Indian Journal of Dental Research

ORIGINAL RESEARCH
Year
: 2015  |  Volume : 26  |  Issue : 3  |  Page : 244--247

Effects of immediate and delayed intraradicular preparation on bond strength of fiber posts


Marina Barbosa Mello Machado1, Luís Fernando dos Santos Alves Morgan1, Giovana Mongruel Gomes2, Walison Arthuso Vasconcellos1, Fabiano Pereira Cardoso1, Rodrigo de Castro Albuquerque1,  
1 Department of Restorative Dentistry, Federal University of Minas Gerais, Belo Horizonte, Brazil
2 Department of Restorative Dentistry, State University of Ponta Grossa, Paraná, Brazil

Correspondence Address:
Luís Fernando dos Santos Alves Morgan
Department of Restorative Dentistry, Federal University of Minas Gerais, Belo Horizonte
Brazil

Abstract

Background: To assist the retention of restorations prepared in endodontically treated teeth, fiber posts are widely used in dental practice. The ideal time to prepare space for the post is still controversial. Aim: The purpose of this study was to evaluate the effects of immediate and delayed postspace preparation on the retention of the self-adhesive resin cement. Materials and Methods: Twelve bovine teeth were used with sectioned roots standardized to 19 mm. The teeth were properly instrumented and filled with gutta-percha and eugenol-free cement AH Plus. Two experimental groups (n = 6) were created based on the different times of post preparation (immediate and delayed). Using cemented cylindrical fiber posts, the teeth were put in acrylic resin and polyvinyl chloride tubes, where the cuts were made. Two slices were obtained from the cervical third, two from the medium third and two from the apical third. Subsequently, the samples were subjected into push-out tests. Statistical analysis were performed using ANOVA and Tukey's test (P = 5%). Results: The results indicated that, for all of the evaluated thirds, delayed preparation showed greater bond strength than immediate preparation. Conclusion: A delayed post preparation of the root space, following the root canal filling, is recommended.



How to cite this article:
Machado MB, Alves Morgan Ld, Gomes GM, Vasconcellos WA, Cardoso FP, Albuquerque Rd. Effects of immediate and delayed intraradicular preparation on bond strength of fiber posts.Indian J Dent Res 2015;26:244-247


How to cite this URL:
Machado MB, Alves Morgan Ld, Gomes GM, Vasconcellos WA, Cardoso FP, Albuquerque Rd. Effects of immediate and delayed intraradicular preparation on bond strength of fiber posts. Indian J Dent Res [serial online] 2015 [cited 2020 Nov 23 ];26:244-247
Available from: https://www.ijdr.in/text.asp?2015/26/3/244/162879


Full Text

Assisting the retention of restorations in endodontically treated teeth, as well as research on and improvement of prefabricated posts and cements, is extensively discussed in the literature.

Several types and brands of posts are commercially available, and there are several choices of cement for the chemical cure and operative steps. Studies have revealed that the different systems and techniques can influence the bond strength of intraradicular posts.[1][2][3][4][5][6][7]

The time of mechanical removal of the filling material during the post preparation not an influence in the integrity of the apical seal,[8] but is important for achieving proper adhesion and retention.[9] When resin cement is used, the removal of cement coated on the intraradicular canal dentin walls during post preparation is important for its retention.[3] In this context, the preparation of immediate or delayed posts is related to their retention. According to some authors, the retention appears to be reduced when the cementation is immediate.[4],[9] Other authors have shown that a significant reduction of leakage was found when the post preparation was made immediately after filling.[10][11][12][13] Other studies have also shown that there is no difference in immediate or delayed postspace preparation.[14][15][16][17] In summary, the timing of postspace preparation after root filling is not well established in the literature.

Regarding adhesive procedures during root canals preparation, the difficulty of finding an optimal adhesive strategy has been well-documented. This difficulty can be explained by anatomical characteristics and the difficulty to access the root canal, especially in the deep regions.[1],[18],[19]

Therefore, the aim of this study was to evaluate the effect of immediate and delayed postspace preparation on the bond strength of the resin cement for a cylindrical fiber post. The null hypothesis was that there is no difference in retention posts between delayed and immediate preparation of the tooth after root canal filling.

 Materials and Methods



Twelve bovine teeth were used after approval of the Ethics Committee on Animal Experimentation. The teeth had the crown sectioned by a precision cutting machine (IsoMet 1000, Buehler, Lake Bluff, Illinois, USA) with a standard root height of 19 mm. The sections were obtained with diamond discs at 250 rpm and under specific oil solution refrigeration.

The canals were instrumented using the system ProTaper Universal (Dentsply, Ballalgues, Switzerland).[20] The working length was set to 18 mm because the root length was standardized to 19 mm. The teeth were irrigated with 2.5% sodium hypochlorite, and they were dried with absorbent paper towels (Dentsply Ind. E. Com. Ltda., Brazil) and filled with gutta-percha and eugenol-free cement AH Plus (Dentsply, Ballalgues, Switzerland) using the vertical condensation technique.

The teeth were divided into two experimental groups based on the different times of post preparation. In Group 1 (G1), six teeth were sectioned to perform the post preparation immediately after the root canal filling, and in Group 2 (G2), the remaining six teeth had their root accesses temporarily filled with glass ionomer cement (Ketac Cem; 3M Espe, USA), were stored at room temperature for 21 days after the filling, and a delayed postspace preparation was then performed.

In both groups, the preparation of the root canal was performed by removing the gutta-percha with number 3, 4 and 5 Largo drills to ensure that the apical seal at 5 mm of gutta-percha had been maintained.[21] The diameters of the postspace preparations were the same for both groups.

After preparing the postspaces, the canals were irrigated with 20 mL of distilled water and dried with conical sterile paper points. The prepared postspace walls were reviewed by radiographic evaluation to check the presence of any residual gutta-percha.

An intraradicular glass fiber resin post (Angelus, Brazil) was used [Table 1]. The post has a cylindrical shape, smooth surface, a length of 16 mm and translucency. The self-adhesive Resin cement Rely-X Unicem (3M ESPE, St. Paul, MN, USA) [Table 1] was used for cementation. The posts were tested, cleaned with alcohol and cemented in accordance to the manufacturer's instructions.{Table 1}

After the root canal was properly dried with absorbent paper and the resin cement was inserted with specific application tips from Rely-X Unicem for intraradicular use. Then, all samples were included in polyvinyl chloride tubes, which had diameters of 10 mm and length of 20 mm, using Duralay acrylic resin (Reliance, Worth, IL, USA). With the assistance of an accuracy cutting machine, two slices of the cervical third (CT), two from the medium third (MT) and two from the apical third (AT) were obtained with a 1.0 mm height. The diameters of the posts were measured under an optical microscope (Mitutoyo, TM) from both sides of the disc (upper side and lower side) and named D and d, respectively. In addition, the height (h) of each slice was measured using a caliper, and the push-out tests were subsequently performed.

The push-out test was used to analyze the bond strength of the post to intraradicular dentin. A compressive load was applied in the cervico-apical direction over the posttrough by a cylindrical plunger with a diameter of 0.65 mm, which was assembled in a universal testing machine (AG-I, Shimadzu Autograph, Brazil). The size of the plunger tip was selected and positioned to connect only with the post, without pressure the surrounding dentin. The compression was applied at a speed of 0.5 mm/min until postdisplacement. The megapascal interfacial strength was calculated by dividing the load in Newton's (N) by the area (mm2). The area (A) was calculated using the following formula: A = P (R + r) [(h2 + (R−r))2] 0.5, where R is the radius of the coronal post, r is the radius of the apical pin, and his the thickness of the section. The results were analyzed using ANOVA and the Tukey test (P = 5%).

 Results



In the comparative analysis between the different timings of postspace preparation (immediate and delayed), Group G2 showed higher adhesive resistance values for all three-thirds than Group G1 [Table 2].{Table 2}

For thirds of the same group, there was no significant difference in G1. However, G2 showed statistically significant differences between AT when compared to CT and MT.

 Discussion



The use of bovine tooth in this research was due to ready availability in the absence of caries or restorations. Quantitatively, the number of dentin tubules has higher mean values in the bovine tooth than in human. However, the number of root dentin tubules in different thirds follows the human pattern, with a great number in CT followed by middle and ATs respectively. Regarding the dentin tubules diameter, both types are similar.[22] For the better chances to find greater similarity with human teeth, the selected older bovine teeth, around 45-month-old, were taken into consideration, according to a recommended general rule.[23] Thus, it can be concluded that bovine primary teeth hard tissue substrates may be regarded as suitable alternatives for human teeth for shear bond testing.[24]

The intraradicular postspace preparation may influence in apical seal and bond strength. The better integrity of the apical seal was associated with delayed preparation for some authors[10] and with immediate preparation for other ones.[25] However, Boone et al.,[26] discuss that neither the type of endodontic sealer used nor immediate versus delayed cementation have been found to be significant factors in this decision.

In relation the fiber postretention, focus of this study, the results show higher bond strength when the postspace preparation is performed following the delayed protocol. Thus, the null hypothesis that there is no difference in retention posts between delayed and immediate preparation of the tooth after root canal filling is rejected. The data of this study are in accordance with those obtained in others reports.[4],[9] These findings suggest that a relationship exists between postretention and cleanliness of the postspace walls. The results showed for Khaliu et al.,[27] that there was no influence of time interval between canal obturation and postcementation after immediate or delayed postspace preparation on the retentive strength of postsluted with resin cements. However, the smaller time preparation analyzed were 24 h after obturation and not immediate with the present study.

Adequate postcementation requires a completely clean root canal,[5] especially when resin cements are used.[3] The patency of the root canal immediately after root canal filling can cause the cementing agent, which is not yet completely polymerized, to spread across the canal.[4] Thus, the bond strength between the cement and the dentin walls is lower,[26],[28] and lower postadhesive resistance values can be verified.[4] Therefore, these results can be explained by the hypothesis that intraradicular preparation performed immediately may result in greater impregnation in dentinal tubules, thereby isolating part of the conduit area walls available for contact and adherence to the cement and resulting in the lower displacement resistance of the intraradicular post. To eliminate variables, only posts specially developed for this study and self-adhesive resin cement were used. The intraradicular post used in this study was specifically made with a cylindrical shape to eliminate the variable taper. The choice of self-adhesive cement was justified by the elimination variables as operative steps such as etching and adhesive system.[29],[30]

One observation that stands out in these results is the fact that, for both groups, the AT showed the highest bond strength when compared to CT and MT. Two hypotheses guide the understanding of these results in particular. Thefirst is that, in both groups, there was slightly more wear in the region of AT than in the other groups to receive a post with a cylindrical shape. Thus, a greater amount of dentin impregnated with the sealer was removed, decreasing or eliminating the effect of the filling material on the displacement resistance of the post.[31] The second observation is that the AT region is an area of greater confinement of cement during the cementing of the post. This confinement promotes the greater compression of the self-adhesive cement in this region of the canal, maximizing its physical properties and, therefore, its values and bond strength.

Regarding the photopolymerization time of the self-adhesive resin, the cement showed lower variation in micro-hardness through root depths regardless different curing protocols[2] and light transmission capacity of these posts is limited,[32] thus did not interfere with our results.

 Conclusion



In summary, is recommended that preparation of the root space that receives a retention post should be performed by following the delayed protocol.

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