Mise en évidence d’une relation entre la force prémolaire et la force molaire dans le cadre d’une approche simplifiée du fonctionnement de l’appareil manducateur

The purpose of this study is to show the existence of a correlation between the premolar and molar clenching forces obtained during a voluntary clenching exercise. The study concerned 32 volunteers aged 21 to 28 with no manducatory problems. The forces were obtained using a device with four Kiowa traducers arranged in a complete Wheatstone bridge. The analysis of the results obtained showed that there was a positive correlation between maximum molar and premolar. The analysis also shows that these results are a direct application of the theory of momentum. This enables us to propose a simple biophysical model to explain the functioning of the mandicatory system.Le but de cette étude est de démontrer l’existence d’une corrélation entre les forces prémolaires et molaires enregistrées pendant un exercice de fermeture volontaire forcée de la mandibule. L’étude porte sur 32 volontaires de 21 à 28 ans, sans pathologie de l’appareil manducateur. Les forces sont enregistrées avec un capteur à quatre jauges Kiowa monté en pont complet. La possibilité d’appliquer le théorème des moments aux valeurs recueillies, montre qu’il existe une corrélation positive entre la force maximale développée au niveau prémolaire et la force maximale développée au niveau molaire. Ceci nous permet de proposer un modèle biophysique simple pour expliquer le fonctionnement de l’appareil manducateur

Détermination de l’intensité des forces maximales prémolaires et molaires au cours de la contraction isométrique des muscles masticateurs par fermeture forcée de la mandibule

The purpose of this study to quantify the activity of the masticatory muscles. For this we recorded the maximum bite force of opposing teeth during voluntary clenching. The study was carried out on 31 students aged 21 to 28 with a satisfactory dental arch. The measurements were obtained on one side only. Nine thicknesses of the traducers were used for the premolar zone and two for the molar zone. We determined an optimal thickness enabling the highest measurement: 6.5 mm for the premolars and 5.2 for the molars. The highest measurements were averaged and the following results were obtained: premolars-35 kgf for females and 50 kgf for males; molars-100 kgf for females and 130 kgf for males.Le but de cette étude est une quantification de l’activité des muscles masticateurs. Pour ce faire, nous avons enregistré la force maximale développée entre les dents antagonistes par fermeture volontaire forcée de la mandibule. L’étude a été réalisée sur 32 étudiants entre 21 et 28 ans possédant un état bucco-dentaire très satisfaisant. Les forces ne sont enregistrées que d’un seul côté. La zone prémolaire a été retenue comme zone d’enregistrement en utilisant neuf épaisseurs croissantes de capteur, la zone molaire en utilisant deux épaisseurs de capteur. Nous avons mis en évidence l’existence d’une épaisseur optimale pour laquelle la force est la plus grande. Cette épaisseur est de 6,5 mm au niveau prémolaire et 5,2 mm au niveau molaire. La valeur moyenne de la force prémolaire de plus grande intensité est de 35 kgforces chez la femme et de 50 kgforces chez l’homme; la valeur moyenne de la force molaire de plus grande intensité est de 100 kgforces chez la femme et de 130 kgforces chez l’homme

Intérêt du laser CO2 pour l’adhésion des résines composites sur la dentine

CO2 laser irradiation brings about structural modifications at the dentin surface. The aim of this study was to compare the tensile strength of composite resin bonded to unlased dentin and lased dentin. Dentin specimens were prepared by vestibular surface sectionning, exposing a plane dentinal surface. 40 specimens received 20 individual laser impacts with a power of 4 W and a duration of 0.1 s. 20 specimens received no laser irradiation. Half of the 60 specimens was treated with Scotchbond 2™ and the other one with Schotchbond Multipurpose™. Composite cylinders were polymerised for 40 seconds to these specimens. Tensile bond strengths were determined at a crosshead speed of 5 mm/min and fractured surfaces were examined at SEM after the test. Unlased dentin had significantly higher bond strength that the lased dentin.Le but de notre étude a été de vérifier si les modifications subies par la dentine, consécutivement au rayonnement d’un laser CO2, amélioraient le collage de certains systèmes adhésifs dentinaires. Après avoir choisi un tir de 4 watts et de 0,1 seconde, nous avons réalisé 20 impacts laser sur des surfaces dentinaires.La moitié des échantillons a été ensuite traitée avec le système adhésif Scotchbond 2™, l’autre moitié avec le système Scotchbond Multipurpose™. Puis des cylindres de composite ont été photopolymérisés sur ces surfaces. Un test de traction a été appliqué sur les échantillons ainsi préparés et sur un groupe témoin n’ayant pas subi de tirs laser. Les surfaces fracturées après le test ont été observées au M.E.B. côté dentine et côté composite. Nous n’avons pas obtenu une amélioration de l’adhésion après le traitement laser avec les deux systèmes adhésifs testés

In vitro magnetic resonance imaging of rodent teeth

International audienc

Proton NMR imaging in dental systems

International audienc

Magnetic resonance imaging of rodent teeth

International audienc

Correlation between NMR imaging disturbances and the magnetic susceptibility of the dental materials

International audienc

Magnetic resonance imaging for the determination of magnetic susceptibility of materials

International audienc

Influence of autoclave sterilization on the surface parameters and mechanical properties of six orthodontic wires

International audienceOrthodontic wires are frequently packaged in individual sealed bags in order to avoid cross-contamination. The instructions on the wrapper generally advise autoclave sterilization of the package and its contents if additional protection is desired. However, sterilization can modify the surface parameters and the mechanical properties of many types of material. The aim of this research was to determine the influence of one of the most widely used sterilization processes, autoclaving (18 minutes at 134degreesC, as recommended by the French Ministry of Health), on the surface parameters and mechanical properties of six wires currently used in orthodontics (one stainless steel alloy: Tru-Chrome(R) RMO; two nickel-titanium shape memory alloys: Neo Sentalloy(R) and Neo Sentalloy with Ionguard(R) GAC; and three titanium-molybdenum alloys: TMA(R) and Low Friction TMA(R) Ormco and Resolve(R) GAC). The alloys were analysed on receipt and after sterilization, using surface structure observation techniques, including optical, scanning electron and atomic force microscopy and profilometry. The mechanical properties were assessed by three-point bending tests. The results showed that autoclave sterilization had no adverse effects on the surface parameters or on the selected mechanical properties. This supports the possibility for practitioners to systematically sterilize wires before placing them in the oral environment

Review of in vitro studies on the biocompatibility of NiTi alloys

International audienceNickel-Titanium (NiTi) alloys exhibit special mechanical properties known as shape memory effect and superelasticity. The first effect relates to the fact that after deformation at low temperature, the material regains its original shape after heating. The second effect denotes an unusual flexibility of the material that is far greater than the flexibility of common metallic materials. These properties can be put to excellent use in various biomedical applications, such as orthodontic wires, orthopaedic implants for osteosynthesis, stents for various applications, bone substitution materials and experimental systems for scoliosis correction. The purpose of the present review is to analyze in vitro NiTi biocompatibility compared to other titanium alloys. The problem of Ni's possible toxicity is discussed. Corrosion properties in an oral environment are investigated. The effect of surface chemical composition and surface roughness on cell adhesion, morphology and proliferation is shown as an example. Sterilization is taken into account and its influence on roughness and mechanical properties, chemical composition, wettability and bacterial adhesion inhibition is evaluated. The conclusion is that NiTi is at least as biocompatible as conventional titanium due to the TiO2 oxide layer, and that only in special chemical conditions can Ni diffuse out of the NiTi material