Selective adhesive luting: A novel technique for improving adhesion achieved by universal resin cements.

OBJECTIVE: We aimed to introduce the concept of "Selective adhesive luting-SAL" which is explained through clinical steps and supported by preliminary laboratory evidence. CLINICAL CONSIDERATIONS: Cementation with rubber dam is difficult to perform in case of short abutment teeth and/or subgingival crown margins. By means of universal resin cements/universal adhesive systems, which can be employed in self-adhesive as well as adhesive luting procedures, this paper presents a novel technique allowing clinicians to perform reliable cementation where rubber dam isolation is difficult. The SAL technique entails the application of a universal adhesive system only on easily accessible abutment surfaces, enabling simultaneous adhesive and self-adhesive luting in different portions of the abutment. The SAL clinical workflow is explained through prosthodontic rehabilitation of maxillary right central incisor affected by microdontia and restored with a lithium-disilicate crown. Furthermore, our laboratory microshear bond strength study supports the rationale behind SAL application demonstrating higher bond strength even when the adhesive resin is placed only on one portion of the cementation substrate. CLINICAL SIGNIFICANCE: This article advocates the application of SAL technique in clinical situations where effective adhesive luting is uncertain, since it can improve the adhesion between the tooth and universal resin cements.

Assessment of impression material accuracy in complete-arch restorations on four implants.

STATEMENT OF PROBLEM: New polyvinyl siloxane (PVS) materials with enhanced properties have been developed to improve and facilitate implant impression techniques. However, studies on their accuracy are lacking. PURPOSE: The purpose of this in vitro study was to determine the accuracy and precision of implant impressions made with some recently introduced materials on a simulated patient requiring an all-on-4 implant-supported prosthesis. Well-established polyether materials were also evaluated as a comparison. The variables considered were material type, consistency, splinting or not splinting techniques, and implant angulation. MATERIAL AND METHODS: A reference master model was made by inserting 4 implants at angles of 0, 5, and 10 degrees. Eighty impressions were made at 37 °C in wet conditions by using a standardized technique. Eight groups (n=10) were created using monophasic, single-viscosity materials (Hydrorise Implant Medium, HIM-ns; Hydrorise Implant Medium, HIM; Honigum Mono, HM; Impregum, IMP), and 2-viscosity materials (Hydrorise Implant Heavy+Light-ns, HIH+L-ns; Hydrorise Implant Heavy+Light, HIH+L; Honigum Heavy+Light, HH+L; and Permadyne and Garant [Heavy+Light, PeH+L]). Hydrorise materials were used with splinting and not splinting (ns) techniques. The reference points located on the connecting platforms of the transfer copings (TCP) were compared with the same points on the implant connecting platforms (ICP) located in the reference model. The accuracy and precision of the impressions were determined as linear 3D errors and standard deviation between each TCP-ICP couple by using an optical coordinate measuring machine (OCMM). RESULTS: PVS materials were generally better than polyether materials, with Hydrorise materials (HIM and HIH+L) showing significantly better accuracy and precision (30.9 ±14.4 µm and 28.7 ±15.5 µm, respectively) than IMP and PeH+L polyethers (44.2 ±16 µm and 43.8 ±17.6 µm, respectively; P<.001). Honigum materials were statistically similar to Hydrorise materials (P=.765). The values shown by Hydrorise nonsplinted groups (HIH+L-ns and HIM-ns) were not statistically different from those of the splinted polyether impressions (P=.386). The viscosities (monophasic or heavy+light) had no effect on accuracy, but monophasic material positively influenced precision (HIM and HIH+L, P=.001). No correlation was found between implant angulation and accuracy (multilevel analysis and Kendall rank correlation coefficient=-0.065; P=.133). CONCLUSIONS: Recently introduced materials designed for implant impressions showed significantly higher accuracy and precision; even with the unfavorable nonsplinting technique, the new materials performed similarly to, or better than, polyether materials. Although the transfer coping splinting technique generally improved the accuracy and precision of Hydrorise materials, the effect was significant only within HIH+L groups.

Fatigue resistance of monolithic lithium disilicate occlusal veneers: a pilot study.

The use of thin lithium disilicate (LD) occlusal veneers is an effective method to increase the vertical dimension of occlusion in cases of tooth wear. However, doubt remains regarding the threshold thickness to be used in this restoration class. This study aims to evaluate the effect of ceramic thickness on the survival rate and failure pattern of LD molar veneer restorations using a simplified fatigue testing machine. Sixty sound, freshly extracted human molars were used. Three groups (n = 20) were randomly created with different ceramic thicknesses (0.5, 0.8, and 1.2 mm), and 60 LD IPS e.max Press LT occlusal veneers were fabricated. The ceramic restorations were luted with a resin cement. The stainless-steel rotating drum of the ball mill contained 10 zirconia (Y-TZP) and 10 stainless steel spheres, in 500 mL of distilled water at 37 ± 1 °C. Crack growth in the LD restorations was evaluated under a stereomicroscope following each fatigue testing run (12 60-min runs). Progressive damage was observed as a function of cycling time. Survival was significantly influenced by the restoration thickness (p = 0.002, log-rank test), with thicker restorations exhibiting a higher survival rate. Thinner restorations (0.5 mm) showed significantly lower survival rate than 0.8- and 1.2-mm restorations (p < 0.016); no significant difference was observed between the 0.8- and 1.2-mm restorations. A threshold value of 0.8 mm may represent an acceptable compromise between fatigue resistance and tooth reduction.

Implant Digital Impression in the Esthetic Area.

The aim of this report is to describe two standardized protocols for digital impression when implant support rehabilitation is used in the esthetic area. The two techniques were used to transfer all provisional crown parameters to definitive restorations in different clinical scenarios. In the direct technique, an impression (STL1) is made of the provisional restorations attached to the implants, with surrounding gingival tissue. The second scan (STL2) captures the sulcular aspect of the peri-implant soft tissue immediately after removal of the provisional restoration. The last impression (STL3) of the complete arch is made with a standardized scanbody attached to the implant to capture the 3D location of the implant. The direct technique is indicated when the peri-implant soft tissues are stable upon removal of the provisional restoration. The indirect technique is used when the gingival tissue collapses rapidly after the removal of the provisional crown. The impressions of the provisional restoration and the position of the implant are similar to those obtained with the direct technique, and the shape of the peri-implant tissue is extrapolated from the negative shape obtained from making the digital impression when the provisional restoration is taken out of the mouth. Finally, in both techniques the 3 scans are superimposed to obtain a file, which contains the details of the peri-implant soft tissue. The direct and indirect digital techniques allowed realization of a predictable definitive restoration in the esthetic zone in different clinical scenarios, reducing the duration of clinical procedures.

Influence of Particle and Air-Abrasion Moment on Y-TZP Surface Characterization and Bond Strength.

PURPOSE: To evaluate the influence of particle and air-abrasion on the surface characterization and shear bond strength (SBS) of a Y-TZP ceramic with a resin cement. MATERIALS AND METHODS: Y-TZP specimens were air-abraded with 50 µm alumina particles; 120 µm alumina particles; 30 µm silica-coated alumina particles (Rocatec Soft); 110 µm silica-coated alumina particles (Rocatec Plus). Air-abrasion was performed before (BS); after (AS); before and after (BAS) zirconia sintering. Surface characterization included roughness (n = 10), wettability (n = 10), morphology (n = 2), and elemental composition (n = 2). For SBS (n = 11), composite resin discs were bonded to the air-abraded and silane-treated zirconia surface, with the resin cement RelyX ARC. Failure mode was determined. Roughness, wettability, and SBS data were analyzed by two-way ANOVA with pairwise interaction and Tukey's test (α = 0.05). RESULTS: Air-abrasion performed with coarser particles at BS and BAS moments provided the highest roughness values, while the lowest roughness values were observed with particles combined with AS moment (p < 0.01). Rocatec Plus provided lower contact angle than the 120 µm alumina particles (p = 0.013), and BAS exhibited lower contact angle than BS (p = 0.002). The combinations 120 µm/BS and the silica-coated alumina particles/AS and /BAS showed the highest SBS (p < 0.05). The combination of each particle/BAS was statistically similar to the same particle/AS. Failure mode was 100% adhesive for all groups. The interaction particle size/air-abrasion moment determined the morphological pattern. Silicon was observed only in the Rocatec groups. CONCLUSIONS: Roughness was influenced by the particle size and was higher when the zirconia was air-abraded in its green stage. The particle composition played an important role in the wettability and both studied air-abrasion moments provided similar wettability than the one in which air-abrasion is usually performed. The highest SBS values were observed in the three moments, by using certain particles for each moment.

Manufacturing of Metal Frameworks for Full-Arch Dental Restoration on Implants: A Comparison between Milling and a Novel Hybrid Technology.

PURPOSE: To determine the trueness and precision of frameworks manufactured with a selective laser melting/milling hybrid technique (SLM/m) and conventional milling by comparing the implant-platform/framework interface with those of the original computer-aided design (CAD). MATERIALS AND METHODS: Using a virtual 6-implant-supported full-arch framework CAD drawing, 27 titanium replicas were manufactured by 3 independent manufacturing centers (n = 9/center) using a hybrid SLM/m technology (labs 1 and 2) or the conventional milling technique (lab 3). Using an opto-mechanical coordinate measuring machine, the frameworks' misfit distribution and patterns were analyzed, and the position error between paired platform positions within each framework was evaluated to calculate the misfit tendency for each group. A multilevel analysis using a mixed-effects model was conducted (α = 0.05). The trueness was evaluated as the dimensional difference from the original, while the precision as the dimensional difference from a repeated scan. RESULTS: The 3 dimensional misfits differed significantly among the 3 groups, with the milled group exhibiting the least accurate outcome (p = 0.005). The mean 3D positioning errors ranged from 8 to 16 µm and from 9 to 22 µm for the SLM/m technique (labs 1 and 2, respectively), and from 20 to 35 µm for conventional milling (lab 3). Regarding the misfit distribution pattern, the misfit increased with the distance between paired platform positions in all groups. CONCLUSIONS: All groups had 3D misfits well within the error limits reported in the literature. The 3D misfits of new hybrid (SLM/milling) and conventional (milling) procedures differed significantly among them, with the milling technique the less accurate and precise. The largest errors in all groups were found between the most distant implants, resulting in a correlation between the framework span and the inaccuracies.

Ceramic Surface Treatment with a Single-component Primer: Resin Adhesion to Glass Ceramics.

PURPOSE: To evaluate the microshear bond strength (µSBS) of composite cement bonded to two machined glass ceramics and its durability, comparing conventional surface conditioning (hydrofluoric acid + silane) to a one-step primer (Monobond Etch & Prime). MATERIALS AND METHODS: Machined slices of lithium disilicate ceramic (LDC) (IPS e.max CAD) and feldspathic ceramic (FC) (VITA Mark II) glass ceramics were divided into two groups (n = 10) according to two factors: 1. surface treatment: HF+S (ca 5% hydrofluoric acid [IPS Ceramic Etching GEL] + silane coupling agent [SIL; Monobond Plus]) or MEP (single-component ceramic conditioner; Monobond Etch & Prime); 2. storage condition: baseline (without aging; tested 24 h after cementing) or aged (70 days of water storage + 12,000 thermal cycles). Composite cement (Multilink Automix, Ivoclar Vivadent) was applied to starch matrices on the treated ceramic surfaces and photoactivated. A µSBS test was performed (0.5 mm/min) and the failure pattern was determined. Contact angle and micromorphological analyses were also performed. Data were analyzed with Student's t-test (α = 5%). RESULTS: For both ceramic materials, HF+S resulted in higher mean µSBS (MPa) at baseline (LDC: HF+S 21.2 ± 2.2 > MEP 10.4 ± 2.4; FC: HF+S 19.6 ± 4.3 > MEP 13.5 ± 5.4) and after aging (LDC: HF+S 14.64 ± 2.31 > MEP 9 ± 3.4; FC HF+S: 14.73 ± 3.33 > MEP 11.1 ± 3.3). HF+S resulted in a statistically significant decrease in mean µSBS after aging (p = 0.0001), while MEP yielded no significant reduction. The main failure type was adhesive between composite cement and ceramic. HF+S resuted in the lowest contact angle. CONCLUSIONS: Hydrofluoric acid + silane resulted in higher mean µSBS than Monobond Etch & Prime for both ceramics; however, Monobond Etch & Prime had stable bonding after aging.

Translucency of IPS e.max and cubic zirconia monolithic crowns.

STATEMENT OF PROBLEM: Although several monolithic zirconia ceramics have recently been introduced, the need for improved optical properties remains. The newest cubic-zirconia has been claimed to have optimal translucency characteristics for esthetic restorations. PURPOSE: This in vitro study evaluated the optical properties of novel cubic ultratranslucent (UT) and supertranslucent (ST) zirconia by comparing them with lithium disilicate (L-DIS) glass-ceramic for the manufacture of monolithic computer-aided design and computer-aided manufacturing (CAD-CAM) molar crowns. MATERIAL AND METHODS: The UT and ST multilayered zirconia and the low-translucency grade L-DIS were milled. Eighty monolithic crowns were made from 2 CAD files, corresponding to thicknesses of 1.0 and 1.5 mm, and subdivided (n=20) into 4 groups: UT1.0, UT1.5, ST1.0, and L-DIS1.5. All groups were shaded using A2 color standard. Translucency of the crowns was measured by total transmission, using a photoradiometer in a dark chamber; furthermore, the contrast ratio was analyzed using a dental spectrophotometer applied to the buccal surface of the crowns. Data were analyzed using the Kruskal-Wallis and post hoc multiple Mann-Whitney U tests with Bonferroni correction (α=.05 divided by the number of tests performed in each set). RESULTS: When the ceramic types were analyzed, using total transmission and contrast methods, they showed significantly different translucency levels: UT1.0>ST1.0>UT1.5>L-DIS1.5 (total transmission P<.001). Contrast ratio evaluation yielded similar results (P≤.006); however, the differences between ST1.0 and UT1.5 were not significant. CONCLUSIONS: Both the ST1.0 and UT1.0 crowns, even at the maximum thickness tested (UT1.5), showed significantly higher translucency than L-DIS. Zirconia translucency was improved by eliminating the tetragonal phase, which is responsible for the toughening effect; thus, further studies are advocated to investigate the mechanical resistance of cubic zirconia.

Evaluation of marginal leakage after mechanical fatigue cycling of composite inlays luted with different cements.

This in vitro study evaluated the marginal microleakage of composite inlays luted with 3 different cement systems. The null hypothesis was that the luting materials would not influence dye penetration, showing the same degree of microleakage. Thirty-six sound molars were selected, mesio-occlusodistal cavities were prepared, and the teeth were randomly divided into 3 groups (n = 12). Composite resin inlay restorations were made and cemented using a dual-curing resin cement (Calibra), a light-curing flowable composite (Charisma Flow), or a self-adhesive resin cement (RelyX Unicem). The restored teeth were subjected to fatigue cycles and immersed in 0.5% basic fuchsin dye for 24 hours. Two orthogonal cuts were made to enable evaluation of dye penetration at the cervical and occlusal margins. The sections were evaluated with a 4-point scale ranging from 0 (no penetration) to 3 (penetration up to the cavity floor [occlusal margins] or axial wall [cervical margins]). The Calibra and Charisma Flow groups showed greater microleakage, notably at the cervical margins, whereas RelyX Unicem specimens showed the least dye penetration. Significant differences were found between the Calibra and Charisma Flow groups and between the Charisma Flow and RelyX Unicem groups (P < 0.05). No statistically significant differences were detected between the Calibra and RelyX Unicem groups. The microleakage associated with the flowable composite was significantly greater than that associated with both resin cements, results that discourage its use for luting of Class II composite inlays.

Marginal Adaptation, Gap Width, and Fracture Strength of Teeth Restored With Different All-Ceramic Vs Metal Ceramic Crown Systems: An in Vitro Study.

This study evaluated marginal adaptation before and after thermomechanical (TCML) loading, gap width and fracture strength of all-ceramic single crowns, as compared to porcelain-fused-to-metal (PFM). Thirty extracted premolars were prepared with a round shoulder of 1.0 mm depth. Specimens were restored with zirconia-ceramic (Group 1), lithium disilicate (Group 2) and metal-ceramic single crowns (Group 3). The replica of each sample was observed with a scanning electron microscope (SEM) to evaluate the crown-cement (c-c) and tooth-cement interface (t-c). After TCML, perfect margins decreased to 91.3% (c-c) and 93.9% (t-c) in Group 1, 94.6% (c-c) and 96.0% (t-c) in Group 2 and 73.5% (c-c) and 53.1% (t-c) in Group 3. The mean fracture strengths were 654.8 ± 98.1 N for Group 1, 551.3 ± 127 N for Group 2 and 501.43 ± 110.1 N for Group 3. All-ceramic systems could substitute for metal-ceramic crowns, but chipping of veneering ceramics, especially in zirconia-based crowns, should be investigated.

Clinical outcomes and success rates of quartz fiber post restorations: A retrospective study.

STATEMENT OF PROBLEM: Cast metal posts and dowels are inherently dark and, when metal-free restorations are used, could impair the definitive esthetic appearance. Quartz fiber posts could represent a reliable choice for restoring abutment teeth. PURPOSE: The purpose of this study was to evaluate the long-term success rate of teeth restored with quartz fiber posts and fixed dental prostheses (FDPs). MATERIAL AND METHODS: Ninety-nine teeth restored with 114 quartz fiber posts and FDPs were evaluated. The evaluation time ranged from 7 months to 9.25 years. The Kaplan-Meier method was used to obtain success curves. The influence of the tooth location, definitive restoration, and failure pattern upon the success function was analyzed with the log-rank test. The Cox regression test was used to evaluate possible predictors among the interactions of the observed parameters. RESULTS: The success rate of the restorations was 85.86% in a mean period of 5.88 ±1.37 years, with an estimated success probability of 85% at 6.17 years. The statistical analysis identified the factors related to the arch (P=.045) and type of definitive restoration (P=.021) as significantly associated with success. Post debonding was the most frequent failure mode, followed by endodontic failure, with the latter not necessarily being related to the post itself. No root fractures were recorded. Twelve teeth out of the 14 that failed were restored again, bringing the overall survival rate of the teeth to 98%. CONCLUSIONS: The rehabilitation of abutment teeth with quartz fiber posts can be considered a reliable procedure; however, adhesive techniques and luting materials require improvement.

Effect of surface treatments on the shear bond strength of luting cements to Y-TZP ceramic.

STATEMENT OF PROBLEM: Because zirconia is a glass-free material, alternative surface treatments such as airborne-particle abrasion or silica coating should be used for long-term bonding. However, these surface treatments in combination with different bonding agents and luting cements have not yet been studied. PURPOSE: The purpose of the study was to evaluate the effect of surface treatments on the shear bond strength (SBS) of luting cements to Y-TZP ceramic. MATERIAL AND METHODS: Zirconia disks (N=240) were airborne-particle abraded with the following particles (n=48): 50 µm Al2O3; 120 µm Al2O3; 30 µm silica-coated Al2O3 (Rocatec Soft); 120 µm Al2O3+110 µm silica-coated Al2O3 (Rocatec Plus); and Rocatec Plus. After silanization of the zirconia surface, composite resin disks were bonded with (n=12) RelyX Luting 2; RelyX ARC; RelyX U100; and Panavia F. The bonded specimens were thermocycled (10 000 cycles) and tested for SBS. Failure mode was determined with a stereomicroscope (×20). The morphology and elemental composition of airborne-particle abraded surfaces were evaluated with scanning electron microscopy (×500) and energy-dispersive x-ray spectroscopy (×50). RESULTS: Surface treatments, cements, and their interaction were significant (P<.001). For RelyX ARC, Rocatec Soft and Rocatec Plus provided the highest SBS. In general, surface treatments did not influence the SBS of RelyX U100 and Panavia F. Regardless of the cement, no significant difference was found between 50 µm and 120 µm Al2O3 particles, between Rocatec Soft and Rocatec Plus, or between Rocatec Plus and 120 µm Al2O3 particles+Rocatec Plus. All groups showed adhesive failures. Different particle sizes provided differences in morphological patterns. The elemental composition comprised Al and Al/Si for alumina and silica-abraded zirconia. CONCLUSIONS: Particle size did not influence the SBS of the groups abraded exclusively with alumina or silica-coated particles. RelyX ARC was more surface-treatment dependent than RelyX U100 or Panavia F.

Bond Strength to Lithium-Disilicate Ceramic after Different Surface Cleaning Approaches.

PURPOSE: To evaluate the effect of different lithium-disilicate (LiSi) glass-ceramic surface decontamination procedures on the shear bond strength (SBS) to resin cement. MATERIALS AND METHODS: Seventy CAD/CAM LiSi ceramic specimens (IPS e.max CAD, Ivoclar) were cut and sintered. Fifty specimens were treated with 5% hydrofluoric acid (HF) for 20 s, while 20 were left untreated. All 70 specimens were then contaminated with human saliva and try-in silicone paste. The following surface cleaning methods were investigated (n = 10): C: water rinsing (control); PA: 37% H3PO4 etching for 20 s; E: 70% ethanol applied for 20 s; CP: cleaning paste (Ivoclean, Ivoclar) brushed for 20 s; HFSEP: self-etching ceramic primer (Monobond Etch&Prime, Ivoclar) rubbed for 20 s; HF: 5% HF applied for 20 s or no HF etching prior to contamination; SEP: self-etching ceramic primer rubbed for 20 s and no HF etching prior to contamination. Composite cylinders were created and luted with an adhesive resin cement to the decontaminated surfaces. After storage for 24 h at 37°C, the SBS test was conducted. Two fractured specimens per group were observed under SEM to perform fractographic analysis. The data were statistically analyzed with p set at <0.05. RESULTS: The type of surface cleaning approach influenced bond strength (p < 0.001). HFSEP, SEP, and HF attained higher SBS (p < 0.001) compared to other groups. None of the approaches were able to completely remove contaminants from the ceramic surfaces. SEM images showed residual traces of contaminants on CP-treated surfaces. CONCLUSIONS: The self-etching ceramic primer enhanced bond strength to contaminated LiSi ceramic surfaces, irrespective of previous treatment with hydrofluoric acid.

Efficacy of surface treatments on the bond strength of resin cements to two brands of zirconia ceramic.

PURPOSE: To compare the shear bond strengths (SBS) of two cements to two Y-TZP ceramics subjected to different surface treatments. MATERIALS AND METHODS: Zirconia specimens were made from Lava (n = 36) and IPS e.max ZirCAD (n = 36), and their surfaces were treated as follows: no treatment (control), silica coating with 30-µm silica-modified alumina (Al2O3) particles (CoJet Sand), or coating with liners Lava Ceram for Lava and Intensive ZirLiner for IPS e.max ZirCAD. Composite resin cylinders were bonded to zirconia with Panavia F or RelyX Unicem resin cements. All specimens were thermocycled (6000 cycles at 5°C/55°C) and subjected to SBS testing. Data were analyzed by three-way ANOVA and Tukey's (HSD) post-hoc test (α = 0.05). Failure mode was analyzed by stereomicroscope and SEM. RESULTS: CoJet Sand and liners promoted significantly higher SBS than their control groups, but had similar results to one another. Panavia F provided significantly higher SBS values than RelyX Unicem (p < 0.01) for nontreated zirconia specimens of both brands. When Lava and IPS e.max ZirCAD were abraded with CoJet Sand, RelyX Unicem promoted significantly higher SBS values than Panavia F (p < 0.001). There was no significant difference between the two cements when the zirconia specimens were treated with their respective liners. The nontreated specimens and those treated with CoJet Sand exhibited a high percentage of adhesive and mixed A failures, while the specimens treated with liners presented an increase in mixed A and mixed C failures as well as some cohesive failure in the bulk of Lava Ceram for both cements. CONCLUSION: CoJet Sand and liners provided the best surface treatment for Lava and IPS e.max ZirCAD. The best surface treatment/cement combinations were CoJet Sand/RelyX Unicem and liner/Panavia F. SBS of Panavia F and RelyX Unicem was not influenced by the zirconia brand.

Effect of particle size on the flexural strength and phase transformation of an airborne-particle abraded yttria-stabilized tetragonal zirconia polycrystal ceramic.

STATEMENT OF PROBLEM: Because airborne-particle abrasion is an efficient method of improving the bond at the zirconia-cement interface, understanding its effect on the strength of yttria-stabilized tetragonal zirconia polycrystal is important. PURPOSE: The purpose of this study was to evaluate the effect of the particle size used for airborne-particle abrasion on the flexural strength and phase transformation of a commercially available yttria-stabilized tetragonal zirconia polycrystal ceramic. MATERIAL AND METHODS: For both flexural strength (20.0 × 4.0 × 1.2 mm) (n=14) and phase transformation (14.0-mm diameter × 1.3-mm thickness) (n=4), the zirconia specimens were made from Lava, and their surfaces were treated in the following ways: as-sintered (control); with 50-µm aluminum oxide (Al2O3) particles; with 120-µm Al2O3 particles; with 250-µm Al2O3 particles; with 30-µm silica-modified Al2O3 particles (Cojet Sand); with 120-µm Al2O3 particles, followed by 110-µm silica-modified Al2O3 particles (Rocatec Plus); and with Rocatec Plus. The phase transformation (%) was assessed by x-ray diffraction analysis. The 3-point flexural strength test was conducted in artificial saliva at 37°C in a mechanical testing machine. The data were analyzed by 1-way ANOVA and the Tukey honestly significant difference post hoc test (α=.05). RESULTS: Except for the Cojet Sand group, which exhibited statistically similar flexural strength to that of the as-sintered group and for the group abraded with 250-µm Al2O3 particles, which presented the lowest strength, airborne-particle abrasion with the other particle sizes provided the highest values, with no significant difference among them. The as-sintered specimens presented no monoclinic phase. The groups abraded with smaller particles (30 µm and 50 µm) and those treated with the larger ones (110 µm and/or 120 µm particles and 250 µm) exhibited percentages of monoclinic phase that varied from 4% to 5% and from 8.7% to 10%. CONCLUSIONS: Except for abrasion with Cojet Sand, depending on the particle size, zirconia exhibited an increase or a decrease in its flexural strength. Airborne-particle abrasion promoted phase transformation (tetragonal to monoclinic), and the percentage of monoclinic phase varied according to the particle size.

Effect of Fluorographene Addition on Mechanical and Adhesive Properties of a New Core Build-Up Composite.

This study aims to develop a restorative material having such mechanical and adhesive properties that it can be used both as a reconstruction material and as a luting cement. The experimental core build-up composite (CBC) was derived from a self-adhesive cement by the modification of its chemical formula, requiring the use of dedicated dentin and ceramic primers. The adhesive properties to zirconia and dentin were analyzed with a micro-Shear Bond Strength test (mSBS). The mechanical properties were analyzed by a flexural strength test. The results were compared with those obtained for other commercially available cements and core build-up materials, both before and after addition of 2 wt.% fluorographene. The CBC obtained average values in the mSBS of 49.7 ± 4.74 MPa for zirconia and 32.2 ± 4.9 MPa for dentin, as well as values of 110.9 ± 9.3 MPa for flexural strength and 6170.8 ± 703.2 MPa for Young's modulus. The addition of fluorographene, while increasing the Young's modulus of the core build-up composite by 10%, did not improve the adhesive capabilities of the primers and cement on either zirconia or dentin. The CBC showed adhesive and mechanical properties adequate both for a restoration material and a luting cement. The addition of 2 wt.% fluorographene was shown to interfere with the polymerization reaction of the material, suggesting the need for further studies.

Could light-curing time, post-space region and cyclic fatigue affect the nanomechanical behavior of a dual-curing cement for fiber post luting?

OBJECTIVE: To evaluate the effects of curing time, post-space region and cyclic fatigue on the micromechanical properties of a fiber-post luting cement. The null hypotheses were that (1) curing time, (2) fatigue and (3) post-space region does not affect the nanoindentation modulus and hardness of the dual-curing cement. MATERIALS AND METHODS: 48 premolars were endodontically treated and a class I cavity and 8 mm deep post space was prepared. Fiber posts were luted with a universal, dualized adhesive system and a dual-curing cement following manufacturer's instructions. Specimens were divided into three groups (16 specimens for each group) according to light-curing time (no light-curing, 20 s light-curing and 120 s light-curing), which was performed with a LED lamp at 1000 mW/cm 2. The coronal part of the cavity was restored using a nano-filled resin composite. After 24 h, 8 specimens for each group were randomly extract in order to undergo to fatigue test in wet condition through a chewing simulator, while the other specimens were kept in distilled water as benchmark. All the restored teeth were then sectioned in 1 mm thick slices perpendicularly to the fiber post axis. Specimen slices were classified in coronal and apical to be tested through a nanoindenter. Data were analyzed through Kruskal-Wallis test with a significance level of 1%, in order to evaluate the influence of treatments (i.e., curing time and cyclic loading) on the micromechanical properties of the tested luting cement. RESULTS: Both fatigue and curing time significantly influenced nanoindentation modulus and hardness of dual-curing cement (p < 0.01). No significant differences were reported for post space region. A significant interaction was found among the analyzed factors (p < 0.01). SIGNIFICANCE: 120 s light-curing time is recommended in order to achieve optimal mechanical proprieties, independently from post space region and cyclic fatigue. As matter of fact, 120 s light-curing allowed to prevent strain hardening induced by the fatigue simulation.

Effect of fiber posts with different emerging diameters on the fracture strength of restored crownless teeth.

The relatively low elastic modulus of fiber posts reduces the risk of root fracture, but it also decreases composite core stabilization. To compensate for the lack of rigidity, larger post sizes can be necessary when restoring crownless teeth that have significant internal destruction of the root canal. This study evaluated the effectiveness of fiber posts with different emerging diameters and shapes on composite core stabilization as measured by fracture strength testing. Fracture strengths ranged from 262.6 ± 81 N to 422.8 ± 56 N. A one-way ANOVA test showed that fracture strength was affected by type of post (p<0.0001); single-tapered posts were weaker than double-tapered posts. Pearson's linear correlation test showed that the fracture strength results appear to have a direct correlation to the emerging diameter of the post (p<0.0001; r(2)=0.6191). The emerging diameter of fiber posts is important to stabilize the core. When restoring crownless teeth, it is advisable to use fiber posts with large emerging diameters; no additional preparation of the internal root dentin is necessary to enlarge the post diameter.

Fatigue failure and success rate of lithium disilicate table-tops as a function of cement thickness.

Purpose Under thin, partial coverage restoration the proper cement thickness to be clinically employed still remains an issue. The aim of this study was to determine the failure and success rates of simplified lithium disilicate occlusal veneers as a function of cement thickness. The null hypothesis was that cement thickness has no effect on the fatigue resistance.Methods Sound human molars were severed in a plane parallel to the occlusal surface to create a flat dentin surface surrounded by enamel edges. Forty-five occlusal veneers 1.0 mm thick (IPS e.max CAD LT) were luted to the teeth with Multilink Automix resin cement, creating 3 experimental groups (n=15) with cement thicknesses of 50, 100, and 200 µm. The restorations were fatigue-cycled using a ball mill machine containing zirconia and stainless steel spheres. Twelve 60 min cycles were performed. Survival statistics were applied to "failure" and "success" events, comparing the three groups using a log-rank Mantel-Cox test and a log-rank test for trends (alpha = 0.05).Results The failure and success rates were not significantly influenced by cement thickness (P = 0.137 and P = 0.872, respectively); thus, the null hypothesis was accepted. However, when log-rank test for trends was applied to failure events, the tendency to have less failures with increasing thicknesses was found statistically significant (P = 0.047).Conclusions The cement thickness within the range adopted here did not have a significant effect on the failure or success rate of lithium disilicate occlusal veneers when exposed to randomized impact stresses generating fatigue phenomena.

Translucency of zirconia copings made with different CAD/CAM systems.

STATEMENT OF PROBLEM: Zirconia cores are reported to be less translucent than glass, lithium disilicate, or alumina cores. This could affect the esthetic appearance and the clinical choices made when using zirconia-based restorations. PURPOSE: The purpose of this in vitro study was to evaluate the translucency of zirconia copings for single crowns fabricated using different CAD/CAM systems, using lithium disilicate glass ceramic as a control. MATERIAL AND METHODS: Using impressions made from a stainless steel complete-crown master die, 9 stone cast replicas were fabricated, numbered, and distributed into 8 ceramic ZrO(2) CAD/CAM system groups (Lava Frame 0.3 and 0.5, IPS e.max ZirCAD, VITA YZ, Procera AllZircon, Digizon, DC Zircon, and Cercon Base) and to a lithium disilicate glass-ceramic control group (IPS e.max Press) using a simple computer-generated randomization method. From each die, the manufacturer's authorized milling centers supplied 5 copings per group without applying any dying technique to the ceramic base material. The copings were prepared to allow for a 40-mum cement layer and were of different thicknesses according to system specifications. Translucency was measured by the direct transmission method with a digital photoradiometer mounted in a dark chamber. The light source was a 150-W halogen lamp beam. Measurements were repeated 3 times for each specimen. Data obtained were analyzed using 1-way ANOVA and the Bonferroni multiple comparison test (alpha=.05). RESULTS: Among ZrO(2) copings, Lava (0.3 mm and 0.5 mm thick) showed the highest (P<.05) values of translucency measured as light flow units (3.572 + or - 018 x 10(3) lx and 3.181 + or - 0.13 x 10(3) lx, respectively). These values represent 71.7% and 63.9%, respectively, of the glass-ceramic control group (4.98 x 10(3) lx). CONCLUSIONS: All ZrO(2) copings demonstrated different levels of light transmission, with the 2 Lava specimens showing the highest values. Translucency of zirconia copings was significantly lower (P=.001) than that of the lithium disilicate glass-ceramic control.