Effect of a retention groove on the shear bond strength of dentin-bonded restorations.

STATEMENT OF PROBLEM: With the increasing use of minimally invasive restorations, effective adhesion becomes more important. Applying mechanical retention to a flat dentin surface might improve the adhesion of ceramic and composite resin restorations. PURPOSE: The purpose of this in vitro study was to evaluate the effect of a groove in a flat dentin surface on the bond strength of various restorative materials. MATERIAL AND METHODS: Dentin specimens of bovine teeth were prepared with or without a groove. Identical disks were fabricated from direct composite resins (Filtek Supreme XTE [FS] and Clearfil AP-X [AP]) and indirect ceramics (Vita Mark II [VM] and IPS E.max CAD [EM]). These materials were bonded directly or cemented adhesively to the dentin specimens. Shear bond strength was tested with a universal testing machine. Finite element analysis (FEA) models of the test arrangement were made to further analyze the stress distribution. RESULTS: VM (no groove, 5.1 ±3.0 MPa; groove, 8.7 ±1.5 MPa) and EM (no groove, 11.4 ±3.7 MPa; groove, 17.7 ±5.2 MPa) showed significant effect of a groove on the shear bond strength. FS (no groove, 18.6 ±4.9 MPa; groove, 16.3 ±4.3 MPa) and AP (no groove, 25.8 ±3.8 MPa; groove, 24.2 ±7.2 MPa) showed no significant effect of a groove. For the composite resins, the retention groove increased the shear stress along the dentin-restoration interface, and debonding at the contact surface started at lower load values than for the specimens without a groove. CONCLUSIONS: Application of a groove to a flat dentin surface improved the shear bond strength for ceramic restorations. For direct composite resin restorations, exhibiting a lower elastic modulus, a groove had no significant effect on the shear bond strength, while it increased the shear stress along the dentin-restoration interface for composite resin.

Staining of dentin from amalgam corrosion is induced by demineralization.

PURPOSE: To evaluate the effect of artificial demineralization upon color change of dentin in contact with dental amalgam. METHODS: Sound human molars (n = 34) were embedded in resin and coronal enamel was removed. Dentin was exposed to artificial caries gel (pH 5.5) at 37 degrees C for 12 weeks (n = 24). Non-demineralized teeth served as controls (n = the 10). A dispersive high-Cu amalgam or conventional low-Cu amalgam was condensed onto dentin surfaces of all groups. After 10 weeks storage in saline, amalgam was removed and teeth were cut into three slices. Surfaces were inspected under optical microscopy and photographed. RESULTS: Penetration of black pigments was observed in dentin underneath both high-Cu and low-Cu amalgams in demineralized specimens. Black deposits were unevenly distributed and observed predominantly in dentin near to pulp horns. Discoloration was not limited to outer demineralized dentin but extended beyond this zone. Evenly distributed bluish-green discoloration was observed underneath all high-Cu amalgam specimens independent of demineralization.

Influence of composite resin consistency and placement technique on proximal contact tightness of Class II restorations.

PURPOSE: To investigate the influence of composite resin consistency and placement technique on proximal contact tightness of Class II composite resin restorations. MATERIALS AND METHODS: A manikin model (KaVo Dental) was used with an artificial first molar in which a standardized MO preparation was ground. This preparation was duplicated 360 times. Cavities were restored using Clearfil Photo Bond (Kuraray) combined with one of three composite resins of different consistencies: a low-viscosity (X-Flow, Dentsply), a medium-viscosity (Clearfil AP-X, Kuraray) and a high-viscosity composite (Tetric Ceram HB, Ivoclar Vivadent). Each composite was combined with 6 different matrix systems and separation techniques (n = 20). Groups 1 and 2: precontoured metal circumferential matrix (KerrHawe 1101-c) in a Tofflemire retainer combined either with hand instrument (OptraContact, Ivoclar Vivadent) or separation ring (Composi-Tight Gold, Garrison Dental Solutions). Group 3: pre-contoured metal sectional matrix (Lite-Flex, Danville Materials) with separation ring. Groups 4 and 5: pre-contoured metal circumferential dead-soft matrix (Adapt SuperCap, KerrHawe) with or without separation ring. Group 6: flat metal circumferential matrix (OptraMatrix, Ivoclar Vivadent) in a Tofflemire-retainer with hand instrument (OptraContact). Proximal contact tightness was measured using the Tooth Pressure Meter (University of Technology, Delft). To determine the effect of experimental variables on the proximal contact tightness, a multiple linear regression model was constructed. RESULTS: Measurements in group 6 were not possible; therefore, this group was excluded. The use of medium- or high-viscosity instead of a low-viscosity composite resin resulted in statistically significantly tighter proximal contacts (p < 0.01). The use of a separation ring resulted in a large, statistically significant increase (p < 0.001) in contact tightness, while the use of a hand instrument resulted in a small, statistically significant increase of contact tightness (p = 0.017). No statistically significant differences were found when a dead-soft matrix or a sectional matrix was used instead of a Tofflemire (p = 0.159, p = 0.261, resp.). CONCLUSION: Use of a separation ring when restoring a Class II composite resin restoration has a greater influence on the obtained proximal contact tightness compared to the influence of the consistency of the composite resin.