Daniel C.N. Chan

Effect of etching and airborne particle abrasion on the microstructure of different dental ceramics

STATEMENT OF PROBLEM The ceramic composition and microstructure surface of all-ceramic restorations are important components of an effective bonding substrate. Both hydrofluoric acid etching and airborne aluminum oxide particle abrasion produce irregular surfaces necessary for micromechanical bonding. Although surface treatments of feldspathic and leucite porcelains have been studied previously, the high alumina-containing and lithium disilicate ceramics have not been fully investigated. PURPOSE The purpose of this study was to assess the surface topography of 6 different ceramics after treatment with either hydrofluoric acid etching or airborne aluminum oxide particle abrasion. MATERIAL AND METHODS Five copings each of IPS Empress, IPS Empress 2 (0.8 mm thick), Cergogold (0.7 mm thick), In-Ceram Alumina, In-Ceram Zirconia, and Procera (0.8 mm thick) were fabricated following the manufacturers instructions. Each coping was longitudinally sectioned into 4 equal parts by a diamond disk. The resulting sections were then randomly divided into 3 groups depending on subsequent surface treatments: Group 1, specimens without additional surface treatments, as received from the laboratory (control); Group 2, specimens treated by use of airborne particle abrasion with 50-microm aluminum oxide; and Group 3, specimens treated with 10% hydrofluoric acid etching (20 seconds for IPS Empress 2; 60 seconds for IPS Empress and Cergogold; and 2 minutes for In-Ceram Alumina, In-Ceram Zirconia, and Procera). RESULTS Airborne particle abrasion changed the morphologic surface of IPS Empress, IPS Empress 2, and Cergogold ceramics. The surface topography of these ceramics exhibited shallow irregularities not evident in the control group. For Procera, the 50-microm aluminum oxide airborne particle abrasion produced a flattened surface. Airborne particle abrasion of In-Ceram Alumina and In-Ceram Zirconia did not change the morphologic characteristics and the same shallows pits found in the control group remained. For IPS Empress 2, 10% hydrofluoric acid etching produced elongated crystals scattered with shallow irregularities. For IPS Empress and Cergogold, the morphologic characteristic was honeycomb-like on the ceramic surface. The surface treatment of In-Ceram Alumina, In-Ceram Zirconia, and Procera did not change their superficial structure. CONCLUSION Hydrofluoric acid etching and airborne particle abrasion with 50-microm aluminum oxide increased the irregularities on the surface of IPS Empress, IPS Empress 2, and Cergogold ceramics. Similar treatment of In-Ceram Alumina, In-Ceram Zirconia, and Procera did not change their morphologic microstructure.

Radiopacity of tantalum oxide nanoparticle filled resins

OBJECTIVES Radiopacity of composite resins allows radiographic distinction of existing restorations and recurrent caries. Current composites must be supplemented with heavy metal-containing glasses or minerals to achieve a desired radiopacity. The purpose of this study was to evaluate the radiopacity of Tantalum oxide (Ta2O5) filled resins at varying percentage loadings. METHODS Methacrylate functionalized Ta2O5 nanoparticles (< 50 nm) in methanol-dissolved or powder forms were mixed into either glycerol dimethacrylate (GDMA) or a bisGMA, TEGDMA, bisEMA mixture (GTE). Specimens were made in a split brass mold (2 x 2 x 15 mm) and compared with an aluminum stepwedge (99.5% pure Al) and a dentin slice of the same thickness. Kodak Ultraspeed periapical X-ray film on a lead plate at a target distance of 45 cm was exposed at 70 kVp and 10 mA, for 0.5 s and processed automatically. Optical density was measured (n = 3) with an RMI Processor Control Densitometer. Radiopacity was calculated as percent relative linear attenuation coefficient (Alpha). ANOVA and Student-Newman-Keuls comparisons were used to determine significance at the 95% confidence level. RESULTS Radiopacity increased significantly with Ta2O5 loading (p = 0.001). Ta2O5 nanoparticle filled resins enter the optimal range of diagnostic detectability (alpha = 150-250) at 50 wt.% and approach equivalence with enamel at approximately 70 wt.%. SIGNIFICANCE The introduction of tantalum oxide nanoparticle filler has potential as a miscible component of a resin composite to provide radiopacity for microfiller-type restorative materials and to circumvent the need for hydrolysis-prone glass reinforcing fillers.

The effects of filling techniques and a low-viscosity composite liner on bond strength to class II cavities

OBJECTIVE The aim of this study was to test the hypothesis that the effects of filling technique, cavity configuration and use of a low-viscosity composite liner influence resin bond strength to the dentin of class II cavities gingival floor; and analyze the failure modes of fractured specimens. METHODS Standardized class II cavities were prepared in the proximal surfaces of freshly extracted third molars, which were randomly assigned to 10 experimental groups. All prepared surfaces were acid-etched, bonded with Single Bond adhesive system and restored with TPH composite, according to each technique: G1 and G2-horizontal layering, G3 and G4-faciolingual layering, G5 and G6-oblique layering, G7 and G8-bulk filling, G9 and G10-control (flat dentin surfaces). Groups were tested, with or without a low-viscosity composite liner (Tetric Flow Chroma). After storage in water for 24h, teeth were vertically serially sectioned to yield a series of 0.8mm thick slabs. Each slab was trimmed into an hourglass shape of approximately 0.8mm(2) area at the gingival resin-dentin interface. Specimens were tested in tension at 0.5mm/min until failure. Fractured specimens were analyzed in an SEM to determine the failure modes. RESULTS No significant difference was found between groups restored with and without a low-viscosity composite liner (p>0.05). Among filling techniques, the bulk filling groups presented the lowest bond strength values (p<0.05), while incremental filling groups did not differ from control (flat dentin surfaces). Failure modes varied significantly among groups restored with and without the low-viscosity composite liner. SIGNIFICANCE Bond strengths were not improved when a low-viscosity composite liner was applied, but it remarkably influenced the failure modes. Incremental techniques improved bond strength.

Occluding effect of dentifrices on dentinal tubules

OBJECTIVES The objective of this study was to evaluate the tubule occluding ability of three commercial available dentifrices (Sensodyne, Emoform and Sorriso) by Scanning Electron Microscopy. METHODS Fifty cervical areas from buccal and lingual surfaces of sound third human molars were used. Cervical enamel was wet abraded to expose flat dentin surfaces and further polished with diamond pastes. Specimens were randomly divided into five groups (n=10): G1-no brushing; G2-brushing without dentifrice; G3-brushing with Sensodyne; G4-brushing with Emoform; G5-brushing with Sorriso. Brushed specimens were treated for 4 min per day, for 7 days in a toothbrushing machine. Specimens were prepared and observed under SEM for calculation of the percentage of occluded tubules. In addition, slurries of toothpastes were analyzed by X-ray microanalysis. Data were statistically analyzed by ANOVA and Tukey test (p<0.05). RESULTS Means of occluded tubules in descending order were: G5-98.83+/-3.31% (a), G4-96.02+/-5.24% (a), G3-80.12+/-24.65% (a), G1-37.31+/-24.22% (b); G2-22.92+/-15.19% (b). The three tested dentifrices produced increased dentinal occlusion as compared to controls (p<0.05) but equivalent occlusion among each other. Calcium from calcium-carbonate abrasive was identified in all dentifrices. CONCLUSIONS Results indicated that the use of all dentifrices occluded tubules more than no brushing and brushing without dentifrices groups. Thus, the tested dentifrices seem effective for desensitization by tubule occlusion.

1-Year clinical study of indirect resin composite restorations luted with a self-adhesive resin cement: effect of enamel etching

In vitro studies have recommended enamel-etching before luting indirect restorations with self-adhesive resin cement. However, there is no scientific proof that this procedure has any clinical relevance. Thus, the aim of this study was to evaluate the effect of enamel-etching on the marginal quality of indirect composite resin restorations (inlay/onlay) using the self-adhesive cement RelyX Unicem clicker. Forty-two posterior teeth were selected from 25 patients that presented one or two teeth with large restorations in need of replacement. All teeth were prepared by the same operator and impressed with polyvinylsiloxane material. The composite resin restorations were built over plaster casts using the incremental technique with a LED device for light-curing the increments. The inlays/onlays were cemented according to one of the following protocols: 1. Etched group (ETR) - selective enamel phosphoric-acid etching + RelyX Unicem clicker; 2. Non-etched group (NER) - RelyX Unicem clicker alone. Each surface was light-cured for 60 s. Recalls occurred after 1 week (baseline), 6 and 12 months when the teeth were evaluated according to previously established scores (modified USPHS criteria). The clinical analysis showed little or no visible changes in the marginal quality after 1 year, even though a probe could detect all the restorations margins. Statistical analysis (Fishers exact test, p<0.05) detected no differences between the groups after 12 months. No restorations failed and no secondary caries were found. Enamel acid etching had no clinical relevance on the marginal quality of indirect composite resin restorations luted with RelyX Unicem clicker after 1 year of follow up.