The effectiveness of adding a supporting implant in stress distribution of long span fixed partial denture (three-dimensional finite element analysis)

Rami Shurbaji Mozayek; Mohammad Yamen Shurbaji Mozayek; Mirza Allaf; Mohammad Bassam Abouharb

doi:10.4103/0972-4052.176533

ORIGINAL ARTICLE

Year : 2016 | Volume : 16 | Issue : 3 | Page : 259-263

The effectiveness of adding a supporting implant in stress distribution of long span fixed partial denture (three-dimensional finite element analysis)

Rami Shurbaji Mozayek¹, Mohammad Yamen Shurbaji Mozayek², Mirza Allaf¹, Mohammad Bassam Abouharb³
¹ Department of Fixed Prosthodontics, Faculty of Dentistry, Damascus University, Damascus, Syria
² Department of Oral and Maxillofacial Surgery, Faculty of Dentistry, Damascus University, Damascus, Syria
³ Department of Mechanical Design, Faculty of Mechanical and Electrical Engineering, Damascus University, Damascus, Syria

Date of Submission	15-Sep-2015
Date of Acceptance	08-Nov-2015
Date of Web Publication	18-Jul-2016

Correspondence Address:
Rami Shurbaji Mozayek
Department of Fixed Prosthodontics, Faculty of Dentistry, Damascus University, Damascus
Syria

Source of Support: None, Conflict of Interest: None

Check

DOI: 10.4103/0972-4052.176533

Abstract

Context and Aims: Long span is seen in many clinical situations; treatment planning options of these cases are difficult and may require: Fixed partial denture (FPD), removable partial denture, or implant supported prostheses. Each option has its own disadvantages: Mechanical, patient relief, and cost, respectively. This article will evaluate the stress distribution of another treatment option, which is adding a single supporting implant to the FPD using three-dimensional (3D) finite element analysis.
Subjects and Methods: Three models, each consisting of 5 units, were created as following: (1) Tooth pontic pontic pontic tooth, (2) tooth pontic implant pontic tooth, (3) tooth pontic pontic implant tooth. An axial force was applied to the prostheses using 3D finite element method, and stress was evaluated.
Results: Maximum stress was found in the prostheses in all models, highest stress values in all shared components of the models were close. Stress in implants was less in the second model than the third one.
Conclusions: Adding a supporting implant in long span FPD has no advantages, whereas it has the disadvantages of complicating treatment and the complications that may occur to the implant and surrounding bone itself.

Keywords: Denture, finite element, long span, supporting implant

How to cite this article:
Mozayek RS, Mozayek MY, Allaf M, Abouharb MB. The effectiveness of adding a supporting implant in stress distribution of long span fixed partial denture (three-dimensional finite element analysis). J Indian Prosthodont Soc 2016;16:259-63

How to cite this URL:
Mozayek RS, Mozayek MY, Allaf M, Abouharb MB. The effectiveness of adding a supporting implant in stress distribution of long span fixed partial denture (three-dimensional finite element analysis). J Indian Prosthodont Soc [serial online] 2016 [cited 2021 May 13];16:259-63. Available from: https://www.j-ips.org/text.asp?2016/16/3/259/176533

Introduction

Fixed partial dentures (FPDs) replacing multiple missing teeth may be associated with more complications and higher failure rate.^[1] Many factors could influence the prognosis of such prostheses. For example: Parafunction, force direction, and span length. Thus, other treatment options are recommended such as implant-supported prostheses (ISP) or removable partial dentures (RPD).

Tooth-ISP (TISP) are also recommended by some authors for some selected cases.^{[2],[3],[4],[5],[6]} This article discusses a mechanical solution of supporting a long span fixed prostheses with an implant as a suggested new treatment option that can improve the mechanical support of poor prognosis prostheses and has a lower cost compared to a fully ISP.

There is a general agreement on the number of missing teeth that can be restored successfully; two abutment teeth could support two pontics as Tylman stated, Ante also implied: “The root surface area of the abutment teeth had to equal or surpass that of the teeth being replaced with pontics.”^[7] Another disadvantage of fabricating long span FPD is flexing under occlusal loads, which can lead to fracture of porcelain veneer, breakage of a connector, loosening of a retainer and an unfavorable tissue response. Flexing of FPD is related to span length and to the cube of the length to be more accurate, the longer the span the greater the flexing.^[1]

Due to previous reasons when totally ISP cannot be fabricated due to anatomical limitations or any other reasons a TISP could be considered.

Previous studies showed that the most important factor in TISP is loading conditions,^[8],[9],[10] bone type,^[9] connector design,^{[8],[11],[12]} and other factors such as teeth-implants configuration is not yet fully understood. The question this study discussing is: Does adding a supporting implant in long span FPD reduce stress?

To answer this question, virtual three-dimensional (3D) models were designed and studied by finite element method (FEM). This method is widely used in all fields, and nothing seems to be out of reach of FEA, nuclear reactor or teeth.^[13],[14]

FEM is a numerical method, which can virtually study any given problem by means of computer software. Problem domain is divided into small elements with simple geometry. Physical laws are then applied to each small element and an approximated solution for the entire system is obtained.^[15]

Subjects and Methods

A 3D model of a long span FPD was created using CAD software (SolidWorks ^® Premium 2011; Dassault Systèmes). The model represented cortical and spongy bone, teeth (dentine, cementum, pulp), periodontal ligament, and a nickel-chromium prostheses, which connected two natural teeth (as abutments) with three pontics in between.

The bone was represented as a block with a 3 mm layer of cortical bone at the neck of teeth and implants and a spongy bone beneath.^[16]

A first lower premolar was chosen to resemble the natural teeth to be able to generalize the outcome of the study for all teeth not only for one case with strict conditions. The premolar was constructed on average dimensions ^[17] [Table 1], cementum constructed to be gradually thicker till it reaches 0.23 at the apex, whereas periodontal ligament has a maximum thickness of 0.35 mm at the apex and minimum 0.1 mm at the mid of root (mean thickness 0.21 mm).^[18] The pulp was constructed on average dimensions also according to the distance from the apex ^[19] [Table 2]. The premolars were prepared for a 0.5 mm chamfer finishing line with 6° taper ^[1] [Figure 1].

Table 1: Dimensions of the modeled lower first premolar

Click here to view

Table 2: Lower first premolar pulp dimensions according to the distance from the apex

Click here to view

Figure 1: Schematic for lower first premolar which was used in the study

Click here to view

The resulted model was referred to by Tooth pontic pontic pontic tooth (TPPPT). In the same method, another two models were created: Tooth pontic implant pontic tooth (TPIPT) and tooth pontic pontic implant tooth (TPPIT); these two models represented adding a supporting implant in the edentulous area between the natural teeth abutments in two different positions for the implant. NobelSpeedy™ Replace (RP 4 × 11.5 mm) from Nobel Biocare was selected, these dimensions were selected to be in the range of the most used implants, which is between 10 and 12 mm for implant length,^[20] and 4.1–4.3 for diameter in the posterior region of mandible or maxilla.^[21] The abutment was NobelDirect™ posterior RP [Figure 2].{Figure 2}

Geometrical models were transferred to the finite element analysis software (ANSYS R.13; ANSYS, Inc., USA), and materials' mechanical properties were assigned as shown in [Table 3]; all materials were assumed to be homogenous isotropic linear elastic.

Table 3: Mechanical properties of the materials represented in the models

Click here to view

The contacts between all bodies were assumed to be bonded in order to prevent relative motion. The models were fixed supported from the bottom in order to allow the bone to bend under load.

An axil load was applied with a magnitude of 300 N,^[22] the loads were on the basis of ideal occlusion,^[17] for implants the load was on the center of its crown (centrally oriented contacts).^[23]

In all models, load was simulated and stress calculated in all of the models parts. Highest von-mises value in each component of the models was compared, and stress graduation was studied by color-coded map, where red is the highest values and blue is lowest.

Results

Tooth pontic pontic pontic tooth

Maximum stress (equivalent von-mises stress) was located in the prostheses especially in the connectors [Figure 3]. Generally, stress distribution was homogenous with some concentrations in the spongy bone at the apices of teeth, whereas the finishing line at the neck of teeth had the highest stress concentrations.

Figure 3: Equivalent von-mises stress in the tooth pontic pontic pontic tooth model

Click here to view

Tooth pontic implant pontic tooth

The cortical bone around the neck of the implant had some stress concentration but still the highest von-mises values were found in the connectors of the prostheses [Figure 4]. Other stress concentrations places were similar to the previous model in the spongy bone at the apices of teeth and at chamfer finishing line.

Figure 4: Equivalent von-mises stress in the tooth pontic implant pontic tooth model

Click here to view

Tooth pontic pontic implant tooth

This model had similar stress distribution to TPIPT model with some differences in the highest von-mises values in some components of the model, primarily the implant itself [Figure 5].

Figure 2: Schematic for NobelSpeedy™ Replace (RP 4 × 11.5 mm) which was used in the study

Click here to view

The highest von-mises value, in each component of the models, is listed in [Table 4].

Table 4: Maximum von-mises in all models' components (MPa)

Click here to view

Discussion

Tooth-implant connecting is still controversial, some studies advised not to connect because of the complications that may occur ^[24],[25] such as bone resorption and tooth intrusion, whereas other studies stated that TISP is an acceptable treatment option where ISP can't be fabricated.^{[2],[3],[4],[5],[6],[26],[27],[28]} Some authors accepted TISP but with special conditions as rigid connector ^{[5],[29],[30]} or good mesiodistal implant angulation.^[31] Special cases like the one this article is highlighting did not take enough studying, and its pros and cons are still unknown yet, the mechanical aspect of this case is discussed here.

The FEM is a virtual numerical analysis that can give acceptable and reliable results if the simulations' conditions were as accurate as possible. On the other hand, FEM is a subjective method that can give different outcome if different programmer “researcher” put his vision of the loading condition, materials properties, and boundary conditions. Therefor FEM cannot be a complete substitute for clinical studies, but it can more likely be a guide especially in cases that is hard to conduct or ethically not acceptable.

For this study, ideal conditions were assumed such as average dimensions as reported in the literature, 100% augmentation happened between the implant and bone, ideal occlusal contacts, and average axial occlusal force.

Comparing maximum von-mises values for all components of TPPPT model to the values of both TPIPT and TPPIT models showed no significant differences in shared components thus no advantages in the mechanical aspect was achieved for adding a supporting implant, this could be due to the fact that periodontal ligament is the damping part and adding an implant did not increase the overall area of the ligament and consequently did not give the desired profit.

Regarding to von-mises values in implants, we can conclude that the position of the implant played a significant role in stress value and distribution. TPIPT had lower von-mises values, and the reason may be decreasing the prostheses length whereas TPPIT had shorter prostheses from one direction but longer one from the other direction. This point could be illustrated as two levers with the implant being a shared fulcrum and teeth are the input force positions because of the mobility, which periodontal ligaments provide [Figure 6], and longer lever arm will result in more stress being concentrated around the fulcrum (implant).

Figure 6: Existing levers in models with an intermediate implant

Click here to view

The stress in implants may lead to complications in the implant system itself like screw loosening or even implant body fracture if significant force was applied as in bruxists. Hence, the supporting implant had no obvious mechanical advantages but will result in a more complicated treatment plan with more complications to worry about. Therefore, the author recommend not to use a supporting implant for long span FPD but instead using RPD or ISP are more acceptable treatment plans.

Conclusions

Within the limitations of this study, it can be concluded that:

The periodontal ligament plays a key role in damping loads and effectively reducing stress
Implant position is an important factor that practitioner can control
Avoiding TISP where possible is a better strategy
Long span with no indication for FPD is not a good candidate for TISP with implant as a supporting abutment
Long span with no indication for FPD is better treated with ISP or RPD.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

References

1.	Rosenstiel SF, Land MF, Fujimoto J. Contemporary Fixed Prosthodontics. 3^rd ed. Missouri: Mosby; 2001.
2.	Chen XP. Clinical observation of implant-natural tooth supported fixed partial denture for replacement of missing teeth in 86 patients. Shanghai Kou Qiang Yi Xue 2008;17:332-4.
3.	Akça K, Cehreli MC. Two-year prospective follow-up of implant/tooth-supported versus freestanding implant-supported fixed partial dentures. Int J Periodontics Restorative Dent 2008;28:593-9.
4.	Gunne J, Astrand P, Lindh T, Borg K, Olsson M. Tooth-implant and implant supported fixed partial dentures: A 10-year report. Int J Prosthodont 1999;12:216-21.
5.	Lindh T, Dahlgren S, Gunnarsson K, Josefsson T, Nilson H, Wilhelmsson P, et al. Tooth-implant supported fixed prostheses: A retrospective multicenter study. Int J Prosthodont 2001;14:321-8.
6.	Hosny M, Duyck J, van Steenberghe D, Naert I. Within-subject comparison between connected and nonconnected tooth-to-implant fixed partial prostheses: Up to 14-year follow-up study. Int J Prosthodont 2000;13:340-6.
7.	Shillingburg HT, Hobo S, Whitsett LD, Jacobi R, Brackett SE. Fundamentals of Fixed Prosthodontics. 3^rd ed. Canada: Quintessence; 1997.
8.	Lin CL, Wang JC, Chang WJ. Biomechanical interactions in tooth-implant-supported fixed partial dentures with variations in the number of splinted teeth and connector type: A finite element analysis. Clin Oral Implants Res 2008;19:107-17.
9.	Lin CL, Chang SH, Wang JC. Finite element analysis of biomechanical interactions of a tooth-implant splinting system for various bone qualities. Chang Gung Med J 2006;29:143-53.
10.	Menicucci G, Mossolov A, Mozzati M, Lorenzetti M, Preti G. Tooth-implant connection: Some biomechanical aspects based on finite element analyses. Clin Oral Implants Res 2002;13:334-41.
11.	Da Silva EF, Pellizzer EP, Quinelli Mazaro JV, Garcia Júnior IR. Influence of the connector and implant design on the implant-tooth-connected prostheses. Clin Implant Dent Relat Res 2010;12:254-62.
12.	Ozçelik T, Ersoy AE. An investigation of tooth/implant-supported fixed prosthesis designs with two different stress analysis methods: An in vitro study. J Prosthodont 2007;16:107-16.
13.	Geng J, Yan W, Xu W. Application of the Finite Element Method in Implant Dentistry. New York: Springer; 2008. p. 1-5.
14.	Karl M, Dickinson A, Holst S, Holst A. Biomechanical methods applied in dentistry: A comparative overview of photoelastic examinations, strain gauge measurements, finite element analysis and three-dimensional deformation analysis. Eur J Prosthodont Restor Dent 2009;17:50-7.
15.	Liu GR, Quek SS. The Finite Element Method: A Practical Course. Oxford: Butterworth-Heinemann; 2003. p. 1-11.
16.	Meijer HJ, Kuiper JH, Starmans FJ, Bosman F. Stress distribution around dental implants: Influence of superstructure, length of implants, and height of mandible. J Prosthet Dent 1992;68:96-102.
17.	Nelson SJ, Ash MM. Wheeler's Dental Anatomy, Physiology, and Occlusion. 9^th ed. China: Saunders; 2010.
18.	Carranza FA, Bernard GW. The tooth-supporting structures. In: Newman MG, Takei HH, Carranza FA, editors. Carranza's Clinical Periodontolgy. 9^th ed. United States of America: Saunders; 2002. p. 35-57.
19.	Vertucci FJ. Root canal morphology and its relationship to endodontic procedures. Endod Topics 2005;10:3-29.
20.	Belser U, Buser D, Bernard JP. Implants in the load carrying part of the dentition. In: Lindhe J, Karring T, Lang NP, editors. Clinical Periodontology and Implant Dentistry. 5^th ed. Slovenia: Blackwell Munksgaard; 2008. p. 945-79.
21.	Hebel KS, Gajjar R. Anatomic basis for implant selection and positioning. In: Babbush CE, editor. Dental Implants the Art and Science. 2^nd ed. Ohio: Saunders; 2010. p. 85-103.
22.	Craig RG, Powers JM. Restorative Dental Materials. 11^th ed. Missouri: Mosby; 2002.
23.	Prashanti E, Sumanth K, Reddy J. Components of implant protective occlusion – A review. Internet J Dent Sci 2008;7:1-5.
24.	Naert IE, Duyck JA, Hosny MM, Van Steenberghe D. Freestanding and tooth-implant connected prostheses in the treatment of partially edentulous patients. Part I: An up to 15-years clinical evaluation. Clin Oral Implants Res 2001;12:237-44.
25.	Naert IE, Duyck JA, Hosny MM, Quirynen M, van Steenberghe D. Freestanding and tooth-implant connected prostheses in the treatment of partially edentulous patients Part II: An up to 15-years radiographic evaluation. Clin Oral Implants Res 2001;12:245-51.
26.	Saker R. Clinical Study of the Prognosis of Implants-tooth Connected with Bridges. Master Thesis: Damascus University, Syria; 2011.
27.	Pesun IJ, Steflik DE, Parr GR, Hanes PJ. Histologic evaluation of the periodontium of abutment teeth in combination implant/tooth fixed partial denture. Int J Oral Maxillofac Implants 1999;14:342-50.
28.	Akça K, Uysal S, Cehreli MC. Implant-tooth-supported fixed partial prostheses: Correlations between in vivo occlusal bite forces and marginal bone reactions. Clin Oral Implants Res 2006;17:331-6.
29.	Mamalis A, Markopoulou K, Kaloumenos K, Analitis A. Splinting osseointegrated implants and natural teeth in partially edentulous patients: A systematic review of the literature. J Oral Implantol 2012;38:424-34.
30.	Hoffmann O, Zafiropoulos GG. Tooth-implant connection: A review. J Oral Implantol 2012;38:194-200.
31.	Ormianer Z, Brosh T, Laufer BZ, Shifman A. Strains recorded in a combined tooth-implant restoration: An in vivo study. Implant Dent 2005;14:58-62.