Comparative evaluation of the pushout bond strength of two root-end materials: An in vitro study.

AIM: The aim of this study is to evaluate the pushout bond strength of two bioceramic materials, two component calcium trisilicate material (biodentine), and premixed calcium trisilicate putty (Endosequence root repair material-fast set putty). SUBJECTS AND METHODS: 20 maxillary incisors were used in the study. Apical sections of 3mm were obtained and retro cavities to a depth of 3mm were prepared using a straight fissure bur. Another transverse section was made 4-mm coronal to the previous section. The specimens were placed into acrylic resin rings and separated into two groups and their cavities filled with the materials. The pushout test was carried out using a universal testing machine at a cross head speed of 0.5 mm/min, and the specimens were examined in a stereomicroscope at to evaluate the modes of failure. STATISTICAL ANALYSIS: The pushout bond strength values were analyzed using the unpaired t-test, and the modes of failure were compared using Fisher's exact test.
RESULTS: The pushout bond strength was seen to be significantly higher (P < 0.001) for the two-component calcium trisilicate material (11.596 ± 3.309). Cohesive failure patterns were observed in both the test groups.
CONCLUSION: Two component calcium trisilicate material demonstrated higher bond strength values to apical dentine. Copyright:

INTRODUCTION

Surgical management of a tooth with apical pathosis, that cannot be managed by nonsurgical endodontics is an objective of apical surgery.[1] The success of an endodontic surgery relies on the choice of a suitable retrograde filling material that meets various requirements such as biocompatibility, adequate strength, and marginal adaptation.[2] The new class of materials that are used as retrograde fillings are bioceramics. Bioceramics are the materials of choice in endodontics due to their integral properties such as decreased moisture sensitivity, insolubility, and tissue inductive properties. The recently introduced silicate-based materials claim to possess shorter setting times, thus overcoming the drawbacks of mineral trioxide aggregate (MTA).[34] These materials are also supplied as premixed formulations, rather than the traditional two-component system. In addition to material characteristics, the adaptation of the retrograde filling to the apical root dentin is vital for the success of the surgical therapy.[5] The adaptation and the interface between the root dentine and the retrograde filling materials have been determined by pushout tests. It is a mechanical test to measure the resistance of the tested material to dislodgment and its adhesive property.[6] Therefore, the present study aimed at comparing the pushout bond strength of two calcium trisilicate-based materials Endosequence root repair material (ERRM) fast set putty (Brassler, Savannah, GA) and Biodentine (BD) (Septodont, Saint Maur des Fossés, France) in the apical third of the root and to assess the failure patterns.

SUBJECTS AND METHODS

Human maxillary central incisors were disinfected in 5% chloramine – T solution for 48 h and preserved in distilled water. After macroscopic and radiographic examination, teeth with surface defects and cracks, calcified roots, open apices, accentuated curvatures, and previous endodontic treatments were excluded, and a total of twenty teeth were selected. Coronal access was obtained with an Endo access bur (#2, Dentsply Maillefer, Ballaigues, Switzerland) and root canal length was measured using a 15K-file (Dentsply Maillefer, Ballaigues, Switzerland). The root canals were prepared using ProTaper universal rotary system (Dentsply Maillefer, Ballaigues, Switzerland) upto F3 (size 30, 0.09 taper) master apical file size inserted in a hand-piece (Coltene pro Cl2). 2.5% NaOCl was used as the irrigant between instrumentation and a rinse with 17% ethylenediaminetetraacetic acid was performed to remove the smear layer followed by rinsing with 5 ml of saline. The canals were dried with absorbent paper points. The roots were sectioned transversally, 3 mm short of the apical foramen at an angle of 90° to the long axis of the tooth using a diamond bur (Mani Inc., Tochigi Ken, Japan). Root-end preparation to a depth of 3 mm was performed using a straight fissure bur (Mani Inc., Tochigi Ken, Japan). Another transverse section was made 4 mm coronal to the previous section using a diamond disc (Horico, Berlin, Germany) and a low-speed handpiece. The specimens were then embedded into acrylic resin rings of 4-mm high and 16-mm diameter. In each specimen, a #30 master gutta-percha cone was placed between the retro preparation and the canal which was retained till the complete set of the material. The specimens were divided into two experimental groups based on the test materials. BD (Septodont) was manipulated conferring to the manufacturer's instructions and compacted into the prepared cavity and condensed using an endodontic plugger. ERRM fast set putty (Brassler) was syringed into the prepared cavity. The specimens were wrapped in a gauze moistened with distilled water and stored at 27°C in an incubator for 48 h. Before subjecting the specimens to pushout test the diameter of each restored surface was measured under a stereomicroscope (Lawrence and Mayo) at ×40 and the bonded area (A) was calculated using the formula: A = 2 × π × r × h, where π = 3.14, a constant, r = mean diameter of the root canal (mm), h = depth of the retrofilling (mm). The pushout test was carried out on each specimen using a universal testing machine (Tecsol TSI-BDS-2kN, Sr No. 170710, Chennai, Tamil Nadu, India) fitted with a stainless-steel plunger of 0.7-mm diameter, under a 2 kN weight scale. The specimens were placed on a stainless – steel slab with a central opening to allow free movement of the plunger [Figure 1]. The compressive load was directed in a coronal to apical path at a crosshead speed of 0.5 mm/min. The plunger had a 0.2 mm clearance from the inner dentinal wall to ensure contact only with the material to be tested. The test was carried out till the complete displacement of the material occurred. The highest load value at the period of dislodgment was recorded in Kgf/mm2. The pushout bond strength was converted to megapascals (MPa) by using the following formula:

Figure 1

Cohesive failure pattern as seen under the stereomicroscope

9.8067 is the conversion constant, (1 kg force/mm2 to MPa = 9.8067)

After the test, the specimens were observed under a stereomicroscope (Lawrence and Mayo) at ×40 magnification to evaluate the type of bond failure. The specimens were categorized based on the failure patterns: adhesive failure, cohesive, and mixed failure. The operator who examined the specimens was not informed about the test groups.

Data were statistically analyzed using Microsoft Excel and SPSS software version 22 (IBM Corp, Armonk, NY). Unpaired t-test was used to compare the mean pushout bond strength between the two groups. The failure patterns were compared using the Fisher's exact test. A value of P < 0.05 is considered to be statistically significant.

RESULTS

BD presented significantly higher pushout bond strength values (11.596 ± 3.309) compared to ERRM fast set putty (0.827 ± 0.3940) (P < 0.001) [Table 1].

Table 1

Mean and standard deviation of pushout bond strength values in all groups

Group	n	Mean±SD	t	P	95% CI of the difference
					Lower	Upper
Biodentine	10	11.595±3.309	10.217	<0.001	8.394	13.142
ERRM-fast set putty	10	0.827±0.394

SD: Standard deviation, CI: Confidence interval, ERRM: Endosequence root repair material

The analysis of failure modes showed a predominance of cohesive failure patterns for both BD and ERRMs [Table 2].

Table 2

Comparison of failure patterns between two groups

Groups	Failure patterns		Total
	Cohesive	Mixed
I
Count	9	1	10
Percentage within group	90.0	10.0	100.0
II
Count	10	0	10
Percentage within group	100.0	0.0	100.0
Total
Count	19	1	20
Percentage within group	95.0	5.0	100.0

DISCUSSON

The adaptation of a root-end filling material to the dentine walls is an important parameter for the success of the endodontic treatment. The knowledge about the ability of the material to bond to the tooth structure can aid in the material selection and to predict the outcome of the procedure.[4] The methodology for the bond strength evaluation in this study was adapted from the study published by Alsubait et al. in their study, root dentine slices with the canal spaces prepared using diamond drills were used.[7] Marques et al. proposed an advanced method, using ultrasonic tips to prepare retrograde cavities.[8] The study differed in terms of using diamond burs to prepare root-end cavities instead of ultrasonic tips. This was done in an attempt to prepare root-end cavities with standardized proportions and to avoid the impact of variables such as tip inclinations during preparation and to create uniform reduction of dentinal walls in all the specimens. Diamond burs produce rough dentine surfaces which would have increased the micro mechanical retention and bond strength.[9] The present study evaluated the pushout bond strength of two calcium trisilicate materials, available in different formulations to root canal dentin.

The pushout bond strength of the two-component calcium trisilicate, BD (Septodont, Saint Maur des Fossés, France) material was significantly higher than that of the premixed tricalcium silicate putty, ERRM fast set putty (Brassler, Savannah, GA). This result is in agreement with the previous studies.[4710] The material chemistry, the fine particle sizes, the low water to cement ratio, and the presence of calcium carbonate, contribute to better bonding of BD to dentine. The liquid contains soluble polymers which enable the reduction of the water to cement ratio, thus enhancing its physical properties.[2] The bond strength of ERRM, MTA, and BD were studied by Nikhade et al., and in disparity, concluded that the bond strength of ERRM putty was significantly higher than those of MTA and BD at both 1 and 3 weeks.[11] Similarly, a few studies have shown the premixed calcium trisilicate putty to have better bond strength in comparison to the other materials, under different situations.[712] The higher bond strength obtained for the premixed calcium trisilicate putty can be attributed to the thickening and filler agents added to make it a putty form.[12] The presence of nanosphere particles with a diameter of 1 × 10−3 μm allows for the material to enter dentinal tubules, interact with the dentine liquid and form a mechanical bond on complete set of the material.[13] The mode of delivery and manipulation of the material also has an effect on the final set and adaptation of the material to the tooth surface.

In the existing literature, there is no difference in the methodology followed for testing the bond strength of root-end filling materials to root dentin and the pushout test for root canal sealers. Mid root slices have been used as substrates. However, the thickness, diameter, and number of dentinal tubules are much lesser in the apical third compared to the middle third.[14] This variation in the test substrate fails to mimic the clinical situation leading to an over or under-representation of the bond strength of root-end filling materials. The present study evaluated the bond strength of root-end materials to the root-end cavities using the methodology proposed by Marques et al.[8] The pushout bond test for the root-end filling materials was evaluated using the apical third slices as substrates. This may be the reason for the variations in the results in our study. During the pushout test, the shaft was introduced in a coronal to apical path, therefore measuring the bond strength along the entire cavity extension. Some authors state that the bond strength is not influenced by the retro preparation technique.[10] In this study, a single diamond bur was used to prepare the cavities, and hence, the differences in bond strength could only be credited to the materials that were used for root-end filling.

Both the materials used in this study are known to penetrate the dentinal tubules and form tags which aid in the retention of the materials. The depth of penetration of the materials into the dentinal tubules and the length of the tags formed have not been studied. There may be a difference in the depth of penetration and the microstructure of the tags formed by the two materials, which may explain the difference in the bond strength values. However, further studies are required to know the true interaction of the materials with dentine. The bond failures observed in all experimental groups were largely cohesive type of failure. The thickness of the tested material in our study was 3 mm. This finding is similar to that of Shokouhinejad et al., Paulson et al. and Alsubait et al.[715] Thinner slices of materials were used in these studies. This can be attributed to the good adhesive properties of the material due to infiltration of the materials into the dentinal tubules and formation of tags. Other studies have reported a higher incidence of adhesive failures.[41617] Therefore, differences in the outcomes can be explained by the disparities in the methodologies followed and sampling techniques used.

In the present study, except for the root-end filling materials, the specimen dimensions, the root canal preparation technique, root-end preparation, and root-end resection were standardized to the best extent possible. It must be considered that all experiments were done in an ideal laboratory condition. Therefore, the effect of various environmental factors such as temperature, moisture, and saliva were excluded. In conclusion, two-component calcium trisilicate material (BD) has better pushout bond strength than premixed calcium trisilicate putty (ERRM fast set putty), and the failure patterns observed were cohesive failures.

CONCLUSION

Within the conditions of this in vitro study, it can be concluded that the two-component calcium trisilicate material (BD) had better push-out bond strength than premixed calcium trisilicate putty (ERRM fast set putty). Cohesive failure patterns were observed in both groups.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.