Flexural properties of polyethylene, glass and carbon fiber-reinforced resin composites for prosthetic frameworks.

OBJECTIVE: High flexural properties are needed for fixed partial denture or implant prosthesis to resist susceptibility to failures caused by occlusal overload. The aim of this investigation was to clarify the effects of four different kinds of fibers on the flexural properties of fiber-reinforced composites. MATERIALS AND METHODS: Polyethylene fiber, glass fiber and two types of carbon fibers were used for reinforcement. Seven groups of specimens, 2 × 2 × 25 mm, were prepared (n = 10 per group). Four groups of resin composite specimens were reinforced with polyethylene, glass or one type of carbon fiber. The remaining three groups served as controls, with each group comprising one brand of resin composite without any fiber. After 24-h water storage in 37°C distilled water, the flexural properties of each specimen were examined with static three-point flexural test at a crosshead speed of 0.5 mm/min. RESULTS: Compared to the control without any fiber, glass and carbon fibers significantly increased the flexural strength (p < 0.05). On the contrary, the polyethylene fiber decreased the flexural strength (p < 0.05). Among the fibers, carbon fiber exhibited higher flexural strength than glass fiber (p < 0.05). Similar trends were observed for flexural modulus and fracture energy. However, there was no significant difference in fracture energy between carbon and glass fibers (p > 0.05). CONCLUSION: Fibers could, therefore, improve the flexural properties of resin composite and carbon fibers in longitudinal form yielded the better effects for reinforcement.

Long-Term Bonding Performance of One-Bottle vs. Two-Bottle Bonding Agents to Lithium Disilicate Ceramics.

The aim of this study was to compare the long-term bonding performance to lithium disilicate (LDS) ceramic between one-bottle and two-bottle bonding agents. Bonding performance was investigated under these LDS pretreatment conditions: with hydrofluoric acid (HF) only, without HF, with a two-bottle bonding agent (Tokuyama Universal Bond II) only. Shear bond strengths between LDS and nine resin cements (both self-adhesive and conventional adhesive types) were measured at three time periods: after one-day water storage (Base), and after 5000 and 20,000 thermocycles (TC 5k and TC 20k respectively). Difference in degradation between one- and two-bottle bonding agents containing the silane coupling agent was compared by high-performance liquid chromatography. With HF pretreatment, bond strengths were not significantly different among the three time periods for each resin cement. Without HF, ESTECEM II and Super-Bond Universal showed significantly higher values than others at TC 5k and TC 20k when treated with the recommended bonding agents, especially at TC 20k. Difference in degradation between one- and two-bottle bonding agents containing the silane coupling agent was compared by high-performance liquid chromatography (HPLC). For both cements, these values at TC 20k were also not significantly different from pretreatment with only Tokuyama Universal Bond II. For LDS, long-term bond durability could be maintained by pretreatment with Tokuyama Universal Bond II instead of the hazardous HF.

Shear Bond Strength of Resin Luting Materials to Lithium Disilicate Ceramic: Correlation between Flexural Strength and Modulus of Elasticity.

This study investigates the effect of the curing mode (dual-cure vs. self-cure) of resin cements (four self-adhesive and seven conventional cements) on their flexural strength and flexural modulus of elasticity, alongside their shear bond strength to lithium disilicate ceramics (LDS). The study aims to determine the relationship between the bond strength and LDS, and the flexural strength and flexural modulus of elasticity of resin cements. Twelve conventional or adhesive and self-adhesive resin cements were tested. The manufacturer's recommended pretreating agents were used where indicated. The shear bond strengths to LDS and the flexural strength and flexural modulus of elasticity of the cement were measured immediately after setting, after one day of storage in distilled water at 37 °C, and after 20,000 thermocycles (TC 20k). The relationship between the bond strength to LDS, flexural strength, and flexural modulus of elasticity of resin cements was investigated using a multiple linear regression analysis. For all resin cements, the shear bond strength, flexural strength, and flexural modulus of elasticity were lowest immediately after setting. A clear and significant difference between dual-curing and self-curing modes was observed in all resin cements immediately after setting, except for ResiCem EX. Regardless of the difference of the core-mode condition of all resin cements, flexural strengths were correlated with the LDS surface upon shear bond strengths (R2 = 0.24, n = 69, p < 0.001) and the flexural modulus of elasticity was correlated with them (R2 = 0.14, n = 69, p < 0.001). Multiple linear regression analyses revealed that the shear bond strength was 17.877 + 0.166, the flexural strength was 0.643, and the flexural modulus was (R2 = 0.51, n = 69, p < 0.001). The flexural strength or flexural modulus of elasticity may be used to predict the bond strength of resin cements to LDS.

Shear bond strength of resin cement on moist dentin and its relation to the flexural strength of resin cement.

We sought to compare the bond strength of resin cement on moist dentin to that on dry dentin, and determine the relationship between the bond strength and flexural strength of resin cement. The water content of the moist and dry dentins was estimated using infrared spectroscopy. Four adhesive and three self-adhesive resin cements were used. At three times of immediately, after one-day storage, and after 20,000 thermocycles (TC 20k), the shear bond strengths were measured. For all resin cements, both the shear bond strength and the flexural strength were the lowest immediately after setting; however, after one day of water storage or TC 20k, these resin cements had the highest values. Regardless of the condition of the dentin surface upon shear bond strength, the flexural strength of each resin cement was correlated with the shear bond strength of the dentin surface.

Effect of spherical silica additions on marginal gaps and compressive strength of experimental glass-ionomer cements.

PURPOSE: To clarify the effects of the addition of silanized (S) and unsilanized (U) spherical silica filler to resin-modified glass-ionomer cement and of powder-liquid ratio on (1) the early marginal gap-width of restorations in both tooth cavities and Teflon molds, (2) the gap-formation of restorations in Class V cavities, and (3) the compressive strength of the cement. METHODS: Resin-modified glass-ionomer powder (Fuji II LC EM, GC) was modified by adding 5 and 10 wt% of powder respectively, of S and U, and then the powder-liquid ratio was increased up to 4.8. Human premolars, extracted for orthodontic reasons, were used for this study. Cylindrical cavities (1.5 mm deep, 3.5 mm in diameter; one cavity was prepared in each tooth in the coronal region and medial surface) were prepared in extracted human premolar teeth and restored with resin-modified glass-ionomer cements. Each restoration margin was inspected immediately after curing and polishing (as the immediate condition was the most severe), the maximum gap-width and the opposing width (if any) were determined microscopically (n = 10). An additional test was conducted in model Class V cavities. After finishing of restorations in model Class V cavities, each tooth was sectioned in a bucco-lingual direction through the center of the restoration, and the presence or absence of gaps along the cavity interface was evaluated (n = 10). Additionally, the maximum marginal gap-width and the opposing-width along margins of restorations in cylindrical Teflon molds were measured (n= 10). The compressive strengths of the restorative materials were determined immediately after light-activation (n = 10). RESULTS: Marginal gap (tooth cavity: 0.32 to 0.25-0.20%, P < 0.05; Teflon cavity: 0.94 to 0.6-0.8%, P < 0.05) and cavity adaptation (no gap in the Class V: 22 to 40-50%, P < 0.05) of the restorations improved with increasing powder-liquid ratio (3.0 to 4.4-4.8) and compressive strength increased (111 to 150-170 MPa, P < 0.05). Highly significant correlation coefficients were found for the relationships between powder-liquid ratio and (1) percentage of marginal gap width in the tooth cavity (r = -0.96, P = 0.002, n = 6), (2) gap-free tooth/cement interfaces (r = 0.90, P = 0.015, n = 6), (3) percentage of marginal gap widths in the Teflon mold (r = 0.98, P = 0.0004, n = 6) and (4) compressive strengths of the cements (r = 0.95, P = 0.004, n = 6).

Phosphate group adsorption capacity of inorganic elements affects bond strength between CAD/CAM composite block and luting agent.

This study aimed to investigate whether inorganic elements of polymer-infiltrated ceramic (PIC) and microfilled resin (MFR) for CAD/CAM would affect initial bond strength to luting agent. Inorganic elements of PIC and MFR were different with shape and ingredient observed by SEM, STEM and EDS. Microtensile bond strengths (µTBS) value of PIC was increased by 10-methacryloyloxydecyl dihydrogen phosphate (MDP) and acetic acid (AA)- or MDP-activated silane treatment, and further increased by succeeding heat treatment (HT). The µTBS of MFR was increased by MDP and MDP-activated silane, but decreased by AA-activated silane without HT. The HT improved the µTBS of MFR with AA-activated silane, but conversely for MDP-activated silane. Only in MFR, phosphoric acid (PA) application before each surface treatment dramatically decreased the µTBS of AA-activated silane. FTIR peaks in MFR shifted according to phosphate group's peak. MFR would possess high phosphate group adsorption capacity, with MDP effectively improving its bonding capability.

Relationships between Flexural and Bonding Properties, Marginal Adaptation, and Polymerization Shrinkage in Flowable Composite Restorations for Dental Application.

To evaluate the flexural and bonding properties, marginal adaptation, and polymerization shrinkage in flowable composite restorations and their relationships, four new generation flowable composites, one conventional, and one bulk-fill flowable composite were used in this study. Flexural properties of the composites and shear bond strength to enamel and dentin for flowable restorations were measured immediately and 24 h after polymerization. Marginal adaptation, polymerization shrinkage, and stress were also investigated immediately after polymerization. The flexural properties, and bond strength of the flowable composites to enamel and dentin were much lower immediately after polymerization than at 24 h, regardless of the type of the composite. Polymerization shrinkage and stress varied depending on the material, and bulk-fill flowable composite showed much lower values than the others. The marginal adaptation and polymerization shrinkage of the composites appeared to have a much stronger correlation with a shear bond strength to dentin than to enamel. The weak mechanical properties and bond strengths of flowable composites in the early stage after polymerization must be taken into account when using them in the clinic. In addition, clinicians should be aware that polymerization shrinkage of flowable composites can still lead to the formation of gaps and failure of adaptation to the cavity regardless of the type of composite.

Flexural Strength of Resin Core Build-Up Materials: Correlation to Root Dentin Shear Bond Strength and Pull-Out Force.

The aims of this study were to investigate the effects of root dentin shear bond strength and pull-out force of resin core build-up materials on flexural strength immediately after setting, after one-day water storage, and after 20,000 thermocycles. Eight core build-up and three luting materials were investigated, using 10 specimens (n = 10) per subgroup. At three time periods-immediately after setting, after one-day water storage, and after 20,000 thermocycles, shear bond strengths to root dentin and pull-out forces were measured. Flexural strengths were measured using a 3-point bending test. For all core build-up and luting materials, the mean data of flexural strength, shear bond strength and pull-out force were the lowest immediately after setting. After one-day storage, almost all the materials yielded their highest results. A weak, but statistically significant, correlation was found between flexural strength and shear bond strength (r = 0.508, p = 0.0026, n = 33). As the pull-out force increased, the flexural strength of core build-up materials also increased (r = 0.398, p = 0.0218, n = 33). Multiple linear regression analyses were conducted using these three independent factors of flexural strength, pull-out force and root dentin shear bond strength, which showed this relationship: Flexural strength = 3.264 × Shear bond strength + 1.533 × Pull out force + 10.870, p = 0.002). For all the 11 core build-up and luting materials investigated immediately after setting, after one-day storage and after 20,000 thermocycles, their shear bond strengths to root dentin and pull-out forces were correlated to the flexural strength in core build-up materials. It was concluded that the flexural strength results of the core build-up material be used in research and quality control for the predictor of the shear bond strength to the root dentin and the retentive force of the post.

Flexural properties, bond ability, and crystallographic phase of highly translucent multi-layered zirconia.

This study investigated the mechanical properties, bond ability, and crystallographic forms of different sites in a highly translucent, multi-layered zirconia disk. Flexural properties, bond ability to resin cement, and phase composition were investigated at three sites of a highly translucent, multi-layered zirconia disk: incisal, middle, and cervical. Flexural strength (FS) and flexural modulus (FM) were measured with static three-point flexural test. Shear bond strength (SB) to resin cement was measured after 24 h storage (37°C). Phase composition under mechanical stress was analyzed using X-ray diffraction. Without air abrasion, FS at the incisal site yielded the lowest value and was significantly lower than the middle and cervical sites. Air abrasion lowered the FS of each site. FM at the incisal site without air abrasion showed the significantly lowest value, and air abrasion increased its FM value. At the middle and cervical sites, their FM values were higher than the incisal site but were not significantly affected by air abrasion. SB value did not show significant differences among the sites. After sintering, cubic zirconia was detected at each site. Rhombohedral phase transformation occurred after mirror polishing. In highly translucent, multi-layered zirconia which was mainly composed of cubic zirconia, rhombohedral phase transformation occurred under mechanical stress and resulted in weakened mechanical properties.

Silane-coupling effect of a silane-containing self-adhesive composite cement.

OBJECTIVE: Hydrofluoric-acid etching followed by silanization is a routine clinical protocol for durable bonding to glass ceramics. Simplifying ceramic-bonding procedures, new technological developments involve the inclusion of a silane coupling agent in a self-adhesive composite cement. To investigate the effectiveness of the incorporated silane coupling agent, shear bond strength (SB) to ceramic and dentin, contact angle of water (CA), transmission electron microscopy (TEM), X-ray diffraction (XRD) and 29Si nuclear magnetic resonance (NMR) assessments were correlatively conducted. MATERIALS AND METHODS: SB to glass ceramic was measured without ('immediate') and with ('aged') 50K thermocycles upon application of (1) the silane-containing self-adhesive composite cement Panavia SA Cement Universal ('SAU'), being light-cured: 'SAU_light', (2) 'SAU_chem': chemically cured SAU, (3) 'SAP_light': light-cured Panavia SA Cement Plus ('SAP'), and (4) 'SAP_CP': SAP light-cured after separate silanization using Clearfil Ceramic Primer Plus ('CP'). CA was also measured on glass ceramic. The cement pastes before and upon mixing were characterized using 29Si NMR. SB of SAU or SAP onto dentin was measured. Finally, the cement-dentin interface was characterized by TEM and XRD. RESULTS: The immediate and aged SB to glass ceramic of SAU did not significantly differ from those of SAP_CP, while they were significantly higher than those of SAP. CA of SAU did not significantly differ from that of SAP_CP, but it was significantly higher than CA of SAP. 29Si NMR revealed siloxane bonds after mixture. SB of SAU and SAP to dentin did not show any significant difference. SEM, TEM and XRD confirmed tight and chemical interaction, respectively. SIGNIFICANCE: Incorporating silane in a 10-MDP-based self-adhesive composite cement combined efficient silane-coupling ability at the ceramic surface with effective bonding ability at dentin.

Class I gap-formation in highly-viscous glass-ionomer restorations: delayed vs immediate polishing.

This in vitro study evaluated the effects of delayed versus immediate polishing to permit maturation of interfacial gap-formation around highly viscous conventional glass-ionomer cement (HV-GIC) in Class I restorations, together with determining the associated mechanical properties. Cavity preparations were made on the occlusal surfaces of premolars. Three HV-GICs (Fuji IX GP, GlasIonomer FX-II and Ketac Molar) and one conventional glass-ionomer cement (C-GIC, Fuji II, as a control) were studied, with specimen subgroups (n=10) for each property measured. After polishing, either immediately (six minutes) after setting or after 24 hours storage, the restored teeth were sectioned in a mesiodistal direction through the center of the model Class I restorations. The presence or absence of interfacial-gaps was measured at 1000x magnification at 14 points (each 0.5-mm apart) along the cavity restoration interface (n=10; total points measured per group = 140). Marginal gaps were similarly measured in Teflon molds as swelling data, together with shear-bond-strength to enamel and dentin, flexural strength and moduli. For three HV-GICs and one C-GIC, significant differences (p<0.05) in gap-incidence were observed between polishing immediately and after one-day storage. In the former case, 80-100 gaps were found. In the latter case, only 9-21 gaps were observed. For all materials, their shear-bond-strengths, flexural strength and moduli increased significantly after 24-hour storage.

Ultrasonic cleaning of silica-coated zirconia influences bond strength between zirconia and resin luting material.

The purpose of this study was to evaluate how ultrasonic cleaning of silica-coated zirconia surfaces would influence the latter's bond strength to resin luting material. Forty zirconia specimens were divided into four groups: one air abrasion group and three silica-coated groups. Silica-coated specimens were cleaned with distilled water using an ultrasonic cleaner after tribochemical silica coating and then divided into three groups according to cleaning durations: 1 minute, 5 minutes, or without cleaning. Following which, resin luting material was polymerized against the specimens. After storage in water for 24 hours, the specimens were subjected to shear bond strength test. Shear bond strength of silica-coated group without cleaning was significantly higher than the other three groups, but there were no statistically significant differences among the three latter groups. SEM images suggested visible differences among the treatment methods. With EDXS analysis, it was revealed that ultrasonic cleaning decreased the silica content on the treated surfaces. Therefore, results showed that ultrasonic cleaning of tribochemically silica-coated zirconia surfaces decreased the adhesion efficacy to resin luting material.

Deformation of mesh type stainless palatal plate of maxillary complete denture and the growth of microorganisms.

PATIENT: An 83-year-old woman visited the hospital for new complete dentures. A mesh type stainless palatal plate (Trutissu plate) was selected, because it enables the patient to experience the taste and temperature of food. Twenty one months after insertion, the patient returned complaining of pain on mucosa under the mandibular denture base. On clinical examination, a small swollen area was observed on the palatine rugae region of the mesh plate. By making a small hole in the swollen part, a creamy mass of dark brown color was discharged from the swollen space between the laminated structure of the Trutissu plate. Three months after the first deformation was corrected, further deformation of the Trutissu plate was observed. The patient admitted that she had not used the ultrasonic cleansing apparatus. A candidiasis-like lesion was observed on the palatal mucosa. DISCUSSION: The formation of Candida biofilms on dentures may assist survival of fungal cells and contribute to the disease process in patients with denture stomatitis. In this case, the patient did not use ultrasonic cleaner, thus resulting in microbial accumulation and morphological change of the laminated mesh plate. However, this is rare in the clinical use of the Trutissu mesh plate, and the only case reported in 20 years. Ultrasonic cleansing was effective in removing microorganisms from the denture. CONCLUSION: Routine ultrasonic cleansing should be performed to avoid the possible accumulation of microorganisms in the laminated mesh structure.

Tensile bond strength between custom tray and elastomeric impression material.

The aim of this study was to investigate how to achieve sufficient and stable adhesive strength between impression material and tray. Impression materials were molded between autopolymerizing resin columns, and tensile strength was measured as a function of these factors: tray storage time (1, 2, 4, 7, and 10 days), adhesive drying time (0, 1, 5, 10, and 15 minutes), and tray surface roughness (air abrasion, bur-produced roughness, and no treatment). Tensile bond strength was not affected by tray storage time throughout the entire evaluation period of 10 days. As for tray adhesive drying time, Reprosil and Exaimplant yielded extremely low values for drying times of 10 minutes or less (P<0.05), while Imprint II and Impregum were not influenced by drying time. Vinyl polysiloxane achieved the highest adhesive strength with bur-produced roughness, which was significantly higher than with air abrasion or no treatment (P<0.05), whereas polyether achieved the lowest value with bur-produced roughness (P<0.05). It was concluded that surface treatment of custom tray should be adapted to the type of impression material used to achieve optimum bond strength.

The design of non-occlusal intraoral appliances on hard palate and their effect on masseter muscle activity during sleep.

This study aimed to reveal whether masseter muscle activity during sleep is affected by the difference in design of non-occlusal intraoral appliances on hard palate. Eight healthy Japanese participants were selected and wore each of the four types of appliances (horse shoe, thin, thick and medium thick) during sleep for one week with a one week interval without appliance during sleep. A masseter muscle electromyograph (EMG) was recorded during sleep. The EMG activities were analyzed by calculating the number of bursts per hour, episodes per hour, and bursts per episode. The EMG parameters with the thick type appliance were significantly lower than the baseline condition without appliance. In this study, it is suggested that a thick type appliance has an active effect on suppression of masseter muscle activity.

Performance of Class I composite restorations when polished immediately or after one-day water storage.

This study investigated the effects on gap formation in Class I restorations (observed by vertical and horizontal forms of inspection) and on the mechanical properties of nine resin composite filling materials when the restorations were subject to finishing immediately after setting or after one-day water storage. Class I restorations with resin composite fillings were polished either immediately (3 min) after setting or after one-day water storage. Interfacial gap formation (observed by vertical inspection) was assessed using 14 gap measurement points along the interface between the restoration and cavity walls and floor (n = 10 per resin composite; total points measured per time point = 140). For marginal gaps formed at cavosurface margins in Class I cavities and in Teflon molds, marginal gap formation (observed by horizontal inspection) was assessed by measuring the maximum gap-width and opposing width (if any). Effects on mechanical properties were assessed by measuring shear bond strengths to enamel and dentin, flexural strength and modulus. After one-day storage, marginal gap-widths in Class I restorations were significantly decreased for all composites, alongside a significant increase in shear bond strengths to enamel and dentin, flexural strength and modulus. Resin composite-filled Class I restorations which were polished after one-day delay presented lower gap formation compared with finishing immediately after setting.

Does acid etching morphologically and chemically affect lithium disilicate glass ceramic surfaces?

BACKGROUND: This study evaluated the surface morphology, chemical composition and adhesiveness of lithium disilicate glass ceramic after acid etching with hydrofluoric acid or phosphoric acid. METHODS: Lithium disilicate glass ceramic specimens polished by 600-grit silicon carbide paper were subjected to one or a combination of these surface treatments: airborne particle abrasion with 50-µm alumina (AA), etching with 5% hydrofluoric acid (HF) or 36% phosphoric acid (Phos), and application of silane coupling agent (Si). Stainless steel rods of 3.6-mm diameter and 2.0-mm height were cemented onto treated ceramic surfaces with a self-adhesive resin cement (Clearfil SA Cement). Shear bond strengths between ceramic and cement were measured after 24-hour storage in 37°C distilled water. RESULTS: SEM images of AA revealed the formation of conventional microretentive grooves, but acid etching with HF or Phos produced a porous surface. Bond strengths of AA+HF+Si (28.1 ± 6.0 MPa), AA+Phos+Si (17.5 ± 4.1 MPa) and HF+Si (21.0 ± 3.0 MPa) were significantly greater than those of non-pretreated controls with Si (9.7 ± 3.7 MPa) and without Si (4.1 ± 2.4 MPa) (p<0.05). In addition, HF etching alone (26.2 ± 7.5 MPa) had significantly higher bond strength than AA alone (11.5 ± 4.0 MPa) (p<0.05). AA+HF, AA+Phos and HF showed cohesive failures. CONCLUSIONS: Etching with HF or Phos yielded higher bond strength between lithium disilicate glass ceramic and self-adhesive resin cement without microcrack formation.

Does 8-methacryloxyoctyl trimethoxy silane (8-MOTS) improve initial bond strength on lithium disilicate glass ceramic?

OBJECTIVES: Dental ceramic surfaces are modified with silane coupling agents, such as γ-methacryloxypropyl trimethoxy silane (γ-MPTS), to improve bond strength. For bonding between lithium disilicate glass ceramic and resin cement, the objective was to investigate if 8-methacryloxyoctyl trimethoxy silane (8-MOTS) could yield a similar performance as the widely used γ-MPTS. METHODS: One hundred and ten lithium disilicate glass ceramic specimens were randomly divided into 11 groups (n=10) according to pretreatment regime. All specimens were pretreated with a different solution composed of one or a combination of these agents: 10 or 20wt% silane coupling agent of γ-MPTS or 8-MOTS, followed by a hydrolysis solution of acetic acid or 10-methacryloyloxydecyl dihydrogen phosphate (10-MDP). Each pretreated surface was luted to a stainless steel rod of 3.6mm diameter and 2.0mm height with resin cement. Shear bond strength between ceramic and cement was measured after 24-h storage in 37°C distilled water. RESULTS: 8-MOTS produced the same bonding performance as γ-MPTS. Both silane coupling agents significantly increased the bond strength of resin cement, depending on their concentration. When activated by 10-MDP hydrolysis solution, 20wt% concentration produced the highest values (γ-MPTS: 24.9±5.1MPa; 8-MOTS: 24.6±7.4MPa). Hydrolysis with acetic acid produced lower bond strengths than with 10-MDP. SIGNIFICANCE: Silane coupling pretreatment with 8-MOTS increased the initial bond strength between lithium disilicate glass ceramic and resin cement, rendering the same bonding effect as the conventional γ-MPTS.

Sandblasting may damage the surface of composite CAD-CAM blocks.

OBJECTIVE: CAD-CAM blocks to fabricate semi-direct and indirect restorations are available in different sorts of ceramics as well as composite. In order to bond restorations prepared out of composite blocks into tooth cavities, it is recommended to gently sandblast the surface prior to the application of a primer/adhesive. Today, the effect of sandblasting composite block surfaces has not thoroughly been investigated. In this study, the ultra-structure of composite CAD-CAM blocks was investigated with special attention to the effect of sandblasting on the surface topography and of silanization on the bonding performance. METHODS: Five different composite CAD-CAM blocks were involved. We correlatively investigated their structural and chemical composition using X-ray diffraction (XRD), energy dispersion spectroscopy (EDS), scanning electron microscopy (SEM) and (scanning) transmission electron microscopy ((S)TEM). The effect of sandblasting was also imaged in cross-section and at the interface with composite cement. Finally, we measured the shear bond strength to the sandblasted block surface with and without silanization. RESULTS: All composite blocks revealed a different ultra-structure. Sandblasting increased surface roughness and resulted in an irregular surface with some filler exposure. Sandblasting also damaged the surface. When the sandblasted composite blocks were silanized, superior bonding receptiveness in terms of higher bond strength was achieved except for Shofu Block HC. SIGNIFICANCE: Sandblasting followed by silanization improved the bond strength to composite CAD-CAM blocks. However, sandblasting may also damage the composite CAD-CAM block surface. For the composite CAD-CAM block Shofu Block HC, the damage was so severe that silanization did not improve bond strength.

Effect of adhesive primer developed exclusively for heat-curing resin on adhesive strength between plastic artificial tooth and acrylic denture base resin.

Despite progress in the development of denture base resin and artificial tooth materials, dental clinics are still plagued with artificial teeth falling off the denture base--due to poor bond strength--after denture delivery. Against this background, this study sought to examine the effect and durability of an adhesive primer developed exclusively for heat-curing resin on the adhesive strength of heat-curing denture base acrylic resin to plastic artificial tooth. Test specimens were divided into four groups according to the treatment method of the artificial tooth's test bonding surface: air abrasion, adhesive primer application, adhesive primer application after air abrasion, and pretreatment only (control). After heat curing of acrylic resin onto the bonding surface, shear test was performed for two storage periods: 24-hour versus 100-day water storage. From the results obtained, it was revealed that the evaluated adhesive primer was significantly effective in increasing adhesive strength between artificial tooth and acrylic resin, although specimens were stored in water for 100 days.