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Showing 3 results for Lithium Disilicate
Effect of three filler types on mechanical properties of dental composite
A. Pahlavan , M. Ataei , Aa. Zandi-Nejad ,
Volume 18, Issue 2 (5-2005)
Abstract

Statement of Problem: Despite the improvements achieved in the field of dental composites, their strength, longevity, and service life specially in high stress areas is not confirmed. Finding better fillers can be a promising step in this task.

Purpose: The purpose of this study was to investigate the effect of the filler type on the mechanical properties of a new experimental dental composite and compare these with the properties of composite containing conventional glass filler.

Materials and Methods: Experimental composites were prepared by mixing silane-treated fillers with monomers, composed of 70% Bis-GMA and 30% TEGDMA by weight. Fillers were different among the groups. Glass, leucite ceramic and lithium disilicate were prepared as different filler types. All three groups contained 73% wt filler. Comphorquinone and amines were chosen as photo initiator system. Post curing was done for all groups. Diametral tensile strength (DTS), flexural strength and flexural modulus were measured and compared among groups. Data were analyzed with SPSS package using one-way ANOVA test with P<0.05 as the limit of significance.

Results: The results showed that the stronger ceramic fillers have positive effect on the flexural strength. Ceramic fillers increased the flexural strength significantly. No significant differences could be determined in DTS among the groups. Flexural modulus can be affected and increased by using ceramic fillers.

Conclusion: Flexural strength is one of the most significant properties of restorative dental materials. The higher flexural strength and flexural modulus can be achieved by stronger ceramic fillers. Any further investigation in this field would be beneficial in the development of restorative dental materials.


The effect of zirconia on flexural strength of IPS Empress 2 ceramic
H. Kermanshah , Sh. Farzin Ebrahimi,
Volume 20, Issue 2 (5-2007)
Abstract

Background and Aim: All ceramic, inlay-retained resin bonded fixed partial denture is a conservative method for replacement of missing teeth, because of minimal tooth reduction. The connector between the retainer and the pontic is the weak point of these bridges. Reinforcement of ceramic core will increase the clinical longevity. The aim of this study was to determine the effect of zirconia on flexural strength of IPS Empress 2 core ceramic.

Materials and Methods: In this experimental in vitro study, twenty eight bar shape specimens (17´3.1´3.1 mm) were made of four different materials: (1) Slip casting in-ceram alumina core (control group) (2) Hot-pressed lithium disilicate core ceramic (IPS Empress 2) (3) IPS Empress 2 with cosmopost (zirconia post) inserted longitudinally in the center of the bar (4) IPS Empress 2 with cosmopost (zirconia post) inserted longitudinally in bottom of the bar. Specimens were subjected to three-point flexure loading with the span of 15mm, at a cross-head speed of 0.5 mm/min. Failure loads were recorded and analyzed using one-way ANOVA and Tomhane Post-hoc tests and p<0.05 was set as the level of significance. Fractured surfaces were then observed by scanning electron microscope (SEM). Four additional samples were made as the third group, and zirconia-IPS interface was observed by SEM before fracture.

Results: Mean values and standard deviations of three point flexural strengths of groups 1 to 4, were: 378.4±44.6, 258.6±27.5, 144.3±51.7, 230±22.3 MPa respectively. All the groups were statistically different from each other (P<0.05), except groups 2 and 4. The flexural strengths of groups 2, 3, 4 were significantly lower than group 1. Group 3 had the lowest flexural strength. SEM analysis showed that the initiated cracks propagated in the interface of zirconia post and IPS Empress 2 ceramic.

Conclusion: Based on the results of this study, inserting zirconia post (cosmopost) in IPS Empress 2 ceramic does not reinforce all-ceramic inlay retained resin bonded fixed partial dentures.
Investigation of the effect of temperature and time of hot-pressing operation on the structural and mechanical properties of lithium silicate blocks for dental applications
Hossein Naghdi Varnosfaderani, Kamran Amini, Mohammad Khodaei,
Volume 39, Issue 0 (3-2026)
Abstract
Background and Aims: It is very important and practical to make machinable blocks with the ability to maintain the edge and at the same time have sufficient hardness for chewing. One of the most important groups of materials for making dental crowns and veneers for dentistry by CAD-CAM is lithium disilicate ceramics such that extensive research is being conducted in the field of modifying their structure and properties. All-ceramic restorations enhance the beauty of teeth due to their closeness to the tooth color and transparency. At the same time, these materials also have high biocompatibility. The main goal of this study was to evaluate the effect of hot-pressing temperature on the microstructure and mechanical properties of the lithium disilicate block fabrication.
Materials and Methods: The present laboratory study was conducted on the lithium disilicate blocks produced by powder metallurgy at Islamic Azad University, Khomeini Shahr Branch. In this regard, initially, the raw materials (including: Tetraethyl orthosilicate, Lithium nitrate, Triethyl phosphate, potassium nitrate) were processed by sol-gel method and the resulting frit (the glassy state of a ceramic) was crushed by a ceramic mortar. Then, the 3 groups of samples (n=3) were subjected to the hot-pressing at different temperatures of 750 and 900 °C for 60 minutes at a constant pressure of 200 kPa. Subsequently, the microstructure and elemental phases of lithium silicate samples were examined using scanning electron microscopy (SEM) and X-ray diffraction (XRD). Statistical analysis of the results was performed using one-way analysis of variance (ANOVA). A p-value of less than 0.05 was considered significant.
Results: X-ray diffraction results on the resulting powder before hot pressing showed the formation of a glass phase with lithium metasilicate and after hot pressing, the formation of a lithium disilicate phase. The results also showed that in all samples, the lithium disilicate phase was formed and had some porosity. In addition, with increasing the pressing temperature, the size of lithium disilicate particles increased. However, with increasing the hot-pressing temperature from 750 to 900°C, the amount of porosity decreased from about 23% to 20%.
Conclusion: The hot-pressing temperature had a significant effect on the microstructure and phases present in the produced ferrite sample. It was concluded that by changing the hot-pressing temperature, the microstructure and consequently the properties of the lithium disilicate blocks can be modified to achieve improved properties for dentistry applications.

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