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Biomedical subjects

C J Goodacre

Publications and source records attributed to C J Goodacre.

At least 55 records · Page 3Linked to original sources
PubMedDate not supplied

Tensile strength of preceramic solder joints formed using an infrared heat source.

Infrared soldering was compared to gas-oxygen torch soldering by testing specimens made from each of the following four classes of metal ceramic alloys: gold-platinum-palladium, gold-palladium, palladium-silver, and nickel-chromium-beryllium. There was no significant difference between infrared and torch soldering for the gold-palladium, palladium-silver, and base metal alloy specimens. However, infrared soldering of the gold-platinum-palladium alloy samples produced significantly weaker joints than those produced by torch soldering.

Chromium Alloys↗
PubMedDate not supplied

The effect of surface treatment on the Knoop hardness of Dicor.

One advantage cited for the use of Dicor over other ceramic materials is a reported Knoop hardness comparable to human enamel. However, when fabricating dental restorations, a Dicor glass-ceramic casting generally is subjected to several different surface treatments because of processing, esthetic, and functional requirements. Therefore, this study compared the Knoop hardness of Dicor specimens under three conditions: (1) cerammed, (2) cerammed and shaded, and (3) sectioned to reveal internal material. Knoop hardness differences between groups were significant (P less than or equal to .05). The cerammed surface was the hardest; it was harder than human enamel. Shaded specimens had a surface hardness comparable to dental porcelain. However, the internal glass-ceramic material, located beneath the shading porcelain and cerammed surface, had a Knoop hardness slightly higher than that of human enamel.

Analysis of Variance↗
PubMedDate not supplied

The effect of tooth preparation design on the breaking strength of Dicor crowns: 2.

Six maxillary first premolar tooth preparation designs for all-ceramic restorations were tested for their effect on the strength of Dicor crowns. Ten crowns were fabricated for each preparation design, and the breaking strengths were measured. Three finish line designs (1.2-mm shoulder with sharp axiogingival line angle, 1.2-mm chamfer, and 0.8-mm chamfer) and two total occlusal convergence angles (5 degrees and 15 degrees) were tested. All preparations possessed 2.0 mm of occlusal reduction. The average breaking strengths of the 10 Dicor crowns were compared to those of 10 metal ceramic control restorations. The three groups of restorations fabricated for preparations with 5 degrees of occlusal convergence were significantly weaker than those made for preparations with 15 degrees of convergence. The metal ceramic restorations were significantly stronger (247.45 kg) than the strongest Dicor crowns (56.2 kg).

Ceramics↗
PubMedDate not supplied

Comparison of microwave-polymerized denture base resins.

Three denture base resins, two designed for microwave polymerization and one for host-water-bath-processing, were compared. Results indicated that all four tested thicknesses (3, 6, 11.6, and 17.7 mm) of the water-bath-polymerized samples and one of the microwave-polymerized resins were porosity-free. When the water-bath-polymerized material was microwave processed, porosity was found when resin thickness exceeded 3 mm. When one resin designed for microwave polymerization was irradiated using the high-wattage (513 W), shorter cycle (4 minutes 52 seconds), porosity also occurred when the thickness exceeded 3 mm. Porosity did not occur until there was 9 mm of thickness when the lower-wattage (75.9 W), longer cycle (15 minutes 26 seconds) was used. No significant differences in transverse strength or hardness were noted between the materials.

Denture Bases↗
PubMedDate not supplied

The effect of tooth preparation design on the breaking strength of Dicor crowns: 3.

The dimensions of 120 maxillary first premolar all-ceramic tooth preparation designs were measured and analyzed to determine relationships between design features and recorded differences in the strengths of restorations fabricated for each preparation design. To assess clinical feasibility, the remaining dentin thickness of each preparation design was measured. A total occlusal convergence angle of 10 degrees provided the best combination of restoration strength and remaining dentin thickness. Five degrees produced the weakest restorations, and 15 degrees and 20 degrees required greater tooth reduction and pulp proximity. Stronger restorations were noted when the shoulder finish line had a sharp axiogingival line angle, possessed minimal cervical inclination, and was located as close as possible to the same occlusocervical level on all four axial surfaces.

Ceramics↗
PubMedDate not supplied

Comparison of two tests to determine the castability of dental alloys.

This study compared castability values in the Whitlock test with those obtained from a new castability monitor based on a dental restoration. Five metal ceramic casting alloys were induction cast with both a carbon-containing and a noncarbon phosphate-bonded casting investment to assess the reliability of the Whitlock mesh test in predicting alloy castability. Alloy performance in the Whitlock test did not parallel that of the replica coping test for all alloy-investment pairs, as would be anticipated for a reliable monitor of castability. In addition, the variability of the Whitlock castability values for some alloys was sufficient to question the test's usefulness in refining the casting process with a specific alloy.

Analysis of Variance↗
PubMedDate not supplied

The effect of tooth preparation design on the breaking strength of Dicor crowns: Part 1.

Six maxillary first premolar all-ceramic tooth preparation designs were tested for their effect on the strength of Dicor crowns. Ten crowns were fabricated for each preparation design, and their breaking strengths were measured. Three finish line designs (1.2-mm shoulder with sharp axiogingival line angle, 1.2-mm shoulder with rounded axiogingival line angle, and 0.8-mm chamfer) and two total occlusal convergence angles (10 degrees and 20 degrees) were tested. All preparations possessed 2.0 mm of occlusal reduction. The average breaking strengths of the 10 Dicor crowns were compared to that of 10 metal ceramic control restorations. The tooth preparation with a 1.2-mm shoulder finish line, sharp axiogingival line angle, and 10 degrees of total occlusal convergence produced the strongest Dicor crowns (88.6 kg). The weakest restorations were observed when a 0.8-mm chamfer finish line (66.8 kg) was used. The metal ceramic restorations were significantly stronger (247.45 kg) than the strongest Dicor crowns (88.6 kg).

Ceramics↗
PubMedDate not supplied

The application of Moire topography to removable prosthodontics.

The study was designed to assess the dental research potential of moire topography--the use of geometrically regular light patterns for measuring three-dimensional objects. One hundred thirty-nine maxillary edentulous casts and 20 mounted cast pairs were evaluated. Results demonstrated that the moire topography techniques can be used to quantitatively evaluate edentulous arch forms, compare edentulous ridge forms and surfaces, determine the amount of overlap of mounted maxillary and mandibular casts, and confirm prime areas for positioning posterior teeth.

Dental Occlusion↗
PubMedDate not supplied

A comparison of resins for fabricating provisional fixed restorations.

Four acrylic resins and two composite resins for fabricating provisional fixed prosthodontic restorations were studied to determine temperature change during polymerization, surface hardness, marginal fit, wear resistance, transverse strength, transverse repair strength, surface roughness and polishability, color stability, and stain resistance. While certain materials exhibited advantageous properties in one or more of the tests, no one material was superior to the others in all tests.

Acrylic Resins↗
PubMedDate not supplied

Microwave energy polymerization of poly(methyl methacrylate) denture base resin.

Several physical property tests were conducted to compare microwave energy and conventional hot water bath polymerization techniques. The two methods of polymerization produced similar dimensional accuracy in complete denture bases. No differences were found in transverse strength, Knoop hardness, density, and residual monomer content of resin test strips. Comparable strength was found between microwave-polymerized and autopolymerized repairs of resin test strips. No porosity was observed in complete or removable partial denture bases polymerized by either technique. The Knoop hardness of microwave-polymerized removable partial denture bases was found to be slightly lower near the metal framework.

Denture Bases↗
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A comparison of the marginal and internal adaptation of titanium and gold-platinum-palladium metal ceramic crowns.

The marginal and internal adaptation of metal ceramic crowns fabricated by electrical discharge machining and conventional metal ceramic alloys were compared. The crowns were cemented using zinc phosphate cement, embedded in epoxy resin, and sectioned in two planes: diagonal and buccolingual. The crowns were then measured at nine sites. The results showed that there were no statistical differences between the external marginal opening of the titanium and the gold-platinum-palladium crowns. The overall marginal discrepancies for the restorations in this study were 61 microns (+/- 34 microns) for the titanium metal ceramic crowns and 47 microns (+/- 17 microns) for the gold-platinum-palladium metal ceramic crowns.

Analysis of Variance↗
PubMedDate not supplied

The effect of finish line form and luting agent on the breaking strength of Dicor crowns.

Molar teeth were prepared to a standardized cylindric form using a lathe. Dicor crowns were luted on these preparations using zinc phosphate, glass-ionomer, and resin cements. The crowns were thermocycled and subjected to fracture loading to compare the effect of the different luting agents on fracture strength. Five finishing lines were used to determine if resin cement and associated bonding procedures could counteract the negative effect certain finish lines produce on all-ceramic crowns. When resin cement was used in conjunction with restoration and tooth precementation bonding treatments, the crowns were significantly stronger than when glass-ionomer or zinc phosphate cements were used. No difference in strength was found between the five finish lines when the crowns were cemented with resin and associated bonding procedures.

Analysis of Variance↗
PubMedDate not supplied

The effect of using custom or stock trays on the accuracy of gypsum casts.

This study examined the linear dimensional stability of nonaqueous elastomeric impressions made from stock and custom trays by measuring casts derived from those impressions at 1 hour, 1 day, and 1 week. There was a small statistical difference among casts produced from stock versus custom trays compared to the master model. However, there was no significant difference in casts produced from impressions poured at 1 hour, 1 day, and 1 week. A custom tray with a 2.0 to 2.5 mm tray spacing had the least amount of variation, yet the differences between custom and stock trays may not be clinically significant.

Analysis of Variance↗
PubMedDate not supplied

Endosseous implant placement in conjunction with inferior alveolar nerve transposition: an evaluation of neurosensory disturbance.

This retrospective study evaluated neurosensory dysfunction and the implant success rate associated with 64 implants placed in 15 patients following transposition of the inferior alveolar nerve. A total of 21 inferior alveolar nerve mobilization surgeries were performed. The mean postoperative follow-up time was 41.3 months, with a range of 10 to 67 months. The effects of surgical technique and implant surface geometry on neurosensory dysfunction were evaluated by using light touch, brush stroke direction, and two-point discrimination. The implant success rate was 93.8% (60/64). The surgical technique that involved detaching the mental foramen resulted in a significantly greater incidence of neurosensory disturbance (77.8%, 7/9) than did the technique that left the bony foramen intact (33.3%, 4/12). The overall incidence of neurosensory disturbance was 52.4% (11/21).

Aged↗