Orientation of retentive matrices on spherical attachments independent of implant parallelism.

Traditionally, it has been advocated that implants planned for use as overdenture abutments be placed parallel to each other to obtain predictable attachment retention and complete seating of the restoration and to prevent premature wear of components. However, it is often difficult or impossible to place implants parallel to each other, and patients with implants that have already been placed in a variety of positions frequently are referred to restorative dentists. This article describes a technique for the fabrication of a matrix-paralleling device as well as 2 of its uses. The device allows proper orientation of the retentive matrices to establish a common path of withdrawal for the prosthesis and all attachments. Provided that the matrices are parallel to each other, spherical overdenture attachments can be used even when the implants are not parallel.

Retentiveness of dental cements used with metallic implant components.

There is limited dental literature evaluating the retentive capabilities of luting agents when used between metal components, such as cast metal restorations cemented onto machined metal implant abutments. This study compared the retentive strengths of 5 different classes of luting agents used to cement cast noble metal alloy crowns to 8-degree machined titanium cementable implant abutments from the Straumann ITI Implant System. Sixty prefabricated 5.5-mm solid titanium implant abutments and implants were used; 30 received the standard surface preparation and the other 30 received an anodized surface preparation. Anodized implant components were used to reflect current implant marketing. Sixty castings were fabricated and randomly paired with an abutment and implant. A total of 12 castings were cemented onto the implant-abutment assemblies for each of the 5 different luting agents (zinc phosphate, resin composite, glass ionomer, resin-reinforced glass ionomer, and zinc oxide-non-eugenol). After cementation, the assemblies were stored in a humidor at room temperature prior to thermocycling for 24 hours. Each casting was pulled from its respective abutment, and the force at which bond failure occurred was recorded as retentive strength. A statistically significant difference was found between the 5 cements at P < or = .001. Of the cements used, resin composite demonstrated the highest mean retentive strength. Zinc phosphate and resin-reinforced glass-ionomer cements were the next most retentive, while glass ionomer and zinc oxide-non-eugenol cements demonstrated minimal retention. In addition, retention was not altered by the use of an anodized abutment surface.

Cement removal from restorations luted to titanium abutments with simulated subgingival margins.

STATEMENT OF PROBLEM: The process of removing excess cement from subgingival margins after cementation of restorations to implant abutments may lead to scratching of the abutments or incomplete cement removal. PURPOSE: The purpose of this study was to investigate and to compare the surfaces of abutments after the removal of three cements (glass ionomer, resin, and zinc phosphate) by use of three instruments (gold coated scaler, rigid plastic scaler, and stainless steel explorer). MATERIAL AND METHODS: Six investigators removed zinc phosphate, glass ionomer, and resin cements with explorers, gold coated scalers, and rigid plastic scalers with a model simulating clinical conditions. The surface of Brånemark abutments with cemented restorations were examined with a microscope at 20x for scratches and cement remnants. RESULTS: Statistical analysis of the results were inconclusive about which combination of instrument and cement worked most effectively. CONCLUSION: A surprising amount of cement remnants and scratching of abutments was observed. Although the six investigators were experienced in prosthodontic and implant procedures, there was variation in the results of their cement removal.

Effect of disinfection of custom tray materials on adhesive properties of several impression material systems.

The effects of impression tray disinfection procedures on the bond strength of impression-material adhesives to two types of resin trays were evaluated with a tensile test. Autopolymerizing acrylic resin and a visible light-curing resin were formed into one-half inch cubes. A screw eye was attached to each cube before polymerization. Perforated trays were fabricated with stops to maintain an even one-eighth inch of impression material over the resin block. Hooks on the opposite side permitted attachment of the metal plate to a mechanical testing machine. Before adhesive was applied, one third of the resin specimens were immersed in a 1:213 iodophor solution; one third in a 10% sodium hypochlorite solution, and one third were kept in the "as fabricated" condition. Polysulfide, polyether, and polyvinyl siloxane impression material-adhesive systems were evaluated. The resin-impression material-metal plate couples were attached to a mechanical testing machine and tensile forces were applied at a separation rate of 5 inches per minute. Mean values for adhesive strength ranged from 3.49 kg/cm2 for the autopolymerizing acrylic resin/iodophor/polyether combination to 10.55 kg/cm2 for the autopolymerizing acrylic resin/untreated/polyvinyl siloxane combination. Differences were detected among materials and disinfecting procedure. Clinically, disinfection of resin trays may adversely affect retention of the impression material to the tray.

Effect of ultrasonic cleaning and air polishing on porcelain labial margin restorations.

This study examined porcelain labial margins after ultrasonic scaling and air polishing. Thirty metal coupons were covered with 1.5 mm thick shoulder porcelain and cemented to acrylic resin blocks. A reference mark divided each specimen into a "treated" and an "untreated" side. The specimens were treated as three groups with: (1) an air polisher; (2) an ultrasonic scaler, and (3) the ultrasonic scaler and the air polisher. Surface roughness was determined and selected specimens were observed under scanning electron microscope. Surface roughness ranged from 0.37 microns to 1.06 microns for the untreated sides and from 0.86 microns to 2.80 microns for the treated sides. Increases in roughness were 69% for the ultrasonic scaler/air-polisher; 127% for the air polisher, and 162% for the ultrasonic scaler. ANOVA indicated a significant difference between the treatments. Specimens treated with the air polisher or the ultrasonic scaler and air polisher combination were less distorted than those treated with the ultrasonic scaler alone. The data suggested that careless use of an ultrasonic scaler or air polisher could substantially alter porcelain facial margins.

Torque generated by handheld screwdrivers and mechanical torquing devices for osseointegrated implants.

This study evaluated the ability of practitioners experienced in the use of Brãnemark implant components to impart a desired torque using handheld screwdrivers. The torque output and variability of mechanical torque devices was also examined. For clinicians using handheld screwdrivers, values ranged from 0.7 to 18.1 Ncm, 1.4 to 33.7 Ncm, and 8.2 to 36.2 Ncm for the 10-Ncm, 20-Ncm, and 32-Ncm torques respectively. The manually operated mechanical torquing devices produced torque values within the tolerances specified by their respective manufacturers at all levels. Significant variation from the manufacturer's set values were noted as a function of tightening speed with the electronic torquing device. The data indicate that there is wide variation in the ability of clinicians to perceive adequate torquing forces applied to implant components. Calibrated torquing devices are mandatory if proper torquing procedures are to be accomplished.

The bond strength of elastomer tray adhesives to thermoplastic and acrylic resin tray materials.

This study evaluated the bond strength of selected impression materials (Permlastic, Express, and Hydrosil) to a thermoplastic custom tray material as a function of drying time of the adhesive after application to a tray material. In addition, bond strengths of a polysulfide impression material to an acrylic resin tray material and to a thermoplastic tray material made directly against wax were evaluated. Bond strengths were obtained directly from values of applied load at failure and important conclusions were drawn.

A holder for dental implant screwdrives.

This article describes an easy procedure for making a holder for the small, short screwdrivers used to tighten and loosen implant superstructures. It can aid significantly during manipulation of the intraoral attachments.

An impression tray hanger for disinfection.

This article describes in detail a method for making a holder for impression trays. The procedure uses a pattern that can easily be made in the office. A mold is made from the pattern and parts are processed in acrylic resin. Many parts can be made from the same mold and several holders can be made before it is necessary to remake the mold.

A survey of crown and fixed partial denture failures: length of service and reasons for replacement.

The mean length of service of all restorations observed in this study was 8.3 years. Caries was the most common cause of failure, affecting 22.0% of the units failed and leading to the necessity for replacement of 24.3% of the units observed. Mechanical problems accounted for 69.5% of the failed units as opposed to 28.5% for oral disease. Resin veneer metal crowns provided the longest service of all crown types observed (13.9 years) and failed most frequently because of worn or lost veneers. The complete veneer metal crown had a life span of 6.1 years and was most likely to fail because of caries or defective margins. Ceramic-metal crowns also showed a relatively short period of service at 6.5 years, needing replacement primarily because of porcelain failure or poor esthetics. The resin-veneer metal crown also provided the longest service as a retainer, with a mean length of service of 14.7 years. This was closely followed by the partial veneer retainer (14.3 years), while the ceramic-metal retainer had the shortest life span (6.3 years). No apparent relationship was found between the span of prosthesis and its length of service. The six-unit canine-to-canine fixed partial denture exhibited the greatest longevity of the prostheses studied (10.4 years), while the two-unit cantilever fixed partial denture provided a mean of only 3.7 years of service before replacement was required.