Dental Traumatology 2014; 30: 302–305; doi: 10.1111/edt.12084
Effect of surface treatments on fracture resistance of root filled teeth with bonded fibre posts Atiyeh Feiz1, Pooran Samimi1, Ali Karami1, Hamid Badrian2, Hossein Goroohi1, Edward J. Swift Jr3 1 Torabinejad Dental Research Center, School of Dentistry, Isfahan University of Medical Sciences, Isfahan, Iran; 2Department of Operative Dentistry, Dental School, Shahid Sadoughi University of Medical Science, Yazd, Iran; 3Department of Operative Dentistry, University of North Carolina, Chapel Hill, NC, USA
Key words: root canal irrigation; fibre posts; fracture resistance; vertical root fracture Correspondence to: Edward J. Swift Jr, Department of Operative Dentistry, University of North Carolina, Chapel Hill, NC 275997450, USA Tel.: +919 537 3981 Fax: +919 537 3990 e-mail: [email protected]
Abstract – Background/Aim: This study examined the effect of several dentin surface treatments on fracture resistance of root filled teeth containing bonded fibre posts. Material and methods: The roots of 84 single-canal premolars were instrumented, filled with gutta-percha and randomly divided into seven groups. The coronal 9 mm of gutta-percha was removed to create a post space. In the experimental groups, canals were irrigated with distilled water, 37% phosphoric acid, 5% sodium hypochlorite, 17% EDTA, 5% sodium hypochlorite followed by 17% EDTA or 5% sodium hypochlorite followed by 10% ascorbic acid. Fibre posts were cemented using Panavia F2.0 resin cement, and the specimens were mounted in acrylic resin blocks. Following 1-week storage in an incubator, specimens were thermocycled and their fracture resistance was determined using a universal testing machine. Data were analysed using the Kruskal–Wallis test. Results: Mean fracture resistance values ranged from 465.8 N in specimens treated with sodium hypochlorite and ascorbic acid to 739.1 N for those treated with sodium hypochlorite only. However, differences in fracture resistance were not statistically significant (P = 0.114). Conclusions: None of the surface treatments improved vertical fracture resistance of root filled teeth containing bonded fibre posts.
Accepted 12 October, 2013
Vertical root fracture is a frustrating complication with poor prognosis that occurs most frequently in root filled teeth (1, 2). This problem can originate during lateral condensation of gutta-percha or when a post is placed in the root canal (3, 4). Root filled teeth, particularly anterior ones and premolars, sometimes require a radicular post for retention of the coronal restoration. The increased demand for aesthetically acceptable posts and cores has led to the introduction of non-metal (fibre) post systems (3). When bonding fibre posts, two potential weak links exist – the post–resin interface and the resin–dentin interface. It is important to optimize adhesion at both interfaces (3). During post space preparation, the drill produces a smear layer consisting of dentin, residual sealer material and gutta-percha that changes into a plastic consistency due to frictional heat. Complete removal of the smear layer, which can interfere with polymerization of resin luting cements, is critical for optimal bonding of the post to dentin using resin-based materials (3). Agents such as sodium hypochlorite (NaOCl), hydrogen peroxide, ethylenediaminetetraacetic acid (EDTA), chlorhexidine digluconate, citric acid and phosphoric acid can be used to enhance micromechanical retention of the resin cement to dentin (3). 302
Previous studies have reported that application of various irrigants in the prepared post space has different effects on resin–dentin bond strengths (3, 5–12). Altogether, the application of EDTA (6–8, 11) or acidetching (5, 10, 12) can result in higher bond strengths, while irrigants such as sodium hypochlorite (3, 9) can have adverse effects. The effects of these various irrigants on fracture resistance of the root have not been examined. This study was designed to evaluate the effects of different surface treatments of radicular dentin on vertical fracture resistance of filled roots containing bonded fibre posts. The null hypothesis was that no surface treatment would improve fracture resistance. Material and methods
This in vitro study was approved by the Torabinejad Dental Research Center and local Ethical Committee of Isfahan University of Medical Science (no. 391035). Eighty-four single-canal premolars, extracted for orthodontic purposes, were stored in 0.2% thymol solution. The crowns were removed using a slow-speed diamond saw, leaving 14-mm roots. The root canals were cleaned and shaped using hand instruments (K-file; © 2013 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd
Dentin treatments and fracture resistance Dentsply Maillefer, Ballaigues, Switzerland) and obturated by lateral condensation of gutta-percha (Gapadent, Tianjin City, China) and AH26 sealer (Dentsply DeTrey, Konstanz, Germany). Specimens were stored in water for 24 h. The coronal 9 mm of gutta-percha was removed from the canal using a no. 3 Peeso reamer. A no. 3 Largo drill (Angelus, Londrina, PR, Brazil) was used to shape the canal for placement of a fibre post. The teeth were then randomly assigned to seven groups. The first group (control) did not receive any surface treatment or post. Root canal dentin in the other six groups was treated with the agents listed in Table 1. Each agent was applied using an irrigation syringe and was rinsed out using air–water spray. Following the assigned surface treatment, a no. 1 fibre post with 1.1 mm diameter (Reforpost; Angelus) was cemented into the canal using ED Primer and Panavia F2.0 resin cement (Kuraray, Osaka, Japan) such that the top of the post was 1 mm below the orifice of the canal (Fig. 1). The resin cement was light-activated using a quartz–tungsten–halogen curing unit (Demetron Kerr, Orange, CA, USA) at 400 mW cm 2 for 20 s. Specimens were mounted in acrylic resin blocks (Acropars, Tehran, Iran), with only the apical 5 mm of the root embedded in the block. A surveyor (DegussaNey, Yucaipa, CA, USA) was used to align the
Table 1. Experimental application times
Application time (seconds)
1 2 3 4 5 6
None (control) Distilled water 37% phosphoric acid gel 5% NaOCl 17% EDTA 5% NaOCl, followed by: 17% EDTA 5% NaOCl, followed by: Ascorbic acid
– 60 15 15 60 15 60 15 15
specimens vertically in the blocks. Following storage in an incubator (Behdad, Tehran, Iran) at 37°C and 100% humidity for 1 week, the specimens were thermocycled (Nemo, Tehran, Iran) 500 times between 5 and 55°C with a dwell of time 30 s in each bath. Fracture resistance (Newtons) was measured using a universal testing machine (Zwick, Ulm, Germany) at a crosshead speed of 5 mm min 1 as illustrated in Fig. 1. The diameter of the plunger tip used to apply force to the teeth was 1.5 mm. The data were analysed by the Kruskal–Wallis test using SPSS software (IBM Corporation, Chicago, IL, USA) at a significance level of a = 0.05. Results
Mean fracture resistance of the control group was 543.3 N. Mean values for the experimental groups ranged from 465.8 N in the sodium hypochlorite + ascorbic acid treatment group to 739.1 N in the sodium hypochlorite group. The data are summarized in Table 2 and in Fig. 2, which shows the median and first and third quartiles for each group. Differences in fracture resistance were not statistically significant (P = 0.114), so no pairwise comparisons were made.
Table 2. Fracture resistance (mean and standard deviation) of root filled teeth restored using fibre posts following different dentin surface treatments Surface treatment
None (control) Distilled water Phosphoric acid NaOCl EDTA NaOCl + EDTA NaOCl + Ascorbic acid
12 12 12 12 12 12 12
543.3 690.0 560.4 739.1 517.5 550.0 465.8
139.9 282.0 196.7 283.1 241.6 138.0 175.0
NaOCI + C6H8O6 NaOCI + EDTA EDTA H3PO4
Fig. 1. Schematic diagram of fracture resistance test in universal testing machine. © 2013 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd
Fig. 2. Fracture resistance of the various treatment groups, indicating medians and first and third quartiles (NaOCl: sodium hypochlorite; H3PO4: phosphoric acid; C6H8O6: ascorbic acid). Differences were not statistically significant.
Feiz et al.
To prevent vertical root fracture, especially in root filled premolars that are reported to have a high incidence of vertical root fracture, it is critical that the intracanal restoration act as an intracanal splint (1). The results of the present study show that applying different irrigants for smear layer removal does not significantly enhance root fracture resistance. The method used in this study followed that of Sedgley & Messer (13) and Apicella et al. (1). To simulate the clinical pattern of vertical root fracture, a wedging force was used in the coronal area until the fracture occurred. Total smear layer removal is required for etch-andrinse adhesive systems, which provide micromechanical retention to dentin via formation of a hybrid layer and resin tags in the dentinal tubules (14). However, total removal of the smear layer reduces the adhesion of self-etch adhesive systems such as Panavia F2.0 cement (15), which was used in the present study because phosphoric acid demineralizes intertubular and peritubular dentin (16). Furthermore, it has been reported that acid-etching leaves microscopic sealer residue (17), another factor that inhibits an effective bond. Thus, it is not surprising that acid-etching did not improve the performance of Panavia in this study. Sodium hypochlorite (NaOCl), the most common irrigant used for smear layer removal, removes collagen and other organic debris and could facilitate the penetration of resin monomers into deproteinized dentin. However, previous studies have shown that irrigation with 5% sodium hypochlorite reduces resin–dentin bond strengths (3, 5, 10), which is partly due to the fact that 5% sodium hypochlorite cannot completely remove the smear layer and residual sealer (3). In addition, increasing the application time considerably decreases shear bond strengths because of residual hypochlorite in underlying porous dentin. Hypochlorite decomposes to sodium chloride and oxygen, which inhibits polymerization of resin monomers and accounts for the reduced bond strengths (3, 18). Moreover, it has been reported that irrigation with high concentrations of hypochlorite for long periods of time weakens the dentin; therefore, a 15-s irrigation was selected to minimize this potential adverse effect (3). The chelating agent EDTA has outstanding lubricant characteristics, making it a widely used irrigant in endodontic treatments. It facilitates canal shaping, smear layer removal and preparing the dentin walls for better adhesion of filling materials. A combined use of 17% EDTA and 5% sodium hypochlorite has been recommended to adequately remove inorganic and organic components of the smear layer (19). In the present study, there was no significant difference between the control group and the group in which 17% EDTA was used after 5% sodium hypochlorite. Previous studies have reported that the use of 17% EDTA for 60 s followed by 5% sodium hypochlorite effectively removes the smear layer, creating a slightly eroded dentinal surface with open dentin tubules (15, 19). In spite of these observations, the present study did not find better fracture resistance as a result of this surface treatment.
Although da Cunha et al. (9) reported that ascorbic acid reversed the deleterious effects of sodium hypochlorite on bond strengths, application of 10% ascorbic acid following the application of 5% sodium hypochlorite did not improve the results in this study. If that occurred in the present study – and it is quite possible that it did not, given the short application time – it had no effect on fracture resistance. Within the limitations of the present study, none of the surface treatments – distilled water, individual use of 5% sodium hypochlorite or 17% EDTA, combined use of those agents or application of 10% ascorbic acid following 5% sodium hypochlorite – improved the vertical fracture resistance of root filled premolars reinforced with bonded fibre posts. Thus, for applying self-etch adhesive resin cement systems, more comprehensive research should be conducted to identify an irrigation method capable of removing gutta-percha and sealer residue without completely removing the smear layer. Conclusion
The results of this study suggest that none of the agents used to treat root canal dentin improved vertical root fracture resistance of root filled premolars containing bonded fibre posts. Acknowledgement
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© 2013 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd
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