The International Journal of Prosthodontics, 04/1996

Records of self assessed complete mandibular denture security were made by visual analogue scale, four-category functional scale, and by self-expressed satisfaction or dissatisfaction on 57 subjects that presented for replacement of complete dentures at an undergraduate clinic. Visual analogue scale scores formed two groups corresponding approximately to the groups of subjects expressing satisfaction or dissatisfaction with the current security of their dentures. The self-assessed visual analogue scale scores enabled variations in denture security to be quantified. Visual analogue scale scores of denture security were not normally distributed, but formed two separate distributions which corresponded approximately with the sets of satisfied (visual analogue scale > 50) and dissatisfied (visual analogue scale 50) patients. The data showed that the visual analogue scale method was superior to the other two types of patient self-assessment.

This investigation studied the metal ceramic interface for two representative high-palladium alloys each of the Pd-Cu-Ga and Pd-Ga systems, using scanning electron microscopy and x-ray energy dispersive spectroscopy. The Pd-Cu-Ga alloys produced complex subsurface oxidation regions with thicknesses ranging from 15 to 20 um for one alloy and 5 to 10 um for the other alloy. Ga, In, and Sn accumulated at the interfaces, and Ga-rich deposits were found in the subsurface scale. One Pd-Ga alloy presented a surface oxidation region which dissolved in the ceramic, producing islands rich in Pd and Ga with a width that ranged from 1 to 2 um. These islands were separated from the alloy by a band rich in Ga and Si which was 1 to 2.5 um thick. While the other Pd-Ga alloy presented similar interfacial microstructures, the islands formed for this alloy were relatively sparse. The Pd-Cu-Ga alloys had a more favorable interface for metal ceramic bonding, which agrees with previous characterization of bond failures beteen these alloys and dental porcelain.

This study evaluated the tensile bond strength of resin composites to a noble alloy for ceramic bonding after various surface treatments. The flat end of bars cast in the alloy were used as test specimens. Eighteen clinically relevant combinations of luting agent, airbone particle abrasion, and surface treatment were applied. After surface treatment, two bars were bonded together. Resin cement, either dual-polymerizing (Twinlock) or chemically polymerizing (Panavia EX, Panavia 21, or RBBC), was used as a luting agent. The specimens were subjected to 1,000 thermal cycles between 15 degrees C before tensile bond strength testing. The highest median bond strengths were obtained using the Silicoater MD method/Twinlook (20.6 to 26.1 MPa) or with tin-plating/Panavia EX (24.0 MPa), but more low values were recorded among the latter specimens. Tin-plating/Panavia 21 gave median tensile bond strengths (18.1 MPa) similar to tin-plating/Panavia EX. The Silicoater MD method resulted in similar bond strengths with or without the addition of a layer of Opaquer. The traditional Silicoater method (8.0 to 12.4 MPa) gave significantly lower median tensile bond strength values, and the lost sugar crystals method resulted in a tensile bond strength of 15.4 MPa

One hundred thirty-seven cantilevered fixed partial dentures made between 1974 and 1990 were clinically and radiographically evaluated. Thirty-three of the prostheses were located in the mandible (11 in the anterior and 22 in the posterior region) and 104 were located in the maxillae (58 anterior prostheses and 46 posterior prostheses). Median duration was 84 ± 3.6 months. During the 18 years, 41 (30%) failed. Of those that failed, 28 (68%) were in the maxillae and 13 (32%) were in the mandible. Reasons for failure included abutment fracture (4), loosening with or without caries (18), secondary caries (9), fracture of prosthesis (2), fracture of extension (1), periodontal problems (6), and apical reaction (1). Failures occurred significantly more when endodontically trated abutments were used. More mandibular restorations failed than did maxillary units, but the difference was not significant. The prosthesis length ratio and the crown length-bone ratio did not influence the failure rate. The overall success rate of cantilever fixed prostheses was 70% over a period of 18 years.

Prosthodontists are often unaware of difficulties faced by dental technicians. Likewise, dental technicians may be unaware of difficulties faced by prosthodontists. By being better education about one another's discipline, prosthodontists and technicians can establish cooperative goals and help each other to identify significant facts and potential difficulties posed by specific materials, techniques, or stages of the work in progress. This article describes specific procedures for prosthesis fabrication and the opportunities each step provides for such cooperation. The steps include diagnostic waxing, provisional restoration, fabrication of master dies, tooth preparation, fabrication of intraoral records, treatment waxing, selection of materials, use of ceramic mucosal simulations, and color selection. If the prosthodontist and dental technician are willing to share responsibility for treatment plans, their mutual understanding can bring new insight to old problems and provide intellectual stimulation to both.

Am experimental model was designed to evaluate the effects of the intramobile connector in reducing stress concentration in an IMZ implant in fixed connection with a natural tooth abutment. The study analyzed the stresses produced at the cervical level of the implant when the superstructure arm was deflected within the limits of physiologic mobility under static axial loads. The designed experimental model was sensitive to changes in strain data with the applied loads and different internal elements. The intramobile connector resilient component reduced strain up to 60% compared to the rigid internal element.

The incidence of latex glove perforation during prosthodontic treatment was investigated on 122 occasions using two methods, a conductivity test and a water inflation test. Latex glove perforation was detected in 38.5% of the treatments by the conductivity test and in 27.9% by the water inflation test. The perforation went unrecognized in 74.7% of the occurrences (35/47 incidents) using the conductivity test and in 64.7% (22/34) when the water inflation test was used. Of the total 55 glove perforations, 21 perforations were detected only by conductivity test, 3 were detected only by the water inflation test, and 31 perforations were detected by both methods, which suggested that the conductivity test is more sensitive than the water inflation test for the detection of glove perforation. The results of this research suggested that even when latex gloves are worn, the risk to prosthodontists of exposure to body fluids remains in four of every six treatments, often without the awareness of the prosthodontist

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.

Retentive clasp components can be created to minimize torquing forces on abutment teeth incorporated in the support and retention of bilateral distal extension removable partial dentures. Functional movement of the combined tooth-mucosa-borne prosthesis about the axis of rotation necessitates consideration of retentive element design modifications, particularly as they relate to bilateral asymmetric distal extension situations.

The tensile mefchanical properties of welded titanium joints were studied, and intact titanium was used as controls. Welded joints were fabricated with either a stereographic laser-welding technique or a gas tungsten arc welding technique. The effect of heat treatment following a simulated porcelain application was also investigated. Heat-treated laser welds had significantly lower ultimate tensile strengths. Heat treatment had no effect on the modulus of elasticity or elongation, but generally significantly decreased the yield strength of the titanium specimens. The gas tungsten arc welding specimens had significantly higher yield strengths and elastic moduli than the other two groups. The elongation of the control specimens was significantly greater than the elongation of the gas tungsten arc welding specimens, which was in turn significantly higher than that of the laser-welded specimens.

This study investigated the occlusal stress distribution to the implant and soft tissue for the implant-retained overdenture. The stress at the molar residual ridge and the strain around the implant were measured on an experimental resin cast using static and dynamic loading. The influence of connecting structures of stud attachments on stress distribution was discussed. The occlusal stress had a tendency to concentrate on the implant, especially in the areas distal to the implant. The modified magnetic attachment system, using a silicone-covered magnet, provided the optimal stress distribution.