Poisson's ratio of glass-polyalkenoate (?glass-ionomer?) cements determined by an ultrasonic pulse method

Abstract

Poisson's ratio has been determined for four glass-polyalkenoate cements; one experimental luting type, one experimental restorative type, one commercial restorative type (Chelon-Fil, ex. ESPE GmbH) and one cermet-reinforced cement EChelon-Silver, also ex. ESPE]. An ultrasonic pulse method was employed for the Poisson's ratio determinations. For the restorative materials, including the cermet-reinforced cement, the values obtained were all in the region of 0.3. For the luting cement, on the other hand, the values found were in the range of 0.35. This difference was consistent with the relatively increased water content and reduced glass content of the luting cement. The cements based on poly(acrylic acid) showed slight, but statistically significant, increases in Poisson's ratio up to 80 days, whereas the cements based on poly(maleic acid) showed no significant changes in Poisson's ratio with time.

Fracture toughness testing: A discriminatory mechanical testing performance indicator for glass-ionomer restoratives?

“…The value of K IC is affected by three properties, these being Young's modulus (E), the Critical Strain Energy Release Rate (G IC ) and Poisson's ratio ( ) through the relationship: K IC = [G IC E/(1 − 2 )] 0.5 . For GIs the value of Poisson's ratio, measured by the ultrasound method (which is appropriate for the research reported in this paper) is in the region of 0.3 for products intended for use as restoratives but increases to 0.35 for luting cement products [46]. The greater water content to produce the necessary flow properties for a luting cement is the reason for the increase in Poisson's ratio [46].…”

“…For GIs the value of Poisson's ratio, measured by the ultrasound method (which is appropriate for the research reported in this paper) is in the region of 0.3 for products intended for use as restoratives but increases to 0.35 for luting cement products [46]. The greater water content to produce the necessary flow properties for a luting cement is the reason for the increase in Poisson's ratio [46]. Whereas this variation is relevant to all the materials in the present research, in practice the effect of the change is minimal [(1 − 2 ) −0.5 is 1.05 for = 0.3 and 1.06 for = 0.35] and can be disregarded in this discussion.…”

“…Therefore, investigators [23,50,55] are in general agreement that although pre-cracking seems theoretically correct, invariably it will introduce errors when investigating brittle dental restorative materials, thereby negating any benefit produced. In the current study, SEN bend test-pieces were prepared with a sharp notch (0.3 m crack tip radius [46]) moulded around a scalpel blade which has previously been shown to yield valid results that are indicative of the K IC of the material [14][15][16][17][18]20,37]. This adequate sharpness was evident on profilometrically scanning the side surfaces of the SEN bend specimens, which highlighted crack tip radii of 0.3 m.…”

Improving the standard of the standard for glass ionomers: An alternative to the compressive fracture strength test for consideration?

“…where a was the radius of the knife-edge support (10 mm) and v was Poisson's ratio (0.3 for GI restoratives 31 ). The thickness of each fractured fragment was measured at the point of fracture using the micrometre and the mean thickness h was determined.…”

Biaxial Flexural Strength of High-Viscosity Glass-Ionomer Cements Heat-Cured with an LED Lamp during Setting

“…The BFS tests were performed with a universal testing machine (Digimess MX5000) at a crosshead speed of 1 mm/min, using a 4 mm diameter ball indenter, loading the specimens centrally. The BFS value was calculated according to the following equation [17]: BFS = P / h 2 ((1 + v )(0.485ln⁡( a / h ) + 0.52) + 0.48), where P is the load at fracture, a is the radius of the support (5 mm), v is the Poisson ratio (0.3 for glass-ionomer restorative cements) [18], and h represents the thickness of the specimen, obtained by the mean thickness value of the two remaining fragments of each disc that is fractured when loaded.…”