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New trends in dental prosthodontic interventions tend to preserve the maximum of "body" structure. With the evolution
of CAD-CAM techniques, it is now possible to measure "in mouth" the remaining dental tissues. The prosthetic crown is
then designed using this shape on which it will be glued on, and also by taking into account the contact surface of the
opposite jaw tooth.
Several theories discuss on the glue thickness and formulation, but also on the way to evolve to a more biocompatible
crown and also new biomechanical concepts. In order to validate these new concepts and materials, and to study the
mechanical properties and mechanical integrity of the prosthesis, high resolution optical measurements of the
deformations of the glue and the crown are needed. Samples are two intact premolars extracted for orthodontics reasons.
The reference sample has no modifications on the tooth while the second sample tooth is shaped to receive a feldspathic
ceramic monoblock crown which will be glued.
This crown was manufactured with a chairside CAD-CAM system from an intra-oral optical print. The software allows
to realize a nearly perfect clone of the reference sample. The necessary space for the glue is also entered with ideal
values. This duplication process yields to obtain two samples with identical anatomy for further processing. The glue
joint thickness can also be modified if required.
The purpose is to compare the behaviour of a natural tooth and its prosthetic clone manufactured with "biomechanical" concepts. Vertical cut samples have been used to deal with planar object observation, and also to look "inside" the tooth.
We have developed a complete apparatus enabling the study of the compressive mechanical behaviour of the concerned
tooth by speckle interferometry.
Because in plane displacements are of great interest for orthodontic measurements1, an optical fiber in-plane sensitive
interferometer has been designed. The fibers are wrapped around piezoelectric transducers to perform "4-buckets" phase
shifting leading to phase variations during the compression test.
In-plane displacement fields from speckle interferometry already showed very interesting data concerning the
mechanical behaviour of teeth: the dentine-enamel junction (DEJ) and the glue junction have been shown including their
interfacing function. Mechanical action of the tooth surrounding medium will also be discussed.
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