The retentive strength of slots with different width and depth versus pins

Pins for direct restorations

Self-threading dentine pins permit the retention of large complex direct restorations but there are problems associated with their placement. Strain and crazing of dentine following pin insertion and pulpal and lateral perforations are common. Perforations can be avoided by operator awareness of tooth morphology. Strain and crazing has been found to be minimized by unscrewing the pin slightly after insertion, by using pins with a tap thread, and by using the smallest pin possible. Twist drill form and dulling affects the pin channel shape which in turn influences pin seating. A lack of standardization of pin and twist drill diameter and length has been implicated as the cause of poor pin retention. Manufacturers, in an attempt to standardize the depth of penetration of pins, have incorporated shoulders at the midpoint of the pin, which has met with varying success. More research in the area of limiting pin penetration is necessary, as well as attempts to improve the quality control of pin and twist drill manufacture.

Parapulpal pins and their effects on the fracture resistance of pin-retained cores

The bending characteristics of various parapulpal pins, the retention of a parapulpal pin in different core buildup materials, and the fracture resistance of pin-retained cores were investigated in an in-vitro study. In amalgam and composite cores, the use of parapulpal pins produced an increase in fracture resistance. The highest fracture resistance values were observed in amalgam cores, and the lowest fracture strength was exhibited by cores of glass ionomer cements (GICs) containing metallic particles. The different parapulpal pins and their flexural rigidity had little effect on the fracture resistance of the pin-retained cores. For extensive pin-retained cores it appears advisable to use GICs with restraint and, particularly in the case of large-scale bridge reconstructions, only after critical examination of the loading conditions.

Retention design for amalgam restorations: pins versus slots

The use of pins or slots to provide retention for amalgam restorations has been shown to be equally effective by some authors whereas the pin method has been shown to be more effective by others. This study was done to determine whether the different methods would be affected by the outline form of the preparation. One hundred forty melamine teeth were prepared in three outline forms determined by the cusp that was removed: (1) mesiopalatal, (2) mesiopalatal and distobuccal, and (3) mesiopalatal, distobuccal, and mesiobuccal cusps. Each outline form was restored with a uniform volume of hand-condensed amalgam with pin or slot retention and milled to an occlusal angle of 30 degrees. A load was placed on the milled occlusion with a stainless steel ball to the point of fracture with an MTS machine. No significant difference was found between the pin or slot design for the outline forms evaluated.

Effect of undercut placement on crown retention after thermocycling

The aim of this study was to examine the effect of undercuts in castings and/or tooth structure on the retention of crowns luted with glass ionomer cement. After routine full-crown preparations had been made in 48 human premolars, wax patterns were fabricated for each tooth. Retentive coves were then produced with a round bur in either the tooth structure or the wax patterns, or in both. One group of teeth and patterns did not receive any undercuts; this was the control group. Castings were made in non-precious metal. All crowns were luted with glass ionomer cement. Half of the samples were thermocycled, and the remainder were kept at 37 degrees C. Crowns were removed using tension (0.012 cm min-1) and the mean bond strengths calculated. The differences in retentive strengths were tested for statistical significance using ANOVA and Scheffe's test. The presence of coves in castings and/or tooth structure significantly increased the retentive strength of castings cemented with glass ionomer, as compared with conventional crown preparations without retentive undercuts. The effect of thermocycling on the retentive strength of castings cemented with glass ionomer was not statistically significant.

Report of the Committee on Scientific Investigation of the American Academy of Restorative Dentistry

Dental research continued to grow during 1988. Unfortunately the quality does not always parallel the quantity of publications. This report obviously does not encompass all of the literature but focuses on studies that are related to trends and to matters that are considered controversial. Likewise the particular interests of the members of the American Academy of Restorative Dentistry were taken into consideration. The subjects covered include periodontics, preventive dentistry, bulp biology, craniomandibular disorders, ceramics, color in restorative dentistry, and dental materials.