Mechanical behavior of endocrowns fabricated with different CAD-CAM ceramic systems.

STATEMENT OF PROBLEM: The mechanical behavior of ceramic endocrowns is unclear. PURPOSE: The purpose of this in vitro and 3-dimensional finite element analysis (3D-FEA) study was to evaluate the mechanical behavior of endodontically treated teeth restored with ceramic endocrowns made by using different computer-aided design and computer-aided manufacturing (CAD-CAM) systems. MATERIAL AND METHODS: Sixty mandibular human molars were endodontically treated, prepared for endocrowns, and divided into 4 groups (n=15) according to the following various ceramic systems: leucite-based glass-ceramic (LC group), lithium disilicate-based glass-ceramic (LD group), glass-ceramic based on zirconia-reinforced lithium silicate (LSZ group), and monolithic zirconia (ZR group). After adhesive bonding, the specimens were subjected to thermomechanical loading and then to fracture resistance testing in a universal testing machine. The failure mode of the specimens was qualitatively evaluated. Three-dimensional FEA was performed to evaluate the stress distribution in each group. Data were analyzed by using a 1-way ANOVA and the Tukey HSD test (α=.05). RESULTS: Statistically significant differences among the groups were observed (P<.05). The outcomes of the LC, LD, and LSZ groups were similar (1178 N, 1935 N, and 1859 N) but different from those of the ZR group (6333 N). The LC and LD groups had a higher ratio of restorable failures, while LSZ and ZR had more nonrestorable failures. Fractographic analysis indicated a regular failure pattern in the ZR group and irregular failure patterns in the other groups. Three-dimensional FEA revealed similar values and stress pattern distributions among the groups. CONCLUSIONS: The mechanical performance of monolithic zirconia was better than that of the other ceramic endocrowns considered in this research; however, monolithic zirconia presented a higher rate of catastrophic tooth structure failure.

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.

Three-dimensional finite element analysis of endodontically treated teeth with weakened radicular walls restored with different protocols.

STATEMENT OF PROBLEM: The restoration of weakened roots with glass fiber posts (GFPs) remains a challenge. PURPOSE: The purpose of this study was to evaluate the stress distribution of endodontically treated teeth with weakened radicular walls restored with different protocols by 3-dimensional finite element analysis (3D-FEA). MATERIAL AND METHODS: The following 4 models of endodontically treated maxillary canines restored with metal ceramic crowns were simulated on the basis of computed microtomographic images to characterize the groups: GNW (control), a nonweakened root restored with a GFP; GW, a weakened root restored with a GFP; GDA, a weakened root restored with a direct anatomic GFP; and GIA, a weakened root restored with an indirect anatomic GFP. Loads of 180 N were applied to the lingual surface on the incisal third of the teeth at 45 degrees. The models were supported by a periodontal ligament and fixed in 3 axes (x=y=z=0). The von Mises stress (VMS) was calculated. RESULTS: All models exhibited VMS concentrations at the loading area and were distributed along the proximal surfaces of the root. The GFP exhibited a homogeneous stress distribution, and similar VMS distributions were observed in all of the reconstructive techniques. CONCLUSIONS: Similar stress distributions were observed in the endodontically treated teeth, regardless of root weakness and the reconstructive technique for the radicular walls.

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 cyclic loading on the vertical microgap of long-span zirconia frameworks supported by 4 or 6 implants.

STATEMENT OF PROBLEM: Few studies have investigated the microgap of long-span complete-arch fixed dental prosthesis zirconia frameworks. PURPOSE: The purpose of this study was to evaluate the effects of cyclic loading on the vertical microgap of maxillary 12-unit prostheses supported by 4 implants and on 14-unit prostheses supported by 6 implants. MATERIAL AND METHODS: One-piece zirconia frameworks were fabricated with a computer-aided design/computer-aided manufacturing technique and divided into 2 groups (n=5): a group of 12-unit prostheses and a group of 14-unit prostheses. The vertical microgap between the frameworks and prosthetic abutments was measured with an optical microscope (80×) under 2 reading conditions. Condition 1 (1-screw test): 1A, the screw on implant 1 was tightened and readings were made on all implants; 1B, the screw was changed to implant 4 (implant 6 for the 14-unit group) and readings were made on all implants. Condition 2: the microgap was measured with all screws tightened before cyclic loading (2A). Specimens were submitted to 200 N underwater (37°C) cyclic loading at a 2-Hz frequency for 1×10(6) cycles. Microgap reading condition 2 was repeated after cyclic loading (2B). The data were submitted to a linear mixed-effects model for statistical comparison (α=.05). RESULTS: A lower (P<.05) vertical microgap (µm) was found for the 12-unit group (reading conditions: 1A, 47.93; 1B, 43.83; 2A, 11.77; and 2B, 11.25) compared to the 14-unit group (1A, 94.87; 1B, 112.56; 2A, 21.28; and 2B, 16.90). No differences were found when each group was compared before and after cyclic loading (P>.05). CONCLUSIONS: The vertical microgap was significantly reduced after tightening all the screws in the framework, possibly leading to a nonpassive situation. Longer-span frameworks showed an increased microgap. Cyclic loading had no influence on the vertical microgap within each group.

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.

Preload evaluation of different screws in external hexagon joint.

PURPOSE: This study compared the maintenance of tightening torque in different retention screw types of implant-supported crowns. MATERIALS AND METHODS: Twelve metallic crowns in UCLA abutments cast with cobalt-chromium alloy were attached to external hexagon osseointegrated implants with different retention screws: group A: titanium alloy retention screw; group B: gold alloy retention screw with gold coating; group C: titanium alloy retention screw with diamond-like carbon film coating; and group D: titanium alloy retention screw with aluminum titanium nitride coating. Three detorque measurements were obtained after torque insertion in each replica. Data were evaluated by analysis of variance (ANOVA), Tukey's test (P < 0.05), and t test (P < 0.05). RESULTS: Detorque value reduced in all groups (P < 0.05). Group A retained the highest percentage of torque in comparison with the other groups (P < 0.05). Groups B and D retained the lowest percentage of torque without statistically significant difference between them (P > 0.05). CONCLUSIONS: All screw types exhibited reduction in the detorque value. The titanium screw maintained the highest percentage of torque whereas the gold-coated screw and the titanium screw with aluminum titanium nitride coating retained the lowest percentage.

Linear dimensional accuracy of stereolithographic surgical guide after chemistry and physics sterilization.

OBJECTIVES: The purpose of this study was to evaluate the dimensional stability of prototyped surgical guides after autoclave and 2% glutaraldehyde sterilization processes. MATERIAL AND METHODS: Twenty prototyped surgical guides were prepared and submitted to two sterilization processes (n = 10): Physics - sterilization by autoclave (saturated water vapor under pressure, temperature of 126 to 130 °C, pressure of 1,7 at 1.9 kgf/cm2, 16 min); Chemistry - sterilization by 2% glutaraldehyde for 10 h. Six pre-established points were measured in the prototyped surgical guides, before and after sterilization, using a digital caliper rule. The comparisons were made using orthogonal contrasts using the linear model of mixed effects (random and fixed). RESULTS: there are no significant differences between autoclave and glutaraldehyde 2% (p>0.05) there are significant differences after autoclave sterilization (p<0.05) and there are not significant differences after 2% glutaraldehyde sterilization (p>0.05). CONCLUSION: autoclave promoted dimensional alteration of the prototyped surgical guides, and the chemical sterilization by glutaraldehyde 2% did not cause dimensional alteration of the prototype surgical guides, being a favorable choice for sterilization. CLINICAL SIGNIFICANCE: the sterilization of surgical guides can be performed through the chemical process with 2% glutaraldehyde without changing the linear precision of the prototype surgical guides.

The effect of mechanical cycling and different misfit levels on Vicker's microhardness of retention screws for single implant-supported prostheses.

PURPOSE: The aim of this study was to evaluate the effect of mechanical cycling and different misfit levels on Vicker's microhardness of retention screws for single implant-supported prostheses. MATERIALS AND METHODS: Premachined UCLA abutments were cast with cobalt-chromium alloy to obtain 48 crowns divided into four groups (n = 12). The crowns presented no misfit in group A (control group) and unilateral misfits of 50 µm, 100 µm, and 200 µm in groups B, C, and D, respectively. The crowns were screwed to external hexagon implants with titanium retention screws (torque of 30 N/cm), and the sets were submitted to three different periods of mechanical cycling: 2×10(4) , 5×10(4) , and 1×10(6) cycles. Screw microhardness values were measured before and after each cycling period. Data were evaluated by two-way ANOVA and Tukey's test (p < 0.05). RESULTS: Mechanical cycling statistically reduced microhardness values of retention screws regardless of cycling periods and groups. In groups A, B, and C, initial microhardness values were statistically different from final microhardness values (p < 0.05). There was no statistically significant difference for initial screw microhardness values (p > 0.05) among the groups; however, when the groups were compared after mechanical cycling, a statistically significant difference was observed between groups B and D (p < 0.05). CONCLUSIONS: Mechanical cycling reduced the Vicker's microhardness values of the retention screws of all groups. The crowns with the highest misfit level presented the highest Vicker's microhardness values.

Impact of Conservative Endodontic Cavities on Root Canal Preparation and Biomechanical Behavior of Upper Premolars Restored with Different Materials.

INTRODUCTION: The purpose of this study was to evaluate the impact of conservative endodontic cavities (CECs) on root canal preparation, restoration, and biomechanical behavior of teeth prepared using different shaping systems and restorative materials. METHODS: Ninety upper premolars with a bifurcated root were matched based on morphology and randomly assigned to a control group (n = 10) or 1 of the following experimental groups (n = 40): traditional endodontic cavity and CEC. Teeth were subdivided according to instrumentation (n = 10) as follows: ProTaper Universal (Dentsply Maillefer, Ballaigues, Switzerland), Reciproc (VDW GmbH, Munich, Germany), Reciproc Blue (VDW GmbH), and Hyflex EDM (Coltene/Whaledent, Altstätten, Switzerland). After canal obturation, teeth were restored using temporary material, conventional composite, regular bulk fill composite, or bulk fill flow combined with conventional composite. Before and after preparation and after obturation, the teeth were scanned using micro-computed tomographic imaging. Canal transportation (CT), the percentage of untouched canal surfaces (UCSs), voids in restoration (VRs), and residual filling material in the pulp chamber were evaluated. Finite element analysis, fracture resistance, and the failure pattern were recorded. The data were analyzed using analysis of variance and the Tukey and chi-square tests. RESULTS: CECs had greater CT, percentage of filling material, and VRs compared with traditional endodontic cavities (P < .0001). The highest CT and UCSs were observed in CEC with ProTaper Universal. Bulk fill flow combined with conventional composite showed a lower percentage of VRs compared with other restorative materials (P < .05). Finite element analysis, fracture resistance, and failure pattern revealed similar behaviors in all groups (P > .05) . CONCLUSIONS: CECs had a negative impact on root canal centralization, UCSs, cleaning of the pulp chamber, and percentage of VRs. Controlled memory instruments were the most adequate for the root canal preparation of CECs. The endodontic cavity did not influence the biomechanical behavior of restored teeth.

Passivity versus unilateral angular misfit: evaluation of stress distribution on implant-supported single crowns: three-dimensional finite element analysis.

The aim of this study was to evaluate the effect of unilateral angular misfit of 100 µm on stress distribution of implant-supported single crowns with ceramic veneering and gold framework by three-dimensional finite element analysis. Two three-dimensional models representing a maxillary section of premolar region were constructed: group 1 (control)-crown completely adapted to the implant and group 2-crown with unilateral angular misfit of 100 µm. A vertical force of 100 N was applied on 2 centric points of the crown. The von Mises stress was used as an analysis criterion. The stress values and distribution in the main maps (204.4 MPa for group 1 and 205.0 MPa for group 2) and in the other structures (aesthetic veneering, framework, retention screw, implant, and bone tissue) were similar for both groups. The highest stress values were observed between the first and second threads of the retention screw. Considering the bone tissue, the highest stress values were exhibited in the peri-implant cortical bone. The unilateral angular misfit of 100 µm did not influence the stress distribution on the implant-supported prosthesis under static loading.

An implant-transfer technique without impression material.

Different transfer impression techniques for implant-supported prostheses have been suggested to obtain a working cast. This article describes and illustrates clinical and laboratory prosthodontic procedures to transfer implant positions with splinted transfer copings and without impression material to form a laboratory analog transfer template. With this technique, a preliminary cast is modified to place the analogs according to a corrected position and obtain the master cast. Although this technique does not record adjacent tissues, it is a simple procedure, less time consuming, and easily performed.

Effect of superstructure materials and misfit on stress distribution in a single implant-supported prosthesis: a finite element analysis.

This finite element analysis study evaluated the optimal material combination for the superstructure of single implant-supported prosthesis with different fit patterns. Two models of a two-dimensional finite element analysis were constructed: group A (control), prosthesis presenting precise fit to implant; and group B, prostheses with unilateral angular misfit of 100 microm. Each group was divided into 5 subgroups according to different materials for framework (gold alloy, titanium, and zirconia) and veneering (porcelain and modified composite resin). Evaluation was performed on ANSYS software with 133-N load applied at the opposite side of misfit on the model. The load was applied with a 30-degree angulation and 2-mm off-axis. The presence of unilateral angular misfit (group B) increased the von Mises stresses in the implant (40%) and retention screw (7%) in comparison to group A. The combination of porcelain/titanium and porcelain/zirconia displayed more favorable stress distribution. When gold alloy was used as a framework material, there was no difference in stress values for both veneering materials in all groups. The use of stiffer and softer superstructures materials did not affect the stress distribution and stress values in the supporting tissue. According to the biomechanical point of view, materials with high elasticity modulus are more suitable for the superstructure of implant-supported prosthesis.

Implant platform switching: biomechanical approach using two-dimensional finite element analysis.

In implant therapy, a peri-implant bone resorption has been noticed mainly in the first year after prosthesis insertion. This bone remodeling can sometimes jeopardize the outcome of the treatment, especially in areas in which short implants are used and also in aesthetic cases. To avoid this occurrence, the use of platform switching (PS) has been used. This study aimed to evaluate the biomechanical concept of PS with relation to stress distribution using two-dimensional finite element analysis. A regular matching diameter connection of abutment-implant (regular platform group [RPG]) and a PS connection (PS group [PSG]) were simulated by 2 two-dimensional finite element models that reproduced a 2-piece implant system with peri-implant bone tissue. A regular implant (prosthetic platform of 4.1 mm) and a wide implant (prosthetic platform of 5.0 mm) were used to represent the RPG and PSG, respectively, in which a regular prosthetic component of 4.1 mm was connected to represent the crown. A load of 100 N was applied on the models using ANSYS software. The RPG spreads the stress over a wider area in the peri-implant bone tissue (159 MPa) and the implant (1610 MPa), whereas the PSG seems to diminish the stress distribution on bone tissue (34 MPa) and implant (649 MPa). Within the limitation of the study, the PS presented better biomechanical behavior in relation to stress distribution on the implant but especially in the bone tissue (80% less). However, in the crown and retention screw, an increase in stress concentration was observed.

Comparison of single-standing or connected implants on stress distribution in bone of mandibular overdentures: a two-dimensional finite element analysis.

This study aimed to compare the influence of single-standing or connected implants on stress distribution in bone of mandibular overdentures by means of two-dimensional finite element analysis. Two finite element models were designed using software (ANSYS) for 2 situations: bar-clip (BC) group-model of an edentulous mandible supporting an overdenture over 2 connected implants with BC system, and o'ring (OR) group-model of an edentulous mandible supporting an overdenture over 2 single-standing implants with OR abutments. Axial loads (100 N) were applied on either central (L1) or lateral (L2) regions of the models. Stress distribution was concentrated mostly in the cortical bone surrounding the implants. When comparing the groups, BC (L1, 52.0 MPa and L2, 74.2 MPa) showed lower first principal stress values on supporting tissue than OR (L1, 78.4 MPa and L2, 76.7 MPa). Connected implants with BC attachment were more favorable on stress distribution over peri-implant-supporting tissue for both loading conditions.

A comparison of patient satisfaction between treatment with conventional complete dentures and overdentures in the elderly: a literature review.

BACKGROUND: It has been stated that mandibular overdentures are more satisfactory than conventional dentures, but problems relating to the use of retrospective ratings, lack of control group and sequential provision of treatment may compromise the findings. OBJECTIVE: To establish a comparison between treatment with conventional complete dentures and implant-retained overdentures in elderly patients by conducting a literature review. MATERIALS AND METHODS: A search of English language peer-review literature was completed using Medline up to 2008 focusing on evidence-based research. Randomised clinical trials (RCTs) and longitudinal prospective studies were favoured in the review, using a general hierarchical classification. Articles that did not focus exclusively on the comparison of patient satisfaction between complete dentures and overdentures were excluded from further evaluation. The last search was conducted in February 2008. Key terms included quality of life, patient satisfaction, edentulism, complete denture and overdenture. RESULTS: Among the 90 articles found in the initial search, 27 met the inclusion criteria. This included 18 RCTs and eight prospective and one cohort study. Most of the articles stated superiority of the mandibular implant-retained overdenture therapy over the conventional complete denture regarding patient satisfaction and quality of life. CONCLUSION: Even with implant treatment presenting higher patient satisfaction and improvement of quality of life, it was not possible to establish a direct comparison between the studies due to differences in adopted methodologies.

Influence of different ceramic materials and surface treatments on the adhesion of Prevotella intermedia.

Ceramics are used in oral rehabilitation; however, these materials are prone to formation of biofilms that may cause periodontal diseases. This study aimed to evaluate the influence of distinct surface treatments on ceramic surface roughness and biofilm formation of oral bacteria (Prevotella intermedia). Eighty-four specimens of the following four ceramic systems were produced: LC - leucite-based glass ceramic, LD - lithium disilicate-based glass ceramic, LSZ - glass ceramic based on zirconia-reinforced lithium silicate, and ZR - monolithic zirconia. These were submitted to three different surface treatment protocols: C - control, G - glazing, and GDB - grinding with diamond bur (n = 7). The surface characteristics were assessed using a confocal laser microscope (Ra) and a scanning electron microscope (SEM). Thereafter, the groups were contaminated with a bacterial strain of P. intermedia ATCC 25611. The biofilms formed were quantified by counting the colony forming units (CFUs) and analyzed with scanning electron microscope (SEM) and confocal laser scanning microscope (CLSM). Data were analyzed by using a 2-way ANOVA and the Tukey test (ɑ = 0.05). Results showed that greater roughness was associated with GDB (p < 0.05). The same was also true for the ceramic material ZR (p < 0.05). There was a statistical significant difference in the CFU counts between the materials (p < 0.05) that revealed a greater amount of bacterial adhesion in the LC and ZR groups (p > 0.05). Thus, it was suggested that the surface roughness of the ceramic materials favored bacterial adhesion; and thus, finishing of ceramic surfaces with GDB should be avoided.

Internal and Marginal Fit and Fracture Strength of Narrow Diameter Dental Implant-Abutment Assembly.

The aim of this study was to assess the internal and vertical marginal fit of metallic copings to abutments and the fracture strength of different narrow diameter dental implant/abutments, either submitted to thermomechanical cycling or not. Sixty-four implant/abutments (n=16) were divided into 4 groups according to diameter and abutment type: G3.5-UAC (morse taper implant Ø3.5mm + universal abutment with beveled chamfer finish); G2.9-UAS (morse taper implant Ø2.9mm + universal abutment with shoulder finish); G2.8-AA (morse taper friction implant Ø2.8mm + anatomical abutment) and G2.5-HP (one-piece implant Ø2.5mm with indexed hexagonal platform). Each group was divided into two subgroups (n=8): submitted and not submitted to thermomechanical cycling (TMC). To assess internal and vertical marginal fit of metallic copings, the assemblies were scanned using microtomography (micro-CT) (n=5). The samples were subjected to the compressive strength test on a universal test machine. Group G3.5-UAC showed the highest marginal misfit regardless of TMC (p<0.05). All other groups were similar after TMC. Group G2.8-AA showed the lowest internal misfit both with and without TMC (p<0.05). Group G2.8-AA showed the highest fracture strength, similar only to G2.5-HP without TMC and G3.5-UAC with TMC. The type of abutment affects the internal and marginal fit of metallic copings and the anatomical abutment led to the best internal and marginal coping fit. The narrow diameter dental implant/abutments differ in terms of fracture strength, the strongest assembly was that composed by implant of type V grade titanium without internal threads (friction implant).

Effect of restorative treatment with endocrown and ferrule on the mechanical behavior of anterior endodontically treated teeth: An in vitro analysis.

This study evaluated the effect of endocrown and ferrule restorative treatment on the mechanical behavior of anterior endodontically treated teeth. Human canines were treated endodontically and distributed in five groups (n = 10): sound teeth (S), crown associated with glass fiber post (GFP) and ferrule (GFPf+) and that without ferrule (GFPf-), and endocrown with ferrule (Ef+) and that without ferrule (Ef-). The crowns were obtained in lithium disilicate-based glass ceramic and cemented with resin. Thermomechanical loading (TL) was performed with progressive load of 80, 120, 160, 200, 240, 280, and 320 N with 20,000 cycles each, 140,000 cycles in total, frequency of 5 Hz, and temperature variation of 5°C-55 °C, followed by fracture resistance testing with load cell of 1000 Kgf and crosshead speed of 0.5 mm/min in a universal testing machine. Failure mode has been evaluated. Data were compared by Kaplan-Meier survival analysis (p < 0.05) for TL and one-way ANOVA and Tukey's test (p < 0.05) for fracture resistance. TL showed higher number of fractures for groups without ferrule (GFPf- = 7, GFPf+ = 3, Ef- = 10, and Ef+ = 2) and lower mean fracture load probability (GFPf+ = 300 N, GFPf- = 280 N, Ef+ = 320 N, Ef- = 188 N) than those with ferrule. Regarding fracture, teeth rehabilitated with GFP were more resistant to endocrowns with ferrule (p < 0.05). A higher percentage of type III failures after fatigue and type II failures after fracture were found. In conclusion, rehabilitation using GFP with ferrule is more favorable for anterior teeth, but the use of endocrown with ferrule proved feasible.

Stress analysis in simulation models with or without implant threads representation.

PURPOSE: This study aimed to evaluate the influence of implants with or without threads representation on the outcome of a two-dimensional finite element (FE) analysis. MATERIALS AND METHODS: Two-dimensional FE models that reproduced a frontal section of edentulous mandibular posterior bone were constructed using a standard crown/implant/screw system representation. To evaluate the effect of implant threads, two models were created: a model in which the implant threads were accurately simulated (precise model) and a model in which implants with a smooth surface (press-fit implant) were used (simplified model). An evaluation was performed on ANSYS software, in which a load of 133 N was applied at a 30-degree angulation and 2 mm off-axis from the long axis of the implant on the models. The Von Mises stresses were measured. RESULTS: The precise model (1.45 MPa) showed higher maximum stress values than the simplified model (1.2 MPa). Whereas in the cortical bone, the stress values differed by about 36% (292.95 MPa for the precise model and 401.14 MPa for the simplified model), in trabecular bone (19.35 MPa and 20.35 MPa, respectively), the stress distribution and stress values were similar. Stress concentrations occurred around the implant neck and the implant apex. CONCLUSIONS: Considering implant and cortical bone analysis, remarkable differences in stress values were found between the models. Although the models showed different absolute stress values, the stress distribution was similar.