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The Influence of Preparation Design in Biologically Oriented Preparation and Horizontal Preparation on Tooth
Abeer Aljareh1, Nabil Alhouri1, Mohanad Kadhim2
1Department of Fixed Prosthodontics, Faculty of Dentistry, Damascus University, Damascus, Syria.
Objectives:
Several clinical scenarios indicate the need for full-coverage crowns. However, these restorations require substantial tooth reduction, which may compromise pulpal vitality and biological principles. This study aimed to evaluate the effect of the biologically oriented preparation technique on the volume and weight of tooth structure removal compared with horizontal preparation when zirconia crowns are used.
Material And Methods:
A total of 160 acrylic teeth representing the maxillary right central incisor, canine, premolar, and molar, were divided into two main groups according to preparation type: biologically oriented preparation with no finish line (n = 80), and horizontal preparation with a 1-mm rounded shoulder (n = 80). Each group was further subdivided into a monolithic zirconia crown subgroup (n = 40) and a bilayered zirconia crown subgroup (n = 40). Teeth were weighed and scanned before preparation. All preparations were performed by a single operator following standardized guidelines. After preparation, the teeth were reweighed and rescanned. The percentage of tooth structure removed was calculated by weight, and the scanned files were analyzed to determine the volume of removed tooth structure.
Results:
A significant difference was observed in the amount of tooth structure removal between the biologically oriented preparation (32.33%) and horizontal preparation groups (41.48%). Bilayered zirconia crowns required significantly more reduction than monolithic crowns (42.55% and 31.26%, respectively). The tooth structure removal also differed significantly according to tooth type. Furthermore, a high degree of interchangeability was found between the two assessment methods, demonstrated by a strong correlation (r = 0.99) and a mean difference of 2.8%.
Conclusions:
Within the limitations of this study, the biologically oriented preparation technique may represent a more conservative alternative to the horizontal shoulder preparation, particularly when paired with monolithic zirconia crowns rather than bilayered zirconia restorations.