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Table of Contents
Year : 2018  |  Volume : 8  |  Issue : 2  |  Page : 56-61

Effect of endodontic rotary instruments on the furcation: An In Vitro Study

1 Private Practitioner, Consultant Periodontist, Bellary, Karnataka, India
2 Department of Periodontics, Bangalore Institute of Dental Sciences and Post Graduate Research Centre, Bengaluru, Karnataka, India
3 Department of Fixed Prosthodontics, Taif University, Taif, Kingdom of Saudi Arabia
4 Department of Orthodontics, Taif University, Taif, Kingdom of Saudi Arabia
5 Department of Pedodontics, Taif University, Taif, Kingdom of Saudi Arabia

Date of Web Publication30-May-2018

Correspondence Address:
Rekha Setty
D/o. S Lakshmi Narayana Setty, Dwaraka Picture Palace, Car Street, Kurugodu (Post), Bellary - 583 116, Karnataka
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/jid.jid_89_17

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Objective: The aim of this study is to evaluate and measure the residual dentin thickness from the furcation entrance to the canal orifice after canal preparation using endodontic rotary instruments in extracted mandibular first molars. Materials and Methods: A total of 15 extracted mandibular molars were included in the study. They are further divided into three groups as follows: Group A, B, and C (n = 5) and subjected to canal preparation using commonly available rotary instruments such as Gates Glidden, Hero Shaper, and Pro Taper, respectively. All the prepared mesiobuccal root canals were subjected to computed tomography imaging technique, to calculate the residual dentin thickness and the distance from the furcation entrance to the canal orifice. Results: The results showed that there was a statistical significant increase in the volume of the mesiobuccal canal of the mandibular first molars with all the three rotary instruments. The comparison made between preoperative, and postoperative measurements showed statistical significance between Group A versus Group C (P = 0.0039*), but no significant difference found between Group A versus B and Group B versus C. Conclusion: Within the limitation of the present study, it can be concluded that the amount of dentin removed from the danger zone in the mesiobuccal canal of the mandibular first molars was more with Protaper than gates Glidden. Hence, the use of newer endodontic rotary instruments in the danger zone may pose a risk for furcation involvement.

Keywords: Computed tomography, danger zone, furcation involvement, radio visio graphy, residual dentin thickness

How to cite this article:
Setty R, Srirangarajan S, Setty M B, Devanna R, Battepati PM. Effect of endodontic rotary instruments on the furcation: An In Vitro Study. J Interdiscip Dentistry 2018;8:56-61

How to cite this URL:
Setty R, Srirangarajan S, Setty M B, Devanna R, Battepati PM. Effect of endodontic rotary instruments on the furcation: An In Vitro Study. J Interdiscip Dentistry [serial online] 2018 [cited 2023 Apr 1];8:56-61. Available from: https://www.jidonline.com/text.asp?2018/8/2/56/233619

   Clinical Relevance to Interdisciplinary Dentistry Top

  • The primary focus of an endodontist during root canal treatment is the root canal anatomy. But other factors that influence the treatment outcomes such as presence of accessory canals, furcation anatomy and remaining dentin thickness in the danger zone should be taken into consideration for a successful and long term results.

   Introduction Top

The anatomical communication between the periodontal tissues and dental pulp is by an apical foramen, lateral, and accessory canals through which the noxious and inflammatory products can be exchanged.[1] The incidence of these accessory canals is found to be in greater number in the furcal region of the mandibular molar than the maxillary molars followed by the maxillary premolars.[2] The invasion of the bifurcation and trifurcation of multi-rooted teeth by the disease is termed as furcation involvement. Various contributing factors for furcation involvement are periodontal disease, pulpal disease, iatrogenic factors (root fractures and root perforations) during endodontic therapy, anatomical factors such as cervical enamel projections, enamel pearls, bifurcation ridges, and trauma from occlusion. These furcation defects present the most challenging task for the periodontal treatment due to limited access.[2]

Furcation involvement by iatrogenic factors (root/strip perforation) is caused by over instrumentation through a thin wall (danger zone) in the root during biomechanical preparation (BMP).[3],[4] In the danger zone, there is less tooth structure compared with a more peripheral portion (safety zone) of the root dentin. The studies conducted by Kessler et al. reported that the danger zone is generally located 4–6 mm below the canal chamber orifice.[4] Excessive removal of the dentin in the danger zone further compromises the strength and integrity of the teeth thereby decreasing the fracture resistance. Hence to maintain the integrity of the canal walls, anti-curvature filing method using nickel–titanium (NiTi) rotary instruments were introduced to perform consistent, predictable, easier, and faster instrumentation of the root canals considerably reducing the iatrogenic damage.[5],[6]

The diagnosis of furcation defects is by periodontal probing, radiography, and intra-operative measurements (surgical inspection).[1] The quality and quantity of the information obtained from radiographic examinations are very important because they affect the diagnosis, treatment planning, and prognostic stability.[7] The conventional intra-oral radiographic technique does not provide enough information on pathological conditions.[8] Technological advances in imaging techniques such as cone-beam computed tomography (CBCT) allows detailed three-dimensional (3D) observation of the anatomy of the roots, amount of dentin removal during BMP of the root canals and the furcation defects with less radiation exposure.[9],[10] Therefore, the aim of this study was to compare the effect of three different powered instruments on the residual dentin thickness from the furcation entrance to the canal orifice during instrumentation in curved mesiobuccal canals of extracted mandibular molars using CBCT.

   Materials and Methods Top

A total number of fifteen permanent mandibular first molar teeth [Figure 1] extracted due to periodontitis or caries, having two separate root canals and portals of exit were included for the study. Teeth with fused roots, resorbed roots, carious roots, taurodontic teeth, and third molars were excluded from the study. The teeth were scaled to remove the calcified debris and tissue fragments from the roots and stored in 10% formalin solution. The specimens were prepared in the following manner: the teeth were divided into Group A, Group B, and Group C (n = 5). Radio visio graphy (RVG –[Figure 2]) and CBCT imaging was performed for analyzing the root canal anatomy and preoperative measurements of dentin thickness of the mesio-buccal canal from the canal orifice to furcation entrance. Further access cavity preparation was carried out using Gates Glidden (Dentsply), Hero shaper (Micro-Mega, Besancon, France), and Protaper (Dentsply Maillefer, Ballaigues, Switzerland) instruments for Group A, B, and C, respectively. Root canal preparation with NiTi rotary systems was carried out in strict accordance with the manufacturer's recommendations.
Figure 1: Study design

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Figure 2: Pre operative Radio Visio Graphic images

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Electric motor with torque control (X-SMART; Dentsply) was used with NiTi systems. Gates Glidden burs (size 3, 2, 1) were used for coronal preenlargement in a crown-down manner and mounted in an electric motor with torque control and constant speed of 800 rpm (X-SMART), each instrument was coated with RC Prep (Premier Products, Plymouth Meeting, PA, USA) as a lubricant. Irrigation was performed with 10 mL 2.5% NaOCl after each file. The canal patency was checked with number 10 K file.

Image analysis

All the teeth were imaged for both pre [Figure 3] and post operatively [Figure 4] by CBCT for remaining dentin thickness in the danger zone. The CBCT machine used for the imaging purpose is Kodak 9000, France. The software is CS 3D Imaging Software 3.2.9 (Carestream Dental a Division of Carestream Health Canada Company, Vaughan, ON LRK 0C5, Canada) with 2.5 mA, 60 kv, the total scan time of 10.8 s, the total number of slices of 188 with each slice thickness of 76 μm. The teeth were aligned with the buccal surface in the anteroposterior position.
Figure 3: Pre operative CBCT images

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Figure 4: Post operative CBCT images

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Measurement of dentin thickness

The distances from canal wall to the root surface at the first 3 cut-planes at coronal level (below the orifice of mesio-buccal canal) were measured by image analysis software [Figure 5]. To measure the dentin thickness two reference points are used: pulpal floor and dome of furcation. The measurements are from:
Figure 5: Measurement of Dentin thickness

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  • The external surface of the root in line with canal orifice
  • Pulpal floor to dome of furcation and
  • Canal orifice to the dome of the furcation.

Statistical analysis

The statistical analysis was performed using SPSS software version 16 (IBM Corporation, www.ibm.com/us-en/marketplace/spss-statistics). The descriptive analysis that included mean and standard deviation were found for all the groups. One-way analysis of variance (ANOVA) was used for comparison between means. The Tukey post hoc test was used for pair-wise comparison between the means when ANOVA test was significant. The significance level was set at *P < 0.05.

   Results Top

Preoperative measurements

The results mentioned in the [Table 1], [Table 2], [Table 3] are relevant to the study and statistical analysis showed no significant differences between the groups.
Table 1: Preoperative measurements

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Table 2: Postoperative measurements

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Table 3: Comparison of pre- and post-operative measurements

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The statistical significant differences were not observed in the preoperative measurements but the postoperative measurements between Group A and B as well as Group A and C showed statistical significant differences [Table 1] and [Table 2]. The comparison between the group A and C measurements showed statistical significant difference with a p value of 0.0049 [Table 3].

   Discussion Top

The anatomic relationship between the dental pulp and furcation area of the multi-rooted teeth is by the apical foramen, lateral, and accessory canals, that provides a pathway for exchange of inflammatory and noxious products between both the tissues. These accessory canals are the result of failed differentiation of odontoblasts due to defect formation in Hertwig's epithelial root sheath.[11] Large numbers of accessory canals are found in furcation area of the mandibular molars.[2] Further the length of the root trunk of mandibular 1st molar is shorter than the 2nd molar;[1] therefore, this area is prone for early involvement by the disease process. The furcation involvement by the pulpal/periodontal disease process or the iatrogenic factors causes loss of periodontal support in this region, presenting a greatest challenge to the clinician; due to its complicated structure that makes the access of this area difficult for treatment and maintenance. In this study, the mandibular molars were considered because the incidence of the accessory canals is higher (56%) compared to the maxillary molars (48%).[2]

During endodontic therapy or postspace preparation,[12] strip perforations [13],[14] and vertical root fractures are possible outcomes of excessive removal of radicular dentin, especially in the danger zones where there is less amount of tooth structure compared to the peripheral portion of the root dentin.[15] In addition to the endodontic mishaps, the presence of accessory canals in furcation areas are other contributing factors that will further compromise the strength and integrity of the teeth resulting in tooth extraction.[16] Hence to prevent such risk, anti-curvature filing by NiTi instruments were employed.[5] There is enormous evidence present that states: use of NiTi instruments removed less radicular dentin in the danger zone when compared to stainless steel hand instruments.[6],[17],[18],[19]

Hence, this study was an attempt to compare and evaluate the amount of remaining dentin in the danger zone after instrumentation with three different rotary instruments Gates Glidden, Hero Shaper and Protaper.

RVG is the first digital radiographic system introduced in dentistry by Trophy 1987.[20] The advantage of using RVG over conventional radiographic techniques include radiation dose reduction (80%), short processing time, elimination of the darkroom, chemical handling, and provides edge enhancement. It allows manipulation of the image produced such as contrast, density, sharpness, and image orientation, without any additional radiation exposure to the patient or the operator. It is especially useful for endodontic treatment for pretreatment evaluation of roots and root canal morphology, calcifications, curvatures, periapical lesions, working length determination, quality, and extent of root canal obturation. Hence, this imaging technique was used in this study for preevaluation of the root canals.[21]

There are various methods used for assessment of canal instrumentation such as scanning electron microscopy,[22] radiographic [23] and photographic assessment,[24] serial sectioning,[25] silicon impressions of the instrumented canals,[26] and computer manipulation techniques.[27] These methods are invasive in nature, labor intensive, loss of specimen, and no accurate repositioning.[28] Technological advances are made to develop techniques that are, noninvasive and provide precise information about the remaining dentin thickness. CT has rendered accurate 3D images that are accurate and reliable.[17] Hence, CT was used in this study to evaluate the dentin thickness pre- and post-instrumentation.

The results of this study show that the amount of residual dentine removed by the rotary instruments is as follows: Group A-0.12 (2.19–2.07), Group B-0.22 (1.91–1.69), and Group C-0.36 (2.07–1.71). The intragroup comparison shows a significant difference between Gates Glidden, Heroshaper (P = 0.0395), and Protaper (P = 0.0500). The intergroup comparison made postinstrumentation showed statistically significant difference between the Groups A versus B and Group A versus C. On comparison between preinstrumentation and postinstrumentation, the results obtained showed statistically significant difference between the Groups A versus C (P = 0.0039) but not with Group A versus B and Group B versus C. Hence, the results of this study state that Gates Glidden removed less dentin in the mesiobuccal canal of the mandibular molars when compared to Protaper and Hero-Shaper which is similar to the studies conducted by Nagaraja and Murthy [29] and as stated by Lertchirakam et al.[30]

This finding may be due to progressive tapered design with convex cross-sectional design of the Protaper that could have led to the aggressive cutting of the root dentin.[18],[19] Further, the Protaper files cut dentin by the machining action which leads to a reduction in remaining dentin thickness on the inner side of the curvature increasing the risk of vertical root fracture or may even result in a strip perforation. Other features of Protaper instruments that contribute to dentinal microfractures are tip design, cross-sectional geometry, taper, pitch design, and flute form.[31]In vitro studies by Yoldas et al.[32] and Ustun et al.[31] concluded that instrumentation with Protaper (Protaper Next and reciprocating instruments) tend to produce microcracks that cause various degrees of dentinal damage, compromising the strength of the teeth. A study conducted by Priya et al.[33] stated that the Protaper files set in reciprocating motion showed less crack formation due to less torsional and flexural stresses and cross-sectional design. Recent advances such as heat-treated NiTi instruments are developed to improve the mechanical properties such as resistance to cyclic fatigue and torsional properties, thereby reducing the dentinal damage.[34]

Therefore, the length of the root trunk and anatomy of furcation area, the presence of accessory canals, postinstrumentation dentin thickness in the danger zone, and the microcrack formation by the endodontic rotary instruments are the other important factors to be considered by the clinicians to prevent furcation involvement and its adverse consequences. Further clinical research is necessary to evaluate the outcome of the root canal treatment in maxillary posterior teeth (molars and 1st premolar) with larger sample size and effect of the advanced NiTi instruments (heat treated) in relation to the furcation.

   Conclusion Top

Within the limitation of this study, it can be concluded that the risk of furcation involvement is more with the use of newer endodontic rotary instruments for coronal enlargement in regard to the danger zone. Hence, the use of conventional instruments is safe, thereby preventing endo-perio problems and further improving the periodontal prognosis.


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Conflicts of interest

There are no conflicts of interest.

   References Top

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  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5]

  [Table 1], [Table 2], [Table 3]


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