Evaluation of ceramic margins for metal-ceramic restorations

This study evaluated various techniques for forming ceramic margins on metal-ceramic restorations. Marginal openings were measured using a scanning electron microscope on replicas derived from elastomeric impressions. Ceramic margins formed with a platinum foil backing showed significantly better fit than those formed with direct-lift techniques. With the platinum foil method these ceramic margins displayed a marginal fit comparable to that obtained with cast metal margins.     

Marginal opening of single and twin platinum foil-bonded aluminous porcelain crowns

The marginal openings of single and twin foil-bonded aluminous porcelain crowns were compared in crowns fabricated indirectly for extracted teeth and directly on typodont teeth. The crowns were cemented with zinc phosphate, embedded in plastic, and sectioned. Marginal opening was measured directly with a traveling microscope. There was no significant difference between the marginal openings of twin- and single-foil crowns fabricated indirectly for extracted teeth. When the crowns were constructed directly on typodont teeth to eliminate the variables of impression-making and die fabrication, the single-foil crowns possessed a significantly smaller marginal opening than the twin-foil crowns. Both the twin- and single-foil complete porcelain crowns resulted in clinically acceptable margins. The single-foil crowns were easier to make.     

Laminagraphic study of mandibular condyle position when recording centric relation.

Laminagraphs were made of each temporomandibular joint of 20 subjects (1) with the mandible forcefully retruded to centric relation and (2) with the mandible positioned by a closing force while an anterior guidance prosthesis was being used. The radiographs were compared by measurements of condylar position; results indicated the condyles to be significantly more superior in the glenoid fossa when anterior guidance was used. The difference in anterior-posterior positioning of the condyles appeared to occur randomly. Measurements of the joint spaces with the mandible in centric relation using anterior guidance indicated that mandibular condyles were not centered in the fossae. There seemed to be a range in the size of the space that could be considered normal.     

A histologic evaluation of tissue response to three currently used temporary acrylic resin crowns.

The subgingival placement of any one of the three types of temporary crowns placed on 28 posterior teeth of seven subjects caused no detectable change in the gingiva over a 3 week period. There is a need for further study of the influence of temporary crowns on the different types of gingival tissue.     

Pin amalgam restoration and pin amalgam foundation

The principles of cavity preparation, retention, pin placement, and finishing of the pin amalgam restoration differ in several respects when applied to the pin amalgam when it is intended to serve as a foundation for a cast restoration. A more conservative extension and removal of undermined enamel is indicated because the amalgam will be covered with a cast restoration. The axial reduction required during crown preparation frequently reduces retention of the pin amalgam foundation; therefore, it is necessary to plan for those alterations during the cavity preparation. The degree of finishing and polishing required is determined by the length of time the pin amalgam foundation is expected to function as an interim restoration.     

Ameloblastomas of the jaws: radiological diagnosis and follow-up

Eleven of 57 tumours and cysts (19 per cent) seen at two major centres over a 4-year period were ameloblastomas, primary in eight and recurrent in three. Computed Tomography (CT) was the most sensitive imaging technique for detecting ameloblastomas. The radiological features were distinctive maxillary and mandibular pathology in primary cases and soft-tissue, maxillary sinus and asymmetrical deep tissue involvement in both primary and recurrent ameloblastomas. Following surgery and pathological confirmation, serial scans were combined with periodic clinical re-evaluation. We identified clinically occult recurrences in two cases and confirmed a clinically-suspected recurrence in one on the basis of the CT findings. Our protocol appears efficacious and is suggested for the necessary long-term follow-up in all pathologically verified ameloblastomas.     

Retention of posts in teeth with nonvital pulps

The results of this study indicate that: 1. Cast posts without grooves are more retentive when cemented with zinc phosphate than with composite resin. 2. Cast posts with grooves in the posts and adjacent grooves in the teeth are more retentive than cast posts without grooves. 3. Cast posts with grooves and with adjacent grooves in the teeth have equal or greater retention than Paraposts with grooves in the teeth when both are placed with composite resin.     

An 18-month clinical evaluation of semiprecious and nonprecious alloy restorations

SEM studies indicate that the control alloy, Minigold, WLW, and Litecast metals presented similar results in relation to marginal fit when proper techniques are followed. Clinical evaluation based on the criteria of gingival irritation, patient sensitivity, and abrasion demonstrated no statistically significant differences between the casting alloys tested and the control. The control alloy had significantly fewer restorations with tarnish and corrosion than either WLW or Litecast. There was no significant difference between the control alloy and Minigold in terms of tarnish and corrosion.     

Errors in oblique cephalometric radiographic projections of the edentulous mandible. Part I: Geometric errors

Geometric errors that occur in oblique cephalometric radiographic projections of the edentulous mandible were calculated for different focal-spot-to-object distances (1500, 3000, and 6000 mm). The horizontal errors from tolerance of the porion and nasion fixation in the cephalostat were calculated. The same was done for the vertical errors caused by the variability of the rest position. From the results of this study it can be concluded that the distance between focal spot and object should be as large as possible. It was also found that it is important to minimize the differences in enlargement that may occur on radiograms of different subjects because of changes in the position of the mandible. This position can be standardized by the use of an individual support.     

Calcifying epithelioma of Malherbe (pilomatrixoma) of the cheek

A case of a large calcifying epithelioma of Malherbe in a 15-year-old Nigerian girl is presented. The tumor was treated by excision and the wound was skin-grafted.     

Effect of occlusal reconstruction on the reproducibility of chewing movements

The jaw movement patterns of five subjects with reconstructed occlusion were compared with those of 10 normal dentate subjects. The degree of conformity between closing and opening pathways in the intercuspal area and the reproducibility of these pathways within and outside the intercuspal zone were measured with a computer-based system. The mean linear separations between opening and closing pathways and deviations around these pathways for the reconstructed group were consistently smaller than those for the control group. The results suggest that reconstructed subjects use displacement patterns which show less variation than do subjects with natural dentitions.     

The kinetics of anterior tooth display.

A survey has been presented that correlates measurements of upper lip type, sex, race, and age of dentulous patients with the amount of exposure of the maxillary and mandibular anterior teeth with the lips gently parted and in the resting position. Perhaps the most interesting finding was the gradual reduction in the amount of maxillary central incisor exposure with an increase in age, accompanied by a gradual increase in the mandibular tooth exposure. The importance of the amount of mandibular teeth seen in complete dentures has not been sufficiently emphasized in previous literature.