Comparison to the scanning electron microscope of professional dental hygiene methods on metal-free layered structures and metal-free monolithic structures processed by different polymerization cycles.

AIM: Aim of the study was to find effective instrumental methodologies and procedures for scaling and deplaquing without compromising the structure of metal-free, monolithic lithium disilicate and layered zirconia prosthetics. METHODS: Of 14 decontaminated, extracted teeth in good anatomical condition, 7 veneers lithium disilicate monolithic and 7 layered zirconia crowns were prepared for testing and divided into 6 treatment groups. Each group was composed of a veneer and a crown. The division of the groups was carried out according to the type of treatment performed- instrumental carbon fiber and steel tips, prophylaxis paste with high and low RDA (Relative dentin abrasion), bicarbonate powder. Samples were examined and observed through a scanning electron microscope (SEM). Afterwards a detailed comparison of the images of treated and untreated samples was performed. The images were at the same magnification, thus showing the differences in the treated samples. RESULTS: The monolithic lithium disilicate presents minor damage to the surface but no excessive changes to the structure in general post treatment. The layered zirconia resulted in notable damage with evident abrasions on the layered ceramic structure after the use of ultrasound with a steel tip and air flow with bicarbonate. Carbon fibre tips and prophylaxis paste containing perlite and low RDA did not create notable changes to the properties of the materials in question. CONCLUSION: The results of the disilicate monolithic appear to show it to be a much more resistant material compared to layered zirconia in ceramic. Its resistance is demonstrated by the lack of notable damage in all the treatment groups.

Effects of surface finishing conditions on the biocompatibility of a nickel-chromium dental casting alloy.

OBJECTIVES: To assess the effects of surface finishing condition (polished or alumina particle air abraded) on the biocompatibility of direct and indirect exposure to a nickel-chromium (Ni-Cr) d.Sign®10 dental casting alloy on oral keratinocytes. Biocompatibility was performed by assessing cellular viability and morphology, metabolic activity, cellular toxicity and presence of inflammatory cytokine markers. METHODS: Discs of d.Sign®10 were cast, alumina particle air abraded and half were polished before surface roughness was determined by profilometry. Biocompatibility was assessed by placing the discs directly or indirectly (with immersion solutions) into contact with TR146 monolayers. Metal ion release was determined by ICP-MS. Cell viability was assessed by trypan blue dye exclusion, metabolic activity by XTT and cellular toxicity by LDH. Inflammatory cytokine analysis was performed using sandwich ELISAs. RESULTS: The mean polished Ra value was significantly reduced (P<0.001) compared with the alumina particle air abraded discs but metal ion release was significantly increased for the polished discs. Significant reductions in cell density of polished compared with alumina particle air abraded discs was observed following direct or indirect exposure. A significant reduction in metabolic activity, increase in cellular toxicity and an increase in the presence of inflammatory cytokine markers was highlighted for the polished relative to the alumina particle air abraded discs at 24h. SIGNIFICANCE: Finishing condition of the Ni-Cr dental alloy investigated has important clinical implications. The approach of employing cell density and morphology, metabolic activity, cellular toxicity levels and inflammatory marker responses to TR146 epithelial cells combined with ICP-MS afforded the authors an increased insight into the complex processes dental alloys undergo in the oral environment.

Surface characteristics of aesthetic restorative materials - an SEM study.

To determine the degree of surface roughness of glass-ionomer cements (GICs) and polyacid-modified resin composite (PAMRC) after polishing and immersion in various foodstuffs. Three tooth-coloured restorative materials were used: a PAMRC (F2000), a conventional glass-ionomer cement (CGIC) (Fuji IX) and a resin-modified glass-ionomer cements (RM-GIC) (Fuji II LC). Disk-shaped specimens were prepared and tested with either a plastics matrix finish or after polishing with wet silicon carbide papers up to 2000-grit. All specimens were immersed in 37 degrees C-distilled water for 1 week, followed by three different foodstuffs (red wine, coffee or tea) for a further 2 weeks. Replicas of specimens were prepared by taking polyvinyl siloxane impressions, casting in epoxy resin, gold sputter-coating and examining using a Field-Emission Scanning Electron Microscope. The polished and matrix finish specimens of F2000 showed many microcracks at low magnification, and eroded surfaces with missing and protruding particles at high magnification in the polished specimens. The surface-polished specimens of Fuji II LC were considerably rougher than the matrix-finish specimens, with large voids and protruding filler particles. The effects of foodstuffs on Fuji II LC and F2000 were not noticeable. The CGIC became noticeably rougher after exposure to coffee and tea. All specimens had the smoothest surface when they were cured against a plastics matrix strip, and all materials had a rougher surface after polishing. None of the foodstuffs produced a perceptible increase in roughness on RM-GIC and PAMRC surfaces, whereas coffee and tea markedly increased the surface roughness of Fuji IX.

Iatrogenic tooth abrasion comparisons among composite materials and finishing techniques.

STATEMENT OF PROBLEM: Many different rotary instruments are available for shaping composite restorations. Whether use of these instruments causes undesirable iatrogenic abrasion of either the tooth surface or the composite restorative material is unknown. Assuming that damage occurs, which technique is least damaging is unknown. PURPOSE: This in vitro study quantified the loss of surface enamel and dentin surrounding Class V preparations during composite shaping and finishing procedures. The susceptibility of 2 types of composites to tooth abrasion was also examined. MATERIALS AND METHODS: Standardized Class V cavities were prepared at the amelodentinal junction of 36 human molar teeth. The teeth were randomly assigned to 6 groups of 6 teeth each. They were restored with either a low- or high-viscosity composite (Revolution or Prodigy Condensable, respectively) and finished with aluminum oxide disks, tungsten carbide burs, or ultrafine finishing diamond burs. The preparations were profiled before and after restoration. After each finishing procedure, morphological measurements of surface changes in the dentin and enamel were made and reported as volume (in cubic millimeters); maximum depth, mean maximum depth, and mean depth (in micrometers); and surface area (in square millimeters). The results were subjected to a 2-way analysis of variance for restorative material and finishing technique (P<.05). RESULTS: Aluminum oxide disks removed significantly less enamel than tungsten carbide burs or ultrafine finishing diamond burs, as measured by volume, maximum depth, mean maximum depth, mean depth, and surface area (P<.05). Conversely, aluminum oxide disks removed significantly greater dentin than either tungsten carbide burs or ultrafine finishing burs as measured by loss of volume, mean depth, and surface area (P<.05). There was no significant difference in the loss of surrounding tooth substance based on resin type (low or high viscosity). CONCLUSION: Within the limitations of this study, the 3 finishing systems tested resulted in varying degrees of iatrogenic abrasion of enamel and dentin. The composite material used had no significant effect on abrasion of the surrounding enamel or dentin.

The abrasive effect of glazed, unglazed, and polished porcelain on the wear of human enamel, and the influence of carbonated soft drinks on the rate of wear.

The abrasive effect of various porcelain surfaces on human enamel was studied in vitro. Sixty pairs of tooth-porcelain specimens were tested under a standard load and rate in distilled water and with and without intermittent exposure to a carbonated beverage. The amount of wear of enamel and porcelain specimens was determined after 5,000, 15,000, and 25,000 cycles. After 25,000 cycles there was no significant difference in the enamel wear between glazed and polished groups, but wear produced by the unglazed groups was significantly higher (P < .05). Overall, exposure to a carbonated beverage significantly increased the amount of enamel wear produced by all porcelain surfaces (P < .001). The finish of the porcelain surface did not influence its wear.

Temperature rise due to finishing of direct restorative materials.

An in vitro study was performed to evaluate the effect of four variables on the temperature rise produced by the finishing of restorations. The four variables were: restorative material, finishing agent, finishing time, and depth of dentin under the restoration. Class V preparations were cut on extracted premolars and restored with amalgam, composite, or glass ionomer cement. Finishing was done with wet pumice and cup, wet pumice and a brush, a grit rubber polishing point, and an aluminum oxide- coated disc. Finishing time was continuous or intermittent for up to 1 minute. Dentin thickness under the restoration was 0.5 mm to 3.0 mm. Amalgam produced the highest temperature rises at the pulp, while composite and glass ionomer were no different than the untreated (virgin) tooth. Aluminum oxide discs produced the largest temperature rise, wet pumice with a brush the least. Temperature rise increased almost linearly with continuous finishing, while intermittent finishing significantly reduced temperature rise in all cases. Thickness of remaining dentin was only significant for the amalgam restoration, and then only at 1.0 and 0.5 mm.