Research: Class of 2010

Brown, ML. “Ion release from a novel orthodontic resin bonding agent for the prevention of white spot lesions: An in vitro study.” Thesis submitted for M.S. in Orthodontics, Oregon Health & Science University, December 2010

Enamel demineralization and formation of white spot lesions is a common side effect of orthodontic treatment. One approach to combating the mineral loss would be to use a specialized bracket bonding agent to provide a source of ions adjacent to the brackets that buffers the acidic environment. The purpose of this study was to measure ion release from four sol-gel bioactive glass-containing orthodontic resin bonding agents (BAG-Bonds) following immersion into simulated body fluid (SBF) at pH 4 and 7.

Methods: Four BAG-Bonds, two containing fluoride, were developed. Prepared in our laboratory, the BAG-Bonds were composed of a mixture of resin monomers and bioactive glasses (BAGs). Workability of the final BAG-Bonds determined the amount of filler added to each, and this varied according to BAG composition. Commercially available Transbond XT was used as the control. Three disks (10mm x 2mm) of each material were individually suspended in 3.5 mL of SBF at pH4 and 7. SBF was analyzed to measure pH and ions released at 1hr, 10 hrs, and 100hrs. Calcium was measured by atomic absorption analysis, phosphate by UV visible spectrometry, and fluoride by an ion-specific electrode. The data were compared by a 3-way ANOVA with p <0.05.

Results: Significant differences in calcium and phosphate ion release were found between the four BAG-Bonds and the control at multiple time-points. Significant changes in pH were also found. There was no measureable release of fluoride from any of the materials.

Conclusions: The BAG-Bonds showed the capacity for buffering acidic oral environments and significant release of calcium ions into their surrounding environment, and hold the potential to be a biomimetic bonding agent that may reduce or eliminate white spot lesion formation.

Delplanche JF. “Evaluating a novel bioactive glass orthodontic bonding agent and its effects on enamel demineralization.” Thesis submitted for M.S. in Orthodontics, Oregon Health & Science University, December 2010

Introduction: The formation of white spot lesions (WSL’s) and enamel decalcification is a potential risk associated with orthodontic treatment, and therefore ion-releasing bonding agents have been proposed as a means to reduce enamel decalcification for orthodontic patients. This in-vitro study used extracted human third molars, and compared the enamel microhardness adjacent to orthodontic brackets bonded with three different bonding agents.

Methods: Thirty unblemished third molars were divided at random into three groups of 10. Each group was bonded with one of the following: 1) a resin bonding agent (TB-XT)
(Transbond XT, 3M Unitek, Monrovia, Calif); 2) a glass ionomer bonding agent (FO-LC) (Fuji Ortho LC, GC America, Chicago, Ill); and 3) a novel bonding agent containing bioactive glass and glass ionomer (BAG-GIC). After 19 days of pH cycling, the teeth were visually evaluated to qualitatively examine the resulting lesions prior to being embedded in plastic and sectioned coronally. Microhardness measurements adjacent to the brackets were compared using 2-way ANOVA, comparing treatment against location, with p <.05.

Results: Visually, teeth bonded with a TB-XT showed the most apparent WSL’s, and teeth bonded with BAG-GIC showed the least apparent WSL’s. At 25 μm and 75 μm beneath the surface, teeth bonded with BAG-GIC had significantly less reduction in hardness than those bonded with the other adhesives (p<.05). Teeth bonded with TB-XT showed significantly greater reduction in hardness at all depths up to 100 μm compared to the other adhesives (p<.05).

Bonding materials that incorporate bioactive glass may help prevent demineralization and the eventual development of WSL’s adjacent to orthodontic brackets.

Houlberg, BJ. “Use of ESPI to evaluate the effect of thread design of orthodontic mini-implants on bone strain.” Thesis submitted for M.S. in Orthodontics, Oregon Health & Science University, December 2010

Introduction: Factors that contribute to the stability of orthodontic mini-implants have yet to be well defined. One variable that has had limited evaluation relates to the thread design of the implants. The purpose of this study was to measure the magnitude of bone strain imparted by orthodontic mini-implants (OMIs) of two different thread designs.

OMIs with uniform thread pitch and diameter (Single-Thread, n=6) were compared against OMIs with two different thread pitches and diameters (Dual-Thread, n=6). The OMIs were inserted into bone analog, subjected to a ramped load from 0-30 N, and strain was detected and measured through electronic speckle pattern interferometry (ESPI). The ESPI method used a laser to project a speckle pattern of light on the bone analog, and as the analog was strained during OMI loading, fringes were produced in the speckle pattern that were detected by a camera and analyzed with custom software to quantify the amount of strain. Specific strain was measured at 1 mm intervals from the OMI center for each OMI.

Results: At 2 mm from the implant, significantly less (p < 0.05) specific strain was observed with Dual-Thread (21.91 με/N) than with Single-Thread (33.59 με/N) and at 3 mm the difference in specific strain between Dual-Thread (15.75 με/N) and Single-Thread (23.01 με/N) was highly significant (p = 0.001). At distances greater than 3 mm, no statistically significant difference in strain was observed between the two OMI types.

Conclusions: This study demonstrated that OMIs with larger diameter and finer-pitch threads in the cortical bone region result in less strain in the bone immediately adjacent to the implants.

Timock, AM. “Accuracy and reliability of buccal bone height and thickness measurements from cone-beam computed tomography imaging.” Thesis submitted for M.S. in Orthodontics, Oregon Health & Science University, December 2010

Introduction: Cone-beam computed tomography (CBCT) imaging has widened opportunities for examining morphological aspects of the craniofacial complex, including alveolar bone, but limitations of the technology have yet to be defined. Through the use of comparisons to direct measurements, the purpose of this study was to investigate the accuracy and reliability of buccal alveolar bone height (BBH) and thickness (BBT) measurements derived from CBCT images.

Methods: 12 embalmed human cadaver heads (5 female, 7 male; mean age: 77 years) were scanned with an i-CAT® 17-19 unit (Imaging Sciences International, Hatfield, Pennsylvania) at 0.3 mm voxel size. BBH and BBT measurements of 65 teeth were made in standardized radiographic slices and compared to direct measurements made by dissection. All measurements were repeated three times by two independent raters and examined for intra- and interrater reliability. Agreement between measurements was assessed by concordance correlation and Pearson correlation coefficients, and measurement means were compared by two-tailed t tests.

Intrarater reliability was very high as were interrater correlations for all measurements (≥ 0.97) except CBCT BBT (0.90). CBCT measurements did not differ significantly from direct measurements. The mean absolute difference in BBH was 0.30 ± 0.27 mm and in BBT was 0.13 ± 0.12 mm with no pattern of under- or overestimation. Agreement between the two measurement methods was higher for measurements of BBH than BBT, as demonstrated by concordance correlation coefficients of 0.98 and 0.86, respectively.

Conclusions: For the protocol used in this study, CBCT can be used to quantitatively assess BBH and BBT with high accuracy (0.30 mm and 0.13 mm mean absolute error, respectively) and reliability (correlation coefficients > 0.90). Comparing the two sets of CBCT measurements, BBH demonstrated greater reliability and agreement with direct measurements than did BBT measurements.