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Resin polymerization problems--are they caused by resin curing lights, resin formulations, or both?
Compendium of Continuing Education in Dentistry. (Jamesburg, N.J. : 1995). Supplement
|March 23, 2002
Summary
Resin formulation, not light type, significantly impacts polymerization issues in dental restorations. Microfill resins showed less shrinkage and lower modulus, while autocure resins performed similarly to hybrids. Surface sealants may mitigate defects.
Area of Science:
- Dental Materials Science
- Polymer Chemistry
- Biomaterials Engineering
Background:
- High-intensity resin curing lights, including lasers and plasma-arc systems, have raised concerns regarding potential negative effects.
- Understanding the interplay between light curing parameters and resin properties is crucial for optimizing dental restorations.
Purpose of the Study:
- To investigate the impact of different resin curing lights, intensities, modes, and times on dental resin properties.
- To determine whether light characteristics or resin formulation are primary drivers of polymerization-related issues such as shrinkage and strain.
Main Methods:
- Six dental resin restorative materials were tested using 14 different curing lights (lasers, plasma-arc, halogen) with varying intensities (400-1,900 mW/cm²), modes (constant, ramped, stepped), and times (1-40 seconds).
- Evaluated parameters included shrinkage, modulus, heat generation, strain, and associated physical changes in teeth and resins.
- Clinical observations focused on marginal integrity, including white lines and enamel cracks.
Main Results:
- Resin formulation was a highly significant factor in polymerization outcomes, whereas light type and curing mode effects were not statistically significant.
- Microfill resins exhibited the least shrinkage and lowest modulus; autocure resins showed comparable or higher values than light-cured hybrids.
- Lasers and plasma-arc lights generated the most heat (up to 21°C surface, 14°C internal), while halogen lights produced minimal heat in the pulp chamber (up to 2°C).
- Significant strain was observed in teeth restored with Z100 Restorative and BISFIL II autocure resin, leading to clinical defects like white lines and enamel cracks.
Conclusions:
- Dental resin formulation is the critical determinant of polymerization problems, outweighing the influence of light curing technology or delivery modes.
- Lower light intensity and modified curing modes (ramped, stepped) did not effectively reduce shrinkage, modulus, strain, or prevent marginal defects.
- The use of low-viscosity surface sealants is recommended as a final step to seal marginal defects until restorative materials with reduced shrinkage and modulus become available.