Three-dimensional characterization and distribution of fabrication defects in bilayered lithium disilicate glass-ceramic molar crowns

Limitations, challenges and prospective solutions for bioactive glasses-based nanocomposites for dental applications: A critical review

Several nanomaterials have been recently used to overcome various challenges in the dental domain. Bioactive glasses, a class of bioceramics, with their outstanding properties including but not limited to their strong biocompatibility, antibacterial characteristics, and bioactivity inside the body's internal milieu have made them valuable biomaterials in a variety of dental domains. The utilization of nanomaterials has improved the performance of teeth, and the incorporation of bioactive glasses has the field of dentistry at an unsurpassed level in different categories such as esthetic and restorative dentistry, periodontics and dental implants, orthodontics, and endodontics. The current study discusses the most recent developments of the bioactive glasses' creation and implementation for dental applications, as well as the challenges and opportunities still facing the field. This work provides an overview of the current obstacles and potential future prospects for bioactive glasses-based nanocomposites to improve their dental uses. It also emphasizes the great potential synergistic effects of bioactive glasses used with other nanomaterials for dental applications.

Influence of veneer pore defects on fracture behavior of bilayered lithium disilicate glass-ceramic crowns

OBJECTIVE

To identify the conditions under which fabrication pore defects within veneering porcelain in bilayered lithium disilicate glass-ceramic (LDG) crowns will influence and jeopardize the mechanical integrity of the structure.

METHODS

Thirty standardized molar crowns (IPS e.max Press) were fabricated and microCT scanned to 3D-analyze the size, morphology and distribution of pores in veneering porcelain, followed by in vitro fracture test and SEM fractographic observation. Finite element analysis (FEA) of the microCT reconstructed models was used to evaluate the stress state.

RESULTS

The volumes of pores in samples ranged from 3241μm³ to 1.29×10⁹μm³ with the equivalent radius between 10μm to 680μm. Deviation of sphericity of pores ranged from 0.10 to 0.81 and the average of 99.97% pores was near 0.63. For the smaller pores their distribution tended to be uniform, while the larger pores were irregular with elongated ellipsoidal form and located at or near the veneer-core interface. During wedge loading blunt contact fracture testing 21 crowns failed from the fissure on the occlusal surface, of which 16 failed from surface or near surface pores, 2 from the midpoint of the oblique ridge, and 7 from larger interfacial pores. FEA analysis indicated that defects were detrimental to veneer integrity only in regions of tensile stress and where the pore radius associated with crack initiation ranged from 30 to 50μm. Pore morphology appeared to have only a minor effect on fracture.

SIGNIFICANCE

Within the limitation of the microCT resolution and FEA, it suggests that pores radius large than 30-50μm and located in the tensile stress area like grooves and fissures on the occlusal surface or near surface as well as cervical margins of veneering porcelain will jeopardize the bilayered structure and mechanical integrity of LDG.

The effect of adhesive failure and defects on the stress distribution in all-ceramic crowns

OBJECTIVES

To explore the effect of adhesive failure and defects between the crown and cement on the stress distribution within all-ceramic crowns and the corresponding risk of failure.

METHODS

An IPS e.max crown of lithium disilicate produced by CAD/CAM for a first mandibular molar was modeled using finite element analysis based on X-ray micro-CT scanned images. Predefined debonding states and interfacial defects between the crown and cement were simulated using the model. The first principal stress distribution of the crown and cement was analyzed under a vertical occlusal load of 600 N. A concept of failure risk was proposed to evaluate the crown.

RESULTS

Stress concentrations in the crown were identified on the occlusal surface surrounding the region of loading, beneath the area of loading and at the margin of the interior surface. Stress concentrations in the cement were also evident at the boundary of the debonded areas. The lower surface of the crown is safe to sustain the 600 N vertical load, but the top surface of the cement would undergo cohesive failure. According to the evaluation of failure risk of the crown, the conditions of highest risk corresponded to the conditions with highest percentage of cement damage. The risk of failure is not only associated with debonding between the crown and cement, but also associated with its distribution.

CONCLUSIONS

Debonding related defects and cementing defects are more deleterious to the interfacial stress than debonding itself. The axial wall plays a critical role in maintaining the principal tensile stress of the crown at an acceptable level.