Jukka Pekka Matinlinna

Aspects of silane coupling agents and surface conditioning in dentistry: an overview.

OBJECTIVES To give an overview of aspects of silane coupling agents and surface conditioning in dentistry. METHODS Currently, silane coupling agents are used as adhesion promoters. Silanes are effective in enhancing adhesion between resin composite and silica-based ceramics. They do not bond effectively to non-silica based dental restorative materials. Surface conditioning of non-silica based ceramics with silica coating improves the bonding. This current overview will focus on the silane coupling agents: their properties, limitations in adhesion promotion and the clinical problems with the use of silanes. It will also focus on the current surface conditioning methods as well as new surface conditioning techniques to enhance the bonding through conventional silanization approaches. RESULTS Several surface conditioning methods are being used clinically to enhance the adhesion of resin composites to non-silica based restorative materials. Other approaches are under investigation. The clinical problem of using silanes in adhesion promotion is the bond degradation over time in oral environment. SIGNIFICANCE The current silane coupling agents are not ideal. The current silane coupling agents can fulfill the minimum requirements in clinical practice to enhance the bonding of resin composite to dental restorative materials. Developments of novel surface conditioning methods and silane coupling agents are required to address the bond durability problem.

Innovations in bonding to zirconia-based materials. Part II: Focusing on chemical interactions

OBJECTIVES The zirconia-resin bond strength was enhanced using novel engineered zirconia primers in combination with selective infiltration etching as a surface pre-treatment. The aim of this study was to evaluate the effect of artificial aging on the chemical stability of the established bond and to understand the activation mechanism of the used primers. METHODS Selective infiltration etched zirconia discs (Procera; NobelBiocare) were coated with one of four novel engineered zirconia primers containing reactive monomers and were bonded to resin-composite discs (Panavia F2.0). Fourier transform infrared spectroscopy (FT-IR) was carried out to examine the chemical activation of zirconia primers from mixing time and up to 60min. The bilayered specimens were cut into microbars (1mm(2) in cross-section area) and zirconia-resin microtensile bond strength (MTBS) was evaluated immediately and after 90 days of water storage at 37 degrees C. Scanning electron microscopy (SEM) was used to analyze the fracture surface. RESULTS There was a significant drop in MTBS values after 90 days of water storage for all tested zirconia primers from ca. 28-41MPa to ca. 15-18MPa after completion of artificial aging. SEM revealed increase in percentage of interfacial failure after water storage. FTIR spectra suggested adequate activation of the experimental zirconia primers within 1h of mixing time. SIGNIFICANCE The novel engineered zirconia primers produced initially high bond strength values which were significantly reduced after water storage. Long-term bond stability requires developing more stable primers.

Ceramic dental biomaterials and CAD/CAM technology: State of the art

PURPOSE Ceramics are widely used as indirect restorative materials in dentistry because of their high biocompatibility and pleasing aesthetics. The objective is to review the state of the arts of CAD/CAM all-ceramic biomaterials. STUDY SELECTION CAD/CAM all-ceramic biomaterials are highlighted and a subsequent literature search was conducted for the relevant subjects using PubMed followed by manual search. RESULTS Developments in CAD/CAM technology have catalyzed researches in all-ceramic biomaterials and their applications. Feldspathic glass ceramic and glass infiltrated ceramic can be fabricated by traditional laboratory methods or CAD/CAM. The advent of polycrystalline ceramics is a direct result of CAD/CAM technology without which the fabrication would not have been possible. CONCLUSIONS The clinical uses of these ceramics have met with variable clinical success. Multiple options are now available to the clinicians for the fabrication of aesthetic all ceramic restorations.

Effect of operating air pressure on tribochemical silica-coating

Objective. Alumina and zirconia are inert to conventional etching and need to be initially conditioned with, for example, silicatization. The aim of the present study was to evaluate the effect of operating air pressure of tribochemical silica-coating method on the shear bond strength of composite resin to ceramic substrates. Material and methods. Alumina (Procera Alumina, Nobel Biocare) and zirconia (LAVA; 3M ESPE and Procera Zirconia; Nobel Biocare) were airborne particle silica-coated (CoJet; 3M ESPE) using selected, clinically available air pressures of 150, 220, 300, and 450 kPa. The surfaces were silanized with silane coupling agent (ESPE Sil; 3M ESPE) and coated with adhesive resin (3M Multipurpose resin; 3M ESPE). Particulate filler resin composite (Z250; 3M ESPE) stubs (diameter 3.6 mm, height 4.0 mm) were added onto ceramics and light-cured for 40 s. The test specimens (n=18/group) were thermocycled (6000×5–55°C) and shear bond strengths were measured with a cross-head speed of 1.0 mm/min. Fracture surfaces were examined with SEM, and an elemental analysis (EDS) was carried out to determine silica content on the substrate surface. Results. The highest bond strengths were obtained with the highest pressures. ANOVA showed significant differences in bond strength between the ceramics (p<0.05) and between the specimens treated at various air pressures (p<0.05). Conclusions. Clinically, the operating air pressure of silicatization may have a significant effect on bond strength to non-etchable ceramics.

Pilot evaluation of resin composite cement adhesion to zirconia using a novel silane system.

Objective. In this study, we evaluated the effect of two silane coupling agents and their blends with a cross-linker silane on the bond strength of a dimethacrylate-based resin composite cement to surface-conditioned zirconia. Material and Methods. A total of 40 planar zirconia specimens were used for 8 test groups. After alumina particle abrasion, followed by tribochemical silica-coating, the specimens were randomly assigned to four silanizations: with 1.0 vol% 3-methacryloyloxypropyltrimethoxysilane or 1.0 vol% 3-mercaptopropyltrimethoxysilane or their blends with 1.0 vol% 1,2-bis-(triethoxysilyl)ethane (all in ethanol/water). The resin composite (RelyX™ ARC, 3M ESPE) stubs (n=10/group) were light-polymerized onto zirconia specimens. Four test groups were tested without water storage and 4 thermo-cycled at 6000 cycles (5±1°C to 55±1°C), with a dwelling time of 30 s. The shear bond strength of the cement stubs to zirconia was measured using a universal testing machine at a constant cross-head speed of 1 mm/min. Scanning electron microscopy was employed for imaging the zirconia surface after conditioning and testing. Failure mode was evaluated visually. A surface chemical analysis was carried out with the EDXA system. Results. The highest shear bond strength was 21.9±8.7 MPa, obtained with a blend of 3-mercaptopropyltrimethoxysilane and 1,2-bis-(triethoxysilyl)ethane (dry storage), and 16.0±1.5 MPa, with 3-methacryloyloxypropyltrimethoxysilane (thermo-cycled). Thermo-cycling decreased the bond strengths significantly (ANOVA, p<0.01), and the silanes differed significantly (p<0.005). Some specimens suffered from spontaneous debonding during thermo-cycling. Conclusions. The luting cement adhesion might be promoted to silica-coated zirconia with 1.0 vol% 3-methacryloyloxypropyltrimethoxysilane and with a blend of 1.0 vol% 3-mercaptopropyltrimethoxysilane and 1.0 vol% 1,2-bis-(triethoxysilyl)ethane.

Isocyanato- and Methacryloxysilanes Promote Bis-GMA Adhesion to Titanium

In dentistry, adhesion promotion with 3-methacryloyloxypropyltrimethoxysilane is usually sufficient, but its hydrolytic stability is a continuous concern. The hydrolytic stability of an alternative, 3-isocyanatopropyltriethoxysilane, was compared with that of conventional 3-methacryloyloxypropyltrimethoxysilane. Two silanes, both in 0.1 and 1.0 vol-% in ethanol-water, were evaluated in the attachment of an experimental bis-phenol-A-diglycidyldimethacrylate (Bis-GMA) resin to grit-blasted (with two different systems) titanium. Silane hydrolysis was monitored by FTIR spectrometry. Bis-GMA resin was applied and photo-polymerized on titanium. The specimens were thermocycled (6000 cycles, 5–55°C). Surface analysis was carried out with scanning electron microscopy. Statistical analysis (ANOVA) showed that the highest shear bond was achieved with 0.1% 3-isocyanatopropyltriethoxysilane (12.5 MPa) with silica-coating, and the lowest with 1.0% 3-methacryloyloxypropyltrimethoxysilane (3.4 MPa) with alumina-coating. The silane, its concentration, and the grit-blasting method significantly affected the shear bond strength (p < 0.05). SEM images indicated cohesive failure of bonding, and, in conclusion, 3-isocyanatopropyltriethoxysilane is a potential coupling agent.

Aspects of bonding between resin luting cements and glass ceramic materials

OBJECTIVES The bonding interface of glass ceramics and resin luting cements plays an important role in the long-term durability of ceramic restorations. The purpose of this systematic review is to discuss the various factors involved with the bond between glass ceramics and resin luting cements. METHODS An electronic Pubmed, Medline and Embase search was conducted to obtain laboratory studies on resin-ceramic bonding published in English and Chinese between 1972 and 2012. RESULTS AND DISCUSSION Eighty-three articles were included in this review. Various factors that have a possible impact on the bond between glass ceramics and resin cements were discussed, including ceramic type, ceramic crystal structure, resin luting cements, light curing, surface treatments, and laboratory test methodology. CONCLUSIONS Resin-ceramic bonding has been improved substantially in the past few years. Hydrofluoric acid (HF) etching followed by silanizaiton has become the most widely accepted surface treatment for glass ceramics. However, further studies need to be undertaken to improve surface preparations without HF because of its toxicity. Laboratory test methods are also required to better simulate the actual oral environment for more clinically compatible testing.

E-Glass Fiber Reinforced Composites in Dental Applications

Fiber reinforced composites (FRCs) are more and more widely applied in dentistry to substitute for metallic restorations: periodontal splints, fixed partial dentures, endodontic posts, orthodontic appliances, and some other indirect restorations. In general in FRCs, the fiber reinforcement provides the composite structure with better biomechanical performance due to their superior properties in tension and flexure. Nowadays, the E-glass fiber is most frequently used because of its chemical resistance and relatively low cost. Growing interest is being paid to enhance its clinical performance. Moreover, various techniques are utilized to reinforce the adhesion between the fiber and the matrix. Oral conditions set special requirements and challenges for the clinical applications of FRCs. The biomechanical properties of dental materials are of high importance in dentistry, and given this, there is on-going scientific interest to develop E-glass fiber reinforced composite systems. FRCs are generally biocompatible and their toxicity is not a concern.

Enhanced resin-composite bonding to zirconia framework after pretreatment with selected silane monomers

OBJECTIVE To evaluate the effect of five experimental silane monomer primers in vitro on the shear bond strength of a phosphate ester resin-composite cement bonded to a silicatized zirconia framework. METHODS A total of 144 planar zirconia (Procera AllZircon) specimens were subjected to tribochemical silica treatment, randomly divided into 12 sub-groups (n=12), and silanized with 1.0%(v/v) activated solutions of 3-acryloxypropyltrimethoxysilane, 3 glycidoxypropyltrimethoxysilane, 3-methacryloxypropyltrimethoxysilane, styrylethyltrimethoxysilane, and 3-isocyanatopropyltriethoxysilane, which had been prepared in 95% ethanol (pH 4.5). A ready-to-use 3-methacryloxypropyltrimethoxysilane (RelyX™ Ceramic Primer) was used as the control. One resincomposite cement (RelyX™ Unicem) stub was bonded to each silicatized and silanized zirconia specimen. Half of the specimen groups were dry-tested and half were thermo-cycled at 6000 cycles between 5°C and 55°C, with a constant dwelling time of 30s. The shear bond strengths of the cement stubs bonded to zirconia were measured using a universal testing machine using a constant cross-head speed of 1mm/min. The silane primer activation was evaluated using Fourier-transform infrared spectroscopy. RESULTS The highest shear bond strength was obtained for 3-acryloxypropyltrimethoxysilane in dry storage, 11.7 MPa (SD, 2.3 MPa) and after thermo-cycling 17.6 (4.1) MPa for glycidoxypropyltrimethoxysilane. The lowest shear bond strength values were obtained with control silane: in dry storage, 4.5 (1.3) MPa, after thermo-cycling 6.5 (2.6) MPa. Thermo-cycling increased the bond strengths significantly (ANOVA, p<0.001) and differently for each type of silane (ANOVA, p<0.001). SIGNIFICANCE Silanization with five experimental silane primers in vitro produced significantly greater shear bond strengths than the ready-to-use control silane.

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.