James M. Leary

Influence of post dimension on stress distribution in dentin

Stress distribution studies can be helpful in determining the appropriate diameter and length of endodontic posts for specific teeth in select occlusal relationships. This study selected the finite element method to predict distribution of stresses in dentin of an endodontically treated tooth restored with cast post and cores with various post dimensions. Peak dentinal shear stresses occurred adjacent to the post at mid-root. Peak shear stresses were elevated as the length of the post decreased. Peak dentinal tensile stresses occurred in the gingival third of the facial root surface, whereas peak dentinal compressive stresses were evident in the gingival third of the lingual root surface. The distribution of tensile and compressive stresses was not affected with variation in the dimensions of the posts.

Vertical root fracture and relative deformation during obturation and post cementation

There are several speculated etiologies of vertical root fractures such as pressure exerted during post placement and excessive forces during lateral condensation. However, there are no reports comparing these two forces by use of the same measurement system. This study determined and compared on single-rooted teeth (1) the amount of strain to the root that occurs during obturation and post cementation and (2) the incidence of incomplete and complete vertical root fractures occurring during the aforementioned procedures. Canals of 32 extracted maxillary central incisors were step-back prepared. Teeth were randomly divided into negative and positive controls and experimental groups. The amount of root distortion was recorded with a strain gauge during each of the following procedures: (1) lateral condensation, and (2) lateral condensation plus cementation of a cast gold post. Relative deformations were compared statistically. Teeth were examined by transillumination and stereomicroscopy for incomplete and complete fractures and compared among groups. Data showed significantly more relative deformation with placement of a post and loading than with obturation alone. The accumulation of strain from both procedures did not significantly increase incidence of vertical root fractures. The results indicate that stresses from cementation of posts is more likely to cause relative deformation of roots.

An evaluation of post length within the elastic limits of dentin

Posted teeth were evaluated to determine the reinforcement capabilities of various post lengths. The results suggest that as internal tooth structure is removed from the tooth the tooth becomes weaker, that teeth with posts do show more reinforcement than nonposted teeth with the same manipulation characteristics, and that some load transfer appears to exist with cemented posts.

Effect of polyethylene fiber reinforcement on the strength of denture base resins polymerized by microwave energy

This study investigated the effect of addition of polyethylene fibers on the transverse strength, deflection, and elastic modulus of two denture base acrylic resins polymerized by microwave irradiation. Specimens of each resin, Lucitone 199 and Acron MC, were fabricated with 0.0%, 0.5%, 1.5%, and 3.0% fiber loading. Specimens were tested with use of a three-point flexure apparatus with an Instron universal testing machine after storage in water for 10 days at 37 degrees C. The results showed that polyethylene fibers significantly decreased the transverse strength of Acron MC resin and slightly increased the transverse strength of Lucitone 199 resin at a loading of 0.5% by weight. Fiber loading did not significantly affect the deflection and the elastic modulus of either material.

Management of dental patients with bleeding disorders: Review and update

Management of the dental patient who has a bleeding disorder requires an understanding of the normal hemostatic system and the patients specific coagulation defect. This patient group can receive quality comprehensive dental care, provided appropriate preoperative planning and evaluation with the patients physician or hematologist is accomplished. Emphasis should be placed on providing appropriate replacement therapy before the dental procedure, selection of conservative treatment approaches, and use of local hemostatic measures to facilitate hemostasis.

Effect of ultrasonic vibration on post removal in extracted human premolar teeth

The purpose of this study was to determine the effectiveness of ultrasonic vibration in removing Paraposts from extracted teeth. Paraposts were cemented in mandibular premolars to a depth of 9 mm with zinc phosphate cement and the teeth placed in four groups. Group 1 received no vibration. Group 2 received vibration for 4 min, group 3 received vibration for 12 min, and group 4 received vibration for 16 min. Tensile forces were applied to the posts and mean dislodgment forces compared. The mean force (kg) required to dislodge the Parapost in group 1 was 24.92 +/- 1.64 SEM; in group 2, 25.01 +/- 1.80; in group 3, 24.08 +/- 2.29; and in group 4, 12.41 +/- 2.60. There was a significant difference between group 4 and groups 1 to 3 (p = 0.0003). Results of this study indicate that 16 min ultrasonic vibration is an effective method for removing Paraposts from human premolar teeth.

Load transfer of posts and cores to roots through cements

This study evaluated differences in load transfer when cast posts are fixed to roots with different cements. Cast posts and cores were cemented with 40 endodontically prepared teeth by using four different cement mediums. The load exerted on the root surface through the post was evaluated using a strain gauge. The increased flexure after cementation was statistically analyzed. In conclusion, there was load transfer from post to root structure when posts were cemented, but no difference was found between cementation mediums.

Multiple cast post and cores for severely worn anterior teeth.

A technique has been presented to simplify the fabrication of multiple direct post and core patterns. When combined with techniques for indirect provisional restorations, this technique merely requires the fabrication of an additional plastic template to form the direct core patterns.

Evaluation of the fracture resistance of a wrought post compared with completely cast post and cores

The intraradicular fracture of a post and core presents a difficult and often unrestorable situation. Attempts to prevent this problem involved the use of materials with increased physical properties. The use of a preformed wrought post with a core cast to it may provide a more fracture-resistant foundation. This investigation compared a commercially available noble alloy-wrought post that had a gold core cast to it with completely cast specimens from three different alloys. A standard pattern was designed to simulate a post and core that would be used in a tooth of limited length and canal space. Patterns were cast and fixed to custom holding devices. Each specimen was subjected to a shearing force until catastrophic failure in a universal testing machine. Significant differences were noted among the groups.

Die recovery technique

A separating disk is used to make proximal cuts and cuts on the underside surface of the cast. The dies can be recovered without damage to the margins.