James T. White

A photoelastic analysis of the stress distribution in bone supporting fixed partial dentures of rigid and nonrigid design.

Within the limitations of the experiment, the following conclusions can be made from this investigation: 1. Under conditions of vertical loading, the rigid fixed partial denture design does not permit independent response by either abutment. The nonrigid fixed partial denture design allows the abutments some independence in response to vertical loading 2. The stress distributions and concentrations produced in the supporting bone are favorably altered by the placement of a fixed partial denture of rigid or nonrigid design. 3. The distribution of stresses in the supporting bone varies with the number and location of the loading sites. 4. Under conditions of vertical loading, the Ney and Stern nonrigid fixed partial denture designs exhibit no significant differences in stress distribution or concentration.

Accuracy of an earpiece face-bow

The validity of the Hanau ear-bow to transfer an arbitrary hinge axis to a Hanau articulator was clinically compared with a Hanau kinematic face-bow. The study was conducted with 18 randomly selected patients. This investigation demonstrated a significant statistical difference between the arbitrary axis located with an ear-bow and the terminal hinge axis. This discrepancy was significant in the anteroposterior direction but not in the superior-inferior direction. Only 50% of the arbitrary hinge axes were within a 5 mm radius of the terminal hinge axis, while 89% were within a 6 mm radius. Furthermore, the ear-bow method was not repeatable statistically. Additional study is needed to determine the practical value of the arbitrary face-bow and to pursue modifications to improve its accuracy.

Technique for cranioplasty prosthesis fabrication

A technique has been described for fabrication of a cranioplasty prosthesis. The primary advantage of this technique is the duplication of the altered working cast. The technique also permits excellent reproduction of cranial contours and a positive seat of the prosthesis on the outer table of the skull. The disadvantage is the time involved in the duplicating procedure.

Visualization of stress and strain related to removable partial denture abutments.

The following conclusions are based on the conditions set forth in this investigation and apply to forces acting through a vertical direction of application only: 1. The unilateral removable partial denture produced no more stress than the bilateral removable partial denture. 2. The fully active Dalbo removable partial denture resulted in the greatest stressbreaking action. 3. The rigid Dalbo removable partial denture resulted in the least ridge displacement. 4. The rigid Dalbo removable partial denture resulted in the greatest stress concentrations in the distal abutment. 5. None of the attachments tested resulted in a distribution of the stresses along the edentulous ridge. 6. The use of two abutments (double abutments) resulted in greater stress concentrations in the distal abutment than the use of single abutments. 7. Forces in the single abutment were resisted along the long axis of the root. 8. Forces in the double abutments were resisted along the long axis of the distal abutment.

Modification of stresses surrounding abutment teeth for fixed partial dentures induced by various levels of periodontal support: A photoelastic study

A photoelastic replica system was used to study stresses produced within the periodontium of abutment teeth for a fixed partial denture. Three replicas, each representing a different level of periodontal support, were constructed. Abutment teeth were subjected to occlusal forces and examined in a polariscope before and after prosthesis construction. Stress distributions and concentrations produced in the periodontium of abutment teeth by an occlusal force were favorably altered by the placement of a fixed partial denture. Stress concentrations produced in the periodontium of abutment teeth were notably altered by a moderate (20%) loss of support. Further (40%) loss of periodontium did not result in appreciably additional change. The stress patterns produced in the periodontium of both replicas which simulated loss of periodontium were also favorably altered by the placement of a fixed partial denture.

Effect of cavity varnish on retention of cemented cast crowns

C avity varnish is applied to prepared teeth before cementation of a cast restoration with zinc phosphate cement for pulpal protection and attenuation of postoperative sensitivity. Dentinal permeability to constituents in acid-containing cements is significantly reduced by the application of a cavity varnishle3 and marginal microleakage is decreased.4 It is unknown, however, whether these advantages are outweighed by the effects of varnish on the retention of the restoration or prosthesis. Cavity varnish has been shown to reduce the retention of cemented pins’ and decrease the tensile bond between two opposed dentinal surfaces when zinc phosphate is used as the luting agent.’ Others have reported no significant difference in the retentive values for inlays cemented into varnished and unvarnished preparations.’ The purpose of this investigation was to compare the retention of full veneer crowns cemented on prepared teeth to which a cavity varnish had been applied with that of crowns cemented on prepared teeth that were unvarnished.

Abutment stress in overdentures

Abstract Using a three-dimensional photoelastic model, the relative merits of five overdenture retainers were compared. The soft liner system produced the highest stress concentrations. The retainer systems with intimate contact between the denture base and the abutment tooth showed similar stress concentrations. Relieving the denture base adjacent to the male portion of the retainer could reduce the stress pattern materially and thereby provide a vertical space between the denture base and the abutment tooth. The resultant vertical stress-breaking effect did not affect the edentulous ridge-bearing area in any manner.

Fabrication of an alloplastic implant for the cranial defect

This article describes the presurgical fabrication of an inlay/onlay alloplastic cranial implant prosthesis. The technique eliminates the need to modify an artificial stone master cast, thus simplifying the technique and decreasing the laboratory time involved. The final prosthesis replaces lost cranial contours and has a positive seat on the unaltered cranium adjacent to the defect.

Multisectional mold for fabrication of prosthetic ears

The use of a multisectional stone mold is advocated for the fabrication of prosthetic ears. Less force is required in the deflasking procedure with this technique, reducing the risk of fracturing the mold or tearing the prosthesis. This technique requires more time and care in the flasking procedure. Convergence of the sections is of particular importance. The potential for multiple section lines may result in a need for more surface finishing of the prosthesis.