The effect of loading on microTBS of four all-in-one adhesives on bonding to dentin.

This in vitro study analyzed the effect of mechanical loading on microtensile bond strength (microTBS) to dentin of four all-in-one adhesives and compared with a total-etch adhesive system. The tested adhesives were Danville Experimental (an unfilled single-component adhesive containing a proprietary organophosphate and hydrophobic monomers; Danville Materials), G Bond (GC), Clearfil S(3) Bond (Kuraray), AdheSE One (Vivadent), and Prelude Total-Etch (Danville Materials). Dentin surfaces were exposed and composite resin (AP-X, Kuraray) build-ups were created. The samples were divided into two subgroups and the first subgroups were subjected to mechanical fatigue loading (5 x 10(4); 50 Nat 0.2 Hz). Testing was performed after 1 week using a "nontrimming" microTBS test at a cross head speed of 1 mm/min. The data was calculated as MPa and statistically analyzed using Multivariate Analysis of Variance. Multiple comparisons were done using t-test. Mechanical loading significantly decreased microTBS of the tested materials (p = 0.000). Prelude Total-etch showed the highest bond strength values when compared to the tested all-in-one adhesives (p < 0.01). G Bond and Clearfil S(3) Bond showed significantly higher bond strength values than Danville Experimental and AdheSE One (p < 0.01).

Conversion-dependent shrinkage stress and strain in dental resins and composites.

The placement of dental composites is complicated by the contraction that accompanies polymerization of these materials. The resulting shrinkage stress that develops during cure of a bonded restoration can induce defects within the composite, the tooth or at the interface resulting in compromised clinical performance and/or esthetics. In light of the substantial efforts devoted to understanding and attempting to control shrinkage stress and strain in dental composite restoratives, this paper offers a perspective on the conversion dependent development of shrinkage and stress. The relationships between polymer property development and the physical evolution of the network structures associated with dental polymers as well as the interrelated kinetics of the photopolymerization reaction process are examined here. Some of the methods used to assess conversion in dental resins and composites are considered. In particular, newly introduced techniques that allow real time analysis of conversion by near-infrared spectroscopy to be coupled directly to simultaneous dynamic measurements of either shrinkage stress or strain are described. The results are compared with reports from the dental materials literature as well as complementary studies in other related fields of polymer science. The complex, nonlinear correlation between conversion, shrinkage and stress are highlighted. A brief review of some of the materials-based approaches designed to minimize polymerization shrinkage and stress is also provided.