The purpose of this review is to summarise recent advances in the design and composition of bioactive surface layers of implantabile biomaterials, and thus the genetic potential of osteoprogenitor cells to recognize and respond to these diverse implanted biomaterials. Changes applied to a biomaterial's surface, in general, could improve its biocompatibility, osseointegration and durability properties, which are required for long-term implantation in the living body. In this review, the implant-bone interface was evaluated and interpreted on the basis of osteoblast cell cultures, i.e., on the genetic potential of osteoblasts to express different phenotype markers depending on the type of biomaterials used. The interface formed by in vitro-grown osteoblasts may be used to identify components of the in vivo implant-bone interface. Over the years, a large number of implant systems consisting of many different biomaterials have been introduced in dentistry and orthopaedics. This paper discusses the performance of currently used metals and other biomaterials, by focusing on the events which occur immediately after implantation and on their impact on the bone-implant interface. The review demonstrates that continuous improvements in composition, surface modality and design of implants may benefit osseointegration and clinical longevity of such implants. No loadbearing conditions or clinical status are discussed. Titanium (Ti) and calcium phosphate ceramics are regarded as the most biocompatible synthetic substances known to be used in hard tissue implantation. These biomaterials are osteoconductive, and do not induce ectopic bone formation. Nonetheless, they provide a physical matrix which is suitable for the deposition of new bone and may guide both the growth and extension of the bone. Comparative investigation evaluated that Ti implant systems appear to be apposed by more bone than ceramic systems, although alternatives concerning the type of Ti alloy and bioactive surface layer engineering, generate extremely diverse osseointegration results. Manufacturers have created an extensive range of inorganic or ceramic coatings on Ti implants in order to achieve better bone healing and osteoconduction. Biologically active molecules, added to the implant surface, represent breakthroughs in guided interfacial osteogenesis. This methodology offers an enormous potential of genetic controlling and promoting osteogenesis. The bone growth factors are not fully understood, but most researchers agree that the contact between the bioactive surface layer of the implant and bone is not static but dynamic and that the above factors may maximise the implant osseointegration.

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To understand the leaching characteristics of bisphenol A (BPA) from composite resins, we prepared experimental composite resins containing known amounts of BPA and examined the BPA elution from the resins in water and methanol at 37°C. The concentration of BPA in each eluate was determined by high performance liquid chromatography. Cumulative BPA release was calculated and plotted against extraction time. The elution of BPA was rapid during a 6-hr period for both solvents, and then declined and continued steadily. Plots of square root of the amount of BPA leached against logarithm of extraction time produced good linear relationships from a 6-hr period thereafter. Extrapolation of the relationship enabled prediction of the amount of BPA to be leached in the long term. The present results suggested that little or no estrogenic effect due to long-term elution of BPA from commercial Bis-GMA-based resins is expected in practice.

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In order to ascertain whether an estrogenic bisphenol A is produced from bisphenol A-related monomers by chemical-induced hydrolysis and to clarify their hydrolytic mechanisms, bisphenol A dimethacrylate (Bis-DMA) and bisphenol A bis (glycidyl methacrylate) (Bis-GMA) were reacted with phosphoric acid, hydrochloric acid, and sodium hydroxide in methanol or methanol/water mixed media at 37°C. Amounts of monomethacrylate intermediates as well as bisphenol A (BPA) were determined by the use of high-performance liquid chromatography (HPLC), and time-conversion curves of hydrolytic products were prepared. BPA and bisphenol A monomethacrylate were produced by acid-catalyzed hydrolysis of Bis-DMA. Bis-GMA was partly converted into monomethacrylate by phosphoric acid and into monomethacrylate and 2, 2-bis [4-(2, 3-dihydroxypropoxy) phenyl] propane (BHP) by hydrochloric acid. Hydrolytic reactions by sodium hydroxide were completed almost within 1 day, resulting in the production of BPA from Bis-DMA, and BHP from Bis-GMA. No BPA was formed from Bis-GMA by chemical-induced hydrolysis. The hydrolytic behaviors of these monomers were discussed.

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We investigated how the thickness of an adhesive layer between two Co-Cr alloy plates affected the mode I fracture toughness of dental adhesive resin by varying the type of resin using a double cantilever beam (DCB) test. Two typical adhesive resins (PV and SB) were used. The adhesive layers of the DCB test specimens were 20, 100 and 200μm thick. The fracture modes of PV differed with the thickness of the adhesive layer, such as interface fracture at 20μm thickness, and similar cohesive fracture at 100 and 200μm thickness. In the case of SB, crackpropagating areas were observed as cohesive fractures in all test specimens with different adhesive layer thickness, and the surfaces of these areas became remarkably rougher as the thickness of the adhesive layer increased. The fracture toughness of PV was not affected by the difference in thickness between the 100 and 200μm adhesive layers, but there was a notable decrease in fracture toughness when the adhesive layer decreased to a thickness of 20μm. That of SB showed a tendency to increase as the adhesive layer became thicker.

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Fifteen kinds of metal particles were examined to establish whether they could induce the setting of UDMA-based monomer containing BPO without amine under the presence of 4-META at room temperature. FT-IR spectra of the resultant set samples and the monomer were analyzed to see if the setting was caused by the polymerization. The effects of 4-META and BPO concentrations on the setting time were also studied using the metal particles that induced the setting very effectively. As-received Cu, Zn, Mo, Sn, Co, and In particles could initiate the polymerization of the monomer in combination with BPO and 4-META when they were moistened with water. All the three kinds of silver alloy particles examined also could initiate the polymerization, although pure silver metal particles could not. The presence of 4-META drastically shortened the setting time of the mixture of Cu particles and the monomer containing BPO, while higher concentration of BPO in the monomer significantly shortened the setting time.

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The polymerization phenomena of zinc particles moistened with a small amount of water, 4-META, and UDMA without amine in the presence and absence of BPO were investigated. The effects of 4-META and BPO on the setting time and the degree of conversion (DC) were studied. Moreover, the effect of zinc ion amount on the setting time was investigated. As-received zinc particles could induce the polymerization either with or without BPO. A higher concentration of 4-META shortened the setting time and increased DC when BPO was absent. However, the presence of BPO generally retarded the setting time and decreased DC, although its effect was dependent on the 4-META concentration. A higher amount of zinc ion retarded the setting reaction in the presence of 4-META. The zinc particles mixed with 10% zinc sulfate and acetic acid solutions could induce the polymerization of UDMA containing BPO when the amine and 4-META were absent.

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Powder-liquid type metal-resin composites, using Ag-Sn irregular particles as the filler, 4-META as coupling agent and UDMA+TEGDMA as resin matrix, were experimentally prepared under 9 different conditions (three different particle sizes and three different filler contents). The flexural strength and flexural modulus were measured. Three different irregular particle size MRCs without redox-initiator at 94% filler content, as well as amalgam, conventional hybrid composite and Ag-Sn spherical particle MRC were evaluated for condensability.
The flexural strength of the Ag-Sn irregular particle MRC was significantly influenced by both the filler particle size and filler contents (p<0.01). It increased when either the filler content increased or the particles size decreased. The highest flexural strength (97.6MPa) was obtained from the condition of particles size <20μm and 94% filler content. The flexural modulus was significantly influenced by filler content and it increased with increasing filler content. The condensability of the Ag-Sn irregular particle MRC was lower than that of amalgam but much higher than presently available conventional composites and spherical particle MRC.

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