P.J. van Mullem

Ultrastructural Study of Epithelial Cell Attachment to Implant Materials

Attachment of gingival tissues to the protruding post of an endosseous dental implant is of great importance for the prognosis of its clinical success. Little is known about the requirements an implant material must meet to secure a durable permucosal seal. The objective of this study, therefore, was to gain insight into the morphology of epithelial cell-implant interfaces for a number of well-known or potential implant materials. Guinea pig epithelial cells were cultured on gold, titanium, carbon, hydroxylapatite, carbonate apatite, and modified polystyrene substrates. The metallic and carbon substrates were obtained by vapor-phase deposition of thin films on polystyrene carriers. This technique allowed for the preparation of ultra-thin sections for transmission electron microscopy containing substrate as well as the cells adhering to it. The cultures on apatite were decalcified prior to sectioning. The results revealed that as attachment structures, focal contacts, extracellular matrix contacts, and hemidesmosome-like contacts could be distinguished. Hemidesmosome-like contacts were only observed on apatite and polystyrene and not on the metallic or carbon surfaces. The results of this study suggest the existence of some, as yet unknown, property of the substrate that determines the nature and the structure of the contact site with epithelial cells.

Biodegradation of four calcium phosphate ceramics;in vivo rates and tissue interactions

To prevent exposure of artificial tooth root implants, a resorbable root implant may be developed, that in time will resorb in a vertical direction at the same rate as the alveolar ridge does after the loss of the natural teeth. Implants of four calcium phosphates: rhenanite, β-tricalcium phosphate, hydroxylapatite and magnesium-whitlockite were measured duringin vivo resorption and their interactions with the surrounding tissues at experimental periods of 6 weeks and 3 months were investigated. It was shown that a sequence of progressive resorptionin vitro does not correlate with the resorption rates found in thisin vivo experiment.In vivo hydroxylapatite was found to be less resorbable than magnesium-whitlockite and rhenanite less resorbable than β-tricalcium phosphate. Tissue interactions showed that resorption of the calcium phosphates was positively related to the number of osteoclast-like cells and did not completely correlate with the resorption measurements insofar that most rhenanite implants showed a more reactive peri-implant with the largest number of osteoclast-like cells, strongly affecting the implant surface. In contrast, two rhenanite implants showed intimate contact with bone after initial resorption. Because of this divergent reaction with rhenanite, furtherin vivo investigation on this material is proposed.

Microleakage of Cavit temporary filling material in endodontic access cavities in monkey teeth

Sealing properties of Cavit-W temporary filling material were tested in vivo in the control group of a usage experiment in which root canal disinfectants were studied. Histologic examination (Brown and Brenn staining) of the root canals showed a statistical significance in the occurrence of microorganisms with increase in time. Microleakage past the filling material was considered to be responsible.

Effect of Histological Decalcifying Agents on Number and Stainability of Gram-positive Bacteria

In tests of the effects of restorative materials on dental pulp, it is important that one evaluate bacterial contamination, and this is usually done histologically. Preceding the usual paraffin-embedding of hard-tissue specimens for microscopical investigations, decalcification is performed. To study the influence of decalcifying agents (nitric acid, formic acid, and ethylenediamine tetraacetic acid) on the number and Gram-stainability of bacteria, we used a model system consisting of suspensions of formaldehyde-fixed Streptococcus faecalis. The Gram-positive organisms were stored in distilled water, in 4% formaldehyde solution, or in the decalcifying agents for various experimental periods. Counts were made by means of a hemocytometer, and smears were stained with the Brown and Brenn staining method. After periods which are averages for the decalcification of teeth, severe reductions of both the number and the Gram-positive stainability were found. After one week in formic acid, only one out of 15 organisms stained blue. With nitric acid and EDTA, the reductions were fewer. Since only blue-staining bacteria can be detected clearly in tissue sections, the results of these experiments indicate that, with limited numbers of organisms, the risk exists for false-negative scores for decalcified hard-tissue sections.

Chemical reactions of calcium phosphate implants after implantationin vivo

Sintered microporous cylinders of hydroxyapatite (OHA), tertiary calcium phosphate (β-TCP and rhenanite (CaNaPO4) were implanted in the bone of the forehead of the domestic pig (Sus scrofa). Implants together with the surrounding bone were retrieved after 6 and 12 weeks. X-ray diffraction showed that OHA and β-TCP maintain their crystal structure upon implantation. However, rhenanite is transformed completely into an apatite within 6 weeks. This apatite later incorporates sodium and carbonate. Both β-TCP and rhenanite implants showed some resorption but were otherwise covered with new bone. Electron microprobe analysis showed that the mineral at the interface had a Ca/P ratio characteristic of new bone. At a certain distance from the interface lower Ca/P ratios were found, characteristic of precursor phases of bone mineral. This suggests that the deposition of new bone starts, at least partially, from the surface of the implant. Therefore, β-TCP as well as rhenanite may be called an osteoconductive biomaterial.

In vivo reactions to particulate rhenanite and particulate hydroxylapatite after implantation in tooth sockets

To gain more information on the in vivo behaviour of rhenanite (CaNaPO4), particles of this material and of hydroxylapatite were mixed with gelatin or saline and inserted in tooth sockets of beagle dogs for periods of 3 and 6 months. Rhenanite appeared to transform into an apatite containing carbonate, sodium and magnesium. Resorption of both calcium phosphate particles was not observed histologically and was not shown histomorphometrically. Calcium phosphates were not found in lymph node tissue. The presence of particles in the sockets gave rise to new bone formation. Histomorphometry demonstrated that statistically significant more bone deposition occurred on rhenanite particles than on hydroxylapatite particles. Also gelatin, meant as a spacer, contributed to new bone formation.

Porous acrylic cement for the correction of craniofacial deformities and repair of defects, animal experimentation and two years of clinical application

Abstract A recently developed self-curing porous acrylic bone cement promises a valuable improvement in craniofacial reconstruction. In situ curing and the open sponge-like porosity are advantageous for good contour reconstruction and fixation to the underlying bone. To date 12 selected patients with a variety of craniofacial deformities have been operated on. The preliminary results of clinical work are presented.

Antimicrobial effectiveness in endodontic therapy using formocresol and two new alcoformol agents

Antimicrobial effectiveness of alcoformol two agents (AF 8.85 and AF 3.5) was studied in a clinical trial by means of bacteriologic examination of the root canals. After the initial culture was taken, one of the disinfectants was sealed in the pulp chamber for one week. At the second visit, the root canal was reamed and a second culture was taken. It was found that AF containing 3.5 percent formaldehyde is a satisfactory disinfectant for root canals of vital teeth. A concentration of 8.75 percent was needed for disinfection of teeth with necrotic pulps.

Porous root replacements: reactions of the surrounding tissues

Artificial tooth roots may help to preserve the volume of the alveolar ridge after the loss of the natural teeth. The suitability of mouldable porous polymethylmethacrylate (PMMA) cement to replace tooth roots is examined in an animal experiment. A description of the material, the method of application and the reactions of the surrounding tissues at several experimental periods up to 54 weeks are presented.

Hard-tissue resorption and deposition after endodontic instrumentation

Hard-tissue resorption and deposition following endodontic instrumentation were studied histologically in forty-one monkey teeth after 2, 7, and 42 days. No medicaments and no root canal filling materials were used. The number and length of lacunae and areas of resorption of the root canal wall, the root surface, and the lamina dura were counted and measured. Resorption, stimulated by instrumentation, was observed after 7 days at all sites. Resorption was slight at the root canal wall and at the root surface and was significantly more severe than normal osteoclastic replacement in the adjacent lamina dura. After 42 days the reaction had subsided at the three sites, but none of the tissue had returned to normal. Inflammatory reaction due to infection of the root canal appeared to enhance resorption after 42 days at the root canal wall and the lamina dura, but this was not observed at the root surface.