Journal of Prosthetic Dentistry
Volume 86, Issue 5 , Pages 474-480, November 2001

The effect of thermocycling on the fracture toughness and hardness of core buildup materials☆☆☆★★★♢♢♢

School of Dentistry, Marquette University, Milwaukee, Wis

Abstract 

Statement of Problem. Thermocycling has been shown to cause surface degradation of many dental materials, but its effect on the fracture toughness and hardness of direct core buildup materials is unknown. Purpose. This study was designed to determine the effect of thermocycling on the fracture toughness and hardness of 5 core buildup materials. Material and Methods. Fifteen specimens were prepared from each of the following materials: Fluorocore, VariGlass VLC, Valiant PhD, Vitremer, and Chelon-Silver. American Standard for Testing Materials guidelines for single-edge notch, bar-shaped specimens were used. Ten specimens of each material were thermocycled for 2000 cycles; the other 5 specimens were not thermocycled. All specimens were subjected to 3-point bending in a universal testing machine. The load at fracture was recorded, and the fracture toughness (KIC) was calculated. Barcol hardness values were also determined. Data were analyzed with 1-way analysis of variance and compared with the Tukey multiple range test (P<.05). Pearson's correlation coefficient was also calculated to measure the association between fracture toughness and hardness. Results. Fluorocore had the highest thermocycled mean KIC and Valiant PhD the highest non-thermocycled KIC. Chelon-Silver demonstrated the lowest mean KIC both before and after thermocyling. One-way analysis of variance demonstrated significant differences between conditions, and the Tukey test showed significant differences (P<.05) between materials for both conditions. Most specimens also showed significant hardness differences between conditions. Pearson's correlation coefficient indicated only a mild-to-moderate correlation between hardness and fracture toughness. Conclusion. Within the limitations of this study, the thermocycling process negatively affected the fracture toughness and hardness of the core buildup materials tested. (J Prosthet Dent 2001;86:474-80.)

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☆ This research was supported by a 1995 Tylman Research Grant and received the second place Tylman competition award at the American Academy of Fixed Prosthodontics 46th Annual Scientific Session, Chicago, Ill., February 1997. A poster abstract of the research was presented at the 74th General Session of the American Association for Dental Research, San Francisco, Calif., March 1996.

☆☆ aPrivate Practice, San Juan, Puerto Rico.

★ bAssociate Professor and Director, Graduate Prosthodontics.

★★ cAssociate Professor, Division of Dental Biomaterials.

♢ dAssociate Professor and Head, Division of Prosthodontics.

♢♢ Reprint requests to: Dr William W. Nagy, Director, Graduate Prosthodontics, Marquette University School of Dentistry 334, PO Box 1881, Milwaukee, WI 53201-1881, Fax: (414)288-6516, E-mail: william.nagy@marquette.edu

PII: S0022-3913(01)80919-7

doi:10.1067/mpr.2001.120110

Journal of Prosthetic Dentistry
Volume 86, Issue 5 , Pages 474-480, November 2001

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