The influence of matrix type on the proximal contact in Class II resin composite restorations.

PURPOSE: This in vitro study evaluated the efficiency of various types of matrices in reconstructing the proximal contact area in Class II resin composite restorations. MATERIALS AND METHODS: Standardized MO cavities were prepared on artificial molars of a manikin model. Resin composite (Spectrum TPH-3) restorations were placed using the following matrices (n=10): a) circumferential straight metal matrix with Tofflemire retainer-A, b) circumferential pre-contoured metal matrix system-B (Adapt SuperCap), c) circumferential pre-contoured transparent matrix system-C (Adapt SuperCap) and d) sectional pre-contoured metal matrix system-D (Palodent). After completion of each restoration, the manikin model was fixed on a tension-meter apparatus and an orthodontic wire was used to assess the contact tightness (CT), length of contact arc (LCA) and position of contact point relative to LCA% (PCP). The same measurements were performed on a group of intact molars (REF). The results were statistically analyzed with one-way ANOVA and the Tukey test, as well as the unpaired t-test (alpha=0.05). RESULTS: Matrix D provided the highest CT with the highest LCA, which presented a statistical difference relative to the intact tooth. Restorations with matrix B provided higher LCA than those with matrices A and C, which were found to be comparable to that of an intact tooth. The contact points (PCP) of the filled teeth were located more cervically in matrix D relative to the intact tooth (lower PCP), whereas matrices A, B and C showed more occlusal location (higher PCP). CONCLUSIONS: Differences were noted among all the matrices evaluated and none was proven sufficient to reconstruct the proximal contact characteristics of an intact tooth.

A study on colour stability of self-etching and etch-and-rinse adhesives.

OBJECTIVES: The purpose of this study was to investigate the color change in two "self-etch" and one "etch and rinse" adhesive under dark/water and photoaging conditions and to evaluate the influence of these changes on the color stability of resin composite restorative systems. METHODS: The adhesives were: One-Up Bond F (OB/Tokuyama), Adper Prompt L-Pop (PL/3M Espe) and Optibond Solo Plus (OS/Kerr). 10 sample disks of each material were prepared (OB(1), LP(1), OS(1)). Additionally, 30 sample discs of TPH Spectrum (Caulk/Dentsply) resin composite were prepared and bonded with the three adhesives tested (OB(2), LP(2), OS(2) groups) to freshly cut dentin discs. 30 days of storage in deionised water (37+/-1 degrees C) in dark conditions was followed by exposure of all samples to UV light photoaging. A colorimetric evaluation (CIEL*a*b* system) was performed immediate after sample photopolymization (baseline), at 7 and 30 days of dark/water storage and after the 360h of UV aging. Color changes (DeltaE*) were calculated between baseline and subsequent measurements. The results were analyzed by independent two-way Anova and Sheffe's statistical tests (a=0.05). RESULTS: All the adhesives evaluated exhibited significant color changes even after early aging time into water. One-Up Bond F presented the highest color alterations under both experimental conditions and Optibond Solo Plus the lowest. The adhesives were proved able to influence the color stability of a resin composite, which is bonded to a dentin substrate. One-Up Bond F induced the strongest effect on color change of the resin composite while no differences were clarified between Adper Prompt L-Pop and Optibond Solo Plus. CONCLUSION: Significant color changes were determined under water and photoaging conditions for the "self-etch" and "etch and rinse" adhesives evaluated and the resin composite combined with these agents.

Curing efficiency of various types of light-curing units.

This study compared monomer conversion (DC), the per cent linear polymerization shrinkage (%LS), the wall-to-wall contraction pattern (per cent of peripheral opening, %DM, and maximal marginal gap, MG) and depth of cure (DOC), of a hybrid resin composite (Spectrum TPH) exposed to different types of light-curing units and exposure modes (Virtuoso-PAC, Elipar TriLight-QTH, and FreeLight-LED). The QTH and LED units were used in two curing modes: the exponential ramp and the continuous output modes. Monomer conversion was investigated by micro Multiple Internal Reflection (MIR)-Fourier-transform infrared (FTIR) spectroscopy and %LS was measured by the deflective disc method. The wall-to-wall contraction method used a cylindrical cavity model in extracted human teeth. The per cent debonded margins relative to the cavity periphery (%DM) and the width of maximum gap (MG) was evaluated. The DOC was determined using Vickers microhardness measurements (200 g load, 20 s) at the top surface (H0), at 2 mm (H2) and at 4 mm (H4) depths, and the results expressed as H2/H0 and H4/H0 ratios. Significantly lower %DC and %LS values were provided by PAC and LED units. No differences were found in %DM among the curing units and PAC exhibited the highest MG. No significant differences were noted among light-curing groups in terms of H2/H0 microhardness values. The QTH, operated in exponential mode, resulted in the highest H4/H0 value. The exponential mode of the QTH demonstrated superior performance for the total of the characteristics evaluated.