Comparison of accuracy of multiunit one-piece castings

An investigation was conducted to evaluate the accuracy of one-piece castings of FPDs consisting of three, four, and five units with a ceramometal alloy cast in a large circular ring. A three-piece aluminum mold with stainless steel dies simulating the various lengths of the FPDs was used. A total of 18 castings, six castings for each FPD, were fabricated. Marginal discrepancies of the castings on the dies and the length of the castings were compared before and after sectioning the castings at the connectors. The following conclusions were drawn from the study. Seating of the castings improved approximately 50% after sectioning, which indicates that the castings were distorted. The distortion was a three-dimensional phenomenon, with the greatest discrepancy on the mesiogingival surface of the anterior retainer and on the distolingual surface of the posterior retainer. The distortion was least for the three-unit FPDs and greatest for the five-unit FPDs. The lingual-facial diameter of the castings at the gingival axial line angle was significantly larger than the dies in most cases. The mesiodistal diameter of the castings at the gingival axial line angle was smaller than that of the dies but was only significant with the three-unit FPDs. Although the castings were slightly oversized or undersized, the primary reason the castings did not seat was warpage.     

Changes in distribution of some crucial elements in masseter myofibers following surgically induced trauma

Experimentally induced surgical trauma of the masseter muscle in rats led to changes in the distribution of some crucial intracellular elements as determined by microprobe analysis. Sulfur, phosphorus, and potassium values were lowered while sodium and chlorine levels were elevated. These changes were accompanied by increased formation of ice crystal artifacts in myofibers. The findings suggest that trauma causes alterations in cytoplasmic macromolecules and in the state of water in the cells. The method of analysis provides a means for the further evaluation of antiinflammatory drugs.     

A method for determining adequate resistance form of complete cast crown preparations

A diagram with various degrees of occlusal convergence, which takes into consideration the length and diameter of complete crown preparations, was designed as a guide to assist the dentist to obtain adequate resistance form. To test the validity of the diagram, five groups of complete cast crown stainless steel dies were prepared (3.5 mm long, occlusal convergence 10, 13, 16, 19, and 22 degrees). Gold copings were cast for each of the 50 preparations. Displacement force was applied to the casting perpendicularly to a simulated 30-degree cuspal incline until the casting was displaced. Castings were deformed at margins except for the 22-degree group. Castings from this group were displaced without deformation, and it was concluded that there was a lack of adequate resistance form as predicted by the diagram. The hypothesis that the diagram could be used to predict adequate or inadequate resistance form was confirmed by this study.     

Arthrogryposis multiplex complex involving the temporomandibular joint

A case of arthrogryposis multiplex complex involving the temporomandibular joints is reported. The anatomy and physiopathology of the arthrogrypotic articulation are reviewed. The role of biomechanical factors in the development and maintenance of joint surfaces is discussed. Treatment modalities are proposed.     

Human blood pressure and pulse rate response to racemic epinephrine retraction cord.

1. The pulse rate of patients after application of racemic epinephrine-impregnated retraction cords depends more on the level of anxiety and stress than on the level of the epinephrine. 2. Blood pressure is elevated by placement of racemic epinephrine-impregnated retraction cords upon an exposed vascular bed or lacerated tissue. 3. Four percent racemic epinephrine-impregnated retraction cords cause less elevation of blood pressure than 8% racemic epinephrine cords. 4. Although the elevations in blood pressure from 8% cord occur within a narrow range, this range may be hazardous to cardiac patients. Therefore, 4% racemic epinephrine cord should be used. 5. A desirable amount of tissue retraction is produced by 4% racemic epinephrine cord. 6. Dry cords do not provide adequate retraction of tissue and are contraindicated for tissue-retraction purposes.     

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.     

Condylar position following mandibular advancement: Its relationship to relapse

Forty-one patients who elected to receive a bilateral sagittal osteotomy to advance the mandible were examined clinically and radiographically to assess condylar position preoperatively and at three specific times post-operatively. Parameters designed to measure changes in condylar and distal fragment position were located on tracings and digitized for statistical analysis. Changes in distal fragment position included advancement and clockwise rotation during the surgical interval and significant posterior relapse with continued clockwide rotation during the period of maxillomandibular fixation. A small amount of counterclockwise rotation associated with interocclusal splint removal was seen following fixation release. No significant condylar movement was seen during the surgical interval. During the period of maxillomandibular fixation, both condyles exhibited a significant superior movement, and the left condyle also moved posteriorly. No changes in condylar position were noted following release of fixation. The clinical significance of these condylar movements is not clear. Despite minimal changes, 18 patients, six of whom had had no preoperative symptoms and one of whom had exhibited reciprocal clicking, complained of temporomandibular joint pain or noise postoperatively. This suggests that maintenance of condylar position during surgery may not prevent temporomandibular joint dysfunction. In addition, the observed 37% relapse in surgical advancement in the absence of significant condylar distraction implies the interaction of other factors in the relapse process.     

Effect of brushing and thermocycling on the shade and surface roughness of CAD-CAM ceramic restorations

Statement of problem

The effects of toothbrushing (B) and thermocycling (TC) on the surface texture of different materials with various fabrication processes have been investigated. However, studies of computer-aided design and computer-aided manufacturing (CAD-CAM) ceramic restorations are limited.

Influence of immediate dentures on oral motor skill and speech.

An investigation was designed to test whether the precision of finely coordinated orofacial movements is influenced by the transition from natural to artificial dentition. The oral motor skill of 16 patients was tested before extraction and within 2 weeks of wearing immediate dentures. Speech recordings were employed to detect changes in voice quality and speech sound production. Results showed that the loss of natural teeth and the wearing of immediate dentures did not alter sensorimotor pathways significant to the precision of oral motor skills. It was also determined that physical characteristics of dentures are significant factors in the production of acceptable speech.     

Effect of splinting on abutment tooth movement

The effect of splinting on abutment tooth movement was investigated in an in vitro study. An acrylic resin mandibular model with missing molars and a removable partial denture framework were constructed. The roots of the premolars and edentulous ridges were coated with silicone rubber. A modified Ney surveyor was used for load application, and abutment tooth movement measurements were made with a macroperiodontometer. Four conditions were tested by applying unilateral loadings: 1. Single abutments of both sides 2. Load side double abutment 3. Nonload side double abutment 4. Double abutments of both sides The results showed that a significant decrease in the magnitude of movement resulted when the abutment teeth were splinted.