Computation of the fracture probability and lifetime of all ceramic anterior crowns under cyclic loading - An FEA study

Thermal stresses in porcelain veneered lithium disilicate and zirconia dental crowns: Comparative analysis using a validated viscoelastic finite element model

This study aims to investigate the effects of material compatibility, variable cooling rates, and crown geometry on thermal stress development in porcelain-veneered lithium disilicate (PVLD) and porcelain-veneered zirconia (PVZ) dental crown systems, and subsequently anticipate parameters for their optimum performance. An anatomically correct 3D crown model was developed from STL files generated using 3D scans of the experimental crown sample. Next, the viscoelastic finite element model (VFEM) based on the 3D crown model was developed and validated for anatomically correct bilayer PVLD and PVZ crown systems. The Vicker's indentation method was used on experimental PVLD and PVZ crown samples to validate the simulated thermal stress results from the VFEM. The validated VFEM was then used to predict thermal transient and residual stresses within the dental crown systems. The comparison between thermal residual stress profiles in PVLD and PVZ crowns showed that the interfacial stress concentrations were comparatively lower for PVLD crowns. However, the PVLD crowns also experienced prominent tensile stresses in the veneer layer. Furthermore, the rapid cooling protocol was seen to cause intensification of compressive stresses on the exterior veneer surface for both PVLD and PVZ crowns which can enhance resistance against crack growth. But faster cooling rates also caused rapid stress evolution which may cause material defects within the crown. This study highlights the importance of material compatibility by comparing stress distribution within the PVLD and PVZ crowns. Moreover, the post-firing cooling protocols showed significant effects on overall thermal stress distribution and consequently, the long-term dental crown performance.

Optimization of grinding parameters in robotic-assisted preparation of cracked teeth based on fracture mechanics: FEA and experiment

BACKGROUND AND OBJECTIVES

If left untreated, cracked teeth can lead to tooth loss, of which the incidence is 70%. Dental preparation is an effective treatment, but it is difficult to meet the clinical requirements when traditionally prepared by dentists. Grinding-based tooth preparation robot (TPR) shows promise for clinical applications to assist dentists. However, current TPR has problems with chipping and crack extension when preparing real teeth.

METHODS

We propose a grinding parameter optimization strategy to solve this problem, specifically including preparation depth and direction. Among them, surface morphology observation technology and thermal-mechanical coupling simulation technology are used. Through theoretical modeling, computer simulation techniques and surface morphology experimental studies, different motion parameters are compared and analyzed to derive the optimal preparation parameters.

RESULTS

One of our contributions is to control the preparation depth based on the different material removal methods, and the brittle removal methods and grinding heat during the preparation process were reduced. Another contribution is to derive the stress intensity factor (SIF) at the crack tip for different preparation directions based on multi-grit and thermal-mechanical coupling finite element model for different preparation stages. The preparation direction was directed and crack extension was minimized. Finally, the experimental system of the TPR was constructed. Based on the proposed morphology and preparation direction optimization method, the material removal method during the preparation process can be controlled in plastic removal. Crack extension was also reduced based on different stages of optimized preparation directions. Based on the guided strategy, the TPR can provide safe assisted dentists.

CONCLUSIONS

In this work, the preparation parameters of the cracked preparation robot were optimized to enable it to perform the preparation of hard and brittle cracked teeth. The surface morphology met the clinical requirements. Intraoral preparation will be considered in the future to advance the robot toward clinical dental applications.

The Effect of Die Material on the Crown Fracture Strength of Zirconia Crowns

BACKGROUND

Determination of the eligibility of several tooth analog materials for use in crown fracture testing.

METHODS

A standardized premolar crown preparation was replicated into three types of resin dies (C&B, low modulus 3D printed resin; OnX, high modulus 3D printed resin composite; and highest modulus milled resin composite). 0.8 mm zirconia crowns were bonded to the dies and the maximum fracture load of the crowns was tested. Twelve extracted human premolars were prepared to a standardized crown preparation, and duplicate dies of the prepared teeth were 3D printed out of C&B. Zirconia crowns were bonded to both the dies and natural teeth, and their fracture load was tested.

RESULTS

There was no statistical difference between the fracture load of zirconia crowns bonded to standardized dies of C&B (1084.5 ± 134.2 N), OnX (1112.7 ± 109.8 N) or Lava Ultimate (1137.5 ± 88.7 N) (p = 0.580). There was no statistical difference between the fracture load of crowns bonded to dentin dies (1313 ± 240 N) and a 3D-printed resin die (C&B, 1156 ± 163 N) (p = 0.618).

CONCLUSIONS

There was no difference in the static fracture load of zirconia crowns bonded to standardized resin dies with different moduli or between a low modulus resin die and natural dentin die.