


ORIGINAL ARTICLE 

Year : 2020  Volume
: 10
 Issue : 1  Page : 3544 

Design and analysis of tooth abutment implant
Shailja Awasthi, Vinay Pratap Singh
Department of Mechanical Engineering, HBTU, Kanpur, Uttar Pradesh, India
Date of Submission  19Mar2019 
Date of Acceptance  26Apr2019 
Date of Web Publication  08Jul2020 
Correspondence Address: Dr. Vinay Pratap Singh Department of Mechanical Engineering, HBTU, Kanpur, Uttar Pradesh India
Source of Support: None, Conflict of Interest: None  Check 
DOI: 10.4103/jdi.jdi_8_19
Abstract   
In human being, tooth loss is a common problem which may be due to various disease and trauma. Dental implants are used to provide support for the replacement of missing teeth. Research on dental implant designs, materials, and techniques is continuously increasing. There is still a lot of work involved in the use of better biomaterials, implant design, surface modification, and functionalization of surfaces to improve the longterm benefits of implant treatment. This paper provides a brief history of dental implants and its parts. This describes the new designs and conventional design of tooth abutment implant and stress distribution using finite element analysis method on the surface of the whole system under various loading conditions. It describes the suitable materials and its properties which can be used for making tooth abutment implant. This also describes how to remove complexities which is associated with tooth abutment implants such as its motion, complex design of screw, and high cost. Background: The attempts to overcome the problem of tooth loss and to find out a way of replacing missing teeth date back to as old as the history of human beings. Many materials, many geometric forms, surgical and prosthetic methods have been tried till now for the dental implants. Scarcely existing archeological reports demonstrate the attempts of different prosthetic devices used as natural and functional replacements. It is found that transplantation procedures and devices are used by Egyptians, Greeks, Romans, Chinese, Indians and Arabs. Furthermore naive artificial units such as shaped stone, wood, cast iron and carved sea shells, bone and natural teeth taken from various animals and even teeth sold by the poor or slaves have been tried as implantation material. A tooth shaped piece of shell is found by an archeologists which is placed into the socket of missing teeth of a women in 1931. Later, in 1970, a Brazilian dental academic, Amadeo Bobbio, investigated that mandibular specimen and in the radiographs he took, he observed bone formation around the implantlike structures. In 18^{th} century, humans donated their teeth in exchange for some fee but human's body precluded the adaptation of foreign materials. Le Mayeur implanted one hundred and seventy donated teeth in 1785 and 1786 but he was not able to get successful results. In 19^{th} century, predicating on a false assumption that precious materials would be well tolerated by biological tissues, gold, silver, platinum and some other metal alloys were used as implant materials, which resulted in extremely poor longterm results. The human's body reject these type of material basically because they were not inert. Venable et al. (1937) found that the metals that are not inert they tend to ionize when they come into contact with body resulting in producing metallic salts causing excessive proliferation of some tissues whereas inhibiting bone formation. The prevention of bone formation around the implant leads to failure of the implantation. The modern breakthroughs in dental implantology emerged as a result of socalled serendipity of a Swedish orthopedic surgeon, Dr. Branemark, in 1952. While studying bone healing and regeneration around 'the rabbit ear chamber', which was a chamber of titanium designed and developed as a part of research conducted in Cambridge University, he observed in microscopic level that bone had grown around titanium surface in so close proximity that he was unable remove the chamber form the rabbit femur. Dr. Branemark investigated this phenomenon through further studies on animal and volunteer human tissues, which all contributed to unveiling the biocompatible properties of titanium. Having initially been considered to be appropriate for applications in the field of orthopedics such as knee or hip surgery, later titanium is realized to be utilized as anchorage for dental prosthesis and artificial crowns. The first titanium implant was inserted into the jawbone of a human volunteer, Gosta Larsson, for providing an artificial root for prosthetic teeth. Also, in 1967, Leonard Linkow presented his bladeform titanium implants providing mechanical stability and function for partial and complete dentures. In 1970 to 1980 many experimental studies were carried out to obtain better designs and geometric forms for titanium dental implants some of which are the IMZ Implants, TPS Implants, ITI HollowCylinder Implants. Throughout this period, Dr. Branemark continued his research and in 1971 he introduced titanium hollow screw implants which resulted in increased success rate, clinical applicability and reduced rate of complications compared to bladeform implants. In 1978, he established a commercial partnership with a Swedish defense company, Bofors AB. In 1981, based on the partnership, Nobel Biocare, one of the largest current dental implant producers in the world, was founded with the aim of focusing directly on dental implantology. In the year 1982, the Toronto Conference on osseointegration in Clinical Dentistry set the first guidelines for successful implant dentistry. The successful integration of hollow screw geometry into bone and high biocompatible characteristics of titanium resulted in that screw form dental implants have become the preferred method of tooth replacement and a standard dental treatment technique. Providing a high rate of success and a wide range of restorative options, today, dental implants, under various brand names, are extensively used worldwide. Current studies are mainly focused on improving aesthetics, reducing healing period and simplifying the use of dental implants. Objectives: Based on the previous work it was observed that the current dental implant suffers from several shortcomings. In order to minimize these shortcomings several objectives are as follows. 1. Make a novel design of tooth abutment implant without using screw because the manufacturing process of screw of small part is difficult and costly. 2. Model the new improved tooth abutment implant and subject it to working load. 3. Model the implant considering cost minimization of tooth abutment implant. 4. Analyze and validate the results of stress analysis. Materials and Methods: Here Titanium alloy is used for making new designs because it has better biocompatibility, bonding strength, high corrosion resistance and it prevents to fracture. Solidworks software is used for modeling and ANSYS software is used for analysis. Results: VonMises stress distribution is calculated under normal load and maximum load on the top surface of the abutment of conventional design and new designs. Conclusions: After comparing the stress distribution of all the new designs with conventional design and ultimate strength of titanium alloy found the best design of tooth abutment implant.
Keywords: Dental implant, endosteal root form, tooth
How to cite this article: Awasthi S, Singh VP. Design and analysis of tooth abutment implant. J Dent Implant 2020;10:3544 
Introduction   
Tooth abutment implants play an important role in prosthodontics and restorative dentistry since the early 1970s.^{[1]} Tooth abutment implant is a type of endosteal dental implant which is classified on the basis of implant design.^{[2]} When some problem occurs in the second premolar tooth of the human being and replacement is require then tooth abutment implant is used as a root and place crown above it. There are three parts of this dental implant these are abutment, implant, and screw.^{[3]} Here screw is used for combining the remaining two parts (abutment and implant). Crown is mounted on the abutment, and implant remains fix in the jaw bone. The success and failure of the implant mainly depend on the osseointegration but there are some other factors which also affect the success of the implant such as bone loss, implant design, implant parameter, and surface properties. One of the reasons for implant failure is occlusal overload or fatigueinduced micro damage.^{[4]} Implants may also fail due to the bone loss which are present surrounding the implant.^{[5]} Bone loss mainly starts from the crestal area of the cortical bone, and it can progress towards the apical region.^{[6]} There are so many factors which affect the stress field around the osseointegrated dental implant such as type of loading (vertical, horizontal or oblique), biomechanical factors, properties of the material which is used for making dental implant, macroscopic body design, and surface properties.^{[7],[8]} In the present work model design of tooth abutment are being analyzed without the use of costly screw which used in conventional abutments. Material for abutment is considered as titanium alloy as it has better biocompatibility, bonding strength, high corrosion resistance, and it prevents to fracture. Titanium alloy is also a homogenous, isotropic and linearly elastic material. Solid works is use for making modeling of the tooth abutment implant and finite element method (Ansys 14) is use for analysis.^{[9]} In the proposed design screw is not considered which makes the tooth implant costly due to machining process required for its manufacturing. In addition, screwed tooth implant becomes loose after some time of usage. New implant design is being designed and modeled to overcome these shortcomings. Here we calculate vonMises stress because we want to calculate its plastic deformation. After modeling we do the analysis. During analysis we apply different type of loading and find out the best design on the basis of stress distribution. Load may be vertical, horizontal or oblique depends on the position of the jaw. Horizontal load generate greater stress than the oblique load and oblique load generate greater stress than the vertical load. Many studies shows that overloading^{[6]} and oblique loading^{[10]} should be considered very important factors in the loss of osseointegration of dental implant which become the main reason of implant failure.^{[11],[12]} The purpose of this study is also to find the effect of external loading under various inclinations on the stress distribution in the dental implant using finite element analysis.
Materials and Methods   
Material for implant
Dental implant materials are selected on the basis of mechanical properties as well as its biocompatibility. Dental implants are subjected to high level of mechanical loads during chewing and biting action. Several studies reported that the maximum value of the human bite force is found to be approximately 760 N and the normal chewing force is in the range of 70–150 N^{[13]} depending on the location of the tooth on the jaw. Titanium alloy is selected for fabricating of the new design of the implant abutment system as this material is highly biocompatible, corrosion resistant, and possess better mechanical properties. The value of properties of titanium alloy are shown in [Table 1].
Procedure for modeling and analysis
Solid works software is used for making the threedimensional model of the new design, and then finite element analysis (ANSYS Software) is performed for the analysis of the proposed designs.
Procedure for finite element analysis
 Preprocessing – In the preprocessing stage, geometric properties, material properties, element type, boundary condition, and input parameter such as load are defined
 Solution – Compute the unknown parameter such as vonMises stress and principal stress
 Postprocessing – Postprocessor software contains sophisticated routines used for sorting, printing, and plotting selected results from a finite element solution
Boundary conditions
It is considered that both the implant and abutment models have homogeneous, linear elastic, and isotropic mechanical properties and are made of titanium alloy. The models were constrained in X, Y, and Zdirections on the implant surface.
Loading
In order to simulate the biting and chewing action of teeth, three different loads are considered. During chewing and biting the force act from a different direction it may be vertical, horizontal and oblique. Hence, apply the different load from different inclination and calculate the stress distribution on the implant abutment system for each design. First choose 135 N load for normal condition, and then 760 N which is approximate maximum vertical load and then find the stress at normal condition under 100 N load at different angle. An average chewing load of 100 N is considered at different angle such as 0°, 15°, 30°, 45°, and 60°.
Designs of tooth abutment implant
[Figure 1](a) shows the conventional design of tooth abutment implant and then four new model designs of tooth abutment implant without screw is being proposed and analyzed.  Figure 1: (a) Conventional design of tooth abutment implant. Parts of design 1: (b) Implant, (c) Abutment, (d) Assemble design 1. Parts of design 2: (e) Implant, (f) Abutment, (g) Cylindrical threaded part, (h) Assemble design 2. Parts of design 3: (i) Implant, (j) Abutment, (k) Assemble design 3. Parts of design 4: (l) Implant, (m) Abutment, (n) Assemble design 4
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Design 1
It consists of two parts in which first is implant and second is abutment as shown in [Figure 1]b and c. The implant consists of internal thread in the inner part and abutment consists of external thread on the lower part. After joining these two parts, a new design will form which is shown in [Figure 1]d.
Design 2
It consists of three parts implant, abutment, and cylindrical threaded part as shown in [Figure 1]e, [Figure 1]f, [Figure 1]g. Implant consist external thread on the upper part in 2 mm and external thread on the abutment as shown in the figure and internal thread on the cylindrical part. These external threads of the implant and abutment will combine with the internal thread of the cylindrical threaded part and form a new design which is shown in [Figure 1]h.
Design 3
There are two parts of this design implant and abutment as shown in [Figure 1]i and [Figure 1]j. It consists of the groove in the implant and key in abutment by pressing join these two parts and then get a new design which is shown in [Figure 1]k.
Design 4
It consist of two different parts implant and abutment as shown in [Figure 1]l and m when combine these two parts then a new design will form which is shown in [Figure 1]n. Implant and abutment consist of internal and external thread both. The internal thread of the implant will combine with the external thread of the abutment and external thread of the implant will combine with the internal thread of the abutment.
Results and Discussion   
vonMises stress distribution under 135 N load vertically, horizontally, and obliquely at 45° and under maximum vertical approximate load 760 N on the top surface of the abutment of design 1 is shown in [Figure 2]  Figure 2: (a) Force direction, (b) vonMises stress distribution on design 1 under 135 N vertical load, (c) Force direction, (d) vonMises stress distribution on design 1 under 135 N horizontal load, (e) Force direction, (f) vonMises stress distribution on design 1 under 135 N oblique load at 45°, (g) Force direction, (h) vonMises stress distribution of design 1 under 760 N vertical load
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The value of maximum vonMises stress, under 135 N load on the top surface of the abutment on design 1 vertically, horizontally, obliquely at 45° are 947.51, 4364.6, 3700.4 MPa, respectively. The number of nodes and elements are 191,078 and 114,011, respectively, and when applying the 760 N force on the top surface of the abutment in design first then the maximum vonMises stress is 5334.1 MPa, this maximum value of stress occur at abutment top surface and mostly at the interface of the implant and abutment.
vonMises stress distribution when applying 135 N load vertically, horizontally, and obliquely at 45° and maximum approximate vertical load 760 N on the top surface of the abutment of design 2 is shown in [Figure 3]  Figure 3: (a) Force direction, (b) vonMises stress distribution on design 2 under 135 N vertical load, (c) Force direction, (d) vonMises stress distribution on design 2 under 135 N horizontal load, (e) Force direction, (f) vonMises stress distribution on design 2 under 135 N oblique load at 45°, (g) Force direction, (h) vonMises stress distribution on design 2 under 760 N vertical load
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The value of maximum vonMises stress when applying 135 N load on the top surface of the abutment on design 2 vertically, horizontally, obliquely at 45° are, 98.467, 344.17, 319.97 MPa, respectively. The number of nodes and elements are 303501 and 191363, respectively. When applying 760 N vertical force on the design 2 on abutment then maximum vonMises stress 554.33 MPa and this occur at top portion of abutment
vonMises stress distribution when applying 135 N load vertically, horizontally, and obliquely at 45° and maximum approximate vertical 760 N load on the top surface of the abutment of design 3 is shown in [Figure 4]  Figure 4: (a) Force direction, (b) vonMises stress distribution on design 3 under 135 N vertical load, (c) Force direction, (d) vonMises stress distribution on design 3 under 135 N horizontal load, (e) Force direction, (f) vonMises Stress distribution on design 3 under 135 N oblique load at 45°, (g) Force direction, (h) vonMises Stress distribution on design 3 under 760 N vertical load
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The value of maximum vonMises stress when applying 135 N load on the top surface of the abutment on design 3 vertically, horizontally, obliquely are, 57.057, 325.9, 266.79 MPa respectively. The number of nodes and elements are 296294 and 189186, respectively.
When applying 760 N force on design 3 then the value of maximum vonMises stress is 321.21 MPa and this maximum stress occur at top surface of abutment and implant–abutment interface.
vonMises stress distribution when applying 135 N load vertically, horizontally, and obliquely at 45° and maximum approximate vertical load 760 N on the top surface of the abutment of design 4 is shown in [Figure 5]  Figure 5: (a) Force direction, (b) vonMises stress distribution on design 4 under 135 N vertical load, (c) Force direction, (d) vonMises stress distribution on design 4 under 135 N horizontal load, (e) Force direction, (f) vonMises stress distribution on design 4 under 135 N oblique load at 45°, (g) Force direction, (h) vonMises stress distribution on design 4 under 760 N vertical load
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The value of maximum vonMises stress when applying 135 N load on the top surface of the abutment on design 4 vertically, horizontally, obliquely, are, 149.78, 1093.5, 667.31 MPa respectively. The number of nodes and elements are 419,939 and 265,102 respectively and when applying 760 N force on design 4 then the value of maximum vonMises stress is 670.15 MPa and this maximum stress occur at top surface of abutment. The values of maximum vonMises stress and maximum Principal Stress under 100 N load are shown in [Table 2].  Table 2: Value of Maximum vonMises stress and Maximum Principal Stress under 100 N Load
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There are four new designs of tooth abutment implant. The biting force applied by the humans during chewing and biting is generally varied from 70 to 150 N, and its maximum value for a human being is approximate 760 N. Hence first, here, choose a normal value of load 135 N and find the vonMises stress distribution on tooth abutment implant for normal condition; then, the value of maximum vonMises stress for design 1, 2, 3 and 4 for vertical is 947.51, 98.467, 57.057, 149.78 MPa, for horizontal is 4364.6, 344.17, 325.9, 1093.5 MPa, and for oblique loading condition at 45° is 3700.4, 319.97, 266.79, 667.31 MPa, respectively. Then, take maximum approximate vertical load 760 N. vonMises stress under 760 N for design 1, 2, 3, and 4 is 5334.1, 554.33, 321.21, and 670 MPa, respectively. The ultimate strength of titanium alloy is 1070 MPa, and when compare it with stresses of the new designs, then it is found that the stress on the first and fourth design is greater than that the value under 135 N horizontal load, so these designs will not suitable. Now apply 760 N vertical force on the first, second, third, and fourth design. After applying 100 N load, the graph obtained for all designs as shown in [Figure 6] and [Figure 7], shows that the value of stress is continuously increasing with the loading angle up to 60° for both maximum vonMises stress and maximum principal stress with loading angle. The designs 2 and 3 can be used because their stress value is lower than the ultimate strength of titanium alloy. Now, designs 2 and 3 are the two best designs which can be used for all conditions, but design 2 is better than design 3 because design 3 will fail when it will disassembled after joining. Hence, design 2 is better. Now, add the tooth on the abutment of design 2; then, the stress distribution on tooth abutment implant under maximum approximate vertical load 760 N is. shown in [Figure 8].  Figure 6: Graph between vonMises stress and Loading angle for designs 1, 2, 3 and 4
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 Figure 7: Graph between maximum principal stress and loading angle for designs 1, 2, 3 and 4
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 Figure 8: (a) Picture of tooth abutment implant of design 2 with tooth (b) Force direction, (c) Stress distribution on tooth abutment implant design 2 with tooth
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When apply the same load (760 N) on the tooth surface which is fitted on the abutment, then the value of maximum vonMises stress will become 199.1 MPa and this maximum stress will occur at the tooth–abutment interface. The number of nodes and elements are 351469 and 176379, respectively. After tooth addition, design 2 will remain safe.
Validation
Conventional design of tooth abutment implant
[Figure 9] shows the conventional design of tooth abutment implant design with a screw which we use at the present time.  Figure 9: Parts of conventional design of tooth abutment design, (a) Implant, (b) Abutment, (c) Screw, (d) Assemble design
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vonMises stress distribution under 135 N load vertically, horizontally, and obliquely at 45° and under maximum vertical approximate load 760 N on the top surface of the abutment of conventional design of tooth abutment implant is shown in [Figure 10].  Figure 10: (a) Force direction, (b) vonMises stress distribution on conventional design under 135 N vertical load, (c) Force direction, (d) vonMises stress distribution on conventional design under 135 N horizontal load, (e) Force direction, (f) vonMises stress distribution on conventional design under 135 N oblique load at 45°, (g) Force direction, (h) vonMises stress distribution on conventional design under 760 N vertical load
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The value of maximum vonMises stress when applying 135 N load on the top surface of the abutment on conventional design vertically, horizontally, obliquely is 188.10, 351.63, 327.01 MPa, respectively. The number of nodes and elements are 402,695 and 260,365, respectively.
When applying 760 N force on conventional design, then the value of maximum vonMises stress is 853.41 MPa, and this maximum stress occur at the top surface of abutment and implant–abutment interface.
[Table 3] shows the value of maximum vonMises stress for conventional design and new designs such as design 1, 2, 3, and 4 under normal and maximum loading conditions.  Table 3: Value of Maximum vonMises stress for new designs and conventional design of Tooth Abutment Implant
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When we compare the vonMises Stress under 135 N vertical, horizontal and oblique (45°) load and maximum force of conventional design with new designs then it is found that the vonMises Stress of designs 1 and 4 is more than conventional design. For design 1 stress is more in all conditions and for design 4 stress is more in horizontal and oblique condition. And for design 2 and 3 its value is less than the conventional design. Hence, the designs 2 and 3 are the better designs because in these designs stress is reducing. Hence, we can use these designs. However, in these two designs (design 2 and design 3), design 2 is better than design 3 because if we want to use the design 3 again after once using then we will get design 3 in deform condition and we cannot use it again, but design 2 can be used again and again.
Conclusions   
In all tooth abutment designs, a homogeneous, isotropic, and linear elastic material is used which is titanium alloy because it has the best biocompatibility, bonding strength, and corrosion resistance. When apply different load on the different design in different inclination, then it gives different stress value, and comparing all these data with ultimate strength and conventional design, it is found that design first and fourth is not suitable and design second and third can be used. However, design 3 cannot be used again if disassemble it once, but design 2 can be used again and again after dissembling it, so the design 2 will better in all conditions.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8], [Figure 9], [Figure 10]
[Table 1], [Table 2], [Table 3]
