Microhardness of resin cements in the intraradicular environment: Effects of water storage and softening treament

Pedreira, Ana Paula R.V.; Pegoraro, Luiz Fernando; de Góes, Mario Fernando; Pegoraro, Thiago Amadei; Carvalho, Ricardo Marins

doi:10.1016/j.dental.2009.01.096

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Volume 25, Issue 7 , Pages 868-876, July 2009

Microhardness of resin cements in the intraradicular environment: Effects of water storage and softening treament

Ana Paula R.V. Pedreira
- Department of Prosthodontics, Bauru School of Dentistry, University of São Paulo, Bauru, SP, Brazil
- Department of Dentistry, Faculty of Health Sciences, University of Brasilia, Brasilia, DF, Brazil
Luiz Fernando Pegoraro
- Department of Prosthodontics, Bauru School of Dentistry, University of São Paulo, Bauru, SP, Brazil
Mario Fernando de Góes
- Department of Dental Materials, Piracicaba School of Dentistry, State University of Campinas, Piracicaba, SP, Brazil
Thiago Amadei Pegoraro
- Department of Prosthodontics, Bauru School of Dentistry, University of São Paulo, Bauru, SP, Brazil
Ricardo Marins Carvalho
- Department of Prosthodontics, Bauru School of Dentistry, University of São Paulo, Bauru, SP, Brazil
- Department of Operative Dentistry, University of Florida College of Dentistry, P.O. Box 100415, Gainesville, FL 32610-0415, USA
- Corresponding author at: Department of Operative Dentistry, University of Florida College of Dentistry, P.O. Box 100415, Gainesville, FL 32610-0415, USA. Tel.: +1 352 273 5850.

Received 19 August 2008; received in revised form 25 November 2008; accepted 14 January 2009.

Abstract

Objectives

To analyze the microhardness of four dual-cure resin cements used for cementing fiber-reinforced posts under the following conditions: after 7 days of storage in water, after additional 24h of immersion in 75% ethanol, and after 3 months of storage in water. Hardness measurements were taken at the cervical, middle and apical thirds along the cement line.

Methods

Root canals of 40 bovine incisors were prepared for post space. Fibrekor^® glass fiber-reinforced posts (Jeneric/Pentron) of 1mm in diameter were cemented using Panavia F 2.0 (Kuraray), Variolink (Ivoclar-Vivadent), Rely X Unicem (3M ESPE) or Duolink (Bisco) (N=10). After 7 days of water storage at 37°C, half the sample (N=5) was longitudinally sectioned and the initial microhardness measured along the cement line from cervical to apex. These same samples were further immersed in 75% ethanol for 24h and reassessed. The remaining half (N=5) was kept unsectioned in deionized water at 37°C for 3 months, followed by sectioning and measuring. Data were analyzed by a series of two-way ANOVA and Tukey tests at α=5%.

Results

Statistically significant differences were identified among the cements, thirds and conditions. Significant interactions were also observed between cements and thirds and between cements and conditions. Panavia F exhibited significantly higher initial microhardness than the other three cements, which showed no statistical difference among themselves. Variolink and Duolink showed significantly higher microhardness values in the cervical third, without significant difference among the thirds for the other cements. Immersion in ethanol significantly reduced the hardness values for all cements, regardless of the thirds. Storage in water for 3 months had no influence on the hardness of most of the cements, with the exception of Unicem that showed a significant increase in the hardness values after this period.

Significance

Results showed heterogeneity in the microhardness of the cements inside the canal. All cements presented some degree of softening after ethanol treatment, which suggests instability of the polymer. The quality of curing of resin cements in the root canal environment seems unpredictable and highly material dependent.

Keywords: Dual-cure resin cements, Fiber posts, Microhardness