Evaluation of Vertical Misfit and Torque Loss of Different Abutments for Tri-Channel Type Internal Connection Dental Implants After Mechanical Cycling.

The aim of this study was to evaluate the mechanical behavior of UCLA and Mini-conical abutments for implants with Tri-channel connections regarding torque loss and vertical misfit. Twenty 3-element metal-ceramic fixed partial dentures (FPD) supported by 2 implants were manufactured and divided into 2 groups (n = 10): UCLA (group 1) and Mini-conical Abutments (group 2). The evaluation of torque loss was carried out before and after mechanical cycling, while the vertical fit was evaluated throughout the different stages of manufacturing the prostheses, as well pre- and postcycling (300,000 cycles, 30 N). Statistical analyses of torque loss and vertical misfit were performed using the linear mixed effects model. Both groups showed torque loss after mechanical cycling (P < .05); however, there was no significant percentage differences between them (P = .795). Before cycling, the groups showed a significant difference in terms of vertical misfit values (P < .05); however, this difference was no long observed after cycling (P = .894). Both groups showed torque loss after the cycling test, with no significant difference (P > .05). There was no significant difference in vertical misfit after mechanical cycling; however, in group 1 (UCLA) there was accommodation of the implant-UCLA abutment interface, while group 2 (Mini-conical abutment) did not show changes in the interface with the implant after the test. Both groups behaved similarly regarding the torque loss of the prosthesis retention screws pre- and postmechanical cycling, with greater loss after the test.

Mechanical Properties, Wear Resistance, and Reliability of Two CAD-CAM Resin Matrix Ceramics.

Background and Objectives: There are limited data regarding the behavior of resin matrix ceramics for current CAD-CAM materials. Further studies may be beneficial and can help clinicians planning to use these materials during prosthodontic rehabilitation. The aim of this study was to evaluate and compare the flexural strength and strain distributions, filler content, wear, and reliability of two resin matrix ceramic CAD-CAM materials. Materials and Methods: Two resin matrix ceramics, Ambarino High-Class (AH) and Vita Enamic (VE), were tested for flexural strength (n = 24), wear (n = 10), and reliability (n = 18). Thermogravimetric analysis was used to determine the percentage of filler by weight, and digital image correlation (DIC) was used for strain analysis in flexural strength test. Reliability of each resin matrix ceramic was compared after accelerated lifetime testing of crowns using a two-parameter Weibull distribution. Data of flexural strength, wear, and thermogravimetry were analyzed by independent t-tests with significance level at 5%. Results: The results of DIC analysis were analyzed by a qualitative comparison between the images obtained. The materials tested showed different flexural strength (p < 0.05) and strain distributions. The filler content was the same as informed by manufacturers. No difference was observed in the wear or reliability analysis (p > 0.05). The flexural strength of material AH was superior to VE, and the strain distribution was compatible with this finding. Conclusions: The two resin matrix ceramics tested showed similar behavior in wear and reliability analysis. Both can provide safe use for dental crowns.

Influence of Torque on Platform Deformity of the Tri-Channel Implant: Two- and Three-Dimensional Analysis Using Micro-Computed Tomography.

Background and Objectives: The insertion of the dental implant in the bone is an essential step in prosthetic rehabilitation. The insertion torque has the potential to distort the prosthetic platform, which can cause future biomechanical problems with the continuous action of occlusal forces. The aim of this study is to evaluate different insertion torques in the deformation of tri-channel platform connections through two- and three-dimensional measurements with micro-CT. Materials and Methods: A total of 164 implants were divided into groups (platform diameter and type): 3.5, 3.75, and 4.3 mm NP (narrow platform), and 4.3 mm RP (regular platform). Each implant-platform group was then divided into four subgroups (n = 10) with different torques: T45 (45 Ncm), T80 (80 Ncm), T120 (120 Ncm), and T150 (150 Ncm). The implant-abutment-screw assemblies were scanned and the images obtained were analyzed. Results: A significant difference was observed for the linear and volume measures between the different platforms (p < 0.01) and the different implant insertion torques (p < 0.01). Qualitative analysis suggested a higher deformation resistance for the 3.75 NP compared to the 3.5 NP, and RP was more resistant compared to the NP. Conclusions: The 0.25 mm increment in the implant platform did not increase the resistance to the applied insertion torques; the 4.3 mm implant was significantly stronger compared to the 3.5 mm implant; and the proposed micro-CT analysis was considered valid for both the 2D and 3D analyses of micro-gaps, qualitatively and quantitatively.

Strain transfer behavior of different planning options for mandibular single-molar replacement.

STATEMENT OF PROBLEM: The loss of the first molar and second premolar could lead to mesial movement of the second molar, thus limiting the restoration space for the 2 missing teeth. Placement of a larger first molar is a common choice, but the best implant number and position option remain controversial. PURPOSE: The purpose of this in vitro study was to test different planning options for replacing the mandibular first molar. MATERIAL AND METHODS: Two polyoxymethylene models simulated first molar edentulous spaces of 11 mm (conventional size first molar: control group) and 14 mm (enlarged first molar: all remaining groups other than control). Models included acrylic resin replicas of a first and second premolar, a second molar, and the first molar edentulous space. The following groups were established: control (CO), ø3.5-mm center implant; center implant (CI), ø3.5 mm; mesial implant (MI), ø3.5 mm; distal implant (DI), ø3.5 mm; center implant (WI), ø5.0; 2 implants (2I), 2 ø3.5-mm implants. Three Co-Cr molar crowns were fabricated for each group by using a computer-aided design and computer-aided manufacturing (CAD-CAM) technique. Model surface strains under a 250-N first molar load were calculated by 3-dimensional digital image correlation. Three regions of interest below the first molar were selected for comparison among groups. A test for unequal variances and a follow-up Welch ANOVA were used for statistical analysis (α=.05). RESULTS: The highest strains were found when the first molar was restored by using a 5.0-mm-wide implant (P<.05). Region of interest 1 showed that two 3.5-mm implants replacing the lost molar showed strain distribution similar to that of only one 3.5-mm implant (P>.05). Mesial and distal placement of the implant showed more neutral strain results than other restoration options (P<.05). CONCLUSIONS: Two small-diameter implants in an increased edentulous space show more optimized surface strain behavior than a single wide-diameter implant. However, a single 3.5-mm implant also showed reduced strains in the restoration of the same edentulous space.

Abutments with reduced diameter for both cement and screw retentions: analysis of failure modes and misfit of abutment-crown-connections after cyclic loading.

OBJECTIVE: The aim of this study was to analyze failure modes and misfit of abutments with reduced diameter for both cement and screw retentions after cyclic loading. MATERIAL AND METHODS: Forty morse-taper abutment/implant sets of titanium were divided into four groups (N = 10): G4.8S-4.8 abutment with screw-retained crown; G4.8C-4.8 abutment with cemented crown; G3.8S-3.8 abutment with screw-retained crown; and G3.8C-3.8 abutment with cemented crown. Copings were waxed on castable cylinders and cast by oxygen gas flame and injected by centrifugation. After, esthetic veneering ceramic was pressed on these copings for obtaining metalloceramic crowns of upper canine. Cemented crowns were cemented on abutments with provisional cement (Temp Bond NE), and screw-retained crowns were tightened to their abutments with torque recommended by manufacturer (10 N cm). The misfit was measured using a stereomicroscope in a 10× magnification before and after cyclic loading (300,000 cycles). Tests were visually monitored, and failures (decementation, screw loosening and fractures) were registered. Misfit was analyzed by mixed linear model while failure modes by chi-square test (α = 0.05). RESULTS: Cyclic loading affected misfit of 3.8C (P ≤ 0.0001), 3.8S (P = 0.0055) and 4.8C (P = 0.0318), but not of 4.8S (P = 0.1243). No differences were noted between 3.8S with 4.8S before (P = 0.1550) and after (P = 0.9861) cyclic loading, but 3.8C was different from 4.8C only after (P = 0.0015) loading. Comparing different types of retentions at the same diameter abutment, significant difference was noted before and after cyclic loading for 3.8 and 4.8 abutments. Analyzing failure modes, retrievable failures were present at 3.8S and 3.8C groups, while irretrievable were only present at 3.8S. CONCLUSIONS: The cyclic loading decreased misfit of cemented and screw-retained crowns on reduced diameter abutments, and misfit of cemented crowns is greater than screw-retained ones. Abutments of reduced diameter failed more than conventional.

Influence of Cyclic Fatigue in Water on Screw Torque Loss of Long-Span One-Piece Implant-Supported Zirconia Frameworks.

PURPOSE: It is still unclear whether four, six, or more implants should be used when restoring fully edentulous maxillae. This research evaluated the in vitro screw torque loss of zirconia frameworks supported by six implants and cantilevered zirconia frameworks supported by four implants. MATERIALS AND METHODS: Computer aided design/computer-assisted machining was used to fabricate 10 one-piece frameworks. Standardized pressable porcelain crowns were fabricated and luted to the frameworks. Specimens were divided into two groups (n = 5): AO4, cantilevered 12-unit full-arch fixed dental prosthesis supported by four implants; AO6, 14-unit supported by six implants. An opposing mandibular dental arch was fabricated with bis-acrylic composite resin. Specimens were submitted to 200 N underwater cyclic load at 2-Hz frequency for 1 × 106 cycles in a controlled 37°C temperature. A digital torque gauge assessed the initial and postload screw removal torque. Linear mixed-effects model was used for statistical analysis (α = 0.05). RESULTS: Significant screw torque loss was found for AO6 after cyclic loading (before: 36.20%/after: 52.82%; p < 0.05). Group AO6 (36.20%) presented lower preload loss before the cyclic loadings compared with AO4 (60.10%) (p < 0.05). CONCLUSIONS: Cyclic loading and lower implant-to-replaced-units ratio do not seem to compromise screw stability compared with higher implant-to-replaced-units ratio; however, a steep drop in preload was found before cyclic loading for both groups.

Torque loss under mechanical cycling of long-span zirconia and titanium-cemented and screw-retained implant-supported CAD/CAM frameworks.

OBJECTIVES: This study evaluated the screw joint stability after cyclic loading of implant-supported titanium and zirconia CAD/CAM frameworks for fixed dental prostheses (FDPs) with different retention methods. MATERIAL AND METHODS: Twenty four one-piece frameworks supported by six threaded implants placed in the maxilla were fabricated using a CAD/CAM technique (NeoShape). Dry-pressed porcelain crowns were luted to the frameworks to standardize the specimens. The specimens were then divided into four groups (n = 6) according to framework material (titanium or zirconia) and retention method for the prosthesis (cement- or screw-retained): G1, Ti-cemented; G2, Ti-screw-retained; G3, Zr-cemented; and G4, Zr-screw-retained. A digital torque ratchet was used to assess the initial preload removal torque. Torque was then reapplied and the specimens were submitted to a 200 N cyclic load, at a frequency of 2 Hz, underwater in controlled temperature of 37°, and for 1 × 106 cycles. An opposing lower dental arch was fabricated using bis-acrylic resin to simulate occlusal contacts in centric. After cyclic loading, postload removal torque was measured. Preload and postload torque loss was expressed as a percentage of the initial load. Data were submitted to a linear mixed-effects model for statistical significance (α = 0.05) to evaluate the effect of cyclic loading in the screw torque loss used with frameworks of different materials and retention methods. RESULTS: Significant screw torque loss (%) was found for the tested groups (before/after cyclic loading, respectively): G1 (39.77/61.83), G2 (37.57/50.96), G3 (34.87/54.10), and G4 (47.56/73.50) (P < 0.05). CONCLUSIONS: The screw removal torque was significantly reduced for all groups in this study after cyclic loading the specimens. Screw-retained zirconia specimens presented the highest torque loss before and after the cyclic loadings compared with the other specimens that were tested.

Effect of different ceramic systems on antagonist dental structure by microtomographic analysis.

OBJECTIVES: This study aims to identify the two-dimensional and three-dimensional analyses and evaluate the loss of tooth structure in the tooth's different constituent elements and the ceramic antagonist's surface. METHODS: In this study, three groups (n = 10) represented by different ceramic systems (lithium disilicate [GDis], lithium silicate reinforced with zirconia [GSil], and monolithic zirconia [GZir]) were evaluated. Each group obtained ten ceramic blocks and submitted them to the sintering/crystallization process. To carry out the wear test, healthy mandibular premolars were used as the specimens and the ceramic blocks as antagonists. The premolars were submitted to two-dimensional and three-dimensional analyses using a computerized microtomography (µTC) before and after the wear test. The wear test was performed with 30 N and 300,000 cycles load, with occlusion, laterality, and disocclusion movements. RESULTS: The statistical analysis comparing the loss of two-dimensional tooth structure showed a statistically significant difference among all groups (p < 0.05). Statistical analysis comparing the percentage of loss of three-dimensional tooth structure showed a statistically significant difference between groups GDis and GSil and between groups GDis and GZir. However, when comparing GSil with GZir, no statistically significant difference was found. The qualitative analysis of the teeth showed that GDis showed considerable enamel loss and dentin exposure, GSil showed enamel wear with flattening the cusp without dentin exposure, and GZir showed minimal enamel wear without dentin exposure. In the qualitative analysis of ceramic antagonists, more significant wear of the ceramic material for GDis was observed, followed by the GSil and GZir groups, respectively. SIGNIFICANCE: The use of the lithium disilicate should be cautious, restricting it to areas with lower masticatory forces. Areas of higher masticatory forces showed a large amount of antagonist wear, with dentin involvement. This can lead to dentinal hypersensitivity, risk of compromising patients' occlusion, by harming group disocclusion guides, causing pain and temporomandibular disorders.

Microbial Leakage through Three Different Implant-Abutment Interfaces on Morse Taper Implants In Vitro.

The objective of this study was to evaluate microbial leakage by means of genome counts, through the implant-abutment interface in dental implants with different Morse taper abutments. Fifty-six samples were prepared and divided in four groups: CMC TB (14 Cylindrical Implants-14 TiBase Abutments), CMX TB (14 Conical Implants-14 TiBase Abutments), CMX PU (14 Conical Implants-14 Universal Abutment) and CMX U (14 Tapered Implants-14 UCLA Abutments). Assemblies had their interface submerged in saliva as the contaminant. Samples were subjected either to thermomechanical cycling (2 × 106 mechanical cycles with frequency of 5 Hz and load of 120 N simultaneously with thermal cycles of 5-55 °C) or thermal cycling (5-55 °C). After cycling, the contents from the inner parts of assemblies were collected and analyzed using the Checkerboard DNA-DNA hybridization technique. Significant differences in the total genome counts were found after both thermomechanical or thermal cycling: CMX U > CMX PU > CMX TB > CMC TB. There were also significant differences in individual bacterial counts in each of the groups (p < 0.05). Irrespective of mechanical cycling, the type of abutment seems to influence not only the total microbial leakage through the interface, but also seems to significantly reflect differences considering individual target species.

Bacterial Detection, Deformation, and Torque Loss on Dental Implants with Different Tapered Connections Compared with External Hexagon Connection after Thermomechanical Cycling.

The relationship between bacterial infiltration and internal conical Implant-Abutment Interfaces (IAIs) with different conicities still requires investigations that can offer valuable information in the clinical understanding of peri-implant health. The present study aimed to verify the bacterial infiltration of two internal conical connections with an angulation of 11.5° and 16° with the external hexagonal connection as a comparative after thermomechanical cycling using saliva as a contaminant. Test (n = 10) and control (n = 3) groups were set up. Evaluations were made on torque loss, Scanning Electron Microscopy (SEM), and Micro Computerized Tomography (MicroCT) after performing 2 × 106 mechanical cycles (120 N) and 600 thermal cycles (5°-55° C) with 2 mm lateral displacement. The contents of the IAI were collected for microbiological analysis. There was a difference (p < 0.05) in torque loss of the groups tested; groups from the 16° IAI obtained a lower percentage of torque loss. All groups presented contamination and the analysis of the results shows that the microbiological profile of the IAI differs qualitatively from the profile found in the saliva used for contamination. The mechanical loading affects the microbiological profile found in the IAIs (p < 0.05). In conclusion, the IAI environment may favor a microbiological profile different from that of saliva and the thermocycling condition may alter the microbial profile found in the IAI.

Mechanical comparison of milled fiber-reinforced resin composite and Co-Cr frameworks with different connector cross-sectional geometries: An in vitro study.

This study compared the effect of using milled fiber-reinforced resin composite and Co-Cr (milled wax and lost-wax technique) frameworks for 4-unit implant-supported partial fixed dental prostheses; and also, evaluated the influence of the connector's cross-sectional geometries on the mechanical behavior. Three groups of milled fiber-reinforced resin composite (TRINIA) for 4-unit implant-supported frameworks (n = 10) with three connectors geometries (round, square, or trapezoid), and three groups of Co-Cr alloy frameworks manufactured by milled wax/lost wax and casting technique, were analyzed. The marginal adaptation was measured before cementation using an optical microscope. Then, the samples were cemented, thermomechanical cycled (load of 100 N/2 Hz, 106 cycles; 5, 37, and 55 ᵒC, a total of 926 cycles at each one), and cementation and flexure strength (maximum force) analyzed. Analysis of stress distribution in framework veneered considering resin and ceramic properties for fiber-reinforced and Co-Cr frameworks, respectively, implant, and bone was by finite element analysis under three contact points (100 N) on the central region. ANOVA and Multiple paired test-t with Bonferroni adjustment (α = 0.05) were used for data analysis. Fiber-reinforced frameworks showed better vertical adaptation (mean ranged from 26.24 to 81.48 µm) compared to the Co-Cr frameworks (mean ranged from 64.11 to 98.12 µm), contrary to horizontal adaptation (respectively, means ranged from 281.94 to 305.38 µm; and from 150.70 to 174.82 µm). There were no failures during the thermomechanical test. Cementation strength showed three times higher for Co-Cr compared to fiber-reinforced framework, as well as flexural strength (P < .001). Regarding stress distribution, fiber-reinforced had a pattern of concentration in the implant-abutment complex. There were no significant differences in stress values or changes observed among the different connector geometries or framework materials. Trapezoid connector geometry had a worse performance for marginal adaptation, cementation (fiber-reinforced 132.41 N; Co-Cr 255.68 N) and flexural strength (fiber-reinforced 222.57 N; Co-Cr 614.27 N). Although the fiber-reinforced framework showed lower cementation and flexural strength, considering the stress distribution values and absence of failures in the thermomechanical cycling test, it can be considered for use as a framework for 4-unit implant-supported partial fixed dental prostheses in the posterior mandible. Besides, results suggest that trapezoid connectors mechanical behavior did not perform well compared to round or square geometries.

Is the Er:YAG laser affect the surface characteristics and bond strength of Y-TZP?

This study evaluated the surface characteristics and bond strength of Y-TZP treated with Er:YAG laser at different focal distances. 120 Y-TZP blocks were divided into five groups (n=24), according to the surface treatment: no treatment (C-); sandblasting with silica-coated aluminum oxide particles (C+); and Er:YAG laser application at focal distances of 1mm (Er:YAG-1), 4mm (Er:YAG-4), and 7mm (Er:YAG-7). Surface characteristics were analyzed using Vickers microhardness, confocal laser microscope, scanning electron microscopy (SEM), and X-ray diffractometer (XRD). For the bond strength test, 100 Y-TZP blocks were subdivided into two subgroups (n=10), according to the resin cement used: with (MDP+) or without 10-methacryloyloxydecyl dihydrogen phosphate (MDP-). The Vickers microhardness and surface roughness were analyzed by one-way ANOVA and bond strength by two-way ANOVA and Tukey's test for both (α=0.05). Vickers microhardness differences were not observed between the groups (p>0.05); C+ showed higher surface roughness values. SEM images showed micromorphological differences between the groups. The XRD data detected tetragonal crystals for C- and, for the other groups, tetragonal and monoclinic peaks. For bond strength, no statistically difference significance were observed among the cements with or without MDP (p>0.05) but showed significant difference between the surface treatments (C+ > C- = Er:YAG1 > Er:YAG4 = Er:YAG7) (p<0.05). Suggested that the Er:YAG laser cannot replace conventional treatment with aluminum oxide particles and the presence of MDP in the resin cement had no influence on the bond strength.

An in vitro study of non-axial forces upon the retention of an O-ring attachment.

OBJECTIVE: The purpose of this study was to evaluate the retention force of an O-ring attachment system in different inclinations to the ideal path of insertion, using devices to compensate angulations. MATERIAL AND METHODS: Two implants were inserted into an aluminum base, and ball attachments were screwed to implants. Cylinders with O-rings were placed on ball attachments and connected to the test device using positioners to compensate implant angulations (0 degrees , 7 degrees , and 14 degrees ). Plexiglass bases were used to simulate implant angulations. The base and the test device were positioned in a testing apparatus, which simulated insertion/removal of an overdenture. A total of 2900 cycles, simulating 2 years of overdenture use, were performed and 36 O-rings were tested. The force required for each cycle was recorded with computer software. Longitudinal sections of ball attachment-positioner-cylinder with O-rings of each angulation were obtained to analyze the relationship among them, and O-ring sections tested in each angulation were compared with an unused counterpart. A mixed linear model was used to analyze the data, and the comparison was performed by orthogonal contrasts (alpha=0.05). RESULTS: At 0 degrees , the retention force decreased significantly over time, and the retention force was significantly different in all comparisons, except from 12 to 18 months. When the implants were positioned at 7 degrees , the retention force was statistically different at 0 and 24 months. At 14 degrees , significant differences were found from 6 and 12 to 24 months. CONCLUSIONS: Within the limitations of this study, it was concluded that O-rings for implant/attachments perpendicular to the occlusal plane were adequately retentive over the first year and that the retentive capacity of O-ring was affected by implant inclinations despite the proposed positioners.

Fracture loads and failure modes of customized and non-customized zirconia abutments.

OBJECTIVE: This study aimed to evaluate the fracture load and pattern of customized and non-customized zirconia abutments with Morse-taper connection. METHODS: 18 implants were divided into 3 groups according to the abutments used: Zr - with non-customized zirconia abutments; Zrc - with customized zirconia abutments; and Ti - with titanium abutments. To test their load capacity, a universal test machine with a 500-kgf load cell and a 0.5-mm/min speed were used. After, one implant-abutment assembly from each group was analyzed by Scanning Electron Microscopy (SEM). For fractographic analysis, the specimens were transversely sectioned above the threads of the abutment screw in order to examine their fracture surfaces using SEM. RESULTS: A significant difference was noted between the groups (Zr=573.7±11.66N, Zrc=768.0±8.72N and Ti=659.1±7.70N). Also, the zirconia abutments fractured while the titanium abutments deformed plastically. Zrc presented fracture loads significantly higher than Zr (p=0.009). All the zirconia abutments fractured below the implant platform, starting from the area of contact between the abutment and implant and propagating to the internal surface of the abutment. All the zirconia abutments presented complete cleavage in the mechanical test. Fractography detected differences in the position and pattern of fracture between the two groups with zirconia abutments, probably because of the different diameters in the transmucosal region. SIGNIFICANCE: Customization of zirconia abutments did not affect their fracture loads, which were comparable to that of titanium and much higher than the maximum physiological limit for the anterior region of the maxilla.

Analysis of the relationship between the surface hardness and wear resistance of indirect composites used as veneer materials.

This study evaluated the surface hardness and wear resistance of indirect composites (Artglass and Solidex) and the existence of a correlation between these properties. Twenty-four specimens (12 per material) were fabricated using a polytetrafluoroethylene matrix (5.0 mm in diameter; 7.0 mm high) following an incremental technique. Polymerization was done with a xenon stroboscopic light curing unit. After polishing, the specimens were stored in water at 37 degrees C during either 1 day (n=6 per material) or 55 days (n=6 per material), after which Vickers surface hardness and wear resistance were assessed. Data were analyzed statistically by unpaired Student t-test, two-way ANOVA and Tukey's test. SURFACE HARDNESS: Artglass had higher surface hardness than Solidex after 1-day immersion period (p<0.01), but after 55 days there was no significant difference between the materials (p>0.05). Comparing the materials at both periods, Artglass means differed significantly to each other (p<0.01), while no significant difference was found between Solidex means (p>0.05). WEAR RESISTANCE: Solidex had higher wear than Artglass after 1-day immersion period (p<0.01), but no significant difference was found between the materials after 55 days (p>0.05). Comparing the materials at both periods, Artglass means differed significantly to each other (p<0.01), with higher wear at 55-day period, but no difference was found between Solidex means (p>0.05). These results suggest that Artglass was better than Solidex in terms of hardness and wear resistance after 1-day water immersion. However, it was more susceptible to degradation, showing greater wear after 55 days. In conclusion, there was an inverse correlation between surface hardness and wear resistance for both Artglass and Solidex indirect composites, that is the higher the hardness, the lower the wear.

Biomechanical behavior of titanium and zirconia frameworks for implant-supported full-arch fixed dental prosthesis.

BACKGROUND: The biomechanical behavior of implant-supported titanium and zirconia full-arch fixed dental prosthesis (FAFDP) frameworks require further investigation. PURPOSE: Strains transferred by implant-supported titanium (Ti) and zirconia (Zr) FAFDP frameworks were analyzed. MATERIALS AND METHODS: Maxillary 14-unit FAFDPs supported by 6 implants and 12-unit FAFDPs supported by 4 implants were tested. One-piece frameworks were fabricated by computer-aided design/computer-aided manufacturing. Four groups were divided (n = 3): G1, Ti-6 implants; G2, Zr-6 implants; G3, Ti-4 implants; G4, Zr-4 implants. A 250 N single-point load was applied on the second premolar. A three-dimensional digital image correlation system recorded framework and maxilla model surface deformation. RESULTS: The following strains (µS) averaged over the length of the second premolar were calculated: frameworks, G1 (321.82 ± 111.29), G2 (638.87 ± 108.64), G3 (377.77 ± 28.64), G4 (434.18 ± 132.21); model surface, G1 (473.99 ± 48.69), G2 (653.93 ± 45.26), G3 (1082.50 ± 71.14), G4 (1218.26 ± 230.37). Zirconia frameworks supported by 6 implants (G2) presented higher surface strains (P < .05). FAFDPs with titanium frameworks transferred significantly lower strains to the supporting maxilla when 6 implants were used (G1) (P < .05). Both framework materials transferred similar strains when supported by 4 implants (G3 and G4) (P > .05). CONCLUSIONS: Zirconia frameworks supported by 6 implants showed higher strains. FAFDPs supported by 6 implants transferred less strains to the supporting maxilla, irrespective of framework material.

Wear resistance and compression strength of ceramics tested in fluoride environments.

Dental ceramics have been widely used because of aesthetic, but wear is still questioned. There are relates that ceramic surface is prone to degradation by acidulated fluoride, that can increase wear rates. The aim of this study was to evaluate the effect of neutral and acidulated fluoride gel, used as preventive agents for professional use, at wear and compression strength of dental ceramics IPS e.max ZirPress (ZIR), IPS Empress Esthetic (EMP) e IPS Inline POM (POM). For this, 30 crowns and 30 disks were obtained by heat-pressing. Crowns and disks were submitted to two-body wear test at machine of mechanical loading, simulating occlusion, lateral movement and disocclusion. It was performed 300,000 cycles at 1Hz frequency under 20N load, to simulate 1 year of mastication. Samples were totally immersed during the test and were divided into three groups according to the gel used for immersion (n=10): control, neutral (sodium fluoride 2%) and acidulated (acidulated phosphate fluoride 1.23%). Samples (crowns and disks) were analyzed for vertical height loss after the test using, respectively, profile projector and stereomicroscope. Roughness of worn surface of crowns and disks was evaluated by laser confocal microscopy. Data of height loss and roughness were evaluated by two-way ANOVA and Bonferroni's test. A crown/disk of each group was analyzed by scanning electronic microscopy. After wear resistance tests, crowns were cemented to their abutments and submitted to compressive load at 30° angulation and 1mm/min speed. Type of failures was compared by qui-square test. Ceramic EMP worn less while ZIR worn more. Control gel worn more at crowns while acidulated gel worn more at disks. Surface roughness of samples tested at acidulated gel was significantly lower. Type of failures found at compression resistance tests was affected by ceramic type, but not by gel used. The results suggest that ceramic and fluoride gel affect wear and roughness of worn surface while type of failure is only affected by ceramic.

Is the Er:YAG laser affect the surface characteristics and bond strength of Y-TZP?

Abstract This study evaluated the surface characteristics and bond strength of Y-TZP treated with Er:YAG laser at different focal distances. 120 Y-TZP blocks were divided into five groups (n=24), according to the surface treatment: no treatment (C-); sandblasting with silica-coated aluminum oxide particles (C+); and Er:YAG laser application at focal distances of 1mm (Er:YAG-1), 4mm (Er:YAG-4), and 7mm (Er:YAG-7). Surface characteristics were analyzed using Vickers microhardness, confocal laser microscope, scanning electron microscopy (SEM), and X-ray diffractometer (XRD). For the bond strength test, 100 Y-TZP blocks were subdivided into two subgroups (n=10), according to the resin cement used: with (MDP+) or without 10-methacryloyloxydecyl dihydrogen phosphate (MDP-). The Vickers microhardness and surface roughness were analyzed by one-way ANOVA and bond strength by two-way ANOVA and Tukey's test for both (α=0.05). Vickers microhardness differences were not observed between the groups (p>0.05); C+ showed higher surface roughness values. SEM images showed micromorphological differences between the groups. The XRD data detected tetragonal crystals for C- and, for the other groups, tetragonal and monoclinic peaks. For bond strength, no statistically difference significance were observed among the cements with or without MDP (p>0.05) but showed significant difference between the surface treatments (C+ > C- = Er:YAG1 > Er:YAG4 = Er:YAG7) (p<0.05). Suggested that the Er:YAG laser cannot replace conventional treatment with aluminum oxide particles and the presence of MDP in the resin cement had no influence on the bond strength.

Resumo Este estudo avaliou as características de superfície e resistência de união de Y-TZP tratado com laser de Er: YAG em diferentes distâncias focais. Cento e vinte blocos de Y-TZP foram divididos em cinco grupos (n=24), de acordo com a superfície de tratamento: sem tratamento (C-); asperização com partículas de óxido de alumínio revestidas por sílica (C +); e aplicação de laser Er: YAG a distâncias focais de 1 mm (Er: YAG-1), 4 mm (Er: YAG-4) e 7 mm (Er: YAG-7). As características de superfície foram analisadas por meio de microdureza Vickers, microscópio confocal a laser, microscopia eletrônica de varredura (MEV) e difratômetro de raios-X (DRX). Para o ensaio de resistência de união, cem blocos de Y-TZP foram subdivididos em 2 subgrupos (n=10) de acordo com o cimento resinoso utilizado (n=12): com 10-metacriloiloxidecil dihidrogenofosfato (MDP+) ou sem (MDP-). Microdureza Vickers e rugosidade de superfície foram analisadas por ANOVA a 1 fator e a resistência de união por ANOVA a 2 fatores e ambos seguidos de teste complementar de Tukey (α=0,05). Não foram observadas diferenças de microdureza Vickers entre os grupos; C+ apresentou maiores valores de rugosidade superficial. Imagens de MEV mostraram diferenças micromorfológicas entre os grupos. Os dados de DRX detectaram apenas cristais tetragonais para C- e, para os outros grupos, picos de zircônia nas fases tetragonal e monoclínica. Para a resistência de união, não foram observadas diferenças estatisticamente significante entre os cimentos com e sem MDP (p>0.05), mas foram observadas diferenças significativas entre os tratamentos de superfície (C+ > C- = Er:YAG1 > Er:YAG4 = Er:YAG7) (p<0.05). Sugere-se que o laser de Er: YAG não pode substituir o tratamento convencional com partículas de óxido de alumínio e a presença de MDP no cimento resinoso não influenciou na resistência de união.

In Vitro Fit and Cementation Resistance of Provisional Crowns for Single Implant-Supported Restorations.

This study aimed to verify marginal fit and the effect of cement film thickness standardization on retention of provisional crowns made with prefabricated acrylic cylinders on abutments, using two temporary luting agents subjected or not to mechanical cycling. Provisional crowns were made from bis-acryl (Luxatemp Fluorescence) or methyl methacrylate (Duralay) resins on acrylic cylinders and marginal fit and cement film thickness were evaluated. For retention evaluation, crowns were cemented with two temporary luting agents: non-eugenol zinc oxide (Tempbond NE) or calcium hydroxide-based (Hydcal) cements and subjected to tensile strength in a universal testing machine. After cleaning, debonded crowns were cemented again, subjected to mechanical cycling and retention was reassessed. The results of marginal fit and cement film thickness were analyzed by Student's t-test while retention of cements before and after mechanical cycling was analyzed using a mixed linear model. Methyl methacrylate crowns presented greater marginal misfit (p=0.001) and occlusal cement film thickness (p=0.003) than the bis-acryl ones. No difference was observed at axial cement film thickness (p=0.606). Resins (p=0.281) did not affect crown retention, but luting agents (p=0.029) and mechanical cycling (p=0.027) showed significant effects. The only significant interaction was mechanical cycling*luting agents, which means that luting agents were differently affected by mechanical cycling (p=0.002). In conclusion, the results showed that bis-acryl resin associated to calcium-hydroxide luting agent provided the best retention and lower cement thickness.

Reliability of FEA on the Results of Mechanical Properties of Materials.

The present study evaluated the reliability of FEA on the results of different mechanical properties (E and v) of materials. Two 3D models of a maxillary canine with endodontic treatment, intracanal post, composite resin core and restored with porcelain-fused-to-metal crown were generated according to micro-CT images. Two groups with different E and ν values for porcelain, metal coping alloy, resin cement and composite resin were established. The materials' properties for group GL were based on literature data, while for group GIE the impulse excitation technique was used. A load of 180 N was applied at 45° on the incisal third of the lingual surface of the canine tooth. All models were supported by the periodontal ligament (x=y=z=0). The von Mises stress (VMS) was calculated. The stress values revealed differences between the groups for both VMS distribution and value. The porcelain (GL: 5.966 MPa; GIE: 7.478 MPa), metal coping (GL: 3.811 MPa; GIE: 0.973 MPa) and core (GL: 4.771 MPa; GIE: 0.026 MPa) were significantly affected. In conclusion, this study showed that the determination of mechanical properties (E and ν) of materials is essential for the reliability on the results of FEA.