Date of Award
Spring 2010
Document Type
Thesis
Degree Name
Master of Science (MS)
Department
Dentistry
First Advisor
Berzins, David W.
Second Advisor
Roberts, Howard W.
Third Advisor
Stafford, Gary L.
Abstract
The acid-base and light polymerization reactions in resin modified glass ionomers (RMGI) have been shown to compete and possibly inhibit one another during early RMGI development. Earlier beginning times of light polymerization initiation may limit the acid-base reaction and if time allowed for the acid-base components to react is increased, the extent of light cure reaction may be lesser. The thermal behavior of a commercially available RMGI was investigated in relation to a light initiation regimen using a differential scanning calorimeter (DSC). The relationship between delay in light initiation or no light initiation and the resultant set matrix of the material was determined by subjecting the material to a dynamic temperature scan between 37oC and 300oC at 10oC/min. Different cure groups (n=10 per cure group for an immediate light cure group, 5 min and 10 min delay light cure groups, and a dark cure group) were stored for specific periods of time (30 min, 1 day, 1 week, 1 month and 3 months; n=10/time group) in an incubator at 100% relative humidity and 37oC. Specimen weight changes due to storage and weight loss due to DSC testing were also computed. The DSC thermograms displayed endothermic peaks reflective of material degradation and thus material structure. All groups of specimens had a characteristic single endothermic peak in the thermograms except the 30 min dark cure specimens which had two endothermic peaks in their thermogram. The endothermic peaks were mainly attributed to the dehydration of bound water in the matrix of the material. Significant differences in endothermic peak enthalpy and peak temperature were observed among the cure and time groups. The results suggest that, in general, the immediately light cured material is of differing structure compared to groups that allow the acid-base reaction to occur either due to delay in light curing or its absence. Additionally, changes in the endothermic peak over time were observed, indicating material maturation occurred and is likely due to changes in the ratio of bound to unbound water in the matrix. Interpretation of weight changes in storage show light curing reduced the moisture sensitivity of the RMGI.