doi:10.1111/iej.12249

Effect of three NiTi files on transportation of the apical foramen

W. Hu, B. Whitten, C. Sedgley & T. Svec Department of Endodontology, Oregon Health & Science University, Portland, OR, USA

Abstract Hu W, Whitten B, Sedgley C, Svec T. Effect of three NiTi

files

on

transportation

of

the

apical

foramen.

International Endodontic Journal, 47, 1064–1071, 2014.

Aim To compare landed and nonlanded rotary file overinstrumentation on transportation of the apical foramen in the curved canals of extracted teeth. Methodology Severely curved molar root canals (n = 45) were distributed into three equal groups (n = 15) according to angle (mean 54°) and radius of curvature (mean 5 mm). Canals were overinstrumented 0.5 mm beyond the foramen to a size 35 master apical file using landed (ProFile ISO), nonlanded (ProFile Vortex) or nonlanded, reduced shape memory (Vortex Blue) files. Post-instrumentation images of the apical foramen were compared with pre-instrumentation control images for differences in area, circularity and ratio of Feret’s diameters. Groups

Introduction Initial working length (WL) in curved canals can become shorter after instrumentation due to straightening of the canal (Weine et al. 1975, Caldwell 1976, Farber & Bernstein 1983, Davis et al. 2002, Khurana et al. 2011). If WL is not adjusted, a preparation error known as a ‘zip’ may occur. This ‘zip’ transportation of the apical foramen can lead to complications in subsequent cleaning and filling procedures (Weine et al. 1975).

Correspondence: Timothy Svec, Department of Endodontology, Oregon Health & Science University, 611 SW Campus Drive, Portland, OR 97239, USA (Tel.: (503) 494-8962; Fax: (503) 494-8486; e-mail: [email protected]).

1064

International Endodontic Journal, 47, 1064–1071, 2014

were compared using ANOVA or Kruskal–Wallis tests with significance of P < 0.05. Results There were no differences between pretreatment groups in the parameters tested. All groups demonstrated alterations in the geometry of the apical foramen. There were no significant differences between ProFile ISO, ProFile Vortex or Vortex Blue in area, circularity and ratio of Feret’s diameters. Conclusions Landed, nonlanded and nonlanded reduced shape memory files all produced transportation of the apical foramen when overinstrumented by 0.5 mm in severely curved canals. There was no difference between these file systems with regard to the degree of this effect. Keywords: apical foramen, curved canals, overinstrumentation, transportation. Received 7 May 2013; accepted 10 January 2014

Transportation of the apical foramen was shown during overinstrumentation of curved root canals created in plastic blocks using stainless steel and nickel titanium (NiTi) hand files, although to a lesser extent with the latter (Lam et al. 1999). A recent study examining the effect of patency filing 1 mm beyond the apical foramen found no transportation in the majority of samples when using small stainless steel files and reamers (Gonzalez Sanchez et al. 2010). However, another study found that when size 10, 15, 20 and 25 K files were used as patency files the probability of transportation of the apical foramen was 33% and 57% for size 10 and 20 K files, respectively (Goldberg & Massone 2002). Currently, there are many rotary NiTi systems available, which feature specific design characteristics that influence cutting efficiency, flexibility and

© 2014 International Endodontic Journal. Published by John Wiley & Sons Ltd

Hu et al. NiTi files and apical foramen transportation

torsional resistance. These include ProFile ISO, Profile Vortex and Vortex Blue systems (Dentsply Tulsa Dental, Tulsa, OK, USA). ProFile ISO instruments have a U-shape cross-sectional design with radial lands and a parallel central core (Hargreaves & Cohen 2011). They have a 20° helical angle, constant pitch, a neutral or slightly negative rake angle and bullet-shaped noncutting tips. These features facilitate a reaming rather than cutting action and allow debris to be transported coronally and effectively removed (Hargreaves & Cohen 2011). ProFile Vortex instruments were introduced in 2009 and are manufactured from M-Wire. They have triangular cross sections, a varying helical angle without radial lands and noncutting safety tips (Gao et al. 2010). ProFile Vortex files were found to have increased flexibility and resistance to cyclic fatigue (Gao et al. 2012). Vortex Blue instruments were introduced in 2011 and have design features similar to ProFile Vortex instruments. However, they are manufactured through a proprietary processing of NiTi wire, which results in the formation of a visible titanium oxide layer that imparts a distinctive blue colour to the instruments. This proprietary processing increases cyclic fatigue resistance, improves torque strength and reduces shape memory of the files (Gao et al. 2012). Landed files have passive, U-file cross-sectional designs, whilst nonlanded files have more actively cutting triangular cross sections (Peters 2004). Studies have shown that files with active cutting, nonlanded cross sections remained centred during canal preparation (H€ ubscher et al. 2003, H€ ulsmann et al. 2003), and the results are similar when compared with landed files (Iqbal et al. 2004). Files with increased flexibility and lands produce less canal transportation when compared to nonlanded files, which concentrate cutting edge pressure entirely on the canal wall with a resulting tendency to straighten the canal (McSpadden 2007). To date, numerous studies have examined canal transportation using different rotary NiTi file systems (Javaheri & Javaheri 2007, Gergi et al. 2010, Iqbal et al. 2010, Kunert et al. 2010, Yang et al. 2011). However only one study has looked at the effects of overinstrumentation on the apical foramen and showed transportation of the foramen when using nonlanded rotary files (Gonzalez Sanchez et al. 2012). No study has quantified the amount of transportation of the apical foramen whilst comparing landed, nonlanded and reduced shape memory files in severely curved canals. Overinstrumentation and

© 2014 International Endodontic Journal. Published by John Wiley & Sons Ltd

transportation of the apical foramen may result in an increased incidence of postoperative pain (Siqueira 2005), periapical tissue trauma and the inability to achieve a good apical seal (Haapasalo et al. 2003). The aim of this study was to compare the effect of overinstrumentation on the apical foramen in curved canals when using landed, nonlanded and a nonlanded file system manufactured with reduced shape memory. The null hypothesis to be tested states there is no difference in effect of overinstrumentation on the apical foramen in curved canals between landed, nonlanded and non-landed reduced shape memory NiTi rotary files.

Materials and methods Selection of root canals A total of 45 mesial buccal and mesial roots from extracted maxillary and mandibular molars with fully formed apices, no apical resorption, no evidence of cracks and no history of endodontic treatment were used. Teeth were cleaned, disinfected and stored in 0.9% saline solution at room temperature. Standard access cavities were made. The nearest cusp tip to the canal to be instrumented was flattened and used as a reproducible reference point during instrumentation. Canals were negotiated using a size 10 K file with 6.15% sodium hypochlorite (NaOCl) as a lubricant, until the tip was just visible and tangent to the apical foramen under 209 magnification using a dental operating microscope. The rubber stop was moved to the reference point, the file was withdrawn and the canal length was recorded using an endodontic ruler to the closest 0.25 mm under 59 magnification. Working length was determined by subtracting 0.5 mm from the canal length. Canals were selected only if they would allow a size 10 hand file (but not a size 15) to be placed within 1 mm of the apical foramen. With a size 10 K file in place, bucco-lingual and mesio-distal periapical radiographs of each tooth were digitally exposed with a Fixott-Everett Post Grid (University of Oregon, Portland, OR, USA) attached to the digital sensor. The radiographs were imported into AutoCad 2013 (Autodesk Inc, San Rafael, CA, USA), and the angle and radius of curvature of the canals were determined as described by Pruett et al. 1997. S-shaped canals were excluded, and the greatest angle of curvature obtained from the radiographic views was used. Canals were divided into three similar groups (n = 15) based upon angle and radius of curvature.

International Endodontic Journal, 47, 1064–1071, 2014

1065

NiTi files and apical foramen transportation Hu et al.

Preparation of the model and root canal instrumentation An asymmetrical reference point was placed on each root apex using nail varnish (Fig. 1). This allowed teeth to be accurately repositioned for post-instrumentation imaging and also kept the plane of the foramen in the same position. Teeth were positioned in a customized jig fabricated from medium body polyvinyl siloxane impression material (Aquasil; Dentsply Caulk, Milford, DE, USA). This jig served to keep the plane of the foramen in the same position relative to the imaging microscope and allowed the foramen to be repositioned for accurate post-instrumentation images. Images were taken using a digital microscope (Dino-Lite Pro AM-413T; AnMo Electronics Corp, New Taipei City, Taiwan) attached to an adjustable stand. A reference bar of known length was created using a software program (DinoCapture 2.0; AnMo Electronics Corp, New Taipei City, Taiwan) to aid in the experimental calculations. The apical foramen was imaged after the use of each instrument. The uninstrumented image served as the control. All images were examined to confirm the absence of cracks. Group 1 roots were instrumented 1 mm beyond WL (0.5 mm beyond the apical foramen) using ProFile ISO (landed) files (Dentsply Tulsa Dental, Tulsa,

OK, USA) to size 35, .04 taper according to manufacturer’s instructions. Canal length was remeasured after instrumentation of the coronal and middle thirds and working length recalculated to avoid instrumentation >1 mm beyond WL. An 8 : 1 reduction handpiece was used with a torque-limited electric motor (Aseptico DTC; Aseptico Inc., Woodinville, WA, USA) at 300 rpm. A glide path was established prior to rotary instrumentation with a size 15 NiTi hand file to WL. Irrigation was performed with 2 mL of 6% NaOCl between each file along with gentle recapitulation of a size 10 K file to the foramen. Each instrument was used to prepare three canals before being discarded. Canals were dried with paper points, and the foramen was dried with air from an air/water syringe before being imaged. Groups 2 and 3 were instrumented to size 35, .04 taper using ProFile Vortex (nonlanded) and Vortex Blue (nonlanded reduced shape memory) files (Dentsply Tulsa Dental, Tulsa, OK, USA), respectively, at 500 rpm. All other procedures were identical to group 1.

Image analysis Pre- and post-instrumentation images of the boundary of the apical foramen were analysed using imaging software (ImageJ; National Institutes of Health,

(a)

(b)

(c)

(d)

(e)

(f)

Figure 1 Example of group 2 tooth overinstrumented with ProFile Vortex files. (a) Pre-instrumentation, (b) after overinstrumentation with size 15, (c) size 20, (d) size 25, (e) size 30 and (f) size 35. Bar represents 1 mm.

1066

International Endodontic Journal, 47, 1064–1071, 2014

© 2014 International Endodontic Journal. Published by John Wiley & Sons Ltd

Hu et al. NiTi files and apical foramen transportation

Bethesda, MD, USA) (Fig. 1 a–f). The boundary of the apical foramen was traced manually using the draw function. The area, circularity and Feret’s diameters of the apical foramen were calculated using ImageJ. Circularity was determined based on a perfect circle having a shape factor of 1.0 versus a line that has a shape factor that approaches 0.0 (Loizides et al. 2007). A ratio of Feret’s diameters was calculated as the ratio of maximum to minimum Feret’s diameter. Feret’s diameter defines the longest distance between two parallel straight lines that are tangents to the shape (Michetti et al. 2010). Images were superimposed in Photoshop Elements 11 (Adobe Systems, Inc., San Jose, CA, USA) using the asymmetrical reference point (Fig. 2).

degrees, respectively. Mean radius of curvature in groups 1, 2 and 3, were 5.03  1.11, 5.06  1.25 and 5.19  1.47 mm, respectively.

Working length, instrument fracture and lost samples

Differences in area, circularity and Feret’s diameter ratio within and between groups were analysed using GraphPad Prism 4.0 (GraphPad Software, San Diego, CA, USA). Differences in area and Feret’s diameter ratio between and within groups did not show normal distributions and were therefore analysed using Kruskal–Wallis and Dunn’s post test with significance set at P < 0.05. Circularity differences showed normal distributions and were analysed using one-way ANOVA and Tukey’s post test with significance set at P < 0.05.

When working length was remeasured after instrumentation of the coronal and middle thirds, a 0.25– 0.5 mm decrease in WL was observed in the majority of canals. Two fractured instruments occurred. In group 1, a size 35 ProFile ISO file fractured during withdrawal after the canal had been overinstrumented. The specimen was retained for data analysis because the instrumentation process had been completed. In group 2, a size 20 ProFile Vortex file fractured during instrumentation and the specimen was excluded from the analysis. No Vortex Blue files (group 3) fractured; however, a size 20 file unwound during instrumentation and was replaced with a new file. One specimen from group 3 was lost due to overinstrumentation whilst using a size 20 Vortex Blue file; the cause was determined to be due to operator error during instrumentation, and this specimen was excluded from the analysis. No cracking of the apical dentine was seen. The final for analyses included 43 canals, 15 in group 1 and 14 each in groups 2 and 3, respectively.

Results

Area, circularity and Feret’s diameter ratio

Analysis of data

Angle and radius of curvature The mean angles of curvature in groups 1, 2 and 3, were 53.8  13.3, 53.9  9.2 and 54.1  12.2

Figure 2 Superimposition of Fig. 1 pre-instrumentation photo and ProFile Vortex size 35 post-instrumentation photo. Bar represents 1 mm.

© 2014 International Endodontic Journal. Published by John Wiley & Sons Ltd

Comparisons of landed and nonlanded files in differences between pre-and post-instrumentation area, circularity and Feret’s diameter ratio are shown in Table 1 and Fig. 3 (a–c). Only significant differences (P < 0.05) are depicted in Table 1. Areas of the apical opening increased in each group with increasing file size (Fig. 3a). Significant differences (P < 0.05) were found within and between groups when different file sizes were compared. However, no statistically significant differences in area were found between groups when the same size file was used in each group. No statistically significant differences were found for circularity either within or between groups (Fig. 3b). Although group 1 (ProFile ISO) showed less difference in circularity when compared to groups 2 (ProFile Vortex) and 3 (Vortex Blue), this difference was not statistically significant. Finally, no significant differences were found in Feret’s diameter ratio either within or between groups (Fig. 3c).

International Endodontic Journal, 47, 1064–1071, 2014

1067

NiTi files and apical foramen transportation Hu et al.

Table 1 Area (medians), circularity (means and standard deviations) and Feret’s diameter ratio (medians), P < 0.05

SD

Feret’s diameter ratio Median (mm/mm)

Effect of three NiTi files on transportation of the apical foramen.

To compare landed and nonlanded rotary file overinstrumentation on transportation of the apical foramen in the curved canals of extracted teeth...
305KB Sizes 12 Downloads 0 Views