Yo Shibata

Cooperation of Phosphate Monomer and Silica Modification on Zirconia

Ceramic restorations with resin-based adhesive systems have been the focus of recent attention in clinical dentistry. Yttrium-oxide-partially-stabilized zirconia (YPSZ) ceramics have optimized physical properties and exhibit favorable fracture toughness, though their bonding properties are problematic. Although functional phosphate monomers and silica-coating by tribochemical modification were expected to improve the bonding properties between YPSZ ceramics and resin-based adhesives, these two methods remain controversial. This study evaluated the efficiency of silica-coating by tribochemical modification of YPSZ ceramics. The application of phosphate monomer and a silane coupling agent on silica-coated YPSZ was also investigated. The silica-coating of YPSZ ceramics by tribochemical modification was not efficient, given the higher mechanical toughness of the densely sintered ceramics. Stable shear bond strength was achieved on silica-coated YPSZ ceramics with the cooperative interaction of phosphate monomer and silane coupling.

A review of improved fixation methods for dental implants. Part I: Surface optimization for rapid osseointegration

PURPOSE Titanium is a primary metallic biomaterial used in load-bearing orthopedic or dental implants because of its favorable mechanical properties and osseointegration capability. This article reviews the current status of surface optimization techniques for titanium implants, whether such concepts are in the form of sufficiently evidence-based, and highlights the related experimental tools. STUDY SELECTION A strong emphasis was placed on the enhanced biological responses to titanium implants by modifying the surface finishing process. On this basis, a clear partition of surface chemistry and topography was critical. RESULTS The intrinsic host tissue response to titanium implants is facilitated by the chemistry or topography of a passive oxide film, although the extent to which the surface characteristics enable rapid osseointegration is still uncertain. CONCLUSION Besides the fundamental requirements, such as the promotion of osteogenic differentiation, the titanium implant surface should accelerate wound-healing phenomena prior to bone ingrowth toward the surface. Moreover, because initial bacterial attachment to the implant surface is unavoidable, infection control by surface modification is also an important determinant in reducing surgical failure. A desirable surface-biological relationship often needs to be characterized at the nanoscale by means of advanced technologies.

The characteristics of in vitro biological activity of titanium surfaces anodically oxidized in chloride solutions.

Photo-functionalized radical reactions on TiO(2) have been correlated with adsorption of organic impurities and decreasing hydrophilicity of titanium-based biomaterials. Such reactive oxygen species (ROS) spontaneously generated on oxidized titanium surfaces may also have important roles against time-dependent degradation of biological ability and adherent micro-organisms. This study examined in vitro biological ability as a function of time and antimicrobial activity on oxidized titanium surfaces without photo-functionalization. Mechanically polished titanium and thermally oxidized titanium surfaces that had been stored for 4 wks showed adsorbed organic impurities with decreased surface hydrophilicity. Even after the storage period, anodically oxidized titanium surfaces enabled super-hydrophilicity without adsorption of organic impurities, because of the ROS and the hydrophilic functional groups generated on the surfaces. The osteogenic gene expressions of osteoblasts cultured on anodically oxidized titanium surfaces with or without storage were significantly higher than those on thermally oxidized titanium and polished titanium surfaces. Titanium surfaces anodically oxidized in a solution with chloride achieved antimicrobial activity against an oral microorganism due to the amount of ROS generated on the surface. Thus, titanium anodically oxidized in solution with chloride may have potential use for titanium-based internal fixation devices.

A new modified laser pretreatment for porcelain zirconia bonding

OBJECTIVES The aim of this study was to compare the effects of three different surface treatments in enhancing porcelain zirconia bonding. METHODS Totally, 160 densely sintered zirconia specimens were prepared and randomly divided into four study groups: control (no treatment, Group C), sandblasting (Group S), sandblasting followed by regeneration firing (Group SH), and laser irradiation (pulse mode) on a CO₂ laser system (Group L). After surface treatment, porcelain powders were veneered on zirconia surface. Half of the specimens in each group were evaluated without aging (initial shear bond strength - initial SBS), and the other half was tested after being stored in water for one month (aging SBS). X-ray diffractometry (XRD) was used to observe any crystallographic transformation at zirconia surface. Results were statistically analyzed using analysis of variance (ANOVA) and Turkey test (=0.05). RESULTS The initial average SBS values of Group S, Group SH, and Group L were 31.3 ± 5.7 MPa, 29.2 ± 7.0 MPa and 32.1 ± 7.5 MPa, respectively. The differences among these three groups were not significant. The control group had significantly lower value, 24.8 ± 6.7 MPa, than those of Group S and Group L. Furthermore, there was no significant difference between initial and aging values in each group. XRD analysis showed that sandblasting caused tetragonal to monoclinic phase transformation. Regeneration firing reversed such a transformation. However, crystallographic transformation could not be detected in laser treated specimens. SIGNIFICANCE Both sandblasting and laser irradiation increased porcelain zirconia bond strength. The presented new modified laser pre-treatment might be an alternative way to sandblasting for improving zirconia/porcelain integration.

Micromechanical Property Recovery of Human Carious Dentin Achieved with Colloidal Nano-β-tricalcium Phosphate

Reconstitution of carious dentin has been recognized as difficult, because it progresses by loss of collagen polymerization and by demineralization under acidic conditions. Recently, colloidal alkaline nano-calcium phosphate, prepared by electrical discharge in a buffered physiological saline solution, has been shown to be effective in the formulation of a bone-like biocomposite by simply being mixed with acidic collagen solution. It was hypothesized that colloidal calcium phosphate was suitable for the reconstitution of carious dentin. Natural caries lesions in dentin from permanent teeth were exposed to colloidal hydroxyapatite and β-tricalcium phosphate for 10 days. The micromechanical properties of these tissues were evaluated by nano-indentation. The elastic modulus of human carious dentin improved after samples were immersed in colloidal β-tricalcium phosphate. The mineral density of carious dentin exposed to β-tricalcium phosphate increased more than that immersed in hydroxyapatite. However, since it was not directly proportional to micromechanical recovery, mineral density alone was not a sufficient indicator of mechanical behavior.

Micro-structural integrity of dental enamel subjected to two tooth whitening regimes

Colour modification of tooth enamel has proven successful, but it is unclear how various bleaching applications affect micro-structural integrity of the whitened enamel. To investigate the internal structural integrity of human intact tooth enamel with the application of two commonly used whitening regimes (in-office power bleaching with 35% hydrogen peroxide and home bleaching with 10% carbamide peroxide), evaluations were performed on teeth of identical colour classification. After the bleaching applications, the enamel mineral density was quantified and visualised with micro-computed tomography. The micro-structural differences between the whitened tooth enamel samples were distinctive, though the colour parameter changes within the samples were equivalent. Home bleaching achieved colour modification by demineralisation, whereas in-office bleaching depended on redistribution of the minerals after treatment and subsequent enhanced mineralisation.

Antimicrobial and osteogenic properties of a hydrophilic-modified nanoscale hydroxyapatite coating on titanium

Hydroxyapatite (HA)-coated titanium (Ti) is commonly used for implantable medical devices. This study examined in vitro osteoblast gene expression and antimicrobial activity against early and late colonizers of supra-gingival plaque on nanoscale HA-coated Ti prepared by discharge in a physiological buffered solution. The HA-coated Ti surface showed super-hydrophilicity, whereas the densely sintered HA and Ti surfaces alone showed lower hydrophilicity. The sintered HA and HA-coated Ti surfaces enhanced osteoblast phenotypes in comparison with the bare Ti surface. The HA-coated Ti enabled antimicrobial activity against early colonizers of supra-gingival plaques, namely Streptococcus mitis and Streptococcus gordonii. Such antimicrobial activity may be caused by the surface hydrophilicity, thereby leading to a repulsion force between the HA-coated Ti surface and the bacterial cell membranes. On the contrary, the sintered HA sample was susceptible to infection of microorganisms. Thus, hydrophilic-modified HA-coated Ti may have potential for use in implantable medical devices. From the Clinical Editor: This study establishes that Hydroxyapatite (HA)-coated titanium (Ti) surface of implanted devices may result in an optimal microenvironment to control and prevent infections and may have potential future clinical applications.

Colloidal β-Tricalcium Phosphate Prepared by Discharge in a Modified Body Fluid Facilitates Synthesis of Collagen Composites

The development of hydroxyapatite/collagen composites that are naturally synthesized and need no additional treatment is required for use in bone repair. Since reducing the diameter can increase the specific surface area of calcium phosphate particles that can conjugate collagen molecules, we expected colloidal calcium phosphates of submicron diameter obtained by discharge to be effective in formulating these composites. Additionally, since biodegradable β-tricalcium phosphate has better osteoconductivity than hydroxyapatite, this study aimed to investigate the synthesis of colloidal hydroxyapatite and β-tricalcium phosphate/collagen composites. Collagen molecules were tightly polymerized in the β-tricalcium phosphate/collagen composite by catalysis of the generated -P-O-P- polyphosphate chain. Bonding strength between collagen NH+ amino groups and -P-O-P-, and cross-linking of the Ca++-RCOO− in the collagen were increased compared with those in the hydroxyapatite/collagen composite. These chemical reactions due to colloidal β-tricalcium phosphate might play a key role in the synthesis of collagen composites.

Micro-organism and Cell Viability on Antimicrobially Modified Titanium

When titanium is anodized by discharge in NaCl solution, both antimicrobial activity and osteoconductivity are conferred. The viability of adherent micro-organisms and cells on antimicrobial titanium remains uncertain. We hypothesized that a thin peroxidation barrier would efficiently destroy adherent bacteria, whereas adherent osteoblastic cells would be viable, since these cells adhere to the surface indirectly though serum proteins. The efficacy of antimicrobial titanium appears to be based on peroxidation, since peroxidation products were detected in parallel with the destruction of bacterial cell-surface structures. The peroxidation effect of antimicrobial titanium was confined to the surface within narrow limits. The viability of osteoblastic cells on the surface was strongly dependent on the presence of serum protein, whereas that of adherent Streptococcus mutans was not affected by the presence of serum proteins. Therefore, differences in the adherent systems used by bacteria and osteoblastic cells are important determinants of their viability on antimicrobial titanium.

A review of improved fixation methods for dental implants. Part II: Biomechanical integrity at bone–implant interface

PURPOSE The purpose of this article is to review the mechanical requirements of the tissue-implant interface and analyze related theories. STUDY SELECTION The osseointegration capacity of titanium implants has been investigated over the past 50 years. We considered the ultimate goal of osseointegration to which form a desirable interfacial layer and a bone matrix with adequate biomechanical properties. RESULTS Occasionally, the interface comprises porous titanium and bone ingrowth that enables a functionally graded Youngs modulus, thereby allowing reduction of stress shielding. However, the optimal biomechanical connection at the interface has not yet been fully clarified. There have been publications supporting several universal mechanical testing technologies in terms of bone-titanium bonding ability, although the separation of newly formed bone quality is unlikely. CONCLUSIONS The understanding of complex mechanical bone behavior and size-dependent properties ranging from a nano- to a macroscopic level are essential in the biomechanical optimization of implants. The requirements of regenerated tissue at the interface include high strength, fracture toughness related to ductility, and time-dependent energy dissipation and/or elastic-plastic stress distribution. Moreover, a strong relationship between strain signals and peri-implant tissue turnover could be expected, so that ideal implant biomechanics may enable longevity via adaptive bone remodeling.