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Effect of variable light intensity on composite shrinkage.
J B Dennison1, P Yaman, R Seir
1Department of Cariology, Restorative Sciences and Endodontics, University of Michigan School of Dentistry, Ann Arbor, MI 48109-1597, USA.
The Journal of Prosthetic Dentistry
|December 6, 2000
Summary
Sequentially increasing light intensity during dental composite curing significantly reduces polymerization shrinkage. This method ensures adequate depth of cure without compromising mechanical properties, offering a promising alternative to standard high-intensity curing.
Area of Science:
- Dental Materials Science
- Polymer Chemistry
- Biomaterials Engineering
Background:
- Polymerization shrinkage in dental composites is a significant clinical issue, potentially leading to adverse outcomes like microleakage and secondary caries.
- High-intensity light curing improves cure depth and mechanical properties but exacerbates shrinkage.
- Optimizing light curing protocols is crucial for mitigating shrinkage without sacrificing material performance.
Purpose of the Study:
- To evaluate the impact of sequentially increasing light intensity on polymerization shrinkage in hybrid and microfill dental composites.
- To assess the effectiveness of different light intensity curing sequences on the depth of cure using Knoop hardness testing.
Main Methods:
- Polymerization shrinkage was measured using a linometer on samples subjected to four curing protocols: full-intensity control, low-intensity control, and two test groups with incrementally increasing light intensity.
- Knoop hardness testing was employed to evaluate the degree of cure for each composite material under the different light intensity sequences.
- Statistical analysis included one-factor ANOVA and Tukey's multiple comparisons test to determine significant differences between groups.
Main Results:
- A significant reduction in mean linear shrinkage was observed in all tested sequential light intensity protocols compared to the full-intensity control group for both composite types (P<.05).
- No significant differences in shrinkage were found among the three non-full-intensity protocols for either composite material.
- Knoop hardness values indicated that the full-intensity control and the most graduated sequential protocol (25% for 10s, 50% for 10s, 100% for 20s) achieved comparable and superior cure depths.
Conclusions:
- A sequential light intensity curing strategy, specifically 10s at 25%, 10s at 50%, and 20s at 100% intensity, effectively minimizes polymerization shrinkage in dental composites.
- This optimized curing protocol achieves a sufficient depth of cure, comparable to full-intensity curing, thus not compromising the material's performance.
- Implementing graduated light intensity curing presents a viable method to reduce adverse effects associated with polymerization shrinkage in dental restorations.