Yukinori Maruo

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.

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.

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

Abstract 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.

Vertical and horizontal polymerization shrinkage in composite restorations

OBJECTIVE Polymerization shrinkage developed in vertical and horizontal directions after light activation of light-curing composite restorative materials. The purpose of this study was to examine the effects of vertical and horizontal polymerization shrinkage on: (a) dimensional changes of resin composites in tooth cavities; (b) shear bond strengths to enamel and dentin; and (c) marginal gap width in a non-reacting Teflon mold. METHODS Vertical and horizontal polymerization shrinkage in tooth cavities were measured immediately (3 min) after light activation. With the same time lapse, shear bond strengths to enamel and dentin and marginal gap widths in Teflon mold were also measured. RESULTS There was a significant correlation between vertical and horizontal polymerization shrinkage (r=0.647, p=0.043) in the tooth cavity. Composite materials which produced small vertical shrinkage also produced smaller horizontal shrinkage. Composite materials which produced small vertical shrinkage in the tooth cavity exhibited greater shear bond strengths to both enamel (r=-0.697, p=0.025) and dentin (r=-0.752, p=0.012). Composite materials which produced smaller horizontal shrinkage produced smaller marginal gap widths in the Teflon mold (r=0.829, p=0.003). No relationships were observed between horizontal shrinkage in the tooth cavity and shear bond strengths to both enamel and dentin (p>0.05). SIGNIFICANCE During the early stage of setting (<3 min) in tooth cavities, the vertical shrinkage of light-activated composite restorative materials was correlated with horizontal shrinkage.

Various Effects of Sandblasting of Dental Restorative Materials

Background Sandblasting particles which remain on the surfaces of dental restorations are removed prior to cementation. It is probable that adhesive strength between luting material and sandblasting particle remnants might exceed that with restorative material. If that being the case, blasting particles adhere to sandblasted material surface could be instrumental to increasing adhesive strength like underlying bonding mechanism between luting material and silanized particles of tribochemical silica coating-treated surface. We hypothesize that ultrasonic cleaning of bonding surfaces, which were pretreated with sandblasting, may affect adhesive strength of a resin luting material to dental restorative materials. Methods We therefore observed adhesive strength of resin luting material to aluminum oxide was greater than those to zirconia ceramic and cobalt-chromium alloy beforehand. To measure the shear bond strengths of resin luting material to zirconia ceramic and cobalt-chromium alloy, forty specimens of each restorative material were prepared. Bonding surfaces were polished with silicon abrasive paper and then treated with sandblasting. For each restorative material, 40 sandblasted specimens were equally divided into two groups: ultrasonic cleaning (USC) group and non-ultrasonic cleaning (NUSC) group. After resin luting material was polymerized on bonding surface, shear test was performed to evaluate effect of ultrasonic cleaning of bonding surfaces pretreated with sandblasting on bond strength. Results For both zirconia ceramic and cobalt-chromium alloy, NUSC group showed significantly higher shear bond strength than USC group. Conclusions Ultrasonic cleaning of dental restorations after sandblasting should be avoided to retain improved bonding between these materials.

Bacterial adhesion not inhibited by ion-releasing bioactive glass filler

OBJECTIVE Bioactive glasses and surface pre-reacted glass-ionomer (sPRG) filler possess cariostatic properties owing to ion release. Many studies investigated potential cariostatic effects; few studies evaluated the surface stability and the structural changes their surfaces undergo in acidic conditions. METHODS The surface resistance against acid attack and the surface receptiveness for bacterial adhesion and biofilm formation of a sPRG-filled (Beautifil ll, Shofu) and conventional glass-filled (Herculite XRV Ultra, Kerr) resin-based composite (RBC), and a conventional glass-ionomer cement (GIC; Fuji IX GP Extra, GC) were examined. Specimens (n=3) were immersed in distilled water or lactic acid (pH 4.0) for 3 days. Bacterial growth and biofilm formation were recorded using optical density and SEM. RESULTS Upon 3-day immersion in lactic acid, the surface of the sPRG-filled RBC revealed multiple holes, while virtually no change in surface integrity was observed for the conventional RBC and GIC. Bacterial growth measurements revealed that none of the materials inhibited Streptococcus mutans (p<0.05). Remarkably, cross-sectional SEM revealed that S. mutans had penetrated the etch pits induced by lactic acid in/around the sPRG filler. Ion-release measurements revealed that sPRG-filled RBC released boron and fluoride, while GIC only released fluoride. However, the concentration of ions released by both materials appeared not sufficient to inhibit bacterial growth. Moreover, the structural surface change and resultant increased surface roughness appeared to have promoted biofilm formation. SIGNIFICANCE While having bioactive potential through ion release, the stability of surface integrity of bioactive materials is a key-parameter to be assessed with regard to their cariostatic potential.

Salivary stress biomarker levels during speech in patients with maxillectomy defect

After resection of maxillofacial tumors, severe functional problems related to mastication, deglutition, and speech are observed in addition to the changes in appearance and psychosocial functioning. Although speech outcome is recovered with prosthetic treatments, patients sometimes complain of continued dissatisfaction with their speech. The purpose of this study was to evaluate the potential dissatisfaction of patients with maxillectomy defects during speech.

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.

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.