J Huazhong Univ Sci Technol［Med Sci］ DOI 10.1007/s11596-011-0265-y 31(2):271-276,2011 J Huazhong Univ Sci Technol［Med Sci］ 31(2):2011
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Fracture Resistance and Failure Patterns of Open Apex Root Teeth with Different Posts after Endodontic Treatment* Qiuhui LI (李秋慧), Ping YAN (闫 萍), Zhi CHEN (陈 智)# Key Laboratory for Oral Biomedicine of Ministry of Education School and Hospital of Stomatology, Wuhan University, Wuhan 430079, China © Huazhong University of Science and Technology and Springer-Verlag Berlin Heidelberg 2011
Summary: The aim of this study is to investigate the influence of different posts on the fracture mechanics of endodontically-treated teeth with open apex. Forty-eight human maxillary anterior teeth were collected, and the root was transversely sectioned 12 mm under the cementoenamal junction (CEJ). These samples were then randomly divided into two groups, i.e., minor diameter open apex root (group A) and major diameter open apex root (group B), with mineral trioxide aggregate (MTA) placed into the apical 4 mm in the root canals. Subsequently, both groups were respectively further divided into three subgroups as follows: fiber-post (subgroup 1), metal post (subgroup 2) and non-post (subgroup 3) group. Teeth were restored with a composite resin crown and tested by using a universal testing machine at the rate of 1 mm/min cross-head. Values of the maximum fracture resistance and failure patterns were recorded and compared among all subgroups. In addition, the changes of MTA properties were carefully examined via X-ray photography. Our results indicate that (1) In group A, the mean value of fracture resistance for teeth restored with fiber posts were statistically higher than that with either metal post or non-post; (2) In group B, there was no statistically significant difference in the mean value of fracture resistance among three subgroups; (3) No statistical significance in the mean value of fracture resistance was found between group A and group B; (4) The failure modes of most samples (58%) were irreparable; (5) MTA in two teeth developed cracks after loading tests. In conclusion, endodontically-treated teeth restored with fiber posts are more resistant to fracture than those restored with either metal posts or non-post, and most of the fracture modes are catastrophic in nature. Key words: fiber post; MTA; open apex; fracture resistance
Post-and-core restoration is the mainstream treatment for residual crowns and roots[1]. The custom-made post-and-core has long been used as the main material for its high strength and workability[2]. However, it possesses obvious deficiencies, including opacity, gum dyeing, sensitization, and interference with magnetic resonance imaging (MRI). With the rapid development of dental materials, fiber post has been widely used clinically due to its superior physical and chemical properties. It satisfies the mechanical and cosmetic requirements for treating the maxillary anterior teeth, while fiber posts combined with resin composite cores are considered to be viable alternatives[3–5]. Special situations are likely to appear in young patients, in which the pulps of anterior teeth may lose their vitality and lead to the arrest of roots development. Many factors, such as caries, trauma, teeth malformation, inQiuhui LI, E-mail:
[email protected] # Corresponding author:
[email protected] * This study was supported by a grant from a program of research and development of Hubei Province (No. 2008BCC 001).
correct orthodontic treatment, etc, may cause severe periapical diseases and root development failure of the immature permanent teeth, which tend to bring about critical complications, including apical region absorption, unclosed apical foramen, weak root canal, or even root fracture[6, 7]. It is well known that posts can be used for retaining coronal restorations in root-filled teeth, but they can not strengthen the root resistance because they change the stress distribution in root canal and expose the teeth to a higher risk of fracture[7, 8]. Therefore, developing an appropriate approach for post-and-core restoration has become one of the keys to the prevention of irreparable failures of the maxillary anterior teeth after root canal treatment[9, 10]. However, whether the fiber post is suitable for restoring and improving the physical properties of weak immature anterior teeth remains unclear and needs further experimental and clinical evaluations. In this study, we devised different post-and-core systems to restore the maxillary anterior teeth with open apex roots and compared the roots of various diameters and restoration methods in terms of the fracture resistance and failure patterns. Moreover, we investigated the applicability of fiber post in the treatment of maxillary
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teeth with open apex root canal, to provide data for clinicians to choose the proper approach for post-and-core restoration. 1 MATERIALS AND METHODS 1.1 Specimen Selection Forty-eight single-rooted human maxillary incisor teeth extracted for periodontal diseases were selected and stored in 0.5% chloramines-T. After pulp and periodontal tissues were removed and cleaned, all teeth were examined under X-ray radiography for root situation. All Groups A1 A2 A3 B1 B2 B3
samples were of similar root size, had straight roots, were free from caries, fracture lines, root absorption, lingual groove and cusp deformity, obvious decay and discoloring, and had not received root canal treatment before. These extracted teeth were randomly divided into group A and group B, and then samples of each group were further divided into 3 subgroups, which were respectively restored by fiber post+composite resin crown (subgroup 1), custom metal post+composite resin crown (subgroup 2) and non-post+composite resin crown (subgroup 3) (table 1). Each subgroup had 8 samples.
Table1 Grouping and materials Open Apex Diameter Apex sealing Post material 0.8 mm MTA Fiber Post 0.8 mm MTA Cast metal post 0.8 mm MTA Non-post 1.2 mm MTA Fiber Post 1.2 mm MTA Cast metal post 1.2 mm MTA Non-post
1.2 Samples Preparation 1.2.1 Preparation of Open Apex Root Model Pulp chambers were opened by using a #245 bur and an Endo Access Bur (AO 1064, Densply, Switzerland) to make a standardized cavity (2 mm in depth and 1.75 mm in diameter) at the root canal entrances. All prepared teeth were randomly divided into two groups (group A and group B), with each group having 24 samples. 1.2.1.1 The Mode of Minor Diameter Open Apex Root (group A) By employing Gates Glidden drills (size 5–1 in sequence, Mailleger Densply, Switzerland) for preparation, the upper 2/3 of the root canal was enlarged. Step-back technique was used with stainless-steel K-files (Maillerfer, Ballaigues, Switzerland). Then, a working length of 1 mm from the apex was completed to a size 30 master apical file. Next, the apical foramen was shaped to 80 ISO by extruding the tips of the 80# K-file exactly 2 mm from the apex (D0, diameter 0.8mm). 1.2.1.2 The Mode of Major Diameter Open Apex Root (group B) The initial preparation of root canals was performed in the same way as in group A. ProTaper F2 rotary instrument was used to extrude apical foramen 9 mm to make a wider root foramen and finished the apex as the file was intruded into the canals foramen 14 mm from the opposite direction. A standardized major diameter open apex mode was then created by retrograde preparation of the canal with the #25 rotary instrument to the coronal length of its cutting blade (D14, diameter 1.20 mm). Before filling the root canals and restoring the access opening, 5 mL 5.25% NaClO, 5 mL 17% EDTA, and 5 mL sterile water were applied. All prepared teeth were kept in moist gauze until obturation. 1.2.2 MTA Filling The root canals were dried with paper points. White MTA (ProRoot, Dentsply, Switzerland) was mixed with a liquid/powder at a ratio of 0.35, and introduced into the canal in a straight direction with a messing gun (EndoGun, USA). The MTA was initially condensed with the thick end of moistened paper points and subsequently compacted with a size #11 endodontic plugger (Hu-Friedy, USA) to create a 4 mm-thick apical
Restoration material Composite resin Composite resin Composite resin Composite resin Composite resin Composite resin
plug. Digital radiographs were taken to ensure void-free MTA placement and plug thickness. If any gap was noted, MTA was removed immediately and then the space was re-filled. All samples were stored at 37°C and 100% humidity for 48 h. 1.2.3 Post-and-core System Restoration After the solidity of MTA was confirmed by using a plugger, the apical seal of the MTA plug was evaluated. Then the remaining canal space was back-filled using Obtura Ⅱ (Spartan, Fenton, USA) with AH plus as a sealer. The gutta-percha was condensed with endodontic pluggers to 2 mm beneath the coronal orifice. Then the prepared teeth were divided into 3 subgroups, each consisting of 8 samples. 1.2.3.1 Subgroup 1 (Fiber Post+composite Resin Crown) The ParaPost Fiber Lux posts system (Coltene/ Whaledent, Altstatten, Switzerland), an adaptable, polymer (PMMA) and resin-impregnated (bis-GMA) unploymerised glass fiber post, was chosen for the esthetic prefabricated posts. Para Cem Universal DC, including Para Bond Adhesive A and B (Coltene/ Whaledent, Altstatten, Switzerland), was selected as a dual cure resin cement for cementation and core building-up. Post spaces were prepared 10 mm deep by using 4.5# burs and 5.5# burs (Coltene/ Whaledent, Altstatten, Switzerland) under water cooling. Posts of two different diameters (4.5#, 1.14 mm, and 5.5#, 1.40 mm) were used to restore the samples in subgroup A1 and subgroup B1, respectively, following the operation. 1.2.3.2 Subgroup 2 (Custom Metal Post+Composite Resin Crown) Coat post-and-core systems were restored routinely, and the coronal tops of the posts were adjusted to 4 mm higher than the surfaces of the crowns, by diamond stones. 1.2.3.3 Subgroup3 (Non-post+Composite Resin Crown) Gutta-percha was maintained in the root canal and non-post was inserted into the root. 1.2.4 Resin Crown and Embedding Filtek Z350 (3M ESPE, USA) was selected as the composite resin for crown material. The first layer (1–2 mm) of particulate filler resin (Filtek Z350) was applied around the post to
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cover the cement and light cured for 20 s. The resin composite crown was built up in layers of approximately 2 mm. A resin composite layer of approximately 1 mm covered the head of the post occlusally. Finally, the restoration of the composite resin crowns was finished using diamond stones and polishing disks. Each tooth was embedded along the long axis in acrylic blocks (20 mm in diameter and approximately 20 mm in height), in such a way that 2 mm of natural root structure upper CEJ was exposed above the acrylic level to mimic the bone. Also the buccal side of the root was located about 1 mm from the outer surface of the acrylic cylinder to mimic buccal bone crest. During the whole process, samples were kept in a wet condition until loading. 1.3 Mechanical Loading Test The samples were stored in sterile water at 37°C for 10 days, and X-ray films were taken for all specimens before loading. These samples were then fixed in a metal holder of a 5500 series universal testing machine (Instron, USA) with the long-axis of the roots at an angle of 45° in the direction of loading (fig. 1). A stainless steel cylindrical bar was used to load the teeth until the fracture, with a crosshead speed of 1.0 mm/min, and the site of loading was 3 mm under the incisal edge of the resin crown. Finally, the maximum pressure load values of the teeth were recorded.
serve the MTA changes before and after the mechanical loading test. The numbers, positions and shapes of the cracks of the MTA in the teeth were recorded. 1.6 Statistical Analysis One-way analysis of variance (ANOVA) was used to compare the data of mean failure loads at a statistically significant level of P=0.05. LSD-t tests were used to compare the frequencies of favorable/unfavorable failures among groups. The analyses were preformed by employing SPSS (version 16.0, SPSS Inc., USA). 2 RESULTS 2.1 The Maximum Fracture Load 2.1.1 Typical Load-time (Displacement) Curve All samples were placed in the universal testing machine at the maximum fracture load, the values of which were then recorded and displayed in a load-time (displacement) curve (fig. 2).
Fig. 2 Typical load-displacement curve
Fig. 1 The loading test
1.4 Failure Patterns Analysis After the loading tests, photos from various angels were taken (buccal, lingual, mesial, and distal surfaces). All teeth were then assessed grossly or radiographically for failure modes. The failure types were verified according to the fracture positions and divided into “favorable failures” and “unfavorable failures”[11]. The former was repairable, which included the partial and/or overall dislocations of post-and-core and the fracture of post-core-tooth complex above alveolar bone. And the latter was irreparable which was composed of vertical root fracture, cracks and fracture of post-core-tooth complex below alveolar bone. 1.5 MTA properties analysis Digital radiographs were examined carefully to ob-
2.1.2 The Maximum Fracture Resistance In group A (the open apex root of minor diameter), the mean values of the maximum fracture resistance were as follows (table 2): Subgroup A1=592.89±139.23N; Subgroup A2= 420.59±127.71N, Subgroup A3=386.92±109.50N. These results indicated that values of subgroup 1 were the highest, and they were statistically different from the values of subgroup A2 and significantly different from values of subgroup 3 (P=0.012) (fig. 3). In group B (the open apex root of major diameter), the mean values of the maximum fracture force were as follows: Subgroup B1=441.75±160.11N; Subgroup B2=359.97±170.52N, Subgroup B3=424.21±181.60N. However, there was no statistical difference in the maximum fracture resistance among all three subgroups (fig. 3). In addition, no statistical difference was noted between group A and group B (P>0.05) 2.2 Failure Patterns All samples and X-ray films before and after the fracture-load test were systematically and comprehensively compared. According to fracture positions, the failure modes fell into 6 types and they were of two models: “favorable failures” and “unfavorable failures” (fig. 4).
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Table 2 Results of mean values of the maximum fracture resistance (N) Groups n Mean Standard deviation A1 8 592.89* 139.23 A2 8 420.59 127.71 A3 8 386.92 109.50 B1 8 441.75 160.11 B2 8 359.97 170.52 B3 8 424.21 181.60 * P
