Minimal intervention dentistry-a review. FDI Commission Project 1-97

Bond strength of repaired anterior composite resins: an it>/it> study

The accuracy of four types of elastomeric impression materials was studied as a function of model location, time of pouring, and repetition of pouring. There was little change in dimension among abutment preparations for all materials, for all times of pour, and with a repeat pouring. It appears that measurements between posts are not sensitive to detecting differences between materials and that other dimensions should be examined to discern where differences might lie. The diameter of the stone post was larger than the standard for the AS and PS materials and was unchanged or smaller than the standard for the CS and the PE. The vertical dimensions of stone posts were, in general, shorter than the standard for all materials, with the AS demonstrating the smallest change. The AS and CS products demonstrated the best recovery from undercuts and the least change in dimensions between an initial and second pour of an impression. The AS and PE were the least affected with delays of 1, 4, and 24 hours in pouring the impression.

Accuracy of four types of rubber impression materials compared with time of pour and a repeat pour of models

Differences in the flexural strength of composites (P-30) repaired with four different adhesive techniques were determined and compared to the flexural strength of unrepaired specimens. Besides investigating the effects of differences in repair methods, both the effect of composite age at repair time and the effect of water storage on flexural strength were evaluated. No significant differences were found between specimens which had been stored for different times (1 or 60 days) before they were repaired. All specimens, including the unrepaired ones, became weaker with time in water. After both 90 and 360 days at 37 degrees C in water, the strength of the repaired specimens ranged between 25 and 50% of the strength of the unrepaired specimens. The weakest group was the one which had been repaired after acid etching, water rinsing, and air drying only.

Variables influencing the repair strength of dental composites.

Five elastomeric impression materials were evaluated: two polysulfides (one lead-cure and one non-lead cure), two silicones (one condensation polymerization and one addition polymerization), and one polyether. These materials were subjected to simulated clinical conditions. Two techniques were evaluated. All materials were evaluated initially with use of a custom tray and manufacturers' adhesive. A second evaluation was performed without using the tray system. Both techniques were subjected to statistical comparison. Conclusions of the research were as follows: 1. All impression materials that were poured immediately and evaluated using a custom tray and adhesive consistently demonstrated superior results in comparison to those tested without the custom tray. 2. Polyether material consistently yielded superior results with or without a custom tray when compared to the other impression materials. The additional polymerization silicone ranked second, followed by the lead-cure polysulfide and the condensation polymerization silicone, respectively.

Comparison of elastomeric impression materials used in fixed prosthodontics

The accuracy of stone casts produced from nine elastomeric impression materials was determined. One polysulfide, five silicone, and two polyether elastomer impression materials were used to compare the accuracy of stone casts reproduced from a master model. The most accurate casts were produced from the polyether rubbers and when the cast pour was delayed for a week, this impression material remained accurate.

https://jada.ada.org/article/S0002-8177(74)93042-6/pdf

Accuracy of casts produced from the three classes of elastomer impression materials

B efore deciding whether to entirely remove and replace a defective restoration or to attempt repair of a defect, the dentist must consider a number of factors. Complete removal and replacement will result in a uniformly cohesive restoration. However, the potential trauma of total re-treatment may be unwarranted. Problems associated with an original cavity preparation close to the pulp or with the management of previously placed retentive pins can occur. Additive repair would be less costly and traumatic but gives rise to concerns about bond strength at the site of repair and the long-term clinical acceptability of the repaired restoration. Numerous in vitro studies have examined the bond strength between matured composite resin and freshly added material.ls5 Even though such bond strengths averaged half or less than those of unrepaired specimens, all of the studies appear to lend support to the concept of additive repair as a viable clinical technique. The purposes of the present study were to (1) measure the interfacial bond strengths of various combinations of a conventional composite resin (Adaptic, Johnson & Johnson, Dental Products Div., East Windsor, N. J.) and a microfilled composite resin (Silar, 3M Co., Dental Products Div., St. Paul, Minn.) and (2) to determine the effects of adherent surface preparation on the flexural bond strengths of the various combinations.

Interfacial bonding strengths of paired composite systems

Effect of zinc oxide-eugenol on shear bond strengths of selected core/cement combinations

T he coronal cast metal restoration continues to be commonly used to restore teeth severely damaged by caries or trauma and to strengthen endodontically treated teeth. Often, however, so little tooth structure remains that a casting could not be adequately supported and retained (either coronally or within the root canal) without an intermediate buildup with a suitable dowel or core. Important factors related to the success of a cast restoration are (1) the ‘design and quality of the tooth or core, and (2) the accuracy of the casting.’ Other factors that contribute to longevity and success include (1) the type of core material to which the casting is cemented, (2) the luting medium and its biophysical characteristics, and (3) the degree of bond strength between the cement and the core material.‘-3 In most instances, the core consists of various combinations of dentin and amalgam alloy, composite resin, noble alloy, or base metal alloy. The bond strength of a luting agent to dentin is an important consideration in the success of the cast restoration. It is equally important that the bond strength of luting agents to various core materials be within the range of clinical acceptability. The bond strengths of various luting agents have been widely reported in the literature, usually presented in terms of tensile characteristics.“’ Fewer studies have dealt with the bond strengths to core materials and dentin in terms of shear strength characteristics.6,7 Both shear and tensile strengths are relevant for retention of a casting. The purpose of this laboratory investigation was to compare the shear bond strength of representative luting agents to materials commonly used as cores for cast restorations.

Relative shear bond strengths of luting media with various core materials.

The comparative stability of two removable die systems was evaluated. Under controlled conditions, ten casts, each with two removable dies, were constructed for each system for a total of 20 casts and 40 removable dies. Base-line pre- and postsectioning measurements to within 0.0001 inch in horizontal and vertical planes were recorded and differences calculated. Each die was removed and re-placed 30 times prior to any postsectioning measurement. The results indicated small inconsistent horizontal deviations and consistent vertical deviations for both systems. The Pindex system deviations were slightly less than those of the Di-Lok system, although t test values preclude any conclusion of significance. The results of this investigation indicate the need for dentists and dental laboratory technicians to exercise care in the utilization of any removable die system so as to obtain optimum accuracy and stability in the relationships of the components of that system.

W.E. Dilts

Papers

Accuracy of casts produced from the three classes of elastomer impression materials

Interfacial bonding strengths of paired composite systems

Effect of zinc oxide-eugenol on shear bond strengths of selected core/cement combinations

Relative shear bond strengths of luting media with various core materials.

Comparative stability of two removable die systems.