Yasunori Ayukawa

Current barrier membranes: Titanium mesh and other membranes for guided bone regeneration in dental applications

Research on guided bone regeneration (GBR) is still ongoing, with evidence mainly from preclinical studies. Various current barrier membranes should fulfill the main design criteria for GBR, such as biocompatibility, occlusivity, spaciousness, clinical manageability and the appropriate integration with the surrounding tissue. These GBR characteristics are required to provide the maximum membrane function and mechanical support to the tissue during bone formation. In this review, various commercially available, resorbable and non-resorbable membranes with different characteristics are discussed and summarized for their usefulness in preclinical studies. Membranes offer promising solutions in animal models; however, an ideal membrane has not been established yet for clinical applications. Every membrane type presents both advantages and disadvantages. Titanium mesh membranes offer superb mechanical properties for GBR treatment and its current efficacy in trials will be a focus in this review. A thorough understanding of the benefits and limitations inherent to various materials in specific clinical applications will be of great value and aid in the selection of an optimal membrane for GBR.

Local application of statin promotes bone repair through the suppression of osteoclasts and the enhancement of osteoblasts at bone-healing sites in rats

OBJECTIVE We investigated whether the local administration of simvastatin affected both the cellular events and the bone formation at surgically created bone defects in rat. STUDY DESIGN Simvastatin (or a vehicle) was injected into a rat bony defect for 3 consecutive days from the day of surgery. Five or ten days after the injection, new bone tissue was collected, and the gene expressions of bone-related proteins were examined. For the histomorphometry, new bone area was measured. RESULTS At day 5, the statin group demonstrated significantly larger new bone area. The number of tartrate-resistant acid phosphatase-positive multinucleated cells in the statin group was less than in the control group. In the statin group, the expressions of both alkaline phosphatase and bone morphogenetic protein 2 mRNA significantly increased. In contrast, the expression of cathepsin K was significantly suppressed in the statin group. Although the levels of both RANK and osteoprotegerin were not affected by statin, the expression of RANKL was depressed. At day 10, there were no significant differences among the groups in either histomorphometric or reverse-transcription polymerase chain reaction analyses. CONCLUSION New bone area increased under the influence of simvastatin; however, the effect did not continue when the administration was terminated. Osteoclast suppression may be the consequence of RANKL depression.

Relationship between the bone density estimated by cone‐beam computed tomography and the primary stability of dental implants

OBJECTIVES The aims of this study were to objectively assess bone quality with density values obtained by cone-beam computed tomography (CBCT) and to determine the correlations between bone density and primary stability of dental implants. MATERIAL AND METHODS Eighteen Straumann implants were inserted into 18 fresh femoral heads of swine. The bone densities of implant recipient sites were preoperatively determined by the density value using CBCT. The maximum insertion torque value of each implant was recorded using a digital torque meter. Resonance frequency, which represented a quantitative unit called the implant stability quotient (ISQ), was measured using an Osstell Mentor immediately after the implant placement. Spearmans correlation coefficient was calculated to evaluate the correlations among density values, insertion torques, and ISQs at implant placement. RESULTS The density values ranged from 98 to 902. The mean density value, insertion torque, and ISQ were 591 ± 226, 13.4 ± 5.2 Ncm, and 67.1 ± 8.1, respectively. Statistically significant correlations were found between the density values and insertion torque (r(s) =0.796, P<0.001), density values and ISQ (r(s) =0.529, P=0.024), and insertion torque and ISQ (r(s) =0.758, P<0.001). CONCLUSIONS The bone quality evaluated by specific CBCT showed a high correlation with the primary stability of the implants. Hence, preoperative density value estimations by CBCT may allow clinicians to predict implant stability. Whether the density values obtained by the CBCT device used in the present study could be applied to other devices requires further elucidation.

Light and electron microscopic studies of bone-titanium interface in the tibiae of young and mature rats.

Bone-titanium contact was examined in young and mature rats on various days after insertion of pure titanium into the tibia. Under light microscopy, on the 14th day, lamellar mature bone was initially formed, and was seen to make direct contact with the titanium in both groups. In young rats on the 28th day, bone-titanium contact was greater than that in mature animals. On 1-micron sections, an amorphous zone 0.5-1.0 micron thick was found around the titanium, and a slender cell layer lay parallel to the implant, forming the superficial layer of the amorphous zone. Ultrastructurally, these slender cells were identified as osteoblastlike cells and made direct contact with the implant via a 20-50-nm thin amorphous zone. Below this cell layer, a collagen-containing, poorly mineralized zone was present and bordered by lamellar bone with a lamina limitans-like structure. However, this cell layer was absent in places, and therefore the thick amorphous zone without slender cell layer consisted ultrastructurally of a 20-50-nm thin amorphous zone and a poorly mineralized zone bordered by the lamellar bone. Sometimes this poorly mineralized zone was absent, and in such cases, the lamellar bone contacted the titanium by the thin amorphous zone formed on the lamina limitans-like structure. Thus, although bone was seen to make contact with the titanium implant, ultrastructurally a 20-50-nm thin amorphous zone, a slender cell layer, and/or a poorly mineralized zone were interposed between the bone and titanium.

An immunoelectron microscopic localization of noncollagenous bone proteins (osteocalcin and osteopontin) at the bone–titanium interface of rat tibiae

This study was designed to investigate by postembedding immunogold method the localization and distribution of osteocalcin (Ocl) and osteopontin (Opn) at the bone-titanium interface in rat tibiae 14 and 28 days postimplantation to determine which bone proteins are present at this interface. Both proteins were widely distributed on the newly formed bone and accumulated predominantly in the region of bone close to the titanium, in electron-dense patches in the bone, and at the osteocytic lacunae. Collagenous osteoid showed little or no labeling for either Ocl or Opn. An amorphous zone (20-50 nm) was interposed between the titanium and interfacial slender cells, osteoid, or bone, and was labeled strongly for Ocl but only weakly for Opn. Furthermore, a second electron-dense layer, the lamina limitans, which faces the titanium, was labeled strongly for Opn but weakly for Ocl. Ocl as a marker protein of osteoblasts was sometimes found in the granules and vesicles of the interfacial cells and extracellularly in their intercellular spaces, close to the titanium. However, Opn was not detected in any granules. This is the first report to show that the amorphous zone contains large amounts of Ocl and small amounts of Opn, and that bone contacts titanium through this Ocl-rich amorphous zone. Furthermore, it is suggested that the interfacial cells seem to be osteoblasts, and that Ocl in the amorphous zone is produced and secreted by these cells and functions with Opn as a regulator of the mineralization front close to the titanium, and as a mediator of cell-matrix and matrix-matrix/mineral adhesion along the titanium.

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.

Topical application of statin affects bone healing around implants

OBJECTIVES 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors (statins) are widely used for hyperlipidemia. Recent studies demonstrate that statins stimulate bone morphogenetic protein-2 expression and lead to bone formation. The aim of this study was to evaluate whether the topical application of statin enhances the osteogenesis around a titanium implant. MATERIALS AND METHODS Ten-week-old female rats received pure titanium rods in both tibiae with or without fluvastatin. Propylene glycol alginate (PGA) was used as a carrier. The rats were divided into five groups: implant-only group, implant with PGA group, low-dose group [implant+PGA containing 3 microg of fluvastatin (FS)], medium-dose group (15 microg of FS), and high-dose group (75 microg of FS). The animals were sacrificed at 1 and 2 weeks after implantation. Peri-implant bone formation was assessed by histomorphometric procedures, i.e., measuring the bone-implant contact (BIC) and peri-implant bone volume (BV). A mechanical push-out test was also performed to evaluate the implant fixation strength. Statistical differences among the groups were determined by ANOVA and P < 0.05 was considered significant. RESULTS At week 1, there was no significant difference in BIC among the groups, however, BV and the push-out strength were significantly higher in the high-dose group than in the implant-only group. At week 2, BIC and BV had significantly increased in the high-dose group in comparison with the non-statin groups. The fluvastatin-treatment group showed a significant increase in push-out strength compared with the non-statin groups. CONCLUSION Our histomorphometrical and mechanical evaluations revealed the positive effect of topically applied fluvastatin on the bone around the implant.

Effects of aging on titanium implants inserted into the tibiae of female rats using light microscopy, SEM, and image processing

We examined the influence of aging on the implant-bone interface of titanium implants inserted transcortically and extending into the medullary canal of rat tibiae, and quantitatively assessed the differences in bone reaction using an image processing system. Three groups of 15 female rats, aged 6 weeks (young group), 22 weeks (adult group), and 80 weeks (old group) were used in this experiment. The animals were sacrificed 28 days after implant placement. Toluidine blue stained undecalcified sections were prepared for histological observation and image analysis, and the implant socket was observed by SEM. There was no difference in the degree of maturation of newly formed bone between the young and adult groups. Titanium implants inserted in the young and adult groups were surrounded with a bone layer. In the old group, however, there was little mature bone tissue around the implants. Quantitative evaluation indicated that the young group showed the highest, the adult group showed a slightly lower, and the old group showed the lowest percent bone contact, thickness of bone contact, and area of bone surrounding the implant.

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.

Study of bone formation around dense hydroxyapatite implants using light microscopy, image processing and confocal laser scanning microscopy

The bone reaction to hydroxyapatite (HA) implants inserted transcortically and extending into the medullary canal of rat tibiae was quantitatively assessed using light microscopy, confocal laser scanning microscopy and an image processing system. Sixty-five male rats (6 weeks old) were divided into two groups, 60 for histological observation and image analysis and five for time-labelling. In the histological observation, control sections of 168 days showed a few bone trabeculae in the fatty bone marrow, and Ti implants had become gradually encapsulated with a thick bone tissue layer; however, HA implants became almost completely encapsulated with a thin bone tissue layer during the 168 day experimental period. Histometrical analysis of the percent bone contact revealed that Ti implants showed a continuous increasing curve, and HA implants showed rapid increase in the initial healing period up to 14 days, with 96% bone contact reaching a plateau at 84 days after operation. There was a significant difference in the percent of bone contact between Ti and HA implants throughout the experimental period. Confocal laser scanning microscopic observations revealed the presence of calcein at the 14th day and only slight alizarin colour layer in the bone tissue at the 28th day, both indicating bone formation. These findings suggest that the activity of bone formation was higher at the 14th day than at the 28th day. Also, the percentage of bone contact of HA is superior to titanium throughout the experimental period, and the ascending patterns of both implants are quite different to each other.