Bones
Dentistry & maxillofacial biomechanics
Aim: The present study addresses the increased fragility of devitalized teeth. Removal of dental tissues during endodontic treatment certainly influences the mechanical behavior of devitalized teeth. From biomechanical aspect, it is questionable how much each particular step in the process of root canal treatment contributes to the weakening of the tooth and thus further affects the prognosis of endodontically treated teeth.
Methods: In order to estimate the decrease in tooth strength, we applied in this study a numerical Finite Element Method (FEM) analysis and experimental validation of combine influence of three dental procedures that are subsequently performed in root canal treatment: two-surface Class II preparation, access cavity preparation and root canal enlargement. To estimate their influence on tooth fracture resistance numerically, Failure Index based on Maximum Stress Criterion (MCS) was applied.
Results: The results showed that each step in root canal treatment had influence on tooth weakening. Preparation of two-surface cavity weakened the tooth for 20%. Nevertheless Failure index showed that this tooth was not likely to fracture even under high occlusal stress (700N). However, after adding access opening preparation, the Failure index reached the point of failure risk under high occlusal force which can occur in posterior area. The enlargement of root canals had additional influence on tooth weakening, making this tooth more susceptible to fracture under high occlusal force.
Conclusion: This study is an efficient framework which, if applied in different cases, could be useful in calculating the potential risk for tooth fracture.
fracture.
Objectives The aim of this study was to use Finite Element Analysis (FEA) to estimate the influence of various mastication loads and different tooth treatments (composite restoration and endodontic treatment) on dentine fatigue. The analysis of fatigue behaviour of human dentine in intact and composite restored teeth with root-canal-treatment using FEA and fatigue theory was performed.
Methods Dentine fatigue behaviour was analysed in three virtual models: intact, composite-restored and endodontically-treated tooth. Volumetric change during the polymerization of composite was modelled by thermal expansion in a heat transfer analysis. Low and high shrinkage stresses were obtained by varying the linear shrinkage of composite. Mastication forces were applied occlusally with the load of 100, 150 and 200 N. Assuming one million cycles, Fatigue Failure Index (FFI) was determined using Goodman's criterion while residual fatigue lifetime assessment was performed using Paris-power law.
Results The analysis of the Goodman diagram gave both maximal allowed crack size and maximal number of cycles for the given stress ratio. The size of cracks was measured on virtual models. For the given conditions, fatigue-failure is not likely to happen neither in the intact tooth nor in treated teeth with low shrinkage stress. In the cases of high shrinkage stress, crack length was much larger than the maximal allowed crack and failure occurred with 150 and 200 N loads. The maximal allowed crack size was slightly lower in the tooth with root canal treatment which induced somewhat higher FFI than in the case of tooth with only composite restoration.
Conclusions Main factors that lead to dentine fatigue are levels of occlusal load and polymerization stress. However, root canal treatment has small influence on dentine fatigue.
Clinical significance The methodology proposed in this study provides a new insight into the fatigue behaviour of teeth after dental treatments. Furthermore, it estimates maximal allowed crack size and maximal number of cycles for a specific case.
Trauma of the Frontal Region Is Influenced by the Volume of Frontal Sinuses. A Finite Element Study
Anatomy of frontal sinuses varies individually, from differences in volume and shape to a rare case when the sinuses are absent. However, there are scarce data related to influence of these variations on impact generated fracture pattern. Therefore, the aim of this study was to analyse the influence of frontal sinus volume on the stress distribution
and fracture pattern in the frontal region.
The study included four representative Finite Element models of the skull. Reference model was built on the basis of computed tomography scans of a human head with normally developed frontal sinuses. By modifying the reference model, three additional models were generated: a model without sinuses, with hypoplasic, and with hyperplasic sinuses. A 7.7 kN force was applied perpendicularly to the forehead of each model, in order to simulate a frontal impact.
The results demonstrated that the distribution of impact stress in frontal region depends on the frontal sinus volume. The anterior sinus wall showed the highest fragility in case with hyperplasic sinuses, whereas posterior wall/inner plate showed more fragility in cases with hypoplasic and undeveloped sinuses.Well-developed frontal sinusesmight, through
absorption of the impact energy by anterior wall, protect the posterior wall and intracranial contents.
The aim of the present study was to investigate the influences of the presence and position of a lower third molar (M3) on the fragility of mandibular angle and condyle, using finite element analysis. From computed tomographic scans of a human mandible with normally erupted M3, two additional virtual models were generated: a mandibular model with partially impacted M3 and a model without M3. Two cases of impact were considered: a frontal and a lateral blow. The results are based on the chromatic analysis of the distributed von Mises and principal stresses, and calculation of their failure indices. In the frontal blow, the angle region showed the highest stress in the case with partially impacted M3, and the condylar region in the case without M3. Compressive stresses were dominant but caused no failure.
Tensile stresses were recorded in the retromolar areas, but caused failure only in the case with partially
impacted M3.
In the lateral blow, the stress concentrated at the point of impact, in the ipsilateral and contralateral angle and condylar regions. The highest stresses were recorded in the case with partially impacted M3. Tensile stresses caused the failure on the ipsilateral side, whereas compressive stresses on the contralateral side.
Biomechanical implications of diverse alveolar bone loss patterns and regenerative therapy over the periodontium
Objectives: To assess the biomechanical aspect of horizontal and vertical periodontal bone loss, and the impact of regenerative periodontal therapy by means of finite element analysis (FEA).
Materials and Methods: Three patient-specific 3D FE models were developed from the acquired CBCT scans, comprising the patient's upper left canine, first and second premolar, and adjacent alveolar bone. Model 1 represented horizontal bone loss, Model 2 included intrabony defect along distal aspect of tooth #24. Model 3 represented the situation six months after the regenerative periodontal surgery. Displacement, Von Mises and principal stresses were evaluated by means of FEA, following the vertical occlusal load of 150 and 200 N.
Results: Vertical bone loss induced significant dispacement of affected tooth and, consequently, higher stresses in the surrounding bone. Six months following the regenerative periodontal therapy, the values of all evaluated parameters were noticeably reduced but still were greater than the values detected in case of horizontal bone loss.
Conclusions: Computer modeling and FEA demonstrated that vertical bone loss affected more displacement and stress distribution in the alveolar bone, PDL, and teeth compared to horizontal bone loss, whereas regenerative periodontal therapy may improve the biomechanical characteristics of the affected teeth and the related periodontal structures.
Clinical relevance: The regenerative periodontal therapy is important to improve the biomechanical characteristics of the affected teeth and supporting structures six months following the surgery. However, the regenerated bone at the previously affected site still has the week point which may be jeopardized in terms of further bone loss.
Understanding of the occlusal load distribution through the mid-facial skeleton in natural dentition is essential because alterations in magnitude and/or direction of occlusal forces may cause remarkable changes in cortical and trabecular bone structure. Previous analyses by strain gauge technique, photoelastic and, more recently, finite element (FE) methods provided no direct evidence for occlusal load distribution through the cortical and trabecular bone compartments individually. Therefore, we developed an improved three-dimensional FE model of the human skull in order to clarify the distribution of
occlusal forces through the cortical and trabecular bone during habitual masticatory activities. Particular focus was placed on the load transfer through the anterior and posterior maxilla.
The results were presented in von Mises stress (VMS) and the maximum principal stress, and compared to the reported FE and strain gauge data. Our qualitative stress analysis indicates that occlusal forces distribute through the mid-facial skeleton along five vertical and two horizontal buttresses. We demonstrated that cortical bone has a priority in the transfer of occlusal load in the anterior maxilla, whereas both cortical and trabecular bone in the posterior maxilla are equally involved in performing this task. Observed site dependence of the occlusal load distribution may help clinicians in creating strategies for implantology and orthodontic treatments. Additionally, the magnitude of VMS in our model was significantly lower in comparison to previous FE models composed only of cortical bone. This finding suggests that both cortical and trabecular bone should be modeled whenever stress will be quantitatively analyzed.