Performance of Different Adhesives to a New Low Shrinkage Composite

Background: The introduction of low shrinkage resin composite may facilitate the placement of large increments without jeopardizing the integrity of the completed restoration and/or the abutment tooth. However, little information is available on the adhesive performance of this resin composite and its compatibility with other adhesive systems. Objective: Compare the bond strengths of pre-etching silorane self-etch adhesive, and two total-etch two-step adhesives to low shrinkage silorane resin composite using self-etch adhesive as control. Methods: 20 extracted third molars were randomly assigned to one of 4 groups: LS System Adhesive (LS, 3M ESPE) (recommended by the manufacturer for silorane composite); dentin etched with 15 seconds phosphoric acid + LS System Adhesive (LSpa); Single Bond (SB, 3M ESPE); Prime&Bond NT (PB, Dentsply Caulk). Occlusal middle dentin was exposed and crowns restored with Filtek Silorane (3M ESPE). After restoration, the specimens were stored in distilled water at 37^oC for 24 hours. Teeth were sectioned in X/Y directions to obtain sticks with a cross section of 0.7±0.2 mm². All sticks were fractured in tension at a crosshead speed of 1mm/min. The data was submitted to ANOVA statistical analysis and Duncan's post-hoc test, at P<0.05 (superscript letters indicate significance). Results: (PTF = pre-testing failures/ spontaneous debonding, N = number of specimens, and Mean ± SD in MPa):

Adhesive	N	PTF	Mean±SD
LS	52	9	55.0A ± 37.1
LSpa	50	0	73.8A ± 4.0
SB	33	22	4.4B ± 5.1
PB	42	38	1.2B ± 1.5

Conclusion: The new low shrinkage resin composite demonstrated compatibility only with its own adhesive. Pre-etching did not significantly improve the bond strengths to low shrinkage resin composite, but resulted in no spontaneous debonding (pre-testing failures).