Max José Pimenta Lima

Effect of surface protection on the permeability of eroded dentin

Context: Eroded dentin might present the opening of dentinal tubules, increasing permeability, and consequently dentinal hypersensitivity. Aims: This study evaluated the permeability of dentin surfaces exposed to different levels of erosion and methods of surface protection. Materials and Methods: Dentine samples (3 mm × 3 mm × 1 mm) were prepared from bovine incisors (n = 90) and divided into three groups according to the method of controlling erosive challenge: Negative control, topical fluoride application, and glass ionomer sealant. Subsequently, they were randomly divided into three subgroups according to the exposure of simulated gastric acid solution (Demineralization – DES) (5% HCl, pH = 2.2), and remineralization (RE); negative control, 9 and 18 cycles DES-RE. The dentin permeability was measured by assessing the hydraulic conductance (μl/min.cmH2O.cm2). Statistical analysis was performed by two-way ANOVA and Tukeys test. Results and Conclusions: Greater permeability was observed after 18 erosive cycles, followed by exposure to 9 cycles and negative control (P < 0.0001). The application of glass ionomer sealant resulted in a major reduction of the hydraulic conductivity, regardless of the erosive challenge. Control groups and topical fluoride application showed similar results. In conclusion, the severity of erosive challenge contributed to the increase of dentin permeability. Besides, the glass ionomer sealant was the only protection agent that promoted significant effects in dentin permeability.

Effect of erosion and methods for its control on the surface roughness of composite resin

Objective: This study evaluated the surface roughness of a nanofilled composite resin submitted to different degrees of erosion and methods of control. Methods: 120 cylindrical composite specimens (6×1.5 mm) were randomly divided into four groups, according to the surface protection against the erosive challenge [negative control, topical application of fluoride, glass-ionomer sealant, resin sealant]. After the application of the respective method, specimens were divided into three subgroups (n=10): a) absence of erosive challenge; b) 9 cycles of DES-RE; c) 18 cycles of DES-RE. Surface roughness (Ra, μm) was recorded and statistically analyzed (2-way Anova/Tukey). Results: The glass-ionomer sealant exhibited less rough surfaces under all the conditions. However, the average roughness was significantly higher after 18 DES-RE cycles. Conclusion: Despite the potential shown by glass-ionomer sealant, it was concluded that no material prevented an increase in surface roughness of the nanofilled composite after an intense erosive challenge.

Evaluation of marginal adaptation and traction resistance of zirconium crowns made up using two different techniques and cemented on pins with three types of cements

Objective: The aim was to assess marginal adaptation of zirconium crowns made up by manual milling (pantograph) and computerized (computer assisted designing/computer assisted machining [CAD/CAM]) before and after cementation; and the efficiency of 3 types of cements in retaining these crowns: Zinc phosphate, resin modified glass ionomer cement (RelyX Luting 2) and resin cement (RelyX U200). Materials and Methods: Out of 30 zirconium crowns, 15 were milled by the pantograph, and 15 by CAD/CAM. Each group was divided into 3 subgroups according to the cement used. Cementation was done over the analog universal pin 4.5 mm × 4 mm and submitted to mensuration of marginal interface of its four faces with stereoscopic magnifier (×20). Then, they were directed to a machine of universal test (EMIC), and submitted to an axial traction with speed of 0.5 mm/min until its displacement. Results: Before cementation, CAD/CAM crowns (47.60; 40.20; 43.40 μm) demonstrated a greater desadaptation comparing to pantograph crowns (28.20; 35.60; 30.40 μm). RelyX Luting 2 showed less marginal desadaptation postcementation on CAD/CAM crowns (53.80 μm ± 8.43 μm) and pantograph (39.80 μm ± 12.696 μm), when compared with zinc phosphate (62.00 μm ± 12.86; 45.20 μm ± 24.035) and to RelyX U200 (73.80 μm ± 44.49 μm; e 53.00 μm ± 10.817 μm). RelyX Luting 2 also obtained better efficiency on traction resistance (9.48 Kgf ± 2.49 Kgf; e 24.54 Kgf ± 6.73 Kgf), when compared to zinc phosphate (8.71 Kgf ± 4.00 Kgf; and 11.85 Kgf ± 3.15 Kgf) and RelyX U200 (8.08 Kgf ± 0.62 Kgf; and 14.78 Kgf ± 5.94 Kgf). Conclusions: Lower values on marginal discrepancy were found on pantograph crowns comparing to CAD/CAM crowns. RelyX Luting 2 obtained not only a lower marginal desadaptation, but also a better efficiency on traction resistance among the three cements. However, there was no significant statistical difference that could prove the influence of desadaptation on displacement resistance.