J Periodontal Implant Sci.  2015 Apr;45(2):46-55. 10.5051/jpis.2015.45.2.46.

Effectiveness of biphasic calcium phosphate block bone substitutes processed using a modified extrusion method in rabbit calvarial defects

• Lim HC
• Song KH
• You H
• Lee JS
• Jung UW
• Kim SY
• Choi SH

• KMID: 2329655
• DOI: http://doi.org/10.5051/jpis.2015.45.2.46

Abstract

PURPOSE
This study evaluated the mechanical and structural properties of biphasic calcium phosphate (BCP) blocks processed using a modified extrusion method, and assessed their in vivo effectiveness using a rabbit calvarial defect model.
METHODS
BCP blocks with three distinct ratios of hydroxyapatite (HA):tricalcium phosphate (TCP) were produced using a modified extrusion method:HA8 (8%:92%), HA48 (48%:52%), and HA80 (80%:20%). The blocks were examined using scanning electron microscopy, X-ray diffractometry, and a universal test machine. Four circular defects 8 mm in diameter were made in 12 rabbits. One defect in each animal served as a control, and the other three defects received the BCP blocks. The rabbits were sacrificed at either two weeks (n=6) or eight weeks (n=6) postoperatively.
RESULTS
The pore size, porosity, and compressive strength of the three types of bone block were 140-170 microm, >70%, and 4-9 MPa, respectively. Histologic and histomorphometric observations revealed that the augmented space was well maintained, but limited bone formation was observed around the defect base and defect margins. No significant differences were found in the amount of new bone formation, graft material resorption, or bone infiltration among the three types of BCP block at either of the postoperative healing points.
CONCLUSIONS
Block bone substitutes with three distinct compositions (i.e., HA:TCP ratios) processed by a modified extrusion method exhibited limited osteoconductive potency, but excellent space-maintaining capability. Further investigations are required to improve the processing method.

Keyword

Bone regeneration; Bone substitute; Calcium phosphate

MeSH Terms

Animals
Bone Regeneration
Bone Substitutes*
Calcium*
Compressive Strength
Durapatite
Microscopy, Electron, Scanning
Osteogenesis
Porosity
Rabbits
Transplants
Bone Substitutes
Calcium
Durapatite

Figure

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  Figure 1 Clinical photographs of the animal surgery. (A) Three biphasic calcium phosphate (BCP) blocks were placed in circular defects 8 mm in diameter produced in rabbit calvaria. (B) A disk-shaped BCP block.

• 

  Figure 2 X-ray diffractometry analysis of the three types of biphasic calcium phosphate blocks with hydroxyapatite (HA) and beta-tricalcium phosphate (TCP) at the following ratios: 80:20 (HA80/TCP20, HA80 group), 48:52 (HA48/TCP52, HA48 group), and 8:92 (HA8/TCP92, HA8 group). Both HA and β-TCP peaks were detected in all groups and a weak α-TCP peak was also observed in the HA8 and the HA48 groups.

• 

  Figure 3 Comparison of the contents of crystalline phases of the three biphasic calcium phosphate (BCP) blocks. Both hydroxyapatite (HA) and beta-tricalcium phosphate (β-TCP) phases were observed in all groups, and a small α-TCP phase was also observed in the HA8 and the HA48 groups. HA8, BCP block with a 8:92 ratio of HA:TCP; HA48, BCP block with a 48:52 ratio of HA:TCP; HA80, BCP block with a 80:20 ratio of HA:TCP.

• 

  Figure 4 Scanning electron microscopy photomicrographs of the three BCP blocks: (A) HA8, (B) HA48, and (C) HA80. Uniformly distributed, partially interconnected porous microstructures were observed in all blocks. The pore size of the three blocks varied according to the HA:TCP ratio. HA8, BCP block with 8:92 ratio of HA:TCP; HA48, BCP block with a 48:52 ratio of HA:TCP; HA80, BCP block with a 80:20 ratio of HA:TCP.

• 

  Figure 5 Comparison of the compressive strength and porosity of the three types of biphasic calcium phosphate (BCP) blocks. The bars in the graph indicate the standard deviation of each value. An inverse relationship was found between compressive strength and porosity. The porosities of the HA8, HA48, and HA80 groups were >80%, ~80%, and >70%, respectively. The compressive strength of the blocks was 4-9 MPa. HA8, BCP block with a 8:92 ratio of HA:TCP; HA48, BCP block with a 48:52 ratio of HA:TCP; HA80, BCP block with a 80:20 ratio of HA:TCP.

• 

  Figure 6 Histologic observations at two weeks postoperatively. All biphasic calcium phosphate blocks showed a significant level of space maintenance compared to the control. New bone was observed near the defect margin and the degree of new bone ingrowth was similar among the HA8 (HA:TCP=8:92), the HA48 (HA:TCP=48:52) and the HA80 groups (HA:TCP= 80:20). (A, B) control group; (C, D) HA8 group; (E, F) HA48 group; and (G, H) HA80 group. Hematoxylin-eosin stain. Scale bars: 2 mm for A, C, E, and G; 200 µm for B, D, F, and H. NB, new bone; arrowheads, osteoblasts.

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  Figure 7 Histologic observations at eight weeks postoperatively. No space collapse was observed in the HA8 (HA:TCP=8:92), the HA48 (HA:TCP=48:52), and the HA80 groups (HA:TCP=80:20). Native bone was well incorporated into the blocks. (A, B) control group; (C,D) HA8 group; (E, F) HA48 group; and (G, H) HA80 group. Hematoxylin-eosin stain. Scale bars: 2 mm for A, C, E, and G; 200 µm for B, D, F, and H. NB, new bone; arrowheads, osteoblasts.

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