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Background: Choosing implant crown materials for restoration remains challenging in clinical practice. This study assesses the impact of all-ceramic restoration instead of porcelain-fused-to-metal (PFM) restoration on the stress distribution within implant components and the surrounding bone. Methods: Four 3D models of a mandibular second premolar were meticulously prepared. The study groups comprised zirconia, lithium disilicate, and zirconia lithium silicate monolithic ceramic crowns cemented onto a zirconia hybrid abutment. A PFM crown cemented onto a cementable abutment was chosen as the control group. A total vertical load of 583 N was applied to the occlusal contact areas. Stress distribution within the crown and implant components was analyzed using von Mises stress analysis. Principal stress analyses were employed to assess stress distribution in the peripheral bone. Results: The PFM model exhibited the highest von Mises stress values for both the implant (428.7 MPa) and crown (79.7 MPa) compared to the other models. The all-ceramic models displayed the highest maximum von Mises stress within the abutment, approximately 335 MPa, compared to the PFM model. von Mises stresses of the abutment and implant in the all-ceramic models were 69% higher and 20% lower, respectively, than those in the PFM model. Screw stresses were relatively consistent across all groups. Principal stresses in spongy bone and minimum principal stress in cortical bone were consistent across all models. Conclusions: All-ceramic restoration with a hybrid abutment, as opposed to traditional PFM restoration with a cementable abutment, does not adversely affect the implant and abutment screw and reduces crown stresses. Stresses within hybrid abutments were notably higher than those within cementable abutments. Spongy bone stresses remained unaffected by the type of crown or abutment.

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BACKGROUND: High percentage of biomechanical complications such as screw loosening in dental implants can be related to implant-abutment (I/A) connection properties which affect the behavior of implant assembly against functional loads in the oral cavity. The aims of the present study were to compare the reverse torque values (RTVs) and failure loads of three abutment types with internal Morse taper connection. MATERIALS AND METHODS: In this experimental in vitro study, eighteen implants (4.5 mm × 10 mm bone level implants, Implantium, Dentium Co, Seoul, South Korea) were divided into three groups with different abutments: two-piece (TP) abutment, one-piece (OP) abutment, and screw abutment (SA), mounted in stainless-steel blocks according to ISO 14801. After completion the torque/detorque protocol, a compressive load (1 mm/min) was applied at 30° off-axis until failure. Mean reverse torque/tightening torque (RT/TT) values and failure loads were analyzed with one-way ANOVA test and Tukey's honest significant difference (α = 0.05). Failure modes were evaluated by radiography and stereomicroscopy. RESULTS: RT/TT values in the TP group were lower than those in other groups (P < 0.001). Highest failure loads were observed in SA group (P = 0.002). In radiographic evaluation, all specimens showed deformation in I/A interface. CONCLUSION: I/A connections with larger surface areas may lead to higher RTVs (e.g., OP and SA groups). Use of an additional screw and indexed area in TP group did not reduce the bending resistance under static loading.

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Abstract Objective: To determine the fracture resistance of endodontically treated teeth restored with three different diameters of glass fiber posts and metal-ceramic crowns. Material and Methods: Thirty human maxillary canines were selected and subjected to root canal therapy. The teeth were randomly divided into three groups of glass fiber posts with 1.4 mm diameter (Group I), 1.6 mm diameter (Group II), and 2.0 mm diameter (Group III). The teeth were restored with metal-ceramic crowns and subjected to the compressive load applied at 45º angle to the longitudinal axis until fracture. The mode of failure was determined. Data were analyzed using ANOVA, followed by Tukey's post hoc multiple comparisons test (p<0.05). Results: The mean fracture resistance of groups I, II and III was 574 ± 91.2 N, 617 ± 85.21 N and 467 ± 99.43 N, respectively. No significant difference was noted between groups I and II, while the fracture resistance was significantly different between groups I and III (p<0.05) and groups II and III (p<0.05). No case of post fracture alone occurred in any group. Conclusion: The diameter of glass fiber posts can affect the fracture resistance of teeth. Based on the results, increasing the diameter of the post up to 1.6 mm may increase the fracture resistance of root, although excessive diameters are not recommended.

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BACKGROUND: Primary stability is one of the prerequisites of immediate loading. The aim of this study was to compare the primary stability of four different implant systems in low-density bone models. MATERIALS AND METHODS: In this in vitro experimental study, 20 fixtures from four implant body designs were selected: Zimmer Tapered Screw-Vent (ZTSV), NobleReplace Tapered (NRT), Replace Select Tapered (RST), and Dentium SuperLine (DSL). Fixtures were inserted in low-density bone models according to manufacturer drilling protocol by one surgeon. Measurement of insertion torque value (ITV), resonance frequency analysis (implant stability quotient [ISQ]), and reverse torque value (RTV) was recorded for each fixture. The data were analyzed with one-way ANOVA and post hoc tests (Tukey honestly significant difference) (P < 0.05). RESULTS: ZTSV had significantly lower amount of insertion torque in comparison to other systems (P = 0.045). RTV was significantly lower in ZTSV in comparison to DSL and NRT (P = 0.004). ISQ value in NRT (ISQ = 67) was significantly higher than other systems (P = 0.000). The lowest amount of ISQ was in RST system (ISQ = 53) with significant difference (P = 0.000). CONCLUSION: This study demonstrated that primary stability of different implant systems was not comparable and implant design was effective on ITV, RTV, and ISQ.

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Severe forms of attrition are frequently found in patients with no or insufficient posterior occlusal support. Management of such patients using fixed or removable prostheses is a complex procedure and is still a challenge for clinicians. The present clinical report describes step by step full mouth rehabilitation of a patient with severely worn dentition using computer-aided design/computer-aided manufacturing- (CAD/CAM-) generated wax patterns, milled zirconia frameworks, and fabrication of removable partial denture (RPD) abutments using a digital-conventional method. The results were satisfactory during 18 months of follow-up.

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OBJECTIVES: The aim of this study was to investigate the stress distribution of different post and core materials in radicular dentin by three-dimensional finite element analysis (3D FEA). MATERIALS AND METHODS: Twelve 3D models of a maxillary central incisor were simulated in the ANSYS 5.4 software program. The models were divided into three groups; the first group included: 1-Gold post and core and 2-Nickel-chromium (Ni-Cr) post and core restored with metal-ceramic restorations (MCRs). The second group included: 1-Stainless steel post, 2-Titanium post, 3-Carbon fiber post, 4-Glass fiber post, and 5-Quartz fiber post with composite cores and MCRs. The third group included: 1-Zirconia post and core, 2-Zirconia post, 3-Carbon fiber post, 4-Glass fiber post, and 5-Quartz fiber post; the last four models had composite cores restored with all-ceramic restorations (ACRs). Each specimen was subjected to a compressive load at a 45-degree angle relative to its longitudinal axis at a constant intensity of 100 N. The models were analyzed with regard to the stress distribution in dentin. RESULTS: Two stress concentration sites were detected in the models. The first group showed the lowest stress levels in the cervical region, while the stress levels detected in the second group were higher than those in the first group and lower than those found in the third group. Fiber-reinforced posts induced a higher stress concentration between the middle and cervical thirds of the root compared to other posts. CONCLUSIONS: According to the results, since cast posts induce lower stresses in dentin, they are recommended for clinical use. Fiber-reinforced posts and ACRs caused the maximum stresses in dentin.

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PURPOSE: According to the so-called All-on-Four protocol, four dental implants are placed in the interforaminal region of the edentulous mandible to support full-arch fixed prostheses. In this design, the posterior implants are tilted distally to a maximum of 45 degrees. The purpose of this finite element study was to evaluate the stress concentration in peri-implant bone during two loading conditions and to compare this design with another design in which the four implants are placed parallel to each other and perpendicular to the occlusal plane. MATERIALS AND METHODS: Three-dimensional finite element models consisted of mandibular bone, four dental implants inserted in two different configurations-with the distal implants tilted (model A) or four parallel implants (model S)-and hybrid superstructures. Two loading conditions (178 N/central incisors or 300 N/left first molar) were considered, and von Mises stress values were determined. RESULTS: During anterior loading, higher stress concentrations were detected in the peri-implant bone of all four implants in model A. During posterior loading, lower stress concentrations were observed around the anterior implants of model A; however, the tilted posterior implants were subjected to higher stresses in every condition. CONCLUSIONS: Application of either of these designs was successful in reducing peri-implant stress in one loading condition. However, neither design demonstrated better performance in both loading conditions; therefore, within the limitations of this study, neither design demonstrated clearly superior performance.

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This clinical report describes the rehabilitation of a 19-year-old girl diagnosed with generalized odontodysplasia. Ten implants were placed in the maxilla and mandible and metal-ceramic implant-supported fixed prostheses were fabricated for both arches. This treatment option seems to be favorable for patients with generalized odontodysplasia.

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PURPOSE: Mandibular flexure may affect stress distribution in implant-supported fixed partial dentures; however, this factor has been overlooked in most finite element analyses of the mandible. The purpose of this study was to investigate the effect of two different superstructures on stress distribution in mandibular bone during mandibular deformation caused by clenching. MATERIALS AND METHODS: Three-dimensional finite element models consisting of the mandibular bone, six implants, and two- or three-piece superstructures were created. Muscle forces with definite direction and magnitude were exerted over areas of attachment to simulate two static bites of incisal and right molar clenching because, during these clenching tasks, a significant amount of mandibular deformation occurs. The stress analysis was performed using von Misses stress values. RESULTS: During right molar clenching, the two-piece superstructure showed increased stress values. During incisal clenching, the three-piece superstructure inhibited mandibular deformation more than the two-piece superstructure. CONCLUSIONS: Mandibular deformation was an important factor in the stress distribution of the models, and it should be considered in the design of implant-supported fixed partial dentures in the mandible.

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PURPOSE: Mandibular flexure may affect the stress distribution in the implant-supported fixed partial dentures, yet the phenomenon has received little attention in finite element analysis studies. The purpose of this study was to evaluate the restraining effects imposed by 1-piece cross-arch superstructure on mandibular flexure and implant stresses. MATERIAL: Mandibular deformation and stress distribution in an implant-supported prosthesis (5 implants and 1-piece superstructure with 16.5 mm bilateral distal cantilevers) were analyzed by a 3-dimensional finite element model of a human edentulous mandible. To determine the effect of 1-piece cross-arch superstructure on mandibular flexure restriction, incisal clenching was simulated. During incisal clenching, maximum contraction of dental arch occurs. For this purpose, 9 pairs of masticatory muscles were simulated by multiple force vectors over areas of attachment. RESULTS: A significant amount of stress (26.2 MPa) at the cortical bone surrounding the neck of the implant located at the symphysis assumed as a consequence of mandibular flexure. At the same area, maximum strain value of 1680 microstrain was detected. Moreover, maximum deformation of 0.35 mm was observed at the mandibular angle. CONCLUSIONS: One-piece implant-supported superstructure restricted mandibular deformation to almost half of the amount observed in unrestricted mandibular models of previous studies. This phenomenon must be considered in finite element analysis studies.

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