal and gingival edges. The FM and MM groups had significantly more adhesive along the occlusal edge than the gingival (P<0.006), whereas, the NB showed no significant difference in the adhesive thickness at the occlusal and gingival (P=0.08). The conversion of C=C was lower at the edge compared to the center for the FM pad (p=0.012) and higher at the center than at the edge for the MM pad (p=0.016). The conversion of C=C was similar at the NB pad edge and center (p=.856).
Conclusions: Bracket pad design significantly influenced the thickness of adhesive resin, pad adaptation, and curing light penetration. However, these significant differences did not appear to affect the bracket pad’s overall bond strength or primary mode of bond failure. Light penetration under the bracket pad was sufficient in all three designs.
Miller, ME. “Accuracy of cone beam computed tomography in measuring alveolar bone height and detecting dehiscences and fenestrations in patients undergoing periodontal surgery.” Thesis submitted in partial fulfillment of M.S. in Orthodontics, Oregon Health & Science University, December 2012
Introduction: Cone-beam computed tomography (CBCT) imaging has provided a multitude of opportunities for examining craniofacial complex morphology, including alveolar bone. However, studies on CBCT accuracy in assessing bone morphology have been limited and most have been conducted with phantoms or on dry human skulls or cadavers. The purpose of this study was to evaluate the accuracy and reliability of CBCT imaging in measuring alveolar buccal bone height (BBH) and in the diagnosis of naturally occurring fenestrations and dehiscences through comparison of the CBCT image and direct in vivo measurements.
Materials and Methods: BBH measurements and the diagnosis of a dehiscence or fenestration were recorded from CBCT images [i-CAT® 17-19 unit (Imaging Sciences International, Hatfield, Pennsylvania) with 0.3 mm voxel size. 5 mA, 120 kVp] in standardized radiographic slices. Measurements were recorded using the original viewing setting (OriCBCT BBH) by Dolphin 3D Imaging® (Dolphin Imaging Systems, Chatsworth, CA) software and again after adjusting for optimal viewing density and contrast (AdjCBCT). All measurements were repeated three times by two independent raters. The presence or absence of a buccal bone dehiscence or fenestration was also recorded. These measurements were compared to in vivo BBH measurements and dehiscence and fenestration diagnosis on patients undergoing a periodontal flapped surgical procedure. These measurements were taken by two independent raters.
Results: Inter-rater reliability was very high with all PCC ≥ 0.994. The OriCBCT BBH measurements were statistically different from the direct measurements; however the AdjCBCT measurements were not. The OriCBCT and the AdiCBCT were not statistically different from each other. The mean absolute difference was 2.3 ± 1.9 mm for OriCBCT and 1.8 ± 2.0 mm for AdjCBCT. A majority of the CBCT measurements were higher than the corresponding direct values. Agreement was adequate for both CBCT methods, with Pearson correlation coefficients of 0.894 for OriCBCTs and 0.903 for AdjCBCTs. When comparing CBCTs, the mean absolute difference was 0.7 ± 1.2 mm. The agreement between the two CBCT methods was strong, with a Pearson correlation coefficient of 0.973. For OriCBCTs and AdjCBCTs fenestration sensitivity and specificity was 1.0. The dehiscence sensitivity was also 1 with both CBCT viewing parameters. Dehiscence specificity was 0.5 for the OriCBCT and 0 for the AdjCBCT.
Conclusions: For the protocol used in this study, CBCT imaging cannot be considered equal to a direct viewing method when determining the presence or absence of alveolar bone. There is a great deal of variability and while it is very accurate for some sites, it is very inaccurate at others.
Moradi, DR. “Comparison of the skeletal and dentoalveolar effects between the Herbst appliance and the Forsus Fatigue Resistant Device in Class II correction.” Thesis submitted in partial fulfillment of M.S. in Orthodontics, Oregon Health & Science University, December 2012
Introduction: This study compared the skeletal and dentoalveolar effects accompanying the correction of Angle Class II malocclusions in patients treated with the Herbst appliance and the Forsus Fatigue Resistant Device (Forsus) in two private practices. The treated samples were also compared to a matched untreated control sample of Class II subjects selected from the American Association of Orthodontists Foundation (AAOF) Craniofacial Growth Legacy Collection.
Materials and Methods: The Herbst group consisted of 38 patients treated with the Herbst appliance in conjunction with fixed appliances. The Forsus group included 38 patients treated with fixed appliances in combination with the Forsus appliance. Subjects in all three groups were matched according to skeletal development. Lateral cephalograms from before treatment (T1) and immediately after comprehensive treatment (T2) were analyzed using a total of 32 sagittal, vertical, and angular cephalometric measurements. Analysis of Variance (ANOVA) and Tukey post-hoc tests were used for comparisons of measurements at T1 and at T2.
Results: Comparisons showed the two groups were similar at T1, except that the Forsus group had a greater Wits appraisal and maxillary incisor proclination and protrusion. Skeletal measurements at T2 showed that both appliance groups had a restrictive effect on the sagittal advancement of the maxilla, with the Herbst appliance showing a significantly greater decrease in the ANB angle by 1.2° and Wits appraisal by 2.4 mm, and a significant increase in the maxillary-mandibular differential. Dentoalveolar comparisons indicated forward movement of mandibular incisors in both treatment groups, with the Forsus demonstrating significantly increased proclination of the mandibular incisors.
Conclusions: Both treatment protocols were effective in the normalization of Class II malocclusions by the end of comprehensive treatment, with the Herbst group showing a mildly enhanced skeletal effect and the Forsus group had greater lower incisor proclination.
Yamakawa, RM. “White pigmented atomic layer deposition coatings on orthodontic archwires: resistance to sliding, durability, and corrosion.” Thesis submitted in partial fulfillment of M.S. in Orthodontics, Oregon Health & Science University, December 2012
Introduction: With the desire of patients to have orthodontic appliances that blend in with their natural dentition, advancements in archwire fabrication to improve their esthetics would be ideal. The purpose of this study was to investigate the resistance to sliding, durability, and corrosion of stainless steel archwires coated with white pigment and atomic layer deposition (ALD).
Materials and Methods: White pigmented ALD coated archwires were tested along with ALD archwires and as-received archwires. A bracket was ligated and pulled parallel to the archwire and force measurements recorded over 5 cm to determine the resistance to sliding. The durability of the coatings was tested by measuring the amount of mass lost following placement of three 0.75 mm second-order step bends in each wire. The ion release from the wires soaked in an acid solution following the resistance to sliding test and from wires not exposed to sliding was determined by inductively coupled plasma mass spectroscopy analysis (ICP-MS). Data was analyzed using ANOVA/ Tukey’s (p<0.05).
Results: The white pigmented ALD coated wire that received two coats of both pigment and ALD had the highest resistance to sliding while the as-received wire had the lowest. The white pigmented ALD two-coat wire had the greatest change in mass following placement of the step bends. The ALD wire that was not slid had the lowest levels of chromium, manganese, iron, and nickel compared to all other wire types but was not significantly different from the as-received wire. There were significantly higher levels of aluminum detected for ALD, white pigmented ALD one-coat, and white pigmented ALD two-coat wires as compared to as-received wires. There were significantly higher levels of manganese, iron, and nickel released for the white pigmented ALD one-coat and two-coat wires. The white pigmented wires that were subjected to sliding had significantly higher levels of aluminum and titanium released compared to wires that were not subjected to sliding. The white pigmented ALD two-coat wire that was slid had the highest values of released titanium, iron, nickel, and copper.
Conclusions: ALD coatings increased the resistance to sliding. The data show trends towards the ALD wires having improved corrosion resistance compared to as-received wires. The addition of the white pigment further increased the resistance to sliding and caused an increase in the ion release from the pigmented ALD layer. The action of the bracket sliding on the archwire affected the ion release. Following placement of the step bends the extent of the damage to the coating of white pigmented ALD wires was limited to the areas where the step plier was applied.