Efficacy of microscopy and dye for determining the presence of root canals in root end resections-an in vitro study

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1 Efficacy of microscopy and dye for determining the presence of root canals in root end resections-an in vitro study SHUE-FEN YANG 1,2 JENN-RONG HSU 1 CHIA-LIN TSAI 1 SHENG-FANG PAI 2 1 Department of Dentistry, Taipei Veterans General Hospital, Taipei, Taiwan, ROC. 2 School of Dentistry, National Yang-Ming University, Taipei, Taiwan, ROC. Previous studies have shown the importance of using a microscope and dye to recognize root canals and isthmuses during periapical surgery. This in vitro study evaluated the efficacy of a microscope and/or methylene blue dye for identifying canals and isthmuses in untreated mesiobuccal (MB) roots of maxillary first molars. A root end resection was performed on the MB root of 30 maxillary first molars at the apical 1/3 and mid-root levels. Color slides of resected roots, with and without methylene blue dye, were made at 1, 7.5, and 25 using a stereomicroscope. The number of root canals and the presence of an isthmus in the MB root of 30 maxillary first molars at different resection levels were determined by 2 experienced endodontists under 25 magnification with dye. The number of root canals and the presence of an isthmus on all slides were also evaluated by 2 endodontic residents. The accuracy of the 2 resident evaluators in determining the number of root canals and the presence of an isthmus under different circumstances was analyzed by comparing their results with those of the experienced endodontists using 25 magnification in the presence of dye. A logistical regression was used for the statistical analysis. Sixty percent of the MB roots had 2 root canals at the apical 1/3 level, and 73.3% of the MB roots had 2 canals at the mid-root level. Our results indicated that the use of both a microscope and methylene blue dye significantly increased (by about 20%) the reading accuracy of the number of root canals by the endodontic residents (p < 0.05) in vitro. We concluded that using both a microscope and methylene blue dye can improve the determination of the number of root canals in the MB root of the maxillary first molars at different root-end section levels. (J Dent Sci, 2(2):97-102, 2007) Key words: microscope, methylene blue, root end resection, maxillary first molar, mesiobuccal root. A dental operating microscope is used to magnify the field of vision which enhances the preparation and sealing of a root apex during apical surgery. This point of view was first reported by Reuben and Apotheker 1. Cambruzzi and Marshall 2 stated that staining with methylene blue dye should be added to apicoectomy procedures. Weller et al. 3 emphasized the important role of using a microscope and dye to recognize root canals and isthmuses during periapical surgery. Any openings on the resected root surface Received: March 7, 2007 Accepted: May 15, 2007 Reprint requests to: Dr. Sheng-Fang Pai, Department of Dentistry, Taipei Veterans General Hospital, No. 201, Shih-Pai Road, Sec. 2, Taipei, Taiwan 11217, ROC. may contain microorganisms or act as a portal of exit for an uninstrumented or unfilled part of the root canal system. Failure to include an isthmus or identify an additional canal during root-end cavity preparation can affect the prognosis of periapical surgery. The use of a microscope or dye increases the visibility of the root canals and isthmuses in endodontic surgery. However, the efficacies of using a microscope only, dye only, and a microscope and dye together for the specific procedure of root end surgery are not known and have not been studied. The purpose of this study was to evaluate the efficacy of a microscope only, dye only, and a microscope and dye together for identifying root canals and isthmuses after root end resection of untreated mesiobuccal (MB) roots of maxillary first molars in vitro. J Dent Sci 2007 Vol 2 No 2 97

2 S.F. Yang, J.R. Hsu, C.L. Tsai, et al. MATERIALS AND METHODS Thirty non-carious human maxillary first molars extracted for periodontal reasons were collected and stored in a 2.3% glutaraldehyde solution. The age and gender of the patients were unknown. The mesiobuccal root of the molars was measured from the cementoenamel junction to the apex. These roots were marked at the 1/2 and 1/3 levels from the apex. The mesiobuccal roots were resected perpendicular to the long axis of the root at the 1/3 level using a fissure carbide bur (SSW FG-557, NJ, USA). Color photographs of the resected surfaces were made at 1, 7.5, and 25 magnifications (Figure 1) under a stereomicroscope (SMZ-U; Nikon, Tokyo, Japan). A cotton swab saturated with methylene blue was A B C D E F Figure 1. Representative photographs demonstrating the root end surfaces of the same mesiobuccal root resected at the apical 1/3 level. Root end cut surface at (A) 1:1, (B) 7.5, and (C) 25 magnification. Root end cut surface with methylene blue staining at (D) 1:1 and (E) 7.5 magnification. A partial isthmus (arrow) is evident between the 2 canals. (F) Root end cut surface with methylene blue staining at 25 magnification. A partial isthmus (arrow) is evident between the 2 canals. 98 J Dent Sci 2007 Vol 2 No 2

3 Magnification and dye for reading root canals applied to the resected surface. Excess methylene blue was removed using a cotton swab. Color photographs of the resected surfaces with methylene blue staining were made at 1, 7.5, and 25 magnifications (Figure 1) under a stereomicroscope. The MB root was resected perpendicular to the long axis of the root at the 1/2 level from the apex. The color slides of the resected surfaces with and those without methylene blue dye were made at 1, 7.5, and 25 magnifications using a stereomicroscope. All color photographic slides of the resected root ends were projected onto the monitor (Kodak Ektagraphic Audio Viewer Projector Model 570AF; New York, NY, USA). Two endodontic residents determined the number of root canals and the presence of an isthmus for each of the specimens using a blinded format. The slides were evaluated in the following sequence. Specimens without dye were evaluated first, and slides of lower magnification were evaluated before those of higher magnification. The number of root canals was determined. The presence of a partial or complete isthmus was respectively registered as either present (+) or absent (-). An isthmus is defined as a narrow, ribbon-shaped, communication between 2 root canals that contains pulp or pulpally derived tissue 3. Two experienced endodontists simultaneously determined the number of root canals and the presence of an isthmus at 25 magnification with dye. Any discrepancies between the 2 experienced endodontists were discussed until final agreement was obtained. The accuracy of the resident evaluators in determining the number of root canals and the presence of an isthmus for the 2 canal specimens was assessed by comparing their results with those determined by the experienced endodontists. The 4 variables were a) without microscopic magnification or dye, b) with microscopic magnification but no dye, c) without microscopic magnification but with dye, and d) with both microscopic magnification and dye. The accuracy of the 2 resident evaluators in determining the number of root canals and the presence of an isthmus for 2-canal specimens in the 4 groups were compared. The accuracy of the group with no magnification and no dye was regarded as the baseline. A logistical regression procedure was used for the statistical analyses. RESULTS Table 1 summarizes the number of root canals and the presence of an isthmus for 2-canal specimens in the MB root of 30 maxillary first molars at different resection levels as determined by the 2 experienced endodontists. The results showed that 60% (18/30) of the MB roots had 2 root canals at the 1/3 level and 73.3% (22/30) had 2 canals at the mid-root level. For those specimens with 2 canals, 33.3% (6/18) of the MB roots had either a complete or partial isthmus at the 1/3 level. At the mid-root level, 72.7% (16/22) of the MB roots had an isthmus. Table 2 shows the comparison of the first resident evaluator in determining the number of root canals and presence of an isthmus for 2-canal specimens at different magnifications and dye applications. Magnification included 7.5 and 25 magnifications because the difference in the evaluations between 7.5 and 25 was not statistically significant (p > 0.05). The accuracy significantly increased from 70.0% to 90.0% when both dye and microscope were used to determine the number of root canals (p = ; odds ratio = 3.857). The accuracy significantly increased from 66.7% to 80.8% when the microscope but no dye was used in determining the presence of an isthmus (p = ; odds ratio = 2.109). The accuracy significantly increased from 66.7% to 84.2% when both dye and microscope were used to determine the presence of an isthmus (p = ; odds ratio = 2.658). Table 1. Number of root canals and the presence of an isthmus in the mesiobuccal roots of maxillary first molars 1/3 level Mid-root level Number of root canals 1 12/30 (40.0%) 8/30 (26.7%) 2 18/30 (60.0%) 22/30 (73.3%) Presence of an isthmus in 2-canal specimens + 6/18 (33.3%) 16/22 (72.7%) J Dent Sci 2007 Vol 2 No 2 99

4 S.F. Yang, J.R. Hsu, C.L. Tsai, et al. Table 2. Comparison of the detection rate of 2-root canals and isthmuses in the mesiobuccal root of maxillary first molars between the first resident evaluator and endodontists for the different magnifications and dye applications No magnification Magnification Number of root canals No dye 70.0% 80.0% Dye 83.3% 90.0%* a Presence of an isthmus in 2-canal specimens No dye 66.7% 80.8%* b * p < a odds ratio = b odds ratio = c odds ratio = Dye 76.7% 84.2%* c Table 3 shows the comparison of the second resident evaluator in determining the number of root canals and presence of an isthmus for 2-canal specimens at the different magnifications and dye applications. The accuracy significantly increased from 51.7% to 72.5% when both dye and microscope were used to determine the number of root canals (p = ; odds ratio = 2.466). The accuracy significantly increased from 51.7% to 70.7% when the dye but no microscope was used to determine the number of root canals (p = ; odds ratio = 2.183). DISCUSSION A wide range of prevalences of a second MB canal in maxillary first molars has been reported regardless of the methods used. Hartwell and Bellizzi 4 reported that 18.6% of maxillary first molars had 4 canals according to clinical records. A scanning electron microscopy investigation by Gilles and Reader 5 showed that 90% of maxillary first molars had 2 canals in the MB roots. Kulid et al. 6 found that 96.1% of MB roots of the maxillary first molars had 2 canals in the coronal half of the root examined using a bur and microscope. In this study, data from the endodontists' readings showed that 73.3% of the MB roots of the maxillary first molars had 2 canals at the mid-root level and only 60% of the MB roots of the maxillary first molars had 2 root canals at the apical 1/3 level. This indicates that approximately 13% of the MB roots had 2 canals at the mid-root level which had converged into a single canal at the apical 1/3 level. Likewise, Weller et al. 3 studied the morphology of the MB root of maxillary first molars under a microscope using methylene blue dye. Their results showed that 60% of the MB roots had 2 canals, and 20% had a type II configuration. A type II configuration has 2 separate canals that merge before reaching the apex to form a single root canal 7. The reported incidence of an interconnection or isthmus in MB roots of the maxillary first molar varies 2,8,9. Pineda 8 found that 4.9% of the MB roots of the maxillary first molars had interconnections between 2 canals by roentgenography. Cambruzzi Table 3. Comparison of the detection rate of 2-root canals and isthmuses in the mesiobuccal root of maxillary first molars between the second resident evaluator and endodontists at different magnifications and dye applications No magnification Magnification Number of root canals No dye 51.7% 65.8% Dye 70.0%*a 72.5%*b Presence of an isthmus in 2-canal specimens No dye 61.7% 74.2% * p < a odds ratio = b odds ratio = Dye 70.0% 72.5% 100 J Dent Sci 2007 Vol 2 No 2

5 Magnification and dye for reading root canals and Marshall 2 reported that 30.1% of maxillary molars had an isthmus joining 2 canals in the MB roots. Weller et al. 3 discussed the concept of a partial isthmus and reported that 2 canals of the MB root of the maxillary first molar contained a complete or partial isthmus 100% of the time 3~4mm from the apex. In this study, the same definition of an isthmus was used as described previously by Weller et al. 3 The results showed that 72.7% (16/22) of MB roots of the maxillary first molars had an isthmus at the 1/2 level for those specimens with 2 canals. A comprehensive survey of perceived values and usage patterns of the endodontic microscope was conducted by Ester et al. 10 The survey showed that the overall perceived benefits from microscope usage are its increased ability to locate canals (63.5%), an increased ability to repair defects (61.4%), an increase in endodontic success (52.7%), and morepredictable treatment (50.2%). Coelho de Carvalho and Zuolo 11 found that the use of an operating microscope increased the number of the root canal orifices located in mandibular molars by 7.8%. Baldassari-Cruz et al. 12 reported that MB roots with 2 canals in the maxillary first molars increased from 51% to 82% at 16 magnification. Stropko 13 reported that MB roots with 2 canals in the maxillary first molars increased from 73.2% to 93.0% as the operators become more experienced and when a microscope was used. Gorduysus et al. 14 demonstrated that the ability to negotiate the 2 canals in the MB roots of the maxillary first and second molars increased from 69% to 80% when using an operating microscope. Buhrley et al. 15 found that the use of a microscope increased the detection rate of 2-root canals in the MB roots of maxillary molars by approximately 3 times compared to that without a microscope. However, Sempira and Hartwell 16 reported that the use of a surgical microscope did not significantly increase the detection of the second MB canal in maxillary molars. Few studies have mentioned the efficacy of a microscope and dye together for identifying root canals and isthmuses in root end resection. Rubinstein and Kim 17 reported that detection and treatment of isthmuses under a microscope increased the success of endodontic surgery in 25% of 94 cases. Isthmuses were found in 81% of molars, 16% of premolars, and 3% of anterior teeth. However, they did used no dye to detect the isthmuses during their surgery. The magnifications used in this study were 7.5 and 25. Rubinstein 18 recommended the range of magnifications from 2.5 to 30 for clinical use. Higher magnifications are used to observe details, while lower magnifications provide a wide field of view. In this study, 25 magnification helped us detect more details, but with dye staining, there was no significant difference in determining the presence of root canals and isthmuses between 7.5 and 25. This study was conducted to test the efficacies of a microscope only, dye only, and a microscope and methylene blue dye together for identifying root canals and isthmus communications in root endresected MB roots of maxillary molars in vitro. The results showed that using the microscope only or dye only increased the accuracy of determining the number of root canals and the presence of an isthmus in the resected root surface. However, there was a statistically significant difference only when using both the microscope and dye together to determine the number of root canals for both evaluators. The accuracy increased from 70.0% to 90.0% (p = ; odds ratio = 3.857) for the first evaluator and from 51.7% to 72.5% for the second evaluator (p = ; odds ratio = 2.466). Using the microscope and dye together provided greater accuracy than using either the microscope or dye alone. According to the findings of this study, we advise that a microscope and dye be used together to determine the number of root canals and the presence of an isthmus during root-end surgery. As a note of caution, methylene blue should not be used in patients with glucose-6 phosphate dehydrogenase (G6PD) deficiency 19, because it works as an oxidant and can cause hemolysis in G6PD-deficient patients. ACKNOWLEDGMENTS This study was supported by a research grant from Taipei Veterans General Hospital (V86A-155). Special thanks go to Ms. Shu-Chiung Chiang for assistance with the statistical analysis as well as Dr. John Corcoran and Dr. William T. Johnson for their revision of the manuscript. REFERENCES 1. Reuben HL, Apotheker H. Apical surgery with the dental microscope. Oral Surg, 57: , J Dent Sci 2007 Vol 2 No 2 101

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