Effect of different gutta-percha solvents on the microtensile bond strength of various adhesive systems to pulp chamber dentin

Objectives

The aim of this study was to evaluate the effect of different endodontic solvents on the microtensile bond strength (μTBS) of various adhesives to pulp chamber dentin.

Material and methods

A total of 120 human third molars were selected. Canals were prepared with the ProTaper Universal system and obturated. The access cavities were then restored with resin composite. After 1 week, a retreatment procedure was applied as follows: control, no solvent was applied to the pulp chamber and experimental groups, three different solvents (chloroform, eucalyptol, and orange oil) were applied to the pulp chamber for 2 min. The canal filling was removed and calcium hydroxide (Ca[OH]₂) was placed into the canals. After 7 days, the Ca(OH)₂ was removed from the canals and the canals were re-obturated. Teeth were then divided into three subgroups according to the adhesive used. The samples were restored with a nanohybrid resin composite using three different adhesives: Clearfil SE Bond (CSE), Adper Easy One (AEO), and Single Bond 2 (SB2). The samples were aged with thermocycling. Teeth were sectioned, and a total of 20 dentin sticks were obtained for each subgroup. μTBS testing was then performed. The debonded surfaces were evaluated using scanning electron microscopy (SEM) analysis. Data were analyzed using two-way ANOVA and Tukey’s post hoc tests.

Results

Chloroform showed statistically lower mean μTBS values (14 ± 7.2 MPa) than control group did (19.2 ± 6.1 MPa) (p < 0.05). Orange oil (18.1 ± 6.3 MPa) and eucalyptol (16.9 ± 6.8 MPa) did not reduce the mean μTBS statistically (p > 0.05). Chloroform showed significantly lower bond strength for all adhesives (p < 0.05). Whereas orange oil did not reduce the mean μTBS values of all adhesive systems significantly (p > 0.05), eucalyptol reduced the μTBS values of all the groups, but the results were only statistically significant for SB2 (p < 0.05). CSE showed statistically higher bond strength (20.4 ± 6.8 MPa) than AEO (14.6 ± 5.3 MPa) and SB2 (16.3 ± 7.2 MPa) did (p < 0.05). There were no statistical differences between AEO and SB2 (p > 0.05). According to the SEM analysis of the debonded surfaces, adhesive failures were the most common type in all the groups, followed by mixed failures.

Conclusions

While chloroform reduced the mean bond strength of the adhesive resins, orange oil did not affect the bond strength of the adhesives. The effect of eucalyptol on bond strength depended on the type of adhesive system.

Clinical relevance

This study shows that endodontic solvents could affect the microtensile bond strength of adhesives to pulp chamber dentin.

     

The effect of TiO2 and SiO2 nanoparticles on flexural strength of poly (methyl methacrylate) acrylic resins

PurposeTiO₂ and SiO₂ nanoparticles are products of nanotechnology which have been incorporated to acrylic resins (AR) in order to induce antimicrobial properties. However, as additives they can affect the mechanical properties of the final product. The aim of this study was to survey the effects of TiO₂ and SiO₂ nanoparticles on flexural strength (Fs) of poly (methyl methacrylate) acrylic resins.MethodsAcrylic specimens (Selecta Plus) in size of 5 × 10 (±0.2) × 3.3 (±0.2) mm were prepared and divided into 7 groups: AR containing nanoTiO₂, SiO₂ and TiO₂ with SiO₂ in two concentration of 1% and 0.5%, in addition to a control group. To prepare nano AR, nanoparticles were added to the monomer. All specimens were stored in 37 °C distilled water and underwent Fs test by universal testing machine (Zwick).ResultsThe maximum mean flexural strength (43.5 MPa) belongs to the control group and AR containing 0.5% of both TiO₂ and SiO₂ demonstrated the minimum mean Fs (30.1 MPa). Resins contained TiO₂, demonstrated lower values of Fs than those contained SiO₂ with the same concentration, but the differences were not significant (P > 0.05).ConclusionIncorporation of TiO₂ and SiO₂ nanoparticles into acrylic resins can adversely affect the flexural strength of the final products, and this effect is directly correlated with the concentration of nanoparticles.     

TiO2 nanoparticles added to dense bovine hydroxyapatite bioceramics increase human osteoblast mineralization activity

ObjectivesThis study evaluated the effect of TiO₂ nanoparticles + dense hydroxyapatite (HA) on human osteoblast cells (SAOS-2).MethodsParticulate bovine HA powder with or without the addition of either 5 or 8 % TiO₂ (HA, HA/TiO₂Np5 % or HA/TiO₂Np8 %) were pressed into disks (Ø = 12.5 mm; thickness = 1.3 mm) uniaxially (100 MPa) and isostatically (200 MPa/1 min) and sintered at 1300 °C. Y-TZP disks were used as control. The following tests were performed: Scanning Electron Microscopy and Dispersive Energy Spectroscopy (SEM/EDS), Atomic Force Microscopy (AFM), cell viability assay (Alamar Blue-AB) and mineralized matrix deposition (Alizarin Red-AR). AB and AR data were submitted to 2-way ANOVA/Tukey tests and ANOVA/Tukey tests, respectively.ResultsSEM revealed that the surface of HA/TiO₂Np5% resembles DPBHA surface, but also contains smaller granules. HA/TiO₂Np8% characteristics resembles HA/TiO₂Np5% surface, but with irregular topography. Y-TZP showed a typical oxide ceramic surface pattern. EDS revealed Ca, O, and P in all samples. C, O, and Zr appeared in Y-TZP samples. AFM data corroborates SEM analysis. AB test revealed excellent cellular viability for HA/TiO₂Np5% group. AR test showed that all groups containing TiO₂np had more mineralized matrix deposition than all other groups, with statistically differences between HA/TiO₂Np8% and HA cultivated in non-osteogenic medium. Culture in osteogenic medium exhibited much more mineralized matrix deposition by TiO₂np groups.SignificanceIn conclusion, the addition of TiO₂np showed chemical, superficial, and biological changes in the reinforced materials. HA/TiO₂Np5% showed the best results for cell viability and HA/TiO₂Np8% for mineralized matrix deposition.     

Response of human fibroblasts to implant surface coated with titanium dioxide photocatalytic films

PurposeThis study was to develop a titanium dioxide (TiO₂)-coated implant abutment, surface with ultraviolet (UV) light-induced hydrophilicity and investigate the initial response of human, fibroblasts to the surface modification.Materials and methodsCommercially pure titanium (JIS 2 grade) disks were coated with TiO₂ to various, thicknesses (1, 2 or 3 μm) using peroxotitanium acid solution. The surface characteristics of each disk, were examined with X-ray diffraction (XRD), surface roughness equipment and scanning electron, microscopy (SEM). The hydrophilic change of each disk was determined by the contact angles at 0–24 h, after 24-h UV irradiation. The biological response at the surface of each disk was examined by using, human periodontal ligament fibroblasts (HPLFs). The data were statistically analyzed with analysis of variance (ANOVA) and multiple-comparison tests.ResultsThe TiO₂-coated disk surface had an anatase structure. Surface roughness did not differ, significantly among the disks; the surface morphology was smooth and had a hydrophilic or superhydrophilic, status. HPLF proliferation significantly increased on the TiO₂-coated disks compared with the uncoated disks and depended upon the coated film thickness.ConclusionAn anatase TiO₂-coated surface under UV irradiation markedly improves the initial response of human fibroblasts.     

The Effect of Laser Treatment on Bonding Between Zirconia Ceramic Surface and Resin Cement

Abstract

Objective. The purpose of this in-vitro study was to evaluate and compare the effects of different surface treatments and laser irradiation on the shear bond strength of resin cement to zirconia-based ceramic. Material and methods. Forty zirconia core specimens (10-mm diameter, 2-mm thickness) were produced and embedded in the centers of autopolymerizing acrylic resin blocks. Subsequently, specimens were randomly divided into four groups, each containing 10 specimens, for different surface treatment methods. The details of the groups are as follows: Group C, no treatment applied (control); Group SB, bonding surfaces of ceramic disks were airborne particle-abraded with 110-μm alumina oxide particles; Group HF, bonding surfaces of ceramic disks were etched with 9.6% hydrofluoric acid; and Group L, bonding surfaces of ceramic disks were irradiated by a CO₂ laser. A total of 40 composite resin disks were fabricated and cemented with an adhesive resin cement to the specimen surfaces. A universal test machine was used for the shear bond strength test at a crosshead speed of 1 mm/min. Results. The highest shear bond strength values were obtained with Group L (20.99 ± 3.77 MPa) and the lowest values with Group C (13.39 ± 3.10 MPa). Although there was no significant difference between Groups C, HF and SB (P > 0.05), Group L showed a significant difference from all other groups (p < 0.05). Conclusion. All surface treatment methods improved the bond strength between resin cement and the zirconium oxide ceramic surface. CO₂ laser etching may represent an effective method for conditioning zirconia surfaces, enhancing micromechanical retention and improving the bond strength of resin cement on zirconia ceramic.     

A new technique for incorporation of TiO2 nanotubes on a pre-sintered Y-TZP and its effect on bond strength as compared to conventional air-borne particle abrasion and silicatization TiO2 nanotubes application on pre-sintered Y-TZP

ObjectiveThis study evaluated the microshear bond strength of a resin cement to Y-TZP after different methods of TiO₂ nanotubes (nTiO₂) incorporation on pre-sintered Y-TZP surfaces.MethodsnTiO₂ were synthesized and incorporated on Y-TZP slices as follows (n = 15): 1) nTiO₂ mixed with isopropyl alcohol/manual application (MAl); 2) nTiO₂ mixed with acetone/manual application (MAc); 3) nTiO₂ mixed with isopropyl alcohol/high-pressure vacuum application (HPVAl); 4) nTiO₂ mixed with acetone/high-pressure vacuum application (HPVAc). As controls, surfaces were sandblasted with Al₂O₃ (OX) or Rocatec silicatization (ROC). All ceramics were sintered after nTiO₂ incorporation. Surface treatments of OX and ROC were made after sintering. Surfaces were characterized by confocal laser microscopy, scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). Resin composite cylinders (1.40 mm diameter and 1 mm height) were cemented with a resin cement, stored in water at 37 °C for 24 h and thermocycled for 10 000 cycles before microshear bond strength evaluation. Data were analyzed with one-way ANOVA and Games-Howell (α = 0.05), and fracture analysis was performed using a stereomicroscope.ResultsEDS confirmed the presence of TiO₂ on treated Y-TZP. The confocal analysis showed higher roughness for HPVAc and OX. There were significant differences between surface treatments (p < 0.001). HPVAl (22.96 ± 10.3), OX (34.16 ± 7.9) and ROC (27.71 ± 9.4) showed higher microshear bond strengths and were statistically similar (p > 0.05). MAC showed intermediary values, and HPVAc and MAl presented decreased bond strength, with a high percentage of premature debonding.ConclusionHigh-pressure vacuum application of nTiO₂ mixed with isopropyl alcohol was able to produce bond strength values compared to conventional air abrasion and Rocatec silicatization.SignificanceThe infiltration of TiO₂ nanostructures on the pre-sintered Y-TZP is an interesting approach that can improve bond strength without the need of sandblasting methods.     

The influence of SiO2 and SiO2–TiO2 intermediate coatings on bond strength of titanium and Ti6Al4V alloy to dental porcelain

ObjectivesThe purpose of this study was to evaluate the bond strength of commercially pure CPTi and Ti6Al4V alloy with SiO₂ and SiO₂–TiO₂ intermediate coatings to Triceram low-fusing dental porcelain.MethodsThe multilayered systems were characterized from the standpoint of microstructure analysis (SEM), the mode of failure, the nature of bonding and the influence of intermediate coatings on the improvement of bond strength. The SiO₂ and SiO₂–TiO₂ intermediate coatings were applied on the substrate materials by the sol–gel dipping technique. The metal–ceramic bond strength was investigated according to ISO 9693 standards using the three-point flexure bond test.ResultsStatistically significant higher bond strength of the metal–porcelain for Ti6A14V alloy (28.24 MPa), Ti6Al4V/SiO₂ (32.17 MPa) and Ti6Al4V/SiO₂–TiO₂ (36.09 MPa) was noted in comparison to CPTi (23.04 MPa), CPTi/SiO₂ (27.98 MPa) and CPTi/SiO₂–TiO₂ (28.84 MPa), respectively. The nature of metal-intermediate coating–porcelain bonding was both mechanical and chemical. The failure in all systems was cohesive and adhesive, mainly adhesive.SignificanceThe application of SiO₂ and SiO₂–TiO₂ intermediate coatings, produced by the sol–gel method, to both CPTi and Ti6Al4V alloy significantly improves the bond strength of metal–porcelain systems in comparison to the metal substrate only after sandblasting, and may have clinical use.     

Effect of hydrothermal and mechanical aging on the fatigue performance of high-translucency zirconias

ObjectivesThis study aimed to evaluate the impact of mechanical fatigue cycling using the step-stress approach along with hydrothermaldegradation (134 ºC with a constant pressure of 2 bars for 20 h), and a novel intercalated hydrothermal/fatigue aging protocol on different aspects of the aging resistance of three generations of dental zirconias.Methods“Y”Z T (VITA), INCORIS “T”ZI (Dentsply Sirona) and “K”ATANA UTML (Noritake Kuraray) ? 1st, 2nd and 3rd generation, respectively-, zirconia disks (N = 153), were divided into 6 groups (n = 3) for monotonic testing and 9 groups (n = 15) for mechanical fatigue testing, according to 3 proposed treatments for each zirconia: CF (control – only mechanical fatigue cycling); AF (aging in hydrothermal reactor at 134 °C for 20 h + mechanical fatigue cycling); AFA (Alternating protocol: 4 steps of 5 h of hydrothermal aging intercalated with mechanical fatigue cycling). Mechanical fatigue aging was performed according to the step-stress approach through biaxial flexural setup (piston-on-3-balls, initial strength: 100 MPa, step: 50 MPa/10,000, frequency: 20 Hz) until failure. Data were analyzed using Kaplan-Meier and Mantel-Cox test (α = 0.05), in addition to Weibull analysis. Fractured disks were analyzed in stereomicroscope, Scanning Electron Microscopy and X-Ray Diffraction.ResultsContinuous hydrothermal and mechanical fatigue cycling decreased the fatigue strength of YAF group (516 ± 38 MPa), while the alternating protocol increased it (730 ± 58 MPa). KATANA UTML showed no differences for both treatments and did not undergo t-m phase transformation. The TAF group showed the highest fatigue strength (810 ± 76 MPa) and cycles for failure (147,000.00 cycles). The fracture origin for all specimens was on the tensile side in pre-existing defects.SignificanceINCORIS TZI zirconia had higher fatigue strength and survival rates after hydrothermal and mechanical fatigue aging. Although less resistant, KATANA UTML did not suffer chemical degradation.     

Bio-mechanical characterization of a CAD/CAM PMMA resin for digital removable prostheses

ObjectiveTo compare the mechanical and biological features of a polymethylmethacrylate (PMMA) disc for CAD/CAM prostheses (test samples, TG) with a traditional resin (control samples, CG).MethodsMechanical analysis was performed using Dynamic Mechanical Analysis (DMA) and Brillouin's micro-spectroscopy. Human keratinocyte morphology and adhesion were analyzed by scanning electronic microscopy (SEM), cytotoxicity by the MTT assay, apoptosis by flow cytometry and p53, p21 and bcl2 gene expression by real time PCR.ResultsTG exhibited a higher elastic modulus than CG (range 5100–5500 ± 114.3 MPa vs 3000–3300 ± 99.97 MPa). The Brillouin frequency was found at ω_B= (15.50 ± 0.05) GHz for TG and at ω_{B_1} = (15.50 ± 0.05) GHz and ω_{B_2} = (15.0 ± 0.1) GHz for CG where two peaks were always present independently of the sample point. SEM analysis revealed that keratinocytes on TG disks appeared to be flattened with lamellipodia. Keratinocytes on CG disks rose above the substrate with cytoplasmatic filaments. MTT viability data at 3 h and 24 h showed TG was significantly less cytotoxic than CG (p < 0.001). No significant differences emerged in apoptosis on CG and TG. Real-time PCR showed p53 expression increased after 3 h by about 9-fold in keratinocytes on TG (p < 0.001) and about 5-fold in those on CG (p < 0.001). High p53 expression persisted after 24 h on both disks. No significant variations were observed in p21 and bcl2 expression at any time-point.SignificancePMMA resins, as used in CAD/CAM technology, displayed suitable biocompatible and mechanical properties for removable prostheses.     

Improvement of mechanical properties of Y-TZP by thermal annealing with monoclinic zirconia nanoparticle coating

ObjectiveTo assess whether a thermal annealing with a monoclinic zirconia (mZrO₂) nanoparticle coating can improve the reliability of sandblasted yttria-stabilized tetragonal zirconia polycrystals (Y-TZP) and maintain its mechanical strength.MethodsCommercially available Y-TZP (Lava Frame, 3M Dental Products) disks were sintered and surface-treated as follows: AS (as sintered, with no treatment); SB (sandblasting); SB-TA (sandblasting followed by thermal annealing at 1000 °C); and SB-mZr-TA (sandblasting followed by thermal annealing at 1000 °C with the mZrO₂ nanoparticle coating). The mZrO₂ nanoparticles of 21 nm in size were prepared by a hydrothermal method, and coated onto Y-TZP sintered disks as a 5 g/L ethanol dispersion. Biaxial flexural strength (S) was measured using the piston-on-three-ball test, and reliability was evaluated by the Weibull modulus (m).ResultsBiaxial flexural tests showed a significant increase in the strength of Group SB (S_SB = 1445 ± 191 MPa) compared with Group AS (S_AS = 1071 ± 112 MPa). The thermal annealing improved the reliabilities of the sandblasted Y-TZP (m_SB-TA = 20.14 and m_SB-mZr-TA = 21.33), as compared with Group SB (m_SB = 7.77). However, the conventional thermal annealing without the mZrO₂ coating caused a significant decrease in the strength of sandblasted Y-TZP (S_SB-TA = 1273 ± 65 MPa). Importantly, the mZrO₂ coating prevented the decrease in the strength caused by conventional thermal annealing (S_SB-mZr-TA = 1379 ± 65 MPa).SignificanceThe thermal annealing with the mZrO₂ nanoparticle coating can improve the reliability of sandblasted Y-TZP and maintain its mechanical strength, which would otherwise be decreased by the conventional annealing process.     

Additive manufacturing of lithium disilicate glass-ceramic by vat polymerization for dental appliances

ObjectivesThe objectives of this study were to evaluate the mechanical properties of lithium disilicate components produced by additive manufacturing (AM) and to assess the effect of build orientation on the resistance to fracture.MethodsOversized bars were printed with a glass-filled photoactive resin using a digital light processing technique. After sintering and post-processing, flexure and chevron notch fracture toughness bars were obtained in three principal orientations (0°, 45°, and 90°) with respect to the build direction. Mechanical properties were obtained according to the relevant ASTM standards. The hardness, indentation fracture resistance, and elastic modulus were measured for each orientation, and a Weibull analysis was conducted with the flexure responses. Fractography of the fracture surfaces was performed to identify the failure origins.ResultsThe 0° orientation exhibited characteristic strength, Weibull modulus, and elastic modulus of 313 MPa, 4.42, and 168 ± 3 GPa, respectively, which are comparable to lithium disilicate materials from traditional processes. However, build orientation contributed significantly to the flexure strength, elastic modulus, and Weibull modulus; the characteristic strengths for the 45° and 90° build orientations were 86 MPa and 177 MPa, respectively. The primary contribution to the orientation dependence was the number of residual build layer-related flaws from incomplete union between printed layers. Of note, hardness and the fracture toughness were not dependent on build orientation.SignificanceAM of lithium disilicate materials can achieve the mechanical properties of materials produced by traditionally processing. Thus, while further process development is warranted, the outlook for dentistry is promising.     

Effects of ZnO/TiO2 nanoparticle and TiO2 nanotube additions to dense polycrystalline hydroxyapatite bioceramic from bovine bones

ObjectivesA bovine dense hydroxyapatite ceramic (HA) was produced as new biomaterial, however, the production of a material with consistently high flexural strength remains challenging. The objective of this study was to evaluate the effects of ZnO nanoparticles, TiO₂ nanoparticles, and TiO₂ nanotubes (1%, 2%, and 5% by weight) on the microstructure and flexural strength of a bovine dense hydroxyapatite ceramic (HA).MethodsDiscs (Ø = 12.5 mm; thickness = 1.3 mm) were prepared and subjected to X-ray diffraction (XRD), and observation with a field emission scanning electron microscope (FE-SEM), biaxial flexural strength (BFS) testing, and Vickers hardness (VH) testing. The BFS and VH data were subjected to ANOVA and Tukey post-hoc tests (α = 0.05) and Weibull analysis.ResultsThe XRD showed that the addition of nanomaterials caused the formation of a secondary phase when 5% of the ZnO nanoparticles was used, or when all percentages of the TiO₂ nanoparticles/nanotubes were used, and the HA crystallographic planes were maintained. Differences were not observed between the higher BFS values obtained with pure HA and those obtained with the 5% addition of TiO₂ nanoparticles. However, the results were different compared with the other groups (α = 0.05). The results obtained by Weibull analysis revealed that the 1%, 2%, and 5% addition of TiO₂ nanotubes, and the 1% and 2% addition of TiO₂ nanoparticles decreased the HA characteristic strength (σ₀), while the Weibull modulus (m) increased when 5% of TiO₂ nanoparticles, 1% and 2% of ZnO nanoparticles, and 2% of TiO₂ nanoparticles were added, but with no statistical difference from the pure HA. The 5% addition of ZnO₂ nanoparticles decreased the σ₀ without changing m. Moreover, the 5% addition of TiO₂ nanoparticles resulted in an m closest to that of pure HA. Regarding the VH results, the blend of HA with 1% and 2% addition of TiO₂ nanoparticles exhibited the higher values, which were similar between the different addition ratios (p = 0.102). Moreover, the addition of 5% TiO₂ nanoparticles resulted in higher value compared with pure HA.SignificanceThis study demonstrated that the HA blend with 5% of TiO₂ nanoparticles has the greatest potential as a bovine HA dense bioceramic reinforcement.     

Effect of Anatase Titanium Dioxide Nanoparticles on the Flexural Strength of Heat Cured Poly Methyl Methacrylate Resins: An In-Vitro Study

Poly methyl methacrylate (PMMA) resin is the most widely used material for fabrication of dentures since 1937 as it exhibits adequate physical, mechanical and esthetic properties. But one of the major problems faced using this material is that, it is highly prone to plaque accumulation due to surface porosities and its food retentive properties. This in turn increases the bacterial activity causing denture stomatitis. In efforts to impart antimicrobial property to these resins, various nanoparticles (NP) have been incorporated viz. Silver, Zirconia oxide, Titanium dioxide (TiO₂), Silica dioxide (SiO₂) etc. However, as additives they can affect the mechanical properties of the final product. Therefore, the aim of the present study was to evaluate and compare the effect of different concentration of TiO₂ NP on the flexural strength of PMMA resins. Specimens made from heat polymerizing resin (DPI) without NP were used as a control group (Group A). The two experimental groups, (Group B and Group C) had 0.5 and 1 % concentration of TiO₂ NP respectively. The specimens were stored in 37 °C distilled water for 50 ± 2 h. A three-point bending test for flexural strength measurement was conducted following ADA specification no. 12. The maximum mean flexural strength (90.65 MPa) belonged to the control group; and acrylic resin with 1 % TiO₂ NP demonstrated the minimum mean flexural strength (76.38 MPa). But, the values of all the three groups exceeded the ADA Specification level of 65 MPa. Conclusion may be drawn from the present study that addition of TiO₂ NP into acrylic resin can adversely affect the flexural strength of the final product and is directly proportional to the concentration of NP.

     

Yttria-stabilized tetragonal zirconia polycrystal/resin luting agent bond strength: Influence of Titanium dioxide nanotubes addition in both materials

PurposeTo evaluate the shear bond strength (SBS) between Y-TZP and a resin luting agent, after 1 of 2 enhancing strategies with TiO_2--nts was applied, either to the resin luting agent or the Y-TZP mass, in different concentrations.MethodsIn the Strategy TiO₂-nts on ceramic, the resin luting agent Panavia F2.0™ (Kuraray) and an experimental Y-TZP with added concentrations of TiO_2--nts (0%, 1%, 2%, and 5% vol/vol) and a commercial Y-TZP, comprised 5 different groups (n = 10). In the Strategy TiO₂-nts on cement, the resin luting agent RelyX U200™ (3 M ESPE) was added with different concentrations of TiO_2--nts (0%, 0.3%, 0.6%, 0.9% wt/wt) luted to a commercial Y-TZP, comprising 4 different groups (n = 10). The Y-TZP discs were included in acrylic bases, and a cylinder (3 × 3 mm) of the correspondent luting agent for each respective group was applied over them. After 24 h, specimens were subjected to SBS assessments in a universal testing machine. Field emission scanning electron microscopy and energy dispersive X-ray spectroscopy analyses were also performed on Y-TZP surfaces. Data were analyzed via analysis of variance and Tukey tests (α = 0.05).ResultsTiO₂-nts on ceramic influenced the bond strength significantly, but not linearly; TiO₂-nts on cement did not influence bond strength when analyzed separately, nor in comparison with the first.ConclusionY-TZP enhancements with TiO₂-nts led to a higher SBS with Panavia F2.0, a 5% TiO_2--nt concentration presented the highest bond strength. Modified Rely X U200 did not improve SBS.     

The effect of a ceramic coating on the cpTi–porcelain bond strength

ObjectivesTo investigate the bond strength between cpTi and low fusing porcelains after different treatments.Methods72 patterns were covered with a ceramic coating and invested with phosphate-bonded material (group A), another 72 were invested with magnesia material (group B) and all cast with cpTi. 31 solid castings were selected from each group. The castings of group B were ground and sandblasted, while the castings of group A were only sandblasted. Aluminum content of the metal surface was determined by EDS and castings were submitted to a 3-point bending test to determine the modulus of elasticity (E). The porcelains Duceratin Plus, Noritake Ti22 and Triceram were applied respectively and specimens were submitted to a 3-point bending test. The fracture mode and the remaining porcelain were determined by optical microscopy and SEM/EDS. Bond strength and fracture mode were calculated by two-way ANOVA.ResultsThe E of groups A and B was 98.3 GPa and 98.6 GPa respectively. The bond strength was 26 ± 3 MPa (Duceratin Plus), 28 ± 3 MPa (Noritake Ti22), 27 ± 2 MPa (Triceram) for group A and 24 ± 1 MPa, 29 ± 2 MPa, 27 ± 1 MPa for group B respectively. No significant differences were found for the same porcelain between the two groups (p < 0.05). A significant difference was found between Duceratin Plus and Noritake Ti22, for group B (p < 0.05). The mode of failure was mainly adhesive for all specimens. A significant reduction in aluminum was recorded in all subgroups.SignificanceThe special coating of patterns makes the Ti casting procedure inexpensive, without reducing the metal–ceramic bond strength.     

Effect of finishing/polishing techniques and low temperature degradation on the surface topography,phase transformation and flexural strength of ultra-translucent ZrO2 ceramic

ObjectiveTo investigate the effect of different surface finishing and polishing regimes and low temperature degradation on flexural strength, phase transformation and surface topography of ultra-translucent ZrO₂ ceramic.Methods300 (n = 15/group) of conventional zirconia (Z: Ice Zirkon Transluzent) and ultra-translucent zirconia (UT: Prettau Anterior) bar-specimens were made and divided according to the "Finishing/Polishing" - (C — Control, B — diamond rubber polishers, P — adjusting with burs, PB — adjusting with burs + diamond polishers, PG — adjusting with burs + glaze), "Low temperature Degradation (LTD)" (with or without a treatment at 127 °C, 1.7 bar/24 h). Then, a 3-point mini flexural test was performed in a universal testing machine (1 mm/min, 500 kgf load cell). SEM, EDS, XDR, AFM, optical profilometry and Weibull analysis were performed. Data were analyzed by 3-way ANOVA and Tukey’s post-test (5%).ResultsGroups ZPB_D (1670 ± 253 MPa), ZB_D (1664 ± 217 MPa), and ZB (1655 ± 3678 MPa) showed significantly higher flexural strength than the UTPG group (372 ± 56 MPa). The Weibull modulus was significantly higher for the ZP_D group compared to the UB, UC_D, UP_D and UPB_D, while UTB, UTC_D and UTP_D had the lowest value. Monoclinic phases were observed only in the conventional zirconia groups and were more evident after LTD. Diamond rubber polishers presented less roughness for both zirconias.SignificanceThe use of diamond rubber polishers is the most suitable finishing/polishing method for zirconia ceramic restorations and that final glazing reduces the fracture resistance of these materials.     

Effect of thermal cycling on flexural properties of carbon–graphite fiber-reinforced polymers

ObjectivesTo determine flexural strength and modulus after water storage and thermal cycling of carbon–graphite fiber-reinforced (CGFR) polymers based on poly(methyl methacrylate) and a copolymer matrix, and to examine adhesion between fiber and matrix by scanning electron microscopy (SEM).MethodsSolvent cleaned carbon–graphite (CG) braided tubes of fibers were treated with a sizing resin. The resin mixture of the matrix was reinforced with 24, 36, 47 and 58 wt% (20, 29, 38 and 47 vol.%) CG-fibers. After heat polymerization the specimens were kept for 90 days in water and thereafter hydrothermally cycled (12,000 cycles, 5/55 °C). Mechanical properties were evaluated by three-point bend testing. After thermal cycling, the adhesion between fibers and matrix was evaluated by SEM.ResultsHydrothermal cycling did not decrease flexural strength of the CGFR polymers with 24 and 36 wt% fiber loadings; flexural strength values after thermocycling were 244.8 (±32.33) MPa for 24 wt% and 441.3 (±68.96) MPa for 36 wt%. Flexural strength values after thermal cycling were not further increased after increasing the fiber load to 47 (459.2 (±45.32) MPa) and 58 wt% (310.4 (±52.79) MPa).SEM revealed good adhesion between fibers and matrix for all fiber loadings examined.ConclusionsThe combination of the fiber treatment and resin matrix described resulted in good adhesion between CG-fibers and matrix. The flexural values for fiber loadings up to 36 wt% appear promising for prosthodontic applications such as implant-retained prostheses.     

Biological and physicochemical implications of the aging process on titanium and zirconia implant material surfaces

Statement of problemChanges in physicochemical properties because of implant material aging and natural deterioration in the oral environment can facilitate microbial colonization and disturb the soft-tissue seal between the implant surfaces.PurposeThe purpose of this in vitro study was to investigate the effect of aging time on the physicochemical profile of titanium (Ti) and zirconia (ZrO₂) implant materials. Further microbiology and cell analyses were used to provide insights into the physicochemical implications of biological behavior.Material and methodsDisk-shaped specimens of Ti and ZrO₂ were submitted to roughness, morphology, and surface free energy (SFE) analyses before nonaging (NA) and after the aging process (A). To simulate natural aging, disks were subjected to low-temperature degradation (LTD) by using an autoclave at 134 ºC and 0.2 MPa pressure for 20 hours. The biological activities of the Ti and ZrO₂ surfaces were determined by analyzing Candida albicans (C. albicans) biofilms and human gingival fibroblast (HGF) cell proliferation. For the microbiology assays, a variance analysis method (ANOVA) was used with the Tukey post hoc test. For the evaluation of cellular proliferation, the Kruskal-Wallis test followed by Dunn multiple comparisons were used.ResultsTi nonaging (TNA) and ZrO₂ nonaging (ZNA) disks displayed hydrophilic and lipophilic properties, and this effect was sustained after the aging process. Low-temperature degradation resulted in a modest change in intermolecular interaction, with 1.06-fold for TA and 1.10-fold for ZA. No difference in biofilm formation was observed between NA and A disks of the same material. After 48 hours, the viability of the attached HGF cells was very similar to that in the NA and A groups, regardless of the tested material.ConclusionThe changes in the physicochemical properties of Ti and ZrO₂ induced by the aging process do not interfere with C. albicans biofilm formation and HGF cell attachment, even after long-term exposure.     

Micro-Raman spectroscopic analysis of TiO2 phases on the root surfaces of commercial dental implants

ObjectivesTo identify the TiO₂ phases of the root surface of commercially available titanium dental implants, subjected to various surface treatments.MethodsThe titanium implants studied were: Allfit (ALF), Ice (ICE), IMZ TPS (TPS), Laser Lok (LLK), Prima Connex (PRC), Ospol (OSP), Osseospeed TX (OSS), Osseotite Full (OTF), Replace Select (RPS), SLA (SLA) and Trilobe (TRB). The root parts of the implants (n:2) were analyzed by Raman microspectroscopy employing argon ion laser excitation (514.5 nm wavelength) and a 100 μm × 100 μm sampling area at two randomly selected sites.ResultsThe spectra of OSP and RPS showed the characteristic peaks of anatase, with traces of rutile (RPS). Complex phases composed of anatase, rutile and amorphous TiO₂ were identified in ALF, ICE and LLK. Rutile and amorphous TiO₂ were found in PRC, OSS, OTF, TPS and TRB, whereas rutile and possibly brookite were traced in SLA. In all implants, except OSP and RPS, peaks assigned to organic impurities (CH₂, CH₃) and carbonates were recorded. Ti₂O₃ was identified in OTF, PRC and Al₂O₃ in TRB.SignificanceGreat variations in the TiO₂ polymorphs were registered among the implant root surfaces tested. Considering the important differences in the biological activity of these polymorphs, it can be concluded that provision of information regarding the TiO₂ state on implant surfaces should be a mandatory task for implant manufacturers.     

Strength and reliability of zirconia fabricated by additive manufacturing technology

ObjectivesTo test strength and reliability of 3D printed compared to milled zirconia.MethodsCylindrical specimens were fabricated from milled (group G1; e.max ZirCAD LT) and from 3D printed (group G2; LithaCon 3Y 230) 3-mol% yttria-stabilized tetragonal zirconia polycrystal (3Y-TZP). While G1 and G2 were sintered in one step, a further series (G3) of 3D printed 3Y-TZP was sintered in two steps including intermediate color infiltration. In each group, two different conditioning strategies were applied (n ≥ 20 samples/subgroup): (1) final polishing with #1200 diamond discs according to ISO 6872, and (2) final polishing with #220 diamond discs resulting in imperfectly polished surfaces. All samples were tested to fracture with a universal testing device (cross-head speed: 1 mm/min). Characteristic strengths and Weibull moduli were calculated. Effects were analyzed by means of either ANOVA (homocedastic data) or Welch ANOVA (heterocedastic data).ResultsFor samples conditioned according to ISO 6872, mean flexural strengths were 1462 ± 105 MPa (G1), 1369 ± 280 MPa (G2), and 1197 ± 317 MPa (G3). For the imperfectly polished subgroups, strength values were 1461 ± 121 MPa (G1), 1349 ± 332 MPa (G2), and 1271 ± 272 MPa (G3). Although all groups showed high mean strength values, the reliability of milled zirconia (Weibull moduli 14 < m <16) outperformed that of the 3D-printed material (3 < m <6).SignificanceEven after color infiltration in a partially sintered state, the tested 3D printed zirconia exceeded the ISO flexural strength criteria for all types of fixed ceramic restorations by far (800 MPa for class 6, ISO 6872), indicating its high potential for clinical use. Further optimization of the internal material structure after sintering might improve the reliability of 3D printed zirconia which is currently inferior to that of milled zirconia.