Simvastatin enhances bone formation around titanium implants in rat tibiae.

Statins are cholesterol-lowering drugs that have been reported to promote bone formation. The purpose of this study was to investigate the effect of simvastatin on the enhancement of bone formation around titanium implants. Thirty-week-old female rats received pure titanium implants in both tibiae. The animals were intra-peritoneally administered 0, 0.125, 1, 5 or 10 mg kg(-1) of simvastatin daily. After 30 days, the animals were sacrificed, and specimens were prepared. The bone contact ratio of the implant, bone density in the medullary canal and percentage of cortical bone were obtained. Markers for bone turnover were also measured using sera collected at the time of euthanasia. In the medullary canal, a scanty amount of bone was observed in the 0, 0.125 and 1 mg kg(-1) groups. In contrast, in both the 5 and 10 mg kg(-1) groups, thicker bone trabeculae were abundant. Histometric observations showed that the bone contact ratio and the bone density of both groups were significantly greater than those of the other groups (anova, P < 0.01). However, no significant difference in the percentage of cortical bone was found between groups. Serum chemistry showed that statin increased bone formation markers and decreased bone resorption markers. In conclusion, although the dose equivalent to that used in human patients with hypercholesterolemia was not effective, a simvastatin dose of 5 mg kg(-1) or higher increased medullary bone formation around the titanium. In contrast, no effect of simvastatin on pre-existing cortical bone was indicated.

Histomorphometric analysis of the response of rat tibiae to shape memory alloy (nitinol).

The bone reaction to nitinol (Ni-Ti), a metal with shape memory, and other materials inserted transcortically and extending into the medullary canal of rat tibiae was quantitatively assessed using an image processing system. The materials examined were implants, all of the same shape and size, composed of nitinol, pure titanium (Ti), anodic oxidized Ti (AO-Ti), a titanium alloy (Ti-6Al-4V) and pure nickel (Ni). While the other four implant materials were progressively encapsulated with bone tissues, Ni was encapsulated with connective tissues through the 168-day experimental period, and the Ni implants showed no bone contact at any time during the experimental period. Histometric analysis revealed no significant difference among the tissue reactions to Ti, AO-Ti and Ti-6Al-4V, but Ni-Ti implants showed significantly (P < 0.01) lower percentage bone contact and bone contact area than any of the other titanium or titanium alloy materials.

Fractures of hydroxyapatite-coated blade implants connected with natural teeth. A histological study using SEM, light microscopy, and an image processing system.

A clinical study was conducted of 59 patients treated with 78 hydroxyapatite (HA)-coated blade implants from August 1986. Five implants in 5 patients were broken at the neck portion, and one implant in one patient was removed from the jaw bone. The histological findings around a broken implant which was removed from the mandible are presented. These sections showed good adaptation of the bone to the implant without a fibrous layer. Histomorphometric evaluation of bone-to-implant contact showed 73.5%. The scanning electron microscopy image of the fractured surface revealed a fatigue fracture. The suspected cause of the fracture was stress concentration at the cervix portion, because of excessive mobility or deleterious change of abutment teeth. Consequently, the osseointegration/biointegration implants should not be connected with natural teeth.

Failing hollow implants examined by light microscopy and image processing.

The purpose of this study was to evaluate the radiologic, histologic, and histometric findings of three failing hollow implants. On periapical radiographs, these implants showed vertical bone loss up to the hollow portion around the implant. Examination of the histologic sections disclosed that the hollow portions of all the implants were almost filled with bone tissue, although slight bone resorption and presence of granulation tissue infiltrated with inflammatory cells was observed coronal to the hollow portion. Histometric analysis disclosed that the average percent bone contact was 93.1% in case 1, 90.9% in case 2, and 84.3% in case 3 and the average percent bone filling was 42.1%, 50.5%, and 33.8%, respectively. Consequently, there seems to be some potential for successful treatment of these implants because the destructive changes were limited to the coronal aspects of the implant.

Abscess formation around a hydroxyapatite-coated implant placed into the extraction socket with autogenous bone graft. A histological study using light microscopy, image processing, and confocal laser scanning microscopy.

The purpose of this study was to evaluate the radiologic, histologic, and histometric findings for a retrieved hydroxyapatite (HA)-coated implant which had been placed into a fresh extraction socket with autogenous bone graft 3 months previously. A periapical radiography disclosed a vertical bone loss around the implant cervix. Examination of histologic section disclosed that granulation tissue including bone chips around the cervix, and newly-formed bone tissue around the grafted bone tissue on the HA coated surface. In the confocal laser scanning microscopic findings toluidine blue-negative bone tissue showed autofluorescence. Histometric analysis indicated that the average percent bone contact was 29.2% (ranged 26.4% to 34.1%). Suspected reasons for failure were an early exposure of the barrier membrane, its early removal, the implant placement into an infected site, inadequate antibiotic premedication, and/or poor control of infections around teeth prior to implant surgery and around implants before and after placement of barrier membrane.

A histologic evaluation of retrieved hydroxyapatite-coated blade-form implants using scanning electron, light, and confocal laser scanning microscopies.

We histologically examined seven hydroxyapatite-coated (HA) blade implants removed from patients. Four of them radiologically showed severe bone loss and were easily removed with an elevator. Three radiologically showed vertical bone loss and were removed by surgical procedure. Our histological evaluation indicated that coating separation from the HA implants had occurred, and HA coating resorption by bone tissues was suspected in an implant left in situ for 8 years. Several multinucleated giant cells were seen with a few released particles of HA coating at the point lacking bone contact with the HA coating. The presence of microorganisms on and in the HA coating layer was also noted.

Histological comparison of early wound healing following dense hydroxyapatite granule grafting and barrier placement in surgically-created bone defects neighboring implants.

The purpose of this study was to examine early wound healing following grafting of dense hydroxyapatite granules (HA granules) and barrier placement in surgically-created bone defects surrounding implants. Eight healthy adult dogs with an average weight of 15 kg were used in this study. Thirty-two bone defects measuring 4 mm x 4 mm were removed with a surgical bur to form continuous bucco-lingual bone defects and 32 implants (16 titanium [Ti]) and 16 hydroxyapatite-coated [HA]) were then placed into the defects. Four implant groups were created: 1) grafting HA; 2) covering with an expanded polytetrafluoroethylene (ePTFE) membrane; 3) grafting HA and covering with ePTFE membrane; and 4) control (no treatment). Animals were sacrificed 28 days after surgery. Histological sections revealed large amounts of newly-formed bone in all bone defects surrounding the implants treated with ePTFE membranes alone. Fibrous encapsulation of HA granules was observed in the defects of the HA granules grafting group. In the group with grafting of HA granules and covering with ePTFE membranes, small amounts of bone tissue were observed among HA granules, but most HA granules were surrounded with fibrous tissue. Bone defects were completely filled with connective tissue in the control group. There were no differences in the histological findings between Ti and HA-coated implants in all cases. Histomorphometric data disclosed that the presence of HA granules in the bone defects significantly arrested bone formation. Our study suggests that the grafting of dense HA into bone defects surrounding implants will result in fibrous healing during the early healing stage.

An immunocytochemical study for lysosomal cathepsins B and D related to the intracellular degradation of titanium at the bone-titanium interface.

The morphological relationship between titanium and lysosomal proteinases, cathepsins B and D, at the bone-titanium interface using titanium-coated plastic implants placed for 28 days in the tibiae of 6-week-old rats was immunocytochemically investigated by the colloidal immunogold-silver method. Under light microscopy the titanium layer appeared to make direct contact with the bone and one or a few layers of slender cells were interposed between the bone and titanium. Ultrastructurally, the titanium came in contact with the bone or the slender cell layer through a 20 to 40 nm thin amorphous zone. The slender cells at the bone-titanium interface consisted of two types; one was an osteoblast type with glycogen granules which was found along the newly-formed bone facing titanium layer. The other was a fibroblast type which came in contact with the titanium layer and occasionally endocytosed the detached titanium fragments. In addition, some of the slender cells also showed degenerative changes. Immunocytochemically, cathepsins B and/or D were sometimes colocalized in some phagolysosomes with titanium fragments. These findings suggested that the fibroblast types at the bone-titanium interface may act as scavengers to remove both cell debris and titanium by means of some endocytotic ability, and lysosomal cathepsins also developed in response to the endocytosed titanium. The osteoblast type also appears to show a high degree of osteogenic activity around the titanium-coated plastic implants.

A study of the regional distribution of bone formed around hydroxyapatite implants in the tibiae of streptozotocin-induced diabetic rats using multiple fluorescent labeling and confocal laser scanning microscopy.

The present study was designed to compare the amount and regional distribution of bone formation around hydroxyapatite (HA) implants in normal (control) rats with that of animals with diabetes mellitus (DM), induced by streptozotocin 2 weeks prior to implant placement. Calcein (CAL), alizarin complexone (AL), and tetracycline (TC) were injected on the 7th, 14th, and 21st days after implantation, respectively, and the rats were sacrificed on the 28th day after implantation. Seventy-microns undecalcified sections of the HA-bone interface in both groups were then prepared for confocal laser scanning microscopy (CLSM) observation. In both groups, bone formation developed from the HA surface to the endosteum, periosteum, or bone marrow. In the control group, around the HA close to the endosteum and periosteum, the new bone showed an extensive lamination pattern of three color layers (CAL, AL, and TC), but in the DM group the labeling density of TC on the 21st day was low. In contrast, on the lateral part of the HA surface (away from the endosteum and periosteum), there was considerably less bone formation in the control group, and in the DM group it was almost completely suppressed. These findings indicate that bone formation around the HA was initiated from the HA surface in the control group, while in the DM group, bone formation along the lateral part of the HA away from the endosteum and periosteum was almost completely suppressed. Furthermore, it is also suggested that in the new bone along the HA close to the endosteum and periosteum, only calcification on the 21st day was depressed.

Ultrastructural and immunoelectron microscopic studies of the peri-implant epithelium-implant (Ti-6Al-4V) interface of rat maxilla.

BACKGROUND: The role played by the internal basal lamina (IBL) and hemidesmosomes between an implant and the peri-implant epithelium (PIE) in the adherence of the epithelium to the implant is controversial. This study used rat maxilla implantation models to clarify the ultrastructure of the PIE-implant interface. METHODS: Ti-6Al-4V implants were inserted either immediately or 2 weeks after the extraction of the upper left first molar of 6- or 4-week-old rats, respectively. The junctional epithelium (JE) of the upper right molars in the same animals was used as a control. Four weeks after implantation, the animals were sacrificed to prepare specimens for light and immunoelectron microscopy. RESULTS: Under light microscopy, the PIE appeared to attach to the implant surface. Ultrastructurally, IBL, consisting of the lamina densa and lamina lucida, and hemidesmosomes were formed only in the lower region, and rarely in the middle region, of the PIE-implant interface. In control teeth, the IBL and hemidesmosomes formed throughout the dento-JE interface. Laminin-1 was found in the IBL and also in the vesicles and vacuoles of the PIE and JE cells. Statistical analysis showed that there was also a significant difference in the amount of IBL between the PIE-implant and dento-JE interfaces. CONCLUSIONS: PIE attached to the implant via hemidesmosomes and IBL in the lower region of the PIE-implant interface. Although PIE cells may secrete laminin-1, which contributes to epidermal cell adhesion, the PIE which attaches to implants only in the lower region of the interface is considered to be the poorly adhered epithelium.

Histologic investigation of hollow implants retrieved for psychological reasons.

OBJECTIVE: The purpose of this study was to radiologically, histologically, and histometrically evaluate bone in the hollow portion of three implants retrieved for psychological reasons. STUDY DESIGN: Three hollow implants retrieved from two patients were studied. We investigated the radiologic and histologic changes of these implants with the use of radiographs, light microscopy, image processing, and fluorescent microscopy. RESULTS: There were no radiologic and histologic degeneration around the implants. Histometric analysis of the hollow indicated that the average percentage of bone contact rate was 33.5% in case 1, 74.5% in case 2, and 18.4% in case 3; the average percentage of bone filling was 25.1%, 33.9%, and 6.6%, respectively. There was a great variation among the three cases in bone to implant contact and bone filling. CONCLUSION: The hollow portion in case 1 that penetrated into the maxillary sinus was encapsulated with fibrous tissue. The amount of bone tissue in the hollow portion seems to depend on the initial bone quality of the recipient sites.

Immunolocalization of proliferating cell nuclear antigen in the peri-implant epithelium.

The aim of the present study was to investigate the proliferating activity of peri-implant epithelium immunohistochemically using proliferating cell nuclear antigen (PCNA). Eight ITI (Internationale Team für Implantologie) implants were placed into simulated sockets in the mandibles of two beagle dogs two months following tooth extraction. As a control, junctional epithelium of the molar teeth in the same animals were used. The nature of staining and the distribution of PCNA immunoreactivity were determined by scoring a minimum of 100 cells on two sections from each of the implants. In the junctional epithelium, the immunoreactivity to PCNA was detected mainly in the basal cells, in some of the prickle cells, and in a few cells attached to the enamel. In peri-implant epithelium, only some of the basal cells were positive for PCNA. The PCNA score of the peri-implant epithelium was significantly lower than that of junctional epithelium. These results suggest that the peri-implant epithelium maintains a lower capacity to act as a proliferative defence mechanism than does the junctional epithelium.