Effect of eugenol-containing sealer and post diameter on the retention of fiber reinforced composite posts.

BACKGROUND: Fiber reinforced composite (FRC) posts are cemented with resin cements. It is reported that using resin cements in canals sealed with eugenol-containing sealers reduces the post retention. However, there is controversy on the subject. AIMS: The aim was to investigate the influence of eugenol-containing sealers and the amount of dentin removal from root canal with different post diameters on retention of FRC posts. SETTINGS AND
DESIGN: It was an in vitro study
MATERIALS AND METHODS: The roots of sixty teeth were cut with 14 mm distance from the apex and were instrumented to the working-length of 13 mm. The teeth were randomly distributed into 2 groups (n = 30). Following storage in normal saline for 7 days, the samples in both the groups were further divided into 3 subgroups (n = 10). Canals in the experimental subgroups (I, II, III) were obturated by gutta-percha and eugenol-containing sealer; and in the control subgroups (IV, V, VI) without any sealer. After storage in normal saline for 7 days, the post space was prepared by #3, #2, and #1 drills of DT Light-Post system. Post was cemented with Panavia-F2.0 resin-cement. A composite core was built for each sample. All samples were thermo cycled for 1000 cycles. The samples were tested for post retention with a mechanical testing machine. STATISTICAL ANALYSIS: Data were analyzed by two-way ANOVA and Tukey-HSD test.
RESULTS: There was not a significant difference in retention between FRC posts #1 and #2 (P > 0.05). Post #3 was more retentive than posts #1and #2 (P < 0.05). ZOE sealer significantly reduced the retention of posts (P = 0.024), however, increasing post-space diameter significantly increased post retention in canals coated with ZOE sealer (P = 0.002).
CONCLUSIONS: Eugenol-containing sealer reduced the retention of FRC posts cemented with resin cement. Removing more dentin from root-canals treated with eugenol-containing sealer for placing larger diameter posts caused an increase in post retention.

INTRODUCTION

Endodontically treated teeth lose a great amount of their coronal structure and thus need intra-radicular posts to provide retention for the restoration.[1-3] Fiber posts are alternatives to cast and prefabricated metal posts due to the similarity of their elastic modulus to dentin, which reduces the risk of root fracture.[4] Fiber posts also bond with most resin-based cements and core materials. Cementation of FRC posts with resin cements causes the creation of a hybrid layer in the dentinal wall of the root canal, reducing the wedging effect of the post within the root canal and the tooth susceptibility to root fracture.[2] Fiber posts also improve esthetics under all-ceramic restorations.[2]

Eugenol-containing sealers are one of the most commonly used root canal sealers in endodontics. Eugenol, like other phenolic compounds, has the ability to collect free radicals. Therefore, it interferes with the polymerization reaction of resin cements[56] and impairs the retention of the post. However, there is controversy over the subject. Some authors believe that eugenol-based sealers impair the retention of fiber posts cemented by resin cements.[7-9] Baldissara et al. reported that the eugenol-containing sealer reduced the retention of fiber posts after mechanical cycling. They suggested the use of resin-based sealers to improve the bonding of fiber posts cemented with resin luting materials.[4] Other studies have not reported any significant reduction in retentive strength.[10-12]

Hagge et al. reported that a long interval between root canal obturation with eugenol-based cements and post placement reduces the retention, presumably due to the deeper penetration of eugenol into the dentinal tubules.[13] As eugenol sealers have slow setting times, deep penetration of phenols into the root dentin may occur.[7] Probably, small amounts of eugenol still permeated the dental tissue at the time of post insertion, despite the dentin removal and acid etching, which are reported to eliminate the eugenol-contaminated dentin.[71415]

It was reported that post diameter is less effective than its length in retention, and small-diameter posts are adequate to provide retention, while minimizing the amount of tooth removal from the root canal.[1617] Although, post diameter is less effective in its retention than length, the amount of dentin removal during root canal preparation of a canal filled with eugenol-containing sealer could probably increase the retentive strength of the fiber-reinforced posts significantly.

Considering the fact that eugenol-containing sealers are the routine materials used by endodontists, the aim of the present study was to investigate the effect of eugenol-containing endodontic sealer, and also the amount of dentin removal from the root canal (post diameter), on retention of FRC posts cemented with a resin cement.

MATERIALS AND METHODS

This in vitro study was performed on 60 human maxillary central incisors extracted for periodontal reasons. The inclusion criteria were: Straight canals, closed apices, absence of any crazing and fracture, no intra-radicular calcifications, no canal obstruction, and no internal resorption on radiographic image. The teeth were debrided and stored in normal saline at room temperature until use.

The crowns were sectioned transversely at a 14 mm distance from the root ends. The root canals were instrumented to the working length of 13 mm (1 mm short of the apex) up to a #50K-file (Dentsply/Maillefer, Ballaigues, Switzerland) using the crown-down technique. During instrumentation, the canals were irrigated with 1 mL of distilled water at every change of files.

The teeth were randomly distributed into 2 experimental and control groups (N = 30). Each group was further divided into 3 subgroups having 10 samples each (n = 10). Subgroups I, II, III were the experimental groups and subgroups IV, V, VI were the control groups. Canal obturation in the experimental subgroups was performed by gutta-percha (Hygienic, Coltene/Whaledent Inc., Mahwah, NJ) and eugenol-containing sealer (Endofill; Dentsply Ind. e Com., Petrópolis, RJ, Brazil) using the lateral condensation technique. The canals in the control subgroups were obturated with gutta-percha without any sealer using the lateral condensation technique.

Canal orifices of all roots were sealed with a temporary material (Coltosol; Vigodent, Rio de Janeiro, RJ, Brazil). After storage in normal saline for 7 days, gutta-percha was removed with a #3 Gates-Glidden to a length of 10 mm; the post space was prepared by #1 drill of DT Light-Post system in subgroups I, IV; #2 drill in subgroups II, V; and #3 drill in subgroups III, VI. DT Light-Post of the related drill size (DT Light-Post System; Bisco, Schaumburg, IL) was cemented into the post space with Panavia F2.0 (Kuraray Medical Inc., Okayama, Japan) dual-curing resin cement according to manufacturer's instructions. Initially, the canals were rinsed and dried with paper points (Dentsply/Herpo). The posts were placed in ethanol for 1 min and air-dried. Post surfaces and canal walls were coated with the Panavia F2.0 adhesive resin system and the excess material was removed from the canal by a paper point after 20 seconds. The Panavia F2.0 cement was mixed with its accelerator and applied on the post surface. The posts were inserted into the post space and cured with a light-curing unit (Demi LED Light Curing System, Kerr Corp, Orange, CA, USA) at a light intensity of 800 mW/cm2 measured with a radiometer.

All the prepared samples were kept in distilled water at 37°C for 7 days. Afterwards, each sample was mounted in a metallic cylinder with acrylic resin; a metallic ring was cemented to the coronal part of the post, which protruded 10 mm from the canal space. A composite core (Filtek Z250, 3M ESPE, St. Paul, USA) was built for each sample. All the teeth were thermocycled for 1000 cycles at 5-55°C with a dwell time of 30 seconds.

The samples were fixed to a mechanical testing machine (Zwik-Roell; Ulm, Baden Wuerttemberg, Germany) at the crosshead speed of 0.5 mm/min until separation of the post from the root canal under the tensile force. The force required to separate the post in Newton was considered as the post retention. Data were analyzed by two-way ANOVA and Tukey HSD test at 0.05 significance level.

RESULTS

Table 1 lists the mean and standard deviation for retentive strengths of the FRC posts bonded with resin cements.

Table 1

Comparison of the retention of resin cementbonded fiber reinforced composite posts with different diameters with and without ZOE sealer

Two-way ANOVA indicated that the ZOE sealer significantly decreased the retentive strength of FRC posts (P = 0.024). It was also indicated that retentive strength of FRC posts significantly enhanced by increasing post diameter and removal of more dentin from root canals treated with ZnO sealer (P = 0.002). However, the interaction of these two factors was not significant (P = 0.714).

Tukey HSD pairwise comparison testes in eugenol-containing sealer groups showed that there is a significant difference between retentive strength of #1 and #3 posts, and also #2 and #3 posts (P < 0.05). In addition, there was a significant difference in retentive strength between #1 and #3 posts, and also #2 and #3 posts in groups treated with the non-eugenol sealer (P < 0.05).

DISCUSSION

The aim of the present study was to evaluate the effect of eugenol-containing sealer and also the amount of dentin removal from root canal during preparation of the root canal for placing posts with greater diameter, on the retentive strength of FRC posts. All the study procedures were performed by a single operator in this study, and all the factors in relation to the posts were constant, except for the post diameter and the use of eugenol-containing sealer.

Gates-Glidden was used to remove the coronal part of the filling materials afterward post drill from the DT light post kit was used for post space preparation according to the manufacturer's instructions.

The results of the present study indicated that obturation of the root canals with eugenol-containing sealer had a detrimental effect on the retention of the fiber posts cemented with resin cement to tooth structure (P = 0.0001). Findings of this study reaffirm the adverse effect of eugenol on the retention of posts luted with resinous cement.[518] In the literature, the decrease in bond strength has been attributed to softening of the resin due to a chemical reaction between composite resin and eugenol.[67919] Menezes et al.[20] and Alferedo et al.[9] also confirm that resin cements should not be used with eugenol-containing sealers.

Eugenol can be released from ZOE sealer and permeate into root canal dentin. It is established that the greatest amount of eugenol is released during the first 14 days of applying ZOE sealer.[21] Post space preparation and post cementation usually take place 7-10 days after root canal therapy; therefore, eugenol released from ZOE sealer can affect the polymerization of resin cement and consequently the retention of the FRC post.[71415]

However, the study of Schwartz et al. does not confirm the results of the present study.[22] The discrepancy in the results might be attributed to the adhesive system used. In the present study, Panavia F 2.0 adhesive cement and a one-step self-etch adhesive was applied according to the manufacturers’ instructions. It has been reported that in case of contact of eugenol compounds with phosphoric acid or ethanol, the retention of posts bonded with resin cement would be equal to the posts cemented with conventional cements.[723]

The adhesive systems applied in these studies were ethanol-based. Eugenol is fully soluble in alcohol. The ethanol in these adhesives can dissolve eugenol and therefore, reduce the negative effects of eugenol on fiber-post retention.[7]

Another factor affecting the results might be the amount of removing the eugenol-contaminated dentin from root canal wall during post space preparation. Using posts with larger diameter needs more dentin removal from root canal internal wall, which means the removal of more layers of eugenol-infected dentin. This can increase post retention by both increasing the bonding surface area and also cleaning the internal eugenol-contaminated wall of root dentin.

The preset study showed that retentive strength increased with an increase in the diameter of the post (P = 0.024). This effect was observed in both subgroups with eugenol-contaminated sealer and in the control subgroups in which no canal sealer was used. These results are consistent with the results of a study by Nergiz et al.[24] Post diameter is directly related to bonding surface area to root dentin. An increase in post diameter results in an increase in the retention of FRC posts. However, increase in the diameter should be restricted due to a decrease in fracture resistance of the tooth[2] and the risk of root perforation.[25]

Eugenol-containing sealer has a more detrimental effect than post diameter on the retention of FRC posts bonded with resin cement. However, the interaction of eugenol-containing sealer and post diameter was not significant (P = 0.71). Therefore, using sealers without eugenol and also posts with maximum diameter in the root canal can prepare higher retentive strength for FRC posts cemented with resin cement.

Within the limitations of the present study, it was concluded that:

The retention of the FRC posts bonded with resin cement in canals without sealer was significantly higher than the canals with eugenol-containing sealers.

Post diameter was effective in the retention of fiber posts to dentin.

There was not a significant difference in retention between FRC posts #1 and #2 in both the experimental and control groups. However, FRC post #3 was significantly more retentive than FRC posts #1 and #2.

Application of FRC posts in canals treated with eugenol-containing sealers is not recommended by the authors. It is recommended that application of FRC posts in canals treated with eugenol-containing sealers be avoided.