EDTA treatment improves resin-dentin bonds' resistance to degradation.

The existence of unprotected collagen fibrils within the hybrid layer compromises the longevity of restorations. This phenomenon may be avoided if solutions other than strong acids are used for dentin demineralization. The hypothesis to be tested is that bond durability may be improved by EDTA demineralization. Dentin surfaces (human and bovine) were bonded: (1) after phosphoric-acid-etching, and after EDTA demineralization with (2) a total-etch adhesive and (3) a self-etching adhesive. After the teeth were sectioned into beams, half of the specimens were immersed in NaOCl, while the other half was immersed in water. Beams were tested to failure in tension. ANOVA and multiple-comparisons tests were used (P < 0.05). No differences in bond strength were found among the 3 bonding procedures, although bonds made to human molars were 43-61% higher than those to bovine incisors. After NaOCl immersion, only specimens subjected to EDTA demineralization maintained the initial bond strength. We conclude that the collagen network is better-preserved after EDTA demineralization.

Effect of thermal and mechanical load cycling on microtensile bond strength of a total-etch adhesive system.

To evaluate the effect of thermal and mechanical cycles on dentin bond strength to cervical margins of Class II restorations, 80 box-type Class II cavities were prepared on the surfaces of bovine incisors. The cavities were restored with Single Bond (3M-ESPE) and Z-250 composite (3M-ESPE) according to manufacturer's instructions. The incisors were divided into four groups: G1-Control, G2- Thermal cycling (2,000 cycles, 5 degrees C-55 degrees C), G3- Mechanical cycling (100,000 cycles; 50N) and G4- Thermal and mechanical cycling (2,000 cycles 5 degrees C-55 degrees C/100,000 cycles; 50N). The restorations were sectioned perpendicular to the cervical bonded interface into 0.7 +/- 0.2 mm-thick slabs. The slabs were further trimmed at the interface to 1.4 +/- 0.2 mm with a fine diamond bur to produce a cross-sectional surface area of 1 mm2. All specimens were then subjected to microtensile bond testing. Means and standard deviations were expressed in MPa. The bond strength data were analyzed by one-way ANOVA and Fisher's PLSD test (p<0.05). Fracture mode analysis was performed using SEM. Bond strengths were significantly lower when thermal and mechanical cycling were performed [G4-2.41 (8.57)] when compared to the other groups [G1-28.15 (14.03); G2-27.60 (10.14); G3-27.59 (8.67)]. No differences were observed among Groups 1, 2 and 3. Interfacial fracture of the control (G1) and thermocycling (G2) groups mainly occurred between the deepest portion of the adhesive resin and the top layer of the demineralized dentin (Interphase). Mixed failure was predominant and increased when mechanical cycling was applied (G3 and G4).

Effect of different filling materials in combination with intraradicular posts on the resistance to fracture of weakened roots.

The preservation and restoration of severely weakened pulpless teeth is a difficult and relatively unpredictable procedure. This study evaluated the resistance to fracture of experimentally weakened bovine roots internally reconstructed with different filling materials in combination with prefabricated post compared with restored roots that were relatively intact. The roots of 75 mandibular bovine incisors with similar bulks were selected. Of these, 60 were internally prepared to standardized dimensions, thereby simulating weakness. All roots were filled with different restorative materials. The specimens were submitted to the fracture resistance testing with the application of a tangential compressive loading at an angle of 135 degrees in relation to the long axes of the roots. Results indicated statistically significant differences in relation to the root conditions. Weakened roots were less resistant to fracture than were controls. The roots restored with the resin cement demonstrated the lowest fracture resistance values, but statistically significant differences were observed only when compared with those restored by the resin-modified glass-ionomer cement. Resin-modified glass-ionomer cement, polyacid-modified resin composite and resin composite behaved similarly without statistically significant differences among them. None of the materials evaluated were capable of achieving the fracture resistance recorded for unweakened controls.

Effect of different filling materials in combination with intraradicular posts on the resistance to fracture of weakened roots / Efeito dos diferentes materiais obturados em combinação com pinos intra-radiculares na resistência da fratura de raízes frágeis

The preservation and restoration of severely weakened pulpless teeth is a difficult and relatively unpredictable procedure. This study evaluated the resistance to fracture of experimentally weakened bovine roots internally reconstructed with different filling materials in combination with prefabricated post compared with restored roots that were relatively intact. The roots of 75 mandibular bovine incisors with similar bulks were selected. Of these, 60 were internally prepared to standardized dimensions, thereby simulating weakness. All roots were filled with different restorative materials. The specimens were submitted to the fracture resistance testing with the application of a tangential compressive loading at an angle of 135 in relation to the long axes of the roots. Results indicated statistically significant differences in relation to the root conditions. Weakened roots were less resistant to fracture than were controls. The roots restored with the resin cement demonstrated the lowest fracture resistance values, but statistically significant differences were observed only when compared with those restored by the resin-modified glass-ionomer cement. Resin-modified glass-ionomer cement, polyacid-modified resin composite and resin composite behaved similarly without statistically significant differences among them. None of the materials evaluated were capable of achieving the fracture resistance recorded for unweakened controls

Effect of collagen removal on microleakage of resin composite restorations.

This study evaluated the effects of collagen removal on the microleakage of two single-bottle adhesive systems. Forty human third molars were selected and each received two root preparations. The roots were randomly assigned for restoration using Prime & Bond 2.1 (Dentsply Ltda, Petrópolis, RJ 90915, Brazil) or Single Bond (3M Dental Products, St Paul, MN 55144, USA). One root in each tooth was treated with 36% H3PO4 for 15 seconds and the other received an additional treatment with 10% NaOCl for 60 seconds to remove the collagen layer before adhesive was applied. All preparations were restored with Z100 restorative resin (3M Dental Products). The specimens were submitted to 5,000 thermal cycles (5-55 degrees C) and stored in 37 degrees C distilled water for one year. The specimens were then coated with a varnish except for 1 mm of tooth structure surrounding the restoration and immersed in 2% buffered methylene blue for four hours. After rinsing, the restorations were sectioned and two independent observers scored the microleakage at the interface between the restorative material and the tooth using an optical microscope at x45 magnification. The scores were submitted to Fisher's Exact Test and the results showed that collagen removal significantly reduced microleakage for Prime & Bond 2.1 and had no effect on microleakage for Single Bond.