6 BRIEF RESUME OF THE INTENDED WORK
6.1 Need for the Study:
Rehabilitation of complete or partial edentulism with implant supported or implant retained prosthesis has became a well accepted treatment modality1. The material of choice has been and still is commercially pure titanium and its alloy, however they have certain aesthetic compromises2. Currently zirconia (YPSZ) is being considered where there is a high demand for aesthetics3.
The longevity of the implants primarily relies on the stability of the implant-bone interface1. The leading sign of implant failure is crestal bone loss which occurs after osseointegration. The bone loss is said to be mainly based on the type of implant, design of abutment, prosthesis, and the supporting alveolar bone. And hence there needs to be a design for comparative stress distribution in the prosthesis, abutment, type of implant and supporting alveolar bone under simulated occlusal force1. To investigate the influence of stress distribution in prosthesis, abutment, type of implant and supporting alveolar bone, a computer software model was developed to apply finite element analysis (FEA). Because the geometries involved with modeling implants and the alveolar process are very complex, FEA is viewed to be the most suitable tool available for analyzing them. This type of analysis allows researchers to predict stress distribution in the contact area between implants and cortical bone as well as around the apex of the implants in trabecular bone.
The purpose of this study is to investigate the stress distribution and its influence on the prosthesis, abutment, implant, and supporting alveolar bone on two types of commercially available dental implants one being titanium alloy and other is being zirconia(YPSZ) under simulated occlusal force.
REVIEW OF LITERATURE:
1. A study conducted to evaluate the influence of commercially available dental implant systems on stress distribution in the prosthesis, abutment, implant, and supporting alveolar bone under simulated occlusal forces, employing a finite element analysis. The implants and abutments evaluated consisted of stepped cylinder implant connected to a screw retained, internal, hexagonal abutment [system 1] and a conical implant connected to a solid, internal, conical abutment [system 2]. In each case, a simulated, 100-N vertical load to the buccal cusp. A finite element model was created based on the physical properties of each component, and the values of the stresses generated were calculated. In system 1 they found greater stress on the alveolar bone and prosthesis and lower stresses on the abutment complex. In contrast, the system 2 furnishes lower stresses on the alveolar bone and prosthesis as compared to that abutment.
2. A study conducted to analyze stress distribution pattern of the bone in Re-implant implants made of commercially pure titanium partially stabilized zirconia (YPSZ). By using Cosmos/M, version 1.65 FEA computer software the maxillary incssor was selected and subjected to oblique occlusal stresses. One was cpTi (grade2) Re-implant implant plus titanium post restored with a metal–ceramic crown. The second version was a YPSZ Re-implant implant plus YPZS post restored with an all-ceramic (empress-1) crown and the model had the maxillary incisor embeded in cortical and cancellous bone. Loads of 10 MPa20 were applied obliquely on the palatal surface at the middle third of the crown. A total of two models with 6,784 elements and 20,444 nodes were constructed. The element type chosen was a solid, 3-D, eight node, hexahedral element. Key regions were selected within the bone-to-implant junction for comparing models. The regions were: (1) the level where the implant enters the cortical bone, (2) within the cortical bone, (3) the cortical–to-cancellous-bone junction, and (4) the apical third of implant-to-bone junction.
For region 2 and 3 (within cortical bone and at the cortical-cancellous bone junction) and for both the models, stress distribution presented a pattern of alternating high-low stress areas. YPSZ showed low, well-distributed, favorable stress distribution patterns similar to titanium implants and can be characterized as favorable or nondestructive. Hence concluded that there are no important differences in resolved stresses between the two different implant-post-crown combinations and Re-Implant root analogue implants present a favorable stress distribution at bone-to-implant junction.
3. The study was to analyze and compare stresses in two different bone-implant interface conditions in anisotropic three dimensional finite element models (FEMs) of an osseointegrated implant of either commercially pure titanium or yatrium-partially stabilized zirconia (Y-PSZ) in combination with different superstructers, (gold alloy or Y-PSZ crown) in posterior maxilla. Three-dimensional FEMs were created of a first molar section of the maxilla into which was embedded an implant, connected to an abutment and superstructers, using commercial software. Two versions of the FEMs were constructed which were either bonded and or contact interface. Compact and cancellous bone were modeled as fully orthotropic and transversely isotropic, respectively. Oblique (200-N vertical and 40-N horizontal) occlusal loading was applied at the central and distal fossae of the crown. The result was maximum Von Mises and compressive stresses in the compact bone in the two interfaces were lower in the zirconia implant groups than in the titanium implant groups. A similar pattern of stress distribution in cancellous bone was observed, not only on the palatal side of the platform but also in the apical area of both type of implants. Hence concluded that biomechanical parameters of the new zirconia implant generated a performance similar to that of titanium implant in terms of displacement, stresses on the implant, and the bone-implant interface; therefore, it may be viable alternative, especially for esthetic regions.
4. This study uses computer simulations to examine clinical situations with IMZ implants in edentulous mandibles, and to identify loading conditions that could lead to bone microfractures. Three dimensional finite element analysis models were used to examine effects of (1) type of edentulous mandibles, (2) veneering materials, (3) the absence of cortical bone, (4) different intra mobile elements, (5) loading directions, and (6) loading levels. Stress distribution patterns were compared and interfacial stresses were monitored specifically at four heights along the bone-implant interface. Stresses were concentrated toward cortical bone (0.8 to 15.0 MPa). There were no differences between types of veneering materials and absence of cortical bone increased interfacial stresses and the use of titanium intramobile element decreased stresses. Oblique loads increased stresses 15 times, and 200 N loads increased stresses 10 times and hence conditions for bone microfracturing were associated with oblique loads, high occlusal stress magnitudes, and absence of cortical bone.
5. The three dimensional Finite Element Method was used to study the influence of porous coated surface topography of an implant on stress and strain distribution pattern in the cortical and cancellous bone during axial and non-axial loading. Two implants, one with porous surface topography and one with smooth surface were embedded in separate geometric models of posterior mandibular region which was generated using a CT scan data. Material properties and boundary conditions were applied. Load of 100 and 50 N were applied on to the abutment from axial and non-axial directions respectively. Porous surface topography appeared to distribute stress in a more uniform pattern around the implant with near absence of stress in the apical region of implant. The porous coated interface was considered to simulate the shock absorbing behaviour of periodontal ligament of natural dentition. Maximum amount of stress concentration was observed in the cortical bone which plays a major role in the dissipation of the stress.
6. A study conducted to evaluate the von mises, compressive, and tensile stresses occurring on the three different zirconia dental implants and surrounding bone with three dimensional finite element analysis. Three different zirconia implants 10 mm in length and 4 mm in diameter, and anterior maxillary bone were modelled using three-dimensional finite element analyses. zirconia implant placed in maxillary central incisor and loading was applied in horizontal and oblique axes.
The result, under oblique loading, von mises stress for all implants were similar under horizontal loading, the highest von mises stress was found at buccal and palatal region of the ziterion implant. They concluded that von mises, were higher in cortical bone compared to trabecular bone. Stress in z-system were higher than in other zirconia implants.
6.3 Objectives of the study
1. To investigate, in a model, and to evaluate the influence on two types of commercially available dental implants one is titanium alloy, another is zirconia(YPSZ), stress distribution in the prosthesis, abutment, implant and supporting alveolar bone.
Materials and Methods:
7.1 Source of data:
The finite element study model of the implant and surrounding bone will be fabricated with the given specifications by a computer software programe.
7.2 Method of collection of data:
The study will be conducted using three dimensional finite element model of a simulated osseointegrated endosseous titanium and zirconia implant in the anterior maxilla. Data acquisition is carried out by using CT techniques. ANSYS finite element analysis program will be used to generate the model.
7.3 DOES THE STUDY REQUIRE ANY INVESTIGATION OR INTERVENTION .TO BE CONDUCTED ON PATIENTS OR OTHER HUMANS, ANIMALS? IF YES PLEASE DESCRIBE BRIEFLY?
7.4 Has ethical clearance been obtained from your Institution in case of 7.3
8. LIST OF REFERENCES:
Kohal RJ, Papavasilious G, Kamposiora P, Tripodakis A, Strub JR. Three-dimensional computerized stress analysis of commercially pure titanium and yttrium-partially stabilized zirconia implants. The Int J prosthodont 2002;15(2):189-194.
Quaresma SET, Cury PR, Sendyk WR, Sendyk C. A finite element analysis of two different dental implants; stress distribution in the prosthesis, abutment, implant, and supporting bone. Journal of oral implantology 2008;34(2):1-6.
Chang CL, Chen CS, Yeung TC, Hsu ML. Biomechanical effect of a zirconia dental implant-crownsystem: A Three dimensional finite element analysis. Int J oral maxillofac implants 2012;27(4):49- 57.
Papavasiliou G, Kamposiora P, Bayen SC, Felton DA. Three-dimensional finite element analysis of stress-distribution around single tooth implants as a function of bony support, prosthesis type, and loading during function. J prosthet dent 1996;76(6):633-640.
Savadi RC, Agarwal J, Agarwal RS, Rangarajan V. Influence of implant surface topography and loading condition on stress distribution in bone around implants: A comparative 3D FEA. J Indian prosthodontic society 2011;11(4):221-231.
Caglar A, Bal BT, Aydin C, Yilmaz H, Ozkan S. Evaluation of stresses occurring on three different zirconia dental implants: Three-dimensional finite element analysis. Int J oral maxillofac implants 2010;25:95-105.
Schrotenboer J, Tsao YP, Kinariwala V, Wang HL. Effect of platform switching on implant crest bone stress: A finite element analysis. Implant dentistry2009;18(3):260-265.