An investigation of dentinal fluid flow in dental pulp during food mastication: simulation of fluid-structure interaction

Role of YAP in Odontoblast Damage Repair in a Dentin Hypersensitivity Model

OBJECTIVES

The aim of this study was to investigate the molecular mechanism underlying odontoblast damage repair in dentin hypersensitivity (DH) and the role of Yes-associated protein (YAP) in this process.

METHODS

The DH model was constructed in Sprague-Dawley (SD) rats, and the in vivo expression of Piezo1, Integrin αvβ3, YAP, and dentin sialophosphoprotein (DSPP) was detected by immunohistochemistry. COMSOL Multiphysics software was used to simulate the dentinal tubule fluid flow velocity and corresponding fluid shear stress (FSS) on the odontoblast processes. MDPC-23 cells were cultured in vitro and loaded with a peristaltic pump for 1 hour at FSS values of 0.1, 0.3, 0.5, and 0.7 dyne/cm2. The expression of Piezo1, Integrin αvβ3, and YAP was detected by immunofluorescence. Verteporfin (a YAP-specific inhibitor) was utilised to confirm the effect of YAP on the expression of dentineogenesis-related protein under FSS.

RESULTS

The level and duration of external mechanical stimuli have an effect on the functional expression of odontoblasts. In DH, the harder the food that is chewed, the faster the flow of the dentinal tubule fluid and the greater the FSS on the odontoblast processes. The expression of Piezo1, Integrin αvβ3, and YAP can be promoted when the FSS is less than 0.3 dyne/cm2. After YAP inhibition, the DSPP protein expression level was reduced at 0.3 dyne/cm2 FSS.

CONCLUSIONS

These results suggest that appropriate FSS can enhance the expression of odontoblast-related factors in odontoblasts via the Piezo1-Integrin αvβ3-YAP mechanotransduction pathway and the YAP appears to play an essential role in the response of odontoblasts to external mechanical stimuli.

FEA Comparison of the Mechanical Behavior of Three Dental Crown Materials: Enamel, Ceramic, and Zirconia

The restoration of endodontically treated teeth is one of the main challenges of restorative dentistry. The structure of the tooth is a complex assembly in which the materials that make it up, enamel and dentin, have very different mechanical behaviors. Therefore, finding alternative replacement materials for dental crowns in the area of restorative care isa highly significant challenge, since materials such as ceramic and zirconia have very different stress load resistance values. The aim of this study is to assess which material, either ceramic or zirconia, optimizes the behavior of a restored tooth under various typical clinical conditions and the masticatory load. A finite element analysis (FEA) framework is developed for this purpose. The 3D model of the restored tooth is input into the FEA software (Ansys Workbench R23)and meshed into tetrahedral elements. The presence of masticatory forces is considered: in particular, vertical, 45° inclined, and horizontal resultant forces of 280 N are applied on five contact points of the occlusal surface. The numerical results show that the maximum stress developed in the restored tooth including a ceramic crown and subject to axial load is about 39.381 MPa, which is rather close to the 62.32 MPa stress computed for the natural tooth; stresses of about 18 MPa are localized at the roots of both crown materials. In the case of the zirconia crown, the stresses are much higher than those in the ceramic crown, except for the 45° load direction, while, for the horizontal loads, the stress peak in the zirconia crown is almost three times as large as its counterpart in the ceramic crown (i.e., 163.24 MPa vs. 56.114 MPa, respectively). Therefore, the zirconia crown exhibits higher stresses than enamel and ceramic that could increase in the case of parafunctions, such as bruxism. The clinician's choice between the two materials should be evaluated based on the patient's medical condition.

An alternate methodology for studying diffusion and elution kinetics of dimethacrylate monomers through dentinal tubules

OBJECTIVE

Ethoxylated bisphenol A dimethacrylate (bisEMA) is a base monomer in several dental resin composites. It was the main aim of the present study to determine if bisEMA can reach the dental pulp by generally passive diffusion through the coronal dentinal tubules stimulated via eluent liquids surrounding the root structures only.

METHODS

In 20 human third molar teeth, standard Class-I occlusal cavities were prepared and provided either with an adhesive system alone or additionally with a composite restoration, according to the instructions of the manufacturer. The teeth were placed in an elution chamber such that the elution media only came into contact with the tooth root/tooth base where they were incubated at 37 °C for up to 7 d. Samples were taken after 1, 2, 4 and 7 d. Gas chromatography/mass spectrometry was used to identify bisEMA and other monomers in ethanol/water (3:1) and aqueous eluates.

RESULTS

bisEMA was only found in ethanol/water eluates, where the teeth had received a composite restoration. Traces of bisEMA with up to three ethylene oxide units could be detected in these eluates. Depending on the dentin thickness, different elution kinetics of bisEMA were determined. Regardless of the treatment of teeth, triethylene glycol dimethacrylate (TEGDMA) and tetraethylene glycol dimethacrylate (TEEGDMA) were found in ethanolic/aqueous eluates in equal amounts. Most TEGDMA and TEEGDMA diffused through the dentin within the first 24 h.

SIGNIFICANCE

Depending on the dentin layer thickness, bisEMA was released for varied time periods, resulting in varied concentrations and exposure times for the different cells of the dental pulp. The concentrations of TEGDMA and TEEGDMA were greatest for cells of the dental pulp within the first 24 h.

Application of computational fluid dynamics models for the evaluation of salivary flow patterns and related bacterial accumulation around orthodontic brackets

OBJECTS

To simulate and compare salivary flow patterns over a tooth surface bonded with different orthodontic appliances using computational fluid dynamics (CFD) and investigate the impact of bracket design on salivary flow in relation to peri-bracket bacterial accumulation.

SETTING AND SAMPLE POPULATION

The models were constructed using computed tomography (CT) data of 81 patients scheduled for fixed orthodontic treatment: 27 patients (10 males, 17 females) for the metal Victory MBT™ bracket; 27 patients (seven males, 20 females) for the ceramic Clarity MBT™ bracket; 27 patients (15 males, 12 females) for the Mini Uni-Twin (MUT) bracket.

METHODS

The salivary flow patterns were simulated by CFD and compared between the groups and the model predictions were validated using a bacteriological experiment.

RESULTS

The MUT bracket was associated with the greatest number of low salivary velocity areas, as it is designed with a connector between double tie wings and a right contact angle between tooth surface and bracket base. After archwire placement, the centred slot in the bracket and the bilateral sites around the bracket had higher bacterial retention and needed special oral hygiene measures. The obtuse contact angle of the ceramic bracket formed a pocket structure in the tie-wing area, retarding salivary flow and contributing to bacteria retention.

CONCLUSION

With the evaluation of CFD models, we demonstrate that salivary flow patterns over a tooth surface with a bracket vary with bracket designs and further promote bacterial retention in specific locations, suggesting the need for additional oral hygiene measures for specific bracket types.

A REVIEW OF FINITE ELEMENT APPLICATIONS IN ORAL AND MAXILLOFACIAL BIOMECHANICS

Finite element method (FEM) is preferred to carry out mechanical analyses for many complex biomechanical structures. For most of the biomechanical models such as oral and maxillofacial structures or patient-specific dental instruments, including nonlinearities, complicated geometries, complex material properties, or loading/boundary conditions, it is not possible to accomplish an analytical solution. The FEM is the most widely used numerical approach for such cases and found a wide range of application fields for investigating the biomechanical characteristics of oral and maxillofacial structures that are exposed to external forces or torques. The numerical results such as stress or strain distributions obtained from finite element analysis (FEA) enable dental researchers to evaluate the bone tissues subjected to the implant or prosthesis fixation from the viewpoint of (i) mechanical strength, (ii) material properties, (iii) geometry and dimensions, (iv) structural properties, (v) loading or boundary conditions, and (vi) quantity of implants or prostheses. This review paper evaluates the process of the FEA of the oral and maxillofacial structures step by step as followings: (i) a general perspective on the techniques for creating oral and maxillofacial models, (ii) definitions of material properties assigned to oral and maxillofacial tissues and related dental materials, (iii) definitions of contact types between tissue and dental instruments, (iv) details on loading and boundary conditions, and (v) meshing process.

INFLUENCE OF THREE DIFFERENT CURVATURES FLEX-FOOT PROSTHESIS WHILE SINGLE-LEG STANDING OR RUNNING: A FINITE ELEMENT ANALYSIS STUDY

Flex foot device was one of the most common prosthesis for the athletes with the transtibial amputation on the recent market. Thus, the results of investigation with biomechanics on the flex foot would be a considerable impact on the performance of disabled athletes wearing the flex foots. This study was designed to investigate the biomechanical condition of the flex foot prosthesis with different curvatures while standing and running by finite element analysis. This study demonstrated finite element models of flex foot established with three different curvatures 20[Formula: see text] (small bending), 35[Formula: see text] (medium bending) and 50[Formula: see text] (big bending). Besides, it simulates and investigates the condition of flex foot while a person is wearing it with single-leg standing or running. The evaluation indices were selected as von Mises stress and displacements at top of socket surface. The results show that the big-bending flex foot generated the higher stress and the larger deformed displacement. Without exceeding the material tolerance of the flex foot, the larger displacement of big-bending flex foot could generate more energy, which possessed larger resilient potential energy and enabled the athletes to have better performance after using the flex foot. As a result, due to its beneficial property of energy storage and return, the large-bending flex foot user could have better effect. In the future, more innovative designs of the flex foot prosthesis can be laid out with the reference of the result in this study.

INVESTIGATING BIOMECHANICS OF DIFFERENT MATERIALS AND ANGLES OF BLADES OF FORCEPS FOR OPERATIVE DELIVERY BY FINITE ELEMENT ANALYSIS

Using of forceps during labors and vaginal delivery accomplished operative deliveries in some circumstances. Forceps may induce fractures in the neonatal skull if excessive force is applied to it during an operative delivery. Therefore, newborns may be affected by forceps. The aim of this study was to investigate the effects of different curve angles and materials of the blades of forceps on neonates during labor or delivery for gynecologists and obstetricians using a finite element analysis (FEA). Computer models of the forceps, neonate’s scalp, and skull, were generated for the FEA. Moreover, the use of different materials (stainless steel and titanium alloy) and three different angles of the blades of forceps (20[Formula: see text], 40[Formula: see text], and 60[Formula: see text]) on a newborn’s head were simulated in a biomechanical analysis. The results indicate that a larger curve angle of the blades of forceps can decrease the stress and pressure on the neck of the newborn but may lead to rotation toward the posterior side. Moreover, forceps made of a lower Young’s modulus material can also reduce the stress and pressure on the neck of the newborn. It is hoped that this research can provide a more reasonable reference for manufacturers to design better medical equipment such as forceps in the future for obstetricians and gynecologists to use to attenuate the stress and pressure on the neck of a newborn.

Biomechanical Analysis of Implanted Clavicle Hook Plates With Different Implant Depths and Materials in the Acromioclavicular Joint: A Finite Element Analysis Study

Clinical implantation of clavicle hook plates is often used as a treatment for acromioclavicular joint dislocation. However, it is not uncommon to find patients that have developed acromion osteolysis or had peri-implant fracture after hook plate fixation. With the aim of preventing complications or fixation failure caused by implantation of inappropriate clavicle hook plates, the present study investigated the biomechanics of clavicle hook plates made of different materials and with different hook depths in treating acromioclavicular joint dislocation, using finite element analysis (FEA). This study established four parts using computer models: the clavicle, acromion, clavicle hook plate, and screws, and these established models were used for FEA. Moreover, implantations of clavicle hook plates made of different materials (stainless steel and titanium alloy) and with different depths (12, 15, and 18 mm) in patients with acromioclavicular joint dislocation were simulated in the biomechanical analysis. The results indicate that deeper implantation of the clavicle hook plate reduces stress on the clavicle, and also reduces the force applied to the acromion by the clavicle hook plate. Even though a clavicle hook plate made of titanium alloy (a material with a lower Young's modulus) reduces the force applied to the acromion by the clavicle hook plate, slightly higher stress on the clavicle may occur. The results obtained in this study provide a better reference for orthopedic surgeons in choosing different clavicle hook plates for surgery.

Role of the compression screw in the dynamic hip-screw system: A finite-element study

The dynamic hip-screw (DHS) system is a common implant for fixation of proximal femur fractures. During assembly, it has been recommended to remove the compression screw after initial compression has been obtained; however, related complications had been reported. So far, the role of compression screw in the reconstructed stability of hip fractures as well as the mechanical strength of the DHS system has rarely been mentioned. This study investigated the function of this screw in the DHS system during fracture healing. Based on the FE method, six numerical models of proximal femur were employed to analyze the mechanical response of a DHS implant with various fracture types and different fixation strategies (with or without a compression screw). The displacement of the femur head and peak von Mises stress were selected as indices of the stability of a fractured femur stabilized by a DHS device and of the risk of implant failure, respectively. Our results showed that a retained compression screw increased reconstructed structural stiffness, reducing the displacement of the femur head. This screw also helped to lessen mechanical failure of side plate by reducing the peak von Mises stress around the connection between the barrel and side plate. Both findings were evident in the proximal femur fracture involving the intertrochanteric part, and even more obvious in the setting of bony defects. Thus, we recommend the maintenance of compression screw in the DHS system while treating the intertrochanteric fracture, particularly in cases with bony defects.

Designing and testing regenerative pulp treatment strategies: modeling the transdentinal transport mechanisms

The need for simulation models to thoroughly test the inflammatory effects of dental materials and dentinogenic effects of specific signaling molecules has been well recognized in current dental research. The development of a model that simulates the transdentinal flow and the mass transfer mechanisms is of prime importance in terms of achieving the objectives of developing more effective treatment modalities in restorative dentistry. The present protocol study is part of an ongoing investigation on the development of a methodology that can calculate the transport rate of selected molecules inside a typical dentinal tubule. The transport rate of biological molecules has been investigated using a validated CFD code. In that framework we propose a simple algorithm that, given the type of molecules of the therapeutic agent and the maximum acceptable time for the drug concentration to attain a required value at the pulpal side of the tubules, can estimate the initial concentration to be imposed.

COMPARISON OF PROXIMAL IN VITRO TOOTH CONTACTS IN CLASS II RESTORATIONS WITH DIFFERENT RESTORATIVE MATERIALS AND CAVITY SIZES USING A NEW MEASUREMENT DEVICE

This study used a newly developed proximal contact strength (PCS) device to evaluate the tightness of proximal tooth contact for Class II cavity size restoration with different materials using an auxiliary separation ring system. A measurement device based on the equilibrium of forces acted on the clamp rod converts a pull-out force between interdental spaces on a force sensing resistor to express the PCS. This device was designed using dental floss as the test end and can be moved with constant speed during measurement through a bevel gear that transforms the rotation of motor shaft into linear movement of clamp rod. A manikin model was used with 60 artificial first molars in which an mesial occlusal (MO) preparation was ground. Samples were divided into six groups (each n = 10) for simulating amalgam and resin composite restoration with three different cavity sizes. The different cavities were defined using the ratio of the actual isthmus width to the intercuspal width (W) to 1/3, 2/3 and 1. The PCS value in each sample was measured after restoration. The result showed that the mean PCS value and standard deviation were 2283.1 ± 216.5 gf, 2419.1 ± 375 gf and 1737.6 ± 372.7 g for 1/3 W, 2/3 W and W cavities of the amalgam restoration, respectively. The corresponding PCS values were 1178.0 ± 230.4 gf, 1205.8 ± 249.1 gf and 1247.0 ± 157.5 gf for 1/3 W, 2/3 W and W cavities of the resin composite restoration. PCS values with amalgam restoration were larger than those for resin composite restorations under the same cavity size. Large cavity (W) PCS might be lost with amalgam restoration. No significant difference was found in resin composite restoration PCS among the different cavity sizes.

Biomechanical analysis of acromioclavicular joint dislocation treated with clavicle hook plates in different lengths

PURPOSE

Clavicle hook plates are frequently used in clinical orthopaedics to treat acromioclavicular joint dislocation. However, patients often exhibit acromion osteolysis and per-implant fracture after undergoing hook plate fixation. With the intent of avoiding future complications or fixation failure after clavicle hook plate fixation, we used finite element analysis (FEA) to investigate the biomechanics of clavicle hook plates of different materials and sizes when used in treating acromioclavicular joint dislocation.

METHODS

Using finite element analysis, this study constructed a model comprising four parts: clavicle, acromion, clavicle hook plate and screws, and used the model to simulate implanting different types of clavicle hook plates in patients with acromioclavicular joint dislocation. Then, the biomechanics of stainless steel and titanium alloy clavicle hook plates containing either six or eight screw holes were investigated.

RESULTS

The results indicated that using a longer clavicle hook plate decreased the stress value in the clavicle, and mitigated the force that clavicle hook plates exert on the acromion. Using a clavicle hook plate material characterized by a smaller Young's modulus caused a slight increase in the stress on the clavicle. However, the external force the material imposed on the acromion was less than the force exerted on the clavicle.

CONCLUSIONS

The findings of this study can serve as a reference to help orthopaedic surgeons select clavicle hook plates.

UNIFORM DESIGN AND DYNAMIC FINITE ELEMENT ANALYSIS FOR MICROMOTION IMPROVEMENT OF SEMADOS DENTAL IMPLANT SYSTEM UNDER DYNAMIC CHEWING LOADS

This study aimed to improve the micromotion of a Semados dental implant system subjected to dynamic chewing loads. Micromotion of the Semados dental implant system with basic dimensions was obtained using dynamic finite element analysis, and five parameters of the implant were selected as the control factors to be improved. A uniform design method was employed to construct a set of experimental simulations. Next, for each experimental simulation, the dynamic finite analysis package ANSYS/LS-DYNA was employed to simulate the behavior of the Semados dental implant model subjected to dynamic chewing loads and then determine the maximum micromotion of the cortical and cancellous bones. Finally, the best design of the experimental simulations that caused the smallest amount of micromotion was selected as the improved design version. Compared to the original design, which experienced micromotion of 74.53 μm, the improved version experienced micromotion of 45.41 μm. The rate of improvement was 39.1%.