PubMed · 5249922
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W Bellavia, S G Ciancio. 1969. Pin-retained amalgam splints.. https://doi.org/10.14219/jada.archive.1969.0124
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AIM: The laser welding technique was chosen for its versatility in the repair of dental metal prosthesis. The aim of this research is to assess the accuracy, quality and reproducibility of this technique as applied to Ni-Cr-Mo and Cr-Co-Mo alloys often used to make prosthesis METHOD: The alloy's ability to weld was evaluated with a pulsed Nd-Yag Laser equipment. In order to evaluate the joining, various cast wires with different diameters were used. The efficiency of the joining was measured with tensile tests. In order to understand this difference, metallographic examinations and X-Ray microprobe analysis were performed through the welded area and compared with the cast part. RESULTS: It was found that a very slight change in the chemistry of the Ni-Cr alloys had a strong influence on the quality of the joining. The Co-Cr alloy presented an excellent weldability. A very important change in the microstructure due to the effect of the laser was pointed out in the welding zone, increasing its micro-hardness. CONCLUSION: The higher level of carbon and boron in one of the two Ni-Cr was found to be responsible for its poor welding ability. However for the others, the maximum depth of welding was found to be around 2mm which is one of the usual thicknesses of the components which have to be repaired.
AIM: This study was devised to test the effectiveness of videotaped demonstrations as opposed to live demonstrations, to small groups of undergraduate dental students. The outcome was assessed by comparing the students' understanding of the clinical and laboratory technical stages of the altered cast impression technique, which is used in the construction of removable partial dentures. METHOD: 31 students watched a series of videotaped demonstrations and 30 received a similar series of live demonstrations. The altered cast procedure was divided into 5 distinct stages, each of which was assessed with the aid of agreed criteria, initially by the students and then by 2 staff assessors and these results were compared. The students were subsequently asked to rate how helpful the videotaped or live demonstration had been on a 5-point scale. RESULTS: The live demonstration group showed better agreement between the students' assessment and the assessors' assessment of the quality of the work for the first part of the clinical stage. There was no difference in the groups' assessment of the final outcome of this clinical stage and the subsequent laboratory technical stages. Students who observed the live demonstrations indicated higher scores for its helpfulness in performance of all the stages of the technique, when compared to those who had observed a videotaped demonstration. CONCLUSION: Both teaching methods developed a similar level of understanding of the principles behind the exercise, although the students preferred the live demonstrations. A carefully produced videotaped demonstration can be a useful alternative to a live demonstration in teaching the short and clear cut technique selected for this study.
STATEMENT OF PROBLEM: Base metal alloys present high values of strength and hardness, which have been associated with the greater abrasion resistance and polishing of metal-ceramic restorations. However, surface hardness has been shown to be a poor indicator of abrasion resistance. PURPOSE: The study aimed to compare the hardness and abrasion resistance of Ni-Cr alloys and determine whether there is a correlation between these 2 properties. MATERIAL AND METHODS: Two Ni-Cr alloys for metal-ceramic restorations with different hardness values were subjected to the following procedures: (1) initial measurement of Vickers hardness, (2) a series of abrasion cycles, (3) measurement of mass loss after each cycle, and (4) Vickers hardness measurements after each cycle. RESULTS: For each alloy, linear regression revealed a negative correlation between hardness and reduction in mass. The higher hardness of alloy A was associated with higher mass loss during abrasion when compared with alloy B. CONCLUSION: There was no significant correlation between hardness and mass loss for either alloy.