Experimental Investigation of Dental Composites Degradation After Early Water Exposure.

While dental composite long-term aging has already been studied in the past, no data exist about the early aging while it might be detrimental regarding the composites' longevity. This study aims to better understand the effects of early water exposure on dental composites. Dental resin composites with different fillers ratio were subjected to water exposure during 24 h, 1 week, or 1 month. After photopolymerization, the samples were stored at different conditions, whether in wet or dry condition (W, D, respectively) and in wet conditions after a first 24 h storage in dry conditions (DW). Three-point bending tests were performed to measure the flexural modulus. The samples were then subjected to a sorption/desorption protocol. While the matrix alone did not undergo any mechanical degradation with exposure time, the composites matrices presented a decrease in elastic modulus. This decrease was the highest for the matrix with nonsilanized fillers. Interestingly, the DW condition was detrimental for all the samples. Regarding the sample with nonsilanized fillers in DW for 1 month presented an elastic modulus lower than the matrix alone. These results were assigned to the sorption capacity of the polymer matrix, suggesting that the diffusion mechanisms and the nature of water molecules are determinant in the composite degradation. This study showed that dental composite early degradation mechanisms after water exposure are involved in the polymer matrix postpolymerization process as soon as after 24 h. Such mechanisms are detrimental in terms of the dental composite efficiency and have to be understood.

The impact of an underactuated arm exoskeleton on wrist and elbow kinematics during Prioritized Activities of daily living.

This study addresses the feasibility of underactuated arm exoskeletons as an alternative solution to the often bulky and heavy exoskeletons which actuate the shoulder with 3 DoF. Specifically, the study investigates how the wrist and elbow joint adapts their kinematics when the shoulder abduction is constrained. Ten healthy participants conducted three different grasping activities of daily living, during natural motion and during constrained shoulder abduction at two fixed angles: the resting position angle and at an angle of 10 ° abduction from the resting position. Motion capture data was collected and used as input for a musculoskeletal computer model adapted to this study. Statistical parametric mapping tools were employed to analyze the joint angles estimated by the model. The results show significant differences within the joint angles when the shoulder abduction is constrained. The wrist flexion angle deviated up to 13.6 ° and the elbow pronation angle decreased by 8.7 ° on average throughout the movement compared to the natural motion during restricted shoulder abduction motion. Thus, the shoulder could be underactuated and the participants could still accomplish the activities of daily living with changes in the wrist and elbow joint kinematic angles.

Experimental Bi-axial tensile tests of spinal meningeal tissues and constitutive models comparison.

Introduction This study aims at identifying mechanical characteristics under bi-axial loading conditions of extracted swine pia mater (PM) and dura and arachnoid complex (DAC). Methods 59 porcine spinal samples have been tested on a bi-axial experimental device with a pre-load of 0.01 N and a displacement rate of 0.05 mm·s-1. Post-processing analysis included an elastic modulus, as well as constitutive model identification for Ogden model, reduced Gasser Ogden Holzapfel (GOH) model, anisotropic GOH model, transverse isotropic and anisotropic Gasser models as well as a Mooney-Rivlin model including fiber strengthening for PM. Additionally, micro-structure of the tissue was investigated using a bi-photon microscopy. Results Linear elastic moduli of 108 ± 40 MPa were found for DAC longitudinal direction, 53 ± 32 MPa for DAC circumferential direction, with a significant difference between directions (p < 0.001). PM presented significantly higher longitudinal than circumferential elastic moduli (26 ± 13 MPa vs 13 ± 9 MPa, p < 0.001). Transversely isotropic and anisotropic Gasser models were the most suited models for DAC (r2  =  0.99 and RMSE:0.4 and 0.3 MPa) and PM (r2 = 1 and RMSE:0.06 and 0.07 MPa) modelling. Conclusion This work provides reference values for further quasi-static bi-axial studies, and is the first for PM. Collagen structures observed by two photon microscopy confirmed the use of anisotropic Gasser model for PM and the existence of fenestration. The results from anisotropic Gasser model analysis depicted the best fit to experimental data as per this protocol. Further investigations are required to allow the use of meningeal tissue mechanical behaviour in finite element modelling with respect to physiological applications. STATEMENT OF SIGNIFICANCE: This study is the first to present biaxial tensile test of pia mater as well as constitutive model comparisons for dura and arachnoid complex tissue based on such tests. Collagen structures observed by semi-quantitative analysis of two photon microscopy confirmed the use of anisotropic Gasser model for pia mater and existence of fenestration. While clear identification of fibre population was not possible in DAC, results from anisotropic Gasser model depicted better fitting on experimental data as per this protocol. Bi-axial mechanical testing allows quasi-static characterization under conditions closer to the physiological context and the results presented could be used for further simulations of physiology. Indeed, the inclusion of meningeal tissue in finite element models will allow more accurate and reliable numerical simulations.

Modjaw® device: Analysis of mandibular kinematics recorded for a group of asymptomatic subjects.

OBJECTIVE: To assess the repeatability and kinematic data of Modjaw® recordings from a group of asymptomatic patients. METHODS: Modjaw® mandibular kinematic data were recorded for 22 asymptomatic volunteers (DC/TMD questionnaire). Sagittal (SCI at 3 and 5 mm) and transversal (TCI at 4 mm) condylar inclination values of the instantaneous center of rotation were measured over two recording sessions. The repeatability of recordings was determined from the intraclass correlation coefficient (ICC), which is based on a one-way random-effects ANOVA. RESULTS: The repeatability of recordings was found to be good to excellent. The mean TCI in mediotrusion was 7.1° ± 5.1, and the mean SCI in protrusion was 51.07° ± 9.43. CONCLUSION: The Modjaw® device reliably records the patient's real hinge axis kinematics during functional mandibular movements. Data can be transferred with the patient's personal reference plane and digital casts to the CAD/CAM software.

Update on the parameters influencing the adjustment of the sagittal and transversal condylar inclination of dental articulators.

OBJECTIVES: The literature review aimed to compile and summarize the results of research relating to the recordings of condylar displacements obtained with extraoral devices, to guide clinicians to set dental (virtual) articulator parameters. The meta-analysis was undertaken to assess the sagittal condylar inclination (SCI) and transversal condylar inclination (TCI, also known as Bennett angle) values according to horizontal reference planes, movement studied, and patient characteristics: dental status, interocclusal relationship, skeletal pattern, and signs and symptoms of temporomandibular disorders (TMD). DATA SOURCES: A bibliographic search was conducted in the three following electronic databases: MEDLINE, EMBASE, and Cochrane Library and Best Evidence. The review was restricted to trials involving participants meeting the following criteria: (1) adult, (2) no previous surgery in the temporomandibular region, and (3) no serious comorbidity conditions. Descriptive statistics were calculated for all study groups and were compared by applying a one-way ANOVA. CONCLUSION: All 20 articles selected corresponded to a total of 933 subjects evaluated. The recording devices and horizontal reference planes had a significant impact on the SCI values. Age, dental status, and the presence of symptoms and signs of TMD in subjects had no influence on SCI values, unlike Angle class II, division 2, the class II sagittal pattern, or the increased vertical skeletal pattern SCI parameters (P < .05). The mean TCI value was 8 degrees and was independent of individual patient characteristics and the extraoral recording device used. For accurate kinematic simulation, the patient's personal plane of reference must be transferred to the system.

Biomechanical assessment of different fixation methods in mandibular high sagittal oblique osteotomy using a three-dimensional finite element analysis model.

With modern-day technical advances, high sagittal oblique osteotomy (HSOO) of the mandible was recently described as an alternative to bilateral sagittal split osteotomy for the correction of mandibular skeletal deformities. However, neither in vitro nor numerical biomechanical assessments have evaluated the performance of fixation methods in HSOO. The aim of this study was to compare the biomechanical characteristics and stress distribution in bone and osteosynthesis fixations when using different designs and placing configurations, in order to determine a favourable plating method. We established two finite element models of HSOO with advancement (T1) and set-back (T2) movements of the mandible. Six different configurations of fixation of the ramus, progressively loaded by a constant force, were assessed for each model. The von Mises stress distribution in fixations and in bone, and bony segment displacement, were analysed. The lowest mechanical stresses and minimal gradient of displacement between the proximal and distal bony segments were detected in the combined one-third anterior- and posterior-positioned double mini-plate T1 and T2 models. This suggests that the appropriate method to correct mandibular deformities in HSOO surgery is with use of double mini-plates positioned in the anterior one-third and posterior one-third between the bony segments of the ramus.

A numerical, theoretical and experimental study of the effect of thermocycling on the matrix-filler interface of dental restorative materials.

OBJECTIVE: Thermocycling is widely used to age dental composites but with very different results from one study to another, even with apparent similar conditions. This study aims at understanding better the relative damaging speed of matrix and fillers, based on theoretical models. METHODS: Eight formulations of an experimental dental material were produced. The same organic matrix was used and silanated barium glass particles were added as fillers with different filler ratios. Samples were thermocycled up to 10 000 cycles. Three-point bending tests were carried out at different steps. The yield stress was measured among other mechanical properties. RESULTS: Composite properties were degraded by thermocycling. The decrease was slight during the first 5 000 cycles whereas it decreased significantly after 10 000 cycles. The Turcsányi model asserts that the interface yield stress is slightly affected in the first 5 000 cycles and then falls down, while the decrease of matrix yield stress is linear. SIGNIFICANCE: Each component of a composite does not age at the same rate. First, the matrix acts as a protector until the water finds its way to the interphase. The filler silanization treatment is highly sensitive to hydrolysis and is damaged rapidly from that moment. Numerical simulations and surface observations confirmed that cracks appear to propagate in the neighbourhood of the interface but not directly within it.

Diagnosis and management of bruxism: Evaluation of clinical practices in France.

Objective: The Evaluation of Clinical Practice (ECP) conducted with a sample of French general dental practitioners aimed to measure the methods used to diagnose and manage bruxism.Methods: The ECP was performed using a declarative online questionnaire-based anonymous survey (SurveyMonkey) of 1388 practitioners. Twenty-two questions were grouped in 5 categories: (1) Sociodemographic characteristics (Q1-6); (2) Knowledge of the prevalence and definition of bruxism (Q7-9); (3) Diagnostic approach (Q10-11) and management (Q12-Q13); (4) The use of occlusal splints (Q14-21); (5) Oral rehabilitation (Q22).Results: The answers obtained (233; 16.8%) revealed a wide disparity and insufficient diagnosis (e.g. only 41% looked for sleep disorders, 22.3% for consumption of stimulants, 3% for upper airway obstruction) and management of bruxism (e.g. only 21.9% of participants proposed cognitive-behavioral therapy).Discussion: The discrepancies detected, such as the use of inappropriate splints (30 to 70%), emphasize the need for more prompt research-to-practice transfer of new knowledge.

Mechanical characterization and identification of material parameters of porcine aortic valve leaflets.

The ideal artificial heart valve does not exist yet. Understanding of mechanical and structural properties of natural tissues is necessary to improve the design of biomimetic aortic valve. Besides these properties are needed for the finite element modeling as input parameters. In this study we propose a new method combining biaxial tests and digital image correlation. These tests are carried out on porcine aortic valves. In this work, we use a modified version of the HGO (Holzapfel-Gasser-Ogden) model which is classically used for hyper-elastic and anisotropic soft tissues. This model can include fiber orientation. The identification of HGO model parameters can be determined using experimental data and two different protocols. One protocol is based on the identification of collagen fibers orientation as well as the mechanical parameters. The second one, is based on a complementary experiment to determine orientation (confocal laser scanning microscope). Both lead to determine different sets of material parameters. We show that the model is more likely to reproduce the actual mechanical behavior of the heart valves in the second case and that a minimum of three different loading conditions for the biaxial tensile tests is required to obtain a relevant set of parameters.

Theoretical prediction of dental composites yield stress and flexural modulus based on filler volume ratio.

OBJECTIVE: A costly advantageous approach in composites development process is to limit experimental tests by predicting mechanical properties with respect to their filler ratio. Models exist for other fields than dentistry. They have been compared to 3-point bending test experimental results for yield stress, flexural modulus and flexural strength. METHODS: Five formulations of the same experimental material were made. They were composed of an organic matrix and different ratios of silanated barium glass particles. The samples were stored in distilled water for 24h at 37°C prior to the 3-point bending test. The Turcsányi model for yield stress was notably investigated, and SEM was used to complete data analysis. RESULTS: The yield stress showed reproducible results and a good fit with Turcsányi model with respect to filler ratio. The flexural modulus data are not scattered but did not fit with the existing models. No trend could emerge for flexural strength and strain because of scattering; these properties are more unpredictable. The SEM observations of fracture areas confirm a good matrix-filler interface quality. SIGNIFICANCE: SEM pictures validated the numerical parameter obtained from Turcsányi model. The latter therefore seems to be applicable to dental composites. Firstly, it enables to predict the evolution of the material yield stress without testing all filler ratios. Secondly, this model provides a good way to get micro-information on the matrix-filler interface from macroscopic tests. The discrepancy between flexural modulus results and theory highlighted the necessity to include an "interface quality" parameter in accurate predictive models.

Material properties of the placenta under dynamic loading conditions.

Trauma during pregnancy especially occurring during car crashes leads to many foetal losses. Numerical modelling is widely used in car occupant safety issue and injury mechanisms analysis and is particularly adapted to the pregnant woman. Material modelling of the gravid uterus tissues is crucial for injury risk evaluation especially for the abruption placentae which is widely assumed as the leading cause of foetal loss. Experimental studies on placenta behaviour in tension are reported in the literature, but none in compression to the authors' knowledge. This lack of data is addressed in this study. To complement the already available experimental literature data on the placenta mechanical behaviour and characterise it in a compression loading condition, 80 indentation tests on fresh placentae are presented. Hyperelastic like mean experimental stress versus strain and corridors are exposed. The results of the experimental placenta indentations compared with the tensile literature results tend to show a quasi-symmetrical behaviour of the tissue. An inverse analysis using simple finite element models has permitted to propose parameters for an Ogden material model for the placenta which exhibits a realistic behaviour in both tension and compression.

Stress distribution in the temporo-mandibular joint discs during jaw closing: a high-resolution three-dimensional finite-element model analysis.

PURPOSE: This study aims at analysing the stresses distribution in the temporomandibular joint (TMJ) using a complete high-resolution finite element model (FE Model). This model is used here to analyse the stresses distribution in the discs during a closing jaw cycle. In the end, this model enables the prediction of the stress evolution in the TMJ disc submitted to various loadings induced by mandibular trauma, surgery or parafunction. MATERIALS AND METHODS: The geometric data for the model were obtained from MRI and CT scans images of a healthy male patient. Surface and volume meshes were successively obtained using a 3D image segmentation software (AMIRA(®)). Bone components of skull and mandible, both of joint discs, temporomandibular capsules and ligaments and dental arches were meshed as separate bodies. The volume meshes were transferred to the FE analysis software (FORGE(®)). Material properties were assigned for each region. Boundary conditions for closing jaw simulations were represented by different load directions of jaws muscles. The von Mises stresses distribution in both joint discs during closing conditions was analyzed. RESULTS: The pattern of von Mises stresses in the TMJ discs is non-symmetric and changed continuously during jaw movement. Maximal stress is reached on the surface disc in areas in contact with others bodies. CONCLUSIONS: The three-dimension finite element model of masticatory system will make it possible to simulate different conditions that appear to be important in the cascade of events leading to joint damage.

Determination of Young's modulus of mandibular bone using inverse analysis.

Development of a numerical model applicable to clinical practice, and in particular oral implantology, requires knowledge of the mechanical properties of mandibular bone. The wide range of mechanical parameters found in the literature prompted us to develop an inverse analysis method that takes into account the exact geometry of each specimen tested, regardless of its shape. The Young's modulus of 3000MPa we determined for mandibular bone using this approach is lower than the values reported in the literature. This difference can be explained by numerous experimental factors, related in particular to the bone specimens used. However, the main reason is that, unlike most previously published papers on the subject, the heterogeneity of bone led us to select a specimen size at the upper end of the scale, close to clinical reality.