Impact of repair protocols on the bond strength to composite resin.

This study evaluated the impact of different repair protocols on a composite resin substrate using distinct bonding agents submitted or not to artificial aging. Unopened sets of a single-step universal adhesive system (UA) and silane-coupling agents, a single-step pre-hydrolyzed (PH) or a two-step immediately hydrolyzed (IH), were used. Half of the sets were subjected to artificial aging being stored at 48 °C for 30 days, while the other half remained unaged. The composite resin substrates were prepared and aged in distilled water, sandblasted (Al2O3), and cleaned. Then the different repair protocols were applied according to the groups. UA was used without a previous silane layer, while PH and IH were applied followed by a single-step etch-and-rinse adhesive system. Adhesive systems were light-activated, and four composite resin cylinders were formed over the substrate. After 24 h, the specimens were subjected to microshear bond strength (µSBS) test and failure mode analysis. The µSBS data were subjected to two-way ANOVA followed by Tukey HSD; Kruskal-Wallis analysis was used for failure mode distribution (α = 0.05). After aging the products, UA showed higher bond strength, while PH had significantly lower results, and IH showed no significant differences (p = 0.157). No significant differences were found for bond strength among the repair protocols when using non-aged products (p > 0.05). The protocols using UA and IH showed no significant differences between aged and non-aged bottles, whereas PH exhibited lower bond strength when comparing aged and non-aged products. More cohesive failures were observed in the resin substrate for the IH group without aging.

Influence of carbonated acid beverage on fracture resistance and marginal gap formation in different restorative approaches to non-carious cervical lesions.

OBJECTIVE: This study is to evaluate fracture resistance, failure mode, and gap formation at the restorative interface of unrestored or restored non-carious cervical lesions (NCCLs) submitted to a short-term erosive environment. MATERIALS AND METHODS: Artificial NCCLs were produced in vitro in bovine incisors, and were randomly divided into four restorative resins groups (n = 22): nanohybrid-NR; bulk-fill-BR; flow with a nanohybrid layer-FNR; bulk-fill with a nanohybrid layer-BNR; and a group unrestored-UR (n = 16). Half of the specimens were submitted to an erosive challenge (per 5 min, 3 × a day for 7 days, before and after restoration), and the other half, was immersed in artificial saliva. After, all teeth undergone thermal (5 ºC, 37 ºC, and 55 ºC, 3600 cycles) and mechanical (50 N, 2 Hz, 300,000 cycles) aging. Eighty teeth were subjected to compressive loading, and resistance and failures were analyzed, while 24 teeth were evaluated for gaps by microcomputed tomography. Statistical tests were performed (p < 0.05). RESULTS: The restorative approaches affected fracture resistance (η2p = 0.14, p = 0.023), and gap formation (η2 = 0.18, p = 0.012) and so did the immersion medium (fracture η2p = 0.09, p = 0.008; gap η2 = 0.09, p = 0.017). BNR showed the highest resistance, while UR the lowest. FNR showed the highest gaps in both immersion media. Neither the resin groups nor the immersion media were associated with failure mode. CONCLUSIONS: The erosive immersion medium based in acid beverages has been shown to affect NCCLs with or without restoration, but when Bulk-Fill resin is covered by nanohybrid resin, the performance is good. CLINICAL RELEVANCE: Erosion negatively affects restorations, but unrestored NCCL shows worse biomechanical performance in stress-bearing situations.

Effect of different materials for conventional and 3D-printed models on the mechanical properties of ethylene-vinyl acetate utilized for fabricating custom-fit mouthguards.

BACKGROUND/AIM: The interaction between the ethylene-vinyl acetate (EVA) with distinct materials utilized for obtaining dental models can affect the performance of resulting mouthguards. This study attempted to evaluate the effect of different materials for conventional (dental stone) or 3D-printed (resin) models on EVA's physical and mechanical properties and surface characteristics. MATERIAL AND METHODS: EVA sheets (Bioart) were laminated over four model types: GIV, conventional Type IV dental stone model (Zhermak); ReG, resin-reinforced Type IV dental stone model (Zero Stone); 3DnT, 3D resin printed model (Anycubic) without surface treatment; 3DT, 3D-printed model (Anycubic) with water-soluble gel (KY Jelly Lubricant, Johnson & Johnson) coating during post-curing process. The EVA specimens were cut following the ISO 37-II standard (n = 30). Shore A hardness was measured before and after plasticization on the contact (internal) or opposite (external) surfaces with the model. The breaking force (F, N), elongation (EL, mm), and ultimate tensile strength (UTS, MPa) were measured using a universal testing machine. Macro-photography and scanning electron microscopy were adopted for classifying the EVA surface alteration. Data were analyzed by one-way ANOVA with repeated measures, followed by Tukey's test (α = .05). RESULTS: Plasticization significantly decreased Shore A values for the tested EVA regardless of the model type (p < .001). Higher F, El, and UTS values were verified for the EVA with 3DT and GIV models compared to ReG and 3DnT (p < .001). 3DnT models resulted in severe surface alteration and a greater reduction of the mechanical properties of the EVA. CONCLUSION: The interaction of EVA with 3D resin-printed models without surface treatment or resin-reinforced Type IV dental stone models significantly affected the physical and mechanical properties of this material. The utilization of water-soluble gel coating during the post-curing process of 3D resin printed models improved the mechanical properties of the EVA, similarly when this material was plasticized over conventional Type IV dental stone model.

A novel simplified method for assessing crystal length and crystalline content in dental ceramics.

The purpose of this study was to introduce a novel and simple method of evaluating the crystal length and crystalline content of lithium disilicate dental ceramics using images obtained from scanning electron microscopy (SEM) and analyzed with ImageJ (NIH) processing software. Three evaluators with varying experience levels assessed the average crystal length and percentage of crystalline content in four commercial lithium disilicate reinforced glass ceramic materials: IPS e.max (Ivoclar Vivadent), Rosetta SM (Hass), T-Lithium (Talmax), and IRIS CAD (Tianjin). The specimens, prepared from partially crystallized CAD/CAM blocks (3.0 mm3), were fully crystallized and treated with 5% hydrofluoric acid for 20 s prior to SEM analysis. After acquiring the SEM images, ImageJ software was used to evaluate the average crystal length and crystalline content on the surface of the different ceramics. An inter-operator agreement was observed (ICC/p = 0.724), indicating that assessments by the various operators were similar across all ceramic materials tested (p < 0.001). When crystal length and crystalline content were compared, IRIS CAD exhibited significant differences compared to the other materials (p < 0.001), showing a less dense crystalline matrix based on the average length of crystals and the percentage of crystals per unit area. The use of this software facilitated the evaluation of crystalline content and average crystal lengths in dental ceramics using SEM images, and demonstrated very low variability among different operators. RESEARCH HIGHLIGHTS: The described method, using ImageJ open-source software, provides precise and reliable measurements of crystal length and crystalline content in lithium disilicate ceramics, with high inter-operator agreement. The proposed method identified higher crystalline content in IPS e.max CAD compared to Rosetta SM CAD and T-lithium CAD ceramics, while IRIS CAD exhibited significantly lower crystalline content and larger average crystal length. The novel, simplified method for assessing crystal length and crystalline content presented in this study may also be useful for evaluating other dental ceramics.

The effect of fiber post presence and restorative technique on the biomechanical behavior of endodontically treated maxillary incisors: an in vitro study.

STATEMENT OF PROBLEM: Unresolved controversy exists concerning the best technique for restoring endodontically treated teeth. Prefabricated posts have been recommended with some debate as a method of restoring pulpless teeth before placement of the final restoration. PURPOSE: The purpose of this in vitro study was to evaluate the effect on the strain, fracture resistance, and fracture mode of endodontically treated human incisors of 4 types of restorations with or without glass fiber posts after thermal cycling. MATERIAL AND METHODS: Ninety human maxillary central incisors were selected and divided into 1 control group and 8 treatment groups (n=10). The teeth were endodontically treated and received 2 large Class III preparations simulating coronal destruction. The teeth were then restored with or without glass fiber posts and by using 4 restorative techniques: direct composite resin, direct composite veneer, feldspathic ceramic veneer, or a feldspathic ceramic crown. After artificial aging by thermal cycling, the incisors were loaded at a 135-degree angle, and the strain was measured by using strain gauges placed on the facial and proximal root surfaces. Specimens were subsequently loaded to the point of fracture. Strain and fracture resistance results were analyzed by a 1-way and 2-way ANOVA, followed by the Tukey HSD and Dunnett tests (α=.05). RESULTS: One-way analyses showed that the control group and the direct composite resin restoration with and without post groups presented significantly higher fracture resistance values (P<.001). Two-way analyses showed no significant differences for the post system. Proximal strain values were higher in the control and composite resin groups and lower in the feldspathic ceramic groups. CONCLUSIONS: The presence of glass fiber posts did not increase the fracture resistance of endodontically treated incisors. Conservative composite resin restorations showed higher fracture resistance values.

Influence of Tip Diameter and Light Spectrum of Curing Units on the Properties of Bulk-Fill Resin Composites.

OBJECTIVE: The aim of this study was to evaluate the influence of different light-curing units (LCUs) with distinct tip diameters and light spectra for activating bulk-fill resins. MATERIALS AND METHODS: The specimens (n = 10) were made from a conventional composite (Amaris, VOCO) and bulk-fill resins (Aura Bulk Fill, SDI; Filtek One, 3M ESPE; Tetric Bulk Fill, Ivoclar Vivadent) with two diameters, 7 or 10 mm, × 2 mm thickness. Following 24 hours of specimen preparation, the degree of conversion (DC) was evaluated using the Fourier-transform infrared unit. Knoop hardness (KHN) readings were performed on the center and periphery of the specimens. Data were assessed for homoscedasticity and submitted to one-way and three-way analysis of variance followed by the Tukey's and Dunnett's tests, depending on the analysis performed (α = 0.05). RESULTS: LCUs and specimen diameter significantly affected the DC. The Tetric Bulk Fill provided increased DC results when light-cured with Valo (54.8 and 53.5%, for 7 and 10 mm, respectively) compared with Radii Xpert (52.1 and 52.9%, for 7 and 10 mm, respectively). No significant differences in KHN results were noted for the conventional resin composite (Amaris) compared with LCUs (p = 0.213) or disc diameters (p = 0.587), but the center of the specimen exhibited superior KHN (p ≤ 0.001) than the periphery. CONCLUSION: The light spectrum of the multipeak LCU (Valo) significantly increased the DC and KHN of the bulk-fill resin composite with additional initiator to camphorquinone (Tetric Bulk Fill) compared with the monowave LCU (Radii Xpert). The tip size of the LCUs influenced the performance of some of the resin composites tested.

The effect of post, core, crown type, and ferrule presence on the biomechanical behavior of endodontically treated bovine anterior teeth.

STATEMENT OF PROBLEM: Unresolved controversy exists concerning the remaining coronal tooth structure of anterior endodontically treated teeth and the best treatment option for restoring them. PURPOSE: The purpose of this study was to evaluate the effect of post, core, crown type, and ferrule presence on the deformation, fracture resistance, and fracture mode of endodontically treated bovine incisors. MATERIAL AND METHODS: One hundred and eighty bovine incisors were selected and divided into 12 treatment groups (n=15). The treatment variations were: with or without ferrule, restored with cast post and core, glass fiber post with composite resin core, or glass fiber post with fiber-reinforced core, and metal- or alumina-reinforced ceramic crown (n=15). The restored incisors were loaded at a 135-degree angle, and the deformation was measured using strain gauges placed on the buccal and proximal root surfaces. Specimens were subsequently loaded to the point of fracture. Strain and fracture resistance results were analyzed by 3-way ANOVA and Tukey HSD tests (α=.05). RESULTS: Ferrule presence did not significantly influence the buccal strain and fracture resistance for the ceramic crown groups, irrespective of core and crown type. Ferrule presence resulted in lower strains and higher fracture resistance in the metal crown groups, irrespective of core. The cast post and core showed lower strain values than groups with glass fiber posts when restored with metal crowns. CONCLUSIONS: Core type did not affect the deformation and fracture resistance of endodontically treated incisors restored with alumina-reinforced ceramic crowns. The presence of a ferrule improved the mechanical behavior of teeth restored with metal crowns, irrespective of core type.

Effect of different cements on the biomechanical behavior of teeth restored with cast dowel-and-cores-in vitro and FEA analysis.

PURPOSE: To test the hypothesis that the type of cement used for fixation of cast dowel-and-cores might influence fracture resistance, fracture mode, and stress distribution of single-rooted teeth restored with this class of metallic dowels. MATERIALS AND METHODS: The coronal portion was removed from 40 bovine incisors, leaving a 15 mm root. After endodontic treatment and standardized root canal relief at 10 mm, specimens were embedded in polystyrene resin, and the periodontal ligament was simulated with polyether impression material. The specimens were randomly divided into four groups (n = 10), and restored with Cu-Al cast dowel-and-cores cemented with one of four options: conventional glass ionomer cement (GI); resin-modified glass ionomer cement (GR); dual-cure resin cement (RC); or zinc-phosphate cement (ZP). Sequentially, fracture resistance of the specimens was tested with a tangential load at a 135 degrees angle with a 0.5 mm/min crosshead speed. Data were analyzed using one-way analysis of variance (ANOVA) and the Fisher test. Two-dimensional finite element analysis (2D-FEA) was then performed with representative models of each group simulating a 100 microm cement layer. Results were analyzed based on von Mises stress distribution criteria. RESULTS: The mean fracture resistance values were (in N): RC, 838.2 +/- 135.9; GI, 772.4 +/- 169.8; GR, 613.4 +/- 157.5; ZP, 643.6 +/- 106.7. FEA revealed that RC and GR presented lower stress values than ZP and GI. The higher stress concentration was coincident with more catastrophic failures, and consequently, with lower fracture resistance values. CONCLUSIONS: The type of cement influenced fracture resistance, failure mode, and stress distribution on teeth restored with cast dowel-and-cores.

Microstructural and mechanical analysis of two CAD-CAM lithium disilicate glass-reinforced ceramics.

The aim of this study was to analyze the structural, morphological and mechanical properties of two different lithium disilicate glass-reinforced ceramics for CAD-CAM systems (IPS e.max CAD and Rosetta SM). Five methodologies were used for both ceramics: microstructure (n = 2) was analyzed using x-ray diffraction (XRD); morphological properties (n = 2) were analyzed by scanning electron microscopy (SEM), with and without hydrofluoric etching; porosity (n = 3) was assessed using 3D micro-computed tomography (micro-CT); flexural strength was measured (n =1 0) using the three-point bending test; and bond strength was determined with self-adhesive resin cement (n = 10), using a microshear bond test. After performing all the tests, the data were analyzed using t-Student test and two-way ANOVA. All the tests used a significance level of α = 0.05. High peak positions corresponding to standard lithium metasilicate and lithium disilicate with similar intensities were observed for both ceramics in the XRD analysis. Morphological analysis showed that the crystalline structure of the two ceramics studied showed no statistical difference after acid etching. Additionally, no significant differences were recorded in the number or size of the pores for the ceramics evaluated. Moreover, no differences in flexural strength were found for the ceramic materials tested, or in the bond strength to ceramic substrates for the resin cements. Based on the study results, no significant differences were found between the two CAD-CAM lithium disilicate glass-reinforced ceramics tested, since they presented similar crystalline structures with comparable intensities, and similar total porosity, flexural strength and bond strength.

Degree of conversion and bond strength of resin-cements to feldspathic ceramic using different curing modes.

OBJECTIVE: The aim of this study was to assess the performance of resin cements when different curing modes are used, by evaluating the degree of conversion and bond strength to a ceramic substrate. MATERIAL AND METHODS: Three resin cements were evaluated, two dual-cured (Variolink II and RelyX ARC) and one light-cured (Variolink Veneer). The dual-cured resin cements were tested by using the dual activation mode (base and catalyst) and light-activation mode (base paste only). For degree of conversion (DC) (n=5), a 1.0 mm thick feldspathic ceramic disc was placed over the resin cement specimens and the set was light activated with a QTH unit. After 24 h storage, the DC was measured with Fourier transform infrared spectroscopy (FTIR). For microshear bond strength testing, five feldspathic ceramic discs were submitted to surface treatment, and three cylindrical resin cement specimens were bonded to each ceramic surface according to the experimental groups. After 24 h, microshear bond testing was performed at 0.5 mm/min crosshead speed until the failure. Data were submitted to one-way ANOVA followed by Tukey test (p<0.05). Scanning electron microscopy (SEM) was used for classifying the failure modes. RESULTS: Higher DC and bond strength values were shown by the resin cements cured by using the dual activation mode. The Variolink II group presented higher DC and bond strength values when using light-activation only when compared with the Variolink Veneer group. CONCLUSION: The base paste of dual-cured resin cements in light-activation mode can be used for bonding translucent ceramic restorations of up to or less than 1.0 mm thick.

Influence of Different Dentin Substrate (Caries-Affected, Caries-Infected, Sound) on Long-Term µTBS.

The aim of this study was to evaluate the µTBS in different dentin substrates and water-storage periods. Twenty-four dentin blocks obtained from sound third molars were randomly divided into 3 groups: Sound dentin (Sd), Caries-affected dentin (Ca) and Caries-infected dentin (Ci). Dentin blocks from Ca and Ci groups were subjected to artificial caries development (S. mutans biofilm). The softest carious tissue was removed using spherical drills under visual inspection with Caries Detector solution (Ca group). It was considered as Ci (softer and deeply red stained dentin) and Ca (harder and slightly red stained dentin). The Adper Single Bond 2 adhesive system was applied and Z350 composite blocks were built in all groups. Teeth were stored in deionized water for 24 h at 37 ºC and sectioned into beams (1.0 mm2 section area). The beams from each tooth were randomly divided into three storages periods: 24 h, 6 months or 1 year. Specimens were submitted to µTBS using EZ test machine at a crosshead speed of 1.0 mm/min. Failure mode was examined by SEM. Data from µTBS were submitted to split plot two-way ANOVA and Tukey's HSD tests (a=0.05). The µTBS (MPa) of Sd (41.2) was significantly higher than Ca (32.4) and Ci (27.2), regardless of storage. Ca and Ci after 6 months and 1 year, presented similar µTBS. Mixed and adhesive failures predominated in all groups. The highest µTBS values (48.1±9.1) were found for Sd at 24 h storage. Storage of specimens decreased the µTBS values for all conditions.

Influence of Hemostatic Solution on Bond Strength and Physicochemical Properties of Resin Cement.

The aim of this study was to evaluate the degree of conversion, color stability, chemical composition, and bond strength of a light-cured resin cement contaminated with three different hemostatic solutions. Specimens were prepared for the control (uncontaminated resin cement) and experimental groups (resin cement contaminated with one of the hemostatic solutions) according to the tests. For degree of conversion, DC (n = 5) and color analyses (n = 10), specimens (3 mm in diameter and 2 mm thick) were evaluated by Fourier transform infrared spectroscopy (FTIR) and CIELAB spectrophotometry (L*, a*, b*), respectively. For elemental chemical analysis (n = 1), specimens (2 mm thick and 6 mm in diameter) were evaluated by x-ray energy-dispersive spectroscopy (EDS). The bond strengths of the groups were assessed by the microshear test (n = 20) in a leucite-reinforced glass ceramic substrate, followed by failure mode analysis by scanning electron microscopy (SEM). The mean values, except for the elemental chemical evaluation and failure mode, were evaluated by ANOVA and Tukey's HSD test. The color stability was influenced by storage time (p<0.001) and interaction between contamination and storage time (p<0.001). Hemostop and Viscostat Clear contamination did not affect the DC, however Viscostat increased the DC. Bond strength of the resin cement to ceramic was negatively affected by the contaminants (p<0.001). Contamination by hemostatic agents affected the bond strength, degree of conversion, and color stability of the light-cured resin cement tested.

Morphometric evaluation and planning of anticurvature filing in roots of maxillary and mandibular molars.

This study aimed to guide the planning of anticurvature filing using pre-determined anatomical points on teeth to establish directions for proper implementation of the technique. Two hundred digital periapical radiographs of human molar teeth were selected and divided into two groups (n = 100): MX (maxillary) and MD (mandibular) molars. Mesiobuccal roots were considered for the MX group and mesial roots for the MD group. Pre-determined anatomical points required for planning the anticurvature filing on the root canal path were located, and the distances between these points obtained. The anticurvature filing was simulated in two different protocols for each group, and the region of dentin removal and the remaining dentin thickness were measured in the safety and danger zones of the root canals. Statistical analysis was carried out at a significance level of 5%. The distances between the anatomical points and the thickness of remaining dentin showed significant differences when the two groups were compared (p < 0.001). No significant differences were found between the two experimental groups regarding the area of dentin removal at the root region, but differences were detected in comparison with dentin removal at the crown (p < 0.001). In terms of wear produced after simulation of both anticurvature filing protocols, significant differences were verified for all regions, except for the dentin remaining at the danger zone. The radiographic location of anatomical points allows for planning and implementation of controlled and efficient anticurvature filing and can be performed in the same manner for maxillary and mandibular molars.

Influence of flexion angle of files on the decentralization of oval canals during instrumentation.

The aim of this study was to evaluate the influence of the flexion angle of files on the decentralization of root canals during instrumentation. Fifteen lower incisors were instrumented with Protaper Universal files and radiographed in two directions (mesiodistal and buccolingual) before and after instrumentation with a #15 K-file in position for evaluating the flexion angle of files. The specimens were also scanned before and after instrumentation using micro-computed tomography to obtain the canal area and the distance from the center position of the file to the canal walls. Sections located 1.0 mm (end of the canal), 3.0 mm (apical third), 9.0 mm (middle third), and 15.0 mm (cervical third) from the apex were verified. After instrumentation, the flexion angles of files decreased by an average of 0.76º in the buccolingual direction and 1.92º in the mesiodistal direction (p < 0.001); the canal area increased by an average of 0.58, 0.37, 0.23 and 0.13 mm(2) from the cervical to the end of the root canal (p < 0.001). Non-instrumented areas were observed on the buccal and lingual walls, and effective action of files was determined on the mesial and distal walls. The sections from the end of the canal showed canal deviation toward the lingual wall, whereas the other sections showed deviation toward the buccal wall. The flexion angles of files influence the final shape of the root canal, resulting in file decentralization along the pathway of the canal.

Microstructural and mechanical analysis of two CAD-CAM lithium disilicate glass-reinforced ceramics

Abstract The aim of this study was to analyze the structural, morphological and mechanical properties of two different lithium disilicate glass-reinforced ceramics for CAD-CAM systems (IPS e.max CAD and Rosetta SM). Five methodologies were used for both ceramics: microstructure (n = 2) was analyzed using x-ray diffraction (XRD); morphological properties (n = 2) were analyzed by scanning electron microscopy (SEM), with and without hydrofluoric etching; porosity (n = 3) was assessed using 3D micro-computed tomography (micro-CT); flexural strength was measured (n =1 0) using the three-point bending test; and bond strength was determined with self-adhesive resin cement (n = 10), using a microshear bond test. After performing all the tests, the data were analyzed using t-Student test and two-way ANOVA. All the tests used a significance level of α = 0.05. High peak positions corresponding to standard lithium metasilicate and lithium disilicate with similar intensities were observed for both ceramics in the XRD analysis. Morphological analysis showed that the crystalline structure of the two ceramics studied showed no statistical difference after acid etching. Additionally, no significant differences were recorded in the number or size of the pores for the ceramics evaluated. Moreover, no differences in flexural strength were found for the ceramic materials tested, or in the bond strength to ceramic substrates for the resin cements. Based on the study results, no significant differences were found between the two CAD-CAM lithium disilicate glass-reinforced ceramics tested, since they presented similar crystalline structures with comparable intensities, and similar total porosity, flexural strength and bond strength.

Influence of ferrule, post system, and length on stress distribution of weakened root-filled teeth.

INTRODUCTION: The aim of this study was to evaluate the influence of a ferrule, post system, and length on the stress distribution of weakened root-filled teeth. METHODS: The investigation was conducted by using 3-dimensional (3D) finite element analysis. A sound tooth and 8 3D models of a weakened root-filled central incisor were generated using computer-aided design/computer-aided manufacturing software. The models were created without a ferrule and with a 2.0-mm ferrule, restored with a relined glass fiber post or a cast post and core (Cpc), and 12.0- and 7.0-mm post lengths. Each 3D model was imported using ∗.STEP files to the finite element software for mesh generation. The models were subjected to 100-N oblique loading at the palatal surface, and the results were evaluated by von Mises criterion and maximum principal stress distribution. RESULTS: Finite element analysis showed that the Cpc models showed elevated stress levels in the root canal regardless of the presence of a ferrule. Relined glass fiber post models showed homogeneous stress distribution to the dentin external surface similar to the sound tooth model. Without a ferrule, Cpc with a 7- or 12-mm length promoted high levels of tensile stress inside the root canal. CONCLUSIONS: Ferrule presence promoted more satisfactory stress distribution to the roots. Post length influenced the stress distribution only for the models restored with a cast post and core. High levels of tensile stress inside the root canals were verified with a cast post and core, which should be avoided to rehabilitate weakened roots, mainly in the absence of a ferrule.

Critical instrumentation area: influence of root canal anatomy on the endodontic preparation.

The aim of this study was to evaluate the root canal anatomy of mandibular incisors before and after endodontic instrumentation, identifying regions inaccessible to the action of files (Critical instrumentation Area - CA) in a three-dimensional perspective. Thirty human mandibular central incisors were selected, assigned to two groups (n=15) and instrumented using ProTaper Universal rotary files. In the RX group, longitudinal digital radiographic images were obtained in the buccolingual (BL) and mesiodistal (MD) views. In the CT group, cross-sectional micro-computed tomography (µCT) images were obtained at 3, 9 and 15 mm from the apex. The canal area of the specimens was evaluated before and after instrumentation using digital images from each group. Data were analyzed using t-test, one-way ANOVA with subdivided parcels and Tukey's test (α=0.05). The canal area found in the MD radiographs was larger than in the BL radiographs, which was also confirmed in the transversal images (p<0.01). The CA was only detected in the MD radiographs and µCT scans. On the root canal configuration, a continuous reduction in the canal conicity was observed in BL radiographs, while in MD view there was a constriction at the cervical third and subsequent increase at the middle third (p<0.01). The conical shape of the root canal was observed only in the BL view. The canal enlargement in BL radiographs was not indicative of homogeneous instrumentation, since unprepared areas (CA) were also verified on the buccal and lingual walls in different images.

Can the cure time of endodontic sealers affect bond strength to root dentin?

The cure time of endodontic sealers may influence the bond strength of fiber posts to root dentin. Forty teeth were selected and endodontically filled using calcium hydroxide cement and then divided into 2 groups according to the time elapsed between endodontic filling and post luting (n = 20): Immediately - glass fiber post luting immediately after endodontic filling; and Delayed - post luting performed 7 days after endodontic filling. The roots were also subdivided according to resin cement used for post luting (RelyX ARC and RelyX Unicem). The specimens were stored at 37°C for 24 h and sectioned in six 1-mm-thick slices from cervical, middle and apical thirds. The slice specimens were submitted to a push-out test at a crosshead speed of 0.5 mm/min, and the bond strength values obtained (MPa) were submitted to two-way ANOVA in a split-plot arrangement and Tukey's test (α=0.05). For both RelyX ARC and Unicem, the bond strength was significantly higher when the posts were cemented 7 days after the endodontic treatment. RelyX Unicem showed significantly higher bond strength values than RelyX ARC for both cementation periods. It was concluded that post luting should be made after the complete setting of the root canal sealer. Self-adhesive resin cement should be preferred for fiber post luting.

Assessment of influence of flexion angles of files in apical stop preparation by using manual and rotary instrumentation techniques.

INTRODUCTION: This study aimed to evaluate the influence of flexion angles produced by files during root canal instrumentation on the final form of the apical stop. METHODS: Sixty human lower incisors were divided into 3 groups (n = 20). After access preparation and working length determination, radiographs were taken from a mesiodistal and buccolingual direction with #15 K-file inserted to working length. Teeth from FlexM group were instrumented with stainless steel Flexofiles up to #40 file. For ProM and ProR groups, hand ProTaper Universal and ProTaper Universal rotary files were used, respectively, up to file F4. New radiographs were taken as previously described. After gutta-percha insertion, the apex of each specimen was ground, allowing gutta-percha visualization, and an image of the apex was captured to identify root canal deformation with computer software. The flexion of files was evaluated from both initial and final radiographs as the angle formed between the divergence of the file path and its virtual image represented by the direction taken by the file in the absence of curvature. RESULTS: FlexM group presented the highest variation in flexion angles compared with ProM (P = .112) and ProR (P = .024) groups. Nickel-titanium rotary system (ProR) reduced apical stop deformation compared with the manual techniques that used nickel-titanium (P = .011) or stainless steel (P = .025) files. CONCLUSIONS: Force vectors caused by the flexion angles of the files during the instrumentation of curved canals promoted apical stop deformation. ProTaper Universal rotary files showed less apical deformation than hand ProTaper Universal and stainless steel files.