Tailor-made endodontic obturator for the management of Blunderbuss canal.

The complex anatomy of the blunderbuss root canal often poses a major challenge to accomplish adequate obturation for a biological seal. Moreover, the roll-cone, Gutta-percha obturation technique, which is routinely practiced, also results in a mismatch and failure to configure to the canal volume in the absence of an apical barrier. Hence, an attempt has been made to tailor-make a heat polymerized polymethyl methacrylate resin as an endodontic obturator, to match the canal volume, which has been ascertained by Spiral computed tomography and mathematical integration. A one-year follow-up examination has revealed that the tooth is asymptomatic, with the repair of the lesion evident radiographically.

INTRODUCTION

Despite every effort being taken to stimulate the genetically programmed formation of root barrier that remains open following early pulp death, apexification is not always achieved. This may be attributed to factors where there is a non-conducive response of the Hertwig's epithelial root sheath in the formation of a biological barrier.[12] Apexification also generally fails in cases where there is a defective access seal, inadequate cleaning and sanitizing of the wide open canals, and environmental contamination during the procedure, which are exaggerated in non-compliant patients. The failure to achieve the desired outcome can often be asserted if closure is yet to occur even after two years.[1]

The ‘blunderbuss’ anatomy of the canal often poses an array of difficulties to achieve adequate obturation for successful endodontic therapy. Customization of the gutta-percha to mold to the shape of the canal has been attempted, but often results in apical extrusion and subsequent trauma to the periodontal tissues, in the absence of an apical barrier.[3] Furthermore, the presence of a thin fragile dentinal wall enhances their susceptibility to fracture during instrumentation and compaction.[9] In a quest to overcome some of these existing pitfalls, the present era of modernization, technology, and availability of various biomaterials have augmented our desire to tailor-make a heat polymerized polymethyl methacrylate (PMMA) resin as an obturating material. This case report highlights the endodontic obturator, which has been equated precisely to the volume of the canal in all dimensions using ‘Spiral CT’ and the ‘Mathematical segmental integration technique.’

CASE REPORT

A 16-year-old male patient reported to our hospital, and presented with pain and discharge in relation to the right maxillary incisor. On elaborating the history of present illness, pain was found to be intermittent in nature, with recurrent sinus tract formation, specific to the right maxillary central incisor (tooth #11). His past dental history reveals apexification being attempted for two years in the same institution, but in vain, due to the patient's incompliance to adhere to the clinical protocol. On intraoral examination, a sinus opening with discharge was located on the mucolabial fold, distal to the apical region of tooth #11. Thermal and electric pulp tests showed that the right maxillary central incisor did not respond to the vitality tests, whereas, all the adjacent teeth displayed a normal response, which suggested that tooth #11 was non-vital. Furthermore, the intraoral periapical radiographs demonstrated an incompletely formed root, with a blunderbuss apex, surrounded by periradicular rarefaction in relation to tooth #11. Also, the radicular dentin was thin and fragile with apically divergent canals, as is evident in Figure 1a.

Figure 1

Intraoral periapical radiographs in relation to tooth # 11. (a) Preoperative radiograph showing the blunderbuss canal with periradicular lesion, (b) Immediate postoperative radiograph showing apical 3 mm of MTA and Endodontic obturator in place

In order to assess the exact nature of the periapical tissues, with the patient's consent, an ultrasound was performed with a modified transrectal probe. A hypoechoic lesion measuring 6.5 × 5.6 mm, with posterior acoustic enhancement, consistent with fluid collection, was seen near the root tip of the right maxillary central incisor [Figure 2a]. This loculation was associated with a focal erosion of the anterior wall of the alveolar socket, confirming the features of a chronic periapical abscess. From the above-mentioned findings, it was decided not to pursue with apexification, and hence, an alternative method of treatment was instituted, which involved the fabrication of a ‘tailor-made endodontic obturator’ for adequate obturation, to precisely match the root canal volume and defect with the aid of ‘Spiral CT’ and ‘Endometrics’.

Figure 2a

Ultrasound showing hypoechoic images with disruption of the anterior wall of the alveolar socket of the tooth involved

The treatment was divided into three phases

Preparatory phase: The access cavity was modified and the coronal third of the canal was prepared to obtain parallelism, with minimal alteration of the effective radicular dentin thickness. A wax pattern of the canal was taken using a 110-size file as a sprue pin, in a manner similar to that of a custom-cast post. The wax pattern was heat processed following the steps of flasking, dewaxing, and acrylization, to obtain a heat polymerized acrylic resin obturator [Figures 3a and b]. The patient was then subjected to spiral CT, which clearly demonstrated the defect in relation to tooth #11 [Figure 2b]. From the spiral CT images, the volume of the canal space was precisely calculated, which was found to be 152.296 cu mm. The volume of the resin obturator was also calibrated using the mathematical segmental integration technique, wherein, the specimens were divided into different segments of 3 mm length, and the width of these segments was measured. Each segment could be considered as a truncated pyramid and the volume was calibrated using the formula:

Figure 3

(a) Wax pattern of the canal with 110-size file used as a sprue pin, (b) Heat polymerized PMMA resin obturator

Figure 2b

Computed Tomographic image demonstrating enhanced canal volume and defect

Volume = H / 3 (A2 + B2 + √AB)

where H was the thickness of specimen, A was the area of the cross-section at the top portion, and B was the area of cross-section at the bottom portion.

The total volume of the entire specimen was computed by integrating the individual segments, which was found to be 149.625 cu mm. The apical 3 mm of the obturator was sectioned with a diamond disk to accommodate for Mineral Trioxide Aggregate (MTA) as a root-end filling material.

Surgical phase: A mucoperiosteal flap was raised in the maxillary anterior region and the bony defect located. Following thorough debridement and curettage of the periapical lesion, the palatal cementum was retained and MTA was placed as a retrograde material and condensed against the resin obturator within the canal, which acted as a template. The resin obturator was then removed and a moist cotton pellet placed in contact with the MTA for 24 hours, to ensure its complete set as suggested by earlier studies.

Obturation phase: After 24 hours the moist cotton pellet was carefully retrieved and obturation was completed by luting the endodontic obturator with dual cure resin cement. The access cavity was sealed with a light activated hybrid composite, as was evident from the postoperative radiograph [Figure 1b]. Six- and twelve-month follow-up radiographs demonstrated a significant reduction of periapical radioluscency, with no symptoms [Figures 4a and b].

Figure 4

Follow-up periapical radiographs in relation to tooth # 11. (a) six-month follow-up radiograph showing reduction in periapical radioluscency, (b) one-year follow-up radiograph with marked reduction in periapical radioluscency

DISCUSSION

The failure of apexification could be attributed to the probable destruction of the Hertwig's epithelial root sheath and the non-conducive environment in relation to the periapical region of tooth #11, which was evident from the hypoechoic images obtained with the ultrasound. Ultrasonography depicts the true nature of the lesion within the bone in three dimensions, and their content in terms of fluids, tissue, and vascularity, with the precise measure of the diameters of the lesion.[56] Roll-cone Gutta-percha obturation with lateral compaction is not the technique of choice, due to lack of resistance of the thin fragile dentinal walls to lateral pressure, as greater bulk of Gutta-percha requires a greater force for compaction.[4] Henceforth, customization of an obturator to match the canal volume without lateral compaction will be attempted using PMMA, which is extensively used in the field of medicine for fixation of orthopedic implants, test kits, diagnostics, and so on, and this demonstrates its excellent biocompatibility with tissues.[7] Also, heat polymerization of PMMA markedly increases the degree of conversion, reducing the availability of free monomers. Furthermore, the inherent ability of these acrylic resins to be custom formulated has enabled us to tailor-make a heat polymerized acrylic resin, as an endodontic obturating material.

Computed Tomography (Spiral CT) was employed to precisely calibrate the volume of the canal in cubic millimeter, and furthermore, the CT images obtained also confirmed the nature of the periapical tissues.[5] The volume of the heat polymerized endodontic obturator was calculated by mathematical integration, in order to precisely equate the canal volume using endometrics. The palatal cementum of the root end was retained for the specific reason that the cementum thickness on the palatal aspect was usually found to be thicker compared to the buccal portion, which facilitated the healing process.[89] MTA was used as a root end filling material, which was placed in two steps, as the two-step retrograde placement technique exhibited less leakage compared to one-step placement. Furthermore, Gray MTA was used in a 3 mm thick barrier in preference to white MTA, because Tetra calcium aluminoferrite was absent in the white formulation, which could be responsible for its altered properties. As both materials appeared clinically set and showed no difference in hardness, it was hypothesized that slight volumetric shrinkage occurred with the white product, which accounted for the increased leakage between MTA and the root dentin, and this substantiated the preference of Gray MTA.[1011] Dual cure resin cement was used for luting the endodontic obturator into the canal, which might compensate for the 1.7% volumetric linear shrinkage exhibited by the resin obturator during fabrication by heat polymerization. Furthermore, the resin cement showed enhanced resistance to shear stress, and the access cavity was sealed with a hybrid light cure composite resin, to ensure an adequate coronal seal.[1213] One of the drawbacks of PMMA was, it was less radio opaque. In future, few radio opaque materials like Barium Sulfate could be added to the endodontic obturator. Retrievability in case of re-treatment, could be accomplished by progressively drilling through the middle of the post like the Fiber Reinforced Composite post.[14]

Despite the potential residual infection and the serious damage caused, MTA at the apical 3 mm, effectively promoted regeneration of the apical tissues, producing a desirable apical barrier, which was evident from the follow-up radiograph after a one-year period.