PubMed · 3333737
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J F Régnier. 1987. [The Reval casting technic].. https://pubmed.ncbi.nlm.nih.gov/3333737/
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Instrumentation studies comparing nickel-titanium with stainless-steel files have been performed without precurving the nickel-titanium files. It is unknown what influence the precurving of nickel-titanium files would have on transportation in small curved canals of varying curvatures. One hundred-sixty resin blocks with simulated canals were used. Eighty blocks had gradual (gradual curve (GC)) 30-degree curves; the remainder had abrupt (abrupt curve (AC)) 30-degree curves. Ten blocks for each curvature and for each degree of precurving (0, 15, 20, 25, 30, 35, 40, and 45) were instrumented with a machine that imparted only an in and out motion. Simulated canals were a size 30 at the apex, and size 30 nickel-titanium files were used to instrument the canals. A transportation "t" index was determined at two levels: T1 (1 mm from the apex) and TB (a line bisecting the curve of the canal). For GC at T1 and TB, 45- and 25-degree curved instruments, respectively, produced significantly less transportation (p < 0.0001). For AC at T1 and TB, 35- and 0-degree curved instruments, respectively, produced significantly less transportation (p < 0.0001). Comparing GC and AC, the transportation for GC was significantly less (p < 0.0015).
Combined retraction and intrusion of the anterior teeth is often needed as part of orthodontic treatment. The use of a statically determinate force system has many advantages over statically indeterminate systems. In the case of the cantilevers the orthodontist can evaluate the line of action of the delivered force directly in the clinical situation. In the present paper the force system delivered by stainless steel and beta titanium cantilevers with an eccentrically placed helix was evaluated. The cantilever consisted of a straight piece of wire bent to form a helix with an external diameter of 3 mm. The wire was fixed into a bracket of sensor 1, touching sensor 2 of a test bench with a 1-point contact to. Activation was induced by rotating sensor 1 into which the wire was tightly fixed. This was done in 2 different modes, one in the direction in which the helix was bent and one in the opposite direction. With an interval of 5 degrees the force system generated with respect to sensor 1 and the direction of the force delivered to sensor 2 (the other bracket) were registered. The results were expressed graphically and the influence of material and activation mode were evaluated statistically by comparing the coefficient of regression. As expected, the influence of the material reflected the relative stiffness of the 2 alloys. As TMA is monocrystalline (i.e. consists of homogeneous crystals) the mode of activation did not reflect any significant Bauschinger effect as seen in the case of stainless steel. Analysis of the force direction confirmed that the suggested wire configuration is useful for delivery of a predetermined combination of horizontal and vertical force. This was confirmed by a finite element analysis.
STATEMENT OF PROBLEM: As adapted for the dental profession, spark erosion technology permits precise machining of retentive metal overdenture frameworks for use in implant prosthetics. PURPOSE: The resultant prostheses are retentive and provide a number of benefits offered by both conventional overdenture and fixed prosthetic designs. MATERIAL AND METHODS: Preliminary data collected from an ongoing 5-year clinical trial were reviewed to qualitatively assess the clinical results obtained from 25 spark eroded implant-retained overdenture prostheses placed in 24 subjects. RESULTS: Throughout an evaluation period of 13.33 months (range 4 to 19 months), subject responses measured by questionnaire were uniformly good. Few complications were encountered and were limited to resin denture base/tooth fractures or retentive component failures that were easily repaired. CONCLUSION: Overdenture prostheses retained by spark eroded milled frameworks offer an acceptable treatment alternative for patients undergoing dental implant therapy.