|Year : 2019 | Volume
| Issue : 1 | Page : 4-11
TTPHIL-ALL TILT™ – An effective technique for loading of dental implants: A comparative study of stress distribution in maxilla using finite element analysis
P Venkat Ratna Nag1, P Sarika2, Ruheena Khan3, Tejashree Bhagwatkar3
1 Department of Prosthodontics, S.B. Patil Dental College and Hospital, Bidar, Karnataka, India
2 Department of Pedodontics and Preventive Dentistry, S.B. Patil Dental College and Hospital, Bidar, Karnataka, India
3 Institute for Dental Implantology, Hyderabad, Telangana, India
|Date of Web Publication||17-Jun-2019|
Dr. P Venkat Ratna Nag
Institute for Dental Implantology, 8-2-598/A/1, GB, Uma Devraj Villa, Road No. 10, Banjara Hills, Hyderabad - 500 034, Telangana
Source of Support: None, Conflict of Interest: None
| Abstract|| |
Objectives: The key objective of the study is to compare the influence of stress on the bone after placement of dental implants using three alternative techniques viz., (i) All-on-4 (2 straight and 2 distally tilt implants) (ii) All-on-6 (6 straight implants) and (iii) All-Tilt-6 (6 tilted implants under the TTPHIL-ALL TILT technique) for rehabilitation of moderate atrophic maxilla.
Materials and Methods: Three dimensional Finite Element Model has been deployed in the study to compare stress distribution on bone using All-on-4, All-on-6, All-Tilt-6 technique. In the Finite Element Analysis, vertical loads of 150N on lateral incisor/canine, second premolar and second molar area were applied for analysis of von Mises stress distribution on the crestal cortical bone, cancellous bone and basal cortical bone.
Results: von Mises stress shows higher values on Crestal cortical bone, Basal cortical bone and Cancellous bone for 'All-on-4' and 'All-on-6' concept. It is comparatively less for'All-Tilt-6' concept.
Conclusion: TTPHIL-ALL TILT (Tall Tilted Pin Hole Immediate Loading) concept is a novel technique which is derived from the 'tilted implant concept' in which bicortical engagement of implant transfers less stress on the bone with reduced chances of bone resorption, failures and no cantileverage.
Keywords: All-on-4, All-on-6, All-Tilt-6, Finite element analysis, Tilted implants, TTPHIL technique
|How to cite this article:|
Ratna Nag P V, Sarika P, Khan R, Bhagwatkar T. TTPHIL-ALL TILT™ – An effective technique for loading of dental implants: A comparative study of stress distribution in maxilla using finite element analysis. J Dent Implant 2019;9:4-11
|How to cite this URL:|
Ratna Nag P V, Sarika P, Khan R, Bhagwatkar T. TTPHIL-ALL TILT™ – An effective technique for loading of dental implants: A comparative study of stress distribution in maxilla using finite element analysis. J Dent Implant [serial online] 2019 [cited 2019 Jul 18];9:4-11. Available from: http://www.jdionline.org/text.asp?2019/9/1/4/260453
| Introduction|| |
Immediate implant placement for rehabilitation of complete atrophied resorbed maxillary edentulous ridges is the most challenging task; especially where sinus pneumatization has occured. It is observed that bone remodeling around the implant because of the drilling osteotome sequence and loading of the prosthesis may result in residual alveolar bone resorption. The complex three-dimensional (3D) vertical and horizontal resorption of the posterior maxilla because of tooth loss, long term edentulism leads to sinus pneumatization and alveolar ridge resorption.,,, In these situations, it is difficult to place axial implants alone without sinus augmentation. Furthermore, lengthy cantilevers are required to compensate for biological limitations. Extensive posterior cantilevers are biomechanically unfavorable because of increased occlusal forces per unit area.,,
In view of the above-mentioned adverse effects, alternative methods such as All-on-4 and All-on 6 and tilted implants have come into play. Still, the cantileverage effect led to the failure of distal implants. The reason behind the success of a pterygoid implant is the availability of dense pterygoid buttress cortical bone for implant engagement which is highly mineralized more resistant to resorption. Pterygoid implants are required to achieve adequate stability for tilted implants and also decrease the number of cantilevers., Pterygoid implants are playing a vital role to overcome cantileverage effect and aid in reducing the anterioposterior spread. The introduction of tilted implants is proven as a significant alternative for restoration of maxillary posterior segments without bone grafting.
The “All-on-4” concept provides rehabilitation of a fully edentulous jaw which has minimal bone volume. The procedure requires short treatment intervals, involves low cost, and improves the quality of life. In this concept, four implants are used to restore the fully edentulous cases. Two implants are placed axially in the anterior region, two implants are placed distally (30°–45°) in the posterior region.,, Implants' cumulative survival report is less due to short arch (10-14 teeth only) span which results in distal cantileverage in All-on-4 concept. However, prosthetic survival rate is slightly lower.
The “All-on-6” protocol involves less stress when compared to the All-on-4 implant concept. In All-on-6 concept (6 straight axial implants), two additional implants are placed in the second molar region. The addition of these two implants provides additional support to anterior four implants, i.e., two implants in the lateral incisor region and two in the second premolar region; this will avoid the distal cantilever and allows fixing complete arch prosthesis. Since bone in the posterior maxilla is very soft, trabecular and has poor density, additional factors like sinus pneumitization and residual ridge resorption lead to implant failure due to poor osseointegration.
To overcome the disadvantages of the above-mentioned techniques, TTPHIL-ALL TILT technique has been developed by the author of this article. In this technique, tall (16–25 mm) and tilted implants (with angulations of 30°–45°) are used. Tall implants provide more surface area for osseointegration and are also engaged in the cortical bone (bi- or multicortical anchorage). The implants are placed in pinhole manner, i.e., flapless. All implants are immediately loaded within 2 days to 1 week with a screw-retained multiunit DMLS prosthesis. The inclination of distal/posterior implants does not have any deleterious biomechanical effect on abutments and it also reduces the cantilever effect on force magnitude from short arch to long arch which is the advantage of TTPHIL-ALL TILT concept over All-on-4 and All-on-6 concepts.,
The finite element analysis (FEA) was introduced into dental biomechanical research in 1973 and since then has been applied to analyze the stress and strain in the field of dentistry for alveolar structures.
Finite element model (FEM) is the representation of geometry in relation to a finite number of elements and nodes. The “elements” present are of the finite number as opposed to a theoretical model with complete continuity. “Meshwork” is formed when the object of interest has to be broken up into a number of nodes. The system of elements is formed when these nodes are connected. For a 2D example, the bricks wall is considered as the network; the bricks are the elements and the four corners where the bricks meet each other are the “nodes.”
The applications of the FEA in dentistry is found in the studies conducted by Thresher and Saito, Knoell, Tanne and Sakuda, Atmaram and Mohammed, and Cook et al. It is observed that in all previous studies,,,,, the FEA can be applied for understanding the strain-stress levels induced in internal structures. Like mathematic models, the FEA also has the potential for analyzing the relationships of a real complex object.
Steps involved in development of FEM were as follows:
- Construction of a geometric model using reverse engineering/computer-aided design (CAD) model from the company
- Conversion of the geometric model to a FEM
- Defining of material property data
- Application of force and boundary conditions
- Solving the system of linear algebraic equation.
The von Mises stress is commonly used as a stress metric. Von Mises stress is the combination of normal and shear stresses occurring in all directions. Such stress is very important in the examination of the effects of restorative materials and the resultant tooth tissue damage.
The objective of the present study is to compare stress values on crestal cortical, basal cortical, and cancellous bone in “All-on-4,” “All-on-6,” and “All-Tilt-6,” i.e., TTPHIL-ALL TILT concepts loaded with vertical forces using FEA.
| Methodology|| |
A fully edentulous maxillary cast was fabricated to simulate an atrophic maxilla that would be rehabilitated with a full-arch fixed dental prosthesis according to the All-on-4, All-on-6, and All-Tilt-6 TTPHIL-ALL TILT concepts. 3D FEMs were created for analyzing stress distribution on the bones.
The whole purpose of geometric modeling is to represent geometry in the study in terms of points, lines, and volume. In this study, a 3D virtual model of fully edentulous maxilla cast was created as per dimensions and morphology of the maxilla. The cortical bone created was of 1.7-mm thickness, and cancellous bone was an internal structure. The final maxilla dimensions for cortical bone were 16.36 mm high, 86.83 mm long, and anterior 45.2 mm and posterior 66.69 mm wide [Figure 1]. For cancellous bone, the measurements were 14.66 mm high, 82.39 mm long, and anterior 44.2 mm and posterior 63.36 mm wide [Figure 2].
CAD models of the maxillary arch were created on which implants and prosthetic components were created at M/s. CADD Solutions (I.T.I ROAD, Vijaywada, Andhra Pradesh, India). CAD images of the implants and prosthetic components were supplied by the manufacturer(Bioline Dental GmbH &Co.KG Akazien str 7 16356 Wermeuchen Germany) [Figure 3]. The locations and characteristics of the dental implant are shown in [Table 1]. Internal connection implants are placed based on All-on-4, All-on-6, and All-Tilt-6 concept. All the structures were modeled using Creo Parametric-5 software (Boston, Massachusetts, United States) [Figure 4], [Figure 5], [Figure 6].
The implants of the same length were placed based on the maxillary sinus and nasal floor using the software. The abutment, prosthetic screw, and prosthetic framework were modeled by reverse engineering. The details of the parameters used in the model are shown in [Table 1].
Prototyping is very useful during fabrication of virtual FEMs, especially for completely edentulous cases. The determination of the correct positioning of the implant is important; sometimes, the success of implant placement would get affected due to the absence of teeth in completely edentulous cases. Improper inclination/distribution of implant in the bone will affect the result. It is very important to ensure that the implants are positioned in the same place in the model. The prototype is considered as an adjunct for 3D virtual models.
To improve the accuracy and confirm the comparability of results, the analysis was carried out by mesh refinement. The 3D models were ported and analyzed on the Hypermesh 17 software (Troy, Michigan, United States) for mesh generation to measure loading stress. In meshwork, 0.6-mm tetrahedral elements with 10 nodes were used. All materials were considered isotropic. The material properties were mentioned by Young's modulus and Poisson's ratio for cortical bone and cancellous bone [Table 2]. The virtual 3D models presented a total of 259,879 elements and 368,796 nodes for All-on-4; 501,003 elements and 693,987 nodes for All-on-6; and 400,658 elements and 564,130 nodes for All-Tilt-6 [Table 3]. [Figure 7]a shows finite element mesh for the model (frontal view) and [Figure 7]b shows finite element mesh for the model (lateral view).
|Figure 7: (a) Finite element mesh for the model (frontal view). (b) Finite element mesh for the model (lateral view)|
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The boundary condition of the finite element was defined at the peripheral nodes of the bone with 0° of movement in all directions. The model was subjected to rigid fixation for the maxilla to prevent displacement in the x-, y-, and z-axis. For the model, it seems implant get osseointegrated to the peri-implant bone. In the FEA, a vertical load of 150 N was applied on lateral incisor/canine and second premolar and second molar area. A total load of 600 N was applied for the All-on-4 concept [Figure 8]a and [Figure 8]b while the load applied was 900 N for All-on-6 and All-Tilt-6 [Figure 9]a and [Figure 9]b.
|Figure 8: Frontal view (a) on the All-on-4 concept. Rigid fixation restriction in the upper maxilla – green lines. Occlusal view (b) of load application (red lines) on the All-on-4 concept. Rigid fixation restriction in the upper maxilla – green lines|
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|Figure 9: Frontal view (a) on the All-on-6 concept. Rigid fixation restriction in the upper maxilla – green lines. Occlusal view (b) of load application (red lines) on the All-on-6 concept. Rigid fixation restriction in the upper maxilla – green lines|
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The contacts between the structures in geometry were surface to surface, while for the mesh, it is node to node. The result was analyzed using Ansys 19 software (Canonsburg, Pennsylvania, United States). von Mises stress (ϭVM) was obtained for principle stress. The maximum and minimum von Mises stress values for three concepts were calculated.
| Results|| |
The stress distribution for crestal cortical, basal cortical, and cancellous bones was evaluated on the basis of the von Mises stresses. [Table 4] shows stress distribution while positioning the implant on peri-implant bone under various concepts.
|Table 4: Stress distribution due to implant on peri-implant bone by various concepts|
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Crestal cortical bone
In cortical bone, the principal stress in the crestal region showed the highest ϭmax (All-on-4 = 56.24 MPa, All-on-6 = 14.58 MPa, and All-Tilt-6 = 11.24 MPa) and ϭmin (All-on-4 = 14.06 MPa, All-on-6 = 3.42 MPa, and All-Tilt-6 = 5.62 MPa) [Figure 10]a, [Figure 10]b, [Figure 10]c. For All-on-4, the highest concentration values were observed in the peri-implant region around the second premolar. For All-on-6, the highest concentration value was observed in the peri-implant region around the lateral incisor, and All-Tilt-6 showed equal distribution of stress in all locations.
|Figure 10: Stress distribution on the crestal cortical bone (a) All-on-4. Stress distribution on the crestal cortical bone (b) All-on-6. Stress distribution on the crestal cortical bone (c) All-Tilt-6|
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In cancellous bone, the principal stress showed highest ϭmax (All-on-4 = 8.99 MPa, All-on-6 = 1.34 MPa, and All-Tilt-6 = 5.75 MPa) and ϭmin (All-on-4 = 1.001 MPa, All-on-6 = 0.30 MPa and All-Tilt-6 = 0.64 MPa) For All-on-4, the highest concentration value was observed in the peri-implant region around the second premolar. For All-on-6, the highest concentration value was observed in the peri-implant region around the second premolar. All-Tilt-6 showed that highest concentration value was observed in the peri-implant region around the canine and second molar [Figure 11]a, [Figure 11]b, [Figure 11]c.
|Figure 11: Stress distribution in cancellous bone (a) All-on-4. Stress distribution in cancellous bone (b) All-on-6. Stress distribution in cancellous bone (c) All-Tilt-6|
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Basal cortical bone
In cortical bone and basal region, the principal stress showed highest ϭmax (All-on-4 = 14.06 MPa, All-on-6 = 4.83 MPa, and All-Tilt-6 = 5.62 MPa) and ϭmin (All-on-4 = 0 MPa, All-on-6 = 1.62 MPa, and All-Tilt-6 = 0.0001 MPa). All-on-4, All-on-6, and All-Tilt-6 showed equal distribution of stress in all locations [Figure 12]a, [Figure 12]b, [Figure 12]c.
|Figure 12: Stress distribution in basal cortical bone (a) All-on-4. Stress distribution in basal cortical bone (b) All-on-6. Stress distribution in basal cortical bone (c) All-Tilt-6|
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| Discussion|| |
Finite Element Analysis (FEA) is a powerful tool in implant technology to analyze the stress and deformation occurring in the structure of geometrical models. It is commonly used to determine the forces that affect the bone/implant interface or to evaluate different clinical and prosthetic options. FEA was used to examine the bone stress distributions in 'All-on-4', 'All-on-6' and 'All-Tilt-6' concepts. The values that FEA gives are variances arrived from non-mathematical calculations.
Bhering et al. evaluated two treatment concepts (All-on-4 and All-on-6) and the effect of framework material on stress distribution of the implant-supported system. This study reveal that All-on-6 showed smaller principal stress values on cortical bone, implant, and cancellous bone. Also, the study concluded that All-on-6 approach showed most favorable biomechanical behavior. In the literature it was mentioned that cantilevers cause implant-prosthetic failures. All-on-4 technique is limited due to this factor. In our analysis, crestal and basal bone loss is higher in the All-on-4 technique, due to the unfavorable stress acting as a result of distal cantilever being present.
The TTPHIL-ALL TILTTM is a novel technique which is derived from the tilted implant concept provides better results when compared to All-on-4 and All-on-6 techniques based on finite element analysis. Use of All-on-6 implant design is limited in resorbed posterior maxillary edentulous ridges due to sinus pneumatization. By adopting All-Tilt-6 design, Tall tilted implants are placed engaging the pterygoid pillar (junction of the palatine process of maxilla, pyramidal process of palatine bone and pterygoid process of the sphenoid bone), thus eliminating distal cantilever along with avoiding of sinus encroachment or any augmentation procedures. The crestal and pterygoid/ nasal cortical engagement (bicortical) reduces micromovement which is important for osseointegration to avoid implant failure. Basal bicortical 18mm implants transfer the loads from the crestal bone to the basal bone, hence crestal bone loss is minimum in the TTPHIL- ALL TILT technique. Distal cantilever is eliminated in this All-Tilt-6 design.
Bruno Salles Sotto-Maior et al. conducted study to evaluate the biomechanical influence of apical bone anchorage using FEA models and found bicortical engagement reduces implant displacement. This study supports bicortical anchorage for best results which reduces stress distribution on basal cortical bone. Serkan Dundar et al. observed that stress was greater in cortical bone than in cancellous bone and the stress in the bone decreased when the distance from the implant is greater.
Studies were conducted to analyze vertical and oblique forces for the implant placement. They observed oblique occlusal forces are important when FEA is applied to dental implants because the stress results in the structures will be more realistic than those obtained using a vertical occlusal force., In this study also tilted implants, i.e TTPHIL-ALL TILT technique got good implementation in terms of vertical force to implant.
Bruno M.T et al. performed a study to compare the outcome of fixed partial prosthesis in posterior maxilla with two axially placed implants or one placed distally tilted and one axially placed implant. They found distally placed implant i.e tilted implant did not compromise the outcome of fixed partial rehabilitation. Although, finite element analysis is used in the present study, which is based on mathematical models. There are also some drawbacks: they cannot simulate oral tissues and they can be used only to explain experimental results; their predictive power is used for comparisons.
| Conclusion|| |
TTPHIL-ALL TILT concept is a novel technique which derived from the tilted implant concept provide better results when compared to All-on-4 and All-on-6 technique based on finite element analysis. The basal bone is highly mineralized bone and highly resistant to bone resorption. Basal bicortical 18mm implants transfer the loads more from the crestal bone to the basal bone, hence crestal bone loss is minimum in the TTPHIL- ALL TILT implants. Within the limitation of the study, implant geometry is considered as an important factor for the success of the implant/bone connection. Implant length and increasing connection surface provide protection of peri-implant bone tissue, hence highly recommended for immediate loading. To the best of knowledge, few studies are present in literature in which comparison of tilt implant concepts with conventional implants and stress distribution of peri-implant bone such as cortical crestal, cortical basal bone and cancellous bone is done.
Limitation of the study is that the stresses on the gum tissue cannot be assessed with the FEA study. Thus; long-term quantitative clinical studies along with other components are required to prove the efficiency of TTPHIL-ALL TILT technique.
Financial support and sponsorship
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], [Figure 11], [Figure 12]
[Table 1], [Table 2], [Table 3], [Table 4]