ORIGINAL ARTICLE Year : 2021  Volume : 13  Issue : 5  Page : 688691 Influence of occlusal bite forces on teeth with altered periodontal support: A threedimensional finite element stress analysis Richa Agrawal, Sumit Narang, Hina Ahmed, Shyam Prasad, Shyamsunder Reddy, Shivaramakrishna Aila Department of Periodontics, Mansarovar Dental College, Bhopal, Madhya Pradesh, India Correspondence Address: Background: Masticatory forces generate various degrees of stress and strain in the periodontium of teeth which determine the clinical functions and loadbearing capacity of the teeth. There are few in vitro studies that have analyzed stress generated due to combined forces acting on the teeth. Thus, the objective of the present study was to do a comparative analysis of the influence of various stresses on the periodontal ligament and alveolar bone of maxillary central incisor with normal bone height and reduced bone height under simulated standard masticatory using finite element stress analysis. Methodology: A 3D model of the tooth was obtained with the help of ANSYS software. These models were subjected to various oblique forces, i.e., 100N and 235.9N, applied at 45° angle on the lingual surface of the maxillary central incisor and stress values were recorded in three dimensions. The results from FE analysis were analyzed using 3D Von Mises Criteria. Results: It was observed that in healthy periodontium; it was observed that among the periodontal structure studied, the maximum stress levels were exerted on root followed by cortical bone, cancellous bone, and PDL, irrespective of the force, as compared to the diseased periodontium, in which the bone height was reduced, the maximum stresses were on root followed by cortical bone, PDL, and cancellous bone. Conclusion: The main factor governing the success of any periodontal procedure depends on the height of the remaining bone and the amount of force exerted on to the tooth and the stress generated within the tooth. The finite element method could be of substantial importance in this respect as it can assess the stresses of various occlusal forces on the periodontal ligament, root, cortical bone, and cancellous bone of teeth in a periodontally healthy and diseased state.
Introduction The finite element method is a threedimensional analysis, applied to understand the stress distribution in hard and soft tissues such as the tooth and periodontium.[1] It helps in generating a 3D model of the tooth using the mathematical equation and 3D geometry and at the same time allows the exertion of different forces at specific points and study the distribution and stresses generated by such forces in the biological tissues.[2] Periodontium of the tooth provides support and strength to the tooth to withstand the various occlusal bite forces and mechanical forces that the tooth is subjected to during mastication, biting, and holding. Thus, the aim of the study was to analyze the influence of various stresses on the periodontal ligament and alveolar bone of maxillary central incisor in health and disease under simulated occlusal bite forces. Materials and Methods In the present study, a 3D finite element model was developed to analyze the distribution of stress on the periodontal ligament and alveolar bone within the maxillary central incisor in a healthy and compromised state. 3D finite element simulation models of maxillary central incisor were developed with the following conditions: Normal height of bone and normal periodontal ligament spaceReduced height of bone and widened periodontal ligament space. The crown length taken was 0.9 mm, root length as 13.8 mm, and periodontal ligament width in normal condition as 0.2 mm while 0.4 mm when there was the widening of the periodontal ligament. The alveolar bone height in normal conditions was considered as 21 mm and 12.5 mm in compromised conditions.[3] The properties such as Poisson's ratio and Modulus of Elasticity for each material were fed in the computer. The model was subjected to 100N and 235.9N forces which are considered to be the standard masticatory force and the average value of maximum bite force on a central incisor, respectively. The forces were applied in oblique direction at 45° angle between the incisal edge and basal tubercule of the central incisor on its lingual surface. Von Mises Criteria was used to analyze the results. The output thus obtained was in the form of colorcoded diagrams where different colors depicting various levels of stresses generating within the periodontal tissues. The warmer the colors obtained, higher are the stresses within the depicted zone. Results In this study, threedimensional Von Mises Criteria was used to analyze the stresses. The comparative analysis has been discussed under the following headings. Comparison of stress distribution on periodontal ligament, root, cancellous bone, cortical bone with the static force of 100N With a normal bone height of 21 mm and a normal PDL space of 0.2 mm it was observed that: The stress exerted on the periodontal ligament was 1.683 MPa. These stresses were further transmitted on root generating stress of 19.456 MPa [Figure 1]. Force exerted on the cancellous bone was observed to be 2.412 MPa and the focus of concentration was at the cervical region as shown in [Figure 2]. Similarly, within the Cortical bone, the stress of 7.73 MPa was observed as shown in [Figure 2]In a situation with the static force of 100N and compromised bone height with increase PDL space was observed that: The stresses on the Periodontal Ligament with widened PDL was 6.97 MPa as shown in [Figure 1]. Similarly, the stresses exerted on to the root was dramatically more, i.e., 64.6 MPa as shown in [Figure 1]. There was a mark difference if we compared with the stresses on the cancellous and cortical bone with normal bone height irrespective of the width of the PDL space as shown in [Figure 2].{Figure 1}{Figure 2} Comparison of stress distribution on periodontal ligament, root, cancellous bone, cortical bone with the static force of 236N With a normal bone height of 21 mm and normal PDL space of 0.2 mm, it was observed that the stress exerted on periodontal ligament was 3.973 MPa. These stresses were further transmitted on root with the stress of 45.915 MPa as shown in [Figure 1]. Force exerted on the cancellous bone was 5.692 MPa, within the cortical bone also it was observed that the stresses did not vary much and the maximum value was 18.243 MPa as shown in [Figure 2]In a situation with the static force of 236N and reduced bone height and widened PDL space was observed that the stresses on the periodontal ligament with widened PDL was 16.45 as shown in [Figure 1]. This establishes the fact that stresses on the periodontal ligament irrespective of the width of PDL spaces are inversely proportional to the height of the alveolar bone. Similarly, the stresses exerted on to the root were 152.5 MPa and the focus of concentration is more towards the apical 1/3rd in widened PDL. This could be one of the reasons establishing the fact that the probability of root resorption increases as the bone height reduces and PDL widens, thus hampering the crown root ratio as shown in [Figure 1]. It was seen that among the cortical and cancellous bone under the maximum stress of 236N, it was the cortical bone which bore maximum stresses as compared to the cancellous bone as shown in [Figure 2]. Discussion Analysis and evaluation of stress exerted on the teeth and periodontium by normal or abnormal forces in the oral cavity is a very vital aspect governing the prognosis of a tooth/teeth. Many stress analysis methods have been developed for the same which include the photoelastic analysis, strain gauge technique also called extensometry, FEM, and electronic speckle pattern interferometry (ESPI). In the photoelastic method, the optic parameters exhibit fringes when viewed through polarized light. The analysis of these colorful patterns shows the stress distribution in the object, but the disadvantage of this method is the exact reproduction of the original experimental model is difficult.[4] The FEM of stress analysis has an advantage as it is versatile, all shapes or structures can be investigated and force applied and stresses generated can be studied in all directions.[5] In the present study, the simulated 3D model for maxillary central incisor was generated by using the various dimensions such as Youngs Modulus and Poisson's were used as given by various researchers.[6],[7],[8] The models consisted of the tooth, the alveolar bone, and the periodontal ligament.[9] A force of 100N was applied as this was the maximum biting force for the maxillary central incisor and a force of 235.9N was applied as this is the average force value of maximum bite on a maxillary central incisor.[10],[11],[12],[13],[14] An oblique force was applied at 45° as it is the average of the anterior angle of function in Angle's class I occlusion.[15] The main factor governing the success of any periodontal procedure depends on the height of the remaining bone and the amount of force exerted on to the tooth. In the present study, it has been observed that the same forces exerted different stress levels on various periodontal structures irrespective of the periodontium is healthy or diseased. In healthy periodontium, it was observed that among the periodontal structure studied, the maximum stress levels were exerted on root followed by cortical bone, cancellous bone, and PDL, irrespective of the force, as compared to diseased periodontium, in which the bone height was reduced, the maximum stresses were on root followed by cortical bone, PDL, and cancellous bone. It was also observed that the location of stress generation on each periodontal structure varied. Conclusion FEM stress analysis could be of substantial importance to evaluate and understand various stresses on the teeth in the periodontally healthy and diseased state as this is the only method that has the versatility to investigate all shapes and structures and can apply force and evaluate the stress generated in all directions. Thus, in the present study, it has been observed that the same forces exerted different stress levels on various periodontal structures irrespective of the periodontium being healthy or diseased. The result also suggests that reduced alveolar bone height generates a lot of stress within the periodontal ligament, thus causing significant mechanical damage to the PDL but at the same time has not much of a negative effect within the alveolar bone. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest. References


