Retention of Class 3 composite restorations: retention grooves versus enamel bonding

This study compared the tensile loads required to dislodge class 3 composite restorations with and without retention grooves. Thirty extracted human maxillary central incisors were divided into two groups of 15 teeth each. A C-shaped class 3 preparation with lingual access was cut into one approximal surface of each incisor to standardized dimensions using a #329 bur. A 0.5-1.0 mm 45 degrees bevel was prepared on the lingual and gingival enamel margins. In one group, an incisal retention point and a gingival retention groove were prepared with a #1/4 round bur to a depth of 0.25-0.5 mm; the other group had no retention grooves/points. A nonretentive 2 mm round "well" with diverging walls was cut 0.5-1.0 mm into the axial dentin to accommodate the head of a pin that was inserted prior to composite restoration. Each pin shaft extended approximally from its incisor. A bonding agent (Universal Bond 3 Primer and Adhesive, L D Caulk) was applied to each preparation, and composite resin (Prisma APH, L D Caulk) was inserted incrementally. Each increment was exposed to 40 seconds of polymerization light. Restoration surfaces were finished and polished with Sof-Lex disks (3M Dental Products). Specimens were thermocycled 6 to 60 degrees C, for 500 cycles, with a 30-second dwell time. They were then positioned in an aligning device, and pins were loaded in tension in an Instron Testing Machine at a head speed of 2 mm/minute to restoration failure. Mean (SD) failure loads in Newtons were: no grooves 83.6 (19.8); grooves 69.6 (18.1).(ABSTRACT TRUNCATED AT 250 WORDS)