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Table of Contents   
ORIGINAL RESEARCH  
Year : 2013  |  Volume : 24  |  Issue : 2  |  Page : 178-182
Connector design in a long-span-fixed dental prosthesis: A three-dimensional finite element analysis


1 Department of Prosthodontics, M. S. Ramaiah Dental College and Hospital, M. S. R. I. T. Post, Bangalore, Karnataka, India
2 Department of Prosthodontics, V. S. Dental College and Hospital, Bangalore, Karnataka, India

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Date of Submission16-Oct-2011
Date of Decision01-Oct-2012
Date of Acceptance29-Nov-2012
Date of Web Publication20-Aug-2013
 

   Abstract 

Objectives: The goal of every prosthetic management is to simulate nature and be in harmony with nature within the physiological limits. The occlusal forces on a fixed dental prosthesis are transmitted to the surrounding structures through pontics, connectors and retainers and more stresses are seen at the connector region. To analyze the stress patterns in cast and soldered connectors between the two pontics and between the retainer and pontic of a four unit fixed dental prosthesis on axial and non axial loading and also to observe and ascertain the need to modify the design of the rigid connectors.
Materials and Methods: Subsequently four models each of cast and soldered connectors with cylindrical and triangular design, of dimension 3 × 4 mm and thickness 0.5 mm was designed for the study. The first premolar and second molar were considered as the abutments and 2 nd premolar and 1 st molar as the pontics. The analysis was done using ANSYS version 8.0 software and by placing axial and non-axial load of 40 Newtons each.
Results: Von Misses stresses were observed at the connector region between the two pontics, especially in the cervical region.
Conclusion: The cylindrical cast connectors showed less stress in comparison to triangular design and the difference in the stress distribution of cast and soldered connectors were marginal.
Clinical Significance: The occlusal forces on a fixed dental prosthesis are transmitted to the surrounding structures through pontics, connectors and retainers with maximum stresses concentrated at the connectors. Hence this three-dimensional finite element analysis study investigated stress distribution in a four unit posterior fixed dental prosthesis, having cylindrical and triangular connector designs.

Keywords: Connector designs, finite element analysis, fixed dental prosthesis

How to cite this article:
Harshitha Gowda B H, Satish Babu C L. Connector design in a long-span-fixed dental prosthesis: A three-dimensional finite element analysis. Indian J Dent Res 2013;24:178-82

How to cite this URL:
Harshitha Gowda B H, Satish Babu C L. Connector design in a long-span-fixed dental prosthesis: A three-dimensional finite element analysis. Indian J Dent Res [serial online] 2013 [cited 2020 Feb 25];24:178-82. Available from: http://www.ijdr.in/text.asp?2013/24/2/178/116673
The tools of nondestructive stress analysis especially finite element analysis has unfolded a new era in treatment planning and designing in areas hitherto considered as impossible to be evaluated clinically. Physiological forces of occlusion, mastication, and parafunction induce stresses in the connectors of the fixed dental prosthesis. [1] Therefore, due consideration should be given to the design, shape, size, fabrication techniques and position of the connectors. Hence, a study was undertaken to analyze the stress patterns in cast and soldered connectors with cylindrical and triangular design in a four unit fixed dental prosthesis on axial and non-axial loading.


   Objective of the Study Top


  • To study the stress patterns of cast and soldered connectors between
    1. Retainer and pontics
    2. Between the two pontics.
  • To study the stress patterns on
    1. Retainer
    2. Pontic
  • To observe and ascertain the need to modify the design of the rigid connectors.

   Materials and Methods Top


A three-dimensional finite element model of the dentulous maxilla was designed to evaluate the stress distribution. As the maximum mastication occur in the 2 nd molar region the forces are more in this region [2] thus the posterior segment was considered in this study.

A personal computer with the following configuration was used for the study,

Hardware: Pentium 4 processor, speed 21 Giga Hertz, MB RAM

Software: ANSYS 8.0 version.

The Poisson's ratio and modulus of elasticity of all the supporting and anatomic structures of the tooth (enamel, dentine, pulp, periodontal ligament, and bone), and of the alloys used for the fixed dental prosthesis were obtained from standard references [3],[4],[5],[6],[7] [Table 1] and [Table 2].
Table 1: Material properties of natural teeth for finite element analysis

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Table 2: Material properties of metals used for finite element analysis

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The height of the connectors was 3 mm × 4 mm and thickness 0.5 mm. [8],[9] The design of both the cast and soldered connectors were triangular and cylindrical based on the contact areas in natural dentition.

All the materials used in this finite element study were considered homogenous and isotropic. The models were hyper meshed and had 9851 elements and to 12830 nodes with three degree freedom in tetrahedral bodies. The Von Misses stresses were calculated throughout the structure.

The four different finite element models that were used for analyzing the stress patterns were as follows:

Experimental models

Model 1: The base metal fixed dental prosthesis with cylindrical cast connectors.
Model 2: The base metal fixed dental prosthesis with cylindrical soldered connectors.
Model 3: The base metal fixed dental prosthesis with triangular cast connectors.
Model 4: The base metal fixed dental prosthesis with triangular soldered connectors.

Analysis

The masticatory load of 40 Newton's (N), was applied both axially and non-axially at 45° inclinations.

The Von Misses stresses were studied using ANSYS solver. The stress distribution was plotted using the general post processor of ANSYS and the results represented in form of a [bar graph 1] [Additional file 1] and [bar graph 2] [Additional file 2].


   Results Top


The distribution of stresses in all the four finite element models are depicted by Von Misses stresses to axial and non-axial loading conditions. The maximum stresses were seen in the connectors between the two pontics in the cervical region. The stresses between the cast and soldered connectors showed marginal differences. The stresses between the premolar retainer and pontic were more than the molar pontic and retainer. Also, the stresses at the pontics were more than those at the retainers. The cylindrical design of the connector revealed less stress than the triangular design. The results are illustrated in the figures and bar graph.


   Discussion Top


The review of literature revealed lack of studies on the stresses induced at the connectors in cast and soldered joints. [10]

It also revealed that there were hardly any studies to analyze the stress induced in long-span fixed dental prosthesis in the connector region. [4],[11]

Studies on stress distribution on three unit fixed dental prosthesis revealed that the maximum stresses are seen in the connector region. [3],[12],[13],[14],[15],[16] Hence, a structurally sound design of the connector is necessary for a successful fixed prosthesis.

Earlier strain gauge analysis, [16] and photo-elastic stress analysis, [17],[18] studies were used to study the stresses at the connectors, but these studies were cumbersome, resulted in errors and did not provide information on internal strain formation, thus yielded less accurate results.

Most of the studies utilized average masticatory load [19],[20] for stress analysis so that the results would be easily deciphered. The connector height of 4 mm × 4 mm is ideal for the stress distribution. However, the complex anatomy of the teeth does not provide such large areas for the connectors. [1],[16],[21]

The general observation of the stresses induced on the fixed dental prosthesis in this study revealed that maximum stresses were present on the premolar abutment and connector region between pontics. Comparing the stresses between cast and soldered connectors for both axial and non-axial loading it was observed that there was a marginal difference. Also, the cylindrical design of connectors showed less stress than the triangular design.

The observation of this study presumes that cylindrical connectors are preferred. The limitation of this finite element study is that the model created was isotropic and homogenous in nature, unlike the bone and teeth which are anisotropic and hence the solutions are approximated.

Due to the singularity of elements, sometimes abnormal stresses are seen in particular regions which cannot be logically explained. The other limitation is cyclic loading which is repetitive in nature is very difficult to simulate in any mechanical model. Thus finite element analysis is unable to simulate oral conditions which are repetitive and cyclic in nature. This study cannot be subjected to statistical analysis.


   Conclusion Top


Within the limitation of this study the following conclusions are drawn:

The maximum Von Misses stresses are concentrated at the connector in between pontic regions.

The stresses are marginally more in cast connectors than soldered connectors for both axial and non-axial loading.

The stress at the first premolar abutment and the premolar pontic was more in all models.

Among the designs of the connectors, cylindrical connector showed less stress than triangular design in nearly all the models.

Model 1: in the base metal fixed dental prosthesis with cylindrical cast connectors the maximum stress on axial and non axial loading were at the connectors between the two pontics [Figure 1] and [Figure 2].
Figure 1: Stress distribution on cast cylindrical connectors on axial loading

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Figure 2: Stress distribution on cast cylindrical connectors on non-axial loading

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Model 2: in the base metal fixed dental prosthesis of cylindrical soldered connectors the maximum stress concentration is seen at the connectors between the two pontics on axial loading and also on non-axial loading [Figure 3] and [Figure 4].
Figure 3: Stress distribution in soldered base metal cylindrical connectors on axial loading

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Figure 4: Stress distribution in soldered base metal cylindrical connectors on non-axial loading

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Model 3: in base metal fixed dental prosthesis with casted triangular connectors maximum stresses are seen at the connectors between the two pontics on axial and non-axial loading [Figure 5] and [Figure 6].
Figure 5: Stress distribution on casted triangular connectors on axial loading

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Figure 6: Stress distribution on casted triangular connectors on non-axial loading

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Model 4: in the base metal fixed partial denture of soldered triangular connectors the maximum stresses are seen at the connectors between the pontics on axial loading and at the connectors between the two pontics and retainer and pontic on non-axial loading [Figure 7] and [Figure 8].
Figure 7: Stress distribution on soldered triangular connectors on axial loading

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Figure 8: Stress distribution on soldered triangular connectors on non-axial loading

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   References Top

1.Badwaik PV, Pakhan AJ. Non-Rigid connectors in Fixed Prosthodontics: Current concepts with a case report. J Indian Prosthodont Soc 2005;2:99-102.  Back to cited text no. 1
    
2.Winkler S. Essentials of complete denture prosthodontics, Ishiyaku Euro. America Inc. U.S.A.: 2 nd ed; 2000. p. 219-20.  Back to cited text no. 2
    
3.Yang HS, Chung HJ, Park YJ. Stress analysis of cantilevered fixed partial denture with normal and reduced bone support. J Prosthet Dent 1996;76:424-30.  Back to cited text no. 3
[PUBMED]    
4.Yang HS, Lang LA, Felton DA. Finite Element Stress analysis on the effect of splinting in fixed partial dentures. J Prosthet Dent 1999;81:721-8.  Back to cited text no. 4
[PUBMED]    
5.Ten A. R Cate, Oral Histology, Development, Structure and Function. 5 th ed. St. Louis, Missouri 63146: Harcourt Asia Pvt ltd; 1999. p. 122,150,219,254,256.  Back to cited text no. 5
    
6.Phillips RW. Skinners Science of Dental Materials. 11 th ed. St. Louis, Missouri 63146: Sounder's Publication; 2003. p. 56.  Back to cited text no. 6
    
7.Ash MM. "Wheeler's Dental Anatomy, Physiology and Occlusion." 8 th ed, St. Louis: Sounder's Publication; 2003. p. 58.  Back to cited text no. 7
    
8.Oh WS, Anusavice KJ. Effect of connector design on fracture resistance of Al-ceramic fixed partial dentures. J Prosthet Dent 2002:87:536-42.  Back to cited text no. 8
    
9.Omar R, Abduljabbar T, Al-Ali K, Smyth M, El- Aqouri R. Dimension of metal frame work components of metal ceramic fixed partial denture constructed in dental school sitting. Quintessence Int 2004;35:820-5.  Back to cited text no. 9
    
10.Cheng AC, Chai JY, Gilbert J, Jameson LM. Investigation of stiffness and micro-structure of joints with gas oxygen torch and Infra red method. J Prosthet Dent 1994;72:8-15.  Back to cited text no. 10
    
11.Goldstein GR, Wesson A, Schweitzer K, Cutler B. Flexion charesteristics of four unit fixed partial denture framework using halographic interferometry. J Prosthet Dent 1992;68:564.  Back to cited text no. 11
    
12.Augereau D, Pierrisnard L, Barquins M. Relevance of finite element method to optimize fixed partial denture design Part-I: Influence of the size of connector on magnitude of strain. Clin Oral Investig 1988;1:36-9.  Back to cited text no. 12
    
13.Sorensen JA, Kang SK, Torres TJ, Knode H. In ceram fixed partial dentures: Three year clinical trial results. J Calif Dent Assoc 1998;26:207-14.  Back to cited text no. 13
    
14.Oh WS, Gotzen N, Anusavice KJ. Influence of connector designs on fracture probability on ceramic fixed partial dentures. J Dent Res 2002; 81:623-7.  Back to cited text no. 14
    
15.Vasconcellos AB, Mori M, Silva M, Andueza A, Matos AB, Guimarres JG. Finite element analysis on metal ceramic and metal free fixed partial denture. Int Assoc Dent Res 2003.  Back to cited text no. 15
    
16.Du JK, Wang CH, Lee HE, Kung CM. Stress distribution of posterior resin bonded bridges. Int Assoc Dent Res 2003.  Back to cited text no. 16
    
17.Farah JW, Craig RG, Eden GT, Grossman DG. Two dimensional photo-elastic stimulation of a castable ceramic fixed partial denture. J Prosthet Dent 1988;59:8-12.  Back to cited text no. 17
    
18.Moulding MB, Holland GA, Sulik WD. Photo-elastic stress analysis of supporting alveolar bone as modified by non-rigid connectors. J Prosthet Dent 1998;59:263-74.  Back to cited text no. 18
    
19.Braun S, Bantleon HP, Hnat WP, Marcotte MR, Honigle K, Johnson BE. A study on bite force Part-I: Relationship to various physical characteristics. Angle Orthodont 1995;65:367-72.  Back to cited text no. 19
    
20.Braun S, Hnat WP, Freudenthaler JW, Marcotte MR, Johnson BE. A study on bite force Part-II: Relationship to various physical characteristics. Angle Orthodont 1996;66:261-4.  Back to cited text no. 20
    
21.Himmel R, Pilo R, Assif D, Aviv I. The cantilever fixed partial denture-a literature review. J Prosthet Dent 1992;67:484-7.  Back to cited text no. 21
    

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Correspondence Address:
B H Harshitha Gowda
Department of Prosthodontics, M. S. Ramaiah Dental College and Hospital, M. S. R. I. T. Post, Bangalore, Karnataka
India
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Source of Support: None, Conflict of Interest: None


PMID: 23965442

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    Figures

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