Posterior composite Class II restorations: in vitro comparison o! preparation designs and restoration techniques K.J. Donly 1. T.W. Wild 1 M.E. Jensen2 1Department of Pediatric Dentistry University of Texas Dental Branch 6516 John Freeman Avenue Houston, Texas 77030 2Dows Institute for Dental Research University of Iowa College of Dentistry Iowa City, Iowa 52242 Received May 8, 1989 Accepted March 1, 1990 *Corresponding author Dent Mater 6:88-93, April, 1990 Abstract-The aim of this study was to evaluate conservative preparation designs for therestoration of Class II lesions with posterior resin composite. Fourteen primary and 14 permanent molars were obtained. Consenvative modified MO and DO preparations were placed in half the teeth; conventional MO and DO preparations were placed in the remaining teeth. Randomly, a glass-ionomer liner was placed over the exposed dentin in one preparation of each tooth; a calcium hydroxide liner was placed in the remaining preparations. Posterior resin composite was placed in all teeth, and the teeth were loaded with a 17-kg force. Teeth were thermocycled, stored in 37°C water, then immersed in 50% silver nitrate solution and placed in developer. The teeth were sectioned and photographed. Microleakage was calculated according to the depth of dye penetration, on a 6-degree scale. Results demonstrated the conservative modified restorations and conventional restorations, when glass-ionomer liner was used, to have less marginal microleakage, in both primary and permanent teeth, than their calcium hydroxide counterparts. R esin composite has progressed to being one of the most widely utilized contemporary restor- ative materials, over the past 20 years. Resin composite has become accepted due to its excellent esthet- ics, relatively low thermal conduc- tivity, preselwation of tooth st~ctta'e in cavity preparation, and continued advancement in the stability of com- positional properties of the material. More recently, resin composites have been recommended for use as pos- terior restorations. Several studies report success with Class II poste- rior composite restorations, as well as Class I posterior restorations, in prhnary teeth (Tonn and Ryge, 1985; Roberts et al., 1985; Oldenburg et al., 1985, 1987; Nelson et al., 1980). When the placement of a Class II posterior composite restoration is under consideration, the knowledge of an acceptable cavity preparation design is necessary. The specific cavity design for resin composite in primary molars is presently contro- versial. Nelson et al. (1980) reports success using a conventional Class II amalgam preparation. Oldenburg et al. (1985) completed a study compar- ing three different preparation de- signs for posterior Class II resin composite restorations. The first de- sign was a conventional Class I] preparation as suggested by Nelson. The second design was a conven- tional Class II preparation with a 1- mm, 45-degree cavosurface bevel. The thh'd design was a modified preparation in which enamel was re- moved only for access to decay, the cavosurface margin also being bev- eled. Findings demonstrated a fail- ure rate of 21.4% for the modified/ bevel preparation design, 8.3% fail- ure rate for the conventional prep- aration design, and 1.3% failure for the conventional/bevel preparation design after two years. Four-year results demonstrated failure rates of 34%, 15%, and 8.3% for the same restorations, respectively (Olden- burg et al., 1987). These findings were in agreement with a similar study performed by Paquette et al. (1983). Therefore, a conventional Class II preparation with a cavosur- face bevel appeared to be the most widely accepted preparation for pri- mary molars. Obviously, a reduction in the loss of tooth structure, during cavity preparation, would be pertinent to OCCLUSAL BEVEL (0.5- 1.0 ram) ~ ~ MARGIN ROUNDED AXIAL-PULPAL LINE ANGLES OCCLUSAL EXTERNAL BEVEL BEVEL ONPROXIMAL- CAVOSURFACE - BEVEL Fig. 1. Schematic diagram illustrating the conservative modified preparation. 88 DONLY et al./CONSERVATIVE CLASS H RESIN COMPOSITE RESTORATIONS