Evaluation of Push out Bond Strength of Fiber Post after Treating the Intra Radicular Post Space with Different Post Space Treatment Techniques: A Randomized Controlled In vitro Trial.

OBJECTIVE: The aim of this study was to evaluate the push out bond strength after treating the post space with different irrigation procedures. STUDY
DESIGN: The study sample comprised of 60 recently extracted premolars. These teeth were placed in 5.25% sodium hypochlorite solution for 5 min and then washed under tap water. De-coronated samples were biomechanically prepared until F3 ProTaper and obturated using AH-Plus and 30# (6%) gutta-percha. The specimens were allowed to set for 24 h and then post space was prepared. The teeth were randomly assigned into three experimental groups based on the treatment technique: Group A - control, Group B - sodium hypochlorite and ethylene diamine tetra acetic acid (EDTA) and Group C - diode laser and EDTA. The samples were sectioned horizontally and push out bond strength was evaluated. The stereomicroscopic examination was done for evaluating the failure mode. One-way ANOVA variance followed by Tukey's post-hoc test was used for statistical analysis using SPSS software.
RESULTS: Use of diode laser does not enhance the bond strength of fiber post.
CONCLUSION: Diode laser at a very low pulse can be used as an irrigant adjuvant to vaporize the cement residues. Using diode laser does not enhance the bond strength. EDTA as final irrigant increases the bond strength of fiber post.

INTRODUCTION

Posts play a significant role in restoring debilitated, endodontically treated teeth. Fiber posts are esthetically appealing, have a modulus of elasticity similar to that of dentin and have the advantage of adhesive bonding.[1] Effective adhesive bonding between post and root canal dentin improves the distribution of forces at dentin post interface.[2] Luting relies on hybrid layer formation into dentin, which depends on the dentinal surface treatment. It improves resin tag formation between adhesive materials and intertubular dentin.[3]

Preparation of post space results in heavy smear layer deposits on dentine walls. Post space irrigation (PSI) may influence the strength of the cement bond within the root canal system.[1]

The purpose of this study was to evaluate the effectiveness of PSI procedures on the pushout bond strength of fiber posts.

MATERIALS AND METHODS

A total of 60 uniradicular teeth extracted for periodontal and orthodontic reasons were used in this study. Inclusion criteria for this study were teeth with single-rooted canals, the absence of resorption, root caries, cracks, and root length >15 mm. The teeth were stored in distilled water. These samples were placed in 5.25% sodium hypochlorite for 5 min and washed under tap water. The samples were decoronated, and working length was standardized to 15 mm. The canals were prepared apically using 15 and 20 size K files. Root canal preparation was completed using ProTaper rotary files (S1, S2, F1, F2 and F3). Samples were irrigated with 5 ml of 5% sodium hypochlorite (Prime DentPro) and 5 ml of 17% ethylene diamine tetra acetic acid (EDTA) (Provest DentPro) after each change of file. Saline was used to stop the reaction of each irrigant. Obturation was done using sealer (AH-Plus; Dentsply DeTrey GmbH) and gutta-percha (Dentsply Mallifer) by single cone technique. An interim filling material (Cavit 3M ESPE) was used to seal the endodontic access cavities.

After the root canal treatment was completed, the roots were stored in gauze dampened with sterile saline for 24 h for the sealer to set. The root canal filling was removed at 10 mm depth with number 1 (0.70 mm) peeso reamer (Mani INC), and preparation was completed using drill number 1 (Hi Rem Endod Drill 201). After post space preparation, the specimens were divided into three groups according to the PSI procedure.

Group A – Control group specimens were irrigated with 5 ml saline (0.9% sodium chloride W/V Nirlife) for 1 min.

Group B – Specimens were irrigated with 5 ml of 5% sodium hypochlorite for 1 min followed by 5 ml of 17% EDTA for 1 min.

Group C – Specimens were treated with a diode laser (Zolar Photon Plus) of 3 watts power. The laser was used in a continuous mode in the presence of 5% sodium hypochlorite for 20 s irradiation time of three cycles. After each cycle, sodium hypochlorite was replenished to compensate the vaporization of the solution.

All the specimens were irrigated with distilled water, After post space treatment, absorbent paper points were used to dry the root canals and self-adhesive resin cement (G Cem LinkAce, GC Pro) was used to lute the fiber posts of size 1 (Hi Rem Over Fiber Post 201) which were seated with light finger pressure. Self-adhesive resin polymerization was initiated using light emitting diode curing unit (Woodpecker LED. D) for 20 s and left for another 4 min for the material to set. After 24 h, the specimens were sectioned horizontally with a water cooled, low speed diamond disc (Premiere dental: Shofu INC). Three slices were obtained from apical, middle, and coronal region. Each slice of sample was standardized to 1 mm thickness. A push out test was applied to slices at 0.5 mm/min using 1 mm diameter metallic plunger in coronal third, 0.7 mm in middle third portions, and 0.5 mm in apical third portion from apical to coronal direction in all samples until the post dislodges from the tooth. A Jig was used to hold the slices in position. Figure 1 shows the specimen preparation and jig apparatus. A computerized universal testing machine (Kalpak) was used to measure the maximum push out bond failure load in newtons (N). Maximum failure load was converted to megapascals for each post to its bonding area of each slice. The total bonding area was calculated using formula A= π(r + R) *h2 + (R − r) where R = coronal post radius, r = apical post radius, and h = slice thickness.[4] The post diameter at coronal and apical portion of each slice and thickness of dentin sections were measured using caliper. Statistical analysis one-way ANOVA of variance and Tukey's multiple comparison test was performed to evaluate the statistical difference between experimental groups (α = 0.05) at different root thirds. Adhesive, cohesive, and mixed failure modes were evaluated with respect to each post space treatment protocol using stereomicroscope.

Figure 1

(a) Post luted specimen cut in coronal, middle and apical third region with 1 mm thickness (b) Push out test apparatus and customized jig for holding the slices

RESULTS

Push out results are shown in Table 1. Statistical analysis showed that both the PSI procedures and section level (root thirds) significantly affected the bond strength values. The interaction between these two factors was not significant. The samples treated with sodium hypochlorite and EDTA showed highest bond strength. The diode group showed lowest bond strength. For the root section level factor, there was a reduction in values from coronal to middle and apical thirds of all samples. The middle and apical third of all groups showed similar bond strength values with no statistically significant difference among them (P = 0.05). The failure mode analyzed using stereomicroscope displayed cohesive failure at dentin in the saline group. A prevalence of mixed failure at post-cement-dentin interface was found. Failure pattern was similar among all the groups [Chart 1].

Table 1

Push out bond strength based on post space treatment techniques at different root sections (Mean±standard deviation)*

Failure mode represented in percentages with respect to Post space irrigation treatment technique

DISCUSSION

The objective of this study was to evaluate the bond strength after different post space treatments at different levels of root sections (apical, middle, and coronal third). Push out bond strength is evaluated as it depicts the polymerization stress at the dentin cement interface. The test was performed to mimic dentin cement interface failure. Push out test is more reliable for testing the bond strength of post cement interface due to premature failure in specimen preparation and large data distribution spread linked with micro tensile testing.[5]

EDTA and sodium hypochlorite group had better efficacy than diode laser and the Sodium hypochlorite group. This is due to the use of EDTA as a final irrigant. This finding coincides with studies done previously. It improves penetration into the dentinal tubules by removing smear layer. EDTA reacts with calcium ions in dentin and forms water soluble calcium chelates. It also causes dentin demineralization and allows penetration of resin monomers.[6] Diode laser of 980 nm is absorbed more by water, whereas 810 nm is absorbed by melanin so it dehydrates the dentin water.[7] Diode laser helps in disinfection of root canal and produces acid etch like appearance.[8] The diode laser does not enhance bond strength. This finding is similar to that of several studies.[910] This is against the finding of the study done by Maenosono et al.[11] in which he used diode laser with low power watts. In the present study, temperature is one of the factors, which affect the bond strength of fiber post. The use of diode laser at 3 weeks for 20 s of three cycles increases the temperature of the dentin.[10] Laser melts the dentinal tubules and vaporizes the irrigating solution. Use of NaOCl as a final irrigant produces free oxygen radicals which inhibit the vinyl free radicals produced in the light activation of adhesives which consequently affects the initiation and propagation of addition polymerization.[12] Sodium Hypochlorite when used as final irrigant, shows no difference in bond strength when compared with non-oxidizing agents according to Morris et al.[13]

Bond strength values were varied at different section levels. This can be due to different tubule density of dentin at different regions of roots, as well as technical sensitivity and difficulty in applying adhesives to post space, limited light transmission to narrow post space.[14] Diode laser at the apical third showed less bond strength. This can be due to the positioning of the optic fiber, which concentrates continuous power delivery at the apical portion. The most likely explanation for low resistance to post dislodgement at apical portion of all samples relies on the decreasing effect of curing light at a greater distance and difficulty in moisture control causing incomplete infiltration of adhesive agent. Moreover, coronal part is easily accessible, easier to etch, and apply adhesive agents. Different types of defects such as bubbles, bonding defects, polymerization defects, and cement residues were observed in the post space in other studies[1] on using different irrigating solutions. The traces of gutta-percha and cement residues remain at apical thirds after post space preparation.

Self-etch adhesives are claimed to require smear layer for proper bonding to dentine. In contrast, Cecchin et al.[15] concluded smear layer removal is necessary for better penetration of self-etch adhesive cements into dentinal tubules.

CONCLUSION

The present study displayed that bond strength of fiber post is affected by post space treatment techniques at various section levels. Use of diode laser does not improve bond strength. Low-level pulsed diode laser can be used only as an adjuvant to other techniques for vaporizing the traces of gutta-percha and cement traces at inaccessible apical third regions.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.