2.2. Surgical Procedure

All animals were fasted for 48 hours before surgery but were allowed water ad libitum. General anesthesia was achieved by intravenous administration of pentobarbital sodium (30 mg/kg). After orotracheal intubation, the animals were monitored by a heart monitor during the entire course of the surgery.

Buccal and lingual full-thickness flaps were made to expose the alveolar crests of the mandibular premolar regions on both sides. Three premolars (P2, P3, and P4) were hemisected on both sides using fissure burs (Figure 1(a)). The canals of all mesial roots were cleaned and filled with gutta-percha. The coronal parts of the pulp chambers were sealed with resin (Clearfil Core; Kuraray, Tokyo, Japan). The distal roots were carefully extracted using elevators and forceps (Figures 1(a) and 1(b)).

Surgical procedures for hemisectioning of the tooth. Teeth were hemisected (a), and the distal roots were extracted (b). The sockets were then sutured (c), and the extraction sockets recovered well (d) 6 months after surgery.

For each hemimandible, three premolar extraction sites were randomly assigned to one of the following treatments: (1) a covering double-layered collagen membrane (Bio-Gide, Geistlich Pharma AG, Wolhusen, Switzerland) (Bio-Gide group), (2) CPC (Rebone Biomaterials Co. Ltd., Shanghai, China) with a covering double-layered collagen membrane (Bio-Gide+CPC group), and (3) a socket left empty (blank group). To achieve primary healing, the buccal and lingual flaps were repositioned and sutured together using interrupted sutures with nonresorbable suture materials (Figure 1(c)). To prevent postoperative infections, the animals were given penicillin and kept on a soft diet for 7 days. Teeth were cleaned with a toothbrush and dentifriced three times per week for 4 weeks. The sutures were removed 2 weeks after the operation.