Objectives. This study was planned to investigate the variations in strains in enamel under different patterns of occlusal loading, using three-dimensional finite element analysis (3D FEA) and strain ...gage measurements in extracted teeth.
Methods. A 3D FEA model of a mandibular second premolar was used to investigate effects of occlusal load on enamel surface strains, particularly in response to oblique directions of cuspal loading. Point loads of 100
N were applied axially and at 45° from the vertical on the buccal or lingual incline of the buccal cusp, either in the bucco-lingual plane or at varying mesio-distal angulations (up to ±20°). Patterns of strain observed in the FEA model were confirmed experimentally using strain gages on extracted premolars mounted in a servohydraulic testing machine.
Results. Strains predicted from the FEA model were in excellent agreement with the strain gage measurements. Strains were concentrated near the cementoenamel junction (CEJ) regardless of load direction. A vertical load on the buccal cusp tip resulted in compressive strains on the buccal surface but small tensile strains in lingual cervical enamel. Strains resulting from oblique loads on buccal cusp inclines were complex and asymmetric, with either tension or compression occurring in any location depending on the site and angle of loading.
Significance. The magnitude, direction and character of strains in cervical enamel are highly dependent on patterns of loading. The asymmetric pattern of strains in buccal cervical enamel in response to oblique occlusal forces is consistent with the common clinical picture of asymmetric non-carious cervical lesions.
This study compared the ultimate tensile strength, micropunch shear strength, and microhardness of bleached and unbleached human dentin. Forty-four intact premolars were root canal treated and ...randomly divided into four groups. Bleaching agents were sealed in pulp chambers, as in clinical use. Group 1 (control) was treated with water, group 2 with 30% hydrogen peroxide, group 3 with sodium perborate mixed with water, and group 4 with sodium perborate mixed with 30% hydrogen peroxide. The teeth were stored in saline at 37°C for 7 days. The teeth were then sectioned and biomechanical tests were carried out on dentin specimens that were obtained from all teeth. Intracoronal bleaching with 30% hydrogen peroxide and sodium perborate used either alone or in combination weakened dentin. Hydrogen peroxide alone tended to be more damaging than sodium perborate used alone or sodium perborate mixed with hydrogen peroxide.
Aim
To evaluate whether application of a total‐etch/separate adhesive layer can enhance the bond of a UDMA‐based sealer to dentine.
Methodology
The root canals of 20 decoronated maxillary premolar ...teeth with two canals were prepared to size 35–45, 0.04 taper using rotary NiTi instruments. The canals of each tooth were treated with application of either a total‐etch/separate adhesive or the manufacturer‐recommended primer, before root filling with sealer plus matching master cone using warm vertical compaction. After setting, roots were sectioned perpendicular to the long axis to obtain 1‐mm‐thick slices, and the root filling was subjected to the push‐out test using a plunger closely matched to canal diameter. The roots of another 15 single‐rooted premolars were sectioned in a bucco‐lingual direction, and the cut surfaces were ground flat for microshear bond strength testing. One‐half of the specimens were coated with a separate total‐etch/adhesive layer, and then, a cylinder of sealer cement 1 mm diameter × 1.5 mm high was bonded to the prepared surface of all specimens. Microshear bond strength was measured in a universal testing machine after 48 h. Data were analysed using anova and paired t‐tests, with significance set at P < 0.05.
Results
Use of a separate total‐etch/adhesive markedly increased both microshear bond strength and push‐out strengths compared with standard primer (P < 0.001).
Conclusion
Application of a separate adhesive layer significantly increases bond strength of UDMA‐based sealers to root dentine.
This study compared the microshear bond strengths (MSBS) of four self-etching adhesives (Adper Scotchbond SE SSE, Clearfil SE Bond CSE, Clearfil S3 Bond CS3 and One Coat 7.0 OC) and an etch-and-rinse ...adhesive (Adper Single Bond Plus SB) when bonded to two conventional glass ionomer cements (GICs) (Fuji IX GP EXTRA and Riva Self Cure). The null hypothesis tested was there is no difference in the adhesive ability of an etch-and-rinse adhesive and self-etching adhesives when bonded to GIC for up to 6 months.
The GICs were embedded in type III dental stone and wet ground with 1200-grit SiC paper. Twenty specimens were bonded for each adhesive according to manufacturers' instructions with a 1.5-mm bonding diameter. Specimens were stored at 100% humidity for 24 hours, 1 month, or 6 months. Microshear bond strengths were obtained using a crosshead speed of 1 mm/min. The results were calculated and analyzed using analysis of variance (ANOVA) and Tukey HSD test.
SB had significantly lower MSBS than the four self-etching adhesives for all storage periods. MSBS at 6 months for SB was significantly lower than at 1 month. There were no significant differences in MSBS among the self-etching adhesives. Cohesive failure within GIC was the most common failure mode observed.
SB showed a lower bond strength than the self-etching adhesives when bonded to conventional GICs for all storage periods. This might be a result of the phosphoric acid etching. However, cohesive strength of GIC was a limiting factor for the MSBS outcomes.
Aim To measure the temperature distribution within tooth structure during and after application of thermal stimuli used during pulp sensitivity testing.
Methodology Extracted intact human maxillary ...anterior teeth were investigated for temperature changes at the labial enamel, the dentino‐enamel junction (DEJ) and pulpal surface during and after a 5‐s application of six different thermal stimuli: hot water (80 °C), heated gutta‐percha (140 °C), carbon dioxide dry ice (−72 °C), refrigerant spray (−50 °C), ice stick (0 °C) and cold water (2 °C). J‐type thermocouples and heat conduction paste were used to detect temperature changes, together with a data acquisition system (Labview). Data were analysed using analysis of variance, with a confidence level of P < 0.05.
Results Temperature change was detected more quickly at the DEJ and pulpal surface with the application of hot water, heated gutta‐percha and refrigerant spray than with carbon dioxide dry ice and ice (P < 0.05). Cold water and refrigerant spray were in the same range in terms of time to detect temperature change at both the DEJ and pulpal surface. Thermal stimuli with greater temperature difference from tooth temperature created a greater thermal gradient initially, followed by a greater temperature change at the DEJ and the pulpal surface. In this regard, ice and cold water were weaker stimuli than others (P < 0.05).
Conclusions Thermal stimuli used in pulp testing are highly variable in terms of temperature of the stimulus, rate of thermal transfer to the tooth and extent of temperature change within tooth structure. Overall, dry ice and refrigerant spray provide the most consistent stimuli, whereas heated gutta‐percha and hot water were highly variable. Ice was a weak stimulus.
It is important to understand subsurface dentin demineralization and caries from the clinical perspective as dentin properties are modified under acidic conditions and mechanical loading. This study ...was conducted to observe the subsurface demineralization of dentin beams at three different pH levels under tension and compression. Bovine dentin beams (10 x 3.75 x 1.45 mm) were fixed at one end and immersed in 0.1 M lactic acid solution at pH levels 4.5, 7, and 10 for 5 days under a load of 6.5 N (663 g), and the subsurface demineralization depth was measured using a polarized light microscope. The mean subsurface demineralization depth was more subjacent to the surface under compression than that under tension at pH 4.5 and decreased as the distance from the fixed end increased. No subsurface demineralization was observed at pH 7 or 10. It was concluded that both stress and low pH are associated with increased subsurface demineralization at the fixed end of the beam.
Summary Dentin‐bonding agents and resin composite materials typically require light activation for polymerization. Light curing generates heat, which may influence dentinal fluid flow (DFF) and ...cuspal displacement. This study investigated the relationship among temperature increase, DFF and cuspal displacement in extracted human maxillary premolars with a mesial occlusal distal (MOD) cavity preparation. Two types of curing light were compared. Temperature changes were measured using thermocouples located on the occlusal cavity floor and at the pulp‐dentine junction, during polymerization of bonding agent and resin composite material. DFF and cuspal displacement were measured simultaneously using automated flow measurement apparatus and direct current differential transformers respectively. Temperature increases of up to 15 °C were recorded during the restoration procedures. A quartz tungsten halogen (QTH) unit produced a significantly greater temperature increase than a light‐emitting diode unit and curing of the bonding agent generated less temperature increase than curing of the resin composite. Heating due to exothermic reaction during polymerization of bonding agent and resin was not significantly different between light sources or between bonding and curing (P > 0·05). The QTH unit produced both greater inward fluid flow and cuspal displacement during the irradiation of bonding agent and resin composite than the light‐emitting diode unit. There was not a simple relationship between temperature increase, fluid movement and cuspal displacement. From a clinical point of view, the light‐emitting diode unit can be considered preferable to the QTH light, because it caused significantly smaller temperature increase, fluid shift and cuspal displacement.
Statement of problem Little information comparing the fracture resistance of internal connection titanium and zirconia abutments exists to validate their use intraorally. Purpose The purpose of this ...study was to determine the fracture resistance of internal connection titanium and zirconia abutments by simulating cyclic masticatory loads in vitro. Material and methods Twenty-two specimens simulating implant-supported anterior single crowns were randomly divided into 2 equal test groups: Group T with titanium abutments and Group Z with zirconia abutments. Abutments were attached to dental implants mounted in acrylic resin, and computer-aided design/computer-aided manufacturing (CAD/CAM) crowns were fabricated. Masticatory function was simulated by using cyclic loading in a stepped fatigue loading protocol until failure. Failed specimens were then analyzed by using scanning electron microscopy (SEM) and fractographic analysis. The load (N) and the number of cycles at which fracture occurred were collected and statistically analyzed by using a 2-sample t test (α=.05). Results The titanium abutment group fractured at a mean (SD) load of 270 (56.7) N and a mean (SD) number of 81 935 (27 929) cycles. The zirconia abutment group fractured at a mean (SD) load of 140 (24.6) N and a mean (SD) number of 26 296 (9200) cycles. The differences between the groups were statistically significant for mean load and number of cycles ( P <.001). For the titanium abutment specimens, multiple modes of failure occurred. The mode of failure of the zirconia abutments was fracture at the apical portion of the abutment without damage or plastic deformation of the abutment screw or implant. Conclusions Within the limitations of this in vitro study, 1-piece zirconia abutments exhibited a significantly lower fracture resistance than titanium abutments. The mode of failure is specific to the abutment material and design, with the zirconia abutment fracturing before the retentive abutment screw.
The objective of this work was to determine the effect on the retention force of full cast crowns cemented on short tooth preparations after preparation of dentine with an erbium, chromium: yttrium ...scandium gallium garnet (Er, Cr:YSGG) laser at different sub-ablative power settings. Thirty teeth were prepared for full cast crowns using a milling machine. The surface area for all preparations was measured. The surfaces of the preparations were irradiated with 0 (control), 0.25 and 0.75 W laser. The crowns were cemented with self-cure resin cement and tested for retention on a Hounsfield Tensometer machine. The 0.75 W power setting produced the highest failure load value (346.2 +/- 86.1 N) and was significantly higher than the other groups. There were no significant differences between the 0.25 W and 0 W control groups
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