A histochemical investigation of the bone formation process by guided bone regeneration in rat jaws. Effect of PTFE membrane application periods on newly formed bone.

BACKGROUND: Guided bone regeneration (GBR) has been widely utilized for the promotion of bone augmentation in bone loss areas. However, little information has been available regarding chronological changes in newly formed bone and alterations in the nature of newly formed bone after removal of a barrier membrane. The present study attempted to establish a GBR model for rat maxillae. We also examined the effects of membrane application periods on newly formed bone and its remodeling process after removal of the membrane in this experimental model. METHODS: Thirty-five Wistar rats were divided into 2 groups: a membrane application group and a membrane removal group. The chronological changes of newly formed bone were evaluated histologically and statistically. RESULTS: At 2 weeks after the GBR procedure, bony cavities had completely filled the newly formed bone in the experimental side. In the control side, corticalization on the surface of the newly formed bone proceeded with a decrease in the bone marrow cavity, whereas the bone marrow space had enlarged by 12 weeks post-surgery in the experimental side. In the membrane removal group, the osteoblasts appeared on newly formed bone at 1 week after membrane removal. Comparatively thick compact bone had formed on the surface of the newly formed bone at 4 weeks after membrane removal, and corticalization proceeded later. CONCLUSIONS: The long-term application of a barrier membrane induces the enlargement of the bone marrow spaces. We suggest that PTFE membrane removal in adequate time promotes the corticalization and maturation of the newly formed bone by the GBR technique.

Tissue response to titanium implants in the rat maxilla: ultrastructural and histochemical observations of the bone-titanium interface.

BACKGROUND: The detailed mechanism of osseointegration, the most appropriate implant-bone interface, remains unclear in jaw tissues at the ultrastructural level in contrast to the many reports using long bones. The present study reports on tissue response to titanium-implantation on an animal model using rat maxilla. METHODS: Animals were sacrificed at 1 to 28 days post-implantation and prepared tissue specimens, freed from implants by a cryofracture technique, were processed for transmission electron microscopy and histochemistry for tartrate resistant acid phosphatase activity (TRAPase). RESULTS: Different patterns in bone formation were recognized between lateral and base areas of implant cavities. In the lateral area with narrow gaps, bone deposition took place from the pre-existing bone towards the implant after active bone resorption by osteoclasts reactive to TRAPase. However, no distinct bone formation appeared in the lateral area where the implant had been installed close to the osteotomy margin. On the other hand, new bone formation was found at the base area without any apparent bone resorption. Interestingly, mononuclear cells reactive to TRAPase, presumably preosteoclasts, frequently occurred near preosteoblasts. Osseointegration around the implants was obtained in this model by 28 days post-implantation except for the lateral area with complete contact with implants, where the thin layer remained in contact with the implant surface. CONCLUSIONS: These findings indicate that ossification proceeds at different modes around the titanium implant in rat maxilla, depending on the nature of the recipient bones and the dimension of the gap between the implant and osteotomy margin.

Long-term changes of hydroxyapatite-coated dental implants.

There are many controversies about the long-term prognosis of hydroxyapatite (HA)-coated implants. Failure may be related to compositional and structural changes of the coating occurring during implantation. Two retrieved and two unused HA-coated blade-type implants were examined by stereomicroscopy, secondary electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, and electron probe microanalysis. The objective was to investigate the HA morphology, composition, and structure, and to characterize the changes that occurred in the retrieved implant coatings. Retrieved implants presented partial loss of the coating, especially at the apical and mesiodistal edges. Remaining HA was thick and flattened in the cervical and central areas and gradually thinner and rougher towards the apical and mesiodistal edges. Increase of Cl and Mg, decrease of OH, and X-ray diffraction peak broadening were found in the retrieved implant coatings, in comparison with the unused implants. Morphological changes of the retrieved implants seem to depend on stress values in the surrounding bone and on implant mobility. Compositional changes and increased amount of lattice imperfections appeared in the retrieved implant coatings, as a result of ion substitutions in the apatite lattice. However, the present study could not confirm the influence of these changes on implant failure.

Tissue inhibitor of metalloproteinases-1, matrix metalloproteinases-1 and -8, and collagenase activity levels in peri-implant crevicular fluid after implantation.

The integrity of connective tissues surrounding dental implants may be influenced by a balance between matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs). The purpose of this study was to provide an overall assessment of TIMP-1, MMP-1 and -8 levels as well as collagenase activities during the wound healing process after implantation and in peri-implantitis lesions. Peri-implant crevicular fluid (PICF) was sampled with sterile paper strips from 10 osseointegrated implants of 6 subjects. Ten implants from 6 patients affected with peri-implantitis were also assessed. Gingival crevicular fluid (GCF) from 11 periodontitis-affected patients and 10 healthy volunteers served as controls. TIMP-1 and MMP-1 and -8 protein levels in the PICF were measured by ELISA, and active and APMA-activatable collagenase activities were determined by functional assays using image-analysis after SDS-PAGE. The experiment showed a significant increase in the TIMP-1 level at 1 week after implantation as compared with that in GCF from healthy periodontium. Four weeks after implantation it had reached the same level as that in the GCF of healthy subjects. The data has also disclosed a higher post-implantation collagenase activity level at 1 week than at weeks 2, 4, and 12. This may be due to the increase in MMP-1 and -8. Furthermore, peri-implantitis and periodontitis were shown to be similar inflammatory lesions in respect to MMP-1 and -8 and collagenase activities, even though the TIMP-1/MMP-1 + MMP-8 ratio was significantly lower in peri-implantitis than in periodontitis. In conclusion, the overproduction of TIMP-1 in the wound area after implantation could, to some extent, inhibit excessive tissue destruction and degradation of the neo-matrix in wound repair due to MMPs.

Influence of prosthesis material on stress distribution in bone and implant: a 3-dimensional finite element analysis.

A 3-dimensional finite element analysis was conducted to assess stress distribution in bone, implant, and abutment when gold alloy, porcelain, or resin (acrylic or composite) was used for a 3-unit prosthesis. A unit force was applied axially and then buccolingually to the center of the pontic. For gold and porcelain, similar maximum equivalent stress was found in each part of the models. In almost all cases, stress in the model with the resin prostheses was similar to or higher than that in the models with the other 2 prosthesis materials. The highest increase in stress with the resins was found in the implant-abutment unit under axial load. The protective role of resin for the implant-bone interface could not be demonstrated under the conditions of this analysis.

A histological study on tissue responses to titanium implantation in rat maxilla: the process of epithelial regeneration and bone reaction.

The present study aimed to establish a titanium implantation model using rat maxillae as well as demonstrate the chronological tissue responses to implantation. Pure titanium implants were inserted in the upper first molar extraction sites of Wistar rats 1 month after tooth extraction. The animals were sacrificed at 1 to 30 days postimplantation, and prepared tissue specimens were processed for light microscopy. The removal of implants from tissue blocks was done using 2 methods: mechanical removal or a cryofracture technique. In the early stages, peri-implant tissues showed severe damage to the oral epithelium and collagen bundles with significant inflammatory cell infiltration. The peri-implant epithelium grew apically along the implant by 10 days postimplantation, and regenerated to show a similar feature of junctional epithelium seen in normal rats at 15 days postimplantation, at which time no signs of inflammation were observed. The regenerated collagen bundles in the connective tissue were arranged circumferentially to the implants in the horizontal sections. New bone formation first appeared around the implants at 5 days postimplantation, covering the entire perimeter of implants by 30 days postimplantation. Scanning electron microscopic observations of the surface texture of the removed implants suggest the probability of an adhesive mechanism between the implants and the peri-implant epithelium and/or the alveolar bone. These findings indicate that this experimental model is useful for detailed analysis of peri-implant tissue because of its easy implantation procedure.

Influence of restoration type on stress distribution in bone around implants: a three-dimensional finite element analysis.

The three-dimensional finite element analysis method was used to assess stress in bone around titanium implants using three treatment designs for a partially edentulous mandible, under axial (AX), buccolingual (BL), or mesiodistal (MD) loads. For each of these loads, highest stress was calculated in the model with a cantilever prosthesis supported by two implants (M2). Less stress was found in the model with a conventional fixed partial denture on two implants (M3), and lowest stress was calculated in the model with three connected crowns supported by three implants (M1). When BL load was applied to M3, cortical bone stress was high, comparable to that calculated for M2 under the same load. When AX or MD load was applied to M3, the cortical bone stress was low, similar to that found in M1 under each of these loads.

Bactericidal efficacy of carbon dioxide laser against bacteria-contaminated titanium implant and subsequent cellular adhesion to irradiated area.

BACKGROUND AND OBJECTIVE: The aim of this study was to assess CO2 laser ability to eliminate bacteria from titanium implant surfaces. The changes of the surface structure, the rise in temperature, and the damage of connective tissue cells after laser irradiation were also considered. STUDY DESIGN/MATERIALS AND METHODS: Streptococcus sanguis and Porphyromonas gingivalis on titanium discs were irradiated by an expanded beam of CO2 laser. Surface alteration was observed by a light, and a scanning electron, microscope. Temperature was measured with a thermograph. Damage of fibroblastic (L-929) and osteoblastic (MC3T3-E1) cells outside the irradiation spot and adhesion of the cells to the irradiated area were also estimated. RESULTS: All the organisms (10(8)) of S. sanguis and P. gingivalis were killed by the irradiation at 286 J/cm2 and 245 J/cm2, respectively. Furthermore, laser irradiation did not cause surface alteration, rise of temperature, serious damage of connective tissue cells located outside the irradiation spot, or inhibition of cell adhesion to the irradiated area. CONCLUSION: CO2 laser irradiation with expanded beam may be useful in removing bacterial contaminants from implant surface.

A histological investigation on tissue responses to titanium implants in cortical bone of the rat femur.

Implant materials are placed under various sites-including cortical bone, spongy bone, and bone marrow-at the same time according to the depth at implantation. Although cortical bone is an important site for the prognosis of implantation, detailed reports on tissue responses to implantation have been meager. The present study aims to reveal tissue responses to pure titanium implantation in rat femoris cortical bone. The rats received titanium bars surgically in their femurs and were sacrificed 1 day to 40 weeks post-implantation. The prepared tissue specimens were processed for light and transmission electron microscopy (TEM). Further histochemical detections were performed. One day post-implantation, empty osteocytic lacunae indicating degeneration of osteocytes were found in pre-existing cortical bone around the implant. Such pre-existing bone was replaced by new bone, but remained in part even 40 weeks post-implantation. Light microscopy showed that direct contact between the implant and new bone was identified 12 weeks post-implantation. Chronological and ultrastructural observation showed that new bone deposition appeared to proceed toward the implant, and that the intervening layer at the interface was derived from the degenerated debris of multinucleated giant cells and/or osteoblasts. Furthermore, it seemed that the width of intervening layer varied in relation to the distance from the blood vessels. The cells showing tartrate resistant acid phosphatase activity possessed cytological features of osteoclasts under TEM; they were frequently observed in perivascular sites near the implants even after osseointegration, suggesting that bone remodeling took place steadily around the implant.

Retention and failure mode after cyclic loading in two post and core systems.

Retention of a prefabricated post and composite resin core system was compared with that of a cast post and core restoration in anterior maxillary teeth on which root canal preparations, enlarged in the coronal part, were performed. The effect of cyclic loading on restoration retention was also investigated. Retention of restorations not subjected to cyclic loading was not influenced by post type, but loaded prefabricated post restorations showed lower retention than both loaded cast post and core restorations and nonloaded prefabricated post restorations. After dislodgement, the failure mode was also determined. The results of this study suggest that if a canal requires extensive preparation, a well-adapted cast post and core restoration may be more retentive than a prefabricated post restoration that does not match the canal shape.

[Follow-up study of periodontal tissues around the abutment teeth in Konus telescope denture].

The purpose of this study was to evaluate the periodontal tissues around the 47 abutment teeth in patients with advanced periodontitis for 5 years maintenance periods. The periodontal and prosthetic treatment were carried out and 16 Konus telescope dentures were applied for 11 patients. During 5 years maintenance therapy, periodontal conditions were observed once a year assessing probing depth, attachment level, tooth mobility index, gingival index, marginal alveolar bone height, width of periodontal ligament and loss of lamina dura. The results showed that increase of probing depth in 0.61 mm and attachment loss in 0.78 mm were observed for 5 years. A slight gingival inflammation occurred and tooth mobility increased in some extent. Enlargement of periodontal ligament space and loss of lamina dura in 40% of abutment teeth were observed for 5 years. There were six decayed teeth, six teeth, from which a intracoronal crown was removed, and two extracted teeth in 47 abutment teeth. In conclusion, the periodontal tissues around abutment teeth in Konus telescope denture changed slightly at one year after denture placement, after which, the periodontal tissues were well maintained.