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Biomedical subjects

J Hemmerle

Publications and source records attributed to J Hemmerle.

10 recordsLinked to original sources
PubMed1992

Effects of carbon dioxide, Nd:YAG and carbon dioxide-Nd:YAG combination lasers at high energy densities on synthetic hydroxyaptite.

The aim of this study was to determine the crystalline structure and chemical alterations of synthetic hydroxyapatite after irradiation with either CO2, Nd:YAG or CO2-Nd:YAG combination lasers at high energy densities of 500-3,230 J.cm2. Further, dissolution kinetics of the lased material were analysed and compared with those of unlased apatite. Electron microscopy showed that the lased material consisted of two kinds of crystals. From the micrographs their diameters varied from 600 to 1,200 A and from 3,000 to 6,000 A, respectively. The larger crystals showed 6.9-Angström periodic lattice fringes in the transmission electron microscope. alpha-Tricalcium phosphate (TCP) was identified by X-ray diffraction. Selective-area electron diffraction identified the large crystals to consist of tricalcium phosphate while the smaller crystals were probably hydroxyapatite. Assays of dissolution kinetics showed that at these high energy densities lased material dissolved more rapidly than unlased synthetic hydroxyapatite due to the higher solubility of TCP.

Aluminum Silicates↗
PubMed1991

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.

Adult↗
PubMed1991

Bacterial invasion of periodontal tissues after experimental immunosuppression in rats.

A moderate gingivitis was produced in 3 groups of 10 adult Wistar rats with diet 2000 of Keyes and Jordan (1964) delivered for 30 days with a controlled feeding unit. The first group served as untreated control. The second group received 5 intraperitoneal injections of cyclosporine A (15 mg/kg body weight) from day 20 to 30 to interfere with the activation of T lymphocytes and interleukin synthesis. The third group received 2 intraperitoneal injections of cyclophosphamide (100 mg/kg on day 20 and 25) which induced a severe neutropenia. The gingival areas between the upper molar regions were prepared for light and transmission electron microscopy. In the untreated control group, a layer of polymorphonuclear neutrophils (PMN) was observed between the dental plaque and the junctional epithelium with a round cell infiltration in the superficial connective tissue. No bacterial invasion was observed. In the cyclosporine group, despite the action on T lymphocytes, no bacterial invasion occurred, but a differentiated PMN layer was present between the apical dental plaque and the junctional epithelium. In the cyclophosphamide group an important bacterial invasion was observed in the interdental epithelium as well as in the underlying connective tissue. In the local absence of PMNs, a mixed flora of Gram positive and negative bacteria of various shapes invaded epithelial as well as connective tissue cells and came in contact with the alveolar crestal bone. Resorption of the alveolar crestal bone scored according to the Keyes and Gold method (1955) was significantly more important in the cyclosporine and the cyclophosphamide group when compared to the controls (p less than 0.05). No statistical difference in bone resorption was noted between the cyclosporine and the cyclophosphamide groups. It can be concluded that the PMN layer constitutes the first line of defense opposed to bacterial invasion of the periodontal tissues.

Alveolar Bone Loss↗
PubMed1989

Ultrastructural study on human root caries.

Superficial root caries lesions of incisors and premolars of 24 patients aged 52-60 years were studied by scanning electron microscopy and transmission electron microscopy. In the predominantly gram-positive bacteria of the root dental plaque, a great number of corncob configurations were observed. Bacterial infiltration into cementum occurred without any gradient of demineralization and mainly followed the borders between calcified cementum bundles as well as incremental lines. The narrow channels which were filled initially by a single row of gram-positive bacteria broadened progressively with simultaneous destruction of the apatite minerals and the collagenous matrix. Root dentin invasion showed great similarities to coronal dentin with an important gradient of demineralization. In the deep layers, sclerosed tubules contained sometimes rhombohedral crystals. In more superficial layers, bacterial invasion occurred initially in still partially sclerosed tubules. Tubular lumens as well as lateral side branches which had lost their peritubular dentin were filled with gram-positive microorganisms. An important diffuse destruction of the apatite minerals was observed at this stage in the intertubular dentin which still presented typical cross-banded collagen fibrils. The confluence of enlarged dentinal tubules filled by numerous microorganisms led to large bacterial zones with complete destruction of root dentin.

Bacteria↗
PubMed1989

[The role of mechanical factors in the development of cervical wedge-shaped erosions].

The surface of single or multiple cervical wedge-shaped defects was studied with a scanning electron microscope. After an initial stage during which the root surface became smooth and polished, the developed lesions had an angular shape with the presence of one or several grooves of 0.2 to 0.3 mm in width at the angle vertex. The presence of these grooves forming horizontal gutters strongly suggested the existence of a horizontal brushing movement. Beside these large grooves, a more or less parallel network of fine striae was observed. The lesion surfaces consisted of dentin with obliquely oriented tubules which were not completely sclerosed. Relatively thin bacterial layers were present on these surfaces. The presence of horizontal wear gutters seemed to confirm the traumatic origin of the wedge-shaped defects connected with toothbrushing.

Adult↗
PubMed1987

Transmission electron microscopy of lattice planes in human alveolar bone apatite crystals.

Periodic fringes corresponding to six different lattice planes have been observed in apatite crystals of human normal alveolar bone by transmission electron microscopy. Three of these sets of fringes have spacings less than 3.5 A corresponding to the Scherzer resolution of the microscope used. The (0002) lattice plane of hydroxyapatite of 3.4 A d-spacings, the (2111) lattice plane with a d-spacing of 2.81 A, and the (3030) lattice plane with a d-spacing of 2.72 A have been identified. The (0002) and (2121) lattice planes have been observed for the first time in bone microcrystals. Some of the crystals studied were characterized by a mean width/thickness ratio of 6.91, typical of platelike habit, whereas observations of crystals aligned along the (1210) and (1211) directions showed a needlelike habit. The mean length of the bone apatite crystals was 470 A. A dark line similar to the one observed in enamel and dentine crystals was also seen. The bone microcrystals observed have shown a high sensitivity to beam damage.

Adolescent↗
PubMed1987

[Ultrastructural study of bone formation after bioapatite implantation in man].

Synthetic hydroxyapatite crystals (Bioapatite) were implanted in a vestibular longitudinal groove made in the alveolar bone, the periodontal membrane and the superficial root dentine of 2 human canines in the absence of periodontal disease. The healing process was followed in scanning as well as in transmission electron microscopy. At 6 months, the aggregate of synthetic hydroxyapatite crystals was surrounded by a fibrous connective tissue, devoid of inflammatory cells. Small apatite crystals, similar to the neighbouring bone crystals, were deposited between the Bioapatite crystals in the central area of the aggregates. These small crystals filled the intercrystalline spaces from the center to the periphery. The mineralization extended then directly in the collagen matrix (osteoid tissue) surrounding the synthetic apatite aggregates. Bone tissue was thus formed around the apatite implants. At 1 year, the thickness of the bone tissue formed around the synthetic hydroxyapatite aggregates was increased. It consisted of bone with a well-oriented collagen matrix, with osteocyte lacunae, osteocytes and interosteocytic canaliculi, with normal ultrastructure.

Alveolar Process↗
PubMed1987

Scanning electron microscopic search for peritubular dentine in some early perissodactyls.

A scanning electron microscopic study has shown the presence of a typical layer of peritubular dentine in Hyrachyus. An homogeneous ring-shaped layer in continuity with intertubular dentine and considered as peritubular dentine despite its acid resistant character was observed around the lumens of dentinal tubules in Protungulatum, Tetraclaenodon and Propachynolophus maldani teeth; there is some evidence that the acid solubility of peritubular dentine has been altered during fossilization. No peritubular dentine was found in Phenacodus, Hyracotherium or Homogalax.

Animals↗