04 March 2021

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Regular and high power polymerization mode: what to expect over time?

Co-authors: A. Comba, F. Florenzano

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Photopolymerization is a complex operation, where a high degree of conversion of the restoration material ensures the quality and the longevity of composite restorations. The introduction of LED technology allowed fabrication of powerful polymerization lamps  that require reduced application time. However, some concerns were raised on the possibility to cause stress at the composite-tooth interfaces due to an increased energy of the curing unit. 

For that reason Cerutti et al decided to compare the marginal quality of composite restorations  light cured with two polymerization  protocols, the regular (RM) and the high power (HPM), and conducted a randomized, split-mouth clinical trial using modified USPHS  and SQUACE  criteria for the clinical evaluation.

Material & Methods

The group of research from the University of Brescia collected 50 patients (mean age: 33 years) who received 100 direct class I or class II restorations on  premolars or molars. Three calibrated operators made the restorations. After conditioning the tooth with 2-step etch-and-rinse adhesive, researchers made restorations incrementally using microhybrid resin composite. Each layer was cured using a curing lamp   operating either in regular mode (600-650 mW/cm2 for 20 s) (RM) or high-power (1200-1300 mW/cm2 for 10 s) mode (HPM). The authors nominated two independent, calibrated operators for restoration evaluation at 1 week (baseline) and 6 months after restoration placement, and thereafter annually up to 10 years using modified USPHS  and SQUACE  criteria. Data were analyzed using the Mann-Whitney U-test (α = 0.05).

Results

Cerutti et al placed a total of thirty-six restorations on premolars and sixty-four on molars. There were no dropouts up to the 5th year; during the last 5 years (up to the 10-year recall), 13 patients could not be evaluated (26%). 

Secondary caries, endodontic complications, fractures, and chipping were not observed in any of the restored teeth.

USPHS alpha scores for marginal adaptation (76% and 74% for RM and HPM, respectively) and marginal discoloration (70% and 72%, for RM and HPM, respectively) did not show significant differences between the two polymerization protocols (p > 0.05). 

SQUACE alpha scores for marginal adaptation (78% and 74% for RM and HPM, respectively) and marginal discoloration (70% for both RM and HPM) were also not significantly different at the 10-year year follow-up (p > 0.05).

Conclusions

According to the clinical trial conducted by the Italian researchers, marginal quality of the micro-hybrid composite tested up to 10 years was not significantly influenced by the polymerization protocol adopted . 

In addition, marginal quality of the resin restorations  was found to decrease at the 10-year follow-up compared to baseline and 5-year recall for both USPHS and SQUACE criteria.

For more informations: Clinical performance of posterior microhybrid resin composite restorations applied using regular and high-power mode polymerization protocols according to USPHS and SQUACE criteria: 10-year randomized controlled split-mouth trial.