Effect of central retainer shape and abduction angle during preparation of teeth on dentin and cement layer stress distributions in endocrown-restored mandibular molars

Abstract

To study the effect of central retainer shape and abduction angle during tooth preparation on stress distribution in endocrownrestored molars via finite element (FE) analysis, we constructed five FE models with different central retainer shapes and abduction angles. Under an oblique load, the distributions of maximum tensile stress in cervical dentin around the endocrown and on the cement layer, as well as maximum shear stress on the cement layer, were more balanced in the FE model in which the central retainer shape was generated based on the anatomical form of the pulp chamber. Moreover, there were no differences in stress distributions among FE models with different abduction angles. Therefore, the shape of the central retainer should be designed on the basis of the anatomical form of the pulp chamber; abduction angle during tooth preparation does not influence the repair effect of endocrown-restored mandibular molars.

Fracture resistance, failure mode and stress concentration in a modified endocrown design

“…Endocrown restoration is more recommended in molars than premolars and anterior teeth because they have a small pulp chamber and they are more subjected to lateral forces [17,19]. The performance of endocrown is related to many factors such as types of material [10,20,21], axis of loading [10,22], and shapes of preparation [23][24][25][26][27][28]. Lithium disilicate glass ceramic (LDS) is the most common material for endocrown restorations [23,24,27] due to its biomechanical properties [29,30].…”

“…Depth and shape of the pulp chamber and form of the finish line (circumferential butt margin or chamfer finish line) are diverse tested preparation designs which can change the mechanical behavior of the endocrowns [14,[23][24][25][26][27][28]31]: Tribst et al showed in FEA study that stress is more concentrated on the restoration more than on the cement line if remaining dental tissue is bigger and if the material has high elastic modulus [26]. Hayes et al [28] and Dartora et al [25] displayed that the fracture resistance is superior with a deeper extension into the pulp chamber.…”

“…Hayes et al [28] and Dartora et al [25] displayed that the fracture resistance is superior with a deeper extension into the pulp chamber. While Zhu et al presented that the central retainer form must follow the anatomical shape of the pulp chamber [24]. But De Kuijper et al showed that extension of the endocrown core into the pulp chamber and type of outline don't significantly influence the fracture resistance of endocrown restorations [23].…”

“…The performance of endocrown is related to many factors such as types of material [ 10 , 20 , 21 ], axis of loading [ 10 , 22 ], and shapes of preparation [ 23–28 ]. Lithium disilicate glass ceramic (LDS) is the most common material for endocrown restorations [ 23 , 24 , 27 ] due to its biomechanical properties [ 29 , 30 ].…”

“…While Zhu et al. presented that the central retainer form must follow the anatomical shape of the pulp chamber [ 24 ]. But De Kuijper et al.…”