A laboratory investigation of the role of guide planes in the retention of cast cobalt-chromium alloy partial denture frameworks.

OBJECTIVES: This in vitro study examined the resistance to displacement offered by guide planes and the displacement mechanics of a bilateral bounded saddle cast cobalt chrome alloy removable partial denture framework under conditions simulating an average initial fit. METHODS: A specially designed model mouth jig fitted with strain gauges to monitor the forces across the guiding plane/guiding surface interfaces was used. Guiding planes of enamel, silver tin amalgam and dental composite with seven combinations of guide planes and three angles of withdrawal were examined. Guiding plane size was also examined for dental enamel. RESULTS: A statistically significant difference in retention was found for all factors examined. Retention increased with increasing angle of withdrawal. Size effects were found but considered unreliable. CONCLUSIONS: It was concluded that with a tight fit guiding plane retention may be readily predicted for any given material, combination of mesial, distal and lingual guiding planes and angulation conditions by the application of mechanical principles providing the basic parameters are known. Attention is drawn to the reasons for further work to fully understand the clinical situation.

Dental twinning.

Dental twinning anomalies influence tooth alignment and interdigitation, arch symmetry, appearance, and associated periodontal tissues. This case report presents a patient with twinning defects involving the maxillary central incisors. The aetiology of dental twinning using traditional nomenclature is also reviewed.

The position and function of the mandibular hinge axis.

It is widely believed that the mandibular hinge axis is anatomically located through the condylar head or its superior surface. This study, using markers placed over the average hinge axis point prior to orthopantograms, an analysis of lateral skull cephalometric radiographs and skull extrapolation, shows that the hinge axis is remote from the condylar head and in the region of the neck of the condyle. This site is consistent with the anatomical consideration of the function of the temporo-mandibular ligament.

Nystatin and amphotericin B in the treatment of denture-related candidiasis.

A double-blind trial of nystatin, amphotericin B, and a placebo was carried out in fifty-two cases of denture-related candidiasis and/or angular cheilitis. The drugs effected a significant clinical cure, but recurrence of the signs was common after withdrawal of the drugs. Concurrent bacteriologic examination showed few cures and continued presence of Candida albicans during the trial. A specimen from a red palate was examined histologically.

Condylar repositioning in mandibular retrusion.

STATEMENT OF PROBLEM: There has been debate about which anteroposterior maxillomandibular relationship should be used in fixed and removable prosthodontics for patients without a definite maximal intercuspation. The choice has important implications for complete denture fabrication in which any guidance to the previous dentulous maximal intercuspal position is missing. PURPOSE: This study was designed to estimate the posterior displacement that takes place at the mandibular condyles and occlusal surfaces when the mandible is moved from maximal intercuspal position to the most retruded mandibular position. MATERIAL AND METHODS: Articulated occlusal models of 18 subjects with a natural dentition and well-defined maximal intercuspation were studied. Models were rearticulated in retruded contact position, and the original vertical dimension of occlusion was restored by eliminating all interfering occlusal contacts on the retruded path of closure. Measurement of change in condylar position was estimated using a SAM2 articulator with condylar position indicator. Posterior displacement at the occlusal surfaces was measured with a traveling microscope. RESULTS: Condylar analog retrusion in the horizontal plane at the initial retruded contact position varied from 0.6 to 2.4 mm (mean 1.0 +/- 0.4 mm); however, after occlusal adjustment to restore the original vertical dimension of occlusion, retrusion was reduced to a range of 0 to 0.4 mm (mean 0.2 +/- 0.1 mm). Retrusion at the occlusal surfaces was found to vary from 0.4 to 1.5 mm (mean 0.7 +/- 0.3 mm) at retruded contact position; however, after occlusal adjustment, retrusion was reduced to a range of 0 to 0.5 mm (mean 0.2 +/- 0.1 mm). CONCLUSION: Posterior displacement at both the occlusal surfaces and the condyles was small when interfering occlusal contacts on the retruded path of closure were removed.

Occlusal contacts in mandibular retrusion.

An investigation into mandibular retrusion and the relationship between the maximum intercuspal position and the most retruded mandibular position was conducted on 15 dental students and nurses who had reasonably intact dentitions and a well-defined intercuspation. A photographic method was used to measure the retrusion that occurred at the occlusal surfaces of the posterior teeth. An average of approximately 0.2 mm retrusion was found, and the explanation of the relatively large "apparent" retrusion led to a discussion of the mandibular axes of opening.

Functional loading of the dentition during mastication.

A method is described whereby the electrical activity in the masseter muscles is used as an index of chewing force. By using the kinesiograph, it was possible to determine the interrelationship of the phases of the chewing cycle and to measure the duration of each phase. On the basis of a pilot study of 10 dentate subjects and two complete denture wearers, it appears that, although the magnitude of the applied load is reduced in denture wearers, this is to some extent compensated for by an increase in the time it is applied. The results also suggest that a greater force is applied to the supporting mucoperiosteum when inverted cusp teeth are used in the construction of the dentures.

The distortion of cast cobalt-chromium alloy partial denture frameworks fitted to a working cast.

PURPOSE: This in vitro study examined the distortion of 10 identically designed cast cobalt-chromium alloy frameworks, individually constructed, and adjusted by 10 technicians to fit one of 10 replicated stone working casts. MATERIAL AND METHODS: The distortion was measured with a specially developed strain gauge apparatus when the frameworks were seated on the maxillary metal analog, the stone working cast, or a stone duplicate cast. RESULTS: A statistically significant difference between the distortion of each of the frameworks was observed. A significant difference in the distortion was also observed for the frameworks when placed on each of the three casts. The distortion was the least when the frameworks were seated on the stone working cast and the greatest when seated on the metal analog. CONCLUSION: This study demonstrated that the distortion of a framework is not related to its closeness of fit as observed by the presence or absence of gaps between the framework components and the teeth.