Early resin luting material damage around a circular fiber post in a root canal treated premolar by using micro-computerized tomographic and finite element sub-modeling analyses

Real-time simulation of the transplanted tooth using model order reduction

The biomechanics of transplanted teeth remain poorly understood due to a lack of models. In this context, finite element (FE) analysis has been used to evaluate the influence of occlusal morphology and root form on the biomechanical behavior of the transplanted tooth, but the construction of a FE model is extremely time-consuming. Model order reduction (MOR) techniques have been used in the medical field to reduce computing time, and the present study aimed to develop a reduced model of a transplanted tooth using the higher-order proper generalized decomposition method. The FE model of a previous study was used to learn von Mises root stress, and axial and lateral forces were used to simulate different occlusions between 75 and 175N. The error of the reduced model varied between 0.1% and 5.9% according to the subdomain, and was the highest for the highest lateral forces. The time for the FE simulation varied between 2.3 and 7.2 h. In comparison, the reduced model was built in 17s and interpolation of new results took approximately 2.10^-2s. The use of MOR reduced the time for delivering the root stresses by a mean 5.9 h. The biomechanical behavior of a transplanted tooth simulated by FE models was accurately captured with a significant decrease of computing time. Future studies could include using jaw tracking devices for clinical use and the development of more realistic real-time simulations of tooth autotransplantation surgery.

Finite Element Study of PEEK Materials Applied in Post-Retained Restorations

Background: This study aimed to investigate the biomechanical behaviors of polyether ether ketone (PEEK) and traditional materials (titanium and fiber) when used to restore tooth defects in the form of prefabricated post or customized post via computational modelling. Methods: First, the prototype of natural tooth, and the prototypes of prefabricated post and customized post were established, respectively, whilst the residual root was restored with dentin ferrule using reverse engineering methods. Then, the stress and strain of CFR-PEEK (PEEK reinforced by 30% carbon fiber) and pure PEEK (PEEK without any reprocessing) post were compared with those made in traditional materials using the three-dimensional finite element method. Results: From the stress point of view, compared with metal and fiber posts, CFR-PEEK and pure PEEK prefabricated post both demonstrated reduced post-core interface stress, post stress, post-root cement stress and root cement stress; moreover, CFR-PEEK and pure PEEK customized post demonstrated reduced post stress, post-root cement stress and root cement stress, while the strain of CFR-PEEK post was the closest to that of dentin. Conclusions: Compared with the traditional posts, both the CFR-PEEK and pure PEEK posts could reduce the risk of debonding and vertical root fracture, whether they were used as prefabricated posts or customized posts, but the biomechanical behavior of carbon fiber-reinforced CFR-PEEK restorations was the closest to dentin, no matter if they were used as prefabricated post or customized post. Therefore, the CFR-PEEK post could be more suitable to restore massive tooth defects. Pure PEEK needs filler reinforcement to be used for post-retained restoration.

Resin Cement Residue Removal Techniques: In Vitro Analysis of Marginal Defects and Discoloration Intensity Using Micro-CT and Stereomicroscopy

The objective was to compare marginal defects and evaluate discoloration for adhesively cemented veneers in vitro when using two cement removal techniques. Twenty premolars were prepared with chamfer and borders in enamel. IPS e.max CAD veneers were cemented using Panavia V5 and divided in two groups (n = 10): cement excess removed with a probe after tack-curing for 3–5 s, or cement excess removed with a brush, then completely polymerized. All teeth were stored in alginate gel until micro-CT examination. Scanning was performed twice: directly after cementation and after thermocycling (5000 cycles, between 5 and 55 °C). To analyze discoloration, teeth were colored using 0.5% basic fuchsine and examined under a stereomicroscope. Depth of dye infiltration was scored 0 (no discoloration) to 5 (discoloration along the entire margin). Statistically significant differences of cement defects before thermocycling were reported, where brushing showed more defects than probing (p = 0.0161). After thermocycling, the defects increased for both groups. Extensive discoloration was the most common (55.56%) when removing excess by probing; by brushing, 90% of the specimens exhibited slight discoloration (p = 0.008). Regression analysis showed no relationship between type of defect and degree of discoloration. Removing cement with a brush causes more marginal defects, however less discoloration after thermocycling.

A critical analysis of research methods and experimental models to study the load capacity and clinical behavior 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.

Do resin core build-ups obtain the benefits of higher bonding ability from direct or indirect technique?

PURPOSE

This study evaluated the effects of different materials (composite resin system including a photo-cure adhesive (DC) vs. resin cement system including a self-etching primer (PV)) and techniques (direct vs. indirect) for resin core build-up on the bonding performance to root canal dentin.

METHODS

The human teeth were decoronated and root canal preparation was performed. All specimens were randomly divided into four groups according to the combinations of the methods (Direct or Indirect) and the materials (DC: Clearfil DC Core, Kuraray Noritake Dental or PV: Panavia V5, Kuraray Noritake Dental). Micro-tensile bond strength (μTBS) and push-out tests were performed. Scanning electron microscope observations of the interface were also performed, and microcomputed tomography and optical coherence tomography were applied to evaluate the sealing ability.

RESULTS

The Indirect group had significantly higher μTBSs than the Direct group in the DC group (P = 0.0076). The PV group had significantly higher bond strengths than the DC group in both the Direct and Indirect groups (P < 0.001). The Direct/PV group demonstrated significantly higher push-out bond strength than the Direct/DC group (P < 0.001). In the Direct/PV group, the formation of resin tags was observed even on the apical side of the canal. Microleakage was more clearly observed in the DC group than in the PV group.

CONCLUSIONS

PV has a higher bonding ability to root canal dentin than DC. When using DC, the indirect technique exhibited a higher bonding ability than the direct technique.

Validated Finite Element Models of Premolars: A Scoping Review

Finite element (FE) models are widely used to investigate the biomechanics of reconstructed premolars. However, parameter identification is a complex step because experimental validation cannot always be conducted. The aim of this study was to collect the experimentally validated FE models of premolars, extract their parameters, and discuss trends. A systematic review was performed following Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Records were identified in three electronic databases (MEDLINE [PubMed], Scopus, The Cochrane Library) by two independent reviewers. Twenty-seven parameters dealing with failure criteria, model construction, material laws, boundary conditions, and model validation were extracted from the included articles. From 1306 records, 214 were selected for eligibility and entirely read. Among them, 19 studies were included. A heterogeneity was observed for several parameters associated with failure criteria and model construction. Elasticity, linearity, and isotropy were more often chosen for dental and periodontal tissues with a Young’s modulus mostly set at 18–18.6 GPa for dentine. Loading was mainly simulated by an axial force, and FE models were mostly validated by in vitro tests evaluating tooth strains, but different conditions about experiment type, sample size, and tooth status (intact or restored) were reported. In conclusion, material laws identified herein could be applied to future premolar FE models. However, further investigations such as sensitivity analysis are required for several parameters to clarify their indication.

Evaluation of early resin luting cement damage induced by voids around a circular fiber post in a root canal treated premolar by integrating micro-CT, finite element analysis and fatigue testing

OBJECTIVE

This study utilizes micro-CT image combined with finite element (FE) analysis and in vitro fatigue testing to investigate the mechanical behavior associating with early resin luting cement damage induced by voids around a circular fiber post in a root canal treated premolar.

METHODS

Six similar mandibular first premolars with root canal treatment were scanned with high resolution micro-CT before and after fatigue testing. Micro-CT images of all teeth were processed to identify various materials (dentin, luting cement and void) to evaluate the volume/position of the void in each reconstructed tooth root canal model. Six corresponding mesh models from CT images were generated to perform FE simulations under receiving oblique concentrated loads (200N) to evaluate the luting cement layer mechanical behavior. All teeth were subjected to the fatigue test with 240,000 load cycles simulating chewing for one year to compare results with those in FE simulations.

RESULTS

The result showed that most voids occurred adjacent to the apical third of the fiber post. Voids induced the fiber post to pull out, creating a stress concentration at the void boundary. Fatigue life in the experimental testing was found decreased with the stress value/micro-motion increasing in FE analysis.

SIGNIFICANCE

This study establishes that micro-CT, FE simulation and fatigue testing can be integrated to understand the early de-bonding mechanism at the luting cement layer in a root canal treated premolar, suggesting that attention must be paid to resin luting cement dissolving/debonding easier when voids occur in the apical and peri-apical areas of fiber posts.

Thermal-stress analysis of ceramic laminate veneer restorations with different incisal preparations using micro-computed tomography-based 3D finite element models

Main objective of this study is to investigate the thermal behavior of ceramic laminate veneer restorations of the maxillary central incisor with different incisal preparations such as butt joint and palatinal chamfer using finite element method. In addition, it is also aimed to understand the effect of different thermal loads which simulates hot and cold liquid imbibing in the mouth. Three-dimensional solid models of the sound tooth and prepared veneer restorations were obtained using micro-computed tomography images. Each ceramic veneer restoration was made up of ceramic, luting resin cement and adhesive layer which were generated based on the scanned images using computer-aided design software. Our solid model also included the remaining dental tissues such as periodontal ligament and surrounding cortical and spongy bones. Time-dependent linear thermal analyses were carried out to compare temperature changes and stress distributions of the sound and restored tooth models. The liquid is firstly in contact with the crown area where the maximum stresses were obtained. For the restorations, stresses on palatinal surfaces were found larger than buccal surfaces. Through interior tissues, the effect of thermal load diminished and smaller stress distributions were obtained near pulp and root-dentin regions. We found that the palatinal chamfer restoration presents comparatively larger stresses than the butt joint preparation. In addition, cold thermal loading showed larger temperature changes and stress distributions than those of hot thermal loading independent from the restoration technique.