Giselle Maria Marchi

Bond Strength of Resin Cements to a Zirconia Ceramic with Different Surface Treatments

This study evaluated the influence of surface treatments and metal primers on the bond strength of resin cements to a yttrium-stabilized tetragonal zirconia (Y-TZP) ceramic. Two-hundred and forty plates of Y-TZP ceramic were randomly assigned to 24 groups (n = 10) according to the combination of surface treatment (none, air abrasion with Al2O3 particles, Er:YAG laser irradiation), metal primer (none, Alloy Primer, Metal Primer II or Metaltite) and resin cement (Calibra [Bis-GMA-based] or Panavia F2.0 [MDP-based]). Fragments of dentin with a cylindrical edge (0.8 mm in diameter) were fixed to ceramic surfaces with the resin cements. The micro-shear bond test was carried out at a 1 mm/minute speed until failure, and the ceramic surfaces were examined after debonding. Bond strengths were analyzed through three-way ANOVA/Tukey test with a 5% significance level. Changes in topography after surface treatments were evaluated with scanning electron microscopy. Surface treatments significantly modified the topography of the Y-TZP ceramic. Air abrasion resulted in increased bond strength for both resin cements. However, air abraded and laser irradiated specimens presented higher bond strength with the Bis-GMA-based resin cement than with the MDP-based cement. Both cements presented similar behavior on untreated surfaces. The three metal primers yielded a significant increase in bond strength, regardless of the surface treatment and resin cement. Adhesive failures were the most prevalent. Air abrasion with Al2O3 particles and the application of metal primers increased bond strength to Y-TZP surfaces for both resin cements.

Evaluation of the surface roughness and morphologic features of Y-TZP ceramics after different surface treatments.

OBJECTIVE This study aimed to investigate the effect of different energy intensities of the Er:YAG laser and of air abrasion with Al(2)O(3) particles on the surface roughness and morphologic characteristics of yttrium-stabilized tetragonal zirconia (Y-TZP) ceramics. BACKGROUND DATA Surface roughness enhances the micromechanical interlocking of luting agents to ceramic surfaces. However, the most appropriate surface treatment for Y-TZP ceramics has yet to be determined. MATERIALS AND METHODS Two Y-TZP materials were evaluated: Cercon Smart Ceramics and Procera Zirconia. Thirty plates from each ceramic material were randomly divided into five groups according to the surface treatment received (none [control], air abrasion, or irradiation with the Er:YAG laser at three different energy intensities [200, 400, or 600 mJ]). After the surface treatments, the ceramic plates were gold-coated and their surface roughness (Ra, microm) was measured using confocal microscopy. For each ceramic system, the surface roughness was analyzed through two-way ANOVA/Tukeys test, with a 5% significance level. Changes in the morphological characteristics of the ceramics were examined through light and scanning electron microscopy. RESULTS For both zirconia-based materials, irradiation with 400 mJ or 600 mJ increased surface roughness and provided significant morphological changes. Air-abraded Cercon surfaces were rougher compared to the ones irradiated with 200 mJ of laser energy, whereas Procera surfaces irradiated with 200 mJ were rougher than the air-abraded ones. CONCLUSIONS Higher laser power settings (400 and 600 mJ) cause excessive material deterioration, making them unsuitable as surface treatments for zirconia surfaces. Irradiation with 200 mJ provides mild surface alterations, with intermediary features between the effects of air abrasion and higher laser intensities.

Y-TZP Ceramics: Key Concepts for Clinical Application

Compared to conventional ceramic systems, Yttrium-stabilized tetragonal zirconia (Y-TZP) ceramics have some superior mechanical properties, ensuring a broad application in dentistry. The current study aimed to present relevant information about Y-TZP ceramics gathered from peer-reviewed papers. A search of the English language peer-reviewed literature was conducted using the PubMed database between 1998 and 2008. Articles that did not focus exclusively on the clinical application of Y-TZP ceramic restorations were excluded from further evaluation. Selected papers describe the chief characteristics of zirconia ceramics and important clinical features, especially those related to cementation procedures. The literature shows that, although new substances and equipment for the surface preparation of zirconia ceramics are in development, the most promising luting protocol seems to be the use of air abrasion with aluminum oxide particles (silanated or not), followed by the application of resin cements or surface primers containing special reactive monomers. However, because zirconia ceramics have only recently been developed for dental applications, there is not enough clinical evidence to support any definitive cementation protocol.

Clinical evaluation of desensitizing treatments for cervical dentin hypersensitivity.

The aim of this study was to compare different treatments for dentin hypersensitivity in a 6-month follow-up. One hundred and one teeth exhibiting non carious cervical lesions were selected. The assessment method used to quantify sensitivity was the cold air syringe, recorded by the visual analogue scale (VAS), prior to treatment (baseline), immediately after topical treatment, after 1 week, 1, 3 and 6 months. Teeth were randomly assigned to five groups (n = 20): G1: Gluma Desensitizer (GD); G2: Seal& (SP); G3: Oxa-gel (OG); G4: Fluoride (F); G5: Low intensity laser-LILT (660 nm/3.8 J/cm(2)/15 mW). Analysis was based on the non-parametric Kruskal-Wallis test that demonstrated statistical differences immediately after the treatment (p = 0.0165). To observe the individual effects of each treatment, data was submitted to Friedman test. It was observed that GD and SP showed immediate effect after application. Reduction in the pain level throughout the six-month follow-up was also observed. In contrast, LILT presented a gradual reduction of hypersensitivity. OG and F showed effects as of the first and third month respectively. It can be concluded that, after the 6-month clinical evaluation, all therapies showed lower VAS sensitivity values compared with baseline, independently of their different modes of action.

Influence of Thermal and Mechanical Load Cycling on Microtensile Bond Strengths of Total and Self-etching Adhesive Systems

This study evaluated the influence of different thermal (TC) and mechanical (MC) cycling protocols on microtensile bond strength (muTBS) to cervical dentin margins of Class II restorations using two total-etch (TE) adhesives and one self-etching (SE) primer. Class II slot cavities were prepared on the mesial surfaces of 168 bovine incisors and were divided into three groups according to the bonding system used: Single Bond, OptiBond Solo Plus and Clearfil SE Bond. All cavities were restored with Filtek Z250 composite. Following restorative procedures, the restored teeth were allocated to seven subgroups (n = 8) according to the thermal/mechanical protocol performed: G1-control (no cycling), G2-100,000 MC, G3-200,000 MC, G4-500,000 MC, G5-100,000 MC+1,000 TC, G6-200,000 MC+1,000 TC, G7-500,000 MC+1,000 TC. TC was performed using 5 +/- 2 degrees C and 55 +/- 2 degrees C baths, with a dwell time of 60 seconds in each bath. MC was achieved with an axial force of 80 N at 2 cycles/second. The restorations were sectioned perpendicular to the cervical bonded interface into two 0.8-1-mm thick slabs. The slabs were trimmed at the interface to obtain a cross-sectional surface area of 0.8-1 mm2. All specimens were then subjected to muTBS (v = 0.5 mm/minute). Fracture mode analysis was performed using SEM. Bond strength mean values (MPa) were analyzed with ANOVA 3-way and Tukeys test (alpha = 5%). Dunnetts test was used to compare tested groups against Control groups of each adhesive system (alpha = 56%). SE primer presented lower mean bond strength values when compared to TE adhesives (p = 0.05). In addition, specimens restored with the SE primer did not resist to the 200,000 and 500,000 MC associated with TC. The application of 100,000 MC did not present a significant decrease in bond strength when compared to the control. Mixed failures were predominant for all groups. The higher the amount of thermal/mechanical cycles, the greater the number of mixed failures and the lower the percentage of adhesive failures.

Effect of remaining dentine structure and thermal‐mechanical aging on the fracture resistance of bovine roots with different post and core systems

AIM To evaluate the influence of remaining dentine thickness around post and core systems and the thermo-mechanical stresses on fracture resistance of bovine roots. METHODOLOGY This study involved 288 bovine incisor roots with standardized dimensions. Roots were randomly distributed into 24 groups (n = 12) according to root conditions [intact, semi-weakened, or weakened] and post and core systems [custom cast core, composite resin core, prefabricated metallic post, or prefabricated carbon fibre post], submitted or not to thermomechanical aging [5000 thermal cycles and 100 000 mechanical cycles at a 135-degree angle to the long axis of the root]. Specimens were submitted to a tangential compressive load (135 degrees angle) at a crosshead speed of 0.5 mm min(-1) until failure. Fracture resistance data were analyzed using 3-way anova and Tukey test: alpha = 5%. RESULTS Roots restored with composite resin cores demonstrated no resistance to mechanical aging. No statistically significant difference was observed between aged and nonaged specimens involving all post-systems. Roots restored with custom cast cores had the highest fracture strength, followed by prefabricated metallic posts and carbon fibre posts, regardless of root conditions and thermomechanical aging. The remaining dentine thickness affected significantly roots restored with custom cast cores; weakened roots had a lower fracture resistance. CONCLUSIONS Although custom cast cores had a higher fracture resistance when compared to the other techniques, the results were highly dependent on remaining dentine thickness. Prefabricated posts performed in a similar manner in intact, semi-weakened and weakened roots reinforced with composite resin.

Transdentinal protective role of sodium ascorbate against the cytopathic effects of H2O2 released from bleaching agents

OBJECTIVES The objectives of this study were to evaluate the transdentinal cytotoxicity of 10% and 16% carbamide peroxide gel (CP), as well as the ability of the antioxidant, 10% sodium ascorbate (SA), to protect the odontoblasts in culture. STUDY DESIGN Human dentin discs of 0.5-mm thickness were obtained and were placed into artificial pulp chambers. MDPC-23 odontoblastlike cells were seeded on pulp surface of the discs and the following groups were established: G1-No Treatment (control), G2-10% SA/6hs, G3-10%/CP6hs, G4-10%SA/6hs+10%CP/6hs, G5-16%CP/6hs, and G6-10%SA/6hs+16%CP/6hs. The cell viability was measured by the MTT assay. RESULTS In groups where 16% CP was used, decreased cell viability was observed. Conversely, the application of 10% SA on the dentin discs, before the use of the CP, reduced the cytotoxic effects of these products on cells. CONCLUSIONS The 16% CP cause a significant decrease in MDPC-23 cell viability and 10% SA was able to partially prevent the toxic effects of CP.

Cytotoxic Effects of Different Concentrations of a Carbamide Peroxide Bleaching Gel on Odontoblast-Like Cells MDPC-23

This study evaluated the cytotoxic effects of a carbamide peroxide (CP) bleaching gel at different concentrations on odontoblast-like cells. Immortalized cells of the MDPC-23 cell line (30,000 cells/cm(2)) were incubated for 48 h. The bleaching gel was diluted in DMEM culture medium originating extracts with different CP concentrations. The amount (microg/mL) of hydrogen peroxide (H(2)O(2)) released from each extract was measured by the leukocrystal violet/horseradish peroxidase enzyme assay. Five groups (n = 10) were formed according to the CP concentration in the extracts: G1-DMEM (control); G2-0.0001% CP (0.025 microg/mL H(2)O(2)); G3-0.001% CP (0.43 microg/mL H(2)O(2)); G4-0.01% CP (2.21 microg/mL H(2)O(2)); and G5-0.1% CP (29.74 microg/mL H(2)O(2)). MDPC-23 cells were exposed to the bleaching gel extracts for 60 min and cell metabolism was evaluated by the MTT assay. Data were analyzed statistically by one-way ANOVA and Tukeys test (alpha = 0.05). Cell morphology was examined by scanning electron microscopy. The percentages of viable cells were as follows: G1, 100%; G2, 89.41%; G3, 82.4%; G4, 61.5%; and G5, 23.0%. G2 and G3 did not differ significantly (p > 0.05) from G1. The most severe cytotoxic effects were observed in G3 and G4. In conclusion, even at low concentrations, the CP gel extracts presented cytotoxic effects. This cytotoxicity was dose-dependent, and the 0.1% CP concentration caused the most intense cytopathic effects to the MDPC-23 cells.

Visual evaluation of in vitro cariostatic effect of restorative materials associated with dentifrices

This study evaluated in vitro the cariostatic effect of 6 restorative materials with and without fluoride release (Fuji II LC, F-2000, Degufil Mineral, Sure Fil and Z-250) associated with a fluoridated and a non-fluoridated dentifrice (Sensodyne Original Formula and Sensodyne Sodium Bicarbonate), on human enamel. Class V-like cavities were prepared on 240 enamel slabs, assigned to 12 groups (6 materials and 2 dentifrices). After cavity restoration, the slabs were submitted to a thermocycling regimen of 1000 thermal cycles and demineralization/remineralization cycles. During pH cycles, slurries of fluoridated and non-fluoridated dentifrices were applied for 5 min. Formation of artificial caries-like lesions was scored independently and blindly by 5 calibrated examiners according to an ordinal scale ranked 0 to 3 by visual examination. The results were analyzed statistically by the Kruskal-Wallis test and pair-wise comparisons (alpha=0.05). There were no significant differences (p>0.05) among the restorative materials associated with the fluoridated dentifrice. When used in association with the non-fluoridated dentifrice, Ketac-Fil showed the highest cariostatic effect followed by Fuji II LC and the other materials. Ketac-Fil was the only material that did not differ statistically when combined with either the fluoridated or the non-fluoridated dentifrice. In conclusion, under the tested experimental conditions, the association of restorative materials and fluoridated dentifrice yielded higher cariostatic effect, except for the conventional glass ionomer cement, whose cariostatic effect was not influenced by the type of dentifrice.

Effect of chemical degradation followed by toothbrushing on the surface roughness of restorative composites.

Objectives The aim of the present study was to assess the effect of the exposure to food-simulating liquids prior to brushing simulation on the surface roughness of five composite materials (Quixfil, Filtek Supreme, Esthet-X, Filtek Z250, Tetric Ceram). Material and methods Twenty cylinders (5 mm diameter and 4 mm height) of each composite were randomly allocated to 4 groups (n=5), according to the food-simulating liquid in which they were immersed for 7 days at 37ºC: artificial saliva, heptane, citric acid, and ethanol. After this period, the top surface of composite cylinders was submitted to 7,500 brushing cycles (200 g load). Measurements of the surface roughness (Ra, µm) were carried out before and after the exposure to the chemicals/brushing simulation. Changes on the morphology of composite surfaces were observed through scanning electron microscopy (SEM). Results The statistical analysis (ANOVA with cofactor / Tukeys test, α=5%) detected a significant interaction between solutions and composite resins. Esthet-X, Filtek Z250 and Tetric Ceram were not affected by the food-simulating liquids/toothbrushing. Citric acid and ethanol increased the surface roughness of Quixfil and Filtek Supreme, respectively. SEM images corroborate the surface roughness findings, demonstrating the negative effect from chemical solutions and mechanical abrasion. Conclusions The surface roughness of composite resin materials are differently affected by the food-simulating solutions, depending on the immersion media.