Effect of Mineral Trioxide Aggregate Apical Plug Thickness on Fracture Resistance of Immature Teeth

Effect of Mineral Trioxide Aggregate Apical Plug Thickness on Fracture Resistance of Immature Teeth

Basic Research—Technology Effect of Mineral Trioxide Aggregate Apical Plug Thickness on Fracture Resistance of Immature Teeth Ersan C ¸ ic¸ek, DDS, P...

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Basic Research—Technology

Effect of Mineral Trioxide Aggregate Apical Plug Thickness on Fracture Resistance of Immature Teeth Ersan C ¸ ic¸ek, DDS, PhD,* Neslihan Yılmaz, DDS,† M. Murat Koc¸ak, DDS, PhD,‡ Baran Can Saglam, DDS, PhD,‡ Sibel Koc¸ak, DDS, PhD,‡ and Burcu Bilgin, DDS‡ Abstract Introduction: The aim of this study was to compare the fracture resistance of simulated immature teeth after using different thicknesses of mineral trioxide aggregate (MTA) apical plugs. Methods: Fifty-two human maxillary anterior teeth were used. Five teeth were the positive control group; they were prepared using Peeso reamers to simulate immature teeth without any access cavity preparation. Access cavities of the 47 teeth were prepared, and the canals were instrumented with Peeso reamers. Five teeth served as the negative control; they were filled with calcium hydroxide. Forty-two teeth were divided into 3 groups; in groups 1, 2, and 3, MTA was placed into canals as a 3-mm and a 6-mm apical plug and a thorough canal length, respectively. The rest of the canals in groups 1 and 2 were filled with guttapercha and AH Plus sealer (Dentsply DeTrey, Konstanz, Germany). After the storage period, the roots were covered with a polyether impression material and were embedded into self-curing resin blocks. Each specimen was then subjected to fracture testing using a universal testing machine. Data were analyzed using 1-way analysis of variance with the Tukey post hoc test for multiple comparisons. Results: The negative group showed the lowest fracture resistance compared with the other groups. The 3-mm apical plug group showed the highest fracture resistance (P < .05). No significant differences were found between the 3-mm and 6-mm apical plug groups (P > .05). Conclusions: MTA should be used as an apical plug instead of root canal filling material to increase the fracture resistance of immature teeth. (J Endod 2017;-:1–4)

Key Words Apical plug, fracture resistance, immature teeth, mineral trioxide aggregate

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raumatic dental inSignificance juries frequently occur During the single-visit treatment of an immature in young and adolescent tooth, an MTA apical plug could be placed up to age and mostly affect the 6-mm thickness. Clinicians should avoid complete maxillary central incisors obturation of a root canal with MTA. (1). Such injuries often result in pulpal necrosis, which could cause the termination of apex formation in developing teeth; these teeth are called immature teeth (2). The treatment of immature teeth is a challenge because of the weak dentinal walls and the high risk of root fracture (3, 4). Root canal instrumentation and the achievement of an adequate apical stop are challenges during the treatment of immature teeth. To allow condensation of the filling material and to provide an apical seal, an artificial apical barrier or closure of the apical foramen with a calcified tissue is essential. Apexification was defined as ‘‘a method to induce a calcified barrier in a root with an open apex or the continued apical development of an incomplete root in teeth with necrotic pulp’’ (5). Although several procedures using different materials have been proposed to induce root-end barrier formation, calcium hydroxide (Ca[OH]2) has gained wide acceptance. Although this technique is efficient with predictable outcomes, it has several disadvantages such as the unpredictable time required to form an apical barrier, the need for multiple visits, patient compliance, reinfection because of the loss of temporary restoration, and predisposition of the tooth to fracture (6, 7). In such cases, the clinician should consider treatment options including regenerative endodontic or apexification treatments (8). The apical barrier technique is commonly used when regenerative treatment has failed or is not considered an option (8). Various materials have been recommended for the apexification of immature teeth. Ca(OH)2 has been used for the induction of an apical barrier in an immature tooth because of its high pH and antimicrobial activity for many years (9, 10). However, Ca(OH)2 has several disadvantages such as requiring multiple visits, microleakage between visits, and the patient’s adaptation (11, 12). Furthermore, Ca(OH)2 treatment may extend up to 1 year, which may decrease the fracture resistance of immature teeth because of the changes in the organic matrix of the dentin (4, 6, 12, 13). Single-visit apexification treatment using mineral trioxide aggregate (MTA) may eliminate such drawbacks (14–16) because of its good physical, chemical, and biological properties. Therefore, MTA was recommended as an alternative material to Ca(OH)2 for the induction of an apical barrier in an immature tooth (17). Bonte et al (17) stated

From the *Private Clinic, Samsun, Turkey; †Oral Health Center, Karab€uk, Turkey; and ‡Department of Endodontics, Faculty of Dentistry, B€ulent Ecevit University, Zonguldak, Turkey. Address requests for reprints to Dr Baran Can Saglam, Department of Endodontics, Faculty of Dentistry, B€ulent Ecevit University, Zonguldak, Turkey. E-mail address: [email protected] 0099-2399/$ - see front matter Copyright ª 2017 American Association of Endodontists. http://dx.doi.org/10.1016/j.joen.2017.05.007

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MTA Plug Thickness and Fracture Resistance

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Basic Research—Technology that apexification with MTA was superior to Ca(OH)2 to achieve an earlier coronoradicular filling and to limit the risk of root fracture. Considering the various drawbacks associated with Ca(OH)2 apexification, the use of the apical plug method could be an alternative treatment option in such cases. In this method, a compact plug is placed into the open area of the root end to induce the formation of a calcified barrier in the periapical region. After the setting of this plug, the remaining part of the canal could be obturated with gutta-percha. The advantages of this technique are shorter treatment time and the development of a good apical seal. A number of materials have been proposed for this purpose (18, 19). Of all the materials available, MTA has been widely used for 1-visit apexification because of its superior sealing ability, biocompatibility, regenerative capability, and antibacterial property; it also enhances the fracture resistance of immature teeth (20–22). Recent studies evaluated the success of MTA in the treatment of immature teeth (17, 20, 21). However, the optimal thickness of an MTA apical plug is controversial. Therefore, the aim of this in vitro study was to compare the fracture resistance of simulated immature teeth after using different thicknesses of an MTA apical plug.

Materials and Methods Tooth Selection Fifty-two extracted human maxillary anterior teeth with a single root and canal were selected. The teeth had been extracted for periodontal reasons that were unrelated to this study. All teeth were inspected under a stereomicroscope (20 Olympus SZ61 with a SC100; Richmond Hill, ON, Canada) to detect any carious lesions, external resorption, cracks, or fracture lines. Periapical radiographs were taken in both the buccolingual and mesiodistal directions to verify the absence of calcification, internal resorption, or an additional root canal. Teeth with carious lesions, a calcified canal, root resorptions, fractures, and/or cracks were discarded. The buccolingual and mesiodistal diameters of the roots were measured at the cervical, middle, and apical levels using a digital caliper (Mitutoyo, Tokyo, Japan). Similar teeth with a length of 20  0.51 mm were selected for standardization. The apical 5 mm of each tooth was removed using a low-speed diamond saw (SP1600; Leica Microsystems, Wetzlar, Germany). Treatment Procedures Five teeth served as the positive control. These teeth were prepared from the apical to the coronal direction of the canal using Peeso reamers up to size 5 to simulate immature teeth without any access cavity preparation. Forty-seven teeth were prepared as follows. Coronal access was prepared using a size 4 round bur (Dentsply Maillefer, Ballaigues, Switzerland) in a high-speed handpiece. The pulps were removed using a barbed broach (Kerr Corporation, Orange, CA) without any instrumentation. The canals were instrumented with Peeso reamers (size 1–5, Dentsply Maillefer) until a size 5 Peeso could easily pass 1 mm beyond the apex to stimulate immature teeth (3). The canals were irrigated with 2.5% sodium hypochlorite during instrumentation. A size 6 Peeso reamer was used to extend the preparation of the canal 3 mm below the cementoenamel junction to approximate Cvek’s stage 3 of root development (3, 4). After the instrumentation, each canal was irrigated with 3 mL 2.5% sodium hypochlorite and then irrigated with 3 mL saline. Five teeth served as the negative control, and the canals were filled with Ca(OH)2 (Calcicur; Voco, Cuxhaven, Germany). The Ca(OH)2 paste was placed into the root canal from the access cavity with a Lentulo spiral (G-Star Medical Co Ltd, Guangdong, China). The access cavity was sealed with a temporary 2

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filling material (Cavit; ESPE, Seefeld, Germany), and the specimens were stored at 37 C and 100% humidity for 4 weeks. Forty-two teeth were divided into 3 experimental groups (n = 14). White MTA (Angelus Solucoes Odontologicas, Londrina, Brazil) was mixed at a powder to liquid ratio of 3:1 (17). MTA was placed into the root canals from the coronal access to provide an apical plug. The apical plug thickness was performed as follows (Fig. 1A–C). In group 1, MTA was placed into the simulated immature roots and condensed with a hand plugger to obtain a 3-mm-thick apical plug. In group 2, MTA was placed into the simulated immature roots and condensed with a hand plugger to obtain a 6-mm-thick apical plug. In group 3, MTA was placed into the simulated immature roots and condensed with a hand plugger to obtain a completely obturated root canal with the material. The homogeneity and thickness of the apical plug were confirmed with 2 radiographs in both the mesiodistal and buccolingual directions. All specimens were stored at 37 C and 100% humidity for 4 hours, and the remaining parts of the canals in groups 1 and 2 were filled with gutta-percha and AH Plus (Dentsply DeTrey, Konstanz, Germany) sealer using the warm vertical compaction technique to the cementoenamel junction. The quality of the obturation was confirmed with radiographs. The access cavities were sealed with resin composite restoration (Clearfil Majesty Esthetic; Kuraray, Tokyo, Japan). The samples were stored at 37 C and 100% humidity for 4 weeks.

Fracture Testing The root surfaces were covered with a polyether impression material to mimic the periodontal membrane. The roots were embedded in self-curing resin blocks (Lucitone; Dentsply International Inc, York, PA) until there was a 2-mm gap between the cementoenamel junction and the top of the resin (23, 24). Each specimen was mounted in a universal testing machine (Instron; AG-IS, Shimadzu, Japan). The spade, which was used to apply the force to the specimen, was placed on the facial surface at 135 to the long axis of the tooth in a buccal/lingual direction at a point 3 mm above the cementoenamel junction to stimulate a traumatic blow on the middle third of the dental crowns (24). The samples were loaded at a crosshead speed of 1 mm/min until the fracture occurred. The peak load to fracture was recorded in newtons. Statistical Analysis SPSS 19.0 software (SPSS Inc, Chicago, IL) was used for statistical analysis. The buccolingual and mesiodistal dimensions and weights were subjected to the Kolmogorov-Smirnov statistical test to test the normality of these continuous variables. The 1-way analysis of variance test was used to evaluate the difference among the buccolingual and mesiodistal dimensions and the weight of the samples. After completing the fracture test, the data were subjected to statistical analysis using 1-way analysis of variance with the Tukey post hoc test for multiple comparisons. The testing was performed at the 95% level of confidence (P < .05).

Results The mean peak load (newtons) and standard deviation of the groups are shown in Table 1. The teeth were fractured horizontally or obliquely through the cervical area of the root. The negative group showed the lowest fracture resistance compared with the other groups (P < .0001). The 3-mm apical plug group showed the highest fracture resistance. No significant differences were found between the 3-mm (727.24  52.85 N) and 6-mm (721.56  32.00 N) apical plug groups (P > .05). JOE — Volume -, Number -, - 2017

Basic Research—Technology

Figure 1. Representative images of a (A) 3-mm and (B) 6-mm apical plug and (C) complete obturation of a root canal with MTA.

Discussion In the present study, to simulate immature teeth, after the resection of the root end, the canals were instrumented with Peeso reamers (1–5) beyond the apex (3). Also, the preparation of the canal was extended 3 mm below the cementoenamel junction using a size 6 Peeso reamer to mimic Cvek’s stage 3 root development (3, 4). Cvek’s stage 3 root development was provided for this model because the root-to-canal ratio in a mesiodistal dimension at the cementoenamel junction is approximately 1:1 at this stage (3, 4). For testing fracture resistance, teeth were embedded in acrylic resin, and periodontal membrane simulation was performed using a polyether impression material to simulate the clinical situation (23). Furthermore, a loading angle of 135 was selected to mimic the average angle of contact between maxillary and mandibular incisors in a class 1 occlusion (3). A survey of recent literature indicated that there was no investigation on the effect of MTA apical plug thickness on the root fracture resistance of the immature teeth. However, there were controversial results regarding the ability of MTA to strengthen the tooth structure (12, 23, 25). Bortoluzzi et al (23) stated that MTA enhanced the resistance to horizontal root fracture when used as an obturation material for immature teeth. Additionally, Andreasen et al (12) reported that MTA improves the cervical fracture resistance of immature sheep incisors more effectively than Ca(OH)2. In contrast to these results, Hatibovic-Kofman et al (25) compared the effects of MTA and Ca(OH)2 on fracture resistance in sheep teeth, and they reported that MTA and Ca(OH)2 reduced the fracture resistances 2% and 28%, respectively. Similarly, White et al (26) reported that MTA reduces the fracture resistance of bovine dentin by 33%; they also showed a weakening of the dentinal structure in the short-term and attributed this effect to the structural alteration of proteins caused by the alkalinity of MTA. The present study revealed that complete obturation with MTA decreased the fracture resistance of the roots compared TABLE 1. The Mean Peak Load (N) and Standard Deviation (SD) of the Groups Groups

Mean ± SD (N)

Minimum

Maximum

Group 1 Group 2 Group 3 Negative control Positive control

727.24  52.85 721.56  32.00 492.10  82.42 346.33  31.27 517.50  51.67

611 675 381 300 428

790 788 596 393 599

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with intact immature teeth without any significance. However, the fracture resistance of the roots that were completely filled with MTA was significantly higher compared with the Ca(OH)2 treatment group. Additionally, the present study showed that Ca(OH)2 had adversely affected the fracture resistance of the root compared with the 3-mm MTA, 6-mm MTA, and full MTA groups, with significance. Ca(OH)2 dressing increases the risk of root fracture (6, 26). The decreased root strength observed in the Ca(OH)2-treated root canals could be associated with the weakened dentin, which might occur as a result of denaturation and hydrolysis taking place in the organic matrix. Dentinal strength is identified by the link between hydroxyapatite and collagenous fibrils. Because of its hard alkalinity, Ca(OH)2 can denature the carboxylate and phosphate groups, provoking a collapse in the dentin complex (26). This proteolytic effect may influence the mechanical properties of dentin (6). Moreover, the access cavity preparation decreases the fracture resistance of teeth compared with intact teeth (27). The fracture resistance of the Ca(OH)2 treatment group was lower than the MTA treatment groups and the intact immature tooth group in the present study. This finding could be associated with the access cavity preparation and temporary filling as well as the adverse effects of Ca(OH)2. Similar to our results, it was reported that Ca(OH)2 significantly decreased the fracture resistance compared with MTA (28). The apical plug should provide a hermetic apical seal. Various studies have reported that 3- to 5-mm thicknesses of MTA provided an effective apical seal (29, 30). Our results showed that complete obturation of the root canal with MTA may cause a tendency to fracture. In contrast to the finding, no difference was found between a 3- and 6-mm MTA apical plug, and both showed similar results. Therefore, MTA may be safely used for performing an apical barrier between 3- and 6-mm thick in immature teeth. Because the use of AH 26 (Dentsply DeTrey) plus gutta-percha increases the fracture resistance of instrumented root canals (31), the use of an elastic material such as gutta-percha could be recommended in the upper part of the canal, instead of an inelastic material such as MTA. In conclusion, an MTA apical plug could be placed into the root canal up to 6-mm thick, if required, during the single-visit treatment of immature teeth without adversely affecting the resistance of tooth structures.

Acknowledgments The authors deny any conflicts of interest related to this study. MTA Plug Thickness and Fracture Resistance

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