Introduction 2 4 8 9 32 41 42 1 27 39 46 5 47 48 38 50 29 25 3 11 15 31 33 49 14 26 33 37 45 34 16 19 21 44 18 19 Therefore, the aim of the present study was to investigate histomorphometrically bone formation to CSA-enhanced and rhBMP-2-biocoated titanium implants after implantation in the mandibula and tibia of dogs in comparison to control titanium implants. Materials and methods Animals Two 3-year-old male mongrel dogs (approximate weight 25 kg) were used in the study. Both animals exhibited a fully erupted, healthy, permanent dentition. During the experiment, the dogs were fed ad libitum with soft-food diet and water. Animal selection, management, and surgery protocol were approved by the Animal Care and Use Committee of Belgrade University (ref. no. 2179). The experimental segment of the study started after an adaptation period of 4 weeks. Study design The study was performed in two surgical phases. In the first phase, extraction of the mandibular second, third, and fourth premolar and first molar (P2–M1) was performed bilaterally. After 4 months of healing, surgical implantation of rhBMP-2-biocoated and rhBMP-2-noncoated screw-typed implants was performed in a submerged healing procedure during the second phase. Throughout the study period, oral hygiene procedures were performed three times a week including tooth and implant brushing. Radiographs were obtained before and immediately after tooth extraction as well as immediately after implant installation. Both animals were killed after a healing period of 4 weeks. Implant preparation 21 43 K 0.5 18 n n 21 21 17 n 2 2 40 18 21 40 n n n n 125 6 6 Surgical procedure for both phases The dogs were anesthetized with 1 mg/kg sodium pentobarbital. To maintain hydration, both animals received a constant rate infusion of lactated Ringer’s solution while being anesthetized. Prophylactic antibiotics were administrated intraoperatively with a combination of 20,000 IU penicillin and 1.0 g streptomycin/10 kg body weight. In the first surgery, P2–M1 were carefully removed after reflection of full thickness mucoperiosteal flaps and tooth separation. After wound closure by means of mattress sutures, the sites were allowed to heal for 4 months. In the second surgery, the test and control implants were randomly allocated to both sides of the mandible (left and right sides, one implant each) and one implant each to either the posterior left or right tibia. In brief, bilateral vestibular incisions were made, and full thickness mucoperiosteal flaps were elevated to expose the respective sites for implant placement in the mandible. Surgical implant sites were prepared bilaterally, at a distance of 10 mm apart, according to the protocol suggested by the manufacturer. All implants in the mandible were sealed with cover screws (Camlog, Wimsheim, Germany). After irrigation, mucoperiosteal flaps were repositioned, and primary wound closure was achieved with consecutive polyglycolic acid 5.0 Polyester sutures (Resorba, Nürnberg, Germany). An area of approximately 15 cm in length and 4 cm in width was depilated on the respective side of the tibia using an electric shaver and a razor blade. After disinfection with polyvidone iodine (Betaisodona, Mundipharma, Limburg/Lahn, Germany), a skin incision was made and a flap was elevated to expose the respective sites of the tibia for implant placement. On the inner-posterior side of the tibias, implants were inserted at a distance of 30 mm apart. All titanium implants were inserted with good primary stability according to a low-trauma surgical technique under copious irrigation with sterile 0.9% physiological saline. After implant placement, the periosteum and fascia were sutured using 3.0 Polyester sutures (Resorba, Nürnberg, Germany). Animal killing and retrieval of specimens 7 Histological and histomorphometric analysis 23 28 Results Clinical observations The postoperative healing was uneventful in both dogs. No complications such as allergic reactions, abscesses, or infections were observed throughout the study period. Histological and histomorphometric analysis 1 2 1 Fig. 1 Lines below and above box plots max control a b c  Fig. 2 a b c d  3 1 2 Fig. 3 a b c d  Discussion 18 21 40 10 40 40 14 26 33 37 45 33 33 45 14 14 34 34 24 22 30 43 Within the limits of the present study, it may be concluded that rhBMP-2 immobilized by covalent and noncovalent methods on CSA-treated implant surfaces seemed to be stable and promoted direct bone apposition in a concentration-dependent manner.