Biomechanical considerations when combining tooth-supported and implant-supported prostheses

Stress Analysis of Endodontically Treated Tooth-Implant Different Connectors Designs in Maxillary Posterior Region: A Finite Element Analysis

OBJECTIVES

 Using finite element analysis (FEA), this study aimed to determine the effect of nonrigid connectors (NRCs) and their position on the success of tooth and implant-supported fixed prostheses in the maxillary posterior region.

MATERIALS AND METHODS

 Three three-dimensional FEA models were designed, presuming maxillary second premolar and first molar to be extracted. Implant (replacing first molar), abutment, bone (spongious and cortical), first premolar (containing dentin, root cement, gutta-percha, and casting post and core), periodontal ligament, and three three-unit cemented porcelain-fused-to-metal prostheses (a rigid one and two nonrigid) were modeled. The NRC was once on the tooth side and once on the implant side. The prostheses were loaded twice. The first molar (180 N) and premolars (120 N) teeth were subjected to progressive vertical and oblique (12-degree) loads, and maximum von Mises stress and strain in teeth and connectors were calculated for each model.

RESULTS

 The findings of the current study showed evidence that tooth-implant design with an NRC has significantly increased the average stress in the tooth. The average stress in dentin was 769.02 for the mesial connector and 766.95 for the distal connector, and this was only 731.59 for rigid connector. Furthermore, it was observed that rigid connector has considerably minimized the stress within the tooth-implant-supported fixed partial denture. The average stress for the crown and metal frame is 346.22 and 526.41 in rigid connector, while it is 1,172.9 and 2,050.9 for the nonrigid mesial connector.

CONCLUSION

 Although distal NRC was more efficient than mesial NRC, using NRC will only reduce the stress applied to cortical bone and is not recommended in the posterior region of the maxilla.

Automated vector analysis to design implant-supported prostheses: A dental technique

The prosthesis loading force is an important factor for dental implant survival. Even if adequate osseointegration of the dental implant has been achieved, if the occlusal forces are not correctly distributed, lateral torque can be generated causing high stress on surrounding tissues. The stress value of implant prostheses could be different whether the direction of load is vertical or oblique, affected by the shape of the occlusal surface. When an implant-supported prosthesis is designed with a dental computer-aided design software program, the average vectors from each occlusal contact point can be visualized. If the visualized vector generates lateral torque, the occlusal surface design can be modified before finalizing the design. The described technique uses automated vector analysis to enable visualization of the occlusal vector to improve prosthesis design, optimizing occlusal forces.

Biomechanical evaluation of bridge span with three implant abutment designs and two connectors for tooth-implant supported prosthesis: A finite element analysis

Background/purpose

Bridge stability under loading was influenced by bridge span with the connector and implant abutment design. Thus, the purpose of this study was to evaluate the effects of rigid and non-rigid connector designs and pontic connections of different abutment systems in the tooth-implant supported prosthesis (TISP) at different span distances on the biomechanical stress distribution of the overall system components.

Materials and methods

For comparative analysis, rigid and non-rigid bridge connections were fitted with three implant abutment systems (one-piece, two-piece and three-piece), and five implant-to-natural tooth distance configurations (12 mm, 14 mm, 16 mm, 18 mm, and 20 mm) were provided.

Results

The maximum stress between TISP components occurred at the distal side of crown margin of cement1 in rigid connector with one-piece group and the bottom of the crown3 in non-rigid connector with one-piece group, while the other groups were more concentrated at the junction between the mesial side of the implant collar and the abutment. In addition, neither the rigid nor non-rigid connector model showed that stress distribution increased proportionally with the bridge span distance.

Conclusion

It was clinically recommended that if the implant with a shorter bridge distance of 12 mm from the natural tooth, the rigid connection of the three-piece abutment can be used as the TISP design. If the bridge distance was 18 mm longer, the non-rigid connection of the three-piece abutment could maintain the physiological movement of the natural tooth and avoid the excessive stress on the bone crest around the implant.

Comparison of Stress Distribution in Fixed Partial Prosthesis Restored with Different Combination of Support: A Finite Element Study

AIM

This study was conducted to evaluate the distribution of stress in the bone around the natural tooth, endodontically treated tooth having post and core, and implant as an abutment in different combinations in fixed partial prosthesis using two-dimensional finite element analysis (FEA).

MATERIALS AND METHODS

Six models were simulated using ANSYS Modeller19. All six models were divided into 12 zones and 4 lines, and stress values were calculated and compared. The study combinations were - tooth supported fixed partial prosthesis, fixed partial prosthesis having the combination of tooth and post- and core-treated tooth, fixed partial prosthesis with the combination of tooth and implant, fixed partial prosthesis having the combination of implant and post- and core-treated tooth, fixed partial prosthesis with the combination of post- and core-treated tooth on both sides, and fixed partial prosthesis having the combination of implant on both sides.

RESULT

On comparing the stress values, the maximum stress value was observed in fixed partial prosthesis having the combination of implant on both sides (306.2434 MPa) followed by Model 4 (223.1255 MPa), Model 3 (154.3952 MPa), Model 5 (136.9041 MPa), Model 2 (116.2034 MPa), and least stress seen in Model 1 (99.6209 MPa), and minimum in tooth supported fixed partial prosthesis (99.6209 MPa).

CONCLUSION

This study concluded that stress concentration in bone was maximum when the implant was used as an abutment in fixed partial prosthesis. The least stress was seen in bone around the natural tooth due to the dampening effect of the periodontal ligament. Further, the modulus of elasticity of a post acts as a vital parameter in the distribution of stress in post- and core-treated tooth.

CLINICAL SIGNIFICANCE

The stress concentration in the bone around the abutments affects the longevity of the prosthesis, hence, the clinically appropriate combination of the abutments should be considered for a fixed partial prosthesis.

A Literature Review on Implant Abutment Types, Materials, and Fabrication Processes

Dental implantology has made great strides since Dr. Brånemark introduced it to the world of dentistry. In terms of materials and fabrication processes, a wide range of implants and their implant abutments are now widely available in the market. Such a wide range would undoubtedly put the clinician in a quandary when it comes to selecting an acceptable abutment, one that is scientifically based and also has a high clinical rate of success. As a result, this literature review is a straightforward attempt to shed light on the wide range of implant-abutment types, materials and fabrications that are now easily accessible on the market, as well as offer an overview of each specific type to avoid further dilemma for its clinical intent.

Biomechanical analysis of rigid and non-rigid connection with implant abutment designs for tooth-implant supported prosthesis: A finite element analysis

BACKGROUND/PURPOSE

The design of the connectors and implant abutments could affect the stress distribution of the tooth-implant supported prosthesis (TISP) entire system after loading. Therefore, the purpose of this study was to investigate the stress distribution of the TISP in different connectors and different implant abutments after loading.

MATERIALS AND METHODS

The TISP design used in this study was divided into six models. R1, R2 and R3 represented the tooth and the one-piece, two-piece and three-piece abutment implant system connected by a rigid connector, respectively, while NR1, NR2 and NR3 were the corresponding tooth-abutment implant systems connected by a non-rigid connector. A vertical occlusal load of 50 N was applied at a right angle on the 6 occlusal points of the occlusal surface.

RESULTS

As a result, regarding the maximum average stress distribution, R1 and NR1 appeared on the implant fixture, and the other four models were on the implant abutment. On the other hand, regardless of the abutment implant system, the maximum von Mises stress generated by the rigid connector was greater than the corresponding non-rigid connector in the cortical bone around implant. In addition, the three-piece abutment implant system had lower von Mises stress than the one-piece and two-piece implant systems in the cortical bone.

CONCLUSION

It is concluded that by adding a flexible non-rigid connector and three-piece abutment device design to TISP, the occlusal load of the implant was dispersed, and the stress could be gradually introduced into the relatively strong implant abutment.

Influence of Different Implants on the Biomechanical Behavior of a Tooth-Implant Fixed Partial Dentures: A Three-Dimensional Finite Element Analysis

This study analyzed the biomechanical behavior of rigid and nonrigid tooth-implant supported fixed partial dentures. Different implants were used to observe the load distribution over teeth, implants, and adjacent bone using three-dimensional finite element analysis. A simulation of tooth loss of the first and second right molars was created with an implant placed in the second right molar and a prepared tooth with simulated periodontal ligament (PDL) in the second right premolar. Configurations of two types of implants and their respective abutments-external hexagon (EX) and Morse taper (MT)-were transformed into a 3D format. Metal-ceramic fixed partial dentures were constructed with rigid and nonrigid connections. Mesh generation and data processing were performed on the 3D finite element analysis (FEA) results. Static loading of 50 N (premolar) and 100 N (implant) were applied. When an EX implant was used, with a rigid or nonrigid connection, there was intrusion of the tooth in the distal direction with flexion of the periodontal ligament. Tooth intrusion did not occur when the MT implant was used independent of a rigid or nonrigid connection. The rigid or nonrigid connection resulted in a higher incidence of compressive forces at the cortical bone as well as stress in the abutment/pontic area, regardless of whether EX or MT implants were used. MT implants have a superior biomechanical performance in tooth-implant supported fixed partial dentures. This prevents intrusion of the tooth independent of the connection. Both types of implants studied caused a greater tendency of compressive forces at the crestal area.

Combined Implant and Tooth Support: An Up-to-Date Comprehensive Overview

Objectives. This article presents a review on the concerned topics and some considerations related to the concept of splinting teeth and implants in the rehabilitation of partial edentulism. Study Selection. An electronic PubMed/MEDLINE and manual search of identified articles and reviews as well as clinical, laboratory, and finite element studies was performed in this project. Due to the shortage in within-subject, long term, randomized, controlled clinical trials regarding the subject a meta-analysis was not possible. Results. Although surrounded with some controversy, joining teeth and implants during the rehabilitation of partial edentulism provides the clinicians with more treatment options where proprioception and bone volume are maintained and distal cantilevers and free end saddles are eliminated. It makes the treatment less complex, of less cost, and more acceptable for the patient. Conclusions. Whenever suitable and justified, combining implant and tooth support might be recommended as an alternative during rehabilitation of partial edentulism. Based on the literature, clinical tips and suggestions were recommended to increase the success of this treatment.

Full mouth rehabilitation with maxillary tooth supported and mandibular tooth and implant supported combination prostheses: a 4-year case report

The primary objectives of successful prosthetic rehabilitation are to provide function, esthetics and comfort to the patient. Combination prosthesis is one which is supported by both natural teeth and implant. The periodontal ligament and osseointegrated interface distribute force differently to the supporting bone. Therefore problems can develop when tooth and implants are combined in the same prosthesis. However, clinicians can apply biomechanical principles, to negate the deleterious leverages exerted by the fixed prosthesis by using non rigid components and to equalize the stress applied by the prosthesis on implant and teeth. A case of partially edentulous situation was rehabilitated successfully with a combination of prostheses. Maxillary arch was restored to function with crowns, fixed dental prosthesis and with an extra coronal castable attachment prosthesis and the mandibular arch with a combination of tooth and implant supported attachment prosthesis. The clinical and laboratory steps for the fabrication of these prostheses are explained in this report.

Influence of the connector and implant design on the implant-tooth-connected prostheses

PURPOSE

The purpose of this study was to evaluate stress transfer patterns between implant-tooth-connected prostheses comparing rigid and semirigid connectors and internal and external hexagon implants.

MATERIALS AND METHODS

Two models were made of photoelastic resin PL-2, with an internal hexagon implant of 4.00 x 13 mm and another with an external hexagon implant of 4.00 x 13 mm. Three denture designs were fabricated for each implant model, incorporating one type of connection in each one to connect implants and teeth: 1) welded rigid connection; 2) semirigid connection; and 3) rigid connection with occlusal screw. The models were placed in the polariscope, and 100-N axial forces were applied on fixed points on the occlusal surface of the dentures.

RESULTS

There was a trend toward less intensity in the stresses on the semirigid connection and solid rigid connection in the model with the external hexagon; among the three types of connections in the model with the internal hexagon implant, the semirigid connection was the most unfavorable one; in the tooth-implant association, it is preferable to use the external hexagon implant.

CONCLUSIONS

The internal hexagon implant establishes a greater depth of hexagon retention and an increase in the level of denture stability in comparison with the implant with the external hexagon. However, this greater stability of the internal hexagon generated greater stresses in the abutment structures. Therefore, when this association is necessary, it is preferable to use the external hexagon implant.

Should we extract teeth to avoid tooth-implant combinations?

The controversy over combining teeth and implants for support of fixed partial dentures still remains after almost three decades of debate. The aim of this review was to evaluate what support that could be found in the literature for extracting teeth in favour of implants, and to elucidate whether tooth-implant prostheses were inferior to solely implant supported constructions in terms of survival and complications. The methods for gathering relevant information entailed electronic searches on PubMed using relevant key words, as well as complementary manual searches in the retrieved publications. The results showed that there was no support for extracting teeth in favour of placing implants. On the contrary, the healthy tooth had a survival that was life-long, which is yet to be shown for the dental implant. Also the use of teeth as abutments in combination with dental implants for support of fixed dental prostheses could be endorsed in certain situations with solid albeit limited scientific support. In a wider sense, such prostheses could be used as a reliable therapy in all regions of the jaws. However the status of the abutment teeth in terms of periodontal support, pulpal status and risk for carious lesions and biomechanical complications should always be considered in relation to the long-term prognosis of the prosthesis. The conclusion was that teeth should not be extracted in favour of placing dental implants without a specific indication, and that tooth-implant supported prostheses should be considered as a viable prosthetic option.

An investigation of tooth/implant-supported fixed prosthesis designs with two different stress analysis methods: an in vitro study

PURPOSE

Tooth/implant-supported fixed prostheses (TIFPs) present biomechanical design problems, because the implant is rigidly anchored within the alveolus, and the tooth is attached by the periodontal ligament that allows movement. While TIFP designs with rigid connectors (RCs) are preferred by many clinicians, the designs containing non-rigid connectors (NRCs) are suggested as a method to compensate for these mobility differences. However, studies have failed to show the advantage of one design over the other. This study examined stresses formed around the implant and natural tooth abutments under occlusal forces, using two dimensional finite element (2D-FEM) and photoelastic stress analysis methods (PSAM).

MATERIALS AND METHODS

Connection of TIFP designs were investigated in distal extension situations using stress analysis interpreted with the 2D-FEM and PSAM. Three TIFP (screw type implant, 3.75 mm x 13 mm) models with various connection designs (i.e., rigidly connected to an abutment tooth, connected to an abutment tooth with an NRC, connected to an abutment implant with an NRC) were studied. The stress values of the three models loaded with vertical forces (250 N) were analyzed.

RESULTS

The highest level of stresses around the implant abutment was noted on the TIFPs with the RC. On the other hand, NRCs incorporated into prostheses at the site of the implant abutment reduced the level of stresses in bone.

CONCLUSION

It could be suggested that if tooth and implant abutments are to be used together as fixed prostheses supports, NRCs should be placed on the implant abutment-supported site.

Analysis of strain around endosseous dental implants opposing natural teeth or implants

STATEMENT OF PROBLEM

Natural teeth and implants have different force transmission characteristics to bone.

PURPOSE

The purpose of this study was to compare strains induced around a natural tooth opposing an implant with strains around occluding implants under static and dynamic loads.

MATERIAL AND METHODS

Occlusion was created between a natural molar tooth and an implant in 1 side, and 2 implants in the contralateral side of acrylic resin models of both jaws. Strain-gauges were bonded around the neck of the natural tooth and implants, and strains were measured under 75 N and 100 N static axial and lateral dynamic loads in separate load situations using a data acquisition system at sample rate of 1000 Hz. The strain data of the natural tooth and implants were compared for each load by Kruskal-Wallis testing followed by the multiple comparison test (alpha=.05).

RESULTS

Compressive strains were induced around natural tooth and implants as a result of static axial loading, whereas combinations of compressive and tensile strains were observed during lateral dynamic loading. Strains around the natural tooth were significantly lower than the opposing implant and occluding implants in the contralateral side for most regions under all loading conditions ( P <.05). There was a general tendency for increased strains around the implant opposing natural tooth under higher loads and particularly under lateral dynamic loading ( P <.05).

CONCLUSION

Under static and dynamic loads, strain magnitudes around a natural tooth were significantly lower than that of an opposing implant and occluding implants in the contralateral side.

Tooth-implant connection: some biomechanical aspects based on finite element analyses

This study investigated, with the use of two- and three-dimensional finite element analysis, the peri-implant stress that occurred during loading of a tooth that was rigidly connected to a distally placed implant. A fixed bond between the bone and the implant was assumed, while the periodontal ligament was represented by means of three-dimensional nonlinear visco-elastic spring elements. Two different loading conditions were compared in the study: i) an axially directed static load of 50 kg that was applied to the tooth for 10 s, and ii) a transitional load of 50 kg that was applied for 5 milliseconds. Load duration appeared to have a greater influence than load intensity on the stress distribution in the bone around an implant and a rigidly connected tooth. Static load is, therefore, potentially more harmful for peri-implant bone than transitional load. The periodontal ligament seems to play a key role in the stress distribution between a tooth and a rigidly connected implant.

Long-term evaluation of single crystal sapphire implants as abutments in fixed prosthodontics

49 patients participated in a prospective study of treatment of total or partial edentulism with fixed prosthodontics supported by Bioceram sapphire implants. 15 patients were treated for maxillary or mandibular edentulism, and 7 for a missing maxillary anterior tooth. The remaining 27 patients, with Applegate-Kennedy Class I-IV residual dentitions, were treated with fixed bridges supported by free-standing implants, or bridges supported by teeth and implants. Implant success, prosthesis stability, radiographic marginal bone level as well as parameters for peri-implant health were evaluated. The study began in 1982, and clinical treatment of the last patients was completed in 1988, i.e., a follow-up period ranging from 7 to 13 years. Of the patients treated for total mandibular edentulism, one implant fractured after 6 years in situ. The bone implant score (BIS) values for those implants were at the time for the bridge cementation 63.5 +/- 1.4 and at 1, 2, 3 and 5 year follow-ups 62.1 +/- 1.4, 61.9 +/- 1.5, 61.5 +/- 1.6, and 60.95 +/- 1.3, respectively. The success rate was 100%, 100% and 97.7% for the mandible at 3, 5 and 10 years, respectively. Of the 7 edentulous patients treated with maxillary fixed bridges, 6 implants in 1 patient had to be removed after 1 year in service. Another 2 patients lost all their implants, 6 each, after 36 months. 6 implants in the 4th patient did not fulfil the criteria for success and were rated as failures at the four year follow-up. The success rate was thus 58.1%, 44.2% and 44.2% for the maxilla at 3, 5 and 10 year follow-ups, respectively. Of the 7 patients in whom single missing teeth were replaced, 1 implant in the premolar region was lost during the 1st year post-operatively, but no other complications or changes in BIS were observed. Of the 27 patients treated for partial edentulism (56 implants total) 1 implant, of a 4-unit free standing maxillary bridge fractured after 6 years and was later replaced. There were no statistically significant differences in BIS changes for the implants when used as abutments for partial maxillary or mandibular edentulism. The cumulative success rates for the implants in the partially maxilla were 96.3, 92.6 and 92.6 at the 3, 5 and 10 years respectively and 100% in the mandible over the whole period.