Influence of restorative material and cement on the stress distribution of endocrowns: 3D finite element analysis

Impact of Margin Type and Material Choice on Stress Distribution in Endocrown Restorations: A 3D Finite Element Study

BACKGROUND Finite element analysis (FEA) for endocrown restorations (ER) on maxillary molars has rarely been investigated, despite its high incidence in gross decay and being treated endodontically. This study aimed to analyze the influence of various preparation features (margin type, pulp chamber extension, occlusal thickness) and restorative material (zirconia, lithium disilicate, nanoceramic resin) on the stress distribution pattern of maxillary first molar ER using three-dimensional FEA. MATERIAL AND METHODS Six three-dimensional finite element models (models A-F) were created for ER maxillary molars, considering preparation features - margins (flat butt, 20° bevel, shoulder), pulpal extension (2 mm/4 mm), and occlusal thickness (3 mm) - for 3 ER materials (zirconia, lithium disilicate, nanoceramic resin). The closing phase of mastication was loaded with 600 Newtons of functional load from an apple bolus. Von Mises Stress (VMS) was used to calculate tooth component and ER stress distributions. Standard criteria were used to calculate cement layer failure risk. RESULTS Resin nanoceramic shoulder margins with 2- and 4-mm PE (models E and F) had higher stress concentrations on the tooth preparation surface, cervical enamel, buccal roots, and ER intaglio surface. Higher elastic modulus (ME) materials had higher stress concentrations inside ER and less stress in the cement layer, facilitating tooth bonding. Resin nanoceramic distributed stresses more uniformly on ER/tooth tissues. CONCLUSIONS Different margin and pulpal extension preparation features and restorative materials cause varied ER stress distribution. Shoulder margin created considerably larger stresses in dental tissue and ER than flat butt margin, regardless of material type. Increased pulpal extension reduced tooth tissue stresses but increased ER.

Fracture Resistance of Provisional Crowns: A Finite Element Analysis of a Semi-Permanent Resin-A Pilot Study

Background/Objectives: Fracture resistance is crucial for provisional crowns, especially under high-stress conditions like bruxism. While semi-permanent materials such as Luxacrown are designed for durability, their performance under extreme occlusal forces remains uncertain. This study uses finite element analysis (FEA) to evaluate the fracture resistance of five common provisional crown materials. Methods: A standardized digital model of a maxillary first molar was developed with uniform crown thickness. Twenty models were created to assess Unifast Trad (self-curing PMMA), Luxatemp Star (bis-acryl composite), Luxacrown (semi-permanent bis-acryl), Protemp 4 (nanofilled bis-acryl), and Telio CAD (CAD/CAM PMMA). FEA simulations evaluated vertical (250 N), lateral (225 N), diagonal (400 N), and bruxism-level (800 N) forces. Stress-to-strength ratios (SSR) and Von Mises stress distributions were analyzed to evaluate material performance and failure risk. Results: Telio CAD exhibited the highest fracture resistance, maintaining SSR values below 100% across scenarios. Luxacrown and Protemp 4 performed adequately under moderate loads but showed increased stress concentrations under bruxism-level forces. Luxatemp Star followed a similar trend, whereas Unifast Trad demonstrated the lowest resistance, accumulating significant stress in all conditions. Conclusions: Material selection is key to provisional crown fracture resistance. Telio CAD showed the highest durability, while Luxacrown and Protemp 4 performed well under moderate loads but struggled under extreme forces, raising concerns about semi-permanent materials. Luxatemp Star showed similar trends, and Unifast Trad, the weakest, is best for short-term use.

Hydroxyapatite Dental Inserts for Tooth Restoration: Stress and Displacement Analysis

Hydroxyapatite (HAP) inserts minimize restoration contraction by constituting a major part of the restoration; however, their effect on the relaxation of tooth tissues has not been previously tested. Finite element analysis was employed to estimate stress and displacement when HAP inserts with a thickness of 1.7 mm or 4.7 mm and a diameter of 4.7 mm were used to substitute for dentin. The volumetric contraction of the composite during polymerization, simulated through steady-state heat transfer analysis, yielded a contraction rate of 3.7%. Descriptive statistics revealed that the incorporation of HAP inserts reduced the displacement of dentin, enamel, and restoration caused by contraction by 44.4% to 66.7%, while maximal stress was reduced by 8.1% to 52%. Subsequent loading on the occlusal tooth surface showed that displacement values decreased by 12.1% to 33.3%, while maximum von Mises stress in enamel decreased by 32.8% to 40.6% with the use of HAP inserts. Although the maximum stress values in dentin were not significantly decreased (3% to 8.8%), the stress located at the bottom of the cavity was notably reduced, particularly in deep cavities at root canal entrances. The use of HAP inserts in restorative dentistry provides benefits for the preservation of prepared teeth, especially in preventing irreparable vertical root fractures of endodontically treated teeth.

Evaluation of mechanical and thermal stress in an endodontically treated cracked premolar with three restorative designs: 3D-finite element analysis

PURPOSE

We aimed to analyze the influence of different designs (inlay, onlay, and crown) on stress distribution and crack propagation in an endodontically treated cracked premolar.

METHODS

Three-dimensional (3D) finite element analysis (FEA) was employed to model an endodontically treated cracked premolar with three different restorations (inlay, onlay, and crown). Six types of loadings (vertical loading of 600 N; hot thermal-600 N vertical coupling loading; cold thermal-600 N vertical coupling loading; oblique loading of 200 N; hot thermal-200 N oblique coupling loading; cold thermal-200 N oblique coupling loading) were applied to simulate the hot and cold food/beverages intake. The Von-Mises Stress (VMS) on the lower margin of the crack surface was measured at 20 points in each model, and the position of the stress concentration on the crack surface was analyzed.

RESULTS

All three restoration types effectively improved stress distribution. The influence of different restorative modalities on the stress distribution at the crack tip exhibited different trends under different loading conditions. Lateral loading and/or hot thermal cycling increased the intensity of VMS, and crown restoration exhibited the highest stress concentration at the crack tip under lateral loading and hot thermal cycling.

CONCLUSIONS

From a mechanical perspective, the outcome of this study suggested that a full crown restoration is not the optimal choice for preventing further crack propagation. Additionally, it is recommended to reduce the consumption of excessively hot foods and beverages daily.

Effect of different restorative design and materials on stress distribution in cracked teeth: a finite element analysis study

OBJECTIVES

To compare the stress distribution and crack propagation in cracked mandibular first molar restored with onlay, overlay, and two types of occlusal veneers using two different CAD/CAM materials by Finite Element Analysis (FEA).

MATERIALS AND METHODS

A mandibular first molar was digitized using a micro CT scanning system in 2023. Three-dimensional dynamic scan data were transformed, and a 3D model of a cracked tooth was generated. Finite element models of four different models (onlay, overlay, and two types of occlusal veneer restored teeth) were designed. Two different CAD/CAM materials, including Lava Ultimate (LU) and IPS e.max CAD (EMX), were specified for both models. Each model was subjected to three different force loads on the occlusal surfaces. Stress distribution patterns and the maximum von Mises (VM) stresses were calculated and compared.

RESULTS

Compared to the base model, all restorations showed that high-stress concentration moved from the lower margin of the crack area towards the top of the crack area. The EMX-restored onlay, overlay, and occlusal veneer 2 had the lower stress in the cracked area and the lower average von Mises stress levels at the lower margin along the cracked line, especially under the 225N lateral force (P < 0.05). The occlusal veneer 1 filled with resin had a poorer stress distribution and higher stress concentration of stress at the remaining crack than the occlusal veneer 2 without resin filled inside.

CONCLUSIONS

The EMX restorations with onlay, overlay, and occlusal veneer 2 showed lower stress concentration at the lower margin of crack surface compared to the LU-restored models. The occlusal veneer with internal resin filler exhibited higher stress on the end of the lower margin of the crack surface.

CLINICAL RELEVANCE

Our results suggest that onlay, overlay ceramic restorations and occlusal veneer (without resin filling inside) may be a favorable method to prevent further crack propagation.

TRIAL REGISTRATION

A protocol was specified and registered with the Chinese Clinical Trial Registry (ChiCTR) on 2022-04-12 (registration number: ChiCTR2200058630).

[Flexural Strength of Resinous Cements: In Vitro Evaluation]

Objective

To evaluate the flexural strength of three dental resin cements.

Materials and methods

Sixty bars measuring 25x2x2 mm were made of RelyX-U200, RelyxTM Universal and Duo-Link Universal cements. These bars were divided into 3 groups according to brand (n=20) and were kept in distilled water for 24 hours at 37ºC. The 3-point bending test was carried out, according to ISO 4049, in a universal testing machine at a speed of 0.5 mm/min until fracture. Statistical analysis was performed with the Python statistical package, using the one-way Anova test and Tukey's multiple comparisons test with a confidence level of 95%.

Results

Duo-Link Universal cement obtained the highest average with respect to flexural strength (104.7±7.8 MPa). Statistically significant differences were found between the three groups (p< 0.001). These differences were present between RelyxTM Universal - Duo-Link Universal (p<.001) and Duo-Link Universal - RelyX U200 (p< .001) cements, while no statistically significant differences were found between RelyxTM Universal and RelyX U200 cements.

Conclusion

Duo-Link Universal cement presents greater flexural strength compared to RelyX-U200 and RelyxTM Universal cements. The results indicate that Duo-Link Universal is ideal for restorations requiring high flexural strength, offering greater clinical durability, especially in areas of greater functional load and extensive restorations such as indirect prostheses or posts.

Fracture Resistance of Anterior Teeth Restored with Post-retained Ceramic Crown vs Ceramic Endocrowns

AIM

To compare the fracture resistance of anterior teeth restored with either glass fiber post (GFP) and conventional lithium disilicate (LDS) crowns or endocrowns made of LDS or hybrid ceramics.

MATERIALS AND METHODS

A total of 21 central incisors with 2-mm ferrule and 1-mm shoulder finish line were applied in this investigation. The teeth were divided into three main groups (n = 7) according to the type of restoration used: PC glass fiber post (GFP) and e-max crown, EE (LDS endocrown), and VE (Vita-Enamic endocrown). Mechanical cyclic loading was conducted in a chewing simulator to simulate 6 months of clinical use. Fracture resistance and failure mode were assessed; further examination of fractured specimens was done with scanning electron microscopy.

RESULTS

Post-hoc Tukey's test was performed to investigate the pairwise differences in fracture resistance among the three groups, and the results were p = 0.0452 between PC and VE groups, which is significant statistically. In contrast, p = 0.0615 between PC and EE groups, which is not significantly different. Chi-square test was made to analyze the results of mode of failure among the three groups, and there was a significant difference; p-value = 0.0289.

CONCLUSION

The LDS endocrowns show fracture resistance similar to that of GFP-supported full coverage LDS crowns, with advantage of more restorable mode of fractures. Vita-Enamic endocrowns, despite having fracture resistance lower than other groups, showed fracture resistance higher than the physiologic load, with restorable fractures more than both LDS endocrowns and GFP LDS crowns.

CLINICAL SIGNIFICANCE

For dental practitioners, endocrowns in damaged anterior endodontically treated teeth provide similar fracture resistance to GFP and full crowns, with the advantage of more restorable fractures if occurred. How to cite this article: Mohamed AA, Badawy MBA, El-Kouedi AMY, et al. Fracture Resistance of Anterior Teeth Restored with Post-retained Ceramic Crown vs Ceramic Endocrowns. J Contemp Dent Pract 2024;25(11):1045-1051.

Fracture resistance of CAD/CAM tooth-colored versus cast metal post-and-core restorations in root filled teeth: An in vitro study

Purpose

This study investigated the fracture resistance and failure modes of custom-fabricated post- and core dental restorations using various CAD/CAM materials.

Materials and Methods

Seventy-five mandibular second premolars were allocated to five groups (n = 15) and prepared for standardized post and core restorations. The groups included a control group comprising cast metal and four CAD/CAM materials: Vita Enamic, Shofu HC, Trilor, and PEKK. Fracture resistance was assessed using a compressive force at a crosshead speed of 1 mm/min until failure occurred. Data were analyzed using one-way analysis of variance (ANOVA) and chi-square tests.

Results

The metal group had the highest fracture resistance (244.41 ± 75.20 N), with a significant variance compared to that in the CAD/CAM groups (p < 0.001). No significant differences were observed among the non-metallic groups.

Conclusions

While several CAD/CAM materials displayed satisfactory flexural properties, cast metal posts showed superior fracture resistance in endodontically treated teeth but were mostly associated with catastrophic failure. The clinical application of CAD/CAM materials for post-core restorations presents a viable alternative to traditional metal posts, potentially reducing the risk of unfavorable fractures.

Comparative Evaluation of Stress Distribution and Deformation in Class II Cavities Restored With Two Different Biomimetic Restorative Materials: A Three-Dimensional Finite Element Analysis

Aim This study aims to comparatively evaluate the stress distribution and deformation in class II cavities restored with EverX posterior and ActivaTM Bioactive restorative material using three-dimensional finite element analysis. Methods On a mandibular first molar tooth model, features of a class II mesio-occlusal cavity were designed. Following the application of EverX Posterior and ActivaTM Bioactive, the model was subjected to a 600 N static occlusal load. Three-dimensional finite element analysis was used to analyze the distribution of occlusal stresses among the remaining components and restorative materials. von Mises and maximum principal stresses were evaluated and compared. Results von Mises and maximum principal stresses of ActivaTM Bioactive components were higher compared to the control group and EverX Posterior model. ActivaTM Bioactive restorations had absorbed more stresses within the material rather than distributing it to enamel and dentin than EverX Posterior material. Also, deformation was extremely high in the ActivaTM Bioactive model, which may be because of less stiffness of the material. Conclusion EverX posterior has a higher capacity to bear stresses in stress-bearing areas than ActivaTM Bioactive Restorative.

Optimizing restorative procedure and material selection for pulpotomized primary molars: Mechanical characterization by 3D finite element analysis

Purpose

This study aimed to assess the stress distribution in pulpotomized primary molars with different types of restorative materials using 3D-finite element analysis (FEA), and provide valuable insights into the selection and application of restorative materials, with the ultimate goal of reducing the risk of pulpotomy failure and protecting residual dental tissue.

Methods

Four 3D models of pulpotomized primary molars with different restorative materials according to the material and its elastic modulus were analysed: resin composite, stainless steel crowns (SSCs), prefabricated zirconia crowns and endocrowns. The food layer was also designed before vertical and bucco-lingual forces were applied to simulate physiological masticatory conditions. The results were obtained by colorimetric graphs of the von Mises stresses (VMS) in the restoration and tooth remnant. The maximum shear stress on the bonding interfaces and pressure stress on the Mineral trioxide aggregate (MTA)-pulp interfaces were recorded.

Results

The results of the 3D-FEA showed that all restorative materials generated stresses and strains on the tooth structure after pulpotomy. In the resin composite group, the marginal enamel exhibited the highest stress peaks. In the zirconia crown and SSC groups, there was a concentration of stress at the dentin-restoration margin. The shear stress concentrations were mainly at the adhesive margins, with lower levels around endocrowns compared to other groups. MTA in the resin composite group experienced more VMS than in the other group. The resin composite group also generated relatively higher pressure stress values at the MTA-pulp interface compared to the other groups.

Significance

In the model of primary teeth following pulpotomy, the three types of restorations covering the occlusal surface can effectively reduce the stress on pulp capping materials under occlusal loads, thereby potentially decreasing the risk of pulpotomy failure. In addition, the group of endocrowns demonstrated reduced stress at the bonding interface and in the stress concentration zone near the dentist-restoration edge, making them more effective at protecting residual dental tissue.

How do different intraoral scanners and milling machines affect the fit and fatigue behavior of lithium disilicate and resin composite endocrowns?

The aim of this in vitro study was to evaluate the effect of the combinations of two different intraoral scanners (IOS), two milling machines, and two restorative materials on the marginal/internal fit and fatigue behavior of endocrowns produced by CAD-CAM. Eight groups (n= 10) were considered through the combination of TRIOS 3 (TR) or Primescan (PS) IOS; 4-axes (CR; CEREC MC XL) or 5-axes (PM; PrograMill PM7) milling machines; and lithium disilicate (LD; IPS e.max CAD) or resin composite (RC; Tetric CAD) restorative materials. Specific surface treatments were applied to each material, and the bonding to its corresponding Endocrown-shaped fiberglass-reinforced epoxy resin preparations was performed (Variolink Esthetic DC). Computed microtomography (μCT) was performed to assess the marginal/internal fit, as well as a mechanical fatigue test (20 Hz, initial load = 100 N/5000 cycles; step-size = 50 N/10,000 cycles until a threshold of 1500 N, then, the step-size was increased if needed to 100 N/10,000 cycles until failure or a threshold of 2800 N) to evaluate the restorations long-term behavior. Complementary analysis of the fracture features and surface topography in scanning electron microscopy was performed. Three-way ANOVA and Kaplan-Meier test (α = 0.05) were performed for marginal/internal fit, and fatigue behavior data, respectively. PS scanner, CR milling machine, and RC endocrowns resulted in a better marginal fit compared to their counterparts. Still, the PM machine resulted in a better pulpal space fit compared to the CR milling machine. Regardless of the scanner and milling machine, RC endocrowns exhibited superior fatigue behavior than LD ones. LD endocrowns presented margin chipping regardless of the milling machine used. Despite minor differences in terms of fit, the 'IOS' and 'milling machine' factors did not impair the fatigue behavior of endocrowns. Resin-composite restorations resulted in a higher survival rate compared to glass-ceramic ones, independently of the digital devices used in the workflow.

Endocrowns: Indications, Preparation Techniques, and Material Selection

Endodontic treatment is often necessary in the field of dentistry. As the tooth structure is lost during such treatment, the tooth may become weaker and lose some of its mechanical qualities. Endodontically treated posterior teeth require cuspal coverage because of their anatomical features. Endocrowns are regarded as a suitable choice for restoring teeth that have undergone endodontic treatment. These restorations are recommended when there is a substantial loss of tooth structure, restricted interocclusal space, or a short clinical crown. They are also contraindicated in case of severe loss of tooth structure where adhesion is not applicable. Endocrowns require a specific preparation design that is distinct from the conventional crown. They can be manufactured by two methods: heat pressing or computer-aided design/computer-aided manufacturing (CAD/CAM). Moreover, several materials have been used in fabricating endocrown restoration. Lithium disilicate glass-ceramic is the most recommended material as it possesses excellent mechanical properties and esthetic results with the ability to bond to tooth structure. In conclusion, several kinds of literature recommend using them for molars. Further research is needed to evaluate this technique for premolar and anterior teeth.

In Vitro Resistance of Natural Molars vs. Additive-Manufactured Simulators Treated with Pulpotomy and Endocrown

Endocrowns are designed to restore endodontically treated teeth with root canal treatment (Rct). Recently, endocrowns were proposed for teeth treated with full pulpotomy (FP). No data exist on in vitro evaluations for this combination. This study aimed to evaluate the mechanical behavior of pulpotomy-treated teeth with endocrowns according to different protocols for preparation design and materials and to assess whether 3D-printed resin simulators could be a reliable alternative for human teeth during in vitro strength tests. One hundred and ten extracted natural molars were randomized into 11 groups according to the type of endodontic treatment, the material used, and the design of peripheric preparation. One hundred and ten resin simulators were separated similarly. The samples were embedded in epoxy resin blocks before being subjected to oblique compressive load until failure. For natural teeth, the variance analysis separated two homogeneous groups, one regrouping the endodontically treated or pulpotomy-treated teeth without coronal restoration and the other one regrouping all the other samples, i.e., the untreated teeth (positive controls) and the treated and restored teeth. The strength resistance was lower for the resin simulators than for natural teeth in all groups. Within the limit of this study, strength resistance is not the most important criterion for choosing the type of material, preparation, or endodontic treatment for endocrowns. Resin simulators are not efficient for in vitro strength studies.

Biomechanical Modelling for Tooth Survival Studies: Mechanical Properties, Loads and Boundary Conditions-A Narrative Review

Recent biomechanical studies have focused on studying the response of teeth before and after different treatments under functional and parafunctional loads. These studies often involve experimental and/or finite element analysis (FEA). Current loading and boundary conditions may not entirely represent the real condition of the tooth in clinical situations. The importance of homogenizing both sample characterization and boundary conditions definition for future dental biomechanical studies is highlighted. The mechanical properties of dental structural tissues are presented, along with the effect of functional and parafunctional loads and other environmental and biological parameters that may influence tooth survival. A range of values for Young's modulus, Poisson ratio, compressive strength, threshold stress intensity factor and fracture toughness are provided for enamel and dentin; as well as Young's modulus and Poisson ratio for the PDL, trabecular and cortical bone. Angles, loading magnitude and frequency are provided for functional and parafunctional loads. The environmental and physiological conditions (age, gender, tooth, humidity, etc.), that may influence tooth survival are also discussed. Oversimplifications of biomechanical models could end up in results that divert from the natural behavior of teeth. Experimental validation models with close-to-reality boundary conditions should be developed to compare the validity of simplified models.

Present status and future directions: The restoration of root filled teeth

This narrative review will focus on a number of contemporary considerations relating to the restoration of root filled teeth and future directions for research. Clinicians are now more than ever, aware of the interdependence of the endodontic and restorative aspects of managing root filled teeth, and how these aspects of treatment are fundamental to obtaining the best long-term survival. To obtain the optimal outcomes for patients, clinicians carrying out endodontic treatment should have a vested interest in the restorative phase of the treatment process, as well as an appreciation for the structural and biomechanical effects of endodontic-restorative procedures on restoration and tooth longevity. Furthermore, the currently available research, largely lacks appreciation of occlusal factors in the longevity of root filled teeth, despite surrogate outcomes demonstrating the considerable influence this variable has. Controversies regarding the clinical relevance of minimally invasive endodontic and restorative concepts are largely unanswered with respect to clinical data, and it is therefore, all too easy to dismiss these ideas due to the lack of scientific evidence. However, conceptually, minimally invasive endodontic-restorative philosophies appear to be valid, and therefore, in the pursuit of improved clinical outcomes, it is important that the efficacies of these treatment protocols are determined. Alongside an increased awareness of the preservation of tooth structure, developments in adhesive bonding, ceramic materials and the inevitable integration of digital dentistry, there is also a need to evaluate the efficacy of new treatment philosophies and techniques with well-designed prospective clinical studies.

Influence of margin design and restorative material on the stress distribution of endocrowns: a 3D finite element analysis

Background

This study aimed to evaluate the stress distributions in endocrown restorations as applied to endodontically treated teeth (ETT), according to the factors of “margin design” (four levels) and “restorative material” (six levels).

Methods

Four 3D-finite elements models were constructed for endocrown restored molars considering different margin designs. Model A was prepared with a flat butt joint margin and received an endocrown with a 2.0-mm occlusal thickness. Model B was prepared with a 20° bevel margin and received an endocrown with a 2.0-mm occlusal thickness. Model C was prepared with an axial reduction and 1-mm shoulder margin and received an endocrown with a 2.0-mm occlusal thickness. Model D was prepared with an anatomic margin and received an endocrown with a 2.0-mm occlusal thickness. The following endocrown materials were used: In-Ceram Zirconia (Zr), Vita Suprinity (VS), IPS Empress (IE), Grandio blocs (GR), VisCalor bulk (VS), and CopraPeek Light (CP). The Load application (600 N) was performed at the food bolus and tooth surface during the closing phase of the chewing cycle. The results for the endocrown and tooth remnants were determined according to the von Mises stress. The failure risk of the cement layer was also calculated based on the normal stress criterion.

Results

Model D (with an anatomic margin) showed the greatest stress concentrations, especially in the irregular and sharp angles of the restoration and tooth remnants. The stress concentrated on the dentin was significantly lower in Model B with a 20° bevel margin (20.86 MPa), i.e., 1.3 times lower than the other three margin designs (27.80 MPa). Restorative materials with higher elastic moduli present higher stress concentrations inside the endocrown and transmit less stress to the cement layer, resulting in lower bonding failure risks. In contrast, materials with an elastic modulus similar to that of dentin presented with a more homogeneous stress distribution on the whole structure.

Conclusions

An endocrown with a 20° bevel margin design could be a favorable preparation option for ETT. Composite resins (GR and VC) exhibit a more even stress distribution, and seem to be more promising materials for endocrown molars.