Sequential software processing of micro-XCT dental-images for 3D-FE analysis

Stress distribution on teeth restored with veneers using various incisal preparation designs: A 3D finite element analysis study

STATEMENT OF PROBLEM

The type of veneer preparation is often chosen according to the patient's tooth structure and occlusion. Taking biomechanics into account in this decision-making process provides the clinician with more technical information on how to improve the clinical longevity of restorations. However, biomechanical analyses of veneer preparation designs are sparse.

PURPOSE

The purpose of this 3-dimensional (3D) finite element analysis with microcomputed tomography (µCT) data obtained from realistic models was to assess the influence of different preparations for ceramic and composite resin veneers on restoration and resin layer stress distribution.

MATERIAL AND METHODS

Four replicas of a central incisor were printed and prepared for laminate veneers with 4 different incisal edge designs: shoulder (SH), palatal chamfer (PC), palatal chamfer and oblique fracture involving the distal angle (OF-PC), and palatal chamfer involving horizontal incisal fracture (IF-PC). After fabrication and cementation of the veneers, the restored replicas were assessed with µCT, and 3D finite element models were built. A 100-N load was applied on the palatal surface at 60 and 125 degrees relative to the longitudinal axis. Maximum principal stress and stress distribution on the veneers, cement layer, and tooth structure were calculated and analyzed.

RESULTS

The SH preparation exhibited better stress distribution than the PC preparation, and the cement layer and the veneer were subjected to lower stress. The IF-PC preparation had better stress distribution than the OF-PC. The shoulder and IF-PC showed higher stress on laminate veneers, but lower stress on the cement layer. Ceramic veneers exhibited lower stress than composite resin veneers.

CONCLUSIONS

The different incisal preparations for laminate veneers influenced stress distribution on restorations and on the resin cement layer. The shoulder type preparation showed better stress distribution and the composite resin veneers showed unfavorable results compared with the ceramic veneers.

Plant microphenotype: from innovative imaging to computational analysis

The microphenotype plays a key role in bridging the gap between the genotype and the complex macro phenotype. In this article, we review the advances in data acquisition and the intelligent analysis of plant microphenotyping and present applications of microphenotyping in plant science over the past two decades. We then point out several challenges in this field and suggest that cross-scale image acquisition strategies, powerful artificial intelligence algorithms, advanced genetic analysis, and computational phenotyping need to be established and performed to better understand interactions among genotype, environment, and management. Microphenotyping has entered the era of Microphenotyping 3.0 and will largely advance functional genomics and plant science.

Anterior provisional fixed partial dentures: A finite element analysis

PURPOSE

The aim of this study was to analyze the stress distribution of fiber-reinforced composite provisional fixed partial denture utilizing a finite element analysis model.

MATERIAL AND METHODS

Three anterior teeth were collected: upper right central, left central, and right lateral incisors. A fiber-reinforced composite strip was applied to the palatal surfaces of the teeth. Micro-computed tomographic scans were acquired of the models in order to generate three-dimensional geometrical replicas. Finite element analysis was used to assess the stress distribution of fiber-reinforced composite provisional fixed partial denture using different pontic types under static applied forces that were 100, 30, and 0 N.

RESULTS

The maximum stress values were found on the unprepared natural pontic. Stress values ranged from 92.2 to 909.8, 116.4 to 646.7, and 93.8 to 393.5 MPa for composite, naturally prepared, and natural unprepared pontic, respectively.

CONCLUSIONS

Using unprepared natural tooth pontic in anterior provisional fixed partial denture to replace missing central incisors is considered superior to other types in terms of stress distribution.

Mechanical behavior of endodontically treated teeth: A three-dimensional finite element analysis using displacement vector

PURPOSE

This study aimed to analyze the effects of core materials, remaining tooth structures, and interfacial bonding on stress distribution in endodontically treated teeth using finite element analysis (FEA).

MATERIALS AND METHODS

Three-dimensional FEA was conducted using a reverse engineering technique based on maxillary premolars scanned by micro-computed tomography. Six models were generated with or without ferrules and with one of the following three abutment systems: metal core, resin core, or resin core with fiber posts. In each model, bonding and debonding were assumed in the dentin and surrounding structures: bonded and debonded models. The maximum principal stress values were recorded, and stress distribution of the entire restored teeth and dentin was generated. Furthermore, the distribution of the displacement vector of the debonded models was generated.

RESULTS

In comparing the bonded and debonded models, the debonded models showed larger values for tensile stresses than those in bonded models for all abutment models. The models without ferrules rotated around the center of the abutment, whereas those with ferrules did not show remarkable displacement in the analysis.

CONCLUSION

FEA assuming fracture of adhesive interface proved to be an effective method to clarify the significance of ferrules. It prevents stress concentration in dentin by reducing the rotation of the abutment, even when the adhesive fails.

Application and limitations of configuration factor (C-factor) in stress analysis of dental restorations

OBJECTIVE

The configuration factor (C-factor) is an index used to evaluate the relationship between cavity configuration and the development of polymerization shrinkage stress in dental restorations. Although C-factor has been widely researched, its correlation with stress analysis in dental restorations remains controversial. This review aims to discuss the application and limitations of C-factor and define the restricted conditions under which the C-factor "rule of thumb" is applicable.

METHODS

A thorough literature review was conducted on the application and limitations of C-factor in stress analysis of dental restorations. This was principally based on MEDLINE/PubMed and Web of Science databases and a review of the relevant studies and publications in scientific papers in international peer-reviewed journals for the specific topic of C-factor and polymerization shrinkage.

RESULTS

The C-factor alone cannot provide an accurate prediction of the shrinkage stress of restorations and the mechanical behavior of material-tooth interfaces. C-factor is only applicable under one condition not typically seen in clinical practice: low, near-rigid compliance.

SIGNIFICANCE

Conditions for the application of C-factor have been explicitly defined. A more accurate and precise understanding and utilization of the C-factor is of benefit as it contributes to better understanding of polymerization shrinkage behavior of restorations.

A Review of Image-Based Simulation Applications in High-Value Manufacturing

Image-Based Simulation (IBSim) is the process by which a digital representation of a real geometry is generated from image data for the purpose of performing a simulation with greater accuracy than with idealised Computer Aided Design (CAD) based simulations. Whilst IBSim originates in the biomedical field, the wider adoption of imaging for non-destructive testing and evaluation (NDT/NDE) within the High-Value Manufacturing (HVM) sector has allowed wider use of IBSim in recent years. IBSim is invaluable in scenarios where there exists a non-negligible variation between the 'as designed' and 'as manufactured' state of parts. It has also been used for characterisation of geometries too complex to accurately draw with CAD. IBSim simulations are unique to the geometry being imaged, therefore it is possible to perform part-specific virtual testing within batches of manufactured parts. This novel review presents the applications of IBSim within HVM, whereby HVM is the value provided by a manufactured part (or conversely the potential cost should the part fail) rather than the actual cost of manufacturing the part itself. Examples include fibre and aggregate composite materials, additive manufacturing, foams, and interface bonding such as welding. This review is divided into the following sections: Material Characterisation; Characterisation of Manufacturing Techniques; Impact of Deviations from Idealised Design Geometry on Product Design and Performance; Customisation and Personalisation of Products; IBSim in Biomimicry. Finally, conclusions are drawn, and observations made on future trends based on the current state of the literature.

Influence of thermal and thermomechanical stimuli on a molar tooth treated with resin-based restorative dental composites

OBJECTIVES

In-vivo experimental techniques to understand the biomechanical behavior of a restored tooth, under varying oral conditions, is very limited because of the invasive nature of the study and complex tooth geometry structure. Therefore, 3D-Finite element analyses are used to understand the behavior of a restored tooth under varying oral conditions. In this study, the distribution of maximum principal stress (MaxPS) and the location of MaxPS on a restored tooth using six different commercially available dental resin composites under the influence of thermal and thermomechanical stimuli are performed.

METHODS

An intact tooth was scanned using µ-CT and segmented to obtain separate geometric models of the tooth, including enamel and dentine. Then, a class II mesial-occlusal-distal (MOD) cavity was constructed for the tooth model. The restored tooth model was further meshed and imported to the commercial Finite Element (FE) software ANSYS. Thermal hot and cold stimuli at 50 °C and 2 °C, respectively, were applied on the occlusal and lingual surface of the tooth model with the tooth's ambient temperature set at 37 °C. A uniform loading of 400 N was applied on the occlusal surface of the tooth to imitate the masticatory forces during the cyclic thermal stimuli.

RESULTS

The results of this study showed that the restorative materials with higher thermal conductivity showed a lower temperature gradient between the restoration and enamel, during the application of thermal stimuli, leading to a higher value of MaxPS on the restoration. Moreover, on applying thermal stimuli, the location of MaxPS at the restoration-enamel junction (REJ) changes based on the value of the coefficient of thermal expansion (CTE). The MaxPS distribution on the application of simultaneous thermal and mechanical stimuli was not only dependent on the elastic modulus of restorative materials but also their thermal properties such as the CTE and thermal conductivity. The weakest part of the restoration was at the REJ, as it experienced the peak stress level during the application of thermomechanical stimuli.

SIGNIFICANCE

The findings from this study suggest that restorative materials with lower values of elastic modulus, lower coefficient of thermal expansion and higher values of thermal conductivity result in lower stresses on the restoration. The outcomes from this study also suggest that the thermal and mechanical properties of a restorative material can have a considerable effect on the selection of restorative materials by dental clinicians over conventional restorative materials.

Substantial regional differences in the biomechanical behavior of molar treated with selective caries tissue removal technique: a finite element study

OBJECTIVES

Selective caries removal (SCR) is recommended over non-selective removal for managing deep carious lesions to avoid pulp exposure and maintain pulp vitality. During SCR, residual carious dentin is left behind and sealed beneath the restoration. The biomechanical effects of such residual lesions on the restored tooth remain unclear and were assessed using finite element modeling (FEM).

METHODS

Based on μ-CT images of a healthy permanent human third molar, we developed five finite element models. Generic class I and II cavity restorations were modeled where residual lesions of variable sizes were either left or fully removed on occlusal and proximal surfaces. The cavities were restored with adhesive composite. All 3D-FE models were compared with a model of a healthy, non-treated molar. A vertical load of 100 N was applied onto the occlusal surface.

RESULTS

Regardless of the lesion size, in molars with occlusal lesions higher mean stresses were predicted along the filling-lesion interface than in all other models. The smallest occlusal lesion (Ø₁ = 1 mm) resulted in the highest maximum stresses at the filling-lesion interface with large stress concentrations at the filling walls indicating failure risk. In conclusion, lesion site and extent are influencing parameters affecting the filling-lesion interactions and thus the biomechanical behavior of the tooth after SCR.

SIGNIFICANCE

Retaining carious lesions around the pulpal floor affects the deformation and stress states in tooth-filling complexes. The higher stresses observed in molars with occlusal lesions may affect restoration stability and longevity. Suprisingly, more extended occlusal lesions may provide a more favorable tooth performance than less extended ones. In contrast, in molars with proximal lesions the residual lesion had only limited effect on the tooth's biomechanical condition.

Stress Distributions for Hybrid Composite Endodontic Post Designs with and without a Ferrule: FEA Study

The aim of the current work was to analyze the influence of the ferrule effect for hybrid composite endodontic post designs consisting of carbon (C) and glass (G) fiber-reinforced polyetherimide (PEI), in upper canine teeth. Starting from theoretical designs of C-G/PEI hybrid composite posts with different Young's moduli (Post A-57.7 GPa, Post B-31.6 GPa, Post C-graduated from 57.7 to 9.0 GPa in the coronal-apical direction) in endodontically treated anterior teeth, the influence of the ferrule effect was determined through finite element analysis (FEA). On the surface of the crown, a load of 50 N was applied at 45° to the longitudinal axis of the tooth. Maximum principal stresses were evaluated along the C-G/PEI post as well as at the interface between the surrounding tooth structure and the post. Maximum stress values were lower than those obtained for the corresponding models without a ferrule. The presence of a ferrule led to a marked decrease of stress and gradients especially for posts A and B. A less marked effect was globally found for Post C, except in a cervical margin section along a specific direction, where a significant decrease of the stress was probably due to local geometric features, compared to the model without a ferrule. The presence of a ferrule did not generally provide a marked benefit in the case of the graduated Post C, in comparison to other C-G/PEI posts. The outcomes suggest how such a hybrid composite post alone should be sufficient to optimize the stress distribution, dissipating stress from the coronal to the apical end.

Endodontic Access Effect on Full Contour Zirconia and Lithium Disilicate Failure Resistance

Objectives:

To evaluate the effect of endodontic access on the failure load resistance of both adhesively and conventionally luted, full-contour monolithic yttria-stabilized zirconium dioxide (Y-TZP) and adhesively luted lithium disilicate (LD) crowns cemented on prepared teeth.

Methods and Materials:

Seventy-two human maxillary molars were prepared per respective guidelines for all-ceramic crowns with one group (n=24) restored with LD and the other (n=48) receiving Y-TZP crowns. Preparations were scanned using computer-aided design/computer-aided milling (CAD/CAM) technology, and milled crowns were sintered following manufacturer recommendations. All LD crowns and half (n=24) of the Y-TZP crowns were adhesively cemented, while the remaining Y-TZP specimens were luted using a conventional glass ionomer cement (GIC). One LD group, one Y-TZP adhesive group, and one GIC-luted group (all n=12) then received endodontic access preparations by a board-certified endodontist: the pulp chambers were restored with a dual-cure, two-step, self-etch adhesive and a dual-cure resin composite core material. The access preparations were restored using a nano-hybrid resin composite after appropriate ceramic margin surface preparation. After 24 hours, all specimens were loaded axially until failure; mean failure loads were analyzed using Mann-Whitney U test (α=0.05)

Results:

Endodontic access did not significantly reduce the failure load of adhesively luted LD or Y-TZP crowns, but Y-TZP crowns with GIC cementation demonstrated significantly less failure load.

Conclusions:

These initial findings suggest that endodontic access preparation may not significantly affect failure load resistance of adhesively luted Y-TZP and LD crowns. Definitive recommendations cannot be proposed until fatigue testing and coronal seal evaluations have been accomplished.

3D modeling: a future of cardiovascular medicine

Cardiovascular disease resulting from atypical cardiac structures continues to be a leading health concern despite advancements in diagnostic imaging and surgical techniques. However, the ability to visualize spatial relationships using current technologies remains a challenge. Therefore, 3D modeling has gained significant interest to understand complex and atypical cardiovascular disorders. Moreover, 3D modeling can be personalized and patient-specific. 3D models have been demonstrated to aid surgical planning and simulation, enhance communication among surgeons and patients, optimize medical device design, and can be used as a potential teaching tool in medical schools. In this review, we discuss the key components needed to generate cardiac 3D models. We highlight prevalent structural conditions that have utilized 3D modeling in pre-operative planning. Furthermore, we discuss the current limitations of routine use of 3D models in the clinic as well as future directions for utilization of this technology in the cardiovascular field.

Metal Posts and the Effect of Material–Shape Combination on the Mechanical Behavior of Endodontically Treated Anterior Teeth

The control of the process–structure–property relationship of a material plays an important role in the design of biomedical metal devices featuring desired properties. In the field of endodontics, several post-core systems have been considered, which include a wide range of industrially developed posts. Endodontists generally use posts characterized by different materials, sizes, and shapes. Computer-aided design (CAD) and finite element (FE) analysis were taken into account to provide further insight into the effect of the material–shape combination of metal posts on the mechanical behavior of endodontically treated anterior teeth. In particular, theoretical designs of metal posts with two different shapes (conical-tapered and conical-cylindrical) and consisting of materials with Young’s moduli of 110 GPa and 200 GPa were proposed. A load of 100 N was applied on the palatal surface of the crown at 45° to the longitudinal axis of the tooth. Linear static analyses were performed with a non-failure condition. The results suggested the possibility to tailor the stress distribution along the metal posts and at the interface between the post and the surrounding structures, benefiting from an appropriate combination of a CAD-based approach and material selection. The obtained results could help to design metal posts that minimize stress concentrations.

Effect of cavity preparation design and ceramic type on the stress distribution, strain and fracture resistance of CAD/CAM onlays in molars

Objective

This study aimed to evaluate the effect of the cavity preparation and ceramic type on the stress distribution, tooth strain, fracture resistance and fracture mode of human molar teeth restored with onlays.

Material and Methods

Forty-eight molars were divided into four groups (n=12) with assorted combinations of two study factors: BL- conventional onlay preparation with boxes made from leucite ceramic (IPS-Empress CAD, Ivoclar Vivadent); NBL- conservative onlay preparation without boxes made from leucite ceramic; BD- conventional onlay preparation with boxes made from lithium disilicate glass ceramic (IPS e.max CAD, Ivoclar Vivadent); NBL- conservative onlay preparation with boxes made from lithium disilicate glass ceramic cuspal deformation (µS) was measured at 100 N and at maximum fracture load using strain gauge. Fracture resistance (N) was measured using a compression test, and the fracture mode was recorded. Finite element analysis was used to evaluate the stress distribution by modified von Mises stress criteria. The tooth strain and fracture resistance data were analyzed using the Tukey test and two-way ANOVA, and the fracture mode was analyzed by the chi-square test (α=0.05).

Results

The leucite ceramic resulted in higher tooth deformation at 100 N and lower tooth deformation at the maximum fracture load than the lithium disilicate ceramic (P<0.001). The lithium disilicate ceramic exhibited higher fracture resistance than the leucite ceramic (P<0.001). The conservative onlay resulted in higher fracture strength for lithium disilicate ceramic. Finite element analysis results showed the conventional cavity preparation resulted in higher stress concentration in the ceramic restoration and remaining tooth than the conservative onlay preparation. The conservative onlays exhibited increased fracture resistance, reduced stress concentration and more favorable fracture modes.

Conclusion

Molars restored with lithium disilicate CAD-CAM ceramic onlays exhibited higher fracture resistance than molars restored with leucite CAD-CAM ceramic onlays.

FE analysis of conceptual hybrid composite endodontic post designs in anterior teeth

OBJECTIVES

To assess conceptual designs of dental posts consisting of polyetherimide (PEI) reinforced with carbon (C) and glass (G) glass fibers in endodontically treated anterior teeth.

METHODS

3D tessellated CAD and geometric models of endodontically treated anterior teeth were generated from Micro-CT scan images. Model C-G/PEI composite posts with different Young's moduli were analyzed by Finite Element (FE) methods post A (57.7GPa), post B (31.6GPa), post C (from 57.7 to 9.0GPa in the coronal-apical direction). A load of 50N was applied at 45° to the longitudinal axis of the tooth, acting on the palatal surface of the crown. The maximum principal stress distribution was determined along the post and at the interface between the post and the surrounding structure.

RESULTS

Post C, with Young's modulus decreasing from 57.7 to 9.0GPa in the coronal-apical direction, reduced the maximum principal stress distribution in the restored tooth. Post C gave reduced stress and the most uniform stress distribution with no stress concentration, compared to the other C-G/PEI composite posts.

SIGNIFICANCE

The FE analysis confirmed the ability of the functionally graded post to dissipate stress from the coronal to the apical end. Hence actual (physical) C-G/PEI posts could permit optimization of stress distributions in endodontically treated anterior teeth.

Evaluation of cavity size, kind, and filling technique of composite shrinkage by finite element

Background:

Cavity preparation reduces the rigidity of tooth and its resistance to deformation. The purpose of this study was to evaluate the dimensional changes of the repaired teeth using two types of light cure composite and two methods of incremental and bulk filling by the use of finite element method.

Materials and Methods:

In this computerized in vitro experimental study, an intact maxillary premolar was scanned using cone beam computed tomography instrument (SCANORA, Switzerland), then each section of tooth image was transmitted to Ansys software using AUTOCAD. Then, eight sizes of cavity preparations and two methods of restoration (bulk and incremental) using two different types of composite resin materials (Heliomolar, Brilliant) were proposed on software and analysis was completed with Ansys software.

Results:

Dimensional change increased by widening and deepening of the cavities. It was also increased using Brilliant composite resin and incremental filling technique.

Conclusion:

Increase in depth and type of filling technique has the greatest role of dimensional change after curing, but the type of composite resin does not have a significant role.

Stress distribution in a tooth treated through minimally invasive access compared to one treated through traditional access: A finite element analysis study

Introduction

The purpose of this study was to compare the stress distributions in the teeth treated through minimally invasive access (MIA) designs to those of the teeth treated through traditional straight-line access and their relationship to the final restoration using three-dimensional finite element analysis (FEA).

Materials and Methods

Four FEA models of an extracted mandibular first molar were constructed. An intact model served as the control, whereas the other three were prepared with either an MIA or traditional straight-line access. Simulated composite access fillings with or without a simulated gold crown were applied to the models, followed by application of an occlusal load of 100 N. Von Mises stresses in the teeth were then calculated and analyzed.

Results

Stress values within the dentin for baseline, MIA with composite filling, MIA with composite filling and crown, and traditional access with composite filling and crown were 10.14 MPa, 6.98 MPa, 11.79 MPa, and 16.81 MPa, respectively. Higher stress values indicate that the tooth is more prone to fracture.

Conclusions

A traditional endodontic access cavity may render a tooth more susceptible to fracture compared with an MIA design.

Stress Distribution, Tooth Remaining Strain, and Fracture Resistance of Endodontically Treated Molars Restored Without or With One or Two Fiberglass Posts And Direct Composite Resin

Objectives:

To evaluate the effects of direct composite resin without a post or with one or two fiberglass posts on the restoration of severely compromised endodontically treated molars.

Methods and Materials:

Forty-five molars with 2 mm of “remaining tooth structure” were divided into three groups: Wfgp, restored with Filtek Z350XT without a fiberglass post; 1fgp, restored with Z350XT with one fiberglass post in the distal root canal; and 2fgp, restored with Z350XT with two fiberglass posts, one in the distal root canal and the other in the mesial-buccal root canal. The teeth were load cycled. Tooth remaining strain was measured using strain gauges (n=10) at two moments: TrSt-100 N, during 100 N occlusal loading, and TrSt-Fr, at fracture load. Fracture resistance was calculated, and fracture mode was classified. The elastic modulus and Vickers hardness were calculated using dynamic indentation (n=5). Stress distribution was analyzed by three-dimensional finite element analysis.

Results:

The use of two fiberglass posts resulted in lower fracture resistance than was noted in the groups with one fiberglass post and without fiberglass posts. The lingual surface of the remaining tooth had higher strain values than the buccal surface, regardless of the restorative technique and moment of evaluation. The absence of a fiberglass post resulted in significantly higher strain values and more irreparable fracture modes than were noted in the other groups. The use of one fiberglass post had a better strain/fracture resistance ratio. Stresses were concentrated in the occlusal portion of the post and in the furcation region. The presence of one fiberglass post resulted in better stress distribution in the entire distal root dentin, reducing stress on the critical areas.

Conclusions:

The use of one fiberglass post for restoring molars with direct composite resin resulted in higher fracture resistance than did the use of two fiberglass posts; it also resulted in better tooth remaining strain and stress distribution and more reparable fracture modes than were seen in the group without a fiberglass post.

Scan-layered reconstructions: A pilot study of a nondestructive dental histoanatomical analysis method and digital workflow to create restorations driven by natural dentin and enamel morphology

OBJECTIVE

This work aims to present a pilot study of a non-destructive dental histo-anatomical analysis technique as well as to push the boundaries of the presently available restorative workflows for the fabrication of highly customized ceramic restorations.

MATERIALS AND METHODS

An extracted human maxillary central incisor was subject to a micro computed tomography scan and the acquired data was transferred into a workstation, reconstructed, segmented, evaluated and later imported into a Computer-Aided Design/Computer-Aided Manufacturing software for the fabrication of a ceramic resin-bonded prosthesis.

RESULTS

The obtained prosthesis presented an encouraging optical behavior and was used clinically as final restoration.

CONCLUSION

The digitally layered restorative replication of natural tooth morphology presents today as a clear possibility. New clinical and laboratory-fabricated, biologically inspired digital restorative protocols are to be expected in the near future.

CLINICAL SIGNIFICANCE

The digitally layered restorative replication of natural tooth morphology presents today as a clear possibility. This pilot study may represent a stimulus for future research and applications of digital imaging as well as digital restorative workflows in service of esthetic dentistry.

Microtensile bond strength of repaired indirect resin composite

PURPOSE

The objective of this study was to investigate the effect of surface treatments on microtensile bond strengths (MTBSs) of two types of indirect resin composites bonded to a conventional direct resin composite.

MATERIALS AND METHODS

Indirect resin composite blocks of Ceramage and SR Nexco were prepared in a plastic mold having a dimension of 10 × 10 × 4 mm. These composite blocks were divided into three groups according to their surface treatments: Group1: Sandblast (SB); Group2: Sandblast and ultrasonically clean (SB+UL); Group3: Sandblast plus silane (SB+SI). After bonding with direct resin composite, indirect-direct resin composite blocks were kept in distilled water for 24 hours at 37℃ and cut into microbars with the dimension of 1 × 1 × 8 mm. Microbar specimens (n = 40 per group) were loaded using a universal testing machine. Failure modes and compositions were evaluated by SEM. The statistical analyses of MTBS were performed by two-way ANOVA and Dunnett's test at α = .05.

RESULTS

Surface treatments and brands had effects on the MTBS without an interaction between these two factors. For SR Nexco, the MTBSs of SB and SB+SI group were significantly higher than that of SB+UL. For Ceramage, the MTBSs of SB and SB+SI were significantly higher than that of SB+UL. The mean MTBS of the Ceramage specimens was significantly higher than that of SR Nexco for all surface treatments.

CONCLUSION

Sandblasting with or without silane application could improve the bond strengths of repaired indirect resin composites to a conventional direct resin composite.

Light transmittance and surface roughness of a feldspathic ceramic CAD-CAM material as a function of different surface treatments

BACKGROUND

The aim of the present study was to determine the effect of different surface treatments on light transmission of aesthetic feldspathic ceramics used in CAD-CAM chairside restorations.

METHODS

Forty eight feldspatic ceramic test specimens were prepared from prefabricated CAD-CAM blocks by using a slow speed diamond saw. Test specimens were prepared and divided into 4 groups (n = 12). In the control group, no surface treatments were applied on the feldspathic ceramic surfaces. In the hydrofluoric acid group, the bonding surfaces of feldspathic ceramics were etched with 9.5 % hydrofluoric acid. In the sandblasting group the feldspathic ceramic surfaces were air-abraded with 30-μm alumium oxide (Al2O3) particles and Er:YAG laser was used to irradiate the ceramic surfaces. The incident light power given by the LED device and the transmitted light power through each ceramic sample was registered using a digital LED radiometer device. Each polymerization light had a light guide with 8-mm-diameter tips. Light transmission of feldspathic ceramic samples was determined by placing it on the radiometer and irradiating the specimen for 10 s at the highest setting for each light polymerization. All specimens were coated with gold using a sputter coater and examined under a field emission scanning electron microscope. Surface roughness measurement each group were evaluated with 3D optical surface and tactile profilometers.

RESULTS

One-way ANOVA test results revealed that both surface conditioning method significantly affect the light transmittance (F:412.437; p < 0.001) and the surface roughness values (F:16.386; p < 0.001). Al2O3 and Er-YAG laser application reduced the light transmission significantly (p < 0.05).

CONCLUSIONS

The laser and Al2O3 applications reduced the light transmission of 1.5 mm thickness feldspathic ceramic material below the value of 400 mW/cm(2) which is critical limit for safe polymerization.

Establishment of sequential software processing for a biomechanical model of mandibular reconstruction with custom-made plate

The aim of this study is to describe the sequential software processing of computed tomography (CT) dataset for reconstructing the finite element analysis (FEA) mandibular model with custom-made plate, and to provide a theoretical basis for clinical usage of this reconstruction method. A CT scan was done on one patient who had mandibular continuity defects. This CT dataset in DICOM format was imported into Mimics 10.0 software in which a three-dimensional (3-D) model of the facial skeleton was reconstructed and the mandible was segmented out. With Geomagic Studio 11.0, one custom-made plate and nine virtual screws were designed. All parts of the reconstructed mandible were converted into NURBS and saved as IGES format for importing into pro/E 4.0. After Boolean operation and assembly, the model was switched to ANSYS Workbench 12.0. Finally, after applying the boundary conditions and material properties, an analysis was performed. As results, a 3-D FEA model was successfully developed using the softwares above. The stress-strain distribution precisely indicated biomechanical performance of the reconstructed mandible on the normal occlusion load, without stress concentrated areas. The Von-Mises stress in all parts of the model, from the maximum value of 50.9MPa to the minimum value of 0.1MPa, was lower than the ultimate tensile strength. In conclusion, the described strategy could speedily and successfully produce a biomechanical model of a reconstructed mandible with custom-made plate. Using this FEA foundation, the custom-made plate may be improved for an optimal clinical outcome.

Influence of cavity design preparation on stress values in maxillary premolar: a finite element analysis

Aim

To analyze the influence of cavity design preparation on stress values in three-dimensional (3D) solid model of maxillary premolar restored with resin composite.

Methods

3D solid model of maxillary second premolar was designed using computed-tomography (CT) data. Based on a factorial experiment, 9 different mesio-occlusal-distal (MOD) cavity designs were simulated, with three cavity wall thicknesses (1.5 mm, 2.25 mm, 3.0 mm), and three cusp reduction procedures (without cusp reduction, 2.0 mm palatal cusp reduction, 2.0 mm palatal and buccal cusp reduction). All MOD cavities were simulated with direct resin composite restoration (Gradia Direct Posterior, GC, Japan). Finite element analysis (FEA) was used to calculate von Mises stress values.

Results

The von Mises stresses in enamel, dentin, and resin composite were 79.3-233.6 MPa, 26.0-32.9 MPa, and 180.2-252.2 MPa, respectively. Considering the influence of cavity design parameters, cuspal reduction (92.97%) and cavity wall thickness (3.06%) significantly (P < 0.05) determined the magnitude of stress values in enamel. The influence of cavity design parameters on stress values in dentin and resin composite was not significant. When stresses for enamel, dentine, and resin composite were considered all together, palatal cusp coverage was revealed as an optimal option. Cavity wall thickness did not show a significant effect on stress values.

Conclusion

Based on numerical simulations, a palatal cusp reduction could be suggested for revealing lower stress values in dental tissues and restorative material. This type of cavity design should contribute to better biomechanical behavior of tooth-restoration complex, consequently providing the long-lasting clinical results.

Quantitative analysis of mechanically retentive ceramic bracket base surfaces with a three-dimensional imaging system

OBJECTIVE

To investigate the three-dimensional structural features of three types of mechanically retentive ceramic bracket bases.

MATERIALS AND METHODS

One type of stainless steel (MicroArch, Tomy, Tokyo, Japan) and three types of ceramic maxillary right central incisor brackets-Crystaline MB (Tomy), INVU (TP Orthodontics, La Porte, Ind), and Inspire Ice (Ormco, Glendora, Calif)-were tested to compare and quantitatively analyze differences in the surface features of each ceramic bracket base using scanning electron microscopy (SEM), a three-dimensional (3D) optical surface profiler, and microcomputed tomography (micro-CT). One-way analysis of variance was used to find differences in bracket base surface roughness values and surface areas between groups according to base designs. Tukey's honestly significant differences tests were used for post hoc comparisons.

RESULTS

SEM revealed that each bracket exhibited a unique surface texture (MicroArch, double mesh; Crystaline MB, irregular; INVU, single mesh; Inspire Ice, bead ball). With a 3D optical surface profiler, the stainless steel bracket showed significantly higher surface roughness values. Crystaline MB had significantly higher surface roughness values than Inspire Ice. Micro-CT demonstrated that stainless steel brackets showed significantly higher whole and unit bracket base surface areas. Among ceramic brackets, INVU showed significantly higher whole bracket base surface area, and Crystaline MB showed a significantly higher unit bracket base surface area than Inspire Ice.

CONCLUSION

Irregular bracket surface features showed the highest surface roughness values and unit bracket base surface area among ceramic brackets, which contributes to increased mechanically retentive bracket bonding strength.

Three-dimensional finite element modelling of all-ceramic restorations based on micro-CT

OBJECTIVES

To describe and apply a method of modelling dental crowns and three-unit fixed partial dentures (FPD) for finite element analyses (FEA) from 3D images obtained using a micro-CT scanner.

METHODS

A crown and a three-unit fixed partial denture (FPD) made of a ceramic framework (Y-TZP) and veneered with porcelain (VM9) were scanned using an X-ray micro-CT scanner with a pixel size of 6.97 μm. Slice images from both structures were generated at each 0.034 mm and processed by an interactive image control system (Mimics). Different masks of abutments, framework and veneer were extracted using thresholding and region growing tools based on X-ray image brightness and contrast. 3D objects of each model were incorporated into non-manifold assembly and meshed simultaneously. Volume meshes were exported to the FEA software (ABAQUS), and the load-generated stress distribution was analyzed.

RESULTS

FEA models showed great shape resemblance with the structures. The use of non-manifold assembly ensured matching surfaces and coinciding nodes between different structural parts. For the crown model, tensile stresses were concentrated in the internal surface of the core, near to the applied load. For the FPD model, the highest tensile stresses were located in the framework, on the cervical area of connectors and pontic.

CONCLUSIONS

Valid 3D models of dental crown and FPD can be generated by combining micro-CT scanning and Mimics software, emphasizing its importance as design tool in dental research.

CLINICAL SIGNIFICANCE

The 3D FEA method described in this work is an important tool to predict the stress distribution, assisting on structural design of dental restorations.

BIOMECHANICAL EVALUATION OF ENDODONTIC POST-RESTORED TEETH — FINITE ELEMENT ANALYSIS

Endodontically treated teeth are usually weak and need prosthodontic restorations. The selection and design of endodontic posts are associated with the biomechanical behavior of teeth. This study analyzed the stress in endodontically treated teeth using the finite element method. The model of a restored tooth consists of the post, core, crown, dentin, periodontal ligament, cortical bone, cancellous bone, and gingiva. The post is given various design parameters: three diameters (1.3, 1.8, and 2.3 mm), four lengths (9.7, 12.7, 15.7, and 18.7 mm), three shapes (cylindrical, tapered, and two-step cylindrical), and five materials (gold alloy, stainless steel, titanium, carbon fiber, and glass fiber). Static loads of 100 N are applied in the vertical, horizontal, and oblique directions on the incisal edge, and the generated von Mises stress is calculated. Results show that increases in the post diameter and elastic modulus decrease the post stress. The dentin stress slightly decreases with increasing post stress. The loading mode greatly affects the peak dentin stress magnitude (horizontal force (37 MPa) > oblique force (28 MPa) > vertical force (9 MPa)) and location. Furthermore, the horizontal force induces harmful bending of the tooth structure.

Numerical fatigue 3D-FE modeling of indirect composite-restored posterior teeth

OBJECTIVE

In restored teeth, stresses at the tooth-restoration interface during masticatory processes may fracture the teeth or the restoration and cracks may grow and propagate. The aim was to apply numerical methodologies to simulate the behavior of a restored tooth and to evaluate fatigue lifetimes before crack failure.

MATERIALS AND METHODS

Using a CAD-FEM procedure and fatigue mechanic laws, the fatigue damage of a restored molar was numerically estimated. Tessellated surfaces of enamel and dentin were extracted by applying segmentation and classification algorithms, to sets of 2D image data. A user-friendly GUI, which enables selection and visualization of 3D tessellated surfaces, was developed in a MatLab(®) environment. The tooth-boundary surfaces of enamel and dentin were then created by sweeping operations through cross-sections. A class II MOD cavity preparation was then added into the 3D model and tetrahedral mesh elements were generated. Fatigue simulation was performed by combining a preliminary static FEA simulation with classical fatigue mechanical laws.

RESULTS

Regions with the shortest fatigue-life were located around the fillets of the class II MOD cavity, where the static stress was highest.

SIGNIFICANCE

The described method can be successfully adopted to generate detailed 3D-FE models of molar teeth, with different cavities and restorative materials. This method could be quickly implemented for other dental or biomechanical applications.