Alginate impressions for fixed prosthodontics. A 20 year follow up study.

The aim of this study was to estimate whether the survival ratios after 20 years of fixed prosthodontics made of alginate impressions was higher, equivalent or lower, compared to the survival ratios, shown in studies, where different impression materials were used. 151 females and 104 males were screened regarding the condition and age of the restorations at the annual check-up in one of the author's surgeries. Average ages were 55 and 54 years respectively, when the fixed prosthodontics were seated. A total of 1.271 units were produced during the twenty years, 911 abutment teeth and 360 pontics. The type of prosthetic work was divided into three groups: 1) larger fixed prosthodontics 6-14 units (469), 2) smaller fixed prosthodontics 2-5 units (541) and 3) single crowns (261). The results show that alginate impressions can produce fixed prosthodontics with survival ratios similar to those presented in other studies, after 5 years (99%), 1o years (93-96%) and 15 years (74-96%). After 20 years the survival ratio was 61-63%. In conclusion, fixed prosthodontics made according to the syringe-tray alginate impression method may have the same success rates after 20 years compared to that of fixed prosthodontics presented in previous longitudinal clinical studies where other impression materials had been used. In this study, caries and root fractures were the main reasons for removing abutment teeth and pontics.

Simulating periodontal effects in dental osseointegrated implants: effect of an intramobile damping element on the fatigue strength of dental implants--an in vitro test method.

OBJECTIVE: The purpose of this study was to develop and adapt a new method for testing dental implant systems and to apply it to existing systems with and without dampers. The parameters examined were the fatigue strength of the superstructure-retaining titanium screw, the deformation of the damper, and the effect on the supporting, bone-stimulating, and embedding material. METHOD AND MATERIALS: Ten pairs of implant specimens were prepared according to standard laboratory procedure and embedded in transparent polymethylmethacrylate (PMMA). Five pairs were provided with polyoxymethylene dampers and five with nondamping titanium connectors. Each pair was connected with a metal beam, and cyclic loads were applied with a pneumatic-driven machine at a frequency of 2 Hz. Chewing forces of 150 to 450 N were transmitted by springs individual to each specimen. For each of the 2 x 10(5) cycles, there was a control of the retaining screw and bonding between the fixture and embedding material by registration of gap propagation in the implant-PMMA interface. RESULTS: A significant damping effect was noticed on the implant--embedding material interface. Damping did affect the superstructure, since the retaining screws were plastically deformed. The screws were unscrewed when the applied load exceeded 300 N, while the undamped system was seemingly unaffected. CONCLUSION: The study method made it possible to evaluate damping effects on different levels of implant systems, while satisfying the requirements for testing in a "clinical-like" way. PMMA was comparable to bone in supporting implants during fatigue testing.

A comparison of strengths of five core and post-and-core systems.

OBJECTIVE: In this in vitro study, the strength of several core and post-and-core systems was compared. A second aim was to compare the strength of posts and cores on root-filled teeth with that of cores on vital teeth. The failure modes of the core and post-and-core systems were also studied. METHOD AND MATERIALS: For root-filled teeth, Composipost carbon fiber dowels and gold alloy posts and cores were tested. For vital teeth, glass-ionomer cement with threaded parapulpal retention pins, resin composite with threaded parapulpal retention pins, and gold alloy with parallel parapulpal pins were tested. Specimens were tested in a Zwick universal material-testing machine. RESULTS: A significant variation in strength was found among core systems of cast gold, resin composite, and glass-ionomer cement constructed on vital teeth. The strength of the systems constructed on root-filled teeth did not vary significantly. The mode of failure varied, depending on the core or post-and-core material. CONCLUSION: Composipost posts and cores and cast gold posts and cores were equivalent in strength and did not vary significantly from gold cores constructed on vital teeth. The low strength values obtained for glass-ionomer cement in combination with threaded retention pins makes this combination a poor choice for core buildup.