Abstract

The purpose of this in vitro study is to investigate the fracture of zirconia in the posterior region and to compare between fracture strength of zirconia crowns and porcelain fused to metal restorations. Twenty human maxillary premolars were prepared for two zirconia all-ceramic crown systems with the following preparation criteria: 6-degree axial taper, 1-mm shoulder finish line, 2-mm occlusal reduction, and occluso-gingival height of 5 mm. All specimens were divided into two groups (n=10) for each ceramic material. In the first group, all prepared premolars were restored by full contour zirconia crowns (mad/mam), while in the second group, all teeth were restored by veneered zirconia crowns. The cores were directly fabricated (Vita In-Ceram blocks) by MAD/MAM and built up with ceramic. All specimens were loaded in a universal testing machine with the compressive load (n) applied along the axis of the specimen. Fracture load was recorded for each specimen. The KruskalWallis test was used first and followed by the Mann-Whitney test. The fracture strength records a highly significant difference between VZ and FZ (p=0 for both tests), irrespective of the type of surface treatment. Contrarily, both tests proved that the surface treatment has no significant effect on fracture resistance, irrespective of the type of material (p=0.72 for median test and p=0.27 for MannWhitney test). The fracture strength of zirconia is high in the posterior region, and full-contour zirconia showed higher fracture strength than veneered zirconia crowns and porcelain fused to metal restorations

Keywords. Fracture Strength, Zirconia

Ab s t rac t

Aim: The aim of this study was to evaluate the efficacy of grape seed extract (GSE) on remineralization of surface and subsurface enamel lesions 

compared to that of sodium fluoride (NaF).

Materials and methods: A total of 20 intact bovine incisor crowns were separated from their roots and immersed in a demineralizing solution 

for 96 hours at 37°C to create artificial enamel lesions. The specimens were randomly divided into two groups (n = 10): 6.5% GSE solution 

and 1000 ppm NaF solution. The specimens were subjected to six daily pH cycles for 8 days. The microhardness test was carried out at three 

different stages: baseline, after artificial caries formation, and after pH cycling. Raman spectroscopy was used to evaluate the depth of enamel 

remineralization. Surface morphology and elemental analysis were assessed using a scanning electron microscope (SEM) and an energy dispersive 

X-ray (EDX) spectroscope, respectively. Statistical analysis was performed using SPSS 22.0 at a significance level of p ≤ 0.05.

Results: There was a significant increase in the mean values of enamel surface microhardness after pH cycles in the two groups compared to 

after artificial caries formation, but there was no significant difference between both groups. The B-type carbonate/phosphate (Ca/P) ratio at 

10 and 40 µm depth revealed no significant difference between the two groups. Scanning electron microscope micrograph revealed occlusion 

of porosities and particle precipitation on the enamel surface of the two groups, while EDX results for the Ca/P ratio of the GSE and NaF groups 

were 1.59 and 1.60, respectively.

Conclusion: Grape seed extract and NaF are equally effective in remineralizing surface and subsurface artificial enamel lesions.

Clinical significance: Grape seed extract can be considered a promising herbal material and a safe alternative to traditional NaF for the 

noninvasive treatment of enamel lesions.

Keywords: Enamel remineralization, Grape seed extract, Microhardness, pH cycling model, Raman spectroscopy, Sodium fluoride.