Indian Journal of Dental Research

ORIGINAL RESEARCH
Year
: 2013  |  Volume : 24  |  Issue : 4  |  Page : 423--427

Finite element stress analysis on the influence of cuspal angle and superstructure materials in an implant-supported prosthesis


G Lambodaran1, N Gopi Chander2, M Vasantakumar2,  
1 Department of Prosthodontics, Meenakshi Ammal Dental College and Hospital, Vanagaram, Chennai, Tamilnadu, India
2 Department of Prosthodontics, SRM Dental College, Ramapuram, Chennai, Tamilnadu, India

Correspondence Address:
N Gopi Chander
Department of Prosthodontics, SRM Dental College, Ramapuram, Chennai, Tamilnadu
India

Abstract

Purpose: To investigate the effect of superstructure materials and cuspal angle in an implant-supported fixed partial denture. Materials and Methods: This finite element analysis study was carried out with varying cuspal angulations of 0°, 20° and 33° and superstructure materials. The simulated models were loaded with 300N forces under different axial and non-axial angulations. The graphical and numerical stresses were investigated. Results: The results demonstrated that the maximum stress occurred in the metal framework in all the materials except acrylic, for which it occurred in the coronal part of the implant. In the acrylic, the maximum stress recorded was 78 MPa with the 20° angulation. Ni Cr recorded a maximum stress of 111 MPa with the 33° angulation. Conclusion: The cuspal morphology and type of superstructure material plays a pivotal role in controlling the stress transferred to the implant and the supporting bone.



How to cite this article:
Lambodaran G, Chander N G, Vasantakumar M. Finite element stress analysis on the influence of cuspal angle and superstructure materials in an implant-supported prosthesis.Indian J Dent Res 2013;24:423-427


How to cite this URL:
Lambodaran G, Chander N G, Vasantakumar M. Finite element stress analysis on the influence of cuspal angle and superstructure materials in an implant-supported prosthesis. Indian J Dent Res [serial online] 2013 [cited 2019 Oct 23 ];24:423-427
Available from: http://www.ijdr.in/text.asp?2013/24/4/423/118384


Full Text

The success of implant-supported prosthesis is influenced by many factors. The material of the superstructure, design of the fixture, cantilever length, mechanism of bone implant interface and occlusion play a significant role. [1] Among these factors, occlusal loading of implants plays a major part in the long-term success of an implant treatment. [2] Lindquist et al.[3] and Weinberg and Kruger [4] affirmed the role of occlusion in controlling the stress concentration on an implant-supported prosthesis.

The selection of an optimal occlusal surface material for implant-supported prosthesis showed varied results. Skalak [1] and Holst et al.[5] demonstrated that the resiliency of acrylic resin can act against overstress and microfracture of the bone-implant interface. Davis and Rimrott [6] reported that porcelain reduced the stress in the bone-implant interface under static loading. Sergotz et al.[7] revealed that the cobalt-chromium framework and the porcelain occlusal surface was the most favorable combination for implant-supported restoration. Bassit [8] and Cibirka et al.[9] confirmed that different occlusal surface materials do not produce diverse stresses on implants. This study was initiated to examine the hypothesis that different superstructure materials might affect stress transmission on implant and supporting bone under functional forces.

 Materials and Methods



A 3D finite element model of Misch [10] D2 mandibular bone with 24.2 mm height and 40 mm width with missing second premolar, first molar, second molar and its superstructures were replicated in this study. A single-stage, cylindrical, threaded 4.1 mm × 13 mm dental implant system for the second premolar region and 4.1 mm × 13 mm for the second molar region were modeled for this study. The implant and its superstructure with cuspal angulations of 0°, 20° and 33° were simulated using the finite-element (Pro/Engineer 2000i) software [Figure 1], [Figure 2] and [Figure 3]. Five different superstructure materials used for analysis were heat-polymerized acrylic (Sample A), gold porcelain crown design (Sample B), base metal (Ni Cr) crown design (Sample C), porcelain-fused base metal (Ni Cr) crown design (PFBM) (Sample D) and in-Ceram porcelain crown design (Sample E). Porcelain and metal thicknesses used in this study were 0.8-2 mm. Luting cement space was ignored due to negligible properties in FEM. All materials used were considered to be linear, elastic, homogeneous and isotropic. The average of the mechanical properties, such as Youngs modulus and Poisons ratio, were considered for the study and are listed in [Table 1]. [10],[11] Bone-implant contact and implant abutment junctions were rigidly connected to replicate osseointegration. Fifty thousand three hundred and twenty-seven elements and 91770 nodes were created, and the models were constrained in all directions at the nodes. A vertical force of 300 N was applied on three points: 100 N on the buccal cusp, 100 N on the mesial fossa and 100 N on the distal fossae [Figure 4]. Static forces were applied and Von Mises stress was documented. Stress values were appraised for each type of material for the three different cuspal angulations. The highest stress value obtained from the models was visualized and recorded.{Table 1}{Figure 1}{Figure 2}{Figure 3}{Figure 4}

 Results



The observed stress values are listed in [Table 2]. The interpretation of the analysis showed that the maximum stresses occurred at the cervical region of all the superstructure materials, irrespective of the cuspal angulations, except for Sample A, where it occurred in the coronal part of the implant. Sample A superstructure had the maximum stress of 111.2 Mpa for the 33° cuspal angulations [Figure 5]. The maximum stress values recorded for Samples B, C, D and E were 140.45 Mpa, 198.3 Mpa, 183.04 Mpa and 157.87 Mpa, respectively [Figure 6], [Figure 7], [Figure 8] and [Figure 9].{Table 2}{Figure 5}{Figure 6}{Figure 7}{Figure 8}{Figure 9}

 Discussion



Biomechanical considerations were recognized as the most important factors for the long-term success of implant-supported restorations. [11],[12],[13] Ciftci, [14] and Gracy et al.[15] stressed the importance of the occlusal considerations on implant restorations. The significance of occlusal materials and cuspal angle were evaluated in this study with the objective of examining the hypothesis that different superstructure materials may affect the stress transmission on an implant-supported fixed partial denture.

The finite element method was used in this study because of its superiority in computer programming methods, computational power and digital imaging technique. [16] The posterior mandibular region (35, 36, 37) was simulated in this finite element analysis study because occlusal forces are more concentrated in this region and, being a load-bearing region, more stress can be anticipated in this partially edentulous region. [17] The Noble replace tapered groove of regular platform was used to have a more standardized study protocol. A force of 300 N was applied at the centric stop points [18] and the stresses were evaluated for different cuspal angulations of 0, 20 and33 degrees and different superstructure materials. For effective evaluation, the stresses were analyzed in the various positions of bone, implant and superstructure (occlusal surface, framework, connector), and the highest stress value observed in the model was documented.

The results showed that the maximum stresses were recorded on the framework in all the materials except for acrylic, in which it was recorded on the implant. The lower elastic modulus of the resins (2.4 Gpa), [19] compared with gold and porcelain, have produced a larger bending of the prosthesis and, consequently, greater bending of the implants toward the pontic thus leading to areas of concentrated stress on the implant and, to a lesser extent, in the cortical bone. [19] The stress transmission to the implant by acrylic prosthesis favors the concept of progressive loading, in which it is considered that a minimum amount of stress is necessary for bone remodeling and osseointegration. [20],[21],[22]

The differences in the stress values among the various materials can be attributed to the difference in the elastic modulus of the different materials, with the rigid materials transferring minimal stress. The metal ceramic and Ni Cr frameworks were more resistant to deformation because of their superior mechanical properties, and the structural differences in frameworks in turn affected the stress distribution in implant structure and bone. [11] Benzing et al.[23] have stated that the rigidity of the superstructure material had an influence on the bone stress concentration and that use of a material with low elastic modulus induced a high risk of mechanical overloading. The stress value observations were similar to those reported in the study done by Papavasiliou et al., [24] Bassit [8] and Cibirka et al. [9] This study indicated that different stress values were obtained but that they did not have any marked significance. All models demonstrated concentration of stresses at the abutment crown junction. A similar pattern of stress was also reported in other FEA of loaded implants with or without superstructure. [25],[26],[27],[28],[29],[30],[31] The location of the stress is consistent with the findings from experiments and clinical studies that demonstrated that bone loss begins around the implant abutment crown interface. [32],[33],[34],[35] These findings support the theory that high stress from inadvertent loading could lead to bone resorption around the implant collar. [33],[34],[35],[36],[37]

With different cuspal angulations in all the models, the stress values increased with an increase in the cuspal angulation. The 33° angulation produced the maximum stresses, which denotes that inclination of cusps generates more stress to the implant.

 Conclusion



Within the parameters, design and limitations of the analyses, the following conclusions were made:

The maximum stress occurred at the framework in all the materials except acrylic, in which it occurred on the implant.In the framework, maximum stress was recorded at the abutment-crown interface.Increased cuspal angulation resulted in greater stress.Using a rigid superstructure material will transfer minimal stress to the implant and the supporting bone.By minimizing the cuspal inclination, lesser stress will be transferred.Although there are variations in the stress values among the different materials, none of them recorded a stress that would be detrimental on the implant and the supporting bone.The designing of the occlusal morphology plays a significant role in the stress transmission to the implant and supporting bone.

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