Aim of study To compare the effect on bone regeneration relative to maintenance period of PTFE membrane in rabbit calcarial defects. Materials and Methods Eight adult New Zealand white female rabbits were used in this study. Four defects were surgically made in their calvaria. Using a trephine bur, 4 'through and through' defects were created and classified into 3 groups, which were consisted of control group(no graft), experimental group 1(autogenous bone)and experimental group 2(deproteinized bovine bone; OCS-BⓇ). The defects were covered with PTFE membrane(CytoplastⓇ). Membranes were removed after 1, 2, 4 and 8 weeks post-GBR in each 2 rabbits. And then, all rabbits were sacrificed, specimens were taken and observed histologically. Results Control group. After 1 week any new bone formation was not evident. After 2 weeks minimum of bridge-shaped new bone are formed. After 4 weeks the defect was filled with new bone, though the regenerated thickness was less than the adjacent bone. After 8 weeks the new bone formation appears incomplete in the bony cavity, with invaded connective tissue on the superficial surface. Experimental group 1. At 1 and 2 weeks the defects were filled with new bone at adjacent bone thickness, but connective tissue was invaded on superficial surface. At 4 and 8 weeks the new bone formation appears complete in the bone cavity without connective tissue and the autogenous bone particle is blended with new bone. Experimental group 2. At 1,2 and 4 weeks the defects were filled with new bone at original bone thickness and appeared light concave on the surface that consists of connective tissue. At 8 weeks the new bone formation appeared complete in the bone cavity without connective tissue and new bone formation around deproteinized bovine bone particle was appeared. Conclusion 1) The use of graft material and membrane was necessary in GBR procedure. 2) When PTFE membranes were removed early, the most favorable bone regeneration was revealed in experimental group I, followed by experimental group II and control group. 3) On GBR, it is recommended that membrane should maintain for 4 weeks with autogenous graft. As well, the use of xenograft need longer maintenance period than autogenous bone.

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