Observation of the Bone Mineral Density of Newly Formed Bone Using Rabbits： Compared with Newly Formed Bone around Implants and Cortical Bone

Abstract

There have been many studies reporting that newly formed bone around implants is spongy bone. However, although the morphology is reported as being like spongy bone, it is difficult to discriminate whether the bone quality of newly formed bone appears similar to osteoid or cortical bone;therefore, evaluation of bone quality is required. The aims of this study were to measure the bone mineral density (BMD) values of newly formed bone around implants after 4, 8, 16, 24 and 48 weeks, to represent these values on three-dimensional color mapping (3Dmap), and to evaluate the change in bone quality associated with newly formed bone around implants.
The animal experimental protocol of this study was approved by the Ethics Committee for Animal Experiments of our University. This experiment used 20 surface treatment implants (Ti-6Al-4V alloy:3.1 mm in diameter and 30.0 mm in length) by grit-blasting. They were embedded into surgically created flaws in femurs of 20 New Zealand white rabbits (16 weeks old, male). The rabbits were sacrificed with an ear intravenous overdose of pentobarbital sodium under general anesthesia each period, and the femurs were resected.
We measured BMD of newly formed bone around implants and cortical bone using Micro-CT, and the BMD distribution map of 3Dmap (TRI/3D Bon BMD, Ratoc System Engineering). The BMD of cortical bone was 1,026.3±44.3 mg/cm³ at 4 weeks, 1,023.8±40.9 mg/cm³ at 8 weeks, 1,048.2±45.6 mg/cm³ at 16 weeks, 1,067.2±60.2 mg/cm³ at 24 weeks, and 1,069.3±50.7mg/cm³ at 48 weeks after implantation, showing a non-significant increase each period. The BMD of newly formed bone around implants was 296.8±25.6 mg/cm³ at 4 weeks, 525.0±72.4 mg/cm³ at 8 weeks, 691.2±26.0 mg/cm³ at 16 weeks, 776.9±27.7 mg/cm³ at 24 weeks, and 845.2±23.1 mg/cm³ at 48 weeks after implantation, showing a significant increase after each period. It was revealed that the color scale of newly formed bone was Low level at 4 weeks, and then it chronologically changed from Low level to Medium level, and Medium level to High level in the BMD distribution map.
The bone quality was clarified in the newly formed bone in the implant surroundings from BMD and BMD distribution map, and was lower than that of cortical bone.