Stephen M. Cameron

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.

Disinfection of denture base acrylic resin

STATEMENT OF PROBLEM During repair or adjustments of acrylic resin removable complete and partial dentures, particles of the acrylic resin from the interior of the prosthesis may expose dental personnel to microbial health hazards if the prosthesis has not been thoroughly disinfected. PURPOSE This study investigates the efficacy of a commercially prepared microbial disinfectant (Alcide) on the external and internal surfaces of acrylic resins. MATERIAL AND METHODS Four groups of acrylic resin were incubated in an experimental model to simulate the oral environment over time. Specimens were treated in 2 groups, disinfected and not disinfected, and then further grouped by breaking and not breaking. Analysis was performed with microbial colony counts, SEM, and statistical analyses. RESULTS Viable microorganisms still remain on the internal and external surfaces of treated resins. CONCLUSION Chlorine dioxide reduces, but does not eliminate, viable microorganisms on these dental prostheses.

Comparison of occlusal contacts in maximum intercuspation for two impression techniques

STATEMENT OF PROBLEM At the insertion of a fixed prosthesis, occlusal interferences in maximum intercuspation are often present. PURPOSE This study investigated and compared the accuracy of interocclusal relationships in maximum intercuspation for mounted casts obtained from a quadrant dual-arch impression technique and conventional full-arch impression techniques. MATERIAL AND METHODS Comparisons were made between an intraoral interocclusal record and interocclusal records made on mounted casts. Irreversible hydrocolloid, reversible hydrocolloid, polysulfide, polyether, and polyvinyl siloxane were used for the full-arch impression technique. For the quadrant dual-arch impression technique, rigid polyvinyl siloxane and light-body polyvinyl siloxane injection materials were used. RESULTS Statistical analysis revealed a statistically significant difference (p = 0.0017) in the median values among treatment groups. All pairwise multiple comparison procedures (Student-Newman-Keuls) indicated the average error of the quadrant dual-arch records was significantly different from the average error of each group of records produced with the full-arch techniques (p < 0.05). Comparison of the records of the full-arch impressions did not reveal any statistically significant differences. The average error of the full-arch records was 72 +/- 33 microns and the quadrant dual-arch average error was 5 +/- 5 microns. CONCLUSION The quadrant dual-arch impression technique produced mounted casts with significantly more accurate maximal intercuspal relationships than mounted casts from full-arch impressions.

Photoelastic comparison of stress induced by using stainless-steel versus nickel-titanium spreaders in vitro

The vertical force applied to an endodontic spreader generates stress along the canal walls. Recognizing the potential for this stress may reduce the incidence of vertical root fractures. A photoelastic acrylic model was fabricated to exhibit the stress produced during obturation of curved canals using the lateral condensation technique. Twenty standardized models simulating curved canals (32 degrees) were formed within PL-2 photoelastic acrylic resin blocks. The canals were fitted with a gutta-percha point, and either a stainless-steel or nickel-titanium finger spreader was inserted. An Instron 4502 universal testing machine applied a vertical force of 20 Newtons to the spreader. Quarter wave and polarizing filters were used with backlighting to generate the fringe patterns in the models. Photographs of the resulting stress lines showed that the stainless-steel spreaders created three areas of concentrated stress. The nickel-titanium spreaders induced stress patterns spread out along the surface of the canals, thus reducing the concentration of stress and the potential for vertical root fracture.

Radiographic verification of implant abutment seating.

STATEMENT OF PROBLEM It is possible to incorrectly seat an abutment on an external hex implant. PURPOSE This study investigated the theoretical and practical limits of radiographic verification of the complete seating of implant abutments on external hex implants. MATERIAL AND METHODS A positioning device that could accurately place the film and/or tube head in any vertical relation desired relative to the implant and abutment was fabricated. For all records, a standard abutment was secured to the implant in both a fully seated position (closed) and with the abutment turned approximately 30 degrees and seated atop the implant external hex (open). Digital radiographs were made with the tube head fixed perpendicular to the implant and the film angled at 0, 5, 10, 15, 20, 25, 30, 35, 40, and 45 degrees. The film was then positioned parallel to the implant and the tube head was angled at 0, 5, 10, 15, 20, 25, 30, 35, 40, and 45 degrees. An image of each position was shown to 36 dentists and they were asked if the image was diagnostic for determining the status of the implant/abutment interface. RESULTS The data were analyzed with a computer statistics program. The group with the tube head changed was analyzed with the Cochrans Q test and revealed a statistically significant (p < 0.0001) change in the diagnostic value of radiographs beginning at 20 degrees. The group with the film angle changed was analyzed with a Pearson chi-square and showed no statistical difference (p = 0.394) for the diagnostic value of any of the film angles. CONCLUSION Maintaining the tube head to less than 20 degrees from perpendicular to the long axis of the implant resulted in a diagnostic radiograph, regardless of the angle of the film.

The effect of primers and surface characteristics on the adhesion-in-peel force of silicone elastomers bonded to resin materials

Facial prostheses, when used in conjunction with craniofacial implants, require a retentive matrix to hold attachments and/or magnets. The retentive matrix is usually fabricated with autopolymerizing acrylic resin or a visible light-polymerized resin. The purpose of this study was to compare the adhesion-in-peel force of a silicone adhesive to autopolymerizing polymethyl methacrylate and light-polymerizing urethane dimethacrylate gel with two surface textures: (1) pumice polish only or (2) pumice polish and bead retention, and two surface primers: (1) Dow Corning 1205 primer or (2) Dow Corning S-2260 primer. The 1205 primer produced an adhesion-in-peel force that was statistically significantly stronger (p < 0.05) regardless of which type of resin or surface preparation was used.

Artifacts in recording immediate mandibular translation: A laboratory investigation ☆ ☆☆ ★ ★★ ♢ ♢♢ ♦

STATEMENT OF PROBLEM Even though immediate mandibular translation has been extensively studied and analyzed, and its clinical significance emphasized, there is controversy as to whether it actually exists or whether it is just an artifact of the pantograph. PURPOSE The aim of this study was to determine whether what appears to be pantographic evidence of immediate mandibular translation can actually be an artifact and, if so, to find a method to avoid it. MATERIAL AND METHODS The first part of this article explains geometrically with computer vector graphics how pure rotation can produce a pantographic tracing on the horizontal plate that is identical to what would be seen for immediate mandibular translation. The second part of the article presents a technique that uses a modified pantograph that eliminates the rotational artifact and thus permits proper interpretation of true immediate mandibular translation. RESULTS This study shows that pure rotation about the sagittal axis mimics immediate mandibular translation on a pantographic tracing when the plates are inferior to the transverse horizontal axis, produces scribings in an opposite direction for plates in a superior position, and produces no scribing when the plates are level with it. By modifying the pantograph so the tip of the scribing pin of the horizontal plate is level with the transverse horizontal axis, true immediate mandibular translation can most easily be differentiated from rotational artifact. CONCLUSIONS AND CLINICAL SIGNIFICANCE Rotation can cause artifacts that mimic immediate mandibular translation. A technique to avoid this problem is presented. This technique provides the foundation for a valid evaluation of patients to determine whether true immediate mandibular translation exists and whether it is clinically important.