Abstract Objectives To measure cuspal deflection and tooth strain, plus marginal leakage and gap formation caused by polymerization shrinkage during direct resin composite restoration of root-filled ...premolars. Methods Thirty-two first and second maxillary premolars were divided into four groups ( n = 8). Group 1 had standardised mesio-occlusal-distal (MOD) cavities and served as the control group. Group 2 had endodontic access and root canal treatment through the occlusal floor of the MOD cavity, leaving the axial dentine intact. Group 3 had endodontic access and root canal treatment with the mesial and distal axial dentine removed. Group 4 had endodontic access and root canal treatment with axial dentine removed and a glass ionomer base (GIC). All groups were restored incrementally using a low shrink resin composite. Cuspal deflection was measured using direct current differential transformers (DCDTs), and buccal and palatal strain was measured using strain gauges. Teeth were immersed in 2% methylene blue for 24 h, sectioned and scored for leakage and gap formation under light and scanning electron microscopy. Results Total cuspal deflection was 4.9 ± 1.3 μm for the MOD cavity (group 1), 7.8 ± 3.3 μm for endodontic access with intact axial dentine (group 2), 12.2 ± 2.6 μm for endodontic access without axial dentine (group 3), and 11.1 ± 3.8 μm for endodontic access with a GIC base (group 4). Maximum buccal strain was 134 ± 56, 139 ± 61, 251 ± 125, and 183 ± 63 μstrain for groups 1–4 respectively, while the maximum palatal strain was 256 ± 215, 184 ± 149, 561 ± 123, 264 ± 87 μstrain respectively. All groups showed marginal leakage; however placement of GIC base significantly improved the seal ( p = 0.007). Conclusion Cusp deflection and strain increased significantly when axial dentine was removed as part of the endodontic access. Placement of a glass ionomer base significantly reduced tooth strain and marginal leakage. Therefore, a conservative endodontic access and placement of a glass ionomer base are recommended if endodontically treated teeth undergo direct restoration with resin composite.
The aim of the study was to determine the extent to which canal size, radius of curvature and proximal root concavity influence fracture susceptibility and pattern. A standardized cross-section of ...the mid-root region of a mandibular incisor was created by averaging the dimensions of 10 extracted teeth, and then the basic finite element analysis (FEA) model was created. By varying canal diameter, shape, and proximal concavity, these factors could be examined for roles in fracture susceptibility and pattern. The factors all interact in influencing fracture susceptibility and pattern, with dentin thickness not the only determining factor. The removal of dentin does not always result in an increased fracture susceptibility.
The objective of the study was to compare 1) the mean micro-shear bond strength and 2) failure mode of cements to metals in nonenclosed and mold-enclosed specimens. Specimens were prepared in ...mold-enclosed and non-enclosed formats from two RMGIC’s and a self-adhesive resin-cement. 3-way ANOVA analysis and Tukey post hoc tests were used to compare mean µSBS results (α=0.05). Failure mode was analysed with Pearson’s chi-square test (α=0.05). µSBS was significantly affected by the factors substrate and method (p<0.001) but not by material (p=0.077). There was an interaction between substrate, method and material F (2,144)=3.57, p=0.031, and method and material (2,144)=5.86, p=0.004. All mold-enclosed specimens for the three cements bonded to titanium and non-precious metal exhibited higher (p<0.001) mean µSBS than the non-enclosed specimens. Within this study, mold-enclosed specimens exhibited significantly higher (p<0.001) mean µSBS and adhesive failure compared to non-enclosed specimens.
Abstract Objectives For root canal fillings, a thin layer of sealer cement is generally recommended. However, with resin-based sealers, lower bond strength to dentin has been shown in thin layers ...compared to thick, contrary to typical behavior of adhesive layers between two adherents. The aim of this study was to evaluate tensile and shear bond strength of thin and thick films of three resin-based sealers (one epoxy-based and two methacrylate-based) materials and to investigate corner effects of one methacrylate-based resin sealer. Methods Freshly mixed sealer cements were placed between metal-to-metal surfaces of plano-parallel stainless steel aligned rods with diameter 4.7 mm. Ten samples were prepared for each type, thickness (0.1 and 1.0 mm) of sealer and test. Tensile and shear strengths were measured after 48 h for the methacrylate-based materials and after 7 days for the epoxy-based material using a universal testing machine at a crosshead speed of 1 mm/min. Corner effects were investigated using one methacrylate-based resin material. Results Film thickness had a highly significant influence on both tensile and shear strengths. For methacrylate resin-based sealers, thin films had higher bond strength than thick ( p < 0.001 for both tensile and shear bond strength). With the epoxy-based sealer either no difference (shear) or lower bond strength in thin films (tensile; p < 0.05) was found, and appeared to result from numerous voids created during mixing. The methacrylate based sealer demonstrated typical engineering behavior for an adhesive material, with corner effects shown as a material property and in good agreement with the tensile bond strength results. Significance The higher tensile and shear bond strength of resin-based sealer in thin films is the opposite of that previously reported for bonding to dentin. The substrate clearly has an important role in failure behavior.
Objective: To compare the macro mean shear bond strength (SBS) and failure mode of three cements to two types of metal using mould-enclosed and non-enclosed cement specimens. Methods: Titanium and ...base metal cobalt-based substrates were finished with 50 μm aluminium oxide. Two resin-modified glass-ionomers (Riva Luting Plus, Fuji Plus) and one resin cement (RelyX Unicem) were prepared as per manufacturers' instructions. Metal mould-enclosed and non-enclosed cement specimens with a bonding area diameter of 3.5 mm were prepared and stressed to failure using a 2 mm blunt edge shear knife at a cross-head speed of 1 mm/min to determine mean SBS. The shear knife was placed against the surface of the substrate. Failure analysis of the failed interface was performed with a stereo microscope at 40× magnification. Results: Two-way Analysis of Variance demonstrated a significant difference in mean SBS between materials (p = 0.004) and cement (p = 0.001). There was also a significant interaction between method and cement on SBS, F(2, 170) = 7.209, p = 0.003. Post hoc Tukey tests demonstrated no significant difference for either resinmodified glass-ionomer cements (RMGIC) (p = 0.864, p = 0.620) when comparing non-enclosed and mould-enclosed test methods bonded to titanium. There was however a significant difference (p < 0.001) between the mean SBS obtained for the resin cement when comparing the non-enclosed and mould-enclosed test methods. For base metal, the RMGIC's SBS was higher than resin cement but no difference was observed between one of RMGIC's and the resin cement non-enclosed mean SBS. Although not the case for RMGIC's bonded to titanium or one RMGIC bonded to non-precious cobalt-based metal, when comparing the test method on each cement, RMGIC and the resin cement showed significant differences between non- and mould-enclosed specimens mean SBS. In the non-enclosed specimen tests, 71% of all specimens tested exhibited adhesive failure, which was statistically different (p < 0.001) to 91% for the mould-enclosed specimens. Failure mode was not always statistically different within groups, however non-enclosed specimens showed higher frequencies of mixed failures. Conclusion: Within the limits of this study, significant differences were found in comparing the mean SBS between mould-enclosed and non-enclosed specimens. A significant difference was found in failure mode between mould-enclosed and non-mould enclosed specimens. Mould-enclosed specimens bonded to metal exhibited a higher frequency of adhesive failure than non-mould enclosed specimens. Relevance: Mould-enclosed specimens used in place of non-enclosed specimens can be used in SBS testing to give a more valid result when bonding to metal.
This study aims to evaluate tensile and shear bond strengths of one epoxy (AH) and two methacrylate resin‐based sealers (EZ and RS) in thin and thick layers bonded to root dentine. An alignment ...device was prepared for accurate positioning of 20 root dentine cylinders in a predefined gap of 0.1 or 1 mm. Sealer was placed in the interface. Bond strength tests were conducted. Mode of failures and representative surfaces were evaluated. Data were analysed using anova and post‐hoc tests, with P < 0.05. The thick layer of sealer produced higher bond strength, except for the shear bond strength of EZ. Significant differences between thin and thick layers were found only in tensile bond strengths of AH and RS. Mixed type of failure was constantly found with all sealers. Bond strengths of thick layers of resin‐based sealers to root dentine tended to be higher than with thin layers.
Previous studies have indicated that vertical root fracture tends to occur in a buccolingual direction, where dentin thickness is greatest. Factors potentially influencing the location and direction ...of root fracture include root canal shape, external root morphology, and dentin thickness. In this finite-element study, simulated root sections were varied systematically with respect to canal size and shape, external root morphology, and dentin thickness to determine their relative contribution to vertical root fracture. Similar models were constructed based on cross-sections of human tooth roots that had been fractured clinically or experimentally. Finite-element models demonstrated that canal curvature seems more important than external root morphology, in terms of stress concentration, and that reduced dentin thickness increases the magnitude but not the direction of maximum tensile stress. Models based on actual root fractures showed a strong similarity between tensile-stress distribution and fracture patterns.
The aim of this study was to investigate the polymerisation shrinkage stress under water of four resin-modified glass-ionomers and three resin composite materials.
Transparent acrylic rods (5mm ...diameter×30mm) were prepared and secured into drill chucks connected to a universal testing machine. A plastics cup was placed around the lower rod and a distance of 1.00mm was established between the prepared surfaces which provided a C-factor of 2.5. For composite only, an adhesive layer (Scotchbond Universal Adhesive) was placed on the rod ends and cured to achieve a bond with the rod end. Materials were placed between the rods and a strain gauge extensometer was installed. Materials were light cured for 40s and the plastics cup was filled with ambient temperature water. To determine polymerisation shrinkage stress (σpol) three specimens of each material were tested for a 6-h period to determine mean maximum σpol (MPa), σpol rate (MPa/s) and final σpol (MPa). ANOVA and post hoc Tukey tests were used to determine significant differences between means.
The highest mean maximum σpol of (5.4±0.5) MPa was recorded for RMGIC and (4.8±1.0) MPa for composite. The lowest mean final σpol of (0.8±0.4) MPa was recorded for RMGIC. For mean maximum σpol,σpol rate and final σpol there were significant differences between materials within groups, although no significant difference (p>0.05) was observed when comparing the RMGIC group to the composite group.
When comparing mean σpol, maximum σpol, and σpol rates between individual RMGIC and composite materials significant differences (p<0.05) were observed. However when comparing the group RMGIC to composite no significant differences (p>0.05) were observed. The null hypothesis that there is no difference in the short term σpol of RMGIC materials when compared to composite materials is only partly rejected.
Limited information is available on the comparison of RMGIC and resin composite σpol levels. This study provides information on the short term levels in a wet environment and will assist in understanding the initial σpol rates RMGIC place in cavities.
Abstract Objective To investigate the role of dentinal tubules in the fracture properties of human root dentin and whether resin-filled dentinal tubules can enhance fracture resistance. Materials and ...methods Crack propagation in human root dentin was investigated in 200 μm thick longitudinal samples and examined by light and scanning electron microscopy. 30 maxillary premolar teeth were prepared for work of fracture ( Wf ) test at different tubule orientations, one perpendicular and two parallel to dentinal tubules. Another 40 single canal premolars were randomly divided into four groups of 10 each: intact dentin, prepared but unobturated canal, canal obturated with epoxy rein (AH Plus™/gutta percha), or with UDMA resin sealer (Resilon® /RealSeal® ). The samples were prepared for Wf test parallel to dentinal tubules. Wf was compared under ANOVA with statistical significance set at p < 0.05. Results Dentinal tubules influenced the path of cracks through dentin, with micro-cracks initiated in peritubular dentin of individual tubules ahead of the main crack tip. A significant difference ( p < 0.001) was found between Wf perpendicular to tubule direction (254.9 J/m2 ) vs. parallel to tubule direction from inner to outer dentin (479.4 J/m2 ). Neither canal preparation nor obturation using epoxy- or UDMA-based resins as sealer cements substantially influenced fracture properties of root dentin, despite extensive infiltration of dentinal tubules by both sealer cements.
The aim of this study was to investigate the interfacial work of fracture of conventional (C-) and resin-modified (RM-) glass-ionomer cements (GICs) bonded to dentin.
One hundred and sixty five ...aries-free human molars were embedded in epoxy resin, sectioned and polished with 300- and 600- grit silicon carbide paper to remove enamel on the occlusal surface. Equilateral triangular-shaped plastic molds (4×4×4×5mm4) were clamped to the prepared dentin surfaces by a stainless steel test apparatus. Teflon tape was placed under one internal vertex of the mold to create a 0.1-mm notch at the material-dentin interface. Interfacial work of fracture (γwofint) in tensile fracture mode-I (opening) was determined for six C-GIC, three RM-GIC, and two GIC luting cements at a cross-head speed of 0.1mm/min and a crosshead distance (L) from the interface of 4.3mm. The debonded surfaces were evaluated for the predominant failure mode. SEM analysis of examples showing interfacial and notch areas was performed.
ANOVA and Tukey's post hoc test demonstrated the highest mean γwofint value (90.16±16.6J/m2) of one RM-GIC was significantly different (p<0.05) from the other materials. ‘High viscosity’ GICs achieved lower results with the lowest recorded at 20.4±10.1J/m2. There was a significant difference observed (p<0.05) between the mean γwofint of luting C-GIC and luting RM-GIC. Although differences were observed between different material mean γwofint, when comparing groups no significant differences (p=0.181) were observed. For all groups, mixed GIC-interface failure (41%) was the most commonly observed, followed by cohesive failure in GIC (25%) and adhesive failure (20%). SEM analysis revealed that specimens generally fractured from the notch initiation point into the GIC or along the dentin–GIC interface.
Within the limits of this study, significant differences (p<0.05) were observed in the γwofint between different glass-ionomer materials. The null hypothesis that there is no difference in the γwofint among different glass-ionomer materials bonded to human dentin was rejected.
In the current study, the interfacial work of fracture (γwofint) of glass-ionomer adhesive interfaces has been reported using a simple method that can be used to study the fracture mechanics of an adhesive interface without the need for complicated specimen preparation.
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