Ultrastructural demonstration of the importance of crystal size of bioceramic powders implanted into human periodontal lesions

Abstract

Stages in bone formation were studied ultrastructurally after the implantation of the following 3 bioceramic powders into human periodontal lesions: (1) beta-tricalcium phosphate whitlockite (Synthograft) consisting of particles with a mean length of 229 +/- 87 microns in SEM and appearing in TEM as crystals with a mean diameter 488 +/- 192 nm; (2) an hydroxyapatite (Bioapatite) which consisted of particles with a mean length of 283 +/- 87 microns in SEM and of crystals with a mean diameter of 146 +/- 47 nm in TEM; and finally (3), a microsized hydroxyapatite consisting of elongated platelets with a mean length of 32 +/- 4 microns in SEM, composed of small crystals with a mean diameter of 38 +/- 16 nm in TEM. In a preliminary experiment in rats, it appeared that the microsized hydroxyapatite implanted into the alveolar region after first molar extraction exhibited biocompatibility. In 6- and 12-month biopsies, it appeared that bone formation in association with the 3 bioceramics tested in human periodontal lesions occurred through similar mechanisms at the ultrastructural level. After the appearance of peripheral fibroblast-like or osteoblast-like cells with an interposed layer reminiscent of an osteoid tissue, collagen fibrils were observed in the intercrystalline spaces. These spaces subsequently underwent mineralization, with deposition of bone apatite crystals followed by the peripheral deposition of a thin inner bone layer with a granular appearance and an outer normal bone layer of either woven bone, lamellar bone or bone with parallel calcified collagen fibrils. These bone nodules, however, formed around the bioceramic particles at highly variable time intervals. Bone formation was observed around Synthograft and Bioapatite implants only in 12-month biopsies, and thicker layers of peripheral bone were observed with the latter hydroxyapatite implant. With microsized hydroxyapatite, a significant amount of peripheral bone formation had already occurred by 6 months, strongly suggesting an important effect of crystal size on bone formation.

Long-term bone response to particulate injectable ceramic

“…This would suggest a mechanism of centrifugal mineralization, that is, a process starting on the surface of ceramic particles and proceeding into the tissue around, as already mentioned in former studies. 19,20 Before being covered by osteoblastic cells, these grains, loose in the bone marrow, probably were subjected to degradation by a solution-mediated process or by cell-mediated dissolution, as observed at earlier evaluation times. This hypothesis would support the concept that partial dissolution of the ceramic precedes mineral reprecipitation in the core and at the surface of ceramic grains and thus would be a prerequisite for bone apposition.…”

Effects of Hydroxyapatite Particles on Periodontal Ligament Fibroblast‐Like Cell Behavior

“…10 However, the complexity of a periodontal bone defect and the numerous factors involved in healing and repair," as well as the discrepancies between data from animal and human experiments, make it difficult to have a clear understanding of the cellular processes which occur in periodontal regeneration when calcium phosphate substitutes are used. 8 As in studies of bone cells or gingival fibroblasts,1215 in vitro investigations facilitate analysis of the effects of HA on periodontal ligament fibroblastic cells in implant colonization and matrix deposition after selection and characterization of cell subpopulations. [11][12][13][14][15][16] The purpose of this study was to investigate the effects of HA particles (< 20 pm) on human periodontal fibroblastic cells.…”

Augmentation of Bone Tunnel Healing in Anterior Cruciate Ligament Grafts: Application of Calcium Phosphates and Other Materials

“…The adsorption of particles on the surface of CaP is related to its crystallinity and influences the biological response to the material. CaP powders of different sizes have been shown to produce differing rates of bone formation in vivo [30]. The reader is referred to a review of bioceramics for more information on general uses and properties of CaP [31].…”