Influence of platform and abutment angulation on peri-implant bone. A three-dimensional finite element stress analysis

The Effect of Abutment Angulation and Crown Material Compositions on Stress Distribution in 3-Unit Fixed Implant-Supported Prostheses: A Finite Element Analysis

Objective

The aim of this study was to evaluate influence of abutment angulation and restoration material compositions on the stress pattern in dental implants and their surrounding bone.

Materials and Methods

In this finite element study, the six different solid 3D models of “mandibular 3-unit fixed implant-supported prostheses” were analyzed. In all of these models, a straight abutment was used for anterior implants at the second premolar site, and in order to posterior implant at the second molar site, abutments with three different angles (straight, 15, and 20°) were used. Also, two different restoration material compositions (porcelain fused to base metal (PFBM) and porcelain fused to noble metal (PFNM)) were considered for fixed implant supported restorations. A 450 N static force was exerted in a straight manner along the longitudinal axis of the anterior implant in a tripod, and the stress distribution was measured based on the restoration materials and abutment angulations of the models in the 3 sites of cortical, cancellous bone, and fixtures. The simulation was performed with ABAQUS 6.13 Software.

Results

In all models, stress values in surrounding cortical bone were more than in spongy bone. Maximum stress levels in an anterior abutment-implant complex were seen in models with angled implants. In models with parallel implants, the stress level of a molar straight abutment-implant complex was less than that of premolar straight ones. In an angled posterior abutment-implant complex, less stress level was detected compared to straight ones. In all PFNB models, stress values were slightly more and distributed in a wider area of premolar straight abutments.

Conclusion

Increasing an abutment angle, increases stress in surrounding bone and straight implant-abutment combination. It seems that the crown material composition affects stress distribution of the implant-abutment combination but does not affect stress distribution of surrounding bone.

Stress distribution and microgap formation in angulated zirconia abutments with a titanium base in narrow diameter implants: A 3D finite element analysis

PURPOSE

This in vitro study aimed to use failure stress and implant abutment interface (IAI) microgap size to find the compromised axial angle range of angulated zirconia abutments with a titanium base in narrow diameter implants in the esthetic region.

MATERIALS AND METHODS

A three-dimensional (3D) finite element model of maxillary central incisor implant prosthesis was reconstructed. Angulated zirconia abutments (0°, 15°, 30°, and - 15°) with a titanium base in narrow diameter implants (3.3*12 mm, Bone level, Roxolid SLActive, Straumann AG, Switzerland) were designed to simulate clinical scenarios of buccal inclination 0°, 15°, and 30°, and palatal inclination 15° of the implant long axis. Straight titanium abutment and pure titanium implant were used as two control groups. An oblique force at 30° inclination to the long axis of the crown was applied 3 mm below the incisal edge on the palatal surface of the prosthesis. Under simulated dynamic chewing force, the stress distribution of the implant components and surrounding bone were investigated. The relative micromotion displacement between the implant and abutment models at the IAI area was recorded, and the influence of tightening torque on the IAI microgap was evaluated.

RESULTS

The angulation of the zirconia abutment could affect the stress value and IAI microgap of implant restorations. When the zirconia abutment angle increased from -15 °to 30°, the stress on the central screw, titanium base, and surrounding bone tissue gradually increased by 9%, 20%, and 23%, respectively. The stress levels of the 30° zirconia abutment group showed the risk of exceeding the threshold. When the long axis of the implant was inclined in the palatal direction, the -15° angle abutment reduced the stress by 3% and reduced the strain level of the implant system by 17% and the surrounding bone tissue by 26%. Under simulated dynamic chewing load, the displacement between the implants and the abutment occurred in each group of the implant system, and the amplitude of the micromotion fluctuated with the change in the load. The horizontal displacement caused a 0.075-1.459 μm palatal microgap and 0.091-0.945 μm distal microgap in the IAI. The microgap between the lip and palate was more evident, and the vertical displacement difference was manifested as the abutment sliding down the implant.

CONCLUSIONS

In cases of upper implant restoration with difficulties such as small gaps and axial defects in the esthetic zone, the abutment angle is highly recommended to be in a slightly palatal-inclined direction or to not exceed 15° when the implant is inclined to the labial side to avoid mechanical damage and leakage caused by the appearance of excessively large micromotion gaps. This article is protected by copyright. All rights reserved.

Evaluation of Stress Generated with Different Abutment Materials and Angulations under Axial and Oblique Loading in the Anterior Maxilla: Three-Dimensional Finite Element Analysis

Purpose

The aim of this study was to assess and correlate the stress distribution in an anterior maxillary implant-supported prosthesis with 0°(degree), 15°, and 25° angulated titanium and zirconia abutments using a three-dimensional (3D) finite element analysis (FEA).

Materials and Methods

Six FEA models consisting of a dentate anterior maxilla with a single bone-level implant of dimension 4.2 × 10 mm placed in the region of left maxillary central incisor and abutments of dimension 4.2 mm made of titanium and zirconia each with angulation 0° (IA and IB), 15° (IIA and IIB), and 25° (IIIA and IIIB) and ANSYS Workbench software were utilized to design a layered zirconia crown. Unilateral axial and oblique loads of 178 N were applied on the palatal aspect of the crown of left maxillary central incisor. Average von Mises stress values were evaluated in the implant and the peri-implant bone quantitatively and qualitatively.

Results

Stress was shown to increase with an increase in angulation in all the areas that were examined. Zirconia abutments showed lesser stress in the implant and surrounding bone than titanium abutments. When compared with the body and apex of the implant, the implant neck values were higher in all models. In between cortical and cancellous bone, the stress recorded was higher in the cortical bone.

Conclusion

Within the limitations of this study, straight abutments generated a more uniform and minimal stress in implant and peri-implant bone than angulated abutments. Titanium abutments generated higher stress levels than zirconia abutments. The stresses generated are directly proportional to an increase in abutment angulation, and therefore, straight abutments are most suitable for favourable stress transmission.

Dental implant primary stability in different regions of the Jawbone: CBCT-based 3D finite element analysis

Aim

This study aimed to analyze the primary stability of dental implant in maxillary and mandibular anterior and posterior regions using a finite element analysis.

Materials and methods

CBCT images of maxillary and mandibular regions were collected from patients’ radiographic data and transformed to 3D models. A Straumann Dental implant was inserted in each bone model and then pulled-out, where amount von-Mises stress was obtained and analyzed for each. A comparison between the insertion and the pull-out was evaluated.

Results

Twenty-four images were randomly selected for analysis from 122 scans. In both the insertion and the pull-out of the dental implant, von-Mises stress was high in cortical as compared to the cancellous bone (p < 0.0001). Maxillary posterior region had a low von-Mises stress (p < 0.001). Bone plastic deformation was higher in cancellous than the cortical bone in all bone regions and was the lowest in maxillary posterior region (p < 0.001). Bone displacement decreased from Type I to type IV bone.

Conclusion

Evaluation of von-Mises stress showed different measurements in maxillary and mandibular regions. Bone deformation was low in the maxillary posterior region.

The importance of correct implants positioning and masticatory load direction on a fixed prosthesis

Background

Through the biomechanical study of dental implants, it is possible to understand the dissipation effects of masticatory loads in different situations and prevent the longevity of osseointegration. Aims: To evaluate the microstrains generated around external hexagon implants, using axial and non-axial loads in a fixed four-element prosthesis with straight implants and implants inclined at 17°.

Material and Methods

Three implants were modeled using CAD software following the manufacturer’s measurements. Then, implants were duplicated and divided into two groups: one with straight implants and respective abutments, and the other with angled implants at 17° and respective abutments. Both groups were arranged inside a block simulating bone tissue. A simplified fixed prosthesis was installed on both groups and the geometries were exported to CAE software. Five loads of 300N were performed at axial and non-axial points on the fixed prosthesis. Stress on the implants and strain on the block were both analyzed. An in vitro experiment was performed following all structures made in FEA in order to validate the model. In each experimental block, 4 strain gauges were linearly placed between the implants and the same loads were repeated with a loading applicator device.

Results

The deformations computed by the gauges were correlated with the FEA results, showing that the group with inclined implants had more damaging biomechanical behavior and was significantly different from the group with straight implants (P<0.005).

Conclusions

The mathematical model used is valid and inclined implants can induce unwanted bone remodeling.

Key words:Finite Element Analysis, Dental Implants, Fixed Prosthesis.

Mechanical Complications Related to the Retention Screws of Prefabricated Metal Abutments With Different Angulations: A Retrospective Study With 916 Implants

OBJECTIVES

The present retrospective study assessed the clinical performance of abutment screws from prefabricated metal abutments and compared technical complication rates between straight and angled abutments.

MATERIALS AND METHODS

Dental charts were selected for patients with dental implant rehabilitations delivered between 1998 and 2012. Abutment angulation, prosthetic screw type, and presence of complications that occurred during the selected time period were collected. Technical complications registered included abutment screw loosening and/or fractures detected during clinical and radiographic examinations. The chi-square test was used for statistical analysis.

RESULTS

Abutment angulations were divided into 2 groups: G1) prefabricated straight abutments and G2) prefabricated angled conical mini UCLA-type abutments. A total of 916 implants (799 straight and 117 angled conical mini UCLA-type abutments) were evaluated. G1 showed 91.1% had absence of failures, which were clinically defined as any screw loosening or fracture; and 8.9% reported some type of technical complication. G2 showed 92.3% and 7.7%, with and without technical complications, respectively.

CONCLUSIONS

No significant differences were observed between abutment angulation and technical complications.

Effects of crown retrieval on implants and the surrounding bone: a finite element analysis

PURPOSE

The aim of this study was to observe stress concentration in the implant, the surrounding bone, and other components under the pull-out force during the crown removal.

MATERIALS AND METHODS

Two 3-dimensional models of implant-supported conventional metal ceramic crowns were digitally constructed. One model was designed as a vertically placed implant (3.7 mm × 10 mm) with a straight abutment, and the other model was designed as a 30-degree inclined implant (3.7 mm × 10 mm) with an angled abutment. A pull-out force of 40 N was applied to the crown. The stress values were calculated within the dental implant, the abutment, the abutment screw, and the surrounding bone.

RESULTS

The highest stress concentration was observed at the coronal portion of the straight implant (9.29 MPa). The stress concentrations at the cortical bone were lower than at the implants, and maximum stress concentration in bone structure was 1.73 MPa. At the abutment screws, the stress concentration levels were similiar (3.09 MPa and 3.44 MPa), but the localizations were different. The stress at the angled abutment was higher than the stress at the straight abutment.

CONCLUSION

The pull-out force, applied during a crown removal, did not show an evident effect in bone structure. The higher stress concentrations were mostly observed at the implant and the abutment collar. In addition, the abutment screw, which is the weakest part of an implant system, also showed stress concentrations. Implant angulation affected the stress concentration levels and localizations.

CLINICAL IMPLICATIONS

These results will help clinicians understand the mechanical behavior of cement-retained implant-supported crowns during crown retrieval.