ORIGINAL RESEARCH IN VITRO EVALUATION OF DENTINAL MICROCRACK FORMATION DURING ROOT CANAL PREPARATIONS BY DIFFERENT NITI SYSTEMS Rahman H*, Chandra A**, Singh S # * Assistant Professor, Department of Conservative Dentistry and Endodontics, Career Post Graduate Institute of Dental Sciences and Hospital, Lucknow, India.**Professor, Department of Conservative Dentistry and Endodontics, Faculty of Dental Sciences, King George Medical University, Lucknow, India. # Reader, Department of Conservative Dentistry and Endodontics, Career Post Graduate Institute of Dental Sciences and Hospital, Lucknow, India. Address for correspondence: Hena Rahman, Dept. of Conservative Dentistry and Endodontics, CPGIDSH, Lucknow -226016, U.P., India Mob : +919415991275 Email: henavns@gmail.com Abstract : The purpose of this study was to compare dentinal microcrack formation while using hand ProTaper (PT), ProTaper and ProTaper Next rotary files. Forty single rooted teeth were selected. 10 teeth were left unprepared and served as control, and the remaining 30 teeth were divided into 3 groups. After preparation with the file system selected, roots were sectioned 3, 6, and 9 mm from the apex, and the cut surface was observed under steriomicroscope and checked for the presence of dentinal microcracks. Data thus obtained were compared by chi-square (χ 2 ) test. A two-sided (α=2) p value less than 0.05 (p<0.05) was considered statistically significant. Analyses were performed on SPSS version 17.0. The study concluded that control group did not show any microcrack. All file systems created microcracks in the root dentin, whereas the PT next file presented minimal dentinal microcracks and hand ProTaper presented highest percentage of microcracks. Keywords: Microcracks, NiTi instruments, root canal preparations, ProTaper Next, vertical root fracture INTRODUCTION Scan this QR code to access article. The goals of endodontic instrumentation are to completely remove microorganisms, debris, and tissue by enlarging the canal diameter and create a canal form that allows a proper seal. Complications such as transportation, ledge formation, and perforation are well documented (1, 2). However, preparation procedures could also damage the root dentin resulting in fractures or craze lines (3). Vertical root fracture and crack formation can also be seen in root dentin during and after endodontic procedures. Vertical root fracture is one of the frustrating complications of root canal treatment, which often results in tooth extraction (4). The root fracture might occur as result of a microcrack or craze line that propagates with repeated stress application by occlusal forces (5). In the last decades, many new NiTi rotary instruments have been developed and introduced by various manufacturers. Most clinicians prefer these systems because of their advantages such as saving time (6) and better cutting efficiency (7). Nevertheless, some functions of NiTi rotary systems such as cleaning ability, increased stress, and the inability to adequately prepare oval canals are still controversial. Additionally, Kim et al (8) have found a potential relationship between the design of NiTi instruments and the incidence of vertical root Downloaded from www.jrdindia.org - 43 -
fractures. They concluded that file design affected apical stress and strain concentrations during root canal instrumentation. The ProTaper rotary instruments have a convex triangular cross-sectional design and a non-cutting safety tip. The basic series of ProTaper files comprise six instruments: three shaping and three finishing files. According to the manufacturer, the auxiliary shaping file SX should be used to produce more shape in the coronal portion of the root canal. The shaping file S1 should be used initially up to 4 mm short of the apex and the shaping files S1 and S2 throughout the working length to progressively enlarge the apical third. The finishing files (F1, F2 and F3) should be used to complete the apical third of the root canal. The ProTaper (Dentsply maillefer) for hand use appeared as an alternative to the ProTaper rotary instruments, embodying the same philosophy, indications and sequence, but at a lower cost, for the instrumentation is entirely manual, thereby dispensing with the use of an electric engine. According to mechanical classification of NiTi instruments ProTaper (PT, Dentsply Maillefer) files are considered second generation NiTi instruments due to lack of radial lands and their individual attempts at addressing increased cutting effficiacy. Recently introduced file system ProTaper Next (PTN) files (Dentsply Tulsa Dental Specialties) is fifth generation file system based on M wire technology which increases its cyclic fatique and flexibility. Fifth generation of shaping files has been designed such that centre of mass or the centre of rotation is offset. There are 5 PTN files available, in different lengths, for shaping canals, namely X1, X2, X3, X4, and X5. In sequence, these files have yellow, red, blue, double black, and double yellow identification rings on their handles, corresponding to sizes 17/04, 25/06, 30/07, 40/06, and 50/06, respectively. The tapers just listed are NOT fixed over the active portion of any given PTN file. Appreciate the PTN X1 and X2 files have both an increasing and decreasing percentage tapered design on a single file; whereas the PTN X3, X4, and X5 files have a fixed taper from D1-D3, then a decreasing percentage tapered design over the rest of their active portions. This file system has rectangular cross section with an offset of particular distribution of the blades developing a swaggering motion to reduce even more cyclic fatigue and better evacuate the canal debris upwards. The purpose of the present study was to compare the dentinal microcrack formation while using hand ProTaper, ProTaper and PTN rotary files under steriomicroscope. MATERIALS AND METHODS Forty single rooted teeth were selected and stored in a purified water. This storage medium causes smallest changes in dentine over time length. All roots were inspected with transmitted light and stereomicroscopy under 5X magnification to detect any pre-existing craze lines or cracks. Teeth with such findings were excluded from the study and replaced by similar teeth. A silicon impression material was used for coating the cemental surface of roots to simulate periodontal ligament space. Then, all roots were embedded in acrylic blocks. Samples were divided in to 4 groups of 10 each. Group 1 was left unprepared and was considered as none group. Group 2 and 3 were prepared with hand ProTaper (HPT) and Protaper (PT) respectively. Group 4 was prepared with ProTaper Next (PTN). Canal patency was established with a #15 K-File (Dentsply Maillefer, Ballaigues, Switzerland). In group 2 and 3 shaping file SX was used in coronal segment, and S1, S2, F1,F2 and F3 files, which correspond to apical size 30, was used as the working length. In the ProTaper (PT, Dentsply Maillefer) and ProTaper Next (PTN) groups, canal preparation was performed with rotary files using a torque and speed-controlled motor (X-Smart; Dentsply Tulsa Dental, Tulsa, OK) at a torque and speed recommended by the manufacturer for each specific system used. In group 4 canal preparation is done by recently introduced PTN files X1,X2,X3 up to working length. In all groups irrigation was performed using 2.5 % sodium hypochlorite between each instrumentation during canal preparation. After completion of canal preparation teeth were rinsed with 2 ml of distilled Downloaded from www.jrdindia.org - 44 -
Rahman H et al IJRD water. All roots were kept moist in distilled water throughout the experimental procedure. Roots were sectioned perpendicular to the long axis at 3,6,9 mm from the apex using a diamond coated saw under water cooling. Samples were then viewed under stereomicroscope (LEICA) at 5X magnification and their images were captured in attached LED monitor. Each specimen was checked by two observers for the presence of dentinal defects. In order to avoid confusing definitions of root fractures four distinct categories were made. No fracture is defined as root dentin devoid of any fracture line or cracks, where both the external surface of the root and the internal root canal wall did not present any evident defects. Partial fracture is defined as fracture line which travels from canal lumen to external surface but didd not reach to external surface. Complete fracture is defined as fracture line which travels canal lumen to the external surface. Other fracture defined as fracture line which travels from external surface but did not reach to canal lumen. STATISTICAL ANALYSIS Discrete (categorical) data were summarized in no and % and compared by chi-square (χ2) test. A twosided (α=2) p value less than 0.05 (p<0.05) was considered statistically significant. Analyses were performed on SPSS version 17.0. RESULTS The outcome measures of the study were no fracture, complete fracture, partial fracture and others (Figure 1 and 2). The primary objective of the study was to compare outcome measures among four groups (None, HPT, PT and PTN Universal). The comparisons of outcome measure among four groups are summarized below in Table I and II DISCUSSION When NiTi rotary instruments are used, a rotational force is applied to root canal walls. Thus, they can create microcracks or craze lines in root dentin. The extent of such a defect formation may be related to the tip design, cross-section geometry, constant or Outcome measures NO FRACTURE 30 COMPLETE FRACTURE PARTIAL FRACTURE 0 OTHERS 0 None 0 Table I showing no of samples undergone different types of fractures (n=30) 100 80 60 40 20 0 none HPT PT PTN Figure 1. The frequency (%) of roots presenting a defect after canal preparations with different instruments. progressive taper type, constant or variable pitch, and flute form (5). Resistance to tooth fracture is an important aim in endodontics because such fractures may decrease the long-term survival rate. Experimental studies have shown that excessive removal of dentin during root canal preparation, post space preparation, and obturation procedures with spreader can create fractures in teeth (9, 10). fracture was seen only ProTaper group, reason removal of dentin. Bier fractures did not occur ISSUE 2, 2014 HPT PT PTN 3 13 20 18 3 0 7 2 0 6 12 10 no fracture complete fracture In present study complete in hand ProTaper and may be the excessive et al (11) suggested that immediately after canal preparation. However, craze lines occurred in 4% to 16%, which may develop into fractures during retreatment or after long term functional stresses like chewing (12). In this regard, root canal preparation with NiTi rotary systems and every following additional procedure in endodontics as obturation Downloaded from www.jrdindia.org - 45 -
and retreatment with rotary systems can create section that decreases file engagement, increases fractures or craze lines. flexibility and maximises debris removal. Frequency (%) None HPT PT PTN No fracture 100 10 43.3 66.7 Complete fracture 0 60 10 0 Partial fracture 0 23.3 6.7 0 Others 0 20 40 33.3 Table II shows frequency (%) of all type of fractures amongst all the groups (p<0.05 was considered statistically significant) In the present study maximum no. of fractures were observed in the hand ProTaper group because of uncontrolled pressure which leads to excessive dentin removal. In case of rotary ProTaper F3 file has a large apical taper of 0.09 which could explain the higher incidence of damage observed in this group as compared with PTN group. The high level of stiffness of the PT may be explained by a larger cross-section because of its progressive taper (13). Furthermore the progressive tapering of PT instrument results in excessive removal of dentinal wall, which in turn result in weakening of instrumented root. Least no. of dentinal defects were observed in the ProTaper Next (PTN) group as it has a progressive taper and an offset design with the rectangular cross The most successful generational design of the past is the mechanical concept of utilising a progressively percentage tapered design on a single file. The patent protected ProTaper Universal NiTi rotary file system utilises both an increasing or decreasing percentage tapered design on a single file. This design feature serves to minimise the contact between a file and dentin, which decreases dangerous taper lock and the screw effect, while increasing efficiency (14). Compared to a similarlysized fixed tapered file, a decreasing percentage tapered file design, strategically improves flexibility, limits shaping in the body of the canal, and conserves coronal two-thirds dentin. Taking advantage of this mechanical design, PTN also utilises progressive tapers on a single file. Research has shown that M-wire, a metallurgically improved version of NiTi, reduces cyclic fatigue by 400% when comparing files of the same D0 diameter, cross-section, and taper (15). A shaping file with an offset mass of rotation will generate a mechanical wave of motion analogous to the oscillation noted along a sinusoidal wave. As a result of this design, any given PTN file can cut a bigger envelope of motion compared to a similarly-sized file with a symmetrical mass and axis of rotation (16). CONCLUSION Even though this in vitro study did not reflect the clinical settings, we can conclude that NiTi instruments tend to induce various degrees of dentinal damage during root canal preparation. On the other hand, PTN files represent satisfactory results with minimal microcrack defects. REFERENCES 1. Schilder H (1974). Cleaning and shaping the root canal. Dent Clin North Am 18,269 96. 2. Pettiette MT, Metzger Z, Phillips C, Trope M (1999). Endodontic complications of root canal therapy performed by dental students with stainlesssteel K-files and nickel-titanium hand files. J Endod 25,230 4. Downloaded from www.jrdindia.org - 46 -
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