Research: Class of 2009

Buck, TF “Self-ligation vs. elastomers: one-year follow-up study examining bracket archwire ligation technique on microbial colonization and white spot lesion formation” Orthodontic Thesis for M.S. degree, Oregon Health & Science University, December 2009
Introduction: Formation of white spot lesions (WSL) is a common risk associated with fixed orthodontic appliances. Maintenance of good oral hygiene is made difficult by orthodontic brackets which results in bacterial plaque accumulation, increasing the risk of WSL. Objectives of this prospective longitudinal study, conducted as a 1-year follow-up study, were to (1) compare plaque bacteria amounts at the bracket-tooth interface with use of elastomeric-ligating (EL) vs. self-ligating (SL) brackets, (2) measure bacteria after initiation of elastomeric chain use, (3) evaluate use of ATP-driven bioluminescence for quantification of total oral bacteria, and (4) analyze formation of WSL by photographic evaluation and laser light fluorescence (DIAGNOdent).


Methods: Thirteen subjects had full, fixed appliance orthodontic treatment where upper and lower lateral incisors were bonded with either an EL or SL brackets. A total of 50 teeth were included in the study (1 subject with only upper laterals included). All other teeth received self-ligating brackets. Plaque samples were collected from facial surfaces of the incisors at 1 year and then 5 weeks later after use of elastomeric chains. Total plaque bacteria were quantified using standard plating methods and by direct measurement of ATP-driven bioluminescence. To evaluate WSL, standardized photographs and DIAGNOdent measurements were analyzed. A 2 X 2 X 2 X 2 mixed-design full factorial ANOVA was conducted to determine significant patterns of differences between EL and SL brackets.


Results: There were no statistical differences in bacterial numbers surrounding the EL vs. SL brackets. ATP-driven bioluminescence values for teeth with EL (GM= 8.192E+07) and SL (GM= 6.950E+07) brackets were similar at 1 year. After five further weeks of elastomeric chain, ATP-driven bioluminescence values increased for teeth with SL brackets, occurring in the maxillary arch only (GM=1.298E+08), with no change observed for teeth fitted with EL brackets (GM= 6.726E+07). ATP-driven bioluminescence values correlated to the numbers of total oral bacteria (r=0.85; p<0.05). DIAGNOdent measurements were found to have low sensitivity (0.45) and good specificity (0.82) when compared to WSL determined using photographic evaluation.


Conclusions: After one year of treatment there were no differences in retention of plaque bacteria or WSL comparing the two bracket types. When elastomeric chains were introduced, in the upper arch only, SL brackets were associated with the retention of higher amounts of plaque bacteria than were EL brackets. ATP-driven bioluminescence values were significantly correlated to the numbers of total oral bacteria. The use of the DIAGNOdent, compared to visual-photographic evaluation, may be of limited utility when evaluating WSL surrounding brackets.


Clark, KJ “Corrosion and nickel ion release of nickel titanium archwires with ion implantation technology in deflected and non-deflected states” Orthodontic Thesis for M.S. degree, Oregon Health & Science University, December 2009


Introduction: Nickel sensitivity is a concern in the dental profession as nickel has been shown to have dermatological, toxicological and possibly mutagenic effects and causes more allergic reactions than all other metals combined. Nickel titanium archwires contain approximately 50% nickel and release small amounts of nickel into the oral cavity as they corrode. The purpose of our research was to test the corrosion capabilities and nickel ion release of nickel titanium archwires with and without nitrogen ion implantation technology in deflected and non-deflected states.


Methods: NeoSentalloy wires with and without IonGuard technology were studied. Potentiodynamic anodic polarization was applied to wire either straight or undergoing deflection with a three point bending force. For the non-deflected samples, a testing apparatus held an exposed straight segment 13.3 mm in length. For the deflected samples, our testing apparatus applied a three point bending force by deflecting the same length of wire by 1 mm. The corrosion of each sample was determined by the zero current potential, area integration, and pitting potential point from the anodic polarization charts. Nickel ion release was determined by inductively coupled plasma mass spectroscopy analysis (ICP-MS). Scanning electron microscopy analysis before and after anodic polarization were also compared.


Results: Our study did not detect a significant effect of ion implantation or deflection. The trends showed IonGuard had a more positive zero current potential (p=.114), which would be protective, but more nickel release (p=.452) and a lower pitting potential point voltage (p=.231), indicating pitting corrosion occurred earlier. Four out of five of the dependent variables had non-significant results for the interaction effect. The data show trends for deflected IonGuard wires to have initial protective effects (more positive zero current potential values p=.458) but to exhibit more intense pitting corrosion (higher pitting potential point current p=.400) and more nickel release (p=.294). There was a statistically significant interaction effect between wire type and deflection state for area integration (p=.021), with deflected IonGuard wires showing the greatest area for corrosion during passivation. Scanning electron microscopy and energy dispersive x-ray analysis showed significant variability in the composition of wires, with large titanium-rich inclusions visible in both NiTi and IonGuard wires. Signs of corrosion were visible after anodic polarization testing.


Conclusions: A significant effect of wire type or deflection state on corrosion and nickel release was not seen in our study. We cannot support the claims that IonGuard protects against corrosion or reduces nickel ion release. In fact, when IonGuard is deflected, we found corrosion occurs more rapidly and more robustly, as seen by the increased area integration during passivation. The data show trends for deflected IonGuard wires to have initial protective effects (more positive zero current potential values) but to exhibit corrosion at a greater intensity (higher pitting potential point current) and more nickel ion release.

Grimslid, HJ “Effect of mini-implant collar design on orthodontic skeletal anchorage” Orthodontic Thesis for M.S. degree, Oregon Health & Science University, December 2009


Introduction: Studies have documented the use of titanium mini-implants in providing skeletal anchorage for orthodontic tooth movement. Clinical success rates have been variable and typically reported between 70% and 100%. The purpose of this in-vitro study was to test the hypothesis that mini-implants with collars give the orthodontist superior force resistance, superior stability (anchorage) and cause less surface bone strain compared with mini-implants without collars.
Materials and Methods: Thirty titanium alloy mini-implants, 1.5 X 10.5 mm, were placed in bone analogue specimens with cortical bone thicknesses 1.0 mm, 1.5 mm and 2.0 mm (n=10 each), and the maximum insertion torque (MIT) was recorded. Half were mini-implants with collars, half were without collars, and all were subjected to a tangential force loading perpendicular to the long axis through a lateral displacement of 1.5 mm. Statistical analyses, consisting of 2 x 3 factorial analysis of variances (ANOVA’s) and Tukey’s post-hoc testing were used to compare mini-implant collar group mean force-deflection values, yield points, MIT’s and slope of the force- deflection curves. Additionally, 8 mini-implants were placed in bone analogue specimens with a cortical bone thickness of 2.0 mm. Half were mini-implants with collars, half were without collars, and all were subjected to a tangential force up to 30 N. Electronic speckle pattern interferometry (ESPI) was used to detect surface strain values on the compression side of mini-implants loaded either once or multiple times (n = 4 each). Specific strain values (με/N), slope of the specific strain–deflection curve and mini-implant displacement were evaluated.


Results: The mean anchorage force resistance values to crosshead displacement 0.5 mm, 1.0 mm and 1.5 mm were greater for mini-implant groups with collars than for mini-implant groups without collars in all cortical bone thicknesses (1.0 mm, 1.5 mm and 2.0 mm). Two by three way analysis of variance for the dependent variable mean anchorage force resistance to crosshead displacement showed a significant difference between mini-implant groups (P<0.001), cortical bone thickness groups (P<0.001), as well as a significant interaction between variables (mini-implant x cortical bone thickness, P<0.05). Tukeys post-hoc analysis showed there was a significant difference in the 1.0 mm cortical bone thickness group (P<0.01), 1.5 mm cortical bone thickness group (P<0.05) and 2.0 mm cortical bone thickness group (P<.001) when mini-implants with collars were compared to a mini-implants without collars. ESPI data showed specific strain values were greater for mini-implants loaded multiple times and mini-implant displacement was greater for mini-implants without collars.


Conclusions: Results suggest that mini-implant collars will provide the orthodontist with superior anchorage force resistance, reduced cortical bone stress, and superior stability compared with mini-implants without collars.


Vest, DR “Effectiveness of dental masks and an industrial mask to filter aerodynamically respirable dust particles created by grinding dental composite adhesives” Orthodontic Thesis for M.S. degree, Oregon Health & Science University, December 2009


Introduction: Quartz has been cited by the International Agency for Research on Cancer (IARC) as a human carcinogen. Exposure to quartz containing aerodynamically respirable aerosols (particle size of 0.5-5.0 μm) is possible during air rotary abrasion to remove the adhesive from teeth following orthodontic bracket debonding. A previous study (Almeida, 2006) characterized the particle size distribution of composite adhesive dust within an aerosol generated by air-rotary abrasion of quartz filled adhesives using an 8-stage impactor device (Cascade Impactor, Tisch, Cleves, OH). The purpose of this study was to: 1) determine the effectiveness of dental masks in removing aerodynamically respirable dust (0.5 – 5.0 μm) created by grinding dental composite adhesives, and 2) determine the effectiveness and accuracy of the 8-stage impactor in filtering and separating dust particles according to size fractions.


Methods: Quartz-containing composite adhesive Transbond XT (3M Unitek) was abraded into an aerosol using high speed air-rotary abrasion, and separated into size fractions using an 8-stage Cascade Impactor. Separate trials using three different masks [1-Kimberly-Clark Tecnol Procedure Mask (Kimberly-Clark, Roswell, Georgia); 2-Kimberly-Clark Tecnol Cone Mask (Kimberly-Clark Worldwide, Inc., Roswell, Georgia); 3-3M Particulate Respirator N95(3M Occupational Health and Environmental Safety Division, model #8214, St. Paul, Minnesota)] placed over the intake orifice of the air sampler were conducted using Transbond XT. For the second part of the study, the Cascade Impactor used in the experiment was tested for accuracy, using particles of known sizes and a Microtrac S3500 laser particle analyzer.


Results: Analysis showed that at least 5% of the total dust generated was potentially aerodynamically respirable (particle size of 0.5 μm – 5 μm). The procedure mask filtered significantly more particles than the cone mask. The cone mask allowed 1-2.5% of the particles generated to pass, while the procedure mask allowed 0.03-0.06% of the particles generated to pass through to the impactor stages. When compared to controls, the procedure mask reduced the collected dust mass by over 99%, while the cone mask reduced the collected dust mass by 84%. The N95 mask was the only mask that completely blocked all particles from entering the impactor. Of the total particles collected in the impactor, at least 19.1% of the particles by mass were aerodynamically
respirable when the procedure mask was used, compared with at least 39.1% of the particles when the cone mask was used. According to the Microtrac S3500 particle analyzer, approximately 95% of the particles were less than or equal to 1.1 μm, while the 8-stage impactor shows that approximately 46% of the particles were less than or equal to 1.1 μm when comparing the same sample.

Conclusions: The 8-stage Cascade Impactor was unable to accurately separate the particles into the appropriate size fractions. Exposure to aerodynamically respirable dust containing quartz particles appears likely during removal of Transbond orthodontic adhesive with a high-speed handpiece. The results showed that use of a dental mask
does not completely protect operators from exposure to particles smaller than 5 μm, which are the greatest risk for inhalation to deeper regions of the lungs. The procedure dental mask performed much better than the cone dental mask at filtering particles, while the N95 mask was able to filter 100% of the particles generated. Further studies are needed to determine the extent of this exposure in clinical settings.