Angelo A. Caputo

Analysis of stress distribution by endodontic posts

Abstract Three commonly used endodontic post designs, their lengths, their methods of insertion, and their abilities to transmit occlusal forces to supporting structures were compared. According to this photoelastic stress analysis, post design affects stress distribution. Stresses tended to concentrate under the post shoulder, especially if sharp angles were present. Also ascertained was the fact that the post length should approximate the length of the anatomic crown.

Cementing mediums and retentive characteristics of dowels.

A previous report has contributed information relative to dowel configuration and retention, primarily utilizing zinc phosphate cement.’ This study was initiated to provide dentists with guidelines for the retention of dowels employing various dental cements. Zinc phosphate, the traditional cement, was compared to the newer polycarboxylate and cyanoacrylate cements. Since, in the future, these new cements may have increased utilization, it seemed pertinent to demonstrate how they may fit into the dentist’s armamentarium for cementation of prefabricated dowels.

Evaluation of photoelastic stress patterns produced by various designs of bilateral distal-extension removable partial dentures.

The results of this study showed that: 1. The design of a retainer with a mesial rest in conjunction with a buccal I-bar or a wrought-wire and cast lingual arm exhibited the most favorable distribution of vertically applied forces. 2. Retainer designs with a distal rest tend to move the clinical crown distally and the root mesially at the apex, resulting in horizontal forces in the bone. 3. Placing rests of distal-extension removable partial dentures more anteriorly provides an axis of rotation that directs applied forces in a more vertical direction. 4. The distal rest in conjunction with circumferential retainers developed greater horizontal forces within the supporting structures.

Photoelastic analysis of stress patterns on teeth and bone with attachment retainers for removable partial dentures

This investigation was designed to evaluate the forces developed in supporting structures by removable partial dentures with attachment retainers. The attachments tested were the (1) Sterngold type 7, (2) Dalbo MK, and (3) Thompson dowel. The study utilized a photoelastic model with stress areas recorded photographically. The results showed that: 1. Splinted abutments are indicated when using the tested attachment retainers. 2. With single abutments, the attachment retainers induced distal force on the teeth which resulted in unfavorable horizontal bone forces. 3. The Dalbo MK attachments produced the most force on the edentulous regions and the least force on the abutment teeth. 4. The Thompson dowel and Sterngold type 7 attachment retainers induced similar stress patterns on single abutments and both produced distal abutment forces. 5. The Thompson dowel induced more favorable stress patterns when the abutments were splinted.

The mechanics of load transfer by retentive pins

Abstract Tests were conducted to determine patterns of stress that are developed by placing various kinds of loads on retentive pins. The effects of the types of pins, spacing between the pins, and depth and angle of insertion of the pins were investigated.

Effect of oxidation on ceramometal bond strength.

The ceramometal bond strength between SMG-3 gold alloy and Ceramco porcelain was evaluated using seven different oxidation cycles. The control group was not oxidized. Three groups were oxidized under vacuum at a temperature of 1,925 degrees F. The metal was heated (1) just until it reached temperature, (2) for 5 minutes, and (3) for 10 minutes. The last three groups were oxidized without a vacuum, with the time-temperature heat regimen the same as for the previous three groups. The group using an oxidation cycle without a vacuum and a temperature of 1,925 degrees F for 10 minutes was the only group that statistically differed from the control group.

Effects of overdentures upon remaining oral structures

This study provided the following guidelines in the selection of specific designs for overdenture abutments: 1. The Dolder bar, which exhibits more cross-arch involvement than the Zest anchor, will share the occlusal load across the arch, between the abutments and the supporting structures. 2. The posterior edentulous regions will receive some physiologic stimulation with the Dolder bar, for it shares more stress here than the Zest anchor. 3. The forces on the Dolder bar produce stress directed more apically than that from the Zest anchor. Since this force is better tolerated, use of the Dolder bar may be indicated for a short-rooted tooth with less supporting bone. 4. The greater stress concentrated around the abutment teeth by the Zest anchor makes use of this design in a tooth that is periodontally sound and has a long root structure well imbedded in supporting bone seem logical.

Photoelastic comparison of posterior denture occlusions.

The development of stress patterns was observed within a photoelastic model under complete mandidular dentures. Characteristic stress patterns were related to type of tooth material. Plastic teeth transmitted less force than porcelain teeth. Cusp teeth induced concentrated regions of force within the model that contrasted with the uniform distribution of force observed with flat teeth. The dentist should be aware of the biomechanical problems associated with any posterior denture occlusion in relation to the residual alveolar ridge.

Effects of cooling methods on silver-palladium castings.

Cast metal specimens for three ceramic metals were subjected to two different types of cooling procedures after casting. One method involved the rapid cooling of the casting as soon as the red glow of the button disappeared. The other method allowed the castings to bench cool to room temperature. Hardness, bond strength, and microstructural determinations lead to the following conclusions. 1. Vickers hardness values for W-1 and Rx-91 alloys for each cooling regimen were not significantly different. Statistically higher hardness values were obtained for the quenched specimens of JP-5 alloys compared with the bench-cooled specimens. 2. Cooling of W-1 and JP-5 alloy specimens by quenching resulted in higher bond strengths than for specimens that were bench-cooled to room temperature. However, bench-cooling Rx-91 alloy lead to higher bond strengths than did quenching. 3. For all of the alloys examined, quenching produced a smaller grain structure than did bench-cooling. 4. From the standpoint of the parameters tested and the saving of processing time, quenching of the silver-palladium ceramic alloys examined is the cooling procedure of choice for W-1 and JP-5 alloys.

The relationship of dental cements, pins, and retention

D I. ms, which are retained by the elasticity of dentin, may traumatize the tooth into which they are placed.‘, ” Although cemented pins have a smaller potential for causing trauma, they also have a lower retentive capacity.“, 5 The authors have recently reported some inherent effects of cement type and thickness upon retention of threaded pins.” The foregoing’ work considered only one threaded pin design. These pins were installed into precise channels prepared with a drill press. This led to a consideration of clinically oriented techniques to determine the optimal retention of cemented pins. The purpose of this study was to evaluate the interactions among various pin types, cement types, and channel sizes to determine the most retentive combinations.