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Year : 2016  |  Volume : 10  |  Issue : 2  |  Page : 58-66

Scanning electron microscope evaluation of morphological changes in dental hard tissue after root resection in apicoectomy by Er,Cr:YSGG laser and #702 TC Bur: Part I

Department of Conservative Dentistry and Endodonics, Dr. R Ahmed Dental College and Hospital, Kolkata, West Bengal, India

Date of Web Publication29-Dec-2016

Correspondence Address:
Prashant Dadasaheb Babar
Department of Conservative Dentistry and Endodontics, Dr. R. Ahmed Dental College and Hospital, 142/A, A. J. C. Bose Road, Kolkata - 700 014, West Bengal
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/2321-1385.196993

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Aim: The aim of this study was to compare surface characteristics and morphological changes in Er,Cr:YSGG laser and bur resected root ends in apicoectomy. Settings and Design: 5 W, 20 Hz, 50% air, 100% water, 300 mJ. Materials and Methods: Forty freshly extracted human central incisors treated endodontically. gutta-percha-obturated teeth were resected apically 3 mm with 0° bevel. Twenty samples were resected with #702 TC Bur while rest half were resected with Er,Cr:YSGG laser with 600 μm sapphire tip. Samples were examined for cemental damage, surface roughness, and cracks under surgical operating microscope (SOM) at ×16. Then, samples were fixed, dehydrated, and gold sputtered for observation under scanning electron microscope (SEM). Statistical Analysis Used: Data obtained were subjected to statistical analysis using Chi-square/Fisher's exact test, Kruskal-Wallis test, whenever required. Results: Under SOM, no cemental damage was detected; while under SEM, 14 bur and 1 laser resected samples exhibited damage (P < 0.001). Under SOM and SEM, bur resected surface showed roughness in 17 and 20 samples, respectively, while laser resected surface appeared to be smoother in 18 and 19 samples, respectively (P < 0.001). Under SOM, cracks seen in only 1 bur resected sample, while in laser resected samples, no cracks revealed. Under SEM, bur root resection revealed cracks in 16 samples; laser root resection revealed cracks in 3 samples (P < 0.001). Conclusions: Er,Cr:YSGG laser resection as compared to #702 TC Bur resection exhibits less damage to cementum, smoother dentinal surface with least or no surface cracks/microcracks.

Keywords: #702 TC Bur, cementum, cracks, dentin surface roughness, Er,Cr:YSG laser, root resection, scanning electron microscope

How to cite this article:
Babar PD, Adhikari HD. Scanning electron microscope evaluation of morphological changes in dental hard tissue after root resection in apicoectomy by Er,Cr:YSGG laser and #702 TC Bur: Part I. J Dent Lasers 2016;10:58-66

How to cite this URL:
Babar PD, Adhikari HD. Scanning electron microscope evaluation of morphological changes in dental hard tissue after root resection in apicoectomy by Er,Cr:YSGG laser and #702 TC Bur: Part I. J Dent Lasers [serial online] 2016 [cited 2020 Sep 20];10:58-66. Available from:

  Introduction Top

With the development of endodontic microsurgery, the success rate in apicoectomy cases has become high. [1],[2],[3],[4] The resection by different types of burs has been practiced. The #702 TC Bur is used by most of the operators for its better performance among the various burs. [5]

An adequate method used during resection should favor more regular and smooth apical surface. Guttman and Harrison [6] recommended that the root resection method be highly refined to favor controlled removal of the radicular apex and to produce smooth and clean surfaces, thus preventing excavations or a sulcus effect.

However, bur resection shows a rough surface with sulcus effect, track lines, sharp edges, or spurs of the root structure which acts as irritant and stimulates a resorptive response during the healing process. The cementum has immense role of healing the cut root-end surface which needs to be entirely covered by new cementum. The bur damages the cemental surface. [7] It is also the fact that bur causes vibrations and produces cracks which may be complete, partial, or intradental. These cracks may contribute to egress of microbes and their toxic products, and vice versa.

The introduction of ERBIUM laser is now the answer to address the pitfalls. It has been seen that laser in comparison to bur produces a smoother surface of cut root-end, absence of vibration, so no crack formation. Smoothness is essentially required for the purpose of better adaptation of retrograde filling material within the perimeter of retrograde cavity preparation, and it contributes in the availability of more dentinal collagen for periodontal ligament (PDL) cell attachment. [8],[9],[10],[11],[12],[13],[14],[15],[16],[17],[18]

Purpose of the study

Keeping this in mind, an in vitro study was designed to evaluate the cemental damage, surface roughness, and cracks in laser and bur resected surface in apicoectomized teeth under surgical operating microscope (SOM) and scanning electron microscope (SEM).

Laser apicoectomized root-end not only exhibits smooth and crackless surface but also provides dentin surface free of debris and smear layer with exposed intertubular collagen. Using appropriate laser parameters, there is absence of charring/carbonization or any sort of thermal damage, which may help in better cementum deposition. All these contribute in achieving healing by regeneration and are the subject matter of rest part (Part II) of this in vitro study.

  Materials and Methods Top

Forty human central incisors of average size, freshly extracted for periodontal cause, were selected. Informed consent was obtained from the patients, and the Institutional Ethical Committee and Review Board, Dr. R. Ahmed Dental College and Hospital, gave ethical clearance for this study. Teeth were stored in normal saline after cleaning. Sample exclusion criteria were incompletely formed apex, resorbed roots, evidence of crack and fracture, calcified canals and canal curvature, etc.

Endodontic treatment was undertaken, gutta-percha-obturated teeth were decoronated so that length of samples remains fixed at 10 mm required for SOM observation. Apical 3 mm was then resected with 0° bevel. [19],[20],[21] Twenty samples were resected with #702 TC Bur while rest 20 were resected with Er,Cr:YSGG laser with parameters 5 W, 20 Hz, 50% air, 100% water, 300 mJ output energy with 600 μm sapphire tip.

All the forty samples were examined under SOM at ×16. Then, the samples were fixed with Karnovsky's fixative, dehydrated in ascending series of 25%, 50%, 75%, and 100% ethanol, dried with critical point dryer using liquid CO 2 and sputter coated with gold ion sputter device for observation under SEM at different magnifications. Data obtained after SOM and SEM observation were subjected to statistical analysis using Chi-square/Fisher's exact test and Kruskal-Wallis test whenever required. For statistical analysis, data were entered into a Microsoft Excel spreadsheet and then analysed by Epi Info software, SPSS 10.0.1 and GraphPad Prism version 5 (GraphPad Software, Inc. 7825 Fay Avenue, Suite 230 La Jolla, CA 92037 USA). The median and the interquartile range have been stated for numerical variables that are not normally distributed. Student's independent sample's t-test was applied to compare normally distributed numerical variables between groups; unpaired proportions were compared by Chi-square test or Fisher's exact test, as appropriate. Once a t value is determined, a P value can be found using a table of values from Student's t-distribution. If the calculated P value is below the threshold chosen for statistical significance (usually, 0.10, 0.05, or 0.01 level), then the null hypothesis is rejected in favor of the alternative hypothesis.

The objective of the present study was to compare the surface characteristics (such as cemental damage, surface roughness, and cracks) of root ends resected with #702 TC Bur and Er,Cr:YSGG laser by light microscopy (SOM) and SEM.

  Results Top

Cementum periphery

Cemental damage

Under SOM, cementum periphery could not be traced properly.

Under SEM, bur root resection showed no cemental damage in 6 (30%) samples while rest 14 (70%) samples showed cemental damage [Figure 1]a and b. Laser root resection showed least or no damage to cemental surface in 19 (95%) samples [Figure 1]c and d out of 20 samples. The difference between both groups is statistically significant [P < 0.001; [Table 1] and Graph 1].
Figure 1: Scanning electron microscope (a and b) bur resected cemental surface reveals damage in 70% samples (arrows); (c and d) lased cemental surface reveals least or no damage in 95% samples (arrows) (a: ×80, b: ×45, c: ×200, d: ×45)

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Table 1: Evaluation of cemental damage

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Surface characteristics

Bur and laser cut surface of both groups was observed for surface characteristics such as relative roughness and smoothness in terms of "rough" and "smoother," respectively.

Under SOM, bur root resection produced smoother dentinal surface in only 3 (15%) samples [Figure 2]a while rest 17 samples produced rough dentinal surface [Figure 2]b and c.
Figure 2: Surgical operating microscope: Bur resected samples revealing smoother in 15% (a) and rough striated surface (arrows) in 85% samples (b and c)

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Laser resected root surface appears to be smoother in 18 (90%) samples [Figure 3] out of 20 samples. The difference between both groups is statistically significant [P < 0.001; [Table 2] and Graph 2.
Figure 3: Surgical operating microscope: Laser resected samples reveals smoother surface in 90% samples

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Table 2: Evaluation of dentin surface characteristics

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Under SEM, at low magnification, bur root resection seems to produce rough, flaky dentinal surface [Figure 4] score 2 and 3 in all 20 samples.
Figure 4: Scanning electron microscope scores used for evaluation of surface roughness are as follows: 0: Smooth surface; 1: Surface with slight roughness; 2: Surface with moderate roughness; 3: Surface with severe roughness (SEM, ×300)

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Stripping [Figure 5]a of dentinal surface and track lines [Figure 5]b (due to rotary instrumentation and smear layer) were also noted at higher magnification.
Figure 5: Scanning electron microscope (high magnification) bur resection showing stripping (arrow) of dentinal surface (a) track lines (arrow) (b) due to rotary instrumentation and smear layer (a: ×950, b: ×800)

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Laser root resection at lower magnification showed smoother wavy surface [Figure 4] score 0 and 1] in 19 (95%) samples out of 20 samples. However, the uniformly micro-irregular dentinal surface was noted at higher magnification [Figure 6]. The difference between both groups is statistically significant [P < 0.001; [Table 2] and Graph 3].{Figure 4}
Figure 6: (a-c) Scanning electron microscope laser resection showing uniformly micro-irregular dentinal surface at higher magnification (a: ×400, b: ×1500, c: ×2000)

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Roughness score

SEM micrographs were taken at ×300 for analysis of surface roughness by two calibrated examiners in a double-blinded fashion using 4-point (0-3) scoring system [Figure 4] as described by Duarte et al.,[22] 0 = smooth surface; 1 = surface with slight roughness; 2 = surface with moderate roughness; 3 = surface with severe roughness. The interexaminer agreement was assessed by the Kendall test. The results obtained for each group were analyzed by nonparametric Kruskal-Wallis test. The significance level was set at 5%. Scores attributed to specimens of bur and laser group for analysis of surface roughness are shown in [Table 3].
Table 3: Roughness scores

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Kendall test showed high interexaminer agreement. Laser resection shows significantly smoother root-end surfaces than the bur resection. Scores were analyzed by Kruskal-Wallis test (P < 0.05).

Dentinal cracks

For crack detection under SOM, ×16 was utilized and under SEM, ×25 to ×100 was utilized. At higher magnification, wherever the microcracks were seen, they were also noted.

Under SOM, bur root resection revealed no cracks in 19 (95%) samples [Figure 7]a, rest one sample revealed a crack [Figure 7]b, while laser root resection revealed no cracks in all 20 samples [Figure 7]c. The difference between the groups is statistically not significant [P = 0.3111; [Table 4] and Graph 4].

Under SEM, bur root resection revealed no cracks in 4 (20%) samples [Figure 8]a, rest 16 samples (80%) revealed cracks [Figure 8]b and c, with microcracks at high magnification in almost all samples [Figure 9]a and b].
Figure 7: Surgical operating microscope bur resected samples (a) no cracks seen in 95% samples; (b) crack (arrow) seen in 5% samples; (c) lased samples no cracks observed in 100% samples

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Figure 8: Scanning electron microscope bur resected samples (a) no cracks in 20% samples; (b and c) cracks (arrows) seen in 80% samples (a: ×25, b: ×60, c: ×50)

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Figure 9: Scanning electron microscope (a) ×400 (b) ×1000 bur resected samples show microcracks (arrows) at high magnification in almost all samples

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Table 4: Evaluation of dentinal surface cracks

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While laser root resection revealed cracks in very few 3 (15%) samples [Figure 10]a and no crack in 17 (85%) samples [Figure 10]b and c out of 20 samples, very few lased samples show microcracks [Figure 11]. The difference between both groups is statistically significant [P < 0.001, [Table 4] and Graph 5].
Figure 10: Scanning electron microscope laser resected samples (a) reveal cracks (arrow) in 15% samples, (b and c) no cracks in 85% samples under scanning electron microscope (a: ×30, b: ×28, c: ×45)

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Figure 11: Scanning electron microscope × 2800 microcracks (arrow) in very few laser resected samples

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  Discussion Top

The ideal goal of apical surgery is to create optimum conditions for healing by sealing any path from the root canal to the periradicular tissues. [23] Therefore, the identification and treatment of possible pathways, such as isthmuses, accessory canals, and cracks or microfractures, is of utmost importance to avoid the recurrence of leakage with subsequent infection. The introduction of microsurgical principles almost 15 years ago, including microinstruments, well-focused illumination, and magnification, led to a realization of the importance of detecting above-mentioned microscopic findings to improve the healing outcome of apical surgery. [1],[2],[24]

The recent experimental studies have evaluated and compared the effectiveness of different visual aids in identifying microstructures after root-end resection. An experimental study showed the enhanced accuracy of crack identification in extracted human teeth with increasing magnification; however, the overall accuracy ranging between 39% and 58% was lower than expected. [25] Using transillumination of the root-end, whether alone or in combination with a dye, was reported as a more accurate way of diagnosing root-end dentinal cracks. [26] Another experimental study compared endoscopy with SEM for the detection of microelements at the cut root face in extracted human teeth after root-end resection. [27]

The present study evaluated the identification of dentinal cracks and smoothness after root-end resection in extracted human incisors under SOM (×16) and SEM (from ×25 to ×30,000). Under SEM, bur group revealed cracks in 16 samples while laser group showed the same only in 3 samples. However, because crack identification was only performed at the resection plane (i.e., 3 mm from the apex), it can be speculated that incomplete canal cracks might be complete canal cracks and vice versa in a different plane. [28] The clinical significance of dentinal cracks identified during apical surgery has not yet been clarified. A complete canal crack might contribute to leakage resulting in the recurrence of periapical infection and might explain surgical (and nonsurgical) failures in an unknown number of cases.

Findings of the present study were in accordance with Slaton et al. [27] as they reported that the dentin around the area of strain became opaque or frosted in appearance [Figure 12]a before a crack developed [Figure 12]b and c. The authors speculated that these changes were caused by the formation of many microscopic cracks that had not yet formed a macrocrack. This finding should heighten the clinician's suspicion that a crack may be present. One of the concerns in apicoectomy is the manner in which root-end resection is performed. [29],[30]
Figure 12: Sample (bur resected) shows (a) opaque frosted appearance (arrows) of dentin under surgical operating microscope (×16) (b and c) crack developed exactly at the same site (arrows) detected under scanning electron microscope (×25 and ×60)

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Hence, depending on the type of instrument used, surface roughness and cracks may occur. [7],[9] Resected root dentine should present smooth and regular surface so as to favor reparation. [8] Stem cells proliferation and differentiation are also known to be dictated by the surface on which the cells grow. [31],[32],[33] Important biologically active growth factors are trapped in the dentin matrix during dentinogenesis. Some of these growth factors such as vascular endothelial growth factor and transforming growth factor beta 1 [34],[35] are known to have a robust effect on differentiation and/or proliferation of mesenchymal stem cells for regeneration of PDL.

The laser used in the present study yielded good results in terms of surface smoothness and regularity and cracks. In this study, root resected with Er,Cr:YSGG laser presented smoother surface, less damage and cracks in Cementum and Dentin as compared to #702 TC Bur [Table 5].
Table 5: Overall comparison between lased and bur resected samples for cemental damage, dentin cracks, and surface characteristics

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Hence, less damage to cementum and dentin leads to more uniform smoother surface with the presence of microroughness, contributes to PDL cell attachment on resected root-end, and is favorable for the creation of conducive microenvironment for better tissue regeneration. [36],[37],[38],[39],[40],[41]

These findings agree with Kinoshita et al., [7] Karlovic et al., [8] Komori et al., [9] Paghdiwala, [10] Asnaashari et al., [11] Wallace, [15] who observed improved surface irregularity and smoothness after apicoectomy performed with laser.

However, in vitro (using endoscope ×64, atomic force microscope, dye leakage/staining) and in vivo studies are necessary to determine the influence of irregularities and topography on the apical healing process after periradicular surgery.

Whether radicular dentinal cracks can enlarge during functioning and in this way result in future leakage pathways or root fractures remains to be investigated. [42] Whether there is a need for extending root-end cavity preparation to include and to obturate canal cracks identified at the resection level is a topic for future clinical research.

  Conclusions Top

Hence, it can be concluded that Er,Cr:YSGG laser root resection as compared to #702 TC Bur root resection exhibits:

  • Less damage to cemental surface
  • Dentinal surface appears to be smoother
  • Less surface cracks and microcracks can be revealed.
In addition to these observations, laser root resection provides a resected surface devoid of smear layer, debris; exposed collagen of dentin surface with absence of any sign of thermal damage-all leads to conducive surface for healing by regeneration remains to be discussed in Part II of the present study.


I would like to thank the Department of Sophisticated Analytical Instrument Facility, Bose Institute, Kolkata, for providing technical and instrumental support; and Dr. Sakshi Jain, Final year PG Trainee, Department of Conservative Dentistry and Endodontics of Dr. R. Ahmed Dental College and Hospital, Kolkata, for technical help to carry out this study.

Financial support and sponsorship


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], [Figure 6], [Figure 7], [Figure 8], [Figure 9], [Figure 10], [Figure 11], [Figure 12]

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


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