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

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.

[Antigen presenting cells during periodontal disease]. / Les cellules présentant l'antigène aux cours des maladies parodontales.

The macrophages have an important function in the presentation of the antigen to the T lymphocytes. This presentation mandatory for the activation of the T lymphocytes is described. The Langerhans cells also play a role in the antigen presentation. These cells especially in the oral mucosa have been studied during the last years.

Clinical evaluation of gingival recession treated by coronally repositioned flap technique.

Thirty-four areas of gingival recession in ten patients were treated by a coronally repositioned flap procedure. All but four of these areas had received a free gingiva graft previously. The postoperative evaluations of the wound healing were made at 2 weeks and at 1, 2, 4, 6 and 12 months after the final surgery. In most cases the amount of gingival recession was reduced with the average tissue gain being 1.82 mm. The gingival sulcus depth was unaffected by the procedure. Several cases showed total root coverage. Although the procedure described has many advantages, the authors feel these must be carefully weighed against the disadvantages before subjecting patients to such surgery.

[Gingivitis and recession in the child (100 cases)]. / Les gingivites et les récessions chez l'enfant (à propos de 100 cas).

An epidemiological study was made on 100 children 5 to 18 years old, from the Paris region, who showed precocious gingival pathology. Then, the various factors, liable to prevent such defects before the point of no return is reached, were investigated. They are hygiene and its type and frequency. The responsibility lies with the dental profession, educators and public dental health services.