Yasumasa Akagawa

Interface histology of unloaded and early loaded partially stabilized zirconia endosseous implant in initial bone healing

Clinical and histologic evaluations of partially stabilized zirconia endosseous implants under unloaded and early loaded conditions in four beagle dogs were performed to examine the possibility of osseointegration of a newly developed one-stage zirconia implant during initial bone healing. No clear difference in clinical features was observed. Direct bone apposition to the implant was generally seen in both implants. However, loss of crestal bone height was quite evident around the loaded implants. These findings suggest that the initial unloaded condition is preferable to achieve osseointegration of one-stage zirconia implants.

Tissue compatibility and stability of a new zirconia ceramic in vivo

Tissue reaction and stability of partially stabilized zirconia ceramic in vivo was evaluated with the use of the subcutaneous implantation test. During the experimental period, zirconia ceramic was completely encapsulated by a thin fibrous connective tissue with less than 80 microns thickness. No changes of weight and 3-point bending strength were detected after 12 months of implantation. The result suggests that zirconia ceramic is biocompatible and no degradation of zirconia ceramic occurred.

Comparison between freestanding and tooth-connected partially stabilized zirconia implants after two years' function in monkeys: A clinical and histologic study

STATEMENT OF PROBLEM Partially stabilized zirconia implants placed by a 1-stage procedure have been previously shown to obtain initial osseointegration under clinically unloaded condition. However, it is unknown whether freestanding and tooth-connected partially stabilized zirconia implants can maintain a long-term direct bone-implant interface. PURPOSE This study examined the possibility of the long-term stability of osseointegration around partially stabilized zirconia implants with a 1-stage procedure with different loading designs. MATERIAL AND METHODS Thirty-two partially stabilized zirconia implants were placed into the mandibles of 8 monkeys. Three months after implant placement, 3 types of superstructure were provided in each animal to obtain different concepts of support as (1) single freestanding implant support, (2) connected freestanding implant support, and (3) a combination of implant and tooth support. At 12 and 24 months after loading, clinical, histologic, and histomorphometric evaluations of peri-implant tissues were performed on 28 implants. RESULTS No clear difference in clinical features was observed among the different types of support. Direct bone apposition to the implant was generally seen in all groups. Histometrically, bone contact ratio ranged between 66% and 81%, and bone area ratio varied between 49% and 78% at 24 months after loading. These values showed almost no difference among single freestanding, connected freestanding, and implant-tooth supports of partially stabilized zirconia implants. CONCLUSION In a primate model, partially stabilized zirconia implants placed with a 1-stage procedure achieve long-term stability of osseointegration with the use of single freestanding, connected freestanding, and implant-tooth supports.

Characterization of a cartilage-derived 66-kDa protein (RGD-CAP/beta ig-h3) that binds to collagen

A 66-kDa collagen fiber-associated protein (RGD-CAP) was isolated from a fiber-rich fraction of pig cartilage by ultrafiltration and collagen-affinity chromatography. Amino acid sequencing and cDNA cloning indicated that the RGD-CAP is identical or closely related to beta ig-h3 protein which is induced in human adenocarcinoma cells by transforming growth factor-beta (TGF-beta) (Skonier, J., Neubauer, M., Madisen, L., Bennett, K., Plowman, G.D., and Purchio, A.F. (1992) DNA Cell. Biol. 11, 511-522). The RGD-CAP, as well as beta ig-h3, has the RGD sequence in the C-terminal region. The native RGD-CAP bound to type I, II, and IV collagens even in the presence of 1 M NaCl. A recombinant preparation of RGD-CAP expressed in Escherichia coli cells also bound to collagen but not to gelatin. The RGD-CAP mRNA was expressed in chondrocytes throughout all stages, although the expression level was highest during the prehypertrophic stage. In addition, TGF-beta increased the RGD-CAP mRNA level in chondrocyte cultures. Since RGD-CAP transcripts were found in most tissues, this novel collagen-binding protein may play an important role in cell-collagen interactions in various tissues including developing cartilage.

Diverse mechanisms of osteoblast spreading on hydroxyapatite and titanium

Hydroxyapatite (HA) is an osteoconductive implant material. We previously demonstrated that RGD peptides regulate the spreading of HOS cells on HA but not on titanium, speculating that the osteoconductivity of HA might be attributed to this RGD domain-dependent spreading of osteoblasts. To confirm this hypothesis, the molecules which regulate the spreading of HOS cells on HA and on titanium were investigated. The 50% effective dose (ED50) of RGD peptide for the spreading on HA was five fold lower comparing to titanium. Anti-alphaV integrin antibody, vitronectin, and fibronectin inhibited the spreading on HA but not on titanium. In Western blot analysis, vitronectin and fibronectin were found in components adsorbed to HA but not to titanium. Taken together, the spreading of HOS cells on HA but not on titanium requires the interaction of alphaV integrin and its ligands. The ED50 of the RGD peptides on titanium but not on HA was remarkably reduced by neuraminidase treatment, that by itself could not inhibit the spreading on both materials. This phenomenon suggests that RGD domain and sialic acid cooperatively but not independently mediate the spreading of HOS cells on titanium. Collectively, the molecules regulating the spreading on HA are apparently different from those on titanium. The spreading of osteoblasts mediated by RGD domain of vitronectin and fibronectin might contribute to the osteoconductive ability of HA.

Action of FGMgCO3Ap-collagen composite in promoting bone formation

To improve the biological properties of materials as bone substitutes, functionally graded CO3 apatite crystals containing magnesium, FGMgCO3Ap, were synthesized to be mixed with atelocollagen and made into a composite pellet. A radio-labeled cell adhesion experiment showed that the degree of adherence of mouse MC3T3E1 osteoblast-like cells to the FGMgCO3Ap-collagen composite was better than to CO3Ap-collagen and much better than to the Ti plate. When the composites were implanted beneath the periosteum cranii of rats, the FGMgCO3Ap-collagen composite was metabolized faster than the CO3Ap-collagen composite and better formation of new bone and osteoblast arrangement at the interface between the composite and the periosteum cranii was observed. When the composites were implanted into the femur of rabbits, clear bone formation with a higher degree of bone density was observed for the FGMgCO3Ap-collagen composite. These results suggest that the Mg2+ ions taken into the apatite crystals may contribute to the acceleration of osteoblast adhesion to apatites and promote bone formation, cross-talking with osteoblasts at the molecular level.

Prolonged antimicrobial effect of tissue conditioners containing silver-zeolite

OBJECTIVES The purpose of this study was to elucidate the in vitro antimicrobial effect of tissue conditioners containing silver-zeolite on Candida albicans and nosocomial respiratory infection-causing bacteria, Staphylococcus aureus and Pseudomonas aeruginosa. METHODS Five commercially available tissue conditioners were selected: Visco-gel (VG), GC Soft-Liner (SL), Fitt (FT), SR-Ivoseal (IV) and Shofu Tissue Conditioner (TC). Samples, 10 x 10 x 2.5 mm in size, contained silver-zeolite (SZ sample) and no SZ (N sample). The antimicrobial effects of these two samples were evaluated as a percentage of viable cells (CFU) in a microbial suspension (100 microliter) in phosphate-buffered saline with or without immersion in artificial saliva for four weeks. The borderline of the antimicrobial effect was determined at 0.1% viable cells. RESULTS With the SZ samples, all tested microbes were killed under both conditions of no immersion and immersion in saliva. In non-immersed N samples, however, no cells of C. albicans (except with VG) and S. aureus survived, whereas the percentage of viable cells of P. aeruginosa was similar to that found in the control. However, with immersion in saliva, viable cells of C. albicans in some N samples (VG, SL and TC) increased compared with non-immersion samples by more than 0.1%. CONCLUSION Tissue conditioners containing SZ have been shown to have antimicrobial effects for four weeks on C. albicans and nosocomial respiratory infection-causing bacteria in saliva in vitro.

The effects of early occlusal loading on one-stage titanium alloy implants in beagle dogs: a pilot study.

The initial stages of bone healing with titanium alloy implants were compared clinically and histologically in three groups of beagle dogs: unloaded one-stage (group 1), loaded one-stage (group 2), and unloaded two-stage (group 3). No implant mobility was reported in any of the three groups. For the most part direct bone contact was achieved, but there was a significant difference in the histologic results of the interface among the animals in all three groups. Significant crestal bone loss was evident in group 2, which showed poor bone apposition to the bottom of the threads in the upper portion of the implant. New bone growth to these same areas of the threads was seen in the animals in groups 1 and 3, with the ratio of direct bone contact significantly higher for those in group 3. These differences could be attributed to the effect of early occlusal loading on the implant during initial bone healing.

Decreased Tongue Pressure Reflects Symptom of Dysphagia

The tongue plays a key role in oropharyngeal swallowing. It has been reported that maximum isometric tongue pressure decreases with age. The risk for dysphagia resulting from low tongue strength remains unclear. This study was designed to reveal the relationship between tongue pressure and clinical signs of dysphagic tongue movement and cough and to demonstrate the clinical value of tongue pressure measurement in the evaluation of swallowing function. One hundred forty-five institutionalized elderly in five nursing homes participated. Evaluation of physical activity with self-standing up capability and mental condition with Mini Mental Status Examination (MMSE) were recorded. Maximum tongue pressure was determined using a newly developed tongue pressure measurement device. Voluntary tongue movement and signs of dysphagic cough at mealtime were inspected and evaluated by one clinically experienced dentist and speech therapist. The relationship between level of tongue pressure and incidence of cough was evaluated using logistic regression analysis with physical and mental conditions as covariates. Tongue pressure as measured by the newly developed device was significantly related to the voluntary tongue movement and incidence of cough (p < 0.05). The results of this study suggest that tongue pressure measurement reflects clinical signs of dysphagic tongue movement and cough and that measurement of tongue pressure is useful for the bedside evaluation of swallowing.

Acid pretreatment of titanium implants

The purpose of this study was to evaluate the effectiveness of several methods of cleaning titanium surfaces as pretreatment for surface modifications by analyzing the chemical interaction of three acids, such as Na(2)S(2)O(8),H(2)SO(4) and HCl, followed by rinsing with acetone or ultrapure water. Chemical evaluation, using X-ray photoelectron spectroscopy (XPS), and mechanical evaluation, using nanoindentation, were employed. XPS revealed that an untreated Ti surface consisted of carbon- and nitrogen-containing contaminant and titanium oxide layer on metallic titanium substrate. The method involving the combination of 10 N HCl and acetone was the most effective of all the methods investigated. Such a combination most effectively reduced values of contamination parameters C/Ti and N/Ti, as well as the intensity of the titanium oxide component in Ti 2p spectra. Chlorine was barely detected from the surface treated with HCl in any concentration. Sulfur from the residual S(2)O(8)(2-) or SO(4)(2-), however, was detected from the samples treated with either Na(2)S(2)O(8) or H(2)SO(4). The S/Ti values depended on concentration of the acidic solution. In addition, nanoindentation measurements revealed that Youngs modulus of the surface treated with 0.1-10 N HCl was not significantly different from that of an untreated surface (p > 0.05). Consequently, the HCl/acetone treatment is proposed as an excellent decontamination method for the surface preparation process of Ti.