Comparative evaluation of microleakage after root-end resection by erbium, chromium: Yttrium-scandium-gallium-garnet (Er, Cr:YSGG) laser and carbide bur with or without placement of mineral trioxide aggregate: An in vitro study.

BACKGROUND: Root-end resection followed by retrofilling is one of the prime requisites to avoid apical microleakage. AIM: It comparatively evaluated the microleakage after root-end resection by erbium, chromium:yttrium, scandium, gallium, and garnet laser and carbide bur with or without placement of mineral trioxide aggregate (MTA).
MATERIALS AND METHODS: In this study, 60 maxillary central incisors were decoronated and biomechanically prepared. Out of 60 samples, 48 were included in the experimental group while the rest 12 were in the control group. The samples in the experimental group were obturated, whereas the samples in the control group were not obturated. The experimental group samples were divided into two: one group resected with the laser and the other half resected with carbide bur. These groups were further subdivided into two - one group retrofilled with MTA and the other half without MTA. The control group had both laser- and carbide bur-resected samples with positive and negative controls. All the samples were dyed, decalcified, and cleared. Digital photograph of each sample was taken, and the area of dye penetration was measured with the help of ImageJ software. STATISTICAL ANALYSIS: Analysis of variance and Tukey's test were done.
RESULTS: The highest microleakage was seen in carbide without MTA and the least was seen with laser with MTA.
CONCLUSION: Laser-resected MTA-retrofilled samples showed minimum leakage. Copyright:

INTRODUCTION

Periradicular surgery involves surgical removal of pathological tissue along with root resection, followed by preparation of root-end cavity and filling the cavity to seal the root canal apically.[12] Majority of root resections are done with burs at slow or fast rotations, but other equipment can also be used such as ultrasonics and lasers.[3]

In recent years, erbium, chromium: yttrium, scandium, gallium, and garnet (Er, Cr:YSGG) laser has been found to be useful in endodontic surgery for root-end resection and root-end cavity preparation with an additional advantage of hemostasis and sterilized environment. This laser cuts hard tissue with highly energized water particles and soft tissue directly with laser energy.[4]

Root-end resection is followed by root-end preparation with filling of root-end cavity with an adequate retrograde filling material to prevent the invasion of bacteria and its products into the root canal. Due to its promising results, mineral trioxide aggregate (MTA) has received crescent interest as a retrograde material.[5]

Hence, considering the advantages of laser and MTA and limited study related to it in the field of surgery, it was decided to comparatively evaluate in vitro, the microleakage after root-end resection by Er, Cr:YSGG, and carbide bur with or without placement of MTA with the help of dye penetration method.

MATERIALS AND METHODS

This study protocol has been approved by local institutional ethical committee. This study consisted of sixty freshly extracted human maxillary central incisors. Teeth were decoronated, and root canal preparation was done with ProTaper rotary file system till the size #F5 (Dentsply) using X-Smart endodontic motor (Dentsply Maillefer, Ballaigues, Switzerland). During each filing, Glyde (Dentsply Maillefer, Ballaigues, Switzerland) was used as a lubricating agent. After every filing, each canal was irrigated with 2 ml of 5% sodium hypochlorite (NaOCl) (PDP, India), and final irrigation was carried out with 2 ml of 17% ethylenediaminetetraacetic acid (PDP, India), followed by 2 ml of 5% NaOCl. Out of 60 samples, 48 were included in the experimental group and 12 were included in the control group. The samples in the experimental group were obturated with thermoplasticized gutta-percha (GP) using E and Q Plus (META BIOMED CO. LTD, Mochung-Dong, Heungduk-Gu, Cheongju City, Chungbuk, Korea) which consists of a heat-carrying unit (pen) and thermoplasticized gutta-percha dispensing gun and AH Plus sealer (Dentsply) and condensed vertically. The access cavities were filled with glass ionomer cement (GC Fuji II). While the samples in the control group were not obturated, the samples in the experimental group were divided into two: one group (n = 24) was resected with Er, Cr:YSGG (Waterlase MD, Biolase Technology, Inc., San Clemente, CA, USA) laser and a G6 laser tip, with the following parameters: 4.5w, 20pps, 20% water, and 50% air. Laser beam was collimated through a flat-ended cylindrical tip (sapphire tip diameter: 600 μm). This tip was placed perpendicular to the long axis of the root, 3 mm from the apex, to obtain root-end resection without a bevel. After resection, the gutta-percha was burnished and the other (n = 24) was resected with surgical carbide bur #701 (SS White, Lakewood, New Jersey, USA). From the apex 3 mm was marked and by placing the bur at 90° to the long axis, resection was done under water flow. After resection, the gutta-percha was burnished. The laser- and bur-resected groups were further subdivided into two – the first group (n = 12) was retrofilled with MTA (ProRoot MTA Dentsply/Tulsa Dental, Tulsa, OK, USA). This subgroup which received MTA, retrocavity of 3mm was made with S” series diamond-coated retro micro-tip (S 12-90 ND) (Satelec) set at medium power, moving the microtip in feather like back and forth motion under constant water spray. MTA was mixed according to manufacturer's instructions, and the root-end cavities were filled with MTA. In the second group, no root-end cavity was prepared (n = 12), which means that there were four experimental subgroups:

Root resection with laser and MTA retrograde restoration (laser with MTA)

Root resection with laser without MTA retrograde restoration (laser without MTA)

Root resection with carbide bur and MTA retrograde restoration (carbide with MTA)

Root resection with carbide bur without MTA retrograde restoration (carbide without MTA).

In the control group, half of the samples were laser resected (n = 6) and another half were carbide bur (n = 6) resected. Both the laser- and bur-resected groups were retroprepared but not retrofilled, were divided into positive (n = 3) and negative (n = 3) control subgroups. The samples from all groups were left in 100% humidity for 72 h. All the samples of the experimental and positive control groups were coated with nail polish keeping the root-end resected surfaces exposed while the entire surface of the negative control group was coated with nail polish and was immersed overnight (18 h) in 1% methylene blue dye (pH: 7) at room temperature. Before clearing procedures, the roots were carefully cleaned, and the nail polish was removed with the aid of periodontal curettes and nail polish remover. They were decalcified at room temperature in the following way: the samples were dipped in 7% formic acid for 3 days, rinsed under running tap water and then dipped into 3% hydrochloric acid for 3 days, and again rinsed and dipped into 8% sodium citrate for another 3 days; thereafter, the samples were rinsed under running water for 2 h. They were thereafter placed in 99% acetic acid for 12 h. The samples were then taken out and were rinsed with distilled water. After this, the samples were immersed in gradually increasing concentration of ethyl alcohol for dehydration in 70%, 80%, 95%, and 100% for 30 min each and thereafter dried. The samples were then rendered transparent by dipping in methyl salicylate (NICE) for 2 days. Digital photographs were obtained from the mesial and distal aspects of each sample [Figure 1a and b]. Thereafter, areas of dye penetration were measured in photograph taken from mesial and distal sides for each sample by two evaluators, who were unaware about sample grouping with the help of ImageJ software (National Institutes of Health, Bethesda, MD). The measurements from two evaluators were averaged and statistically analyzed using analysis of variance (ANOVA), followed by Tukey's test, and t-test was used to test the means. P < 0.05 was taken to be statistically significant.

Figure 1

(a and b) Digital photographs of cleared samples showing leakage penetration with the help of ImageJ software (a) Mesial (b) Distal

RESULTS

When the mean of dye penetration of two evaluators was compared, there was no significant difference (P > 0.05) [Figure 2]. The positive control subgroup showed total dye penetration, whereas the negative control subgroup showed no dye penetration.

Figure 2

Diagrammatic representation of comparison of mean of the area (mm2) measured by the two evaluators. t-test showed that there was no significant difference in measurements between two evaluators (P > 0.05)

The highest microleakage was seen in carbide without MTA (0.88 ± 0.39), followed by laser without MTA (0.75 ± 0.32) and then carbide with MTA (0.42 ± 0.23), and the least was seen with laser with MTA (0.20 ± 0.16) [Table 1 and Figure 3].

Table 1

Mean±standard deviation, median, and range of microleakage in the experimental subgroups

Subgroups	Mean±SD	Median	Range (minimum-maximum)
Carbide with MTA	0.42±0.23	0.45	0.0-0.80
Carbide withoutMTA	0.88±0.39	1.02	0.33-1.58
Laser with MTA	0.20±0.16	0.21	0.0-0.48
Laser without MTA	0.75±0.32	0.73	0.32-1.44

SD: Standard deviation, MTA: Mineral trioxide aggregate

Figure 3

Diagrammatic representation of comparison of mean area of microleakage in the experimental subgroups

ANOVA depicted that this difference was statistically significant (P < 0.01) [Table 2].

Table 2

Analysis of variance table for experimental subgroups

Source	df	Sums of squares	Mean sum of squares	F	P
Between subgroups	3	3.47	1.15	13.24	<0.01
Residual	44	3.85	0.08
Total	47	7.32	-	-

There was significant difference in microleakage among different experimental subgroups (F3, 44=13.24; P<0.01). df: Degree of freedom, F: Value of F-statistic

DISCUSSION

Under the condition of this study, the highest microleakage was seen in carbide without MTA and the least was seen with laser with MTA. These findings were supported by the study of Camargo Villela Berbert et al.[6] where leakage was less in laser resection because of its vibration-free procedure which ultimately preserved the apical seal of GP and dentinal wall. However, Sullivan et al.[7] found a higher mean dye leakage in the Er, Cr:YSGG group as compared to the carbide-resected group. This may be attributable to fault in laser resection and not achieving a smooth surface. Furthermore, cut ends were not seen under scanning electron microscope (SEM). Ayranci et al.[8] in their study also reported that the erbium: yttrium–aluminum–garnet (Er:YAG) laser produced a rougher resected root surface than the carbide burs; however, the diamond-coated tip provoked many dentinal crack formations compared to the Er:YAG laser and tungsten carbide bur.

Laser resection is better than that of carbide resection, and it is possibly attributed to the fact that laser produces smoother surface than bur resection. This was supported by the study of Kinoshita et al.[9] who proved in their SEM study that Er, Cr:YSGG laser-treated dentin surface had no smear layer or debris and no thermal destruction and there was a minimum gap between dentin and GP while the bur-resected surfaces were rough with cracks and there was a significant difference between dentin and GP interface. A similar study was performed by Babar and Adhikari[10] who confirmed that Er, Cr:YSGG-lased root surface provided better surface morphology and more conducive surface for the regeneration of periodontium as compared to bur root resection.

Gouw-Soares et al.[11] also conducted a study with human teeth where apicoectomies were performed with Er:YAG laser along with other devices. The use of lasers resulted in smoother surfaces, and Paghdiwala[12] also found that thermal ablation with Er:YAG laser causes the breakdown of mineral components and binding of amorphous particles, without crystallization, thus resulting in clean and even surface.

The subgroup which received MTA as root-end filling material demonstrated less amount of microleakage, which is in agreement to in vitro studies of Fischer et al.,[13] Saini et al.,[14] and Rosales-Leal et al.[15] who indicated MTA to be the most effective and gold standard root-end filling material. Even Biodentine which is considered to be a replacement for MTA has poorer marginal adaptation when compared to MTA.[16]

In the present study, several factors may have influenced the difference in mean dye leakage between retrofilled MTA groups and the groups without it. The ultrasonic instrumentation in the MTA group included preparation of isthmuses and removal of these areas that might retain bacteria and their by-products.

In the GP group, the root tip with the apical delta was resected; however, no cleaning of isthmus areas was performed. Furthermore, in the MTA group, the prepared cavity was thoroughly packed with MTA in an attempt to obtain a good seal. However, it is questionable whether the smoothing of GP with the burnisher improved the apical seal. Furthermore, the GP material was often fragile and tended to break into pieces when trying to improve the apical seal.

The selection of tooth sample may affect the extent of microleakage. Kontakiotis et al.[17] in their in vitro study reported that maxillary incisors showed less microleakage as compared to mandibular incisors and premolars. Therefore, in the present study, maxillary incisors were used.

Methylene blue dye was used in this study because it easily allows quantitative measurement of the amount of dye penetration. Methylene blue and butyric acid which is a cytotoxic bacterial metabolite with low molecular weight (88) have been shown to have similar leakage configuration.[18] Thus, methylene blue can serve as a guideline of leakage.

Methylene blue (acidic) may get reacted with dentin and be converted into leucomethylene, a resulting substance that modify the tonality of dye making it troublesome to be visualized. Variation in pH from 1 to 5 may lead to mineral loss in the apical area, when compared to a neutral pH. To avoid such problem in the present study, methylene blue with pH 7 was used.[19]

The Er, Cr:YSGG laser set at 5.0 W and 20 Hz has fine-cutting capacity without inducing carbonization of the root-end surface.[20] Camargo Villela Berbert et al.[6] experienced carbonization at this setting, so they reduced it to 3.5 W. However, Sullivan et al.[7] used 4.5 W as power setting and got an acceptable result. Therefore, in this study, the power setting of 4.5 W was used to prevent overheating and other unwanted effects on dental tissue, and also, air percentage was chosen as 50% as the previous study by Shinkai et al.[21] concluded that lower percentage of air has a better dentin-cutting efficacy than higher percentage of air, when the percentage of air was between 50% and 70%.

Root-end resection was performed at 90° and at 3 mm from apical end because such angle and distance resulted in less microleakage than when apical resection was beveled.[2223]

Clearing technique was chosen because it provides a three-dimensional view of root canal filling which in turn assures the possibility to locate atypical anatomical configurations as well as technical standard of root canal filling and sealer. In addition, clearing technique has an advantage of not hampering root morphology.[24]

Dye penetration was not uniform around the margins of the root-end filling material. Therefore, in the present study, instead of linear measurements, the total area of dye penetration from mesial as well as distal aspects of the root was considered.

Another aspect cannot be overlooked that according to Wu et al.,[25] MTA provokes a 73% reduction in the optical density of methylene blue, which can give imprecise results in microleakage studies. The reduction of the staining capacity of methylene blue in contact with MTA may have occurred in this study also, resulting in variation in the observed dye penetration.

CONCLUSION

Within the limitations and parameters of the present study, it can be concluded that Er, Cr:YSGG laser resection is better than bur resection, and apical microleakage may be better prevented when MTA is used as retrofilling material in laser resected roots. However, still, there is a need for further in vitro and clinical studies with increased number of parameters and sample size to arrive at a conclusion.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.