Effect of irradiance and exposure time on the adhesive properties of universal adhesives after 2 years of storage.

OBJECTIVE: This study aims to evaluate the effects of exposure time and irradiance on the dentin bonding properties (microtensile bond strength (µTBS) and nanoleakage (NL)) of the Clearfil Universal Bond Quick (CUQ) adhesive and Scotchbond Universal Adhesive (SBU) immediately and after 2 years of water storage. MATERIAL AND METHODS: Hence, 128 human molars were randomly assigned to 16 groups based on adhesive strategy, irradiance/exposure times, and storage time for each universal adhesive tested. The adhesives were applied using the etch-and-rinse and self-etch strategies and were light-cured using four different irradiance/exposure times: 1400 mW/cm2 for 5 s (1400 × 5), 1400 mW/cm2 for 10 s (1400 × 10), 3200 mW/cm2 for 5 s (3200 × 5), and 3200 mW/cm2 for 10 s (3200 × 10). Then, each sample was restored and sectioned into a resin-dentin bonded stick to be tested for µTBS and NL (immediately and after 2 years of water storage). The mean µTBS and NL of all resin-dentin bonded sticks from the same hemi-tooth (factor time) were statistically analyzed using a three-way ANOVA and Tukey's test (a = 0.05). RESULTS: Despite a significant decrease in the µTBS values for all groups after 2 years of water storage, the 3200 × 5 group showed higher µTBS values, whereas the 3200 × 10 group showed lower µTBS values for both universal adhesives tested. Although a significant increase in the NL values was observed for all groups after 2 years of water storage, the 3200 × 10 group showed higher NL values than the other groups (p < 0.001). CONCLUSION: Results indicate that light-curing the adhesive layer with 14-16 J/cm2 led to an improvement in the stability of the resin-dentin adhesive interface. A longer exposure time (10 s) coupled with a higher irradiance (3200 mW/cm2) resulted in a greater degree of degradation of the adhesive interface. CLINICAL SIGNIFICANCE: To guarantee better stability of the adhesive interface, clinicians could be preferred a light-cured universal adhesive layer with 14-16 J/cm2. Higher irradiances should be avoided.

Effect of Resin Cement Mixing and Insertion Method into the Root Canal on Cement Porosity and Fiberglass Post Bond Strength.

PURPOSE: To evaluate the method of resin cement mixing and insertion into the root canal on resin cement porosity and fiberglass-post push-out bond strength (PBS). MATERIALS AND METHODS: One hundred twenty human single-rooted teeth were sectioned to a length of 15 mm, en-do-dontically filled, and received a fiberglass post cemented with 3 self-adhesive resin cements (RelyX U200, seT, Panavia SA) using 4 mixing methods/insertion techniques (handmix/endodontic file, handmix/Centrix syringe, automix/conventional tip, automix/endo tip). The samples were scanned using micro-CT. Two slices from the cervical, middle, and apical thirds were submitted to push-out bond strength (PBS) testing, and failure modes were classified. The PBS, volume of resin cement, and porosity data were analyzed using ANOVA and Tukey's test. RESULTS: The porosity was lowest in the cervical third and highest in the apical third, irrespective of the resin cement. The porosity was lower in the the automix/endo tip group compared to the handmix/endodontic file group. The use of Centrix or endo tip reduced the porosity and increased the PBS in the apical third compared with the use of endodontic files. The root canal depth reduced the PBS for U200 and seT when handmix/endodontic files were used. U200 and seT using the automix method increased the PBS, thus eliminating the effect of root region, irrespective of the insertion technique. In general, U200 showed higher PBS and Panavia lower PBS. Adhesive failure between root dentin and resin cement was predominant. CONCLUSIONS: Automixing the cement and using an endo tip produces fewer voids and increased the bond strengths.

Influence of Er,Cr:YSGG laser on dentin acid resistance after erosive challenge.

PURPOSE: To evaluate the influence of the Er,Cr:YSGG laser with or without the 5% fluoride varnish on the acid resistance of dentin after erosive challenge. METHODS: 36 incisors were selected and sectioned, obtaining 72 specimens of 4 mm × 4 mm and randomly divided into eight groups (n = 9). In G1: application of Er,Cr:YSGG (0.1W; 5Hz, air 55%); G2: laser (0.25W; 5Hz, air 55%); G3: fluoride varnish + laser (0.1W; 5Hz, air 55%); G4: fluoride varnish + laser (0.25W, 5Hz, air 55%); G5: fluoride varnish + laser (0.1W; 5Hz, without air); G6: fluoride varnish + laser (0.25W, 5Hz, without air); G7: fluoride varnish and G8: no treatment. When used, the laser was irradiated without water cooling, scanning mode during 10 seconds. The surface roughness data were subjected to ANOVA. For wear profile, we used Kruskal-Wallis test and Dunn post-hoc, all with α= 0.05. RESULTS: The results showed no statistically significant difference when comparing the groups as regards to the surface roughness (P> 0.05). Regarding the percentage of lost volume, the G5 and G6 groups presented the best results (G5 = 7.8% and G6 = 8.5%), with the lowest loss of dentin volume compared to other groups (P< 0.05). The G8 group (no treatment) had the highest lost volume (G8 = 39.1% followed by the G7 group (fluoride varnish), which had 25.9%. CLINICAL SIGNIFICANCE: The use of Er,Cr:YSGG laser and fluoride varnish can be an effective method to increase the acid resistance of dentin after erosive challenges, and limit problems related to hypersensitivity.

Influence of impacted canines on the stress distribution during dental trauma with and without a mouthguard.

BACKGROUND/AIM: Maxillary canines have a high incidence of impaction which may be associated with unexpected damage during maxillofacial trauma. The aim of this study was to evaluate how an impacted canine could influence the stress distribution in the dentoalveolar complex during a simulated impact before and after surgical removal plus the protective effect offered by a mouthguard. MATERIALS AND METHODS: Cross-sectional finite element models of the central incisor and support structures of a patient with an impacted canine in a transverse position were made using ImageJ and Marc/Mentat software. The following impact conditions were simulated: (a) incisor with impacted canine; (b) incisor with surgical socket after impacted canine extraction; and (c) incisor after bone healing. The impacts were also simulated with a 3 mm custom-fitted ethylene vinyl acetate mouthguard. A non-linear dynamic impact finite element analysis was performed in which a rigid object hit the model at 1 m/s. Maximum and minimum principal stresses as well as von Mises stresses were analyzed. RESULTS: Higher values of compressive and tensile stresses occurred on the cortical bone in the models after impacted canine extraction. The highest stress concentrations in the enamel and dentin structures were observed after bone healing. The mouthguard reduced the stress in the alveolar bone and dental structures. CONCLUSIONS: Use of mouthguards during impact reduced the compressive and tensile stresses in the alveolar bone, mainly in the fragile regions of the impacted canine or surgical socket.

Effect of acidic drinks on shade matching, surface topography, and mechanical properties of conventional and bulk-fill composite resins.

STATEMENT OF PROBLEM: Posterior composite restorations may be negatively affected by acidic and colored drinks. Little information is available about the effect of acidic drinks on bulk-fill composite resins. PURPOSE: The purpose of this in vitro study was to investigate the effect of acidic drinks on the different properties of conventional and bulk-fill composite resins. MATERIAL AND METHODS: A conventional composite resin and 2 representative bulk-fill composite resins were used to prepare disk-shaped specimens. The degree of conversion (DC) was monitored by spectroscopy (n=5). The specimens were divided into 5 groups: control, artificial saliva, acai juice, red wine, and Coca-Cola and were maintained for 30 days of challenge (3 periods of 15 min/d). Surface topography parameters were measured by interferometry (n=5). Elastic modulus (E) and Vickers hardness (VH) were determined by microhardness dynamic indentation (n=5). Diametral tensile strength (DTS) was determined at 0.5 mm/min (n=5). Shade matching was evaluated by using the Vitapan Classic Shade Guide. The DC, Sa, Ssk, Sku, Sdq, and DTS were statistically analyzed using 2-way ANOVA, followed by the Tukey HSD tests. E and VH were statistically analyzed by 3-way ANOVA, followed by Tukey HSD tests (α=.05). Shade matching was analyzed with the Kruskal-Wallis test. RESULTS: DC values were similar for the immediate evaluation and after 24 hours, regardless of the composite resin (P<.05). All surface topography parameters increased significantly after the acidic drinks and were greatest for Coca-Cola. The E, VH, and DTS decreased significantly for all composite resins tested (P<.05). Acai juice and red wine produced more surface staining than Coca-Cola. CONCLUSIONS: Acidic drinks negatively influenced the physical and mechanical properties of conventional and bulk-fill composite resins.

Three-dimensional finite element stress analysis of teeth adjacent to a traumatized incisor.

BACKGROUND/AIMS: Dental trauma is the cause of several consequences to the injured tooth. However, the stresses and strains at adjacent teeth non-directly impacted as a possible cause of sequelae are still unknown. The aim of this study was to evaluate the stress distribution in incisors adjacent to an upper central incisor when it suffers a frontal impact in order to identify a potential explanation for sequelae in non-traumatized teeth. MATERIALS AND METHODS: A three-dimensional (3D) finite element model of the maxillary central incisors, lateral incisors and canines was created from a cone-beam scan of a patient with normal occlusion. Non-linear dynamic impact analysis was performed, simulating the right central incisor being impacted by a steel ball with a velocity of 10 m/s. A functional chewing load (100 N) on the palatal surface of the central incisor was simulated for comparison. Displacements, strains and modified von Mises stresses were calculated for the adjacent teeth. RESULTS: During impact on the central incisor, the adjacent teeth showed root displacement. Considerable stress concentrations were observed on the palatal surfaces, proximal and labial surfaces of teeth adjacent to the traumatized incisor. Stresses in the adjacent teeth were higher than stresses calculated during functional biting. Compressive stresses were concentrated at the proximal areas of the adjacent incisors. High levels of deformation were found in the root dentin of adjacent teeth during the traumatic event. CONCLUSIONS: A frontal impact on an anterior tooth generated stresses at the roots of adjacent teeth. These stresses may play a role in clinically observed sequelae of teeth adjacent to traumatized teeth.

Dental trauma on primary teeth at different root resorption stages-A dynamic finite element impact analysis of the effect on the permanent tooth germ.

BACKGROUND/AIM: Dental trauma is a common emergency in children with primary teeth. The aim of this study was to determine stress propagation to the permanent tooth germ and surrounding bone and soft tissues during dental trauma to primary central incisors with three levels of physiological root resorption. MATERIAL AND METHODS: Stresses were determined using finite element analysis (FEA). Cross-sectional models were created using cone-beam computed tomography images of 3.5, 5, and 6 years olds, representing three different physiological root resorption stages of a maxillary primary central incisor. The models included periodontal ligament, bone, and soft tissues. An impact with an asphalt block moving at 1 m/s,was simulated for two impact two directions, frontal on the labial tooth surface, and on the incisal edge. Stresses and strains were recorded during impact. RESULTS: The impact caused stress concentrations in the surrounding bone and soft tissues and permanent tooth germ, regardless of the direction of impact and the primary tooth resorption stage. Impact stresses in dental follicles and surrounding bone increased in models with more physiological root resorption of the primary tooth. Incisal impact generated higher stress concentrations in surrounding bone and soft tissues and permanent tooth germ regardless of physiological root resorption stage. The primary incisor with no physiological root resorption showed high stress concentrations at its root apex. CONCLUSION: During impact to a primary incisor, stresses most significant for potential damage to the formation of permanent enamel and dentin were at the dental follicle and surrounding bone tissue with the three levels of physiological root resorption.

Effects of Lectin (ScLL) on osteoclast-like multinucleated giant cells' maturation-A preliminary in vitro study.

BACKGROUND/AIM: Lectin (ScLL) has been recently evaluated in the oral cavity due to its anti-inflammatory activities. ScLL could be a promising agent for blocking osteoclast activity and preventing root resorption. The aim of this study was to evaluate the effect of ScLL on the viability of the RAW 264.7 macrophage lineage, osteoclast-like maturation and the release of TNF-α and nitric oxide (NO). MATERIALS AND METHODS: The viability of RAW 264.7 cells was determined by MTT and Alamar Blue assays after ScLL treatment for 24 hours. ScLL effects on RANKL-induced osteoclast-like maturation were assessed by tartrate-resistant acid phosphatase (TRAP) staining and F-actin ring formation. The supernatant was collected to detect the release of TNF-α using ELISA and NO using a nitrite assay. RESULTS: ScLL suppressed osteoclast-like maturation by decreasing TRAP activity as well as F-actin ring formation. ScLL at 10 µg/mL showed the highest values of NO release compared with all other groups (P < .05). Lower levels of TNF-α were found for the negative control. CONCLUSIONS: ScLL at 5 µg/mL suppressed osteoclast-like maturation in vitro and had no cytotoxic effect on RAW cell cultures.

The effect of antagonist tooth contact on the biomechanical response of custom-fitted mouthguards.

BACKGROUND/AIM: Custom-fitted mouthguards are devices used to prevent dental injuries. The aim of this study was to verify the influence of the antagonist contact on the stresses and strains of the anterior teeth, shock absorption and displacement of EVA custom-fitted mouthguards during a horizontal impact. MATERIALS AND METHODS: Finite element models of human maxillary central incisors with and without a mouthguard for different occlusion conditions (with and without antagonist contact) were created based on tomography. A nonlinear dynamic impact analysis using the single-step Houbolt method was performed in which a rigid object hit the model at 1 m s-1 . Strain and stress were evaluated by means of Von Mises and Critical modified Von Mises criterion and shock absorption during impact were calculated as well as the mouthguard displacement. RESULTS: The model without mouthguard and without antagonist contact showed the highest stress and strain values at the enamel and dentin in the tooth crown on impact compared to the model without mouthguard and with antagonist contact. Mouthguard presence reduced the stress and strain values regardless of the occlusion condition. The mouthguard displacement decreased with the mandibular antagonist contact. CONCLUSIONS: Mouthguards are efficient at decreasing the stress and strain values on the tooth in front of an impact reaching more than 90% of shock absorption. A mouthguard with balanced occlusion and maximum number of contacts with mandibular anterior teeth should be considered because it reduces mouthguard displacement.

Heat generated during light-curing of restorative composites: Effect of curing light, exotherm, and experiment substrate.

PURPOSE: To investigate temperature rise, separating heat caused by irradiation and exotherm for three composites polymerized with three curing lights. The effect of substrate on temperature measurements was also determined. METHODS: Composite samples (n= 5) (Filtek Supreme Ultra, Filtek LS, and EsthetX HD) were placed on a thermocouple tip inside three substrates (aluminum, Delrin, and tooth). The composites were photoactivated using three curing lights (Elipar 2500 QTH, SmartLite Max LED, DemiUltra LED) at 1 mm distance. Irradiance was 798, 980, and 1,135 mW/cm2, respectively. Exotherm was determined by subtracting post-cure from the polymerization temperature curves. ANOVA and Student-Newman-Keuls post-hoc tests were used to analyze differences among peak temperatures and exotherms (significance level 0.05). RESULTS: SmartLite LED curing light resulted in higher peak temperatures and exotherms compared to the DemiUltra LED and QTH for all tested composites (16.9-20.4°C vs 12.3-14.7°C vs 8.9-9.7°C). Thus, the LEDs produced higher temperature rises than the QTH, and the LED with lower irradiance caused higher temperature rise than the LED with higher irradiance. The silorane-based Filtek LS generated significantly higher exotherm than the methacrylate-based EsthetX HD and Filtek Supreme Ultra (6.2-7.6°C vs 3.6-4.5°C vs 2.7-3.6°C). Substrate affected temperatures significantly. Temperature profiles found in Delrin substrate were comparable to tooth substrate, while aluminum substrate reduced temperatures 10-20 degrees. CLINICAL SIGNIFICANCE: Curing of restorative composites raises the temperature under a restoration due to irradiation and exothermic reaction; how much the temperature increases depends on curing light design, type of composite, and surrounding substrate. The silorane-based Filtek LS generated significantly higher exotherm than the methacrylate-based EsthetX HD and Filtek Supreme Ultra.

Effect of occlusal loading and mechanical properties of resin composite on stress generated in posterior restorations.

PURPOSE: To investigate the effect of the occlusal load condition in association with the mechanical properties of resin composite, expressed by elastic modulus and post-gel shrinkage, on stresses in a premolar restored with various composites. METHODS: Five resin composites (4 Seasons, Beautifil II, Filtek LS, Filtek Z250, and Z100) indicated for restoring posterior teeth were tested. Elastic modulus was measured using Knoop indentation tests (n=5). Post-gel shrinkage was measured with strain gauges (n = 10). Finite element analysis was used to calculate the stresses in a two-dimensional pre-molar model under four conditions: (We, without occlusal contact, representing stresses due to composite shrinkage only; Ct: contact generated between enamel of restored tooth and antagonist tooth; Cm: contact on tooth/composite restoration margin; Cc: stable centric contact on the composite restoration). RESULTS: Elastic modulus varied between 12.6 (Filtek LS) and 21.5 (Z100) GPa; post-gel shrinkage varied between 0.11 (Filtek LS) and 0.96 (Z100) vol%. Composites with higher elastic modulus and post-gel shrinkage increased stress in the restored tooth. Occlusal contact on the tooth/composite restoration margin increased the stresses around the margin of the restoration. Stable centric contact on the restoration resulted in better stress distribution.

Effect of gamma radiation on bonding to human enamel and dentin.

PURPOSES: This study evaluated the effect of gamma radiation on the microtensile bond strength of resin-based composite restoration to human enamel and dentin performed either before or after radiotherapy. METHODS: Thirty sound human third molars were sectioned mesio-distally into buccal and lingual halves and then randomly divided into enamel or dentin groups. Enamel and dentin substrates were randomly divided into three sub-groups (n = 10): Control, which received no irradiation; specimens were irradiated before restoration protocol; and specimens were irradiated after restoration protocol. Radiation therapy was defined by application of 60-Gy dose fractionally with daily exposures of 2 Gy, 5 days a week, over 6 weeks. Restorations were carried out using Adper Single Bond adhesive system and Filtek Z250 resin composite. The specimens were sectioned producing 4 sticks per specimen and submitted to microtensile on a testing machine. Data were submitted to two-way ANOVA followed by Tukey test (p < 0.05). Failure modes were examined under optical microscopy and SEM. RESULTS: Bond strength to enamel was significantly higher than to dentin irrespective radiation therapy. Radiotherapy applied before restoration significantly reduced the bond strength to both substrates. A predominance of adhesive failures was detected for control groups and groups restored before radiotherapy. Cohesive failures in dentin and enamel increased when the specimens were restored after irradiation. CONCLUSIONS: The gamma radiation had a significant detrimental effect on bond strength to human enamel and dentin when the adhesive restorative procedure was carried out after radiotherapy.

Does bonding to dentin reduce microleakage of composite restorations?

This study evaluated the effect of adhesive application only to enamel on the marginal microleakage of composite resin restorations performed with different adhesive systems. Standardized cylinder-shaped cavities were prepared on the buccal surface of eighty bovine incisors. Two etch-and-rinse (Adper Scotchbond Multi-purpose [3M ESPE, St. Paul, MN USA] and Adper Single Bond 2 [3M ESPE]) and two self-etching (Clearfil SE Bond [Kuraray, Osaka, Japan] and Adper Prompt [3M ESPE]) adhesive systems were evaluated. The adhesives were applied only to enamel or to both dentin and enamel. After adhesive light-activation, the cavities were restored with composite resin. The samples were coated with two layers of nail polish, except an area of 1-mm wide around of the restoration, and immersed in a methylene blue solution. Afterwards, the specimens were ground in order to obtain powder which was immersed in absolute alcohol. The solutions were centrifuged and the supernatant was analyzed using an absorbance spectrophotometer. Linear regression was used to estimate the dye concentration. Data were analyzed using ANOVA and Tukey's tests (alpha = 0.05). The etch-and-rinse adhesives showed lower microleakage means compared to those of the self-etching adhesives. Adper Prompt presented higher microleakage means. There was no difference between the modes of application of the adhesive on the cavity for all adhesive systems, except for Clearfil SE Bond. This showed lower microleakage when applied to the whole cavity. Bonding to dentin may not reduce microleakage of composite restorations.

Dental undergraduate students' ability in the diagnosis of root fractures: Comparative analysis of different imaging methods.

OBJECTIVE: The aim of this study was to evaluate the diagnostic ability of dental undergraduate students to detect horizontal and oblique root fractures (ORFs) using different imaging techniques. MATERIALS AND METHODS: Nine teeth were selected and randomly divided in three groups in order to create a fracture line without fragments separation: control (without fracture), horizontal root fracture (HRF), and ORF. The root fracture was created using perpendicular force and was confirmed by transillumination. A model with two adjacent teeth was created, and different imaging techniques were performed: conventional periapical radiograph; mesially and distally shifted periapical radiographs; cone-beam computer tomography (CBCT). Twenty students that had participation on dental trauma clinic at the year of 2019 were invited to identify root fractures by a five-point scale: (i) fracture definitely not present, (ii) fracture probably not present, (iii) uncertain whether fracture is present or not, (iv) fracture probably present, and (v) fracture definitely present. Data were analyzed by Kappa test for agreement evaluation. RESULTS: Comparing each student to the gold standard, there was a variation in reproducibility and performance from poor to substantial (0.042-0.667). Reproducibility values ranged from poor to good for all periapical radiographs both in the diagnosis of ORF (-0.33-0.667) and in HRF (0-1). CONCLUSIONS: In CBCT images, the students' ability was lower in HRF detection in comparison with the oblique ones. The students showed limited capacity to diagnose root fractures; however when CBCT was used, the performance was more satisfactory than when periapical radiographs were used.

Surface/interface morphology and bond strength to glass ceramic etched for different periods.

This study evaluated the influence of etching periods on the surface/interface morphology and bond strength to glass ceramic with or without application of an unfilled resin after silane. Ceramic discs were divided into 12 groups, defined by etching time with 10% hydrofluoric acid: G1/G7--etching for 10 seconds, G2/G8--20 seconds; G3/G9--40 seconds; G4/G10--60 seconds; G5/G11--120 seconds and G6/G12--60 + 60 seconds. All the groups were silanated after etching and G7 - G12 received a layer of unfilled resin after silane. Microshear testing using resin cement was performed, with 12 resin cylinders tested per group. The data was submitted to two-way ANOVA and the Student-Newman-Keuls' test (p<0.05). Evaluation of the etching pattern and bonding interfaces was conducted by SEM. The bond strength means (MPa) were: 19.4 +/- 3.5, 22.3 +/- 5.1, 22.2 +/- 3.2, 17.8 +/- 2.1, 15.3 +/- 3.0 and 14.3 +/- 1.8 for G1-G6 and 17.4 +/- 4.8, 21.3 +/- 2.1, 21.1 +/- 2.3, 24.7 +/- 5.8, 20.4 +/- 2.2 and 18.5 +/- 4.6 for G7-G12. Poor etching was detected after 10 seconds of conditioning; whereas deep channels were extensively observed on surfaces etched for 120 and 60 + 60 seconds. Unfilled voids underlying the ceramic-cement interface were detected when only silane was applied. Full completion of the irregularities on G11 was detected using unfilled resin. When only silane was applied, the 60-second group and those etched for longer periods showed lower bond strengths. When both silane and unfilled resin were applied, all etching periods generally showed similar values. In conclusion, the etching period influenced the surface/interface topography and bond strength to ceramic. The application of unfilled resin was able to infiltrate all unfilled voids beneath the ceramic-cement interface, except on re-etched surfaces.

Effect of X-ray radiation dose on the bond strength of different adhesive systems to dentin.

PURPOSE: To investigate the influence of different x-ray radiation doses on the bond strength of adhesive restorations to dentin using different bonding strategies. MATERIALS AND METHODS: Flat dentin surfaces on human molars were obtained and cylinder-shaped specimens for the microshear bond test were built up with a composite (Z250, 3M ESPE), using three adhesive systems: a two-step etch-and-rinse (Single Bond 2--SB2, 3M ESPE), a two-step self-etching (Clearfil SE Bond--CSE, Kuraray), or a single-step self-etching (Adper Prompt--ADP, 3M ESPE). The specimens were assigned to 4 groups (n = 10), according to the x-ray dose: 0 (control), 5, 35, or 70 Gy. Radiation was directed to the surface of the resin cylinders. Microshear testing was conducted after 24 h, and the failure modes classified under magnification (200X). Data were submitted to two-way ANOVA and Holm-Sidak's test (p < or = 0.05). A nonlinear regression analysis was carried out with bond strength as dependent variable. RESULTS: Bond strength results were dose and material dependent. SB2: control > 5 = 35 > 70; CSE: control = 5 > 35 = 70; ADP: control = 5 = 35 = 70. Generally, SB2 > CSE > ADP. The nonlinear regression plots showed that in general, an increase in radiation dose may predict a decrease in bond strength (R2 > or = 0.905). Failure modes were dependent on the bonding system, generally with no significant influence of radiation. CONCLUSION: X-ray radiation might present a dose-dependent detrimental effect on the bond strength of resin composite restorations to dentin.

Biomechanical behavior of maxillary premolars with conservative and traditional endodontic cavities.

OBJECTIVE: The objective was to evaluate the effects of the configuration of endodontic cavities with parallel or divergent walls, versus traditional endodontic cavities, on stress distribution, fracture resistance, and fracture mode of maxillary premolars by using both fracture-strength and finite element tests. METHOD AND MATERIALS: Thirty-two maxillary first premolars were divided into four groups (n = 8), according to the type of endodontic cavities: without endodontic cavities (control); conservative; conservative with diverging walls; and traditional. After performing root canal treatment and restoration, fracture resistance was evaluated by oblique compressive load. The stress distribution was evaluated by nonlinear finite element analysis by means of micro-computed tomography, operated at 50 kV and 800 mA. The fracture resistance data were analyzed by statistical software. RESULTS: Higher stress concentration was observed on the coronal portion of the palatal cusp and the palatal root dentin. Stress concentration on the palatal root dentin was similar for all groups. The stress level on the palatal cusp and at the proximal crests was slightly increased in the traditional endodontic cavities group compared with conservative endodontic cavities. Stress distribution in restored teeth was similar to that of intact teeth. No significant differences were observed in the fracture resistance among different endodontic cavities' design (P = .32). All groups had values similar to those of the control group (P > .05). CONCLUSIONS: Regardless of the cavity design, conservative endodontic cavities that preserve marginal ridge integrity did not affect the resistance to fracture, failure mode, or stress distribution in maxillary premolars restored with composite resin. Endodontically treated teeth displayed biomechanical behavior similar to sound teeth.

Finite element analysis and bond strength of a glass post to intraradicular dentin: comparison between microtensile and push-out tests.

OBJECTIVE: This study tested the hypothesis that the stress distribution and bond strength of glass posts to intraradicular dentin is influenced by the mechanical testing methodology. METHODS: Thirty single rooted endodontically treated teeth were prepared for luting of tapered fiber-glass posts (Reforpost, Angelus, Londrina, PR, Brazil) with a conventional adhesive system and resin luting cement (Adper Scotchbond Multi-purpose, Rely X ARC, 3M ESPE, St. Paul, MN, USA). The teeth were randomly divided (n=10 per group) into micro-push-out (Mpo), hourglass- (Mh) and rectangular stick-shaped (Ms) microtensile testing groups before sectioning each root into five 1-mm-thick specimens. During specimen preparation for microTBS testing 46/50 stick and 4/50 hourglass specimens prematurely failed; therefore, the Ms group could not be included in the mechanical testing. The remaining specimens were tested at 0.5 mm/min until bond failure. Stress distribution within each specimen type for the three mechanical test methods was analyzed by finite element analysis (FEA). Qualitative analyses were carried out through Von Mises, XY and Sy criterion. RESULTS: Mpo and Mh had a mean microTBS of 11.89+/-6.55 and 14.98+/-12.72 MPa, respectively, which was not significantly different (p=0.1311). The push-out test demonstrated a more homogenous stress distribution by FEA and less variability in mechanical testing. SIGNIFICANCE: Therefore, the recommended testing method for determining the bond strength of glass posts to intraradicular dentin is by Mpo.

Mouthguard Biomechanics for Protecting Dental Implants from Impact: Experimental and Finite Element Impact Analysis.

PURPOSE: The purpose of this study was to evaluate mouthguard shock absorption ability, strain, and stress generation during impact on dental implants placed in the anterior maxilla. The mouthguard material was also characterized. MATERIALS AND METHODS: Sixty experimental models were created and divided into six groups (n = 10): implant type, external hexagon (EH) and Morse taper (MT); without and with two mouthguards (MTG), EVA custom-fitted (Ct-MTG) and standard self-adapted (St-MTG). The Shore A hardness, EVA sheet and mouthguard thickness, and elastic modulus were measured to characterize the mouthguard material. A strain gauge was attached to the palatal surface of the implant abutment, which was subjected to an impact test. Distortion of the abutment and implant was determined after impact from centroid displacements in standardized radiographic images. Two-dimensional finite element models were created to represent the six groups and were submitted to nonlinear dynamic impact analysis. The data were statistically analyzed using analysis of variance (ANOVA) and Tukey test (α = .05). RESULTS: Ct-MTG resulted in higher Shore A hardness (P < .001). After the heat-forming process, the St-MTG maintained the original thickness, but the Ct-MTG thickness had decreased. The elastic modulus of EVA was 18.1 ± 0.5 MPa. The mouthguard presence reduced strain values significantly (P < .001), particularly for Ct-MTG. There was no significant difference between implant connection types EH and MT (P = .547). CONCLUSION: The external hexagon abutment resulted in higher stress and micro-displacement values. The mouthguard was able to absorb 40% to 46% of the energy caused by the impact on the dental implant.

Use of scientific evidence by dentists in Brazil: Room for improving the evidence-based practice.

This study investigated the use of scientific evidence and the practice of evidence-based dentistry (EBD) among dentists working in Brazil. An online questionnaire was emailed to dentists registered with Brazilian state dental councils. The questionnaire assessed the demographic, educational, and work characteristics of the sample, along with habits in reading scientific articles and other updating resources. Data were analyzed descriptively and by using Bonferroni, Kruskal-Wallis, ANOVA, and T-test statistical methods (α = 0.05). A total of 795 responses were received between June, 2015 and January, 2016. The response rate was not calculated because it was not possible to determine precisely how many dentists received these e-mails. Over 77% of the responding dentists completed postgraduate training. They referred mainly to books, scientific or clinical journals, conferences, and short-term courses for updating their knowledge. Dentists who reported having a habit of reading scientific journals (60.9%) showed a preference for reading case reports, clinical research articles, and literature reviews. Most dentists (77.5%) reported changing their clinical behaviors or procedures based on information gleaned from journal articles. The types of articles that led them to change their clinical practices were primarily clinical research articles and case reports. Working in the public sector was also associated with a lower prevalence of a habit of reading scientific journals and practicing EBD (i.e., self-reported practice). The results suggest that dentists are interested in reading journal articles, especially those addressing clinical outcomes, and that there is room for improving the practice of EBD, particularly in the public sector.