[Calculation of optimized and individualized hip prosthesis. A study of feasibility]. / Calcul d'une prothèse de hanche optimisée et individualisée. Etude de faisabilité.

As logical consequence of a series of basic research studies on human femoral bones with unipodal support and under static stress, performed with physicomathematic modelling methods (finite-elements method) then confirmed by direct visualization of deformations resulting from such stress using holographic interferometry, the authors have worked on the definition of an optimized and individualized hip prosthesis. Thick CT sections digitized with a table and entered into a specially programmed computer allowed three-dimensional modelling of the femur as a volume, i.e. with its external contour and its medullary canal, and therefore of the implantable space. The prosthesis was then defined taking a number of hypotheses into account: necessity to regularize cortical bone spicules inside spongious bone, which are so often present opposite the rough line, partial machining at the level of the calcar, reduced tail length, presence or absence of collar. Thus an optimized and individualized prosthesis was defined. A prototype corresponding to a given femoral bone could then have been produced. However, the authors found it preferable to use simulation with computer synthetic images to check easy insertion and removal.

[Unproven treatments in cancerology]. / Traitements non prouvés en cancérologie.

A socio-ethnologic study of 21 patients localized or metastatic cancer with which consisted of 8-hour in-depth interview and family interviews determined 3 categories of cancer patients which used unproven methods. The first category (No 5) decided to use unproven methods immediately after classical treatment in order to improve the possibility of cure. These patients had already used unproven methods for benign illness. The second category (No 11) used unproven treatments a certain while after the completion of all classical treatment, to reduce the adverse effects of radiotherapy or chemotherapy and to prevent recurrences. The last category (No 5) used the unproven treatments before any classical treatment was treatment carried out, due to fear or lack of confidence in classical treatment. The frequency of unproven treatment among cancer patients is estimated at 52%. In most cases patients who were not representative of a specific socioeconomic level used classical treatment in parallel with unproven methods prescribed either by non medical (No 12) or medical doctors (No 9). Among these very few are permanent prescriptor and advice patient to take exclusively the unproven methods. A better information of patients and better relationships between patient and doctor can improve the chance of cure.

A physico-mathematical model for the human femur, with and without a prosthesis, under the static constraints of one-legged stance.

The authors present a physico-mathematical model of a human femur, under "monopodal" static constraints, using the finite elements method. Three examples are considered: a normal femur, a femur implanted with a short-stem prosthesis without cement, and a femur implanted with a long-stem prosthesis without cement. The lines of isoconstraints were compared in the three examples, as well as the main constraints (direction and intensity). From the results, the authors suggest that a prosthesis made of titanium is currently best even though its YOUNG's modulus differs from that of the bone. A prosthesis of composite material is possible in the future. While the intensity of the constraints is nearly the same at the level of the epiphysis for the short-stem and long-stem prosthesis it seems that the short-stem prosthesis fitted accurately without cement is the best solution. The introduction of a hip prosthesis modifies the normal curve of the loaded femur by changing the center of this curve.

Study of the deformations of the isolated mandible under static constraints by simulation on a physicomathematical model.

The authors have studied the deformations of a mandible isolated from its muscular environment and submitted to statical constraints, with the help of a "modified model" and the finite elements method: the general deformation of the mandible and its modifications according to the direction of the application of the pressure, the rotation phenomenon or "torsion" in cross sections (identified by computer) of the mandible, the respective deformations of the internal and external corticals have successively been calculated. Particular mechanical phenomenons corresponding to the areas where the anatomo-clinical forms of the mandibular fractures take place have clearly been shown. The authors draw the conclusion that the mandible behaves mechanically in a similar way to a tridimensional composite.

Study of the mandible under static constraints by holographic interferometry. New biomechanical deductions.

In order to try to determine the nature of the mechanical structure of the mandible, the authors have compared, with the help of holographic interferometry, the behavior of the fresh mandible of a corpse, of a representative iron angle, and of a block of carbon-carbon under static constraint. There are no similarities between the behavior of the human mandible and that of a polycrystalline steel. On the contrary, the behavior of the mandible and of the carbon-carbon block are very similar. It would be hasty to state that bones are a heterogeneous composite. We can only prove, in a first approach, that they behave similarly under identical experimental conditions. The authors also demonstrated that the mandible presents a "mechanical hysteresis" phenomenon. This means that, when subjected to a small strain, its shape changes, but this change tends to neutralize itself in part in the course of time.

The mandible, an overhanging mechanically suspended structure. Considerations on the system of attachment and servo-command of the mandible.

The mandible, owing to its form, surrounding muscles and "position" in the craniofacial unit can be assimilated to an overhanging mechanically suspended structure. The hypothesis, according to which the temporomandibular joints would be submitted to pressure during mastication should be abandoned on the basis of anatomical and clinical findings. Furthermore, this hypothesis is in disagreement with the results of simulation on a physicomathematical model of the mandible. Accordingly, it is reasonable to assume that the mandible is a suspended structure and that the elevator muscles of mastication, especially the masseter and medial pterygoid (together forming the mandibular sling), and probably also the anterior belly of the temporalis muscle play a twin role in the suspension of this bone. These muscles obviously command the movement of closure. They also constitute the suspensory apparatus of the mandible and, by mechanical computation, should display a certain degree of elasticity and undergo most of the mechanical constraints developed during mastication. One can also consider the cranio-facio-mandibulo-hyoid group as a suspended structure. The comparison of this type of system to the basic principles of servo-robotics allows to understand that such a structure is capable of extremely precise movements in all spatial planes with a minimum of effort.

A physicomathematical approach to the structure of the mandible.

Classical methods of anatomical study and experimentation have reached an endpoint with respect to the advancement of our knowledge of certain aspects of bone, i.e. its mechanical properties, investigation of the constraints acting on bone and the organization of bone allowing resistance to such mechanical stress. Indeed, current knowledge is rather limited regarding bone as a material. Furthermore, bone from the cadaver cannot be considered a reliable source of study material since its physicochemical composition and mechanical properties are highly different from those of living bone. The types of experimentation used to date, although allowing to study the phenomena occurring on the surface of the bone, do not allow to evaluate those that occur within the bone without modification of its mechanical features. Finally, the number and complexity of the parameters to be taken into account in this respect largely supersede the possibilities of classical study techniques. Accordingly, new types of methodology are required to evaluate the many parameters involved, to perform the corresponding computations and resolve the great number of unknown variables. Such methodology must allow experimentation to be performed without modifying the object of study and to determine the phenomena occurring within the bone itself, i.e. the mandible. A method of computer assisted simulation of a physicomathematical model was used to analyse the structural properties of the mandible.(ABSTRACT TRUNCATED AT 250 WORDS)

[Application of a 3-dimensional model using computer technology in the study of the structure of the mandible]. / Application d'un modèle tridimensionnel par informatique à l'étude de la structure de la mandibule.

Previous studies employing a plane "model" on the hemi-mandible confirmed the concept of a "bees-nest" structure of the mandible. As this plane model did not permit demonstration of maximal zones of iso-stress in the horizontal rami, the whole mandible was examined by means of a three-dimensional model. This gave more precise information, and thus produced more realistic results confirming previous findings. This new reliable type of model can be employed for any such exploratory procedure, and in studies totally different from those for which it was developed.

[Plea for the application of statistical methods by computer to stomatological research]. / Plaidoyer pour l'application des méthodes statistiques par informatique à la recherche en stomatologie

In face of the double reflex of fascination and defiance which is right away created by statistical methods by computers, the authors have attempted by means of precise examples to demystify these methods by recalling: 1) That computer statistics can be defined as the association of a service and a machine, the combination should be considered as an instrument and only an instrument. 2) That the application of computer statistics to odonto-stomatological research of course evidently enables the resolution of problems which would be otherwise insoluble, but above all considerably enlarges the field of research by rendering visible phenomena which would otherwise remain hidden. In this way, statistical methods by computer can be compared with the microscope; a low magnification with the optical microscope justifies only an overall view of the section while changing to higher magnifications permits the demonstration of details which would remain unsuspected. Use of the electromicroscope opens up another world for research. 3) In the same way as the biologist who uses the microscope, if he knows the principle of it is not in so far a specialist in optics, neither does the research woker who uses statistics necessarily have to be a trained statistician, on the one condition that evidently he disposes of professional computer logistics. This is the case of the ACB (Nantes) rush technical units, who cosigned this work, where the engineers who pose the problems to be resolved and emit the working hypotheses from the results supplied by the statistical studies are not the same people who carry out these very studies. 4) An essential fact, the research worker's independance is complete, only he can pose the problems and emit the hypothesis from the correlation, i. e. point of fact concomitance between the various isolated parameters. It therefore does not seem that weighty statistical techniques presently occupy the place of choice which should be theirs in stomatological research and more particularly in research concerning growth and development of the face where their use seems to be electively implied in face of the number and complexity of the parameters looked at.