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ORIGINAL ARTICLE
Year : 2018  |  Volume : 8  |  Issue : 2  |  Page : 123-127

The alignment of ultrasonic root-end cavity preparations using an in situ cadaver model


1 Department of Dentistry, Prince Sultan Military Medical City, Riyadh, Kingdom of Saudi Arabia
2 Department of Dentistry, King Faisal Specialist Hospital and Research Centre, Riyadh, Kingdom of Saudi Arabia
3 Department of Dentistry, Al Wakra Hospital, Hamad Medical Corporation, Al Wakra, Qatar

Date of Web Publication5-Apr-2018

Correspondence Address:
Dr. Abdullah Ali Al-Sharif
Department of Dentistry, Prince Sultan Military Medical City, Postal Box 7897, Riyadh 11159
Kingdom of Saudi Arabia
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/sej.sej_79_17

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  Abstract 

Aim: This study aims to compare the alignment of root-end cavities prepared with ultrasonic tips with the root canal outline in teeth with and without root canal fillings using an in situ cadaver model.
Materials and Methods: Twenty-eight bilaterally matched pairs of human teeth from five cadavers were equally divided into two groups: teeth with root canal fillings (RCF) and teeth without root canal fillings (NRCF). The resected root surface was stained with methylene blue and examined under magnifying loops; then, the root-end cavities were prepared in both groups using ultrasonic tips and filled with amalgam. The teeth were carefully extracted, mounted in resin blocks, radiographed from two angles, and then sectioned at 3 mm from the root end. The alignment of root-end cavities in both groups was compared using defined criteria.
Results: The RCF group had a significantly higher incidence of centered root-end preparations than NRCF group on the buccolingual (79% vs. 64%) and mesiodistal (64% vs. 24%) directions. However, both groups showed high incidence of deviated cavities at the horizontal cross-section and the difference between them was not significant.
Conclusions: The presence of root canal filling improved the alignment of root-end cavities prepared with ultrasonic tips.

Keywords: Cadaver model, periapical surgery, retrograde filling, root-end cavity, ultrasonics


How to cite this article:
Al-Sharif AA, Almanea EA, Ahmad IA. The alignment of ultrasonic root-end cavity preparations using an in situ cadaver model. Saudi Endod J 2018;8:123-7

How to cite this URL:
Al-Sharif AA, Almanea EA, Ahmad IA. The alignment of ultrasonic root-end cavity preparations using an in situ cadaver model. Saudi Endod J [serial online] 2018 [cited 2019 Sep 15];8:123-7. Available from: http://www.saudiendodj.com/text.asp?2018/8/2/123/229357


  Introduction Top


The major objective of periapical surgery is to prevent the invasion of bacteria and their by-products from the root canal system into periradicular tissues.[1],[2] It is indicated for teeth with failed previous root canal treatment where nonsurgical retreatment is technically difficult or impractical or when a biopsy is required.[3],[4]

Root-end cavity preparation is an important step in establishing an apical seal. The goal is to prepare a cavity in the resected root surface that is dimensionally adequate for placing the root-end filling while avoiding unnecessary damage to the root-end structures. According to Carr, an ideal root-end preparation should (i) clean and shape the apical 3 mm of the root; (ii) be parallel to and coincident with the anatomic outline of the pulp space; (iii) has adequate retention form, and (iv) remove all isthmuses tissue without weakening the remaining dentinal walls.[5]

Over the years, many root-end preparation techniques were used including burs, sonic devices, ultrasonic devices, and lasers.[6],[7],[8],[9],[10],[11],[12] In 1957, Richman [13] introduced ultrasonics to endodontics and used a modified periodontal chisel scaler for canal debridement and apicoectomy. Later, Bertrand et al.[6] presented a modified cavitron device for root-end preparation. In the early 1990s, Carr introduced specifically designed ultrasonic tips for root-end cavity preparation.[5] Since that time, different commercial products were marketed and evaluated for their efficiency and safety.

The major advantages of ultrasonics technique over the traditional bur technique include deeper and more conservative cavities that follow the outline of the root canal space, better preparation of anatomical difficulties such as isthmuses and smaller size of bony crypts and minimal bevel of the root-end are needed.[8],[10],[14] Furthermore, this technique has a significantly better treatment outcome compared to bur technique.[15],[16] Based on these advantages, the ultrasonic tips are currently considered the ideal tools for root-end cavity preparations.

The majority of the aforementioned studies compared the quality of root-end preparations in root canal-filled teeth. However, the clinician may encounter clinical situations where periapical surgery is indicated in teeth without root canal fillings (i.e., calcified or blocked canals). Beling et al.[17] compared the occurrence of cracks during ultrasonic root-end preparation in gutta-percha filled roots and uninstrumented roots and found no significant differences between the two groups with regard to the number and type of cracks. However, these authors did not evaluate the alignment of root-end preparation with the root canal outline in filled and unfilled roots. Therefore, the aim of this study was to evaluate whether the presence of root canal filling affects the alignment of the root-end cavities prepared using ultrasonic tips with the root canal outline.


  Materials and Methods Top


The study was conducted in full accordance with the World Medical Association Declaration of Helsinki, and ethical clearance was obtained from the ethical committee in the institution.

Study sample

Twenty-eight bilaterally matched permanent teeth (14 anteriors, 8 premolars, and 6 first molars) from five adult human cadavers were selected. The teeth were evaluated with preoperative radiographs and transillumination to exclude the presence of previous root canal treatment, endodontic surgery, post, tooth crack, or root fracture. Radiographs were taken at 70 kVp and 15 mA (SS White, model 90s) using Kodak E-speed film (Eastman Kodak, Rochester, NY, USA).

The included teeth were equally divided into two groups: teeth with root canal fillings (RCF) and teeth without root canal fillings (NRCF). All the subsequent procedures were performed by one experienced endodontist. In RCF group, access cavity preparation was made, and working length was determined radiographically from a coronal reference to a distance 0.5 mm short of the radiographic apex. After coronal flaring with sizes #2 and #3 Gates Glidden drills (Caulk/Dentsply, Milford, DE), root canals were instrumented manually using a balanced force technique with standardized K-files to size 35 master apical file. The canals were irrigated with 5.25% sodium hypochlorite during the instrumentation phase. Then, the canals were dried with sterile paper points and obturated with laterally condensed gutta-percha and AH26 sealer (Dentsply, Milford). The teeth in NRCF group were neither instrumented nor obturated.

Surgical procedures

In order to stimulate the clinical situation, skulls were mounted with yellow stone and manikin and attached to the dental chair. In addition, all subsequent surgical procedures were performed by the same endodontist at 4 o'clock position approach.

The apices of all roots were located using the preoperative radiographs, and the apical bone was removed using a high-speed round bur. The size of bony crypt was determined by the need for access and visualization to complete root-end preparation and filling. Then, the roots were resected 3 mm from the apex perpendicular to their longitudinal axis using a surgical bur # 701 (Shanghai S and D Dental International Co) under constant water coolant.

The resected surface was stained with methylene blue dye (Roth International, Chicago, IL, USA) and examined under magnifying loops (×4.5) to determine root outline, locate apical foramen, and exclude any crack after apical resection. Later, a 3-mm root-end cavity was prepared with S #13 Neosonic ultrasonic tip (Amadent Co., Cherry Hill, NJ, USA) using a feather-like back and forth motion with slight coronal pressure. The unit was set at power 10 W with constant water coolant to avoid overheating. Then, the cavities were washed, dried, and an amalgam filling (Valiant Ph.D., Caulk/Dentsply, Milford, DE) was placed with a Messing gun (Union Broach Corp., Emigsville, PA, USA) and condensed using retrofilling condensers (MAR-SAC#1 and #5). Excess amalgam was removed from the root-end surface, and the filling was burnished (MAR-B#3 and #4).

The included teeth were extracted carefully, and the roots were inspected visually for any perforation. The palatal roots of maxillary molars were not included in this study and were removed with no. 557 bur. Then, the teeth were mounted in an acrylic resin, and two radiographs from the straight (buccolingual) and proximal (mesiodistal) directions were taken. The alignment of the cavity preparation with the long axis of the root was evaluated by measuring the angle between the long axis of the amalgam filling and the long axis of the root canal [Figure 1]. Each radiograph was evaluated by two endodontists who agreed on a score according to the criteria outlined in [Table 1]. Finally, each root was sectioned perpendicular to its long axis at 3 mm from the apical end. Each resected surface was stained with methylene blue and viewed under light microscope (Carl Zeiss Microscopy, Germany) at ×25 magnification. The deviation of the root-end filling from the canal outline was evaluated by measuring the distance between the inner edge of the filling and the outer edge of the canal according to the following criteria: no deviation (0 μm), mild deviation (<250 μm), moderate deviation (250–500 μm), and severe deviation (>500 μm). Comparisons between the two groups were analyzed with Chi-square test with the significant level set at P < 0.05.
Figure 1: Alignment of the root-end preparation was assessed radiographically by measuring the angle between the long axes of the root canal (green line) and the root-end filling (red line)

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Table 1: Radiographic evaluation criteria

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  Results Top


During the study, four roots fractured (three during obturation and one during extraction) and they were excluded from the study along with their contralateral roots. Therefore, a total of 66 root-end preparations remained for evaluation.

None of the root-end preparations had root perforation or stripping. [Table 2] summarizes the radiographic deviation of root-end fillings from the long axis of the root canals. In the RCF group, the incidence of deviation was 21% on the straight and 36% on the proximal radiographic projections [Figure 2] and [Figure 3]. The NRCF group had a greater deviation in both the straight and proximal projections (36% and 76%, respectively). The statistical analysis showed that the RCF group had a significantly less deviation on both radiographic projections than the NRCF group.
Table 2: Radiographic assessment of retrograde filling deviation from root canal outline

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Figure 2: Alignment of root-end cavity in a root canal-filled tooth. (a) Buccolingual view and (b) mesiodistal view

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Figure 3: Alignment of root-end cavity in a tooth without root canal filling. (a) Buccolingual view and (b) mesiodistal view

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The deviation of the root canal fillings from the canal outlines at 3 mm from the root-end surface is shown in [Table 3] and [Figure 4]. Although the deviation of the fillings in the RCF group was lower than the NRCF group (60% vs. 64%), the difference was not statistically significant.
Table 3: Microscopic assessment of retrograde filling deviation from the root canal outline

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Figure 4: Examples of microscopic alignment of root-end cavities found in the current study. (a) Centered preparation and (b) severely deviated preparation

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  Discussion Top


The current study evaluated the alignment of root-end cavities with the root canal outline in RCF and NRCF. An unfilled apical portion of the canal may be found in canals with coronal calcifications or blockage due to fractured instruments or ledge formation. In addition, it is not unusual to detect missed canals during periapical surgery. In these clinical situations, root-end preparation becomes more challenging as improper orientation of the cavity may weaken the apical portion of the root and jeopardize the apical seal.

To replicate the clinical situation, this study used bilaterally matched teeth from human cadavers instead of extracted teeth. The presence of the periodontal ligament around cadavers' teeth reduces the stress on the roots during nonsurgical and surgical endodontic treatment by distributing the generated forces to the surrounding tissues.[18],[19] The generated forces in the current study were also reduced by manual preparation of the root canals, preparation of root-end cavities with light coronal pressure under constant water cooling, and atraumatic extraction of teeth after the surgical treatment was done. Bilaterally matched pairs of teeth were used in an attempt to minimize differences between the two groups with regard to tooth morphology and circumstances of the patient's dentition such as occlusal dysfunctions or trauma.[20]

Clinically, treatment outcome of periapical surgeries is primarily based on evaluation of periapical radiographs. The main disadvantage of this approach is the fact that these radiographs provide only a two-dimensional view of the teeth. To overcome this shortcoming, a second radiograph was taken from the proximal surface. A number of materials have been used to seal root-end cavities including amalgam, composite resins, super-ethoxy benzoic acid, mineral trioxide aggregate, and biodentine. Although amalgam is not commonly used nowadays as a retrograde filling material, it was used in the current study because it is easily manipulated and has a high radiopacity that facilitated evaluation of the orientation of the end-preparations relative to their canal outlines. In the current study, the NRCF group showed a significantly higher deviation than the RCF group on both the straight and proximal radiographic views [Table 2]. Mehlhaff et al.[14] used a similar radiographic technique and found that all root-end cavities prepared with burs showed deviation from the canal's outline compared to 2.6% of ultrasonically prepared cavities. The difference between this study and our findings may be attributed to the criteria used to measure the deviation. Mehlhaff et al. considered the cavity deviated if the base of the filling material was outside the canal space, while in the current study, we measured the angle between the root-end filling and the canal space and considered cavity deviated even if there was a small angle between them. A higher incidence of deviation in both groups was also noted in the current study when the roots were sectioned horizontally 3 mm from the root end. This can be explained by the fact that we measured the distance between the filling material and the canal outline in both the buccolingual and mesiodistal directions and recorded the highest value.

The findings of the current study showed that the alignment of root-end cavity preparations varied according to the presence of root canal filling material and the radiographic view. The cavities prepared in RCF group deviated less than those in NRCF group, suggesting that the root canal filling can serve as a guide for the ultrasonic tip during cavity preparation. The radiographs taken from the proximal direction had higher deviation than those taken from the buccal direction. This may be explained by the fact the buccolingual dimension of the roots is usually wider than the mesiodistal dimension. The ultrasonic tips have round cross-sections, and therefore, the ability to center the tip during the preparation is better when the distance between the root's walls is smaller. Clinically, radiographs taken from the buccal view are used to evaluate the quality of root-end fillings, and therefore, they should be interpreted carefully as they may give an illusion of centered root-end preparations in otherwise deviated preparations. Other factors such as the presence of root curvature and the location of the tooth may affect the alignment.

There are several clinical tips that can be used to improve the alignment of the root-end preparations with the root canal outline. The apical region should be carefully evaluated on periapical radiographs taken at different angulations. Advanced radiographic techniques such as cone-beam computed tomography may be also used to provide three-dimensional information regarding the location and orientation of the root apex and its relationship with the adjacent anatomical structures in challenging cases. All surgical procedures should be conducted under dental operating microscope as it provides proper illumination and magnification of the operating field and enhances treatment efficiency and outcome. The root surface should be resected with no or minimal bevel and stained with a dye to delineate the root outline. Then, the ultrasonic tip should be aligned with the long axis of the root and used in “sweeping” motion, especially in the buccolingual dimension, with periodic evaluation of the preparation.


  Conclusions Top


The presence of root canal filling improved the alignment of root-end cavities prepared with ultrasonic tips. Greater deviation of the cavities was noted in the buccolingual dimension of the roots which cannot be viewed on periapical radiographs taken from the straight projection.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

 
  References Top

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    Figures

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

  [Table 1], [Table 2], [Table 3]



 

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