Tsuneo Suetsugu

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.

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.

Correlation between inclination of occlusal plane and masticatory movement

OBJECTIVES The purpose of this study was to investigate the relationship between the inclination of the occlusal plane and masticatory movement. METHODS Masticatory movements of 41 young adults were measured using the three-dimensional Mandibular Movement Analyzing System. The inclination of the occlusal plane was measured in the sagittal plane using a three-dimensional digitizer. RESULTS In the sagittal plane, the masticatory closing path and the occlusal plane were consistent in maintaining a perpendicular relation with each other regardless of the inter-individual variation of the inclination of the occlusal plane. Subjects with an anteriorly inclined occlusal plane showed a vertical closing path, and subjects with a posteriorly inclined occlusal plane showed a flat closing path in the frontal plane. These characteristics were explained by the variation of the timing on the balancing-side condylar return correlated with the inclination of the occlusal plane. CONCLUSIONS There is a significant correlation between the inclination of the occlusal plane and the direction of the closing path during mastication.

The relationship between inclination of the occlusal plane and jaw closing path

The occlusal plane is determined according to morphologic guides such as Campers plane and the position of the retromolar pad. However, there is no information available about the functional orientation of the occlusal plane. The purpose of this study was to investigate the relationship between the inclination of the occlusal plane and jaw closing movement path in the sagittal plane. Data from 38 young dentate subjects were obtained with a system that measures jaw movements. It was found that the occlusal plane and the masticatory closing path were consistent in maintaining an almost perpendicular relationship regardless of the variation in the inclination of the occlusal plane. This finding appears to be based on the functional formation of the occlusal plane according to the growth and change of masticatory muscles. The correlation between the inclination of the occlusal plane and masticatory closing movement could serve as the background for the functional significance of the occlusal plane.

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.

Long-term evaluation of bone-titanium interface in rat tibiae using light microscopy, transmission electron microscopy, and image processing

We conducted a 2-year histologic and histometric evaluation of the tibial bone-titanium (Ti) implant interface in male rats. Thirty male 6-week-old rats were used in this study. They were divided into two groups: 15 for day 28 and 15 for day 730. Microscopic observation at day 28 revealed that the newly formed bone around the implant almost surrounded the implant, but fibroblastlike cells were interposed in some histologic sections. At day 730, in contrast, such cells were rarely seen, and the bone around the implant presented a lamellar structure. Transmission electron microscopic observation at day 28 disclosed mature or poorly mineralized bone near the implant; however, an electron-dense amorphous zone about 50 nm in thickness was interposed between the bone and Ti. In places slender cells were interposed between the bone and Ti. The amorphous zone was also observed at the cell-Ti interface. At day 730, a poorly mineralized layer remained in some areas between the mature bone and the titanium, and the interposed amorphous zone was still observed. Occasionally, a 200-nm-thick layer, thought to be cell remnant, was seen. As calculated in an image-processing, system analysis, the percent bone contact and the thickness and area of the surrounding bone for the Ti implant at day 28 were 43.6%, 30.4 microns, and 0.10 mm2, respectively, and those at day 730 were 89.9%, 53.5 microns, and 0.19 mm2, respectively. In summary, although the passage of time may affect bone maturity, interfacial cells remain at the bone-Ti interface as a uniform layer together with unmineralized bone.

A stent for presurgical evaluation of implant placement.

This article describes a method of fabricating a stent with barium sulfate and stainless steel tubes for the accurate radiographic evaluation of the relationships of the predesigned superstructure, the scheduled implant placement, and the anatomic structure. The barium sulfate in the stent depicts the outline of the predesigned superstructure, and the stainless steel tubes indicate the intended location and inclination of the implants on the computed tomographic scans. In addition, this stent can be used as a surgical stent to guide the pilot drill to the desired site.

The influence of anterior guidance and condylar guidance on mandibular protrusive movement.

This study reveals the influence of the incisal and condylar guidance on mandibular protrusive movement. The protrusive movements were measured on 54 young adults (27 females, 27 males) using a three-dimensional mandibular movement analysing system. The inclinations of the sagittal paths on the incisor, canine, 1st molar, 2nd molar and condylar points were calculated, and multiple regression analysis was performed to evaluate the influence of the incisal and condylar paths on the path of each tooth quantitatively. The influence of the incisal path on any tooth path was consistently greater than that of the condylar path. The condylar path had a greater influence on the paths of posterior teeth than on the paths of anterior teeth, especially in the female subjects. The influence of the condylar path on the molar paths was twice as great in the female than that in the male subjects. It was concluded that the influence of the incisal and condylar guidance on the protrusive movement path varies according to the kind of tooth and the gender of the subject. These guiding system characteristics were confirmed by morphological analysis.