09 May 2021

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AUTOMATIC OCCLUSAL ANATOMY COMPARED TO DENTAL TECHNICIAN’S DIGITAL ANATOMY OF MONOLITHIC ZIRCONIA CROWNS

Co-authors: A. Comba, F. Del Bianco

Lorenzo Breschi

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In recent years, cad-cam technologies were introduced in dentistry in order to improve accuracy  and reduce operative time and production costs of prosthetic restorations.
Cad-Cam software are based on standard libraries and often require several time consuming adjustments by the dental technician, during crown design,   and by the dental clinician during  the cementation appointment. To overcome the problem, the correlation technique was proposed to design the occlusal surface of a crown by replicating the anatomy of the original tooth thanks to a preliminary intraoral scan, thus avoiding library based cad-cam projects. This technique could also be employed for duplicating the occlusal surface of the provisional prosthesis to the definitive one.
In this context, Di Fiore et al. conduct a controlled clinical trial to compare the static and dynamic contacts (SDC) of monolithic zirconia crowns designed by using library technique compared to correlation techniques applied on provisional crowns.

Material & Methods
Di Fiore et al. included twenty-four patients in the study for a total of 28 molars. The authors fabricated an interim crown for each abutment tooth and collected two digital scans , with and without the interim crown in place. Two single crowns were designed using the correlation and the library techniques. After that fifty-six monolithic zirconia crowns were milled and evaluated intraorally for SDC using a 24-μm-thick blue articulating foil by the researchers. Photographs were also taken of to calculate the SDC area using  a software (ImageJ). 

Results
The results collected by the authors showed that the average and standard deviation (SD) of area of the occlusal marks of the interim crowns was 32.27 ± 3.45 mm2 while that of the definitive crowns designed by using the correlation technique was 31.01 ± 3.73 mm2 and that of  the library technique was 36.85 ± 5.78 mm2.
Di Fiore et al found a significant difference between the areas of occlusal marks of the interim and definitive crowns designed by using the library technique, and between the areas of occlusal marks of definitive crowns designed by using the correlation and library techniques (p < 0.001). 

Conclusion
The authors of the present study concluded that the average area of the SDC of monolithic zirconia crowns designed by using the correlation technique was similar to that of interim crowns. Moreover, the library technique resulted to be less effective when replicating the SDC compared to the correlation technique. 

(Photocredit: Dott. Federico Del Bianco)

For additional information: Automatic Digital Design of the Occlusal Anatomy of Monolithic Zirconia Crowns Compared to Dental Technicians’ Digital Waxing: A Controlled Clinical Trial.