Cuspal Movement in Premolar Teeth Restored with Different Filling Materials

Objective: During setting of resin composites the polymerization shrinkage induces contraction stress, which can result in fracture of tooth structure during or shortly after curing. The aim of this study was to investigate which factor, shrinkage, contraction stress, or the Young's modulus, is predominant in the cuspal movement in extracted premolars with an MOD restoration. Methods: The volumetric shrinkage was determined by a mercury dilatometry and shrinkage stress and tensile modulus were measured with a tensilometer. The composites used in this study were Herculite XRV (Kerr), Heliomolar (Ivoclar Vivadent), Clearfil Photo Posterior (Kurarary Dental), Filtek A110 (3M Espe), Point 4 (Kerr), and Beautifill (Shofu). These composites are especially selected to cover a wide range of shrinkage/contraction stress properties. The MOD preparation in the upper premolar was restored in bulk with one of the composites and Clearfil SE Bond (Kurarary) as the adhesive system. The composites were cured with two lamps simultaneously (800 mW/cm², 30s) and cuspal deflection was measured with the aid of a laser scan micrometer and digitally recorded up to 5 min after curing. Results: All restored teeth showed a decrease of the bucco-lingual width during and after curing the composite, but most of the deflection was observed directly after the curing cycle was finished. The composites Herculite XRV, Heliomolar, and Clearfil Photo Posterior gave significant less cuspal deflection compared to Filtek A110, Point 4, and Beautifill. A good regression (r² = 0.78) between the cuspal movement and shrinkage was observed. No regression was observed between the cuspal movement and contraction stress, and cusp movement and tensile modulus. Conclusion: Cuspal movement in a premolar with an MOD restoration is mainly due to shrinkage of composite.