Jon P. Standlee

Retention of endodontic dowels: effects of cement, dowel length, diameter, and design.

The retentive capacity of three preformed endodontic dowel designs was compared at two lengths and two diameters, with three different cements. The greatest single factor influencing retention of these devices was the design used. Of the types tested in this study, the most retentive were threaded, parallel-sided dowels screwed into tapped channels. Serrated, parallel-sided dowels cemented in matched cylindrical channels provided intermediate retention, and smooth-sided tapered posts were the least retentive. Another major factor in retention was the length of imbedment into dentin. An increase in dowel imbedment depth usually corresponded to increased retention. The effect of cement type was significant only with tapered dowels. Zinc phosphate cement was most retentive, carboxylate cement exhibited intermediate retention, and the epoxy cement was least retentive. For the other post designs, cement type had no significant effect on retentive capacity. Finally, variations in dowel diameter had no significant effect on retentive ability.

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.

The retentive and stress-distributing properties of a threaded endodontic dowel

A threaded, parallel-sided endodontic dowel that has a longitudinal split was tested to determine its retention and stress distribution properties. Photoelastic stress analysis revealed high installation stresses unless the dowels were counterrotated. Axial loading created stresses at the threads, with elevated coronal and apical stresses. Even higher coronal stresses were recorded with inclined loads, and shorter dowels generated greater stresses than longer dowels. The retentive values were generally lower than those in comparable studies.

Endodontic dowel retention with resinous cements.

This study compared the capability of three composite resin cements to sustain a standard endodontic dowel. All of the systems incorporated some form of smear layer removal on the dentin of the endodontic channel. One system that used a methyl ethyl ketone drying agent provided inadequate clinical resistance to dislodgment of 5.4 DaN. A second cementing system that used only smear layer removal resisted loads at 54.7 DaN. The third cementing regimen that included a surface-initiated dentinal adhesive and smear layer removal recorded retention of 77.4 DaN. This study supported the concept that passively cemented dowels with composite resin can be as effective as actively seated dowels.

Dowel retention with glass-ionomer cement

The retentive capacity of the Whaledent Parapost system utilizing ASPA cement was compared at two lengths, three diameters, and with respect to the effect of both medication and citric acid pretreatment. The greatest single factor influencing retention was embedment depth into dentin. No significant differences were observed between the retention values for medicated and unmedicated teeth. Finally, no increase in retention was noted over previously reported values for zinc phosphate, carboxylate, and epoxy resin cements. The glass-ionomer cement tested offers no advantage for post retention.

Clinical and Materials Sciences Stress Trajectories within the Mandible Under Occlusal Loads

A human mandible was duplicated in birefringent resin. The distribution and effect of occlusal forces within the mandible was demonstrated utilizing birefringent resin models compared to natural specimens. The results of this study reinforce those theories that assign function a major role in bone remodeling in the mandible. Further, the condyle is seen to be a stress-bearing structure.A human mandible was duplicated in birefringent resin. The distribution and effect of occlusal forces within the mandible was demonstrated utilizing birefringent resin models compared to natural specimens. The results of this study reinforce those theories that assign function a major role in bone remodeling in the mandible. Further, the condyle is seen to be a stress-bearing structure.

Effect of surface design on retention of dowels cemented with a resin

This study compared the retentive ability of endodontic dowels cemented with a resin when the surfaces of the dowels were varied. Dowels of standardized material, shape, length, and diameter were cemented with an unfilled Bis-GMA resin. Four dowel surface configurations were tested: transverse serrated, crosshatched, threaded, and longitudinal spirals. The results indicated that the dowel surface design can significantly influence the retention of a resin-cemented dowel. Dowels with transverse serrations or crosshatching were retained better than dowels with longitudinal spirals or threads.

Dynamic stresses encountered in impression removal

A ccurate dental impressions are essential in dentistry. Elastic impression material is often used to obtain a negative reproduction of the oral tissues and is subjected to complex states of stress as it is removed from the mouth. Undercuts, sharp line angles, and interproximal spaces all influence the elastic deformation of the impression material and are not always under the control of the dentist. On the other hand, certain controllable influences (such as, tray design, bulk of impression material, and rate and direction of removal of the impression from the mouth) may be used to prevent permanent deformations. Previous studieslV3 have resulted in development of a photoelastic modeling material which simulates the physical and mechanical properties of mercaptan rubber. An investigation of this material was undertaken to determine the dynamic stresses encountered during removal of impressions from various geometric designs.

In vitro analysis of self-shearing retentive pins

Combining stress, analysis, microscopic examination, mechanical testing of the shear mechanism, and retention of the Reten Pin leads to the following conclusions: 1. The suggested 0.006 inch pin-channel mismatch induces high lateral and apical stresses. Microscopically, this was seen to correlate with injury to the dentin. 2. The degree of retention was increased by using a smaller pin-channel mismatch. This correlates with smaller stresses and reduced dentinal damage. 3. The shear mechanism acts in a uniform manner, with a relatively small variation from the mean. It is suggested that for the best results the manufacturer should supply larger twist drills and pins with a somewhat deeper self-shearing groove to minimize apical involvement during shearing of the handle from the pin.

Stresses Exhibited in a Hydrocolloid Under Load

A reversible hydrocolloid impression material that exhibits birefringent characteristics was developed. Tests were performed to establish the stress-optic characteristics of the hydrocolloid for use in photoelastic analysis. Physical characteristics are reported which are relevant to the clinician and dental researcher.