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Treatment of Teeth with Open Apices Using Mineral Trioxide Aggregate

During tooth development, the inner and outer dental epithelia fuse and form the cervical loop, which results in Hertwig’s epithelial tooth sheath, a structure responsible for root formation.1 The presence of healthy pulp is essential for root development and apical closure. An injury sustained between the ages of 6 and 14 can adversely affect a patient’s pulpal health and interrupt or arrest root development.2 When the pulp is vital and the apex is not fully formed, it is imperative to maintain pulp vitality for dentin formation.3 Apexogenesis, which allows continued root formation and normal apical closure, is generally the optimal treatment for traumatized immature teeth with vital pulps. The severity of the injury influences the vitality of the pulp, which can be maintained by either direct pulp capping or pulpotomy. Successful treatment, however, is dependent on the extent of pulpal damage and the potential of restoring the involved tooth.4 Materials that have traditionally been used for pulp capping or pulpotomy include calcium hydroxide,5 osteogenic protein-1,6 dentin bonding agents,7 and mineral trioxide aggregate (MTA).8

When a severely inflamed or necrotic pulp in a tooth with an immature apex requires removal, root canal therapy is difficult to accomplish due to the presence of thin, fragile walls and the open apex.9 In these instances, apexification (root-end closure) is generally the preferred treatment. This procedure involves removal of the inflamed or necrotic pulp from the root canal, asepsis of the system, and provision of an environment for closure of the apical foramen. It has been suggested that control of the infection enables the apical development in nonvital teeth to be resumed.10 Numerous materials have been recommended to enhance apexification, including Tricresol and Formalin,11 antibiotic pastes,12 tricalcium phos­phate,13 collagen-calcium phosphate gel,14 calcium hydroxide in various mixes,9,15 as well as growth factors and bone morphogenic proteins.16,17 One widespread treatment for immature teeth with severely inflamed or necrotic pulps is apexification utilizing calcium hydroxide as an intracanal medication. The inherent disadvantages of this technique are the necessity of multiple visits over an extended period, the unpredictability of treatment results, and the reliance on patient compliance. An alternative to apexification requires the placement of an apical barrier to prevent the extrusion of filling materials during obturation. Various materials (ie, tricalcium phosphate,18 dentin chips,19,20 calcium hydroxide powder,21 and MTA17) have been utilized for this purpose.

The MTA material is characterized by its favorable sealing ability and biocompatibility. It has demonstrated significantly less dye and bacterial leakage when compared to investigations of amalgam, IRM, and Super EBA.22,23 In 1996, Ford et al also reported the use of MTA as a pulp-capping material.8 In a recent canine study, Shabahang et al demonstrated that apical hard tissue formation with MTA was significantly more predictable than calcium hydroxide or osteogenic protein-1.17 Mineral trioxide aggregate has also been successfully used for the repair of lateral24 as well as furcal perforations,25 and has been observed to stimulate cytokine production in human osteoblasts.26 The following three case presentations demonstrate the use of MTA in vital pulp therapy (ie, apexogenesis) and the formation of an apical barrier in permanent teeth with open apices.

Case Presentations

Case 1

An 8-year-old girl presented with a fracture of tooth #8(11). The patient suffered a traumatic injury 6 days previously and was referred for endodontic evaluation. The patient’s medical history was noncontributory and no known drug allergies were noted. Although the patient experienced sensitivity during biting, the trauma caused no further discomfort or pain. The exposure of the pulp horn was revealed by clinical examination under 310 magnification with a surgical microscope and probing with a size 50 (ISO) endodontic file, and the presence of an open apex was confirmed via radiographic evaluation (Figure 1A). These examinations and an elevated, nonlingering response to cold indicated the presence of reversible pulpitis in the tooth, which had normal periradicular tissues. It was determined that a shallow pulpotomy would enable further root development.

Under local anesthesia (2% lidocaine with 1:100,000 epinephrine) and rubber dam isolation, an access cavity was prepared and the coronal 2 mm of the pulpal tissue was removed using a sharp, round diamond bur in a high-speed handpiece under copious water irrigation. Following irrigation with sodium hypochlorite (NaOCl), the surface of the exposed pulp was disinfected for 5 minutes using a cotton pellet saturated with 5.25% NaOCl. A thick mixture of MTA was placed over the exposed pulp and subsequently covered with a moist cotton pellet to ensure the complete setting of the material (Figure 1B). The access cavity was then restored with a provisional sealing material.

The initial healing of the site was evaluated 2 weeks postoperatively, at which time no sensitivity to percussion or palpation was noted on the maxillary incisors. Utilizing a direct composite resin procedure, the tooth was restored by the patient’s general practitioner. At the 6-month recall evaluation, no complications were evident in the treated site, and all teeth were within normal testing limits.

Eight months postoperatively, the patient experienced pain associated with tooth #9(21). Following thermal testing, the tooth was diagnosed with reversible pulpitis, and a shallow pulpotomy was performed using MTA. The existing composite restoration — placed to restore the fractured incisal edge following injury — was removed, and access was gained into the pulp chamber. At the time of initial injury, this tooth responded within normal limits to thermal testing as well as percussion and palpation. Using a sterile diamond bur, 2 mm of pulpal tissue was removed; bleeding was controlled by irrigation with 5.25% NaOCl and direct pressure, which was applied with cotton pellets. A thick barrier of MTA was placed over the exposure site, and a wet pellet was placed over the material. The access cavity was provisionally restored as aforementioned.

Two weeks following the second pulpotomy, the teeth responded within normal limits to pulp testing. Upon 3-month reevaluation, no sensitivity to percussion or palpation was determined. Each incisor responded to electric pulp testing, and no periodontal pocket measurements greater than 3 mm were noted (Figure 2A). At 1 year, all teeth continued to be free of symptoms and responded to pulp vitality testing. Radiographic examination demonstrated continued root development with closure of the apical foramen in both central incisors (Figure 2B). Apical closure and normal periapical tissues were evident in the 2-year postoperative radiograph of the site (Figure 3). At this interval, the teeth demonstrated normal responses to thermal and electric pulp testing, and no palpation or percussion sensitivity was observed.

Case 2

A 10-year-old boy presented for treatment of an anterior tooth 1 month following dental trauma. Clinical evalua­tion revealed an incisal edge fracture of tooth #8(11). Further­more, an intraoral swelling and a sinus tract stoma were noted superior to this central incisor. Radiographic exami­nation demonstrated the presence of a partially developed root and a periapical radiolucent lesion that was associated with the maxillary right central incisor (Figure 4). Pulp testing was performed, and all teeth — except tooth #8(21)—responded to thermal testing. The maxillary right central incisor was diagnosed as necrotic with a chronic periradicular abscess. The available treatment options were discussed with the patient and his parents, and root canal therapy using MTA as an apical barrier was selected.

Under local anesthesia (2% lidocaine with 1:100,000 epinephrine) and rubber dam isolation, the necrotic tissues were removed, and the canal was thoroughly debrided and irrigated with 5.25% NaOCl. A thick mixture of calcium hydroxide powder and sterile saline was placed in the canal as an intracanal dressing and maintained for 3 weeks. During the subsequent appointment, the canal was rinsed with NaOCl to remove the calcium hydroxide, dried, and a 3 mm apical plug of MTA was placed using a small carrier and pluggers (Figure 5). A moist cotton pellet was placed over the MTA and the access cavity was sealed with provisional filling material. One month following this procedure, the cotton pellet was removed and the remainder of the canal was obturated with warm gutta-percha and sealer. The definitive composite resin restoration was placed to seal the access cavity using a direct technique (Figure 6A). Upon reevaluation 6 months postoperatively, no sensitivity was noted to percussion or palpation. The sinus tract over the right central incisor had healed completely, and the perio­dontal pocket depths measured 3 mm or less. Radio­graphic evaluation demonstrated the complete healing of the periapical lesion and the formation of a band of hard tissue that surrounded the MTA plug (Figure 6B).

 

Case 3

An 8-year-old boy presented for treatment following a luxation injury to the maxillary left central incisor. In order to achieve stabilization, the tooth was splinted for a 2-week period. The patient was recalled after 4 months, at which time the presence of ankylosis was noted (Figure 7). During the 2-year recall appointment, clinical and radio­graphic examinations revealed the infraocclusion of the maxillary left central incisor and radiographic indications of replacement resorption (Figures 8 and 9). Further evaluation demonstrated the presence of a supernumerary lateral incisor between teeth #6(13) and #7(12). The maxillary central incisor was extracted and the supernumerary tooth was transplanted into this site and stabilized in the arch (Figure 10). Due to the presence of an incompletely developed root apex, endo­dontic therapy was not initiated in the weeks following transplantation in order to facilitate the possibility of revascularization. Three months postoperatively, the gingival tissues had healed and exhibited minimal indications of marginal adaptation or healing.

During the 18-month recall, pulp testing elicited no response from the transplanted tooth, which had developed a periradicular lesion (Figure 11A). A necrotic pulp and chronic periradicular periodontitis were diagnosed in the tooth. Due to the necrosis of the pulp prior to the completion of root development, an open apex that required attention prior to completion of endodontic therapy was present. The root canal system was chemomechanically debrided with K-type endodontic files and 5.25% NaOCl to remove necrotic tissues, the canal was medicated with a thick paste of calcium hydroxide, and the access cavity was sealed with a provisional filling material. An apical barrier was placed 7 days postoperatively. The calcium hydroxide paste was removed with 5.25% NaOCl and the canal was dried. A thick layer of MTA was placed in the apical 3 mm of the root and allowed to set for 1 week in the presence of moisture provided coronally by a moist cotton pellet. The remainder of the canal was subsequently obturated with warm gutta-percha and sealer (Figure 11B), and a composite resin restoration was placed in the access cavity. One year postoperatively, a thick layer of calcific tissue formed apical to the MTA barrier, and the periradicular tissues had healed (Figure 12). Clinical examination revealed normal soft tissue architecture with no indications or symptoms of periradicular pathosis. Two years following treatment, the additional thickening of the apical hard tissue barrier and healthy periradicular tissues were evident radiographically (Figure 13).

(Continued from page 1 )

Discussion

The prevention of bacterial leakage is a critical factor in the healing of the pulpal and periapical tissues.27 While MTA can be used for vital pulp therapy, the success of this treatment is based on the removal of all carious dentin and residual bacteria with a NaOCl solution. Previous investigations of the traumatically exposed pulp have indicated that infection and inflammation do not extend beyond 2 mm during the initial 2 weeks post­injury.5 Further recontamination of the pulp was prevented by the placement of MTA, which has been demonstrated to provide an adequate seal.22,23 Mineral trioxide aggregate may offer an advantage over calcium hydroxide for pulp capping and has been demonstrated to provide an adequate seal.22,23 Mineral trioxide aggregate may offer an advantage over calcium hydroxide for pulp capping and pulpotomy due to its superior sealing ability, biocompatibility, and reduced solubility. It is essential to note that in the presence of moisture, MTA sets in approximately 3 hours.28 Its compressive strength, however, appears comparable to that of provisional filling materials, which renders MTA unsuitable as a permanent restorative material.28 Therefore, it is necessary to complete pulp capping and pulpotomy procedures in two appointments. When the entire cavity preparation is restored with MTA during the initial visit, it is imperative that the patient refrains from eating or drinking for a period of three hours until the MTA has completely set.

Mineral trioxide aggregate can also be utilized to perform apexification; the principles of this procedure are similar to those of pulp capping and pulpotomy. Hence, it is necessary to remove the bacteria and their by-products from the canal using irrigation with sodium hypo­chlorite and intracanal medication with calcium hydroxide for a minimum of one week; the latter has been demonstrated to eliminate bacteria in the root canal when applied for this period.29 In addition, MTA permits an adequate seal of the canal to be maintained and prevents bacterial leakage and interaction with the periradicular tissues. Mineral trioxide aggregate is easily manipulated to the apical extent of the canal, and in instances where the material is slightly extruded beyond the confines of the root apex, cementum will form around it.17

Conclusion

The MTA material has numerous applications in endodontic therapy that range from apexification to pulpotomy. The primary advantages of this material as an apical barrier include a reduction in the number of appointments required to complete the treatment, the development of a proper apical seal, and the ability to induce a deposition of hard tissue. This article has demonstrated a series of clinical procedures that utilize MTA to facilitate apexification in the vital roots of permanent teeth and has highlighted the importance of protecting the dental structures from bacterial inflammation and contamination. Although additional research is necessary to determine additional indications for MTA, its use in endodontics certainly appears favorable.

 

References

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