Lafayette Nogueira Junior

Effect of multiple firing and silica deposition on the zirconia-porcelain interfacial bond strength

OBJECTIVESnTo test the hypothesis that multiple firing and silica deposition on the zirconia surface influence the bond strength to porcelain.nnnMATERIALS AND METHODSnSpecimens were cut from yttria-stabilized zirconia blocks and sintered. Half of the specimens (group S) were silica coated (physical vapor deposition (PVD)) via reactive magnetron sputtering before porcelain veneering. The remaining specimens (group N) had no treatment before veneering. The contact angle before and after silica deposition was measured. Porcelain was applied on all specimens and submitted to two (N2 and S2) or three firing cycles (N3 and S3). The resulting porcelain-zirconia blocks were sectioned to obtain bar-shaped specimens with 1mm(2) of cross-sectional area. Specimens were attached to a universal testing machine and tested in tension until fracture. Fractured surfaces were examined using optical microscopy. Data were statistically analyzed using two-way ANOVA, Tukeys test (α=0.05) and Weibull analysis.nnnRESULTSnSpecimens submitted to three firing cycles (N3 and S3) showed higher mean bond strength values than specimens fired twice (N2 and S2). Mean contact angle was lower for specimens with silica layer, but it had no effect on bond strength. Most fractures initiated at porcelain-zirconia interface and propagated through the porcelain.nnnSIGNIFICANCEnThe molecular deposition of silica on the zirconia surface had no influence on bond strength to porcelain, while the number of porcelain firing cycles significantly affected the bond strength of the ceramic system, partially accepting the study hypothesis. Yet, the Weibull modulus values of S groups were significantly greater than the m values of N groups.

Pulpal temperature increase with high-speed handpiece, Er:YAG laser and ultrasound tips

The aim of this study was to compare intrapulpal temperature increase produced by high-speed handpiece, Er:YAG laser and CVDentus ultrasound tips during cavity preparation. Thirty bovine mandibular incisors with an enamel/dentin thickness of 4 mm at buccal surface had their roots amputated and were allocated to the following groups (n=10): Group I- high-speed handpiece; Group II- noncontact Er:YAG laser (250 mJ/4Hz); and Group III- CVDentus ultrasouns tips. All devices were used with water cooling. Class V cavities were prepared to a depth of 3.5 mm, measured with a periodontal probe. A type T thermocouple was placed inside the pulp chamber to determine the temperature increase (°C), which was recorded by a data acquisition system ADS 2000 IP (Lynx Technology) linked to a notebook computer. Data were analyzed statistically by oneway ANOVA and Tukeys test (p=0.05). The mean temperature rises were: 1.10°C (±0.56) for Group I, 0.84°C (±0.55) for Group II, and 3.00°C (± 1.34) for Group III. There were no statistically significant differences (p>0.05) between Groups I and II, but both of them differed significantly from Group III (p<0.05). In conclusion, the use of Er:YAG laser and high-speed handpiece for cavity preparation resulted in similar temperature increase. Although ultrasound tips generated significantly higher intrapulpal temperature increase, it remained below the critical value of 5.5°C and may be considered safe for use.

Effect of Diamond-Like Carbon Thin Film Coated Acrylic Resin on Candida albicans Biofilm Formation

PURPOSEnThe purpose of this study was to evaluate the effect of diamond-like carbon thin films doped and undoped with silver nanoparticles coating poly(methyl methacrylate) (PMMA) on Candida albicans biofilm formation. The control of biofilm formation is important to prevent oral diseases in denture users.nnnMATERIALS AND METHODSnForty-five PMMA disks were obtained, finished, cleaned in an ultrasonic bath, and divided into three groups: Gc, no surface coating (control group); Gdlc, coated with diamond-like carbon film; and Gag, coated with diamond-like carbon film doped with silver nanoparticles. The films were deposited using a reactive magnetron sputtering system (physical vapor deposition process). The specimens were characterized by optical profilometry, atomic force microscopy, and Rutherford backscattering spectroscopy analyses that determined differences in chemical composition and morphological structure. Following sterilization of the specimens by γ-ray irradiation, C. albicans (ATCC 18804) biofilms were formed by immersion in 2 ml of Sabouraud dextrose broth inoculated with a standardized fungal suspension. After 24 hours, the number of colony forming units (cfu) per specimen was counted. Data concerning biofilm formation were analyzed using ANOVA and the Tukey test (p < 0.05).nnnRESULTSnC. albicans biofilm formation was significantly influenced by the films (p < 0.00001), reducing the number of cfu, while not affecting the roughness parameters (p > 0.05). The Tukey test showed no significant difference between Gdlc and Gag. Films deposited were extremely thin (∼50 nm). The silver particles presented a diameter between 60 and 120 nm and regular distribution throughout the film surface (to Gag).nnnCONCLUSIONnDiamond-like carbon films, doped or undoped with silver nanoparticles, coating the base of PMMA-based dentures could be an alternative procedure for preventing candidosis in denture users.

Edentulism in Brazil: trends, projections and expectations until 2040

The aim of this study was to examine the edentulism rates in Brazil and make projections for the next years. Data were collected from three national oral health surveys. The percentage of edentulous jaws was calculated. Projections were made for the years 2020, 2030 and 2040, assuming that edentulism follows a logistic function. Population projections were also performed. Annual change in proportion of edentulous jaws was -0.04% for teenagers, -0.96% for adults and 0.76% for the elderly. By 2040, edentulous jaws will be virtually zero among teenagers, 1.77% among adults and 85.96% among the elderly. Teenagers will slightly decrease in number; adults will increase and subsequently decrease; the elderly will continue to increase. In teenagers and adults, the number of edentulous jaws will decrease, being approximately 616,000 in 2040. In the elderly, it will increase alarmingly, reaching over 64 million in 2040. Edentulism is declining in Brazil among teenagers and middle-aged adults, but is still increasing and will continue to increase for the next decades among the elderly.

The effect of a bonding agent and thermo-mechanical cycling on the bond strength of a glass-ceramic to gold and cobalt-chromium alloys

To evaluate the effects of bonding agent and thermo-mechanical cycling on the flexural bond strength of a gold and cobalt-chromium alloy to a feldspathic ceramic. Sixty-four metal bars were fused (3 × 25 × 0.5 mm3): 32 with a gold alloy and 32 with a cobalt-chromium (Co-Cr) alloy. Over the bars’ central area (8 × 3 mm2), a bonding agent and two glass-ceramic layers were fired, totaling 1 mm in ceramic thickness. Eight specimens of each alloy were randomly divided according to the bonding agent (application or the absence thereof) and the thermo-mechanical cycle (3,000 thermo-cycles and 20,000 mechanical-cycles; or no cycling). The flexural bond strength between the metal alloy and the ceramic was evaluated by a three-point bending test and data were subjected to three-way ANOVA and Tukey’s test (αu2009=u20090.05). The failure mode was classified. No significant interactions were observed among the three factors evaluated (alloy, bonding agent, and thermo-mechanical cycling; pu2009=u20090.5734). There was no statistically significant difference between the alloys (pu2009=u20090.8559). The interaction between alloy/bonding agent (pu2009=u20090.0001) showed that, for the gold alloy, the group with the bonding agent showed mean values of flexural bond strength significantly higher than those of the group without the bonding agent, while, for the Co-Cr alloy, the groups with or without bonding agent had similar mean values of flexural bond strength. The interaction between alloy/thermo-mechanical cycling (pu2009=u20090.0001) showed that, for the gold alloy, the non-cycled group had flexural bond strength mean values significantly greater than those of the cycled group, while for the Co-Cr alloy, both non-cycled and cycled groups had similar mean values. The bonding agent significantly improved the flexural bond strength between the ceramic and the gold alloy, but had no influence on the Co-Cr alloy. Thermo-mechanical cycling decreased the flexural bond strength of the gold alloy specimens, but did not affect the Co-Cr specimens.

Stress distribution around implants with abutments of different materials: a comparison of photoelastic, strain gage and finite element analyses

Objective: To compare stress transmission around implants with abutments made of three differentxa0materials using photoelastic, strain gage (SGA) and finite element (FEA) analyses. Methods: Three abutments – UCLA calcinable, cast in Ni-Cr; UCLA calcinable with a Cr-Co cervicalxa0collar, overcast with Ni-Cr; and a zirconia abutment – were installed on implants embedded inxa0photoelastic resin. Vertical and oblique loads were applied to the abutments to the photoelasticxa0and SGA analyses. Data were analyzed by Kruskal-Wallis and Mann-Whitney tests (a=0.05). Thexa0assembly was modeled to FEA simulation. Results: Similar fringe orders were observed in the apical region under vertical load. The greatestxa0fringe orders were observed in the coronal region of the opposite side of load application (contralateralxa0side) under oblique load. By SGA, no statistical difference was observed among the abutmentsxa0(P=0.061) under vertical load, and no difference was found between tensile and compression sidesxa0under oblique load. FEA showed no difference in stress distribution. The oblique load generated thexa0greatest stress values on the contralateral side in the coronal area. Conclusion: Although it was not possible to establish an agreement among the analytical methodsxa0tested, different abutment materials did not influence the transmission of stresses around implants.