PubMed · 3906786
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H Levy. [The functionally generated path applied to metal-ceramics].. https://pubmed.ncbi.nlm.nih.gov/3906786/
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The principles used in the bonding of porcelain veneers may also be applied to full-coverage restorations, with such crowns luted using resin-based materials. For these full coverage restorations, dentine bonding agents, preferably of low film thickness, may be used to treat areas of exposed dentine prior to placement. These 'dentine-bonded' all-ceramic crowns may exhibit many favourable characteristics, including those of good aesthetics and peripheral blend with gingival tissues and the potential for placement on conservative preparations which may minimise the risk of pulpal damage. Indications include cases in which conventional crowns require replacement, those in which minimal preparation techniques are appropriate, and those in which there has been tooth surface loss. Contraindications include subgingival margins, extreme occlusal interferences and insufficient tooth substance for bonding. However, the longevity of these restorations is, as yet, unknown, in the absence of long-term clinical data.
OBJECTIVES AND METHODS: The casting shrinkage of thin-walled castings was measured using a tungsten die method. The thickness and the surface area of the casting were simulated to those of either partial veneer crowns or complete denture frameworks. Gold alloys were cast at two different pressures (0.35 and 0.49 MPa) and the shrinkage measurement was made at different locations on the castings to investigate the effect of these factors. RESULTS: Both overall and local shrinkages were significantly influenced by size and casting pressure. These shrinkages were significantly lower for the denture-sized (DS) specimens than for the crown-sized (CS) specimens, and significantly decreased with the increase of the casting pressure. The effect of location on the local shrinkage significantly varied with the change of the other two factors, size and pressure. At the higher casting pressure, the DS specimens sustained a significantly smaller shrinkage at the margin than at the centre, whereas the CS specimens had a significantly smaller shrinkage at the centre than at the margin at the lower pressure. CONCLUSIONS: The results suggest that the casting shrinkage of a thin-walled casting is influenced by the temperature gradient in the alloy and the resultant time difference in alloy solidification as well as the volume supply of the molten alloy in the mould.
Clinical experiences for the past 9 years have demonstrated the practicability of the O-ring coping attachment, a modification of the telescopic crown-and-sleeve coping retainers, for removable partial dentures. A circumferential groove placed in the primary coping receives an elastomeric O-ring that fits into a corresponding groove made in the internal surface of the telescopic crown. The O-ring not only provides controllable retention but also acts as a shock absorber. Long-term retention of the prostheses can be easily maintained by periodic replacements of the O-rings. Sophisticated procedures and expensive machines are not required to make the prostheses. Excellent patient acceptance and the versatility in clinical applications make this system one of the winning designs for removable partial prosthodontics.