FEM and Von Mises analysis on prosthetic crowns structural elements: evaluation of different applied materials

The aim of this paper is to underline the mechanical properties of dental single crown prosthodontics materials in order to differentiate the possibility of using each material for typical clinical condition and masticatory load. Objective of the investigation is to highlight the stress distribution over different common dental crowns by using computer-aided design software and a three-dimensional virtual model. By using engineering systems of analyses like FEM and Von Mises investigations it has been highlighted the strength over simulated lower first premolar crowns made by chrome cobalt alloy, golden alloy, dental resin, and zirconia. The prosthodontics crown models have been created and put on simulated chewing stresses. The three-dimensional models were subjected to axial and oblique forces and both guaranteed expected results over simulated masticatory cycle. Dental resin presented the low value of fracture while high values have been recorded for the metal alloy and zirconia. Clinicians should choose the better prosthetic solution for the teeth they want to restore and replace. Both prosthetic dental crowns offer long-term success if applied following the manufacture guide limitations and suggestions

Influence of Progressive vs. Minimal Canal Preparations on the Fracture Resistance of Mandibular Molars: A Finite Element Analysis

INTRODUCTION: Several file systems have been recently introduced with the objective of preserving coronal dentin. There is limited research comparing the role of canal shaping on preservation of pericervical dentin and its role in fracture resistance. The aim of this study is to investigate the effect of minimal canal taper on residual tooth strength and stress distribution after root canal treatment. Methods: Two pre-accessed mandibular molar TruTeeth (Acadental Endo 3DP, Lenexa, KS) were subject to simulated endodontic treatment in this study. One tooth was instrumented with ProTaper Gold (Dentsply, Tulsa, OK) to F2 (25/0.08v progressive taper) in the mesial canals and F3 (30/0.09v progressive taper) in distal canals using manufacturer protocol. The other tooth was instrumented with V-Taper 2H (SSWhite Dental, Lakewood, NJ) to 25/0.06v (minimal taper) in mesial canals and 30/0.06v (minimal taper) in the distal canals. The two teeth were scanned using microcomputed tomography (micro-CT,) and STL (stereolithography) surface meshes were developed for Finite Element Analysis (FEA). Four models were evaluated assessing the type of instrumentation and presence of resin access filling. The results of the FEA provided quantitative and qualitative measurements for Von Mises (VM) stress distribution and total deformation. Results: Under a 200-N multipoint load, the maximum VM stress was greater in the Pro-Taper Gold prepared models than in the V-Taper 2H prepared models. The models without an access restoration had higher total deformation values than the models with a resin filled access. In all models, total deformation values were highest in the clinical crown on the buccal aspect of the tooth. The greatest stress values were found in the pericervical dentin, and stresses decreased apically through the root. Conclusions: Within the limitations of this study, it can be concluded that the maximum stress values within the tooth prepared by ProTaper Gold were higher than those in the tooth prepared by V-Taper 2H. The minimally invasive instrumentation of the V-Taper 2H system preserves more pericervical dentin which may increase the resistance to fracture

A critical analysis of research methods and experimental models to study the load capacity and clinical behaviour of the root filled teeth

The prognosis of root-filled teeth depends not only on a successful root canal treatment but also on the restorative prognosis. This critical review discusses the advantages and limitations of various methodologies used to assess the load capacity or clinical survivability of root-filled teeth and restorations. These methods include static loading, cyclic loading, finite element analysis and randomized clinical trials. In vitro research is valuable for preclinical screening of new dental materials or restorative modalities. It also can assist investigators or industry to decide whether further clinical trials are justified. It is important that these models present high precision and accuracy, be reproducible, and present adequate outcomes. Although in vitro models can reduce confounding by controlling important variables, the lack of clinical validation (accuracy) is a downside that has not been properly addressed. Most importantly, many in vitro studies did not explore the mechanisms of failure and their results are limited to rank different materials or treatment modalities according to the maximum load capacity. An extensive number of randomized clinical trials have also been published in the last years. These trials have provided valuable insight on the survivability of the root-filled tooth answering numerous clinical questions. However, trials can also be affected by the selected outcome and by intrinsic and extrinsic biases. For example, selection bias, loss to follow-up and confounding. In the clinical scenario, hypothesis-based studies are preferred over observational and retrospective studies. It is recommended that hypothesis-based studies minimize error and bias during the design phase.info:eu-repo/semantics/publishedVersio

Direct resin composite restoration of endodontically-treated permanent molars in adolescents: bite force and patient-specific finite element analysis

Objective: To evaluate the influence of three levels of dental structure loss on stress distribution and bite load in root canal-treated young molar teeth that were filled with bulk-fill resin composite, using finite element analysis (FEA) to predict clinical failure. Methodology: Three first mandibular molars with extensive caries lesions were selected in teenager patients. The habitual occlusion bite force was measured using gnathodynamometer before and after endodontic/restoration procedures. The recorded bite forces were used as input for patient-specific FEA models, generated from cone-beam computed tomographic (CT) scans of the teeth before and after treatment. Loads were simulated using the contact loading of the antagonist molars selected based on the CT scans and clinical evaluation. Pre and post treatment bite forces (N) in the 3 patients were 30.1/136.6, 34.3/133.4, and 47.9/124.1. Results: Bite force increased 260% (from 36.7±11.6 to 131.9±17.8 N) after endodontic and direct restoration. Before endodontic intervention, the stress concentration was located in coronal tooth structure; after rehabilitation, the stresses were located in root dentin, regardless of the level of tooth structure loss. The bite force used on molar teeth after pulp removal during endodontic treatment resulted in high stress concentrations in weakened tooth areas and at the furcation. Conclusion: Extensive caries negatively affected the bite force. After pulp removal and endodontic treatment, stress and strain concentrations were higher in the weakened dental structure. Root canal treatment associated with direct resin composite restorative procedure could restore the stress-strain conditions in permanent young molar teeth

Микроструктурна адаптација коштаног ткива фацијалног скелета на дистрибуцију оклузалног оптерећења код особа са пуним зубним низом и њена улога у настанку прелома фацијалног скелета

Occlusal forces have traditionally been explained to transfer through the facial skeleton along specific osseous trajectories known as buttresses. These regions were assumed as zones of strength due to their thick cortical bone structure, while the areas between the buttresses containing thin cortical bone were considered weak and fragile. However, recent studies revealed that both cortical and trabecular bone of the mid-facial skeleton of dentulous individuals exhibit remarkable regional variations in structure and elastic properties. These variations have been frequently suggested to result from the different involvement of cortical and trabecular bone in the transfer of occlusal forces, although there has been no study to link bone microarchitecture to the occlusal loading. Moreover, although the classical concept of buttresses has been extensively studied by mechanical methods, such as finite element (FE) analysis, there is still no direct evidence for occlusal load distribution through the cortical and trabecular bone compartments individually. Additionally, relatively less scientific attention has been paid to the investigation of bone structure along Le Fort fracture lines that have traditionally been assumed as weak areas at which the mid-facial skeleton commonly fractures after injury. Papers published so far in this field focused mainly on the epidemiology and the role of injury mechanism in the fracture development, without considering the structural basis of increased bone fragility along the Le Fort fracture lines...Према традиционалном објашњeњу, пренос оклузалног оптерећења кроз кости лица током жвакања обавља се дуж специфичних путања унутар кости званих трајекторије или „батреси“. Ови делови костију лица сматрани су јаким зонама јер их изграђује кортикална кост велике дебљине, док су делови кости смештени између трајекторија сматрани слабим и фрагилним због њихове танке кортикалне грађе. Међутим, недавним истраживањима је откривено да и кортикална и трабекуларна кост средњег масива лица код особа са пуним зубним низом показују значајне регионалне варијације у грађи и еластичним својствима. Ове се варијације често сматрају адаптацијом кортикалне и трабекуларне кости на различито оптерећење у преносу оклузалних сила током жвакања, иако повезаност микроархитектуре кости и оклузалног оптерећења до сада није испитивана код људи. Штавише, иако је класични концепт преноса оклузалног оптерећења дуж трајекторија интензивно проучаван механичким методама, као што је метод коначних елемената, још увек није испитано на који начин се оклузалне силе преносе појединачно кроз кортикалну и трабекуларну кост. Значајно мању научну пажњу је привлачило испитивање грађе костију лица дуж Le Fort линија које су традиционално сматране најчешћим местима прелома костију фацијалног скелета узрокованих механичким силама. Досадашње студије у овој области су биле фокусиране углавном на епидемиолошка истраживања и улогу механизма повреде у настанку ових прелома, док структурна основа повећане фрагилности кости дуж Le Fort линија није испитивана..

Identifying Optimal Composite Resin Depth to Maximize Fracture Resistance when Restoring Immature Endodontically Treated Teeth

Introduction: This study compared stress distribution of an immature central incisor restored with intracanal composite resin placed at different depths. Methods: Five pre-accessed models were prepared, to simulate immature central incisors, and endodontically treated using a mineral trioxide aggregate plug and different amounts of composite resin with gutta-percha in between the composite resin and mineral trioxide aggregate. (Group 1) Composite resin restored from the cemento-enamel junction, (group 2) composite resin restored from 2 mm apical to the cemento-enamel junction, (group 3) composite resin restored from 4 mm apical to the cemento-enamel junction, (group 4) composite resin restored from the mineral trioxide aggregate, (group 5) no material placed in the canal or access. Teeth were scanned and surface meshes were made for finite element analysis. Each model underwent a 240 Newton load at a 120-degree angle on the palatal fossa to provide evaluations for Von Mises stress distribution. Results: The results showed that placement of composite resin 2 mm apical to the cemento-enamel junction produced the least amount of stress deformation, followed by, in order, composite resin placed 4 mm apical to the cemento-enamel junction, composite resin placed to the mineral trioxide aggregate, and composite resin placed to the cemento-enamel junction. Conclusions: Placement of composite resin 2 mm apical to the cemento-enamel junction increased the fracture resistance of an immature endodontically treated tooth. Placement of composite resin at the cemento-enamel junction or more apical than 2 mm was determined to be unnecessary, as it decreased the fracture resistance

Strain Mapping in Teeth with Variable Remaining Tooth Structure

Problem: The effect of remaining tooth structure on strain in compromised teeth is not fully understood. Different remaining tooth quantities may affect stress and strain concentration within the remaining structure and potentially the longevity of the related restoration. Objectives: The aim of this project was to map and evaluate tooth strain levels at different stages and areas of structural tooth loss created by dental preparation (simulating caries created lesions) or soft drink demineralisation (simulating external acid erosion lesions), before and after restoration, and to evaluate and compare different strain measurement techniques: strain gauges (SG), the surface displacement field measured using digital image correlation (DIC), electronic speckle pattern interferometry (ESPI), and finite element analysis (FEA). In addition, testing teeth affected by erosion required testing and verifying different acid demineralisation protocols. Material and methods: Part I: Enamel samples (sound, polished) were subjected to extended 25 hours (hr) soft drink immersion protocols (accelerated, prolonged) with different salivary protection conditions (no saliva, artificial saliva, and natural saliva) to compare enamel surface loss. Moreover, enamel surface loss of extended erosion periods simulating different levels of clinical erosion lesions was calculated by different imaging methodologies. Microscopic analysis was performed to compare subsurface changes of early and extended erosion protocols. Part II: Strain under static loading was compared in teeth with different stages of unrestored occlusal and buccal accelerated soft drink demineralisation lesions and after restoration using different techniques (strain gauges, electronic speckle pattern interferometry, and finite element analysis). Part III: Strain under static loading was compared in prepared teeth with different remaining tooth dimensions and different restorations using strain gauges and digital image correlation techniques. Results: Part I: No statistical significance was detected in enamel thickness loss between sound and polished enamel samples in the accelerated erosion groups under all salivary conditions or between early and extended erosion groups tested. Part II: All testing methodologies measured an increased strain reading after 1 day in occlusal erosion group followed by gradual decrease, while, continuous increase in strain was observed with buccal erosion progression. For both groups, all restorative materials used were able to restore strain close to pre-treatment level. However, strain distribution pattern was more favourable in ceramic and gold occlusal onlays than composite onlays. Part III: for both strain gauges and digital image correlation, remaining tooth height ≥ 3 mm and width of 1 to 1.5 mm of the remaining tooth structure had a positive effect on strain. Tooth compositions of enamel and dentine resisted strain better than dentine counterparts at all dimensions. Both core restorations (with and without cuspal coverage) were found to support the remaining tooth structure and reduce strain. However, only cuspal coverage recorded significantly lower strain than their unrestored counterparts. Conclusion: Restorations bonded to advanced erosion induced lesions restored strain levels to pre-treatment condition and produced a more favourable strain distribution pattern highlighting the role of adhesion in reducing strain. Remaining tooth structure suffers less strain under loading when enamel is part of the structure and when the minimum dimension of 3 mm in height and 1.5 mm in width is preserved. Bonding of core restoration or cusp coverage aids in reducing strain under loading. All strain measuring methodologies were comparable, where similar strain behaviour was recorded. Remineralisation of enamel and dentine is effective in the management of initial erosion

The State of the Art in Endodontics

Nowadays, we use the term “modern endodontics” thanks to new technologies, novel materials, and revolutionary techniques. Various equipment is available to facilitate and improve our endodontic treatments, such as operating microscopes, ultrasounds, lasers, modern alloys for rotary files, powerful irrigation systems, new materials for filling root canals, 3D radiology, and several more. With the aid of the previously mentioned advances, complex endodontic treatments can be carried out safely, hence guaranteeing patients a high level of care and, above all, saving teeth that would otherwise be doomed for extraction. General practitioners and, even more importantly, specialists in endodontics should implement these modern technologies in their practice. This Special Issue will focus on modern endodontics regarding all the recent updates. Full papers of original articles, short communications, and review articles are all invited