Prosthetic Screw Research Articles

Effect of the geometry of butt-joint implant-supported restorations on the fatigue life of prosthetic screws

Statement of problemDental implant geometry affects the mechanical performance and fatigue behavior of butt-joint implant-supported restorations. However, failure of the implant component has been generally studied by ignoring the prosthetic screw, which is frequently the critical restoration component. PurposeThe purpose of this in vitro study was to evaluate the effect of 3 main implant geometric parameters: the implant body diameter, the platform diameter, and the implant-abutment connection type (external versus internal butt-joint) on the fatigue life of the prosthetic screw. The experimental values were further compared with the theoretical ones obtained by using a previously published methodology. Material and methodsFour different designs of direct-to-implant dental restorations from the manufacturer BTI were tested. Forty-eight fatigue tests were performed in an axial fatigue testing machine according to the International Organization for Standardization (ISO) 14801. Linear regression models, 95% interval confidence bands for the linear regression, and 95% prediction intervals of the fatigue load-life (F-N) results were obtained and compared through an analysis of covariance (ANCOVA) to determine the influence of the 3 parameters under study on the fatigue behavior (α=.05). ResultsLinear regression models showed a statistical difference (P<.001) when the implant body diameter was increased by 1 mm; an average 3.5-fold increase in fatigue life was observed. Increasing the implant abutment connection diameter by 1.4 mm also showed a significant difference (P<.001), leading to 7-fold longer fatigue life on average. No significant statistical evidence was found to demonstrate a difference in fatigue life between internal and external implant-abutment connection types. ConclusionsIncreasing the implant platform and body diameter significantly improved (P<.001) the fatigue life of the prosthetic screw, whereas external and internal connections provided similar results. In addition, experimental results proved the accuracy of the fatigue life prediction methodology.

Influence of Framework Material and Posterior Implant Angulation in Full-Arch All-on-4 Implant-Supported Prosthesis Stress Concentration.

This study evaluated the influence of distal implants angulation and framework material in the stress concentration of an All-on-4 full-arch prosthesis. A full-arch implant-supported prosthesis 3D model was created with different distal implant angulations and cantilever arms (30° with 10-mm cantilever; 45° with 10-mm cantilever and 45° with 6-mm cantilever) and framework materials (Cobalt–chrome [CoCr alloy], Yttria-stabilized tetragonal zirconia polycrystal [Y-TZP] and polyetheretherketone [PEEK]). Each solid was imported to computer-aided engineering software, and tetrahedral elements formed the mesh. Material properties were assigned to each solid with isotropic and homogeneous behavior. The contacts were considered bonded. A vertical load of 200 N was applied in the distal region of the cantilever arm, and stress was evaluated in Von Misses (σVM) for prosthesis components and the Maximum (σMAX) and Minimum (σMIN) Principal Stresses for the bone. Distal implants angled in 45° with a 10-mm cantilever arm showed the highest stress concentration for all structures with higher stress magnitudes when the PEEK framework was considered. However, distal implants angled in 45° with a 6-mm cantilever arm showed promising mechanical responses with the lowest stress peaks. For the All-on-4 concept, a 45° distal implants angulation is only beneficial if it is possible to reduce the cantilever’s length; otherwise, the use of 30° should be considered. Comparing with PEEK, the YTZP and CoCr concentrated stress in the framework structure, reducing the stress in the prosthetic screw.

Effect of Splinting of Tilted External Hexagon Implants on 3-Unit Implant-Supported Prostheses in the Posterior Maxilla: A 3D Finite Element Analysis.

To assess the effects of tilted external hexagon implants and splinted restorations in terms of stress distribution on the bone tissue, implants, and prosthetic screws, using three-dimensional finite element analysis. Six models were used to simulate a posterior maxilla bone block (type IV) from the first premolar to the first molar. Each model included three 4.1-mm-diameter external hexagon implants with varying inclinations (0°, 17°, and 30°) and crown designs (splinted and nonsplinted restorations). The forces applied were as follows: 400 N axially (50 N for each slope of the cusp) and 200 N obliquely (45° only on the buccal slope of the cusp). Stress distribution on the implants and prosthetic screw was evaluated using Von Mises stress, while the maximum principal stress was used to evaluate the stress distribution in the bone tissue. The oblique load increased the stress on all the structures in all the models. Increased inclination of the implants resulted in higher stress concentration in the bone tissue, implants, and prosthetic screws. However, splinted restorations contributed to reduction of the stress for the oblique loading, mainly in the bone tissue and prosthetic screw of the first molar, as the stress was shared between the first and second premolar restorations. Tilted implants increased proportionally the stress on bone tissue and prosthetic screws of models. Additionally, splinting restorations reduced the stress concentration area in the simulated bone tissue, implants, and prosthetic screws in the first molar, as the stress was shared with the adjacent implants.

Prosthetic Complications of Screw-Retained Restoration Using Multiunit Abutments Versus Intraoral Luting on Titanium Base in Implant-Supported Complete Overdentures Randomized Clinical Trial

BACKGROUND: This trial aims to study the difference between prostheses screwmented on full-arch implants using the intraoral luting cement technique on titanium bases versus transmucosal abutments in terms of prosthetic complications. MATERIALS AND METHODS: Twenty patients were recruited in this trial, there were mainly two groups. A screw-retained full-arch implant-supported prosthesis was constructed over four dental implants on upper or lower jaws. For the control group, multiunit abutments were used to construct a screw-retained prosthesis. As for the experimental group, Ti-base abutments were used over the dental implants to construct a screw-retained prosthesis. In both groups, the prosthetic framework was made using polyether ether ketone (PEEK) material and luted intraorally over the titanium sleeve using resin cement. A binary outcome of prosthetic complication was taken in 6 and 12 months. Abutment screw loosening, prosthetic screw loosening, prosthetic screw fracture, abutment screw fracture, veneer fracture, framework fracture, Ti-base decementation, and overall prosthetic loosening were the prosthetic complications included in the trial. RESULTS: At the end of the study, a total of 19 patients adhered to the trial. Throughout the exposure process of implants, two implants failed in one patient from the Ti-base group. This patient was excluded from the study on his request. There was no statistically significant difference present between Ti-base and multiunit abutment groups in terms of abutment and prosthetic screw loosening, abutment and prosthetic screw fracture, veneer and framework fracture, Ti-base decementation, and overall prosthesis loosening for 6 and 12 months. Data were explored for normality using Kolmogorov–Smirnov and Shapiro–Wilk tests, data showed non-parametric (not-normal) distribution. Qualitative data were presented as frequencies and percentages. Wilcoxon and Mann–Whitney tests were used to compare the qualitative outcomes in this study. CONCLUSION: Both multiunit and Ti-base are considered a viable line of treatment to construct a screw-retained full arch implant-supported prosthesis.

Evaluation of physical changes due to simulated loading on prosthetic screw supporting 4- and 6-unit implant prosthesis: An in vitro study.

Screw loosening is a very common cause of failures in implant prosthodontics. In order to avoid screw fracture, it is imperative to understand the mechanical behavior of the screw and the dynamics it is subjected to intraorally. The present study was conducted to qualitatively evaluate and compare the morphological changes, surface defects, and cracks observed under a scanning electron microscope (SEM) in the prosthetic screw. Two Stainless steel edentulous mandible models were fabricated on the basis of all on four and all on six concepts by using CAD design. Screw retained prosthesis were fabricated for both the models and total number of 80 prosthetic screws were made up of Ti6Al4V. Eighty prosthetic screws (N = 80) used in four- and six-unit implant-retained cast hybrid denture were subjected to cyclic loading of 1.5 million cycles and 3 million cycles, simulating a 5 and 10 years of usage, respectively. Once the simulated cycles had been completed in all subgroups, each prosthetic screw was inspected under SEM (×150-×1000) for any changes. The data thus obtained were statistically analyzed using SPSS 12.0 software and P < 0.005 was considered statistically significant. The study revealed statistically significant (P < 0.005) changes (like morphological changes, surface defects, crack initiation, and propagation) in the prosthetic screws after exposing them to predefined test conditions (P < 0.001). It can be concluded that the prosthetic screws need to be changed after a period of clinical use of 5 years irrespective of the number of implants used for rehabilitation. Further, the tilt of the abutment and numbers of implants also contribute to the stresses on the implant-supported prostheses.

Biomechanical investigation of maxillary implant-supported full-arch prostheses produced with different framework materials: a finite elements study.

Four and six implant-supported fixed full-arch prostheses with various framework materials were assessed under different loading conditions. In the edentulous maxilla, the implants were positioned in a configuration of four to six implant modalities. CoCr, Ti, ZrO2, and PEEK materials were used to produce the prosthetic structure. Using finite element stress analysis, the first molar was subjected to a 200 N axial and 45° oblique force. Stresses were measured on the bone, implants, abutment screw, abutment, and prosthetic screw. The Von Mises, maximum, and minimum principal stress values were calculated and compared. The maximum and minimum principal stresses in bone were determined as CoCr < ZrO2 < Ti < PEEK. The Von Mises stresses on the implant, implant screw, abutment, and prosthetic screws were determined as CoCr < ZrO2 < Ti < PEEK. The highest Von Mises stress was 9584.4 Mpa in PEEK material on the prosthetic screw under 4 implant-oblique loading. The highest maximum principal stress value in bone was found to be 120.89 Mpa, for PEEK in 4 implant-oblique loading. For four and six implant-supported structures, and depending on the loading condition, the system accumulated different stresses. The distribution of stress was reduced in materials with a high elastic modulus. When choosing materials for implant-supported fixed prostheses, it is essential to consider both the number of implants and the mechanical and physical attributes of the framework material.

Metal-Ceramic and Polyether Ether Ketone-Composite Maxillary Fixed Prosthesis Supported by Four Implants and Opposed by Removable Distal Extension Partial Dentures: A Comparative Study of Clinical and Prosthetic Outcomes.

This study aimed to evaluate clinical and prosthetic outcomes of metal-ceramic and polyether ether ketone (PEEK) fixed prostheses supported by four maxillary implants and opposed by distal extension removable partial dentures. Thirty participants with edentulous maxillary and distal extension mandibular ridges received four implants according to the All-on-4 treatment concept. The implants were immediately loaded by fixed acrylic prostheses. After 6 months, patients received either metal frameworks covered with porcelain teeth (metal group) or PEEK framework veneered with composite teeth (PEEK group). Plaque Index (PI), Gingival Index (GI), pocket depth (PD), implant stability quotient (ISQ), peri-implant marginal bone loss (MBL, using digital periapical radiographs), and implant survival were measured at baseline, 1 year, and 3 years. Prosthetic complications were measured on the patient and implant levels after 3 years. No implant failures occurred after insertion of the definitive prosthesis, and the implant survival rate was 100% in both groups. PI, GI, PD, ISQ, and MBL increased significantly with time. The most frequent complications were veneer fracture for the PEEK group and prosthetic screw loosening for the metal group. The metal group showed significantly higher PI, PD, and MBL than the PEEK group after 3 years. PEEK was associated with significantly higher veneer fracture than metal, while metal was associated with significantly higher prosthetic screw loosening than PEEK. Within the limitations of this study, the PEEK framework veneered with composite may be a suitable alternative to a metal porcelain prosthesis for All-on-4 implant rehabilitation in patients with maxillary edentulous arches opposed by distal extension mandibular ridges, as it was associated with favorable clinical and prosthetic outcomes after 3 years. However, it was associated with an increased rate of veneer or artificial gingiva fracture.

Comparison of Mechanical Resistance to Maximal Torsion Stress in Original and Nonoriginal or Compatible Prosthetic Implant Screws: An In Vitro Study.

Micromovements of the implant-abutment connection influence peri-implant bone preservation. The maximal torque after a cycle of implant prosthetic screw tightening using original components of different manufacturers and replicas produced by other companies is evaluated and quantified in this study. A total of 30 Mis Seven® standard platform implants and 30 interfaces were used, and 30 standard platform screws were tested, 10 Mis®, 10 Iconekt®, and 10 Exaktus®. The screws were tightened with an MIS® torquemeter until their respective fracture, and the fracture point was measured through the equipment's load cell, CS-Dental Testing Machine®. The screws were analyzed under an Olympus® SZ61 microscope. The fracture points were recorded and compared among all samples. To compare the mean values of the fracture torques, t-tests were performed using the reference values associated with each brand and the sample results. The variable “Place of Fracture” between the original Mis® brand and the Exaktus® replica compared to the Iconekt® replica presented a statistically significant difference (p < 0.001). When analyzing the variable “Fracture Torque,” although it was verified that the replica screws (Iconekt® and Exaktus®) had a lower maximum torque, 65.11 Nm and 62.89 Nm, respectively, compared to the original Mis® brand (70 Nm and 69 Nm), there were no statistically significant differences p > 0.05. Nonoriginal screws did not present different fracture resistances compared to the original Mis® brand screws. The fracture site of Iconekt® screws showed a different pattern compared to the other brands.

Effect of number of implants, distal implant inclination, and angled abutment on stresses in fixed complete dentures: a nonlinear finite element analysis

Objectives: This nonlinear three-dimensional finite element analysis (FEA) study evaluated the effect of the number of implants, distal implant inclination, and use of angled abutments on stress magnitude and distribution in cortical bone (CB), abutment screw (AS), and prosthetic screw (PS) of implant-supported fixed complete dentures. Methods: Nonlinear 3D FEA models of mandibular fixed complete dentures were created with five, four, or three parallel straight implants (5S, 4S, 3S) and with tilted distal implants (5T, 4T, 3T). In addition, the 5T model was tested using angled abutments over the tilted distal implants to re-align the implant inclination. A 100-N axial load was applied over the first molar region (cantilever) to analyze the von Mises stresses in selected points (CB, AS, and PS). Results: The implant adjacent to the load showed the highest stresses in CB, AS, and PS. The model with three implants showed higher stresses than the ones with four and five implants. Peak stresses in the AS increased 40% from five to four implants and 100% from five to three implants. Tilting the distal implants increased stresses in CB. Peak stress in the PS increased 150% from 5S to 5T models and 100% from 4S to 4T models. Angled abutments generated lower stresses on CB and AS but higher stresses on PS. Conclusions: The results suggest that stresses in the cortical bone, abutment screw, and prosthetic screw increase when tilting the posterior implants and reducing the number of implants. The use of angled abutments decreased stresses at the bone-implant interface and in abutment screws but increased stresses on prosthetic screws.

Clinical outcomes of dental implants placed in the same region where previous implants failed due to peri-implantitis: a retrospective study

PurposeThere is paucity in the studies that assess dental implants replacing failed dental implants due to peri-implantitis. This study aims to evaluate the clinical outcomes of these implants in terms of implant survival and marginal bone loss.MethodsPatients in this retrospective study were selected if having one or more implants removed due to peri-implantitis and the placement and loading of dental implants in the same region from April 2010 to December 2019. Information was collected about the patient's demographic data, implant dimensions, surgical and prosthetic variables. Changes in peri-implant bone level, cumulative implant survival rate and technical complications were assessed.ResultsThree hundred and eighty one dental implants in 146 patients that were placed in the same position or one-tooth position mesially/distally to the site of explantation were included. The patients' mean age was 63 ± 10 years. Ninety seven patients were females and 49 were males. After a mean follow-up of 34 ± 17 months, two implants failed. The cumulative survival rate was 99%. The marginal bone loss was −0.1 ± 0.6. Immediate or delay replacement of the failed implant did not affect implant survival or marginal bone stability. All the prostheses were screw-retained and presented the following complications: ceramic chipping (3 events), resin tooth fracture (1 event) and prosthetic screw loosening (1 event).ConclusionsDental implants replacing failed implants due to peri-implantitis would be an option in the management of peri-implantitis. They showed high survival rate and marginal bone stability.

Impact of Mechanical Complications on Success of Dental Implant Treatments: A Case-Control Study.

Objective This study aimed to investigate the impact of mechanical complications on outcome measures for implant dentistry. Materials and Methods This case–control study included 282 patients with mechanical complications occurring in fixed prosthetic rehabilitation supported by immediate function implants with external connection (cases) and 282 individuals without mechanical complications (control). Pairing was performed for sex, age (range = 3 years), and follow-up months (range = 11 months). The primary outcome measure was implant survival, while the secondary outcome measures were marginal bone loss and biological complication parameters (peri-implant pathology, soft tissue inflammation, fistula formation, and abscess formation). Statistical Analysis Cumulative implant survival was estimated by using life tables. Descriptive statistics with 95% confidence intervals (CI) and inferential statistics (Chi-square test) were performed to evaluate differences between cases and controls. The significance level was set at 5%. Results The average follow-up duration was 8.5 years. Mechanical complications included prosthetic fracture ( n = 159), abutment loosening ( n = 89), prosthetic screw loosening ( n = 20), milled abutment ( n = 12), milled prosthetic screw ( n = 1), and decemented crown ( n = 1). Implant failure occurred in one patient from the control group, with survival rates of 100 and 99.6% for cases and controls, respectively ( p = 0.317). The average marginal bone loss was 1.72 (95% confidence interval [CI]: 1.60–1.84) for cases and 1.55 (95% CI: 1.45–1.65) for controls ( p = 0.068). Biological complications were observed in 90 patients, with significant differences between cases ( n = 54) and controls ( n = 36; p = 0.038). Conclusion Mechanical complications did not significantly influence survival or marginal bone loss; nevertheless, there is a need for studies with longer follow-up duration. Mechanical complications also significantly influence the incidence of biological complications.

Mechanical Response of PEKK and PEEK As Frameworks for Implant-Supported Full-Arch Fixed Dental Prosthesis: 3D Finite Element Analysis.

Objective Polymeric framework represent an innovative approach for implant-supported dental prostheses. However, the mechanical response of ultra-high performance polymers as frameworks for full-arch prostheses under the “all-on-four concept” remains unclear. The present study applied finite element analysis to examine the behavior of polyetherketoneketone (PEKK) and polyetheretherketone (PEEK) prosthetic frameworks. Materials and Methods A three-dimensional maxillary model received four axially positioned morse-taper implants, over which a polymeric bar was simulated. The full-arch prosthesis was created from a previously reported database model, and the imported geometries were divided into a mesh composed of nodes and tetrahedral elements in the analysis software. The materials were assumed as isotropic, elastic, and homogeneous, and all contacts were considered bonded. A normal load (500 N magnitude) was applied at the occlusal surface of the first left molar after the model was fixed at the base of the cortical bone. The microstrain and von-Mises stress were selected as criteria for analysis. Results Similarities in the mechanical response were observed in both framework for the peri-implant tissue, as well as for stress generated in the implants (263–264 MPa) and abutments (274–273 MPa). The prosthetic screw and prosthetic base concentrated more stress with PEEK (211 and 58 MPa, respectively) than with PEKK (192 and 49 MPa), while the prosthetic framework showed the opposite behavior (59 MPa for PEEK and 67 MPa for PEKK). Conclusion The main differences related to the mechanical behavior of PEKK and PEEK frameworks for full-arch prostheses under the “all-on-four concept” were reflected in the prosthetic screw and the acrylic base. The superior shock absorbance of PEKK resulted in a lower stress concentration on the prosthetic screw and prosthetic base. This would clinically represent a lower fracture risk on the acrylic base and screw loosening. Conversely, lower stress concentration was observed on PEEK frameworks.

Stress analysis of a single prosthesis on a poorly positioned implant

The mechanical positioning behavior of a mal-positioned implant was evaluated in the finite element method. Models were created in SolidWorks Professional 2013® software with a single implant rehabilitation. The following were analyzed: Control Group, crown aligned to the implant long axis; Experimental Group, crown shifted 3 mm mesial proximally to the implant axis. Compressive stresses in cortical and medullary bone, and Von Mises stresses in implants and components were evaluated. With 100 N occlusal loading at 5 points. The peak von Mises stresses in the prosthetic screw of the experimental group (138.45 MPa) were 43.60% higher compared to the control group (96.41 MPa). The stresses in the prosthetic pillar were localized in the abutment region and the experimental group showed (875.63 MPa), 28% higher than the control group (683.88 MPa). Regarding the implant, the maximum stress peaks were located in the implant platform and the experimental group showed stress values of (1081.4) MPa and was 26.42% higher than the control 855.39 MPa. The cortical bone tissue of the experimental group showed shear stress values 10.81% higher than the control. The stress values were 151.36 MPa for the experimental group and (136.59 Mpa) for the control. The medullary bone showed shear stress (8.31 MPa) and was 12.29% higher than the control (7.40 MPa). A maximum peak was obtained in the cervical region of the medullary bone, adjacent to the cortical bone. The experimental group with a mal-positioned implant showed the highest maximum stresses for all simulated prosthetic components.

Novel and simplified optimisation pathway using response surface and design of experiments methodologies for dental implants based on the stress of the cortical bone.

Dental implants are widely used as a long-term treatment solution for missing teeth. A titanium implant is inserted into the jawbone, acting as a replacement for the lost tooth root and can then support a denture, crown or bridge. This allows discreet and high-quality aesthetic and functional improvement, boosting patient confidence. The use of implants also restores normal functions such as speech and mastication. Once an implant is placed, the surrounding bone will fuse to the titanium in a process known as osseointegration. The success of osseointegration is dependent on stress distribution within the surrounding bone and thus implant geometry plays an important role in it. Optimisation analyses are used to identify the geometry which results in the most favourable stress distribution, but the traditional methodology is inefficient, requiring analysis of numerous models and parameter combinations to identify the optimal solution. A proposed improvement to the traditional methodology includes the use of Design of Experiments (DOE) together with Response Surface Methodology (RSM). This would allow for a well-reasoned combination of parameters to be proposed. This study aims to use DOE, RSM and finite element models to develop a simplified optimisation analysis method for dental implant design. Drawing on data and results from previous studies, two-dimensional finite element models of a single Branemark implant, a multi-unit abutment, two prosthetic screws, a prosthetic crown and a region of mandibular bone were built. A small number of combinations of implant diameter and length were set based on the DOE method to analyse the influence of geometry on stress distribution at the bone-implant interface. The results agreed with previous studies and indicated that implant length is the critical parameter in reducing stress on cortical bone. The proposed method represents a more efficient analysis of multiple geometrical combinations with reduced time and computational cost, using fewer than a third of the models required by the traditional methods. Further work should include the application of this methodology to optimisation analyses using three-dimensional finite element models.

Fatigue performance of prosthetic screws used in dental implant restorations: Rolled versus cut threads

Statement of problemCold rolling is widely used for screw thread manufacturing in industry but is less common in implant dentistry, where cutting is the preferred manufacturing method. PurposeThe purpose of this in vitro study was to compare the surface finish and mechanical performance of a specific model of prosthetic screw used for direct restorations manufactured by thread rolling and cutting. Material and methodsThe thread profiles were measured in an optical measuring machine, the residual stresses in an X-ray diffractometer, the surface finish in a scanning electron microscope, and then fatigue and static load tests were carried out in a direct stress test bench according to the International Organization for Standardization (ISO) 14801. Finally, linear regression models and 95% interval confidence bands were calculated and compared through ANCOVA for fatigue tests while the t test was used for statistical comparisons (α=.05). ResultsThe surface finish was smoother, and compressive residual stresses were higher for the roll-threaded screws. Linear regression models showed a fatigue life 9 times higher for roll-threaded screws (P=1) without affecting static behavior, which showed statistically similar static strengths (P=.54). However, the thread profile in the roll-threaded screws was not accurately reproduced, but this should be easily corrected in future prototypes. ConclusionsRolling was demonstrated to be a better thread-manufacturing process for prosthetic screws, producing improved surface quality and fatigue behavior.

Failures in Single Extra-Short Implants (≤ 6 mm): A Systematic Review and Meta-analysis.

The aim of this systematic review with meta-analysis was to compare the survival rate of single crowns supported by extra-short implants (≤ 6 mm) to those supported by conventional implants, with or without previous maxillary sinus augmentation. The proportion of failures was described according to the type of complication and follow-up periods. Randomized and prospective clinical trials were selected from six databases and gray literature. The risk of bias was evaluated by Joanna Briggs Institute Critical Appraisal Checklist, and the certainty of the evidence was analyzed with Grading of Recommendations Assessment, Development, and Evaluation. Meta-analyses were processed with RevMan and MedCalc Statistical Software. Single crowns supported by extra-short implants had a similar risk of failure to those supported by conventional implants, regardless of previous maxillary sinus augmentation (P > .05). Overall failure proportion of extra-short implants was 5.19%, but it varied according to follow-up (1.18% before loading, 1.56% at 12 months, 1.20% at 24 months, 2.10% at 48 months). Biologic failure complications were 37.90% for bleeding on probing, 22.45% for peri-implantitis, and 11.29% for infection. Prosthodontics failure complications were 14.88% for abutment failures and 14.73% for prosthetic screw loosening. Considering the risk of bias, most studies were classified at moderate risk. The risk of failure of single crowns supported by extra-short implants is similar to those supported by conventional implants, regardless of previous maxillary sinus augmentation or follow-up period. The most frequent biologic and prosthetic complications were bleeding on probing and abutment failures, respectively.

Biomechanical evaluation of 3-unit fixed partial dentures on monotype and two-piece zirconia dental implants

This study aimed to evaluate the biomechanical behavior, stress distributions and bone microstrain of fixed partial dentures (FPD) with ceramic abutments supported on monotype zirconia implants, titanium implants and two-piece zirconia implants, using finite element analysis. A three-dimensional model of the jaw was simulated containing 1.0 mm thick cortical bone and cancellous bone tissue. A FPD and implant models (4.1 x 10 mm) were modeled containing a cement-retained implant abutment. These models were replicated in three groups with similar geometries: Titanium Implant and Zirconia Abutment (Ti-Zr); Zirconia Implant and Zirconia Abutment (Zr-Zr) and Monotype Zirconia Implant (Zr-S). An axial load of 300 N was applied to the center of the first premolar. The microstrain (με) and the Von-Mises stress (MPa) were assumed as failures criteria. For the three groups, a higher stress concentration was observed in the region of FPD connectors. The Ti-Zr group showed a higher stress concentration in the prosthesis and implant when compared to the other groups. However, the smaller elastic modulus of the titanium implant, in relation to the zirconia, provided a lower stress in the abutment and in the prosthetic screw. The monotype implant system allowed a more homogeneous stress distribution and its strain were predominantly located in the cervical region of the peri-implant bone tissue. Monotype or two-piece zirconia implants can be used for rehabilitation with FPD. However, the absence of separation between implant and abutment in the monotype system avoids the stress concentration in the prosthetic screw and reduced the peri-implant bone strain.

Clinical outcomes and biological and mechanical complications of immediate fixed prostheses supported by zygomatic implants: A retrospective analysis from a prospective clinical study with up to 11 years of follow-up.

Zygomatic implants alone or in combination with conventional implants have been used for severe atrophic maxillary arches. Long-term outcomes of extramaxillary technique need validations. To retrospectively assess the clinical outcomes and the prevalence of surgical, biological, and prosthetic complications of implant-fixed complete dental prostheses (IFCDPs) supported by zygomatic implants up to 11 years of follow-up. Dental records of 34 subjects treated between October 2008 and June 2019 were reviewed. Patients received an immediate fixed full-arch prosthesis supported solely by zygomatic implants or by a combination of zygomatic and conventional implants. A total of 90 zygomatic implants and 53 standard implants were placed. Up to 11 years of follow-up, two conventional implants were lost, leading to 96.2% success rate for conventional implants and 100% for zygomatic implants. Marginal bone loss for conventional implants averaged 0.85 ± 0.17 mm after the first year and 1.36± 0.12 mm after 10 years, resulting in full implant success. No prosthesis was lost. The main surgical complication was the perforations of the Schneiderian membrane, occurring in five patients and in seven sinus cavities. Considering the biological complications, mucositis for standard and zygomatic implants ranged between 21%-35% and 26%-40%, respectively. No peri-implantitis were reported. Soft tissue hypertrophy ranged between 1.8% and 30% for conventional implants and 1.1%-35% for zygomatic implants. Inflammation under the prosthesis ranged between 33% and 50%. For the mechanical complications, abutment loosening was recorded in 5.8% of cases (two patients), tooth debonding and fracture of the prosthesis happened in five subjects (14.7%), and loosening of the prosthetic screws was reported in one patient (2.9%). Immediate rehabilitation of the severely atrophic maxilla with zygomatic implants alone or in combination with standard implants could be considered a viable treatment modality.

Influence of Implant-Abutment Contact Surfaces and Prosthetic Screw Tightening on the Stress Concentration, Fatigue Life and Microgap Formation: A Finite Element Analysis

The purpose of this in silico study was to investigate the effect of abutment screw torque and implant-abutment contact surfaces on the stress generation, microgap formation and simulated fatigue life of an external hexagon connection under oblique loading. Three-dimensional numerical models of the external hexagon implant were modeled containing two different implant-abutment contact surfaces (with and without contacting the hexagon axial walls) as well as using screw torques of 20 Ncm or 30 Ncm. Following the ISO 14801, an oblique load of 100 N was applied to the prosthesis. The von Mises stress, microgap formation, safety factor and fatigue life were obtained. The stresses in the abutment screw and implant were minimally influenced by the screw torque. However, this minimal stress in the screw with a 30 Ncm torque reduced the calculated fatigue life in comparison with 20 Ncm when the external hexagon axial walls were not in contact at the implant-abutment interface. The safety factor for the implant was higher when using minimal surfaces at the abutment-interfaces; however, it compromised the screw safety factor increasing its failure probability. The higher the screw torque, the lower was the microgap formation at the implant-abutment interface. However, the calculated residual stress is proportional to the applied torque, reducing the fatigue life in the screw. This effect can be attenuated using an implant-abutment system with more contacting surfaces.

The prosthetic screw loosening of two-implant supported screw-retained fixed dental prostheses in the posterior region: A retrospective evaluation and finite element analysis

The study was aimed to investigate the prosthetic screw loosening of two splinted implants-supported, screw-retained (2–4-unit) fixed dental prostheses (TIS-FDPs) in posterior region and to explore the underlying mechanism. In the retrospective study, a study group of TIS-FDPs (n = 23) presenting prosthetic screw loosening and a control group of TIS-FDPs (n = 32) absent of prosthetic screw loosening during observation period were included. The prosthesis height (PH), inter-implant distance (ID) and cantilever distance (CD) of TIS-FDPs were measured and compared within two groups. In the finite element analysis (FEA) part, three serials of models presenting different clinical scenarios were constructed based on the abovementioned PH, ID and CD values respectively. In the clinical evaluation, the values of pH and CD in study group were statistically higher than those in control group, whereas the values of ID had no significant difference. In the FEA, the results indicated that there was no linear correlation between the increased ID values and the maximum von Mises stresses and the rotation angles. On the other hand, the increased PH and CD values would result in a strong linear growth of the maximum von Mises stresses and the rotation angles. Besides, it was found that the regression coefficients in PH model were all higher than those in ID and CD models. When TIS-FDPs were delivered in posterior region, the PH and the CD, rather than the ID, seemed to have a significant impact on the stress concentration of the prosthetic screws and the incident of prosthetic screws loosening.