Ammar A. Mustafa

Fracture strength and fractographic analysis of zirconia copings treated with four experimental silane primers

This study evaluated and compared the effect of new four experimental silane coupling agents on the fracture strength of zirconia copings. The findings were supported with fractographic and finite element analyses. All together 125 zirconia copings with a ‎wall thickness of 0.6 mm were fabricated on identical nickel-chromium master dies and then divided randomly into five groups (n = 25). Four test groups were prepared according the experimental silane primer (labeled: OIWA1, OIWA2, OIWA3 and OIWA4) ‎and one control group without silanization. The silane monomers used were: ‎3-methacryloxypropyltrimethoxysilane (in OIWA1), ‎3-acryloxypropyltrimethoxysilane (in OIWA2), ‎3-‎isocyanatopropyltriethoxysilane (in OIWA3) and styrylethyltrimethoxysilane (in OIWA4). Tribochemical sandblasting (silica-coating) treatment was performed to the inner surface of the copings in the ‎test groups. All the specimens were silanized at the inner surfaces of the zirconia copings. Self-‎adhesive universal resin cement was used to cement the copings to ‎the underlying master die. Zirconia copings were vertically loaded on the ‎cusp ‎area until the first crack failure was occurred using Precision Universal Tester ‎at a ‎constant crosshead speed of 1 mm/min. Then, the machine ‎was manually controlled to cause more failure ‎to further determine the texture of fracture. Three dimensional finite element analysis and fractography were performed to support the fracture strength findings. Based on the finite element analysis results, zirconia silanized with ‎3-acryloyloxypropyltrimethoxysilane showed the highest fracture strength with a mean of ‎963.75‎ N (SD 4.5 N), while zirconia copings silanized with ‎3-methacryloyloxypropyltrimethoxysilane showed a mean fracture strength value of ‎925.65 N (SD 2.4 N). Styrylethyltrimethoxysilane-silanised zirconia showed mean fracture strength of 895.95 N (SD 3.5 N). Adding silane coupling agents to the resin-zirconia interface increased the fracture strengths significantly (ANOVA, p < 0.05). Silanization with four new experimental silane primers in vitro produced significantly ‎greater fracture strength than the control group not treated with the test silane.‎

The influence of experimental silane primers on dentin bond strength and morphology: a laboratory and finite element analysis study

STATEMENT OF PROBLEM The inconsistency of dentin bonding affects retention and microleakage. PURPOSE The purpose of this laboratory and finite element analysis study was to investigate the effects on the formation of a hybrid layer of an experimental silane coupling agent containing primer solutions composed of different percentages of hydroxyethyl methacrylate. MATERIAL AND METHODS A total of 125 sound human premolars were restored in vitro. Simple class I cavities were formed on each tooth, followed by the application of different compositions of experimental silane primers (0%, 5%, 25%, and 50% of hydroxyethyl methacrylate), bonding agents, and dental composite resins. Bond strength tests and scanning electron microscopy analyses were performed. The laboratory experimental results were validated with finite element analysis to determine the pattern of stress distribution. Simulations were conducted by placing the restorative composite resin in a premolar tooth by imitating simple class I cavities. The laboratory and finite element analysis data were significantly different from each other, as determined by 1-way ANOVA. A post hoc analysis was conducted on the bond strength data to further clarify the effects of silane primers. RESULTS The strongest bond of hybrid layer (16.96 MPa) was found in the primer with 25% hydroxyethyl methacrylate, suggesting a barely visible hybrid layer barrier. The control specimens without the application of the primer and the primer specimens with no hydroxyethyl methacrylate exhibited the lowest strength values (8.30 MPa and 11.78 MPa) with intermittent and low visibility of the hybrid layer. These results were supported by finite element analysis that suggested an evenly distributed stress on the model with 25% hydroxyethyl methacrylate. CONCLUSIONS Different compositions of experimental silane primers affected the formation of the hybrid layer and its resulting bond strength.

Effect of experimental silane‐based primers with various contents of 2‐hydroxyethyl methacrylate on the bond strength of orthodontic adhesives

AIM To evaluate in vitro the effect of different concentrations of 2-hydroxyethyl methacrylate (HEMA) in experimental silane-based primers on shear bond strength of orthodontic adhesives. METHODS Different volume percentages of HEMA were tested in four experimental silane-based primer solutions (additions of HEMA: 0, 5.0 vol%, 25.0 vol% and 50.0 vol%). An experimental silane blend (primer) of 1.0 vol% 3-isocyanatopropyltrimethoxysilane (ICMS) + 0.5% bis-1,2-(triethoxysilyl) ethane (BTSE) was prepared and used. The experimental primers together with the control group were applied onto acid-etched premolars for attachment of orthodontic brackets. After artificial aging by thermocycling the shear-bond strength was measured. The fractured surfaces of all specimens were examined under scanning electron microscopy (SEM) to evaluate the failure mode on the enamel surface. RESULTS The experimental primers showed the highest shear-bond strength of 21.15 MPa (SD ± 2.70 MPa) and with 25 vol% showed a highly significant increase (P < 0.05) in bond strength. The SEM images showed full penetration of adhesive agents when using silane-based primers. In addition, the SEM images suggested that the predominant failure type was not necessarily the same as for the failure propagation. CONCLUSIONS This preliminary study suggested that nonacidic silane-based primers with HEMA addition might be an alternative to for use as adhesion promoting primers.

Use of Porous Alumina Bioceramic to Increase Implant Osseointegration to Surrounding Bone

A new experimental porous glass ceramic coating for dental implants was prepared with a new formula consisted of a sintered glass ceramic based on alumina, silica glass and boron trioxide. The resultant sintered objects were anodized by one step anodization method at a constant potential of 40V and at a temperature of 22°C. X-ray diffraction analysis was performed to investigate the phase structure of the new material in addition to SEM investigation for surface texture and pores size and distribution. The new experimental material was subjected to failure under universal testing machine for compressive strength. The results showed a promising material to use as coating for implants as X-ray diffraction exhibited an amorphous phase diagram for the material structure whereas SEM results revealed that the pores in the specimens prepared by anodization method were highly ordered and the mean average pore size was 6.5-8.5 nm. The compressive strength test showed that the test-porous glass ceramic coating has a mean numerical value of up to 7.5 MPa which indicates an ambitious result for the new material.

The Effect of Incorporating Lithium Fluoride on the Compressive Strength and Diametric Tensile Strength of Glass Ionomer Cement

Experimental glass ionomer cement was prepared for the purpose of this study. Twenty disk specimens (16mm diameter x 10mm height) of test-GIC were prepared for the diametral tensile strength (DTS) test and twenty cylindrical specimens (6 mm diameter x 16mm height) were prepared for the compressive strength (CS) test. Specimens were stored in an artificial saliva at 37º C and (50±10%) of relative humidity in an incubator until testing. Five specimens of each GIC were submitted to CS and DTS test in each period, namely 1 hour, 24 hours, 7 days and 28 days. The specimens were tested in a Universal Testing Machine (Instron 1122, Instron corp., High Wycombe, U.K.) at a crosshead speed of 1.0mm/min for CS and 0.5mm/min for the DTS test until failure occurred. The results have revealed that incorporation of lithium fluoride in the formula of the test GIC might impart an increase in the mechanical properties of the GICs