Comparative evaluation of the effect of surface treatment of fiber-reinforced posts and prefabricated metal posts on adhesion of a resin-based luting cement: An in vitro study.

BACKGROUND: The purpose of this study was to evaluate the effect of surface treatment of fiber-reinforce post and metal post of adhesion of a resin luting cement.
MATERIALS AND METHODS: Sixty methyl methacrylate specimens were fabricated with a customized metal rod. The samples were segregated into six groups (F1, F2, F3, M1, M2, and M3) of 10 specimens (n = 10) each. The first three groups (F1, F2, and F3) were for fiber posts and (M1, M2, and M3) were for metal posts. The postspace preparation was done with dedicated drills supplied by the postmanufacturers to a length of 14 mm. F1 and M1 were the control groups. The posts in F2 and M2 groups were treated with airborne-particle abrasion with 70 μm Al2O3 particles for 5 s at a constant distance of 20 mm, cleaned with alcohol and cemented in the postspace. The posts in the F3 and M3 groups were treated with airborne-particle abrasion followed by primer application. After cementing the posts into the postspace, the acrylic blocks were sectioned with a motor-driven jigsaw to obtain four specimens each of 3-mm thickness. These sections were then subjected to push-out tests on a universal testing machine.
RESULTS: There was a statistically significant increase in the bond strength of both fiber and metal posts to resin cement after airborne-particle abrasion with Al2O3 particles and airborne abrasion followed by primer application.
CONCLUSION: There is an increase in the bond strength of the resin cement with the prefabricated posts after the various surface treatments.

INTRODUCTION

The restoration of endodontic teeth have been studied extensively however it also remains as an area of major controversy regarding which material is appropriate for the restoration of endodontically treated teeth.[1] An endodontically treated tooth should restored only when it is believed to make a positive contribution to the patient's total oral health.[2] Posts are one of the most widely methods used for the restoration of these teeth when there is insufficient coronal tooth structure to retain a core for the definitive restoration.[3] Among the various post available, the prefabricated posts are mostly widely used because they can provide satisfactory results while saving chair time and reducing costs.[45] The success of the restoration also depends on the mechanical and chemical treatment of postsurface as well as changes in the post's matrix composition appear to influence the bond strength between resin materials and fiber reinforced and metal posts.[6] The possibility of improving adhesion between prefabricated fiber-reinforced posts and metal posts and resin-based luting agent after various surface treatments have been investigated to a somewhat lesser extent.[7] The purpose of this in vitro study is to evaluate and compare the influence of various surface treatments on bond strength of resin-based luting agent to fiber-reinforced posts and prefabricated metal posts.

MATERIALS AND METHODS

Source of data

A total of 60 posts were divided into six groups of 10 each, respectively [Figure 1].

Figure 1

Representation of the materials used

Methodology

Fabrication of the test specimen

A wax block was fabricated out of modeling wax (Hindustan modeling wax No. 2, Hindustan Dental Products, Hyderabad) with dimensions 2 cm × 1 cm. This wax block was then flasked and dewaxed to create a mold space. Separating medium was applied and mold space was filled with self-cure acrylic resin to create a model. Self-cure acrylic resin (DPI Cold Cure Acrylic Improved – Denture Base Polymer) was dispensed and mixed in an acrylic mixing jar and then poured into the putty mold of the model. The customized rod was then inserted in the center of the mold up to the length of 17 mm to create a space of diameter 3.5 mm for composite resin. Sixty similar specimens were prepared by a single investigator and stored in water at room temperature until further manipulation [Figure 2]. The space created in the acrylic model was etched with 37% phosphoric acid (N-Etch, Ivoclar Vivadent, LOT P44991) and bonded with a light-cured bonding agent (Prime and Bond NT Nanotechnology Light-cured Dental Adhesive, Dentsply, LOT 100125). Subsequently, space was filled with composite resin (Ceram X nano-ceramic restorative composite, Dentsply) in 2-mm increments and polymerized with a light curing unit (Monitex, BlueLEX LD-105) for 40 s. The postspace preparation for a length of 14 mm was prepared with dedicated drills provided by the postmanufacturer (Peeso reamer No. 3 [1.5 mm] for Glassix posts and No. 6 [1.5 mm] for ParaPostposts, respectively). The posts were luted into these artificial postspaces using a self-adhesive resin-based luting agent (Rely X U200, 3M ESPE). The cement was carried into the postspace with a lentulo spiral, and the post was also coated with the cement before inserting into the postspace.

Figure 2

Sixty acrylic specimens divided into six groups

Surface treatment of posts

The posts in the control group were cleaned with surgical spirit, and then resin cement was mixed and coated over the post and to the postspace with a lentulo spiral (Mani Paste carriers). The posts were inserted into the postspace, and excess material was gently removed with a cotton pellet. For the airborne abrasion group, the posts were abraded with 70 μm aluminum oxide particles in an extraoral sandblasting device (Basic duo, Renfert GmbH and Com, Germany) for 5 s at a distance of 2 cm from the tip of the sandblasting unit. The posts were then cemented into the postspace as described earlier. In the group of airborne abrasion followed by primer application, after the airborne abrasion, silane coupling agent (Ultradent Silane and Ultradent Products) was applied to the glass-fiber post. The post was allowed to air dry and then luted with the resin cement into the postspace. In case of metal posts, alloy primer (3M Unitek Transbond XT Light cure Orthodontic Adhesive, Monrovia, USA, LOT DK4JU) was applied to the post after air abrasion and cleaning with alcohol. The alloy primer was light cured according to the manufacturer's instructions and cemented into the postspace.

Application of test

Each specimen was sectioned with a machine-driven jig saw resulting in four specimens, each 3-mm thick. The push-out test was performed at a crosshead speed of 1.2 mm/min using a computerized universal testing machine. The maximum failure load was recorded in Newtons (N) and converted into megapascals (MPa). The maximum stress was calculated from the recorded peak load divided by the computed surface. The calculation is as follows:

Area of the specimen = pie × d2/4, pie = 3.14 and d = 1.5 mm.

Area = 1.767 mm2.

Bond strength (MPa) = push-out load (N)/Area (mm2).

Statistical analysis

The mean, standard deviation, and coefficient of variation were calculated for the specimens (n = 10) in each of the six groups. One-way analysis of variance (ANOVA) test was performed for the comparison followed by the Tukey's multiple post-hoc procedures.

RESULTS

The mean, standard deviation, and coefficient of variation of the six groups were calculated as given in Table 1.

Table 1

Summary statistics of six groups (F1, F2, F3, M1, M2, and M3)

Groups	n	Means	SD	CV
F1	10	65.65	11.38	17.34
F2	10	117.71	21.64	18.38
F3	10	78.66	9.79	12.44
M1	10	77.53	19.98	25.76
M2	10	130.73	21.08	16.13
M3	10	105.26	13.12	12.47

SD: Standard deviation, CV: Coefficient of variation

The comparison of the six groups using one-way ANOVA test indicates a highly statistically significant difference between the study groups (P < 0.00001) [Table 2].

Table 2

Comparison of six groups (F1, F2, F3, M1, M2, and M3) using one-way analysis of variance

SV	df	Sum of squares	Mean sum of squares	F	P
Between groups	5	33262.2754	6652.4551	23.3517	0.0000*
Within groups	54	15383.5863	284.8812
Total	59	48645.8617

*P<0.05. SV: Successive variation

The pair-wise comparison of six groups (F1, F2, F3, M1, M2, and M3) was performed by Tukey's multiple post-hoc procedures. This comparison indicates a highly statistically significant influence of the surface treatments on the bond strength of the resin-based luting agent to fiber-reinforced posts and metal posts (P < 0.0000).

DISCUSSION

Prefabricated posts have enabled dentists to restore such teeth successfully at minimal cost without laboratory procedures.[8] A literature review was done by Lawrence Stockton on the factors that affect the retention of the post. The variables reported to affect retention include length, diameter, and design of the post, canal shape and preparation, luting medium, method of cementation, and location in the dental arch.[45]

Failure of posts and cores include loss of retention, fracture of the root, and fracture of the post or core. Loss of retention is the most frequent type of failure.[91011] Failure of restorations using posts due to dislodgment of the post occurs most frequently at the postadhesive junction.[2] In an attempt to maximize the adherence of resin cement to posts, different types of surface treatments have been investigated.[12]

The aim of the present investigation was to evaluate the bond strengths between posts and luting agents after different surface treatments of the two types of prefabricated post systems. Therefore, the posts were inserted into methyl methacrylate blocks with an artificially created postspace. If the posts were luted into extracted teeth, bonding to dentin might have influenced the bond strength values. Even if the bond strengths to dentin seem clinically relevant, this investigation was focused on bond strengths between posts and luting agents and not with the dentinal surface.[13141516]

The glass fiber posts used in this study have manifested satisfactory survival rates over relatively long follow-up periods. The clinical effectiveness has been ascribed to the more biomimetic behavior of fiber-reinforced concrete posts. The prefabricated stainless steel ParaPost (Coltene Whaledent, USA) used in the present study possesses the shape and surface texture suitable for a prefabricated post. Given equal lengths and diameters, ParaPosts have illustrated more retention than cast-gold dowels. This increased retention is attributed to the serrated surface of the post.

The effect of different surface treatments on the bond strength in the current study was investigated between the prefabricated posts and a resin-based luting agent. The use of resin cement has been found to significantly increase the retention of posts and fracture resistance of the tooth compared with other cements.[1718] Previous studies on ParaPost retention with zinc phosphate, zinc polycarboxylate, glass ionomer, and composite resin showed no correlation between the retention and cement type.[3] In situations in which maximal retention is required, such as excessive loss of tooth structure or a short root, use of a resinous cement may be prudent.[12]

In the present study, air abrasion was done with 70 μm Al2O3 particles at 2.5 bar pressure for 5 s from a distance of 20 mm.[4] Air abrasion of fiber posts with 50 μm Al2O3 particles at 2.5 bar pressure for 10 s and from distance of 15 mm produced pronounced dimensional changes in the form of posts.[11] Hence, the distance and time were standardized to be 20 mm and 5 s (because of smaller bonding surface).

It has been proven that silanization alone does not produce a significant difference in bond strength.[1] Most commercially available fiber posts contain epoxy resin as the matrix connecting the individual fibers, including the Glassix post system used in this study, which has no functional groups to react with a silane coupling agent. The post systems-containing silicates, such as Style post (Metalor Dental AG, Switzerland) contain hydroxyl (-OH) groups on the surface of silicate-based fiber, which can form covalent bonds with the silanol group of the silane coupling agent.[1] The highly cross-linked polymers of the matrix in fiber-reinforced posts do not have functional groups for chemical reaction with silane molecules.[14] According to this mechanism, it may be that the silane coupling effect of enhanced bond strength of the post to resin cement is increased when fiber posts with more superficial fibers are used.[19] Sahafi et al. reported that silanization did not improve bond strength between fiber-reinforced posts and resin cement unless it was preceded by airborne-particle abrasion, a finding that is consistent with the results of the current study. The surface of the fiber-reinforced post is primarily covered with epoxy resin, and it can be assumed that prior surface treatment with air abrasion, which would expose the fibers, would increase the surface area available for chemical bonding with the alcoxy groups of the silane molecules. This would, therefore, increase the bond strength between the post and the cement.

CONCLUSION

Within the limitations of this in vitro study, the following conclusions were drawn:

The bond strength of the resin-based luting agent to the fiber-reinforced post was influenced by the postsurface treatment

Surface treatment with airborne-particle abrasion resulted in significantly higher bond strength of the resin-based luting agent to the fiber reinforced and prefabricated stainless steel posts, (P < 0.0001)

Airborne-particle abrasion followed by primer application did not produce a statistically significant increase in bond strength when compared to the control group in glass fiber posts.(P = 0.0521)

Airborne-particle abrasion followed by primer application produced a statistically significant increase in the bond strength of prefabricated metal post to the resin-based luting agent (P < 0.007)

The retention values of various surface treatments were higher with prefabricated metal posts in comparison to the glass fiber posts owing to the serrations present on the metal posts.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.