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Biomedical subjects

J A Hood

Publications and source records attributed to J A Hood.

At least 19 recordsLinked to original sources
PubMed1992

Effect of peroxide bleaches on resin-enamel bonds.

Human third molar teeth were divided into three groups: untreated control; enamel treated with 35% hydrogen peroxide for 2 hours; and enamel treated with 10% carbamide peroxide gel for 14 days. All teeth were ground to present a flat enamel surface, to which cylinders of light-cured composite resin were bonded. Shear bond strengths were determined for each specimen. The mean shear bond strengths of resin-enamel bonds after pretreatment with both 35% hydrogen peroxide and 10% carbamide peroxide were significantly lower than those for untreated controls. External bleaching with these materials prior to resin bonding procedures may reduce the quality of resin-enamel bonds.

Acrylates↗
PubMed1991

Why amalgam?

Explore the source record for details and available documents.

Dental Alloys↗
PubMed1991

Biomechanics of the intact, prepared and restored tooth: some clinical implications.

The practice of restorative dentistry has changed for many and varied reasons. They include changes in the epidemiology of dental caries due to fluoridation, and availability of new equipment and techniques for cavity preparation and new or improved restorative materials. Changes driven by these 'new' materials frequently do not provide the benefits anticipated. In the context of this paper, it is argued that, regardless of restorative materials and techniques, the biomechanics of intact, prepared and restored teeth must be understood to attain a satisfactory clinical outcome.

Biomechanical Phenomena↗
PubMed1990

Effectiveness of sterilisation and disinfection procedures for dental amalgam carriers.

The potential for cross infection through dental amalgam carriers was investigated in 37 Dunedin dental practices and in the University of Otago School of Dentistry. Eighteen practitioners had autoclavable carriers, but only 2 autoclaved them at least daily. The School of Dentistry disinfected plastic carriers and autoclaved metal carriers. Microbiological examination, by culturing from the most commonly contaminated carrier site, showed that the School of Dentistry method for disinfection of plastic carriers was unreliable. Autoclaving was confirmed as the preferred method of sterilisation, but many existing carriers are not suited to this technique.

1-Propanol↗
PubMed1990

Influence of cavosurface configuration and composite resin type on impact fracture resistance of Class IV restorations.

The fracture behaviours of intact maxillary central incisor teeth, and teeth restored by five different composite resins utilising uninstrumented fractured etched margins and bevelled etched margins, were determined by a pendulum impact method. It was established that: 1. Intact teeth fractured in a predictable manner when struck by a pendulum hammer at predetermined points on the labial surfaces close to incisal angles. 2. The impact resistance of teeth with bevelled margin restorations was significantly greater than that of teeth restored using the uninstrumented fractured margins. 3. Differences in impact resistance between intact teeth and teeth restored with bevelled margins were not significant. 4. There was no significant difference in fracture energy between any of the composite resin materials in either the uninstrumented joint or bevelled joint modes. 5. For all restorations placed on uninstrumented margins, the fracture paths were at or near the adhesive interface; no restorations failed cohesively. 6. Fracture paths in the bevelled joint mode were variable, with fracture occurring either entirely in enamel, or entirely in composite resin, or at the interface.

Acrylic Resins↗
PubMed1989

Thermocycling, silane priming, and resin/porcelain interfaces interfaces--an electrical leakage study.

High 24-hour tensile and shear bond strengths have been reported for silane-primed resin/porcelain interfaces, but bonds often failed after prolonged water storage. This study was designed to determine the influences of both a silane primer and thermocycling on interfacial leakage between a light-cured BisGMA resin and dental porcelain. Porcelain discs measuring 10 mm in diameter and 1.5 mm in thickness were fired. Axial cylindrical cavities were prepared through the discs with a diamond bur. Four groups of eight discs each were restored in the following modes: groups 1 and 2 with light-cured bonding agent and light-cured microfilled resin, and groups 3 and 4 with a silane primer followed by the same bonding agent and resin. Specimens were water-stored for 24 hr, after which those in groups 2 and 4 were thermocycled 200 times between 4 degrees C and 60 degrees C. Specimens were then sealed to steel anodes and placed in 1% KCl, maintained at 21 degrees C, around a stainless steel cathode. Leakage currents were recorded daily for 30 days and after six months, by application of a 10 V potential difference between the cathode and each anode. Positive and negative controls gave massive and nil readings, respectively. The mean leakages were consistently greatest in group 2 (being significantly greater than for the other groups). Results suggest that silane priming minimizes leakage at the resin/porcelain interface after thermal cycling.

Bisphenol A-Glycidyl Methacrylate↗
PubMed1989

Influence of casting procedure on silver-palladium endodontic posts.

Silver-palladium alloys have been endorsed on clinical grounds as substitutes for gold alloys in posts and cores. However, carbon absorption during heating and casting can adversely affect the mechanical properties of silver-palladium alloys. In this study the tensile characteristics of endodontic posts cast in silver-palladium alloy using either a graphite or a ceramic crucible were determined. Graphite crucibles were associated with a significantly lower (2P less than 0.00001) percentage elongation than were ceramic crucibles. The need for a carbon-free casting environment for silver-palladium alloys was confirmed. The configuration of the cylindrical, serrated, vented post used in these tests resulted in mechanical properties lower than those achieved with standard metallurgical test procedures.

Ceramics↗
PubMed1989

The effects of disposable and custom-made impression trays on the accuracy of impressions.

This study indicates that some non-rigid impression trays, including disposable plastic trays and custom-made acrylic resin trays, may produce unreliable results when used with some medium-bodied elastomers. The study does not question the well-documented clinical accuracy of these elastomers when they are used with rigid trays. Disposable plastic trays are found to be acceptable when used with a combination of reversible and non-reversible hydrocolloid impression materials.

Alginates↗
PubMed1988

Force-displacement properties of a modified cross-linked silicone compared with facial tissues.

A dimethyl siloxane triacetoxy terminated silane, Type A adhesive, was modified with the base component of a medium grade polydimethyl siloxane with vinyl groups, MDX 4-4210, to produce a more pliable maxillofacial prosthesis. Force-displacement curves of various ratios of Type A adhesive/MDX 4-4210 were determined and compared with force-displacement curves obtained from human subjects. Within the force range of 0.4 to 1.2 N, the force-displacement slopes obtained on human subjects compared favourably with some of the Type A adhesive/MDX 4-4210 test specimens. The force-displacement slopes for the elastomers and humans were not in agreement for forces below 0.4 N.

Biocompatible Materials↗
PubMed1987

Impact-fracture energy of human premolar teeth.

The fracture strength of contralateral pairs of premolar teeth was determined by an in vitro method wherein impact loads of equal energy were applied to the medial aspects of the buccal cusps. Absorbed energy values quantified the fracture resistance of unprepared teeth and teeth restored with MOD amalgams, MOD amalgam overlays, MOD gold overlays, and full gold crowns. It was established that unprepared lower premolar teeth had a greater resistance to fracture than upper premolar teeth, and lower first premolar teeth were more resistant to fracture than the other premolar teeth; the fracture resistance of premolar teeth restored with MOD amalgams was significantly reduced compared with unprepared control teeth; MOD amalgam overlays in premolar teeth produced fracture resistances not significantly different from those for the unprepared controls; and restoration of premolar teeth with MOD gold overlays and full gold crowns enhanced fracture resistance to a level much greater than that of the unprepared control teeth.

Bicuspid↗
PubMed1987

Properties of a modified cross-linked silicone for maxillofacial prostheses.

A dimethyl siloxane-triacetoxy terminated silane, Type A adhesive, can be modified with the base component of a medium grade polydimethyl siloxane with vinyl groups, MDX 4-4210, to produce more pliable maxillofacial prostheses. The mechanical properties of samples with various Type A adhesive/MDX 4-4210 ratios were determined. Addition of the MDX 4-4210 base decreased the hardness, modulus, and ultimate tensile strength, while the percentage elongation increased. The initial tear strength was relatively constant for the various ratios except for the 50/50 mix, where a 50% decrease was observed. The ability to obtain different mechanical properties by using various ratios of Type A adhesive and MDX 4-4210 could result in the production of maxillofacial prostheses which will more closely stimulate the properties of facial tissues.

Adhesiveness↗