Thermal protective effects of an RMGIC liner during irradiation

Objectives: High power curing lights are being marketed to the dental profession as faster curing, time saving and ultimately money saving improvements. However, these higher power lights may cause an unacceptable increase in temperature during curing. This study investigated the thermal protective effects of a resin modified glass ionomer cement liner when irradiated by currently available high power curing lights.

Methods: A 4mm deep Class I preparation was prepared in an extracted human maxillary molar. Two thermocouples were threaded through the palatal root, one positioned in the center of the chamber and the other in the pulp horn. 1mm diameter tubing was placed over the mesial and distal roots and water flow was set at 0.025ml/min at a temperature of 37°C. Several curing lights were tested including varieties of PAC, QTH, and LED lights. Heat transfer was measured when the preparation was empty (simulating bonding agent cure), and while curing a 1mm increment of either a flowable composite or an RMGIC(Vitrebond) liner.

Results: Significant thermal changes were observed in the pulp horn only. In the empty preparation, only the PAC light was able to significantly increase pulpal temperature above 5.5C°(Zach & Cohen, 1965). With 1mm of flowable composite, all three varieties of lights were able to significantly increase pulpal temperature beyond 5.5C°. None of the curing lights tested showed a significant increase in temperature while curing the RMGIC liner. Significance is defined as p<0.01.

Conclusions: High power curing lights have the potential to cause irreversible temperature damage to the pulp during polymerization. The pulp horn experiences a greater temperature increase than does the mid-chamber. An RMGIC liner helps prevent significant heat transfer to the pulp as it does not require a cured bonding agent prior to placement. Funding for this project was provided by Dalhousie University.