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Biomedical subjects

V Piddock

Publications and source records attributed to V Piddock.

At least 19 recordsLinked to original sources
PubMed1999

Recent advances in ceramic materials and systems for dental restorations.

The unsurpassed aesthetic and biocompatible qualities of ceramic materials still provide the stimulus to seek to overcome their limitations. Much of the materials research since the mid 1960s has been directed towards producing stronger, reinforced restorations with improved marginal accuracy and, although a new wave of ceramic products appeared in the 1980s, most of the materials currently available are developments derived from ideas established more than 20 years ago. This paper outlines some interesting aspects of recent developments and considers the present state of the art with respect to both materials and techniques.

Biocompatible Materials↗
PubMed1998

Magnetron sputtered tin coatings on unbiased ceramic substrates.

OBJECTIVES: The aim of this work was to study the application of tin oxide coatings on alumina, with a view to developing improved bonding for high-alumina dental ceramics. METHODS: By use of a magnetron sputtering technique, alumina was coated with tin which was subsequently oxidized, and the bond strength of coated surfaces to a resin-based dental cement was measured in tension. Tensile bond strength data were assessed for their degree of skewness and the homogeneity of the residual variances with a view to applying appropriate transformations prior to performing ANOVA with subsequent Tukey's analysis as necessary. The color of coatings, as a function of the amount of oxidation of the surface, was noted. Coatings were characterized by SEM and EDAX. It has been found possible to produce esthetic tin oxide coatings on alumina using a simplified magnetron sputtering apparatus in conjunction with post-deposition oxidation. RESULTS: Although mean tensile bond strength (TBS) values in excess of 15 MPa were recorded for a number of groups, no causal relationship was found between coating time and mean TBS. SIGNIFICANCE: The need exists for improved bonding of alumina-based ceramics; further development of a magnetron sputtering technique may provide the means for achieving this.

Aluminum Oxide↗
PubMed1997

Ceramics update.

OBJECTIVE: The aim of this paper is to review recent developments in dental ceramics related both to the refinement of existing materials and technologies and to the development of new techniques. DATA SOURCES: The appropriate literature has been reviewed and the relevant information selected for inclusion in this article. CONCLUSION: It is concluded that the main advances are related to developments aimed to overcoming the mechanical shortcomings of ceramic materials, such as their inherent brittleness. Several new systems have been developed, some of which appear to be very promising, but there are, as yet, no data related to the long term performance of restorations by these new techniques.

Ceramics↗
PubMed1996

Colour changes in acrylic teeth--comparison of an objective and subjective method.

Colour changes in four currently used brands of acrylic dental teeth were measured objectively and assessed subjectively following the application of heat, acrylic monomer and light. The data indicated that no clear correlation existed between the results of visual inspection and opto-electronic measurements. It is suggested that visual assessment is an unreliable method of detecting colour change, and an objective colorimetric method is therefore recommended.

Acrylic Resins↗
PubMed1996

An evaluation of the fit of porcelain inlays.

The effect of die spacer usage and three different porcelain build up techniques on inlay fit were investigated by impression wash methods and image analysis of sectioned replicas. All inlays were produced on machined cavities. Data from the impression wash technique indicated a mean misfit value of just over 100 microns. Image analysis showed a smaller mean misfit of 40-60 microns. In general, the use of die spacer resulted in a poorer fit and there were no significant differences between methods of porcelain application detected by either method.

Analysis of Variance↗
PubMed1995

Development and assessment of an objective method of colour change measurement for acrylic denture base resins.

Current standard specifications for the laboratory evaluation of denture base materials require subjective assessment of colour stability. This study evaluates a new objective measurement technique for translucent denture base materials, by comparing quantitative data with the results obtained from a standard subjective method. Preliminary work on three representative commercial acrylic materials resulted in the selection of a white background for the quantification of colour change of these translucent materials. One half of each sample was exposed to artificial sunlight for 24 h. The colour of both exposed and unexposed resin was measured on the CIE L*a*b* scale using a photo-electric colorimeter. Significant changes in the b* and E* values (P < 0.01) were observed following light exposure. Objective data for a wide range of commercial materials were compared with the results of a subjective evaluation and it was shown that a change in b* of 1.5 units was discernable subjectively by eye for 100% of the cases. It is suggested that this method and limit value could form the basis of a new objective colour change specification for polymeric dental materials.

Acrylic Resins↗
PubMed1995

Dental CAD/CAM: a millstone or a milestone?

The number of dental computer-aided design/computer-aided manufacture (CAD/CAM) systems commercially available is growing. These systems range in complexity and application, from manual copy milling of inlays to full computer-controlled systems with a complex library of tooth forms enabling the automated production of crowns and bridges. All CAD/CAM systems permit the production of restorations at the chairside and, at least in theory, eliminate potential inaccuracies associated with the traditional, multistage production of indirect restorations. Their use also minimizes cross-infection. However, the capital costs of these systems are great and a high throughput of restorations is required in order to achieve financial viability. Long-term clinical studies are required before a final judgement may be made of the use of these relatively new systems.

Computer-Aided Design↗
PubMed1993

A comparison of two in vitro methods for assessing the fitting accuracy of composite inlays.

Composite inlays were fabricated in standardised cavities cut into aluminum and perspex blocks using a computer controlled milling process. Four materials were used to construct the inlays. These were fabricated using an indirect technique following the manufacturers' recommendations, where applicable. In addition, for one of the composites, the fabrication procedures were modified. The fitting accuracy of the restorations was assessed by taking elastomeric impression wash replicas of the luting space and by examination of sectioned restored units using image analysis. The former method indicated significantly reduced fitting accuracy when either use of die spacer or secondary curing was omitted from restoration construction resulting in incomplete seating. The sectioning technique indicated that more factors appeared to significantly reduce fitting accuracy including bulk packing, alteration in curing time, omission to die spacer and the final polishing procedure. This method also provided more specific information concerning sites of premature contact. One material gave rise to significantly greater film thicknesses using both methods of assessment. No direct correlation was found between the two techniques of fit evaluation but both methods taken together provided complementary information.

Acrylic Resins↗
PubMed1993

Dental education in Japan.

Expanded roles for chairside assistants, infrequent use of amalgam, and dental technician courses over-subscribed by three to one. Perhaps this isn't the classic image of the advanced society that Japan has become over the last 40 years, yet the dentists working and researching in this economic spearhead were full of enthusiasm for their profession. On our journey to the far east we would be greeted with many surprises, especially in dental practice and hygienist education.

Dental Amalgam↗
PubMed1993

The effect of glass heat treatment on the properties of a novel polyalkenoate cement.

The effect of heat treating the glass component of a novel glass-ionomer (polyalkenoate) cement on cement properties has been determined, with specific reference to the reactivity of the glass, and the mechanical properties of the resultant cement. It has been shown that heat treatment is a suitable method of decreasing the glass reactivity and improving the handling characteristics of the mixed cement. Under some conditions, an increase in compressive strength was found, although the effect on tensile properties was not significant.

Glass Ionomer Cements↗
PubMed1993

In vitro comparison of conventional crowns and a new all-ceramic system.

Thirty-three crowns of similar size and shape were constructed to fit a standard brass die. Eleven crowns were manufactured from each of the following groups of materials: metal-ceramic, aluminous porcelain and a new all-ceramic system based on a glass infiltrated alumina coping. The overall fitting accuracy of each crown was determined using a low viscosity silicone paste, prior to cementation onto brass dies with zinc phosphate cement. The average film thickness was 95, 154 and 123 microns respectively. Each cemented crown was loaded to fracture. The mean load to failure of the glass infiltrated alumina crowns was significantly greater than that of the aluminous porcelain jacket crowns (P < 0.0001), but not significantly different from the metal-ceramic crowns.

Aluminum Oxide↗
PubMed1992

Development of novel dental cements. I. Formulation of aluminoborate glasses.

Aluminoborate glasses were formulated as potential novel glass-ionomer cement components, and their reactivity with a polyalkenoic acid was assessed by means of working and setting time measurements. Of the 20 prepared formulations, some containing fluoride, eight were found to have acceptable manipulative characteristics, and three of these formed hard set materials.

Aluminum Silicates↗
PubMed1992

Development of novel dental cements. II. Cement properties.

Following earlier work, three novel aluminoborate glasses have been studied as potential cement components. Factors studied include the effect of batch size on composition and manipulative characteristics, and the effect of tartaric acid and conditions of storage on mechanical properties. It was concluded that two materials have potential for application as dental luting agents.

Aluminum Silicates↗
PubMed1992

Fitting accuracy of indirect restorations: a review of methods of assessment.

The current interest in indirectly manufactured, tooth-coloured restorations has highlighted a need to identify factors pertinent to the success of both these and other indirect restorations. Although restoration longevity is limited by the degree of adaptation to the prepared tooth, there exists no standard method for either the assessment of marginal adaptation or the overall accuracy of fit. This review examines methods of assessment of both of these important parameters, and considers the problems associated with existing in vivo and in vitro techniques.

Crowns↗
PubMed1991

Tin oxide coating of aluminous porcelain by reactive ion plating.

Alumina reinforced dental porcelain has been coated directly with tin oxide by reactive ion plating. Samples were prepared at different distances from the tin source in the ion plating rig. Tensile bond strengths of treated and untreated porcelain discs to a commercially available phosphate-methacrylate based dental cement were determined. Bond strengths of certain coated samples were found to be in excess of the cohesive strength of the porcelain substrates (greater than 7.8 MPa), whereas untreated porcelain achieved an average bond strength of only 3.4 MPa. The microstructures of coatings produced under conditions similar to those which yielded the maximum bond strength were examined in a scanning electron microscope and were found to be approximately 0.5 microns thick. It is believed that ion plating has great potential for rendering inert ceramic surfaces capable of direct bonding to dental cements.

Adhesives↗
PubMed1991

The strength of dental ceramics.

Considerable changes have taken place in the range of ceramic materials available for dental use. Although the appearance of dental porcelain is good and biocompatibility excellent, its mechanical properties are somewhat limited. As a consequence, a number of distinct developments have taken place primarily to achieve greater strength; other goals having been to improve accuracy and simplification of production procedure. Progress has been made, but at the present time newer ceramics must still be regarded as complementary to established porcelains.

Ceramics↗