08 January 2019

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Prosthetic stability: Which preparation is better between the parallel and the convergent one?

Massimo Gagliani

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The types of prosthetic preparations in the anterior teeth have always raised more or less heated debates. Regardless of the line or end of preparation area, it has always seemed of great interest to consider the vestibular and palatal walls as determining the stability of the final prosthetic device. Safeguarding the palatal girdle has been considered by most as an element of resistance and stability that can not be disregarded for the future duration of the final restoration. 
In this study published in the Journal of Prosthetic Dentistry, the authors examined two types of preparation: a group of incisors was prepared keeping the buccal and palatal walls parallel to each other, while a second group of analogous dental elements was prepared keeping the buccal and palatal walls converging, with an angle of about 20°. The preparations thus obtained were then coated with ceramic prosthetic products and these items were loaded with compressive and tensile forces, used to verify the retentive capacity obtainable with the two different types of preparation. The results, as regards the retentive force, were in favor of the group in which the preparation was carried out with the parallel walls while, on the contrary, the resistance to the compressive load was in favor of the group in which the preparations were carried out with converging walls. 

CONCLUSIONS
The preparation has always determined different mechanical behaviors in prosthetic products, the evidence of this study highlights some aspects that, clinically, could be interesting. That is, to reserve types of preparation parallel to those cases in which the resistance to the occlusal load is not relevant while it is possible to envisage wall preparations converging to those patients in which the chewing forces could urge the anterior dental elements significantly.

For additional informations:
In vitro assessment of retention and resistance failure loads of two preparation designs for maxillary anterior teeth.