Reza H. Heshmati

Measure of microhardness, fracture toughness and flexural strength of N-vinylcaprolactam (NVC)-containing glass-ionomer dental cements

OBJECTIVES To investigate the effects of N-vinylcaprolactam (NVC)-containing terpolymers on the fracture toughness, microhardness, and flexural strength of conventional glass-ionomer cements (GIC). METHODS The terpolymer of acrylic acid (AA)-itaconic acid (IA)-N-vinylcaprolactam (NVC) with 8:1:1 (AA:IA:NVC) molar ratio was synthesized by free radical polymerization and characterized using (1)H NMR and FTIR. Experimental GIC samples were made from a 50% solution of the synthesized terpolymer with Fuji IX powder in a 3.6:1 P/L ratio. Specimens were mixed and fabricated at room temperature. Plane strain fracture toughness (K(Ic)) was measured in accordance with ASTM Standard 399-05. Vickers hardness was determined using a microhardness tester. Flexural strength was measured using samples with dimensions of 2 mm×2 mm×20 mm. For all mechanical property tests, specimens were first conditioned in distilled water at 37°C for 1 day or 1 week. Fracture toughness and flexural strength tests were conducted on a screw-driven universal testing machine using a crosshead speed of 0.5mm/min. Values of mechanical properties for the experimental GIC were compared with the control group (Fuji IX GIC), using one-way ANOVA and the Tukey multiple range test at α=0.05. RESULTS The NVC-modified GIC exhibited significantly higher fracture toughness compared to the commercially available Fuji IX GIC, along with higher mean values of flexural strength and Vickers hardness, which were not significantly different. SIGNIFICANCE It was concluded that NVC-containing polymers are capable of enhancing clinically relevant properties for GICs. This new modified glass-ionomer is a promising restorative dental material.

Shear bond strength of orthodontic brackets bonded to provisional crown materials utilizing two different adhesives.

OBJECTIVE To test the hypothesis that there is no difference in the shear bond strength of brackets bonded to provisional crown materials (PCMs) using two adhesive agents. MATERIALS AND METHODS Four PCMs were tested: Integrity, Jet, Protemp, and Snap. Forty cylindrical specimens of 10 mm diameter x 5 mm were prepared for each PCM. Ten specimens from each group were bonded to one of the two brackets, Clarity or Victory, using one of the two adhesives, Fuji Ortho LC or Ortho Bracket Adhesive. The brackets were debonded in shear at a cross-head speed of 5 mm/min, and the shear bond strength (SBS) was calculated. The type of failure was visually determined. The numeric data were analyzed using three-way analysis of variance and Tukey multiple range test at alpha = .05. RESULTS The mean SBSs ranged from 2.81 MPa to 9.65 MPa. There was a significant difference between Snap and the other three materials (P < .0001). There was no significant difference between the two brackets or the two adhesives (P > .05). The bond failure for all the specimens was of the adhesive type between the PCM and the adhesive resin. CONCLUSIONS The PCM Snap yielded a significantly lower mean SBS value compared to the other three materials. No significant differences were found between the brackets or the adhesives. The bond failure was of the adhesive type.

Early rehabilitation of facial defects using interim removable prostheses: report of two clinical cases.

Postsurgical facial defects often pose a challenge to patient rehabilitation. Such defects can have a severe adverse effect on patient perceptions of body image and self-esteem. When immediate surgical repair of the defect is not feasible, an interim removable facial prosthesis may be considered. This prosthesis can be fabricated and placed as soon as several days after surgery to provide a cosmetically acceptable appearance, permitting the patient to more comfortably and confidently resume social interactions during the postoperative healing period. This article presents two case reports describing the use of interim facial prostheses to provide rapid patient rehabilitation.

Using a Porcelain Furnace to Debond Cement‐Retained Implant Crown from the Abutment after Screw Fracture: A Clinical Report

When a screw fracture occurs on a cement-retained, implant-supported restoration, the abutment and restoration are completely separated from the implants internal connection. Traditionally, an access hole is drilled through the crown to retrieve the broken screw, and the restoration can be placed again as a screw-retained restoration. This clinical report documents a patient whose broken abutment screw was retrieved from the restoration by burning off the cement and separating from the abutment without drilling an access hole.

Potentiodynamic polarization study of the corrosion behavior of palladium-silver dental alloys

Statement of problem: Although palladium‐silver alloys have been marketed for over 3 decades for metal‐ceramic restorations, understanding of the corrosion behavior of current alloys is incomplete; this understanding is critical for evaluating biocompatibility and clinical performance. Purpose: The purpose of this in vitro study was to characterize the corrosion behavior of 3 representative Pd‐Ag alloys in simulated body fluid and oral environments and to compare them with a high‐noble Au‐Pd alloy. The study obtained values of important electrochemical corrosion parameters, with clinical relevance, for the rational selection of casting alloys. Material and methods: The room temperature in vitro corrosion characteristics of the 3 Pd‐Ag alloys and the high‐noble Au‐Pd alloy were evaluated in 0.9% NaCl, 0.09% NaCl, and Fusayama solutions. After simulated porcelain firing heat treatment, 5 specimens of each alloy were immersed in the electrolytes for 24 hours. For each specimen, the open‐circuit potential (OCP) was first recorded, and linear polarization was then performed from –20 mV to +20 mV (versus OCP) at a rate of 0.125 mV/s. Cyclic polarization was subsequently performed on 3 specimens of each alloy from –300 mV to +1000 mV and back to –300 mV (versus OCP) at a scanning rate of 1 mV/s. The differences in OCP and corrosion resistance parameters (zero‐current potential and polarization resistance) among alloys and electrolyte combinations were compared with the 2‐factor ANOVA (maximum‐likelihood method) with post hoc Tukey adjustments (&agr;=.05). Results: The 24‐hour OCPs and polarization resistance values of the 3 Pd‐Ag alloys and the Au‐Pd alloy were not significantly different (P=.233 and P=.211, respectively) for the same electrolyte, but significant differences were found for corrosion test results in different electrolytes (P<.001 and P=.032, respectively). No significant interaction was found between the factors of alloy and electrolyte (P=.249 and P=.713, respectively). The 3 Pd‐Ag silver alloys appeared to be resistant to chloride ion corrosion, and passivation and de‐alloying were identified for these alloys. Conclusions: The Pd‐Ag alloys test results showed excellent in vitro corrosion resistance and were equivalent to those of the high‐noble Au‐Pd alloy in simulated body fluid and oral environments. Passivation, de‐alloying, and formation of a AgCl layer were identified as possible corrosion mechanisms for Pd‐Ag alloys.