Smooth flexible versus active tapered shaft design using NiTi rotary instruments
http://endodonticsjournal.com/articles/103/1/Smooth-flexible-versus-active-tapered-shaft-design-using-NiTi-rotary-instruments/Page1.html
By JofER editor
Published on 09/24/2008
L. Bergmans, J.Van Cleynenbreugel, M. Beullens, M.Wevers, B.VanMeerbeek & P. Lambrechts
Departments of Conservative Dentistry, Leuven BIOMAT Research Cluster,
Radiology and Electrical Engineering, ESAT,
Informatics and Telematics, LUDIT,
Metallurgy and Materials Engineering, MTM, Catholic University of Leuven, Belgium.
Aim.
The aim of this study was to evaluate the influence of a smooth flexible versus active tapered shaft design on canal preparation by NiTi rotary techniques.
Conclusions.
In conclusion, under the conditions of this study, the smooth flexible (Lightspeed) as well as the active tapered (GT-rotary) shaft design was capable of preparing canals with good morphological characteristics in curved canals. Further studies are required to focus on other criteria for canal preparation such as efficiency, debris removal, resistance to deformation and/or fracture, time requirements and production costs.
Departments of Conservative Dentistry, Leuven BIOMAT Research Cluster,
Radiology and Electrical Engineering, ESAT,
Informatics and Telematics, LUDIT,
Metallurgy and Materials Engineering, MTM, Catholic University of Leuven, Belgium.
Aim.
The aim of this study was to evaluate the influence of a smooth flexible versus active tapered shaft design on canal preparation by NiTi rotary techniques.
Conclusions.
In conclusion, under the conditions of this study, the smooth flexible (Lightspeed) as well as the active tapered (GT-rotary) shaft design was capable of preparing canals with good morphological characteristics in curved canals. Further studies are required to focus on other criteria for canal preparation such as efficiency, debris removal, resistance to deformation and/or fracture, time requirements and production costs.
Introduction - Materials and methods.
L. Bergmans, J.Van Cleynenbreugel, M. Beullens, M.Wevers, B.VanMeerbeek & P. Lambrechts
Departments of Conservative Dentistry, Leuven BIOMAT Research Cluster,
Radiology and Electrical Engineering, ESAT,
Informatics and Telematics, LUDIT,
Metallurgy and Materials Engineering, MTM, Catholic University of Leuven, Belgium.
Introduction.
Root-canal instrumentation should provide a tapered canal form with adequate deep shape to allow three dimensional obturation (Schilder & Yee1984). However, realizing this objective in small curved canals is often difficult when using traditional instruments. In recent years, nickel-titanium (NiTi) rotary techniques have been developed to improve root-canal preparation (Glosson et al. 1995). In fact, owing to the unique properties of the alloy (e.g. shape memory, superelasticity and superior resistance to torsional fracture), NiTi files were able to improve both the morphological characteristics and safety of root-canal preparation (Walia et al. 1988). Various NiTi file designs for taper, blades, grooves and tip have been suggested. In general, neutral groove angles and radial land areas allow a continuous reaming motion. In addition, the Lightspeed system (Lightspeed Technology Inc., San Antonio, TX, USA) incorporates a smooth flexible shaft with a short cutting head (Fig.1). It represents a design that was originally developed to make stainless steel hand files more flexible (Wildey & Senia 1989). Disadvantages of this system include the fact that it tends to produce a round parallel preparation; flare (taper) can be achieved only using a step-back sequence with numerous instrument sizes (Thompson & Dummer1997a). On the other hand, the GT-rotary system (Dentsply Maillefer, Ballaigues, Switzerland) has an active shaft with greater taper (Fig.1). The increased flare along the active shaft makes the instrument less flexible but it produces the flare required in the final canal shape more efficiently. In addition, this feature allows the practitioner to manage a variably tapered file concept (i.e. changing taper either larger or smaller in the sequence of canal preparation).
In conclusion, one may question whether the existence of a smooth flexible shaft design is still beneficial when using Ni Ti rotary instruments during root-canal preparation. Indeed, the inherent flexibility of the NiTi alloy may reduce the need for a smooth and flexible design. In that case, an active tapered but less flexible design that allows a faster realization of the shaping objective might be favorable if other factors (e.g. debris removal, resistance to deformation and/or fracture and production costs) are not considered.
The purpose of this study was to evaluate the influence of the smooth flexible (Lightspeed) versus active tapered (GT-rotary) shaft design on canal preparation by NiTi rotary instruments in curved human root canals. The comparison was done using high-resolution X-ray microfocus computed tomography (XMCT) and custom- made software, according to a method described by Bergmans et al. (2001).
Specimen selection and preparation.
Ten extracted mandibular molars, stored in 0.5% chloramine in water, were selected for the present study, based on their morphological appearance (i.e. fully formed apices and a similar degree of mesial root curvature on visual inspection).Access openings were made, occlusal surfaces flattened and distal roots removed. Next, ISO 10 K-Files (Dentsply Maillefer) were inserted into the mesial canals so that their tips were just visible at the apical foramina. Individual working lengths were calculated 1.0 mm short of these positions. Finally, the teeth were mounted in sample holders, placed into a sodium hypochlorite solution (2.5%) for 30 min, and again stored in 0.5% chloramine in water.
Scanning of uninstrumented teeth (PRE).
The hardware device used in this study was a desktop X-ray microfocus CT scanner (SkyScan 1072, SkyScan b.v.b.a., Aartselaar, Belgium) (Fig. 2). A first scanning procedure was completed for all teeth using9 0.7 kV, 300 mA and13x magnification resulting in a pixel size of 30x30 mm. The scanning procedure contained two stages and approximately 3.5 h were needed for one scanning. During acquisition, hundreds of two-dimensional projections through 1808 of rotation were saved in digital form in a computer disk. In order to gain the third dimension, the data stored as projections were then transformed into 250 new two-dimensional images (cross-sections).This data was stored for later use by software. After scanning, the samples were replaced into a 0.5% chloramine in water solution for 24 h to recover from dehydration.
Each mesial root (n =10), containing two similar canals, was instrumented by both systems (randomly distributed to the buccal and lingual canals) and groups were defined as ‘Smooth’and ‘Active’. ‘Smooth’ used the Lightspeed system (Fig.1). The files have a smooth flexible shaft (nontapered), short cutting heads (0.254-1.75 mm in length) with blades of U-design (neutral rake angle), and a noncutting tip. The complete set incorporates 22 instruments of ISO sizing2 0-100, with half sizes between 20 and 65. ‘Active’ used the GT-rotary system (Fig.1). The files are made by grinding three equally spaced U-shaped grooves around the shaft of a tapered NiTi wire. The instruments have flutes with flat outer edges, known as radial land areas and a noncutting pilot tip. The standard set contains four taper sizes (.12, .10, .08, and.06). In addition, a series of .04 tapered files, with variable tip sizes (15, 20, 25, 30, 35 and 40) and16-mm cutting surface, is available for a second-stage instrumentation after gauging of the original apical constriction diameter.
All canals were instrumented by the same operator (LB) and according to the manufacturers’ instructions (see below). No attempt was made to create coronal preparing with Gates-Glidden burs because it would have reduced the magnitude of apical transportation (Montgomery1985). Cleaning and shaping was initiated using a size no.10 K-File followed by a size no.15 K-File, both in a watch-winding motion. All files were used with the pulp chamber containing a combination of 2.5% sodium hypochlorite and Glyde (Dentsply Maillefer). Irrigation was delivered with a 27-gauge needle (Monoject, Sherwood Medical, St Louis, MO, USA) and2 mL of irrigation were used between each file size. All files were used with light apical pressure and constant speed in a torque- control handpiece powered by an electric stepper motor (Endostepper, SET, Germany). This motor provided presettings for each instrument type and size for optimal performance. In addition, new files were used for each canal.
Group ‘Smooth’- Lightspeed system (LS).
Canals assigned to group‘Smooth’ (n =10) were prepared with LS-instruments at a speed of1300 r.p.m. Apical instrumentation was initiated with a size 20 LS-instrument and continued with sequentially larger sizes until reaching size 45 (MAR). If any instrument failed to go to the working length, then the previous one was reused. Apical preparation was completed with a stepback of1.0 mm at a time with the next four larger instruments. Finally, mid-root instrumentation was continued by continuing the step-back ‘by feel’, as described by the manufacturer, to a size 70; recapitulation to working length was completed with the MAR to confirm canal patency.
Group ‘Active’- GT-rotary system (GT).
Canals assigned to group‘Active’ (n =10) were prepared with GT-instruments in a modified double flare concept (Fava1983) at speeds of 350 r.p.m. First, the sequence of four variably tapered instruments (.12/20, .10/20, .08/ 20 and .06/20) was repeated in a crown-down manner until the canals were instrumented to an apical size 20 with taper varying from .06 for the smallest canals to .08 for the larger ones. Canal preparation was completed by using. 04 tapered instruments with increasing tip sizes at full working length for apical preparation to a size 35 or 40. After mechanical preparation, the samples were irrigated with10% citric acid solution, placed into an ultrasound bath for 5 min to remove dentine chips and debris, and again stored in 0.5% chloramine in water.
Scanning of instrumented teeth (POST).
After repositioning, a second scanning procedure was completed for all teeth. Previous parameter settings (90.7 kV, 300 mA and 13_ magnification) were applied, thereby providing data that were stored for later use by software.
Image analysis.
Medical image volume fusion software described by Maes et al. (1997) was employed to geometrically register the image volumes resulting from both scanning procedures (PRE and POST). Next, a previously described methodology was applied on the registered image volumes (Bergmans et al. 2001). According to this method, qualitative analysis was done by visual inspection (3608 rotation) and quantitative analysis was performed at five perpendicular reslices. A first level was taken just below the furcation, and four more slices were made at equally spaced intervals (Fig.3a). The most apical slice was within 1-2 mm of the apical terminus. Values for transportation (Fig. 4a) and net transportation (Fig. 4b) were automatically (i.e. operator has no influence on the results) calculated in 36 directions and these values were grouped to reduce the amount of information. This procedure resulted in values for the buccal, mesial, lingual and distal direction (each representing the mean of three of the original 36 measurements), and values for the directions in between (each representing the mean of six of the original measurements). Those eight directions were coded as illustrated in Fig.3b. Centring ability (Fig. 4b) of the instrument towards the original canal was calculated by the ratio of net transportation and canal diameter after preparation (i.e. centring ratio). To compare rootcanal curvature, a quantitative description of the global root-canal anatomy was provided by the ‘smoothed out’ version of the PRE-axis, and the association of a Frenet-Serret coordinate frame a long the mid-point of the curve as described by Bergmans et al. (2001). Finally, subvolumes (i.e. in between the different horizontal reslices) were calculated, and by subtracting the PRE-subvolumes from the POST-subvolumes, the volumes of removed dentine for the coronal, middle-coronal, middle, middle-apical and apical 1/5th of the root-canal region was known.
The Shapiro Wilk test was used to test the assumption of normality of the data. The multiway factorial anova was then used to test for significant differences between means. When the overall F-test indicated a significant difference, the multiple comparison Tukey-Kramer procedure was taken to investigate which means differ from which other means. Regarding volumes and curvatures, the t-test or Wilcoxon test procedure was used.
Departments of Conservative Dentistry, Leuven BIOMAT Research Cluster,
Radiology and Electrical Engineering, ESAT,
Informatics and Telematics, LUDIT,
Metallurgy and Materials Engineering, MTM, Catholic University of Leuven, Belgium.
Introduction.
Root-canal instrumentation should provide a tapered canal form with adequate deep shape to allow three dimensional obturation (Schilder & Yee1984). However, realizing this objective in small curved canals is often difficult when using traditional instruments. In recent years, nickel-titanium (NiTi) rotary techniques have been developed to improve root-canal preparation (Glosson et al. 1995). In fact, owing to the unique properties of the alloy (e.g. shape memory, superelasticity and superior resistance to torsional fracture), NiTi files were able to improve both the morphological characteristics and safety of root-canal preparation (Walia et al. 1988). Various NiTi file designs for taper, blades, grooves and tip have been suggested. In general, neutral groove angles and radial land areas allow a continuous reaming motion. In addition, the Lightspeed system (Lightspeed Technology Inc., San Antonio, TX, USA) incorporates a smooth flexible shaft with a short cutting head (Fig.1). It represents a design that was originally developed to make stainless steel hand files more flexible (Wildey & Senia 1989). Disadvantages of this system include the fact that it tends to produce a round parallel preparation; flare (taper) can be achieved only using a step-back sequence with numerous instrument sizes (Thompson & Dummer1997a). On the other hand, the GT-rotary system (Dentsply Maillefer, Ballaigues, Switzerland) has an active shaft with greater taper (Fig.1). The increased flare along the active shaft makes the instrument less flexible but it produces the flare required in the final canal shape more efficiently. In addition, this feature allows the practitioner to manage a variably tapered file concept (i.e. changing taper either larger or smaller in the sequence of canal preparation).
In conclusion, one may question whether the existence of a smooth flexible shaft design is still beneficial when using Ni Ti rotary instruments during root-canal preparation. Indeed, the inherent flexibility of the NiTi alloy may reduce the need for a smooth and flexible design. In that case, an active tapered but less flexible design that allows a faster realization of the shaping objective might be favorable if other factors (e.g. debris removal, resistance to deformation and/or fracture and production costs) are not considered.
The purpose of this study was to evaluate the influence of the smooth flexible (Lightspeed) versus active tapered (GT-rotary) shaft design on canal preparation by NiTi rotary instruments in curved human root canals. The comparison was done using high-resolution X-ray microfocus computed tomography (XMCT) and custom- made software, according to a method described by Bergmans et al. (2001).
Figure 1. Upper: Lightspeed shaft design.
Lower: GT-rotary shaft design.
Specimen selection and preparation.
Ten extracted mandibular molars, stored in 0.5% chloramine in water, were selected for the present study, based on their morphological appearance (i.e. fully formed apices and a similar degree of mesial root curvature on visual inspection).Access openings were made, occlusal surfaces flattened and distal roots removed. Next, ISO 10 K-Files (Dentsply Maillefer) were inserted into the mesial canals so that their tips were just visible at the apical foramina. Individual working lengths were calculated 1.0 mm short of these positions. Finally, the teeth were mounted in sample holders, placed into a sodium hypochlorite solution (2.5%) for 30 min, and again stored in 0.5% chloramine in water.
Scanning of uninstrumented teeth (PRE).
The hardware device used in this study was a desktop X-ray microfocus CT scanner (SkyScan 1072, SkyScan b.v.b.a., Aartselaar, Belgium) (Fig. 2). A first scanning procedure was completed for all teeth using9 0.7 kV, 300 mA and13x magnification resulting in a pixel size of 30x30 mm. The scanning procedure contained two stages and approximately 3.5 h were needed for one scanning. During acquisition, hundreds of two-dimensional projections through 1808 of rotation were saved in digital form in a computer disk. In order to gain the third dimension, the data stored as projections were then transformed into 250 new two-dimensional images (cross-sections).This data was stored for later use by software. After scanning, the samples were replaced into a 0.5% chloramine in water solution for 24 h to recover from dehydration.
Figure 2. SkyScan1072 X-ray microfocus CT scanner.
Each mesial root (n =10), containing two similar canals, was instrumented by both systems (randomly distributed to the buccal and lingual canals) and groups were defined as ‘Smooth’and ‘Active’. ‘Smooth’ used the Lightspeed system (Fig.1). The files have a smooth flexible shaft (nontapered), short cutting heads (0.254-1.75 mm in length) with blades of U-design (neutral rake angle), and a noncutting tip. The complete set incorporates 22 instruments of ISO sizing2 0-100, with half sizes between 20 and 65. ‘Active’ used the GT-rotary system (Fig.1). The files are made by grinding three equally spaced U-shaped grooves around the shaft of a tapered NiTi wire. The instruments have flutes with flat outer edges, known as radial land areas and a noncutting pilot tip. The standard set contains four taper sizes (.12, .10, .08, and.06). In addition, a series of .04 tapered files, with variable tip sizes (15, 20, 25, 30, 35 and 40) and16-mm cutting surface, is available for a second-stage instrumentation after gauging of the original apical constriction diameter.
All canals were instrumented by the same operator (LB) and according to the manufacturers’ instructions (see below). No attempt was made to create coronal preparing with Gates-Glidden burs because it would have reduced the magnitude of apical transportation (Montgomery1985). Cleaning and shaping was initiated using a size no.10 K-File followed by a size no.15 K-File, both in a watch-winding motion. All files were used with the pulp chamber containing a combination of 2.5% sodium hypochlorite and Glyde (Dentsply Maillefer). Irrigation was delivered with a 27-gauge needle (Monoject, Sherwood Medical, St Louis, MO, USA) and2 mL of irrigation were used between each file size. All files were used with light apical pressure and constant speed in a torque- control handpiece powered by an electric stepper motor (Endostepper, SET, Germany). This motor provided presettings for each instrument type and size for optimal performance. In addition, new files were used for each canal.
Group ‘Smooth’- Lightspeed system (LS).
Canals assigned to group‘Smooth’ (n =10) were prepared with LS-instruments at a speed of1300 r.p.m. Apical instrumentation was initiated with a size 20 LS-instrument and continued with sequentially larger sizes until reaching size 45 (MAR). If any instrument failed to go to the working length, then the previous one was reused. Apical preparation was completed with a stepback of1.0 mm at a time with the next four larger instruments. Finally, mid-root instrumentation was continued by continuing the step-back ‘by feel’, as described by the manufacturer, to a size 70; recapitulation to working length was completed with the MAR to confirm canal patency.
Group ‘Active’- GT-rotary system (GT).
Canals assigned to group‘Active’ (n =10) were prepared with GT-instruments in a modified double flare concept (Fava1983) at speeds of 350 r.p.m. First, the sequence of four variably tapered instruments (.12/20, .10/20, .08/ 20 and .06/20) was repeated in a crown-down manner until the canals were instrumented to an apical size 20 with taper varying from .06 for the smallest canals to .08 for the larger ones. Canal preparation was completed by using. 04 tapered instruments with increasing tip sizes at full working length for apical preparation to a size 35 or 40. After mechanical preparation, the samples were irrigated with10% citric acid solution, placed into an ultrasound bath for 5 min to remove dentine chips and debris, and again stored in 0.5% chloramine in water.
Scanning of instrumented teeth (POST).
After repositioning, a second scanning procedure was completed for all teeth. Previous parameter settings (90.7 kV, 300 mA and 13_ magnification) were applied, thereby providing data that were stored for later use by software.
Image analysis.
Medical image volume fusion software described by Maes et al. (1997) was employed to geometrically register the image volumes resulting from both scanning procedures (PRE and POST). Next, a previously described methodology was applied on the registered image volumes (Bergmans et al. 2001). According to this method, qualitative analysis was done by visual inspection (3608 rotation) and quantitative analysis was performed at five perpendicular reslices. A first level was taken just below the furcation, and four more slices were made at equally spaced intervals (Fig.3a). The most apical slice was within 1-2 mm of the apical terminus. Values for transportation (Fig. 4a) and net transportation (Fig. 4b) were automatically (i.e. operator has no influence on the results) calculated in 36 directions and these values were grouped to reduce the amount of information. This procedure resulted in values for the buccal, mesial, lingual and distal direction (each representing the mean of three of the original 36 measurements), and values for the directions in between (each representing the mean of six of the original measurements). Those eight directions were coded as illustrated in Fig.3b. Centring ability (Fig. 4b) of the instrument towards the original canal was calculated by the ratio of net transportation and canal diameter after preparation (i.e. centring ratio). To compare rootcanal curvature, a quantitative description of the global root-canal anatomy was provided by the ‘smoothed out’ version of the PRE-axis, and the association of a Frenet-Serret coordinate frame a long the mid-point of the curve as described by Bergmans et al. (2001). Finally, subvolumes (i.e. in between the different horizontal reslices) were calculated, and by subtracting the PRE-subvolumes from the POST-subvolumes, the volumes of removed dentine for the coronal, middle-coronal, middle, middle-apical and apical 1/5th of the root-canal region was known.
The Shapiro Wilk test was used to test the assumption of normality of the data. The multiway factorial anova was then used to test for significant differences between means. When the overall F-test indicated a significant difference, the multiple comparison Tukey-Kramer procedure was taken to investigate which means differ from which other means. Regarding volumes and curvatures, the t-test or Wilcoxon test procedure was used.
Figure 3. (a) Measurements were made at five horizontal levels (perpendicular reslices).
(b) Representation of eight horizontal directions.
Figure 4. (a) Definition of transportation (T =d1 _d2).
(b) Definition of net transportation (NT + (T _ T0)) and centring ability (ratio = NT/D).
Results.
Experimental groups.
Initial analysis of canal curvature and PRE-volume indicated no significant differences between the two groups (Table 1) (t-test).
Qualitative analysis.
Volume rendering revealed detailed images of general and local canal shape before (PRE) and after (POST) instrumentation (Fig.5). Visual inspection of the POST-volume images in 3608 rotation disclosed no aberrations.
Dentine removal.
Quantitative analysis revealed that instrumentation resulted in increase in total canal volume (mean _ SD) of 0.97 _0.39 mm3 for the ‘Smooth’ (LS) group, and 1.43 _0.85 mm3 for the ‘Active’ (GT) group. Differences between the two groups were not statistically significant (Wilcoxon test). However, the amount of horizontal region-dependent dentine removal indicated more significant (P < 0.05) dentine removal in the middle to apical third of the root for the ‘Active’ (GT) group when compared to the ‘Smooth’ (LS) group (Wilcoxon test) (Table 2).
The ability of the instrument to remain centred is more important than the volume of dentine lost. No significant differences were observed in amount of canal transportation between the two groups at all five levels studied. However, significant differences were observed in the direction of transportation (Tables 3 and 4). Both groups showed significantly (P < 0.0001) more transportation towards the furcation area (directions 3 and 4) at the most coronal level (level 5) (Table 3). For the ‘Smooth’ group (LS), this effect was also significant (P < 0.001) at the middle-coronal level (level 4). In addition, the ‘Active’ group (GT) showed significantly (P < 0.01) more transportation towards the outer aspect of the curve (directions 7 and 8) than towards the inner aspect (directions 4 and 5) at the apical level (level1).
Net transportation and centring ability showed comparable results for both groups (Table 4).At the most coronal level (level 5), the net transportation and centre displacement was more (P < 0.0001) towards the inner side (directions 3 and 4) than towards the outer side of the curvature (directions 7 and 8). At mid-curvature (level 3), more dentine was removed at the outer part of the curve (P < 0.01), resulting in a centre displacement towards the mesio-buccal or mesio-lingual direction (direction 8). More apical to this point (levels 1 and 2), the outer relocation (directions 1, 7 and 8) of the centre was even more generalized (P < 0.0001).
Initial analysis of canal curvature and PRE-volume indicated no significant differences between the two groups (Table 1) (t-test).
Qualitative analysis.
Volume rendering revealed detailed images of general and local canal shape before (PRE) and after (POST) instrumentation (Fig.5). Visual inspection of the POST-volume images in 3608 rotation disclosed no aberrations.
Table 1. Morphometric data determined for uninstrumented mandibular mesial root canals (means +SD, n =10).
Figure 5. Representative 3D computer-generated images of the canal shape for the two instrumentation groups.
Dentine removal.
Quantitative analysis revealed that instrumentation resulted in increase in total canal volume (mean _ SD) of 0.97 _0.39 mm3 for the ‘Smooth’ (LS) group, and 1.43 _0.85 mm3 for the ‘Active’ (GT) group. Differences between the two groups were not statistically significant (Wilcoxon test). However, the amount of horizontal region-dependent dentine removal indicated more significant (P < 0.05) dentine removal in the middle to apical third of the root for the ‘Active’ (GT) group when compared to the ‘Smooth’ (LS) group (Wilcoxon test) (Table 2).
Table 2. Dentine removal (means +SD) (mm3) related to instrument type and horizontal region.
The ability of the instrument to remain centred is more important than the volume of dentine lost. No significant differences were observed in amount of canal transportation between the two groups at all five levels studied. However, significant differences were observed in the direction of transportation (Tables 3 and 4). Both groups showed significantly (P < 0.0001) more transportation towards the furcation area (directions 3 and 4) at the most coronal level (level 5) (Table 3). For the ‘Smooth’ group (LS), this effect was also significant (P < 0.001) at the middle-coronal level (level 4). In addition, the ‘Active’ group (GT) showed significantly (P < 0.01) more transportation towards the outer aspect of the curve (directions 7 and 8) than towards the inner aspect (directions 4 and 5) at the apical level (level1).
Net transportation and centring ability showed comparable results for both groups (Table 4).At the most coronal level (level 5), the net transportation and centre displacement was more (P < 0.0001) towards the inner side (directions 3 and 4) than towards the outer side of the curvature (directions 7 and 8). At mid-curvature (level 3), more dentine was removed at the outer part of the curve (P < 0.01), resulting in a centre displacement towards the mesio-buccal or mesio-lingual direction (direction 8). More apical to this point (levels 1 and 2), the outer relocation (directions 1, 7 and 8) of the centre was even more generalized (P < 0.0001).
Discussion - References.
Discussion.
In recent years, the performance of NiTi rotary systems has been compared with those of traditional stainless steel hand instruments. However, owing to the dissimilarity in use, design and alloy of both groups, this type of study rarely reveals the influence of one specific feature. Additionally, coronal flaring with Gates-Glidden burs may reduce the ability to detect canal transportation because only the apical one-half of the canal remains to show the effects of instrumentation.
The present study evaluated two NiTi rotary systems (i.e. Lightspeed and GT-rotary) that were used in continuous mechanical rotation with no preparing with Gates-Glidden burs. For that reason, variation in canal preparation was attributed to a difference in instrument design (i.e. smooth flexible vs. active tapered). Furthermore, mesial canals of the same roots were used for both techniques to eliminate the variables encountered in root canals in different teeth (e.g. curvature, dentine hardness, canal diameter and length), thereby reducing the crucial amount of samples. The determination of canal curvatures and initial (PRE) root-canal volumes by software confirmed the similarity of the two experimental groups. All canals showed moderate global curvatures (ranging from 143 to 1778) as seen in regular clinical circumstances. The acceptance of more severe curvatures would increase the number of samples and the working load .
Despite efforts to ensure two distinct mesial canals, 83% of the roots hadanisthmus or excessively prolonged fin in at least one level. Parts of these prolongations and fins are impossible to reach with endodontic instruments. For that reason, main areas of the root canals were initially determined through visually fitting an oval figure (long/short diameter ratio _ 2) within the total canal contour on the level of each cross-section, whilst blocking out the remaining surrounding part (Fig.6). Visualization of canal shape before (PRE) and after (POST) instrumentation provided impressions of global preparation characteristics. In both groups, no canal aberrations occurred. For all canals, the irregular initial shape had become more gradually tapered during preparation, although objective criteria to determine canal flow and taper were missing.
Far more interesting is the amount of quantitative information on instrumentation effects that was obtained. Under the conditions of the present study, statistical analysis (multiway factorial anova) could not reveal any difference between the ‘Smooth’ (LS) and ‘Active’ (GT) group as for the amount of transportation, net transportation and centring ability. The lack of significance between the two groups may be a consequence of an insufficient number of samples. After all, canal preparation characteristics may be dictated more by anatomy than by the difference in instrumentation method. Although a high degree of similarity between the two groups was confirmed, the variety of root-canal anatomy within the groups produced relatively high dispersion of the data. On the other hand, any unobserved differences between the two instrumentation methods may, therefore, be so small that they are irrelevant for clinical practice.
At mid-curvature, net transporation and centre movement was towards the outer side of the curvature. This finding was consistent with previous work of Thompson & Dummer (1997b,c,1998a,b, 2000) regarding preparation characteristics of ProFile .04 Taper Series 29, NT Engine/McXim, Mity Roto 3608 and Naviflex, Quantec Series 2000 and Hero 642. However, after Lightspeed instrumentation, the same investigators found centre movement towards the inner aspect of the canal at all positions except for the end-point (Thompson & Dummer 1997a). At the apical section in this study, the direction of net transportation was to the mesio-buccal or mesio-lingual direction, thus towards the outer side of the curve. Once more, the values for net transportation were fairly small and therefore no zipping or ledging could be found. Centring ratios for preparation with stainless steel instrumentation techniques were reported ranging from 0.21 to 0.47 (Leseberg & Montgomery 1991). In the present study, the highest mean centring ratio was only 0.15. Glosson et al. (1995) reported similar centring ratios of 0.12 for the apical, and 0.16 for the middle level for the Lightspeed group.
Finally, it is important to notice that, in general, dentine was removed in all directions at all levels, indicating that most areas of the root canal were touched. On the other hand, it should be emphasized that parts of the prolongations and fins were initially blocked out. Ideally, when experiments are carried out to compare different preparation techniques, the diameter of the apical preparation is of importance. In the current experiment, canals assigned to the ‘Smooth’ (LS) group had size 45 master apical rotaries and the maximum apical preparation diameter in the ‘Active’ (GT) group was size 35-40. The reason for this discrepancy is three-fold. First, morphometric video analysis of the Lightspeed system demonstrated that the diameter of the instrument’s head was frequently under-sized (Table 5) (Marsicovetere et al. 1996). Second, the dissimilarity in instrument design (Table 5) combined with the difference in use (step-back vs. crown-down) explains the fact that expected apical root-canal dimensions after preparation are comparable (Table 6). Third, the perpendicular reslices were made at equally spaced intervals and the most apical reslice was within 1-2 mm from the apical terminus because equal distribution of measuring points over the total length of the root presented amore individual approach than measuring at fixed distances from the apex.
The present study evaluated root-canal geometry using microfocus computer tomography (XMCT). This technique is nondestructive and, if combined with appropriate software, provides data in three dimensions based on high-resolution images of extracted human teeth under natural conditions (Bergmans et al. 2001). The use of XMCT in endodontic research is new. Recently, more suitable measurement software has become available on a prototype basis, allowing evaluation of matched specimens before and after preparation (Peters et al. 2000, Bergmans et al. 2001). The software used in the present study provides objective quantitative information because the examiner has no role in the calculating process. The processing takes place based on previously determined standardized criteria.
In recent years, the performance of NiTi rotary systems has been compared with those of traditional stainless steel hand instruments. However, owing to the dissimilarity in use, design and alloy of both groups, this type of study rarely reveals the influence of one specific feature. Additionally, coronal flaring with Gates-Glidden burs may reduce the ability to detect canal transportation because only the apical one-half of the canal remains to show the effects of instrumentation.
The present study evaluated two NiTi rotary systems (i.e. Lightspeed and GT-rotary) that were used in continuous mechanical rotation with no preparing with Gates-Glidden burs. For that reason, variation in canal preparation was attributed to a difference in instrument design (i.e. smooth flexible vs. active tapered). Furthermore, mesial canals of the same roots were used for both techniques to eliminate the variables encountered in root canals in different teeth (e.g. curvature, dentine hardness, canal diameter and length), thereby reducing the crucial amount of samples. The determination of canal curvatures and initial (PRE) root-canal volumes by software confirmed the similarity of the two experimental groups. All canals showed moderate global curvatures (ranging from 143 to 1778) as seen in regular clinical circumstances. The acceptance of more severe curvatures would increase the number of samples and the working load .
Despite efforts to ensure two distinct mesial canals, 83% of the roots hadanisthmus or excessively prolonged fin in at least one level. Parts of these prolongations and fins are impossible to reach with endodontic instruments. For that reason, main areas of the root canals were initially determined through visually fitting an oval figure (long/short diameter ratio _ 2) within the total canal contour on the level of each cross-section, whilst blocking out the remaining surrounding part (Fig.6). Visualization of canal shape before (PRE) and after (POST) instrumentation provided impressions of global preparation characteristics. In both groups, no canal aberrations occurred. For all canals, the irregular initial shape had become more gradually tapered during preparation, although objective criteria to determine canal flow and taper were missing.
Far more interesting is the amount of quantitative information on instrumentation effects that was obtained. Under the conditions of the present study, statistical analysis (multiway factorial anova) could not reveal any difference between the ‘Smooth’ (LS) and ‘Active’ (GT) group as for the amount of transportation, net transportation and centring ability. The lack of significance between the two groups may be a consequence of an insufficient number of samples. After all, canal preparation characteristics may be dictated more by anatomy than by the difference in instrumentation method. Although a high degree of similarity between the two groups was confirmed, the variety of root-canal anatomy within the groups produced relatively high dispersion of the data. On the other hand, any unobserved differences between the two instrumentation methods may, therefore, be so small that they are irrelevant for clinical practice.
Figure 6. Representation of the blocking-out process: The main area of the upper root canal was initially determined through visually fitting an oval figure (long/short diameter ratio _ 2) within the total canal contour, whilst blocking out the remaining surrounding part (yellow).
At mid-curvature, net transporation and centre movement was towards the outer side of the curvature. This finding was consistent with previous work of Thompson & Dummer (1997b,c,1998a,b, 2000) regarding preparation characteristics of ProFile .04 Taper Series 29, NT Engine/McXim, Mity Roto 3608 and Naviflex, Quantec Series 2000 and Hero 642. However, after Lightspeed instrumentation, the same investigators found centre movement towards the inner aspect of the canal at all positions except for the end-point (Thompson & Dummer 1997a). At the apical section in this study, the direction of net transportation was to the mesio-buccal or mesio-lingual direction, thus towards the outer side of the curve. Once more, the values for net transportation were fairly small and therefore no zipping or ledging could be found. Centring ratios for preparation with stainless steel instrumentation techniques were reported ranging from 0.21 to 0.47 (Leseberg & Montgomery 1991). In the present study, the highest mean centring ratio was only 0.15. Glosson et al. (1995) reported similar centring ratios of 0.12 for the apical, and 0.16 for the middle level for the Lightspeed group.
Finally, it is important to notice that, in general, dentine was removed in all directions at all levels, indicating that most areas of the root canal were touched. On the other hand, it should be emphasized that parts of the prolongations and fins were initially blocked out. Ideally, when experiments are carried out to compare different preparation techniques, the diameter of the apical preparation is of importance. In the current experiment, canals assigned to the ‘Smooth’ (LS) group had size 45 master apical rotaries and the maximum apical preparation diameter in the ‘Active’ (GT) group was size 35-40. The reason for this discrepancy is three-fold. First, morphometric video analysis of the Lightspeed system demonstrated that the diameter of the instrument’s head was frequently under-sized (Table 5) (Marsicovetere et al. 1996). Second, the dissimilarity in instrument design (Table 5) combined with the difference in use (step-back vs. crown-down) explains the fact that expected apical root-canal dimensions after preparation are comparable (Table 6). Third, the perpendicular reslices were made at equally spaced intervals and the most apical reslice was within 1-2 mm from the apical terminus because equal distribution of measuring points over the total length of the root presented amore individual approach than measuring at fixed distances from the apex.
Table 5. File dimensions of both systems.
Table 6. Expected apical root-canal dimensions after preparation.
The present study evaluated root-canal geometry using microfocus computer tomography (XMCT). This technique is nondestructive and, if combined with appropriate software, provides data in three dimensions based on high-resolution images of extracted human teeth under natural conditions (Bergmans et al. 2001). The use of XMCT in endodontic research is new. Recently, more suitable measurement software has become available on a prototype basis, allowing evaluation of matched specimens before and after preparation (Peters et al. 2000, Bergmans et al. 2001). The software used in the present study provides objective quantitative information because the examiner has no role in the calculating process. The processing takes place based on previously determined standardized criteria.
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