Effectiveness of Removal of Hard Tissue Debris from the Mesial Root Canal System of Mandibular Molars using Different Supplementary Irrigation Protocols: An Original Study

ABSTRACT

Introduction:

An instrumented and endodontically treated tooth may sometimes impede disinfection by trapping hard tissue as well as the other canal contents at the isthmus level of the canal. Thus, the current in vitro study was piloted to assess the competence of two irrigating systems.

Methods:

Twenty mandibular with two mesial canals convergent into a single foramen and joined by an isthmus of the human permanent teeth were compared for the two irrigation systems of continuous and intermittent ultrasonic (US) motions of the irrigation. The teeth were prepared by a single rotary system and were imaged using the “Scanning electronic microscopy-SCM”. The parameters were compared before and after the irrigation of the canal with the intended US systems for the removal of hard tissue debris. The appropriate statistical tools were used to find the significance, the value of which was kept at P < 0.05.

Results:

Significant percentage reduction of the hard tissue debris was achieved after the application of the supplemental irrigation protocols (P < 0.05). However between the groups, there was no significant difference.

Conclusions:

Comparable removal of the hard tissue debris was obtained in both the irrigation systems. Though not significant, the GentleWave performed better than the Irrisafe.

INTRODUCTION

The success of endodontic treatment largely depends on the disinfection of the canal. This is made possible by physical and the chemical methods. Instrumentation is one method that removes the contents of the canal while the chemical method helps in removing the debris as well as softening the hard tissue contents that are deemed to be removed. The proper effectiveness of these methods is a factor of the canal anatomy. In curved or blocked canals, the chemicals may not reach all the areas. This may lead to endodontic failure. This is due to the fact that the microbes may act as the nidus for further canal infections. Previous studies have established that the areas of the curved canals, narrow canals, and the isthmus are the most notorious for bacterial lodgements.[1–5]

The isthmus is the area of the canal that accumulates hard tissue debris during instrumentation with files. Hence the canals are irrigated with saline to washout the hard tissues that are chiselled off during mechanical preparations. However, this may not be always possible in some teeth.[6–10] Like in the mandibular molars that are the most common to receive endodontic therapy, the mesial root may have two canals that are connected by the isthmus. The prevalence of the isthmus in the distal and the mesial canals is as great as 20% and 55%, respectively.[11,12] This may prevent the debris that has hard tissue from being washed out during the routine irrigation protocols.[13] Hence, supplemental irrigations are commonly employed in these canals when the routine methods fail to do the debridement.

Irrigation techniques have improved over time to improve the administration of an irrigant to the intricate canal system. During ultrasonically stimulated methods, irrigation solutions may be applied intermittently or continuously while being agitated by ultrasonic waves.[14,15] There are two methods in ultrasonic (US) irrigation: continuous and intermittent agitation of solutions. In the continuous method, the canal is irrigated by “an ultrasonically activated irrigation needle” that has an unhindered flow of the liquid. The intermittent method uses a needle that is activated in the canal and needs refills after every cycle of the activation. The GentleWave system (Sonendo Inc, Laguna Hills, CA) is a revolutionary continuous irrigation US system. The technology concurrently removes tissue, debris, and biofilms from the canal.[16–18] Recent clinical approval for the device’s usage in endodontics calls for independent assessment. Only one study has, till date, demonstrated histologically how effective the GentleWave (GW) system is at removing debris.[19] For the purpose of determining if the GW system can improve isthmus cleansing, the use of non-destructive assessment techniques is needed. Thus, this in vitro study was conducted to compare the two irrigation methods. The null hypothesis was that the two irrigation systems would remove the hard tissue debris in the same manner.

MATERIAL AND METHODS

The study piloted was designed to be in vitro in nature. Ethical clearance was obtained since human tissues were used. Extracted human teeth were collected for the present study. Caution was taken to collect adult permanent teeth, specifically mandibular molars with two mesial canals convergent into a single foramen and joined by an isthmus. The teeth had no developmental aberrations. Prior intra oral periapical (IOPA) radiographs were taken for all the collected teeth to rule-out the abnormalities of the dental tissues. Care was also taken to check if the canals were patent and had no obstructions. The teeth that were thus collected and finalized after the acceptable IOPA interpretations were grouped randomly to avoid bias and assure homogeneity. All the teeth had similar lengths of the canals and had comparable degree of the curvature of the canal. The submerging of the teeth was done using the hypo for one day. Later the external debris was cleaned and the teeth were stored using the saline. The file system used was WaveOne Gold. Twenty teeth were randomly divided into groups of 10 each. The tested irrigation systems were the following:

• Irrisafe (IS) (intermittent irrigation): n = 10 teeth

• GentleWave (GW): n = 10 teeth

Specific tooth selections and the variables destined to be calculated

Teeth with Vertucci type II configurations were selected for the study. Each tooth underwent micro–computed tomography (CT) for 400 milliseconds with 180° rotations. The scan took place for 60 minutes. Post-threshold-based segmentation was used to obtain three-dimensional reconstruction data, which were then collected using specialized software. Later, images were analyzed using CT scan software (Bruker microCT, Version 1.13.5.1). The segmentation threshold was determined using the micro-CT absorption histogram’s inflection point. Each specimen’s mean values were calculated. An experienced radiologist measured each image. For each group, before the experimental procedures, the parameters calculated were “the length (in mm), volume (in mm³), surface area (in mm²), and structure model index (SMI) of the mesial canals were estimated” to assure anatomical similarity among the specimens [Table 1].

Table 1.

Mean of 3D parameters calculated

Parameters	Timing	IS	GW	P
Untouched area (%)	After preparation	13.6±4.2	14.5±6.5	0.6
Volume	Before preparation	3.6±1.5	3.6±1.3	0.1
	After preparation	10.6±1.2	8.3±1.8	0.09
Surface area	Before preparation	43.5±10.6	46.3±12.0	0.8
	After preparation	65.3±10.7	59.3±9.2	0.4
SMI	Before preparation	1.4±0.5	1.5±0.2	0.4
	After preparation	2.3±0.4	2.1±0.1	0.1
Length	Average of canal before preparation	9.5±1.5	9.6±0.6	0.1

Preparation of a canal

The mesio-buccal canals of the teeth were used for this study. The access cavity was prepared using diamond burs. The access was initially achieved by using file no. 10. Complete canal patency was achieved. All the preparations were done using the crown-down technique. The files were kept 0.5 mm short of the actual opening. The apexes were sealed with glue. With an electrical endodontic handpiece mounted on the crown-down technique, canal preparation was carried out for each group (X-Smart). In between each instrument, hypo was used to irrigate the canals. After instrumentation, the smear layer was cleared by irrigating the canals with a chelating agent. Once again, it was irrigated with the hypo ad washed with saline solution was used to cleanse the canals. After being utilized in three canals, all of the instruments in all of the groups were abandoned. A skilled endodontist who had received training in using the rotary systems carried out all of the preparations. Both the groups of teeth were prepared using the same protocols. Both the irrigation systems were used as per the manufacturers’ instructions.

The volume of the hard tissue debris that was left over was calculated based on a study by Chan et al.[20] In the present study, all measurements were made by an examiner who was not aware of the specimens’ grouping. The images were produced using the Environmental scanning electron microscope (S-3400N; Hitachi, Tokyo, Japan) that was utilised to study the parts of the root after the post-irrigation CT scans to corroborate the method. This was done to confirm the presence of hard tissue debris in the isthmus areas after the final irrigation protocol. Later, the mesial canals were broken open with a chisel to check the actual presence of the hard tissue debris.

Analytical statistics

Means with standard deviations were used to express variables. Comparisons were made between the two groups for hard tissue debris, before and after the canal preparations and after the supplemental irrigation protocols. The variables were compared for significance using the Chi-squared tests. The Statistical Package for the Social Sciences (SPSS) version 23 (IBM Corp., Armonk, NY) was used to analyze data. The value was considered as significant if the P < 0.05 was achieved.

RESULTS

Comparison of the parameters between the groups after canal preparation and before irrigation

The two groups showed similar distribution of the hard tissue debris for all the teeth specimen for various canal characteristics such as SMI, surface area, volume, and length of the canal, preoperatively and postoperatively, as confirmed by the SEM and micro-CT [Table 1].

Comparison of the parameters between the groups after canal preparation and after irrigation

Supplemental irrigation procedures significantly decreased hard tissue debris in all groups. The variations were significant in both the groups when compared for the steps after preparation and the irrigation protocol. However, when the two groups were compared, there was no significant difference between them for the change in volume (percentage reduction) at the isthmus and for the entire canal [Table 2].

Table 2.

Mean hard tissue debris after irrigation

Parameters	Timing	IS	GW	P
Canal
Volume	After preparation	0.7±0.1	0.6±0.3	0.23
	Irrigation protocol	0.07±0.08	0.02±0.02	0.21
Percentage reduction	Irrigation protocol	91.2±5.2 (P<0.05)	96.4±4.2 (P<0.05)	0.15
Isthmus
Volume	After preparation	0.4±0.4	0.3±0.1	0.25
	Irrigation protocol	0.03±0.07	0.005±0.007	0.58
Percentage reduction	Irrigation protocol	93.5±5.0 (P<0.05)	97.9±2.1 (P<0.05)	0.6

It was also observed from the SEM that the debris persisted even after the supplemental irrigation of the canals for all the twenty specimen. However, the volume reduced after the irrigation.

DISCUSSION

The failure of the endodontically treated tooth is multifactorial. The most common reason is the microbial factor. Hence, the emphasis in endodontics is chiefly for the removal of microbial sources like the infected pulp and the canal walls. Care is taken to eliminate the pathogens and render the canal as aseptic as possible. This is mostly done by the use of antibiotics as well as the chemical irrigant in the canal.[21–25] The biofilm in the canal is considered as one of the most notorious for disinfection. Recently, focus has shifted to stringent methods for the removal of the biofilm.[19,20] The isthmus region is considered one of the toughest regions for the disinfections. The hard tissue debris that may be clogged at that region may lodge a great amount of pathogens.[2–4] The irrigation of the canals is done for the removal of the hard tissue debris. In the current study, two systems of supplemental irrigation was checked. The areas of the canals that were assessed were the isthmus and the inaccessible locations of the canals. Care was taken to distribute the specimen as homogenously as possible. The same was established using the micro-CT and the SEM. The amount of hard tissue debris that was left out in all the teeth of both the groups was nearly 16% of the canal volume. This was similar to the previous study by Robinson et al.[23] The null hypothesis was accepted in this study since there was a no significant dissimilarity between the two groups.

The GentleWave system reduced hard tissue debris by nearly 95% in the canals and by 98% (isthmus) in the sections of the mesial canals. These findings confirmed GentleWave’s ability to thoroughly clean the intricate canal system. The other irrigation system, Irrisafe, also removed the hard tissue debris, though it was comparatively lower than that of GentleWave. Irrisafe decreased AHTD from the canals and isthmus areas by approximately 91% and 94%, respectively. Compared to the previous studies, the values obtained in the current study are higher.[10,24] In a study by Freire et al.,[24] the volume of the hard tissue removed was <60% in the canal and at the isthmus. The main reason for this disparity may have been the higher activation impulses in the current study than the previous studies.

The deeper penetration of the solutions in the canals was also observed in the current study comparatively.[25–30] Comparing the two irrigation systems the GentleWave system delivers irrigation with higher penetration than other US systems.[25] With the canals narrowing down to the apical sections of the canal, it is anticipated that the motion of the oscillating file used by US irrigation devices could be hampered.[25–27] The GentleWave system, in contrast, disperses fluids all through the canal system using a wide range of sound waves. Multi-sonic energy, which the GentleWave system emits, allows for the efficient delivery of high energy irrigation into micro-sized dentinal tubules at a high flow rate, as opposed to ultrasonic energy, which is disseminated at a single frequency.[18,25] A cavitation cloud is induced by the interaction of the static fluid inside the pulp chamber and the continuous flow of irrigation solution, which produces a strong shear force. Multi-sonic energy is produced by the implosion of cavitation bubbles and includes vortical acoustic streaming and a wide range of acoustic waves.[18]

Dentin debris has been demonstrated to drastically influence the effectiveness of intracanal disinfectant solutions despite the fact that the clinical effects of hard tissue debris are still unknown. Additionally, hard tissue debris inhibits the effectiveness of commonly used irrigation solutions by reducing the free chlorine.[31–33] By creating a physical barrier between the irrigant and the pathogens, the hard tissue debris may also shield microorganisms stuck in difficult-to-reach places.[33] Additionally, AHTD can obstruct the root filling’s seal.

There are limitations to this study. The main limitation was the small number of specimens. This may be due to specific selection of the type of canal (Vertucci type 2). The blinding of the researchers was not done. The new system of irrigation, GentleWave, has to be compared with other continuous ultrasound irrigation systems to corroborate our findings.

CONCLUSION

None of the irrigant methods examined could entirely remove dentin debris from the canals and isthmus regions of the specimen in this in vitro experiment. The GW system showed greater efficiency in the elimination of hard tissue debris from the canal and isthmus regions when compared to IS. Both the irrigation systems were efficient and comparable in debris removal.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.