Date of Award
Master of Science (MS)
Bradley, Thomas G.
Despite advances in caries research and the development of protective mechanisms and materials, orthodontic white spot decalcification remains a significant problem. Increased plaque buildup around orthodontic appliances, combined with inadequate hygiene and a susceptible patient, can lead to unesthetic demineralized lesions in enamel.
Relatively new to the arena of caries prevention, NovaMin, a bioactive glass, has shown some promise in areas of remineralization of early lesions, protection against acidic challenge, and has demonstrated antiplaque properties. This study explored a new application of the material, incorporation into an orthodontic bonding composite resin. Objectives of the study were: to determine if the experimental resin could release ionic precursors to enamel formation in solution, and the effects on bracket shear bond strength.
For ion release, NovaMin concentrations of 7.5, 15 and 22.5 wt% were incorporated into a commercially available resin, TransBond LV. Resin discs were immersed in 5 mL of both deionized water and lactic acid (pH~5). Calcium ion concentrations were measured using a calcium-selective electrode. Solutions were replaced every 24 hours for the first week, then remained unchanged for an additional 5 weeks. Controls were the resin without the modification and solutions without a resin disc. Concentrations declined rapidly over the first two days, reaching levels below that of the control solutions. Without solution replacement, a significant increase in calcium ion concentration was observed for NovaMin levels of 15 and 22.5%.
For bond strength, 39 extracted human premolar teeth were tested in three groups of 13. Standard twin brackets were bonded with either TransBond LV or the same resin with 15 or 22.5% NovaMin incorporated. Shear bond strength was tested using a universal testing machine. ARI scores were also obtained. There was no significant difference in mean shear bond strength between the three groups (TransBond LV (15.13 ± 4.18MPa), TransBond LV + 15% NovaMin 13.55 ± 2.84MPa), and TransBond LV + 22.5% NovaMin (13.27 ± 4.34MPa)). There was, however, a significant difference in ARI scores between the group without the modification and both NovaMin groups, with the as-provided TransBond LV showing less residual adhesive on the enamel after debond.