Effect of different storage media on root dentine composition and viability of fibroblasts evaluated by several assay methods.

AIM: To perform multiparametric analysis of the effects of soya milk (SM), whole milk (WM) and Hank's balanced salt solution (HBSS) on the viability of fibroblasts (HGF). The study also aimed to evaluate the influence of these solutions on bovine root dentine according to OH- and PO43- on the surface. METHODOLOGY: The HGF cytotoxicity was determined according to XTT, NR and SRB assays at 1, 3 and 6 h. Root dentine fragments were assessed by Fourier infrared (FTIR) spectrophotometer before and after immersion in the solutions for the same periods. The positive control group included cells and tooth fragments maintained in Dulbecco's modified Eagle's medium (DMEM), and the negative control included tooth fragments that were kept dry. Data were analysed using anova and Tukey's test. RESULTS: No significant difference was found in cell viability evaluated by XTT (P > 0.05). Using the NR assay, WM and HBSS had significantly lower cell viability compared to the positive control group at 6 h (P < 0.05). SM had similar cell viability to the positive control group at all periods evaluated when assessed using all three tests (P > 0.05). A significant difference was found in values of OH- for the negative control group at 1 h (P = 0.002). CONCLUSIONS: Soya milk promoted better cell viability, whereas on dentine composition, the solutions behaved similarly. The association of different assay methods is promising for improving cell viability analysis. The 1-h time-point is a crucial factor in the prognosis of dental replantation because the teeth remain more hydrated and help maintain cell viability.

Powdered coconut water as a storage medium to preserve the viability of periodontal ligament cells: a laboratory study.

AIM: To investigate the ability of newly developed powdered coconut water formulas (ACP) with different osmolarities to maintain the viability of periodontal ligament (PDL) cells over time compared with other solutions. METHODOLOGY: Dogs teeth were extracted and stored for two periods, 3 h or 24 h, in the following media: long-shelf life CW (CW), pH-adjusted long-shelf life CW (pH-CW) and powdered CW that was pH and osmolality adjusted (ACP-404-I, 250 mOsm kg-1 H2 O; pH 7.0; ACP-404-II, 372 mOsm kg-1 H2 O; pH 7.0; ACP-404-III, 300 mOsm kg-1 H2 O; pH 7.4). The positive control group (Pc) corresponded to immediate measurement after tooth extraction, and two negative controls (Nc) corresponded to 3 h and 24 h of dry time. PDL cells were extracted, and cell viability analysed by Trypan blue exclusion. Data were analysed statistically using two-way anova followed by the Tukey test and one-way anova followed by the Dunnett test (P < 0.05). RESULTS: At 3 h and 24 h, ACP-404-I had a performance similar to those of ACP-404-II and pH-CW, with significantly higher (P = 0.004) percentages of viable cells than ACP-404-III and CW. The positive control group had a significantly higher (P = 0.002) percentage of viable cells than the negative control groups, CW and ACP-404-III, irrespective of the period evaluated. CONCLUSION: Powdered coconut water formulas, ACP-404-I and ACP-404-II, preserved viability for up to 24 h.

Fracture resistance and stress distribution of simulated immature teeth after apexification with mineral trioxide aggregate.

AIM: To evaluate the effect of adhesive restorations on fracture resistance and stress distribution in teeth with simulated immature apices and apical plugs of mineral trioxide aggregate (MTA). METHODOLOGY: Sixty bovine incisors were sectioned 8 mm above and 12 mm below the cemento-enamel junction (CEJ). The root canal was enlarged using a diamond bur, resulting in remaining root canal walls with 0.1-0.2 mm of thickness. A 5-mm apical plug of MTA was placed and the teeth were restored according to the following groups: GP--the root canal was filled with gutta-percha and endodontic sealer; CR--the root canal was filled with light-cured composite resin inserted incrementally; FP--a fibre post was cemented into the root canal; and RFP--the fibre post was relined with composite resin prior to the cementation into the root canal. A load was applied on the crown of all teeth at 135° to their long axis until fracture. Data was analysed by one-way anova and SNK tests (α = 0.05), whilst the fracture pattern was evaluated according to the position of the fracture. Stress distributions in the restored teeth were verified by finite element analysis. RESULTS: Teeth restored with fibre posts and relined fibre posts were associated with the highest fracture resistance, whilst the GP group had the lowest values. GP and RC groups had similar fracture resistance values (P = 0.109). All fractures types involved the cervical and middle thirds of roots. The GP model had high levels of stress concentration in the cervical and middle thirds of roots. No difference was found amongst the stress concentration in the RC, FP and RFP models. CONCLUSION: Restorative protocols alter the fracture resistance and stress distribution of immature teeth after placement of MTA apical plugs.

Effect of a 3-second Off-label Exposure on the Depth of Cure of Eight Resin-based Composites.

OBJECTIVES: This study evaluated the depth of cure (DoC) of eight resin-based composites (RBCs) photocured using one multipeak light-curing unit (LCU) on the standard output setting for the manufacturer's RBC recommended exposure time and at a higher irradiance for 3 seconds. METHODS: Three conventional RBCs: Tetric EvoCeram (Evo), Tetric N-Ceram (Cer), Tetric Prime (Pri); and five bulk-fill: Tetric N-Ceram Bulk Fill (CerBF), Opus Bulk Fill APS (OpusBF), Opus Bulk Fill Flow APS (OpusF), Tetric PowerFill (PFill) and Tetric PowerFlow (PFlow) were examined. Only PFill and PFlow are formulated to be photocured in 3 seconds. The RBCs were packed into a metal mold and photocured using a Bluephase PowerCure LCU for the RBC manufacturer's recommended exposure time on the standard mode and using the 3-second high irradiance mode. After photocuring, the specimens were immersed in a solvent for 1 hour. The length of the remaining RBC was measured and divided by 2. Data were analyzed using two-way analysis of variance (ANOVA) followed by the Tukey post hoc multiple comparison test (α=0.05). RESULTS: There was no significant difference in the DoC values for PFill and PFlow when photocured using the 3-second high irradiance protocol compared to the lower irradiance standard mode protocol. All other RBCs had significantly lower DoC values (p<0.001) when photocured off-label using the 3-second high irradiance mode. CONCLUSION: Of the eight RBCs tested, only PFill and PFlow achieved the same DoC when the high irradiance 3-second curing method was used compared to when their longer lower irradiance protocol was used.

Mechanical and Optical Characterization of Single-shade Resin Composites Used in Posterior Teeth.

OBJECTIVES: This study aimed to evaluate the optical and mechanical performance of two single-shade resin-based composites (RBCs) compared to those of a conventional RBC for restoring posterior teeth. METHODS: Two single-shade RBCs, Omnichroma (Tukoyama) and Vittra Unique APS (FGM), and a conventional RBC, Filtek Z350XT shade A2 (3M Oral Care), were evaluated in this study. The optical shade-matching performance was measured using a spectrophotometer. The light emitted by VALO Grand (Ultradent) and transmitted through the 2.0-mm RBC specimens was evaluated using beam profiling. Knoop hardness (KH, N/mm2), degree of conversion (DC, %) at the top and bottom, flexural strength (FS, MPa), elastic modulus (E, GPa), postgel shrinkage (Shr, %), and shrinkage stress (MPa) were evaluated. Scanning electron microscopy (SEM) was used to characterize the filler. Data for FS, E, and Shr were analyzed by one-way analysis of variance (ANOVA) and KH and DC by repeated one-way ANOVA measurement followed by Tukey test (α=0.05). The modified von Mises stress values, light transmission, and SEM images were analyzed qualitatively. RESULTS: All single-shade RBCs exhibited higher chromatic adaptation than the Filtek Z350XT (p<0.001). Omnichroma exhibited less color difference than Vittra Unique APS, irrespective of the shade. The light transmitted through Omnichroma and Vittra Unique APS increased during polymerization. KH and DC values were significantly reduced from the top to the bottom of the specimens for all RBCs (p<0.001); however, the ratio values were always higher than 80%. In general, all RBCs demonstrated similar mechanical properties. All RBCs exhibited a similar FS (p=0.083) and Shr value (p=0.144). Filtek Z350XT exhibited significantly higher E (p<0.001) than both single-shade RBCs. All RBCs exhibited similar shrinkage stress during restoration and similar residual stress during occlusal loading. CONCLUSIONS: Single-shade Omnichroma and Vittra Unique APS increased light transmission during light-activation, demonstrating better chromatic adaptation than conventional Filtek Z350XT. In general, Omnichroma and Vittra Unique APS exhibited similar mechanical properties and shrinkage stress distributions as Filtek Z350XT during light-activation and occlusal loading.

Analysis of Calcium and Phosphate Ion Extraction From Dental Enamel by Bleaching Gels Using Ion Chromatography, Micro-CT, and SEM.

OBJECTIVES: To evaluate the volume and depth of enamel loss promoted by 37.5% and 7.5% hydrogen peroxide (HP) gels, and quantify the loss of calcium (Ca) and phosphate (P) ions by using ion chromatography (IC) analysis after bleaching. METHODS: Sixty bovine enamel specimens were randomly divided into three groups: Control - no bleaching gel; HP37.5%, application of HP 37.5% for 45 minutes for 14 days; and HP7.5%, application of HP 7.5% for 3 applications of 8 minutes. The surface analysis (n=5) was performed using a scanning electron microscope (SEM) and dispersive energy system (EDS) to calcium and phosphorus dosage. The micro-CT was used for the enamel loss analysis (n=5). IC was used to analyze extracted Ca and P (n=10). Data were analyzed by one-way ANOVA and two-way repeated measures ANOVA, followed by Tukey and Dunnett's tests (α=0.05). RESULTS: Significantly higher volume and depth of enamel loss were found for bleached groups compared with the control group. HP7.5% had significantly higher enamel change than HP37.5%. SEM showed higher enamel porosity for HP37.5% and HP7.5% compared to control. The IC demonstrated a significant increase of Ca incorporated into the gel, however, only HP7.5% had a higher P presence than the control group. The HP7.5% showed higher Ca and P ion exchange than HP37.5% (p<0.001). CONCLUSION: HP37.5% and HP7.5%, caused enamel mineral changes compared with the control group. The IC method was demonstrated to be an effective methodology for detecting enamel mineral loss by the bleaching gel.

Effect of Radiant Exposure on the Physical and Mechanical Properties of 10 Flowable and High-viscosity Bulk-fill Resin Composites.

OBJECTIVES: To evaluate the effect of the different radiant exposures from a multipeak light curing unit on the physical and mechanical properties of flowable and high-viscosity bulk-fill resin-based composites (RBC). METHODS: Five flowable bulk-fill RBCs (Tetric N-Flow Bulk-fill, Ivoclar Vivadent; Filtek Bulk Fill Flow, 3M Oral Care; Opus Bulk Fill Flow APS, FGM; Admira Fusion x-base, Voco and; and SDR Plus Bulk Fill Flowable, Dentsply Sirona) and five high-viscosity bulk-fill RBCs (Tetric N-Ceram Bulk-fill, Ivoclar Vivadent; Filtek One Bulk Fill, 3M Oral Care; Opus Bulk Fill APS, FGM; Admira Fusion x-tra, Voco; and SonicFill 2, Kerr) were photo-cured using a VALO Cordless light (Ultradent) for 10, 20, and 40 seconds at an irradiance of 1200, 800, or 400 mW/cm2, resulting in the delivery of 4, 8, 12, 16, 24, 32, or 48 J/cm2. Post-gel shrinkage (Shr) was calculated using strain-gauge test. The degree of conversion (DC, %) was calculated using FTIR. Knoop hardness (KH, N/mm2) and elastic modulus (E, MPa) were measured at the top and bottom surfaces. Logarithmic regressions between the radiant exposures and mechanical properties were calculated. Radiodensity was calculated using digital radiographs. Data of Shr and radiodensity were analyzed using two-way analysis of variance (ANOVA), and the DC, KH, and E data were analyzed with two-way ANOVA using split-plot repeated measurement tests followed by the Tukey test (a = 0.05). RESULTS: Delivering higher radiant exposures produced higher Shr values (p<0.001) and higher DC values (R2=0.808-0.922; R2=0.648-0.914, p<0.001), KH (R2=0.707-0.952; R2=0.738-0.919; p<0.001), and E (R2=0.501-0.925; R2=0.823-0.919; p<0.001) values for the flowable and high-viscosity RBCs respectively. Lower KH, E and Shr were observed for the flowable bulk-fill RBCs. All bulk-fill RBCs had a radiopacity level greater than the 4-mm thick aluminum step wedge. The radiant exposure did not affect the radiopacity. CONCLUSION: The Shr, DC, KH, and E values were highly correlated to the radiant exposure delivered to the RBCs. The combination of the higher irradiance for longer exposure time that resulted in radiant exposure between 24 J/cm2 to 48 J/cm2 produced better results than delivering 400 mW/cm2 for 40 s (16 J/cm2), and 800 mW/cm2 for 20 seconds (16 J/cm2) or 1200 mW/cm2 for 10 seconds (12 J/cm2). All the bulk-fill RBCs were sufficiently radiopaque compared to 4 mm of aluminum.

Effect of calcium hydroxide and endodontic irrigants on fibre post bond strength to root canal dentine.

AIM: To analyse the effect of calcium hydroxide paste, endodontic irrigants and time of application on the bond strength of fibre posts to root canal dentine. METHODOLOGY: Seventy bovine incisors were divided into 7 groups according to removal of calcium hydroxide and distilled water (CHW) (immediate - I; 21 days - 21 days; 6 months - 6 months) and endodontic irrigant (1% sodium hypochlorite - SH; 1% sodium hypochlorite + 17% EDTA - SHE). Fibre posts were cemented (RelyX U100), after which the roots were serially sectioned and submitted to a micro-push-out test. Data were analysed using two-way anova followed by the Tukey's and the Dunnett's tests (α = 0.05). RESULTS: The CHW groups were not significantly different from the control group in 13 of the 18 associated factors (P > 0.05). There were significant reductions in bond strength in the cervical (P = 0.0216) and middle (P = 0.0017) thirds of the root at 6 months in groups irrigated with SH. Irrigation with SHE reduced the bond strength significantly in the middle (P = 0.0488) and apical (P = 0.0252) thirds of the roots in the immediate groups and in the middle third (P = 0.0287) in the 21-day group. Bond strength was greater in the cervical than in the apical thirds of all immediate and 21-day groups (P < 0.05). CONCLUSIONS: Bond strength of groups that received CH paste was similar to that found in the control group in 13 of the 18 associated factors. EDTA and SH reduced bond strength in specimens in the immediate (middle and apical thirds) and 21-day (middle third) groups. There was a significant reduction in bond strength in the groups irrigated with SH and tested at 6 months (cervical and middle thirds). There was a predominance of adhesive failures between resin cement and dentine in all groups.

Effect of Activated Charcoal Toothpaste on Color Stability of Bleached Teeth Immersed in Different Drinks.

OBJECTIVE: This study aimed to evaluate the effect of activated charcoal toothpaste on the color stability of teeth subjected to tooth bleaching and pigmenting agents. METHODS: A total of 120 bovine crowns were randomly divided into 12 groups (n=10) according to two study factors: staining solutions (three levels): saliva (control), coffee, and red wine; and toothpaste (four levels): BPC, Bianco Pro Clinical (Bianco Oral Care) (Control); BIW, Black is White (Curaprox); BCA, Bianco Carbon (Bianco Oral Care); and NAT, Natural Suavetex (Suavetex). The samples were subjected to office bleaching with a 35% hydrogen peroxide-based gel (Whiteness HP Blue, FGM), followed by immersion in the solution for 45 minutes per day and daily toothbrushing for 7 days. The color (ΔE) and luminosity changes (ΔL*) were measured using reflectance spectroscopy (Vita EasyShade). The CIE values (L*, a*, b*) were measured at baseline after bleaching (T0) and immediately after immersion in solution each day (Ti1-Ti7) and after all toothbrushing cycles (Tb1-Tb7). ΔE and ΔL were analyzed using a two-way analysis of variance and Tukey's test (α=0.05). The clinically unacceptable level of ΔE > 3.3 was used to evaluate the color change. RESULTS: The color change was significantly influenced by the staining solutions and toothpastes (p<0.001). The color change (ΔE) was significantly higher when immersed in wine than in coffee, and lower ΔE values were observed for artificial saliva (control), irrespective of the toothpaste used. In artificial saliva, BPC, BIW, and BCA resulted in significantly lower ΔE values than NAT, which presented a clinically unacceptable level of dental color change (ΔE>3.3). Coffee resulted in a lower (L*) reduction than wine, irrespective of the toothpaste used. CONCLUSION: Charcoal toothpastes resulted in a color change on the surface of the tooth enamel (ΔE). The bleaching effect of the charcoal toothpastes and control evaluated in this study partially reduced the color changes on the surface of the tooth enamel caused by staining solutions but was unable to reestablish the measured values to the baseline. For teeth immersed in artificial saliva, the color change was not noticeable in BCA, BIW, and control-BPC (ΔE≥3.3), except for NAT, which showed a significant color change.

Effect of Ceramic Thickness on Light Attenuation, Degree of Conversion, Knoop Hardness, and Elastic Modulus of Four Luting Resins.

OBJECTIVES: This study evaluated the influence of the thickness of disilicate ceramic on the light attenuation (mW/cm2), degree of conversion (DC, %), Knoop hardness (KH, N/mm2) and the elastic modulus (E, MPa) of four luting resins. METHODS: Three resin cements: RelyX Veneer (RV, 3M Oral Care, Monrovia, CA USA); Allcem Veneer APS (AC, FGM); Variolink Esthetic LC (VE, Ivoclar Vivadent, Schaan, Liechtenstein) and one flowable resin composite Tetric N-Flow (TF, Ivoclar Vivadent) were photocured for 20 seconds. The irradiance (mW/cm2) and emission spectrum (mW/cm2/nm) from a broad-spectrum LED light unit (Bluephase G2, Ivoclar Vivadent) were measured over the luting material (control) and through 0.3 mm, 0.7 mm, and 1.0 mm thick ceramic discs (e.max CAD, Ivoclar Vivadent). RESULTS: The LED light delivered 26.1 J/cm2 to the surface and 6.2 J/cm2 through the 1.0 mm thick ceramic. The distribution of violet and blue light across the light tip of the light-curing unit (LCU) was relatively homogeneous, but there was less violet range. The irradiance and spectral radiant power decreased significantly as the ceramic thicknesses increased (p<0.001). The luting material type had significant effect on KH and E values (p<0.001). The RV had the greatest KH and E values, and VE had the lowest. Ceramic thickness had no significant effect on KH (p=0.213) and E (p=0.130). The KH (p=0.265) and E (p=0.165) were also not influenced by the location where these measurements were made across the specimens. No significant reduction of the DC was observed as the ceramic thickness increased (p=0.311). CONCLUSION: Increasing the ceramic thickness exponentially reduced the irradiance. This reduction was more pronounced at the shorter wavelengths (violet) of light, with an 82% decrease for 1 mm-thick ceramic. Increasing the ceramic thickness did not affect the DC, irrespective of photoinitiators used in the tested resins. The position of the violet and blue LEDs within the body of the LCU did not influence KH or E in any of the resins tested. The KH and E of VE were significantly lower than the other 3 luting materials tested.

Influence of Mono- and Multiwave Light-curing Units on the Microhardness and Degree of Conversion of Light-cured Resin Cements.

OBJECTIVES: This study evaluated the Knoop hardness (KH, N/mm2) and degree of conversion (DC, %) on the margins of light-cured resin cements with different photoinitiators using a single light-curing unit (LCU) with two heads (mono- and multiwave). METHODS AND MATERIALS: Three types of resin cements were used with different photoinitiators: Megalink Esthetic (Odontomega, São Paulo, Brazil) with a camphorquinone photoinitiator; Allcem Veneer (FGM, Joinville, Brazil) with the Advanced Polymerization system (APS), and Variolink Esthetic LC (Ivoclar Vivadent, Schaan, Liechtenstein). Thirty samples were collected and divided into six groups (n=5 each). The resin cement samples were made into the shape of a maxillary right central incisor and photoactivated under a 0.5-mm-thick ceramic sheet. A single LCU (Radii Xpert, SDI) with two heads (mono- and multiwave) was used. The tip of the LCU was positioned at the center of the sample in a standardized manner. Raman spectroscopy was performed to evaluate the DC, and KH was evaluated through the Knoop microhardness test. Five regions were evaluated: cervical, mesial, buccal (center), distal, and incisal. RESULTS: There was a significant difference in the DC only for the type of cement (p<0.001), indicating that the cement with the APS photoinitiator presented excellent results. There were significant differences in the type of cement (p<0.001), type of light (p<0.001), region (p<0.001), and the interaction between the type of cement and type of light (p<0.001). The resin cement with the APS photoinitiator cured with monowave light showed the highest KH values. The beam profiles of all groups, with and without the interposition of ceramic and resin cement, were examined by light transmission. CONCLUSIONS: The cement with the APS photoinitiator presented the best results with respect to the DC and KH. In comparison with mono- and multiwaves, the LCU may not be a determining factor for the properties of light-cured resin cements. The buccal region showed the best results for DC and KH, indicating the need for a greater amount of light-curing at the cementation margins.

Effect of Using Manufacturer-recommended Exposure Times to Photo-activate Bulk-fill and Conventional Resin-based Composites.

OBJECTIVES: To analyze the effect of using the resin-based composite manufacturer's recommended exposure time on the degree of conversion (DC), Knoop hardness (KH), and elastic modulus (E) of conventional and bulk-fill resin-based composites (RBCs). METHODS: Three resin-based composites (RBCs) were tested: Tetric EvoCeram Bulk Fill (TET), Opus Bulk Fill APS (OPU), and RBC Vittra APS (VIT). They were photo-activated in 2 mm deep, 6 mm diameter molds for their recommended exposure times of 10 seconds, 20 seconds, or 40 seconds from four light-curing units (LCUs). Two delivered a single emission peak in the blue light region (Optilight Max and Radii-Cal) and two delivered multiple emission peaks in the violet and blue region (VALO Cordless and Bluephase G2). After 24 hours of dry storage at 37°C in the dark, the KH (Kgf/mm2), E (MPa) and DC (%) at the top and bottom surfaces of specimens (n=5) were measured and the results analyzed by 2-way analysis of variance (ANOVA) followed by a Tukey test (α=0.05). RESULTS: The irradiance (mW/cm2) and spectral irradiance (mW/cm2/nm) from the LCUs were reduced significantly (8-35%) after passing through 2.0 mm of RBC (p<0.001). The DC at the bottom of VIT and TET was less than at the top surface (p<0.001). OPU had the same DC at the top and bottom surface (p=0.341). The KH and E values at the top surface of VIT and TET were substantially higher than at the bottom (p<0.001). OPU exposed for 40 seconds achieved higher mechanical properties than TET that was photo-activated for 10 seconds (p<0.001). The opacity of different bulk-fill RBCs changed differently during the polymerization; OPU became more opaque, whereas TET became more transparent. When exposed for their recommended times, the 2 mm thick RBCs that used Ivocerin or the APS photoinitiator system were adequately photo-activated using either the single or multiple emission peak LCUs (p=0.341). CONCLUSION: After 24 hours' storage, all the 2 mm thick RBCs photo-cured in 6 mm diameter molds achieved a bottom-to-top hardness ratio of at least 80% when their recommended exposure times were used. TET, when photo-activated for 10 seconds, achieved lower mechanical properties than OPU that had been photo-activated for 40 seconds. The change in opacity of the RBCs was different during photo-activation.

Influence of resin cement and post configuration on bond strength to root dentine.

AIM: To evaluate the effect of luting agent and fibreglass post design on bond strength to root dentine at different depths within the canal. METHODOLOGY: Ninety single-rooted teeth were root filled and prepared to receive either a parallel-sided and serrated fibreglass post (Reforpost no. 2) or a tapered and smooth fibreglass post (Exato Cônico). The posts were cemented with the following resin cements: dual-cured resin cement (Rely X ARC), two self-adhesive resin cements (Rely X Unicem and MaxCem) and a self-cured resin cement (Cement-Post). The roots were cross-sectioned to obtain two 1-mm-thick discs for each cervical, middle and apical third of the prepared root portion. The posts were submitted to a micropush-out test at a speed of 0.5 mm min(-1), and the bond strength values (MPa) were submitted to anova in a split-plot arrangement and Tukey's test (P < 0.05). RESULTS: The RelyX Unicem demonstrated significantly higher bond strength values (P < 0.001) along the root dentine. The RelyX ARC and Cement-Post had similar bond strength values in the cervical third; however, the bond strength decreased significantly (P < 0.001) in an apical direction for the RelyX ARC. Significantly lower bond strength values (P < 0.001), irrespective of canal region, were found for MaxCem cement. The bond strength was similar for both post configurations irrespective of the resin cement and canal region. CONCLUSIONS: The retention of glass fibre posts remained unaffected by surface roughness but was influenced by resin cement type. The self-adhesive cement RelyX Unicem yielded a significantly greater (P < 0.001) bond strength value when cementing the fibreglass posts.

Fracture resistance and mode of failure of various types of root filled teeth.

AIM: To investigate ex vivo the influence of the post system on fracture resistance and failure mode of root filled incisor, canine, premolar and molar teeth. METHODOLOGY: Eighty human teeth were divided into eight groups (n = 10) resulting from the interaction between the two study factors: post system (glass fibre post; cast Ni-Cr alloy post and core) and type of tooth (maxillary incisors, maxillary canines, maxillary premolars and mandibular molars). All roots were prepared with a 2-mm ferrule and restored with metal crown. Fracture resistance (N) was assessed in a mechanical testing device, and the data were analysed by two-way anova (4 × 2) followed by Tukey's test (α = 0.05). The failure mode was evaluated using an optical stereomicroscope and classified according to the location of the failure. Failure mode data were analysed by two-factor anova and Student-Newman-Keuls (SNK) tests (α = 0.05). Correlation between fracture resistance and failure mode was analysed by linear regression. RESULTS: Glass fibre and cast posts and cores had similar fracture resistance, regardless of the type of tooth. Canines and molars had significantly higher fracture resistance (P < 0.001) than premolars. Incisors teeth had significantly lower fracture resistance (P < 0.001) than premolars. The fracture mode for incisors, premolars and molars was more amenable to restoration when the teeth were restored with glass fibre posts. Fracture resistance had no correlation with fracture mode, regardless of the post system and type of tooth analysed. CONCLUSIONS: Post system had no significant effect on fracture resistance, regardless of the type of tooth. The mode of fracture was more restorable with glass fibre posts.

Effect of the Sample Preparation and Light-curing Unit on the Microhardness and Degree of Conversion of Bulk-fill Resin-based Composite Restorations.

OBJECTIVE: To evaluate the effect of the sample preparation and light-curing units (LCUs) on the Knoop hardness (KH, N/mm2) and degree of conversion (DC, %) of bulk-fill resin-based composite restorations. METHODS: Two molds were made using human molar teeth embedded in acrylic resin. One was a conventional tooth mold where the molar received a mesio-occluso-distal (MOD) preparation. In the other, the tooth was sectioned in three slices (buccal, middle, and lingual). The center slice received a MOD preparation similar to the conventional mold. Both tooth molds were placed in the second mandibular molar position in a Dentoform with a 44-mm interincisal opening. Restorations were made using Opus Bulk Fill (FGM) high viscosity bulk-fill resin-based composite (RBC) and light cured using two different lights: VALO Cordless (Ultradent) and Bluephase G2 (Ivoclar Vivadent). The RBC was placed in one increment that was light-cured for a total of 80 seconds (40 seconds at the occluso-mesial and occluso-distal locations). The RBC specimens were then prepared as follows: EmbPol - tooth mold specimen was embedded in polystyrene resin and polished before testing; Pol - tooth mold specimen was not embedded, but was polished before testing; NotPol - sectioned tooth mold, specimen not embedded nor polished before testing. The KH was measured in different depths and regions of the specimens, and the DC was measured using Raman spectroscopy. RESULTS: The results were analyzed using a 2-way analysis of variance (ANOVA) or repeated measures followed by the Tukey post-hoc test (α=0.05). The preparation method (p<0.001), depth of restoration (p<0.001), and the interaction between method and depth (p=0.003) all influenced the KH values. Preparation method (p<0.001), tooth region (p<0.001), and the interaction between method and tooth region (p=0.002) all influenced DC values. The KH values were reduced significantly from the top to the bottom of the restorations and also at the proximal box when compared with the occlusal region. This outcome was most significant in the proximal boxes. The NotPol method was the most effective method to detect the effect of differences in KH or DC within the restoration. A lower DC and KH were found at the gingival regions of the proximal boxes of the restorations. When the KH and DC values were compared, there were no significant differences between the LCUs (KH p=0.4 and DC p=0.317). CONCLUSION: Preparation methods that embedded the samples in polystyrene resin and polished the specimens reduced the differences between the KH and DC values obtained by different preparation techniques. The NotPol method was better able to detect differences produced by light activation in deeper areas.

Effects of Adjacent Tooth Type and Occlusal Fatigue on Proximal Contact Force of Posterior Bulk Fill and Incremental Resin Composite Restoration.

OBJECTIVES: To measure the proximal contact force in newtons (N) between incremental and bulk fill class II resin composite restorations and implant molar teeth or adjacent premolar teeth with simulated periodontal ligament. METHODS: The model used was created with a typodont first molar tooth with two bilateral occlusal-proximal class II cavities, an adjacent tooth simulating an implanted molar tooth (Titamax CM, Neodent, Curtiba, PR, Brazil) and a premolar with simulated periodontal ligament. Two resin composite restorative techniques were used: Inc-Z350XT, (Filtek Z350, 3M Oral Care, St. Paul, MN, USA) inserted incrementally and Bulk-OPUS, (Opus Bulk Fill APS, FGM, Joinville, SC, Brazil) high viscosity bulk fill resin composite (n=10). As a control, a typodont having intact teeth without restorations was used. After the restorative procedure, each specimen was radiographed using a digital system (Dürr Dental, Bietigheim-Bissingen, Germany). The proximal contact force (N) was measured using dental floss with a microtensile machine (Microtensile ODEME, Luzerna, SC, Brazil). The specimens were then subjected to mechanical fatigue cycling to simulate 5 years of aging. All the parameters were measured after aging. The X-rays were blindly qualitatively analyzed by two operators to identify the loss of proximal contact. One-way ANOVA was used for comparing the initial contact force between restored and intact teeth. Two-way ANOVA followed by Tukey testing was performed for contact area data and for the contact force/contact area ratio. The proximal contact force data were analyzed using one-way repeated measurement ANOVA followed by Tukey testing (α=0.05). The X-ray proximal contact analyses were described by the frequency. RESULTS: The initial proximal contact force was similar for intact and restored teeth. The contact force and contact area with the molar were significantly higher than with the premolar; however the contact force/contact area ratio was similar for all tested groups. The bulk fill technique showed a contact force similar to the incremental filling technique. Fatigue resulted in a significant reduction in the proximal contact force (p<0.001), irrespective of the region analyzed or restorative material used. The digital X-rays detected no alteration in the proximal contact after occlusal fatigue. CONCLUSIONS: Larger contact area resulted in higher proximal contact force. Proximal contact force decreased with 5 years of simulated occlusal fatigue. The bulk fill technique showed a proximal contact force similar to that of the incremental filling technique.

Use of Computerized Microtomography, Energy Dispersive Spectroscopy, Scanning Electron Microscopy, and Atomic Force Microscopy to Monitor Effects of Adding Calcium to Bleaching Gels.

OBJECTIVES: The aim of this study was to evaluate the mineral content, expressed by calcium (Ca) and phosphate (P), in dental enamel exposed to bleaching agents using micro-computed tomography (micro-CT), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and atomic force microscopy (AFM). METHODS: Sixty bovine dental enamel specimens were randomly divided into three groups (n=20): HP35ca (bleached using 35% hydrogen peroxide with Ca); HP35wca (bleached using 35% hydrogen peroxide without Ca); and control (without bleaching). Five specimens from each group were used for SEM and EDS analyses, 10 specimens were used for AFM analysis, and the remaining five specimens were used for micro-CT analysis. The pH of the gels was measured using a pH meter. The EDS and micro-CT data were analyzed using one-way ANOVA and Pearson's correlation test. The AFM data were analyzed using one-way ANOVA (α=0.05). RESULTS: The weight percentages of Ca and P obtained using EDS were similar between the bleached and control groups. Small, superficial changes were observed by SEM in the HP35wca group. The HP35ca group showed similar patterns to the control group. AFM results showed no significant changes in the enamel roughness in any of the tested groups. No significant difference in the volume or depth of structural enamel loss was found between gels with and without Ca. No mineral loss was observed in the dentin substrate. The EDS and micro-CT analysis data exhibited a high correlation (p<0.001). CONCLUSION: The addition of Ca to the bleaching gel had no beneficial effect on the bleached tooth enamel in terms of composition, mineral loss, and surface roughness. Micro-CT results exhibited a high correlation with the EDS results.

Effects of Charcoal Toothpaste on the Surface Roughness, Color Stability, and Marginal Staining of Resin Composites.

OBJECTIVE: This study was designed to evaluate the effects of charcoal toothpaste on the surface roughness, color stability, and marginal staining of resin composite restorations. METHODS: A total of 100 bovine incisors was collected. The crowns were sectioned and randomly divided into 10 groups (n=10) according to two study factors: toothpaste groups and nanoparticle resin composite groups. Five toothpastes-Bianco Pro Clinical (Bianco Oral Care, Uberlândia, MG, Brazil) - Control group; Bianco Carbon (Bianco Oral Care); NAT, Natural Suavetex Carvão Ativado (Suavetex, Uberlândia, MG, Brazil); Nano Action Black Be Emotion (Polishop, Jundiaí, SP, Brazil); and BIW, Black is White (Curaprox, Curaden AG, Kriens, Switzerland)-and two resin composites-Z350XT (Filtek Z350XT, 3M Oral Care) and Vittra (Vittra APS FGM, Joinville, SC, Brazil)-were used. Circular cavities with a diameter of 4 mm and a depth of 1 mm were prepared on the buccal face of the tooth crowns and restored with resin composites. The specimens were subjected to three months of simulated toothbrushing. The surface roughness (right angle [Ra], in micrometers [µm]) of the resin composites was measured before and after toothbrushing in five areas per specimen. The resin composite color and luminosity changes (ΔE and ΔL, respectively) were measured using reflectance spectroscopy (Vita EasyShade). Macro photographs were taken before and after toothbrushing to qualitatively analyze the marginal staining (MSt) of the resin composite restorations. Scanning electron microscopy (SEM) was performed before and after the simulated toothbrushing. Ra data were analyzed using two-way analysis of variance with repeated measures and the Tukey HSD test; MSt was analyzed using Kruskal-Wallis and Dunn tests (α=0.05), and the resin composite color change was analyzed using the clinically unacceptable level of ΔE > 3.3. RESULTS: Simulated brushing increased Ra irrespective of the resin composite or toothpaste used. No significant differences were found in Ra between the control group and all groups on which the charcoal toothpastes were tested. A clinically unacceptable level of resin composite color change (ΔE>3.3) was found after the use of most charcoal toothpastes. Use of Bianco Carbon resulted in marginal staining similar to that of the control group and was lower than that of the other charcoal toothpastes. Vittra brushed with black toothpaste showed the highest marginal staining. CONCLUSION: Use of charcoal toothpaste resulted in Ra values of resin composites similar to those found with conventional toothpastes. Charcoal toothpaste generally resulted in clinical resin composite color changes (ΔE). All charcoal toothpastes, except Bianco Carbon, caused marginal staining of the resin composite restorations.

Influence of Irradiance and Exposure Times on the Mechanical and Adhesive Properties of Universal Adhesives with Dentin.

OBJECTIVES: This study evaluated the influence of irradiance/exposure time on the Knoop hardness (KHN) and polymer cross-linking density (PCLD), as well as microtensile bond strength (µTBS), nanoleakage (NL), and in situ degree of conversion (DC) of universal adhesives. METHODS AND MATERIALS: Two universal adhesive systems, Clearfil Universal Bond Quick (CUQ) and Scotchbond Universal Adhesive (SBU), were light-cured using various 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). Adhesive disks from each group were used to measure PCLD by KHN. One hundred and twenty-eight human molars were randomly assigned to 16 groups according to the following variables: adhesive system vs adhesive strategies vs radiance/exposure times. After restoration, specimens were sectioned into resin-dentin sticks and tested for µTBS, NL, and DC. The data from PCLD (%), KHN, µTBS (MPa), NL (%), and DC (%) data were subjected to ANOVA and Tukey's test (α=0.05). RESULTS: Significant reductions in KHN, µTBS, and DC (p=0.00001) values and an increase in NL and PCLD (p=0.00001) values were observed for 3200*10 when compared with other groups. Higher KHN, µTBS, and DC (p=0.000001) values were observed for 3200*5 in comparison with the other groups. The 1400*5 (7 J/cm2) and 1400*10 (14 J/cm2) groups showed intermediate values (p=0.000001). CONCLUSION: Although similar results in terms of hardness, polymer cross-linking density and nanoleakage were observed when 5 seconds at 3200 mW/cm2 and 10 seconds at 1400 mW/cm2 groups were compared, the use of higher irradiance (3200 mW/cm2) for only 5 seconds showed better results in terms of bond strength and degree of conversion for both universal adhesives to dentin. The prolonged exposure time (10 seconds) at the higher irradiance (3200 mW/cm2) showed the worst results.

Three-point bending testing of fibre posts: critical analysis by finite element analysis.

AIM: To evaluate the effect of taper, specimen supports and the isotropic and orthotropic properties of the posts on flexure and stress response during three-point bending using finite element analysis. METHODOLOGY: A three-dimensional finite element model of a fibre post was created. The occlusal portion was cylindrical whilst the apical portion was tapered. Five different support positions were evaluated during a simulated three-point bending test: M1 - support distance of 10 mm centralized and no tilt; M2 - 10 mm centralized with tilt; M3 - 10 mm not centralized and no tilt; M4 - 10 mm not centralized with tilt; M5 - 6 mm not centralized with no tilt. A sixth post model (M6) was a centralized post without tapered section. The applied properties were elastic and orthotropic. RESULTS: Tilting the tapered posts to level them in the test setup had little effect on the outcome. Flexure increased when 50% of the bent portion involved taper (M1, M2). If only 20% of the bent post involved taper (M3, M4), the flexure values were close to M6 (no taper). The orthotropic properties also caused increased flexure compared to an isotropic post. Maximum stresses were only a little higher when 50% of the bend structure involved taper, whilst the orthotropic properties had little effect. CONCLUSIONS: Regardless of levelling, the flexural stress determination with tapered fibre posts in the three-point bending test was valid as long as the tapered portion was limited in length.