Bone augmentation by octacalcium phosphate and collagen composite coated with poly-lactic acid cage

Abstract

Objective: Although octacalcium phosphate and collagen composite (OCP/Col) has demonstrated excellent bone regeneration, it has never achieved bone augmentation. The present study investigated whether it could be enabled by OCP/Col disks treated with parathyroid hormone (PTH) and covered with a poly-lactic acid (PLA) cage.

Materials and methods: The prepared OCP/Col disks with three different types of PLA cages (no hole, one large hole, several small holes) were implanted into subperiosteal pockets in rodent calvaria. Histological, and histomorphometric analyses were conducted at 12 weeks after implantation.

Results: Implants with all PLA cage variants achieved sufficient bone augmentation, and analyses showed that new bone was formed from the original bone and along the PLA cage. While the PLA cage variant with no holes sporadically evoked new bone formation even at the central area of the roof of the PLA cage, the PLA cage variants with holes had no new bone in the area of the hole or beneath the periosteum.

Conclusions: These results suggest that sufficient bone augmentation could be achieved by treating the OCP/Col disks with PTH and covering them with a PLA cage, and periosteum might not have been involved in the bone formation in this experiment.

Keywords: bone regeneration; collagen; octacalcium phosphate; parathyroid hormone; poly-lactic acid.

Figure 1

Poly‐lactic acid (PLA) cages of the N, B, and S groups. The PLA cage was 10 mm outside diameter, 8.5 mm inside diameter, 2.5 mm outside height, and 1.5 mm inside height. The cage covered the upper surface and side of the octacalcium phosphate and collagen composite (OCP/Col) disc. The PLA cages had three variants (no hole (N), one large hole (B): φ6 mm × 1, and several small holes (S): φ1 mm × 7), Bars: 3 mm

Figure 2

Implantation procedure of samples. The periosteum of the calvarium was ablated after the incision reached the skull, and a subperiosteal pocket was prepared on the calvarium (a). An octacalcium phosphate and collagen composite (OCP/Col) disk treated with parathyroid hormone (PTH) (1.0 μg/0.1 ml) was covered with a poly‐lactic acid (PLA) cage (sample), and it was placed on the calvarium (b). The sample was inserted into the created subperiosteal pocket by moving it backward on the bone surface and placed under the periosteum so that it was in contact with the bone surface of the calvarium (c). After that the sample was covered with the ablated periosteum and the incision was sutured with absorbable thread to prevent the sample from escaping the subperiosteal pocket (d). Bars: 3 mm

Figure 3

Histomorphometrically analysis of histological sections. Histomorphometrical analysis of the histological sections of the implanted sample discs (a) divided into four areas (b) (lower marginal [LM], upper marginal [UM], lower central [LC], and upper central [UC]). The percentage of newly formed bone (n‐Bone%) was calculated as the area of newly formed bone/the area surrounded by the cage (c, d) × 100 for all areas and the area in each region

Figure 4

Micro‐computed tomography (CT) at 4 and 12 weeks after implantation. The top of the images indicate the skin side, and the bottom is the original bone side. In the N and S groups, radiopacity in the octacalcium phosphate and collagen composite (OCP/Col) implanted area was more abundant than radiolucency in the area at 4 weeks after implantation. After 12 weeks, the increased radiopacity in marginal area was greater than that in central area. In the B group, radiolucency in the OCP/Col implanted area was more abundant than radiopacity in the area at 4 weeks after implantation. After 12 weeks, the radiopacity had increased in the OCP/Col implanted area, but it was still lower than other groups. Bars: 3 mm

Figure 5

Histological results at 12 weeks after implantation for the total area of experimental group. The top of the figure indicates the skin side, and the bottom is the original bone side. It was observed bone augmentation in all groups (N, B, and S), and newly formed bone was extended from the original bone toward the skin side and developed along the poly‐lactic acid (PLA) cage. Bars: 3 mm; B, newly formed bone; P, PLA cage; F, fibrous tissue

Figure 6

Histological results at 12 weeks after implantation in each section by experimental group. The top of the figure indicates the skin side, and the bottom is the original bone side. Each section was composed of upper marginal (UM), upper central (UC), lower marginal (LM), and lower central (LC). Newly formed bone was nucleated by the implanted octacalcium phosphate and collagen composite (OCP/Col) and extended from the original bone toward the skin side and developed along the poly‐lactic acid (PLA) cage. And it occasionally, contacted with the roof of the PLA cage (N‐UM and UC, B‐UM, and S‐UM). It was abundant near the original bone and in the marginal area, and it demonstrated a mosaic pattern (N‐LM and LC, B‐LM and LC, and S‐LM and LC). In the N group, the newly formed bone was contacted with the roof of the PLA cage including central area. (N‐UM and UC). In the PLA holed groups (B and S groups), fibrous tissue filled the hole in the PLA cage and the area near the hole, and there was no bone in the hole of the PLA cage and beneath the periosteum (B‐UC and S‐UC). However, newly formed bone was occasionally observed on the skin side covered by the PLA cage in the S group (S‐UC). Bars: 200 μm; asterisk, OCP/Col; B, newly formed bone; P, PLA cage; F, fibrous tissue

Figure 7

Quantitative analysis of newly formed bone of total area of experimental group. Although n‐Bone% of S group in total area was higher than those of N group and B group, there was no significant difference among these groups

Figure 8

Quantitative analysis of newly formed bone in each section by experimental group. In every group, the percentage of newly formed bone (n‐Bone%) in the lower marginal (LM) area was highest, followed in order by lower central (LC), upper marginal (UM), and upper central (UC). In the N group, the n‐Bone% of UC was significantly lower than those of LM and LC. In the B group, the n‐Bone% of UC was significantly lower than those of LM, LC, and UM. Additionally, the n‐Bone% of UM was significantly lower than those of LM and LC. In the S group, the n‐Bone% of UC was significantly lower than those of LM and LC, and the n‐Bone% of UM was significantly lower than that of LM