Evaluation of debris and smear layer formation using three different NI-TI rotary instrument systems: An in vitro scanning electron microscope study.

Aim: The aim of the study is to evaluate of debris and smear layer formation after using rotary ProTaper Universal, Twisted File, and XP Endo file systems under scanning electron microscope. Materials and
Methods: Forty freshly extracted mandibular second premolar teeth were taken to decoronate at the cementoenamel junction to make the remaining root length 15 mm. Specimens were divided into four groups of 10 teeth each, Group I (control) - no instrumentation. Group II - ProTaper Universal rotary file (F2), Group III - twisted file (ISO size 0.25 and 6% taper), Group IV - XP Endo file (ISO size 0.25). During instrumentation, 5 ml normal saline was used as irrigating agent. Grooves parallel to the longitudinal axis of the root were made on the mesial and distal surface of each specimen to split it into two halves and examined under scanning electron microscope at ×1500 and ×5000 magnification. Photomicrographs were taken to evaluate debris and smear layer. Evaluation of photomicrographs was done using a score index.
Results: One-way analysis of variance (ANOVA) was used to compare more than one means at a time. Tukey's critical difference followed by ANOVA was used to compare the mean values pair wise. P <0.05 was considered to be statistically significant. Among all the file systems, Group II showed maximum amount of debris (3.50 ± 1.109) followed by Group III (2.83 ± 1.238) and least amount was showed by Group IV (2.65 ± 1.122) at all levels (cervical, middle, and apical third). Among all the experimental groups, Group II showed maximum amount of smear layer (2.75 ± 1.149) followed by Group III (2.40 ± 0.982) and least amount of smear layer shown by Group IV (2.10 ± 0.841) at all levels (cervical, middle and apical third), the result was statistically significant (P < 0.05). Conclusions: At all the levels (cervical third, middle third, and apical third), among all the experimental groups, highest amount of debris and smear layer was formed by ProTaper Universal rotary file followed by Twisted file and least amount showed by XP Endo file system. In all the levels, control group showed highest amount of debris but least amount of smear layer. Copyright:

INTRODUCTION

Root canal treatment usually involves the chemicomechanical removal of infected dentin, bacteria, and their byproduct from within the root canal system followed by disinfection of the canal wall and obturation. For success of root canal treatment, three-dimensional sealing of root canal using obturating materials is most important. However, to achieve this, most obstructing factors are debris and smear layer developed in root canal wall during instrumentation. Several researchers have strived to understand the effect of the smear layer on the root canal seal.[1]

Whenever dentin is cut, the mineralized tissues are shattered and not shredded or cleaved to produce considerable quantities of debris.[2] Smear layer is ultrathin deposit of organic and inorganic material which contains bacteria and their by-products. Much of this, made up of very small particles of mineralized collagen matrix, is spread over the surface to form the smear layer.[3] The first researchers to describe the smear layer in instrumented root canal surfaces were McComb and Smith (1975).[4] Cohen defined smear layer as – an amorphous, relatively smooth layer of microcrystalline debris whose featureless surface cannot be seen with the naked eye. Debris was defined as dentin chips, and vital or necrotic pulp remnants loosely attached to the canal walls (Hülsmann M et al. 1997).

There is controversy regarding whether to preserve or removing the smear layer, some authors support maintaining the smear layer. They believe that smear layer blocks the dentinal tubules and will limit bacterial penetration by making the dentin relatively impermeable.[56]

Others believe that the smear layer should be completely removed from the root canal surface. They argue that the smear layer being a loosely adherent structure can shelter bacteria and provide a pathway for leakage.[78]

Debris and smear layer removal depends not only on the methods of irrigation but also on the use of endodontic instruments, like the way the instrument is used and the method of preparation.[9]

NiTi instruments such as ProTaper Universal (Dentsply, Maillefer, Switzerland) one of the most commonly used systems. Convex triangular cross-sectional design of ProTaper Universal resembles that of a reamer, with three machined cutting edges and convex blade.[10] Various recently introduced NiTi instruments such as Twisted Files which are manufactured by SybronEndo (Orange, CA, USA) came in the market in 2008 and XP Endo file system introduced by FKG Dentaire SA. Switzerland (2017). This new XP Endo files have serpentine motion in the canal and instrument the canal three dimensionally.

Thus, the aim of the in vitro study was to compare the debris and smear layer formation after instrumentation in the root canal space under scanning electron microscope (SEM) at ×1500 and ×5000 magnification using these three different NiTi rotary instrumentation systems.

The null hypothesis proposed was that there will be no difference in term of debris and smear layer formation in the root canal system after using different NiTi instruments.

MATERIALS AND METHODS

Forty human mandibular second premolars extracted for orthodontic reasons with inclusion criteria – (i) teeth with single canal, (ii) fully formed apices, (iii) straight root with moderate curvature (<25°) according to Schneider's method were collected and exclusion criteria – (i) teeth with caries or restorations, (ii) teeth with severe anatomic variations, (iii) root fractures, (iv) teeth with calcified canals were collected for the study. Immediately after extraction, teeth were cleaned to soft tissue debris with moist cotton and with ultrasonic scaler if any calculus and stains present. Occupational safety and health administration and the Centers for Disease Control and Prevention (CDC) recommendations and guidelines were followed for disinfecting the samples.

Armamentarium used in the study

Canal preparation

Mesiodistal and buccolingual radiographs were taken to verify the presence of a single canal. All the specimens were decoronated just above the cementoenamel junction to make a flattened reference point and to set the remaining length of the root at 15 mm. The patency of the canals was verified with a no. 10 K file.

Specimens were then randomly divided into four groups with ten samples each. Group I: Root canal without instrumentation (control), Group II: ProTaper Universal rotary file system, Group III: Twisted file, and Group IV: XP Endo shaper and finisher rotary instrument were used to prepare root canal.

Instrumentation of root canals

All the instrumentation was done according to manufacturer's instructions at the recommended rotary speeds using a 16:1 gear reduction handpiece powered by a torque-controlled endomotor (X-Smart; Dentsply, Maillefer, CA, USA). The instrumentation done in Groups II with ProTaper Universal with 250 rpm using crown-down canal preparation using a gentle brushing action; in Group III, twisted file at 500 rpm using crown down canal preparation using a gentle in-and-out motion. Instrumentation was done up to 0.06 taper size 30, and in Group IV, Xp Endo shaper followed by Xp Endo finisher at 800 rpm. Xp Endo shaper was used for 10 s with in-and-out motions and an amplitude of 3–4 mm up to the WL. Using gentle movements of insertion and withdrawal, XP Endo Finisher was applied in each canal during 1 min.

Sample preparation for scanning electron microscope examination

The canals were dried with absorbent paper points, and orifices protected with a cotton pellet. Longitudinal grooves parallel to the longitudinal axis of the root were made with diamond disk on the mesial and distal surface of each specimen using a diamond disk without entering the root canals. The grooves were then used to split the specimen into two halves longitudinally, using chisel and hammer with light stroke. One segment from each split specimen was selected, based on how well the splitting was done. Dentinal wall of the cervical, middle, and apical thirds of root canals was observed at magnification of ×1500 and ×5000 for the presence or absence of debris and smear layer.

Scoring and evaluation

Each samples were visualized at the area where most debris and smear layer were detected under SEM at low magnification and at that specific area photographs were taken. The final result of the smear layer analysis was obtained for each specimen on the screen. The raw data were recorded and analyzed statistically. Amount of debris and smear layer present were scored according to Hulsmann Scoring Criteria (1997)[11] as follows:

For residual debris

For residual smear layer.

Data were recorded accordingly to different groups and statistical analysis was done.

RESULTS

Statistical analysis was performed with the help of Epi Info (TM) 7.2.2.2 software Epi Info is statistical software for epidemiology developed by Centers for Disease Control and Prevention (CDC) in Atlanta, Georgia (US). Using this software, the mean with corresponding standard deviations was calculated. One-way analysis of variance (ANOVA) was used to compare more than one means at a time. Tukey's critical difference followed by ANOVA was used to compare the mean values pair wise. P < 0.05 was considered to be statistically significant [Figures 1-7].

Figure 1

Hulsmann Scoring Criteria for residual Smear Layer (1997)

Figure 7

Scanning electron microscope images of smear layer removal

Hulsmann Scoring Criteria for residual debris (1997)

Mean debris layer in cervical, middle and apical area

Mean Debris layer in different groups

Mean smear layer removal in different groups from cervical, middle and apical third

Comparison of total smear layer removal in different groups

Cervical, mean debris layer scoring was 3.70 ± 0.949 in Group I, 3.50 ± 0.963 in Group II, 1.80 ± 0.422 in Group III, 1.80 ± 0.422 in Group IV, and 2.73 ± 1.109 in total. Difference of mean in four groups was statistically significant. In middle, mean debris layer scoring was 4.20 ± 0.789 in Group I, 3.30 ± 1.494 in Group II, 2.20 ± 0.789 in Group III, 1.90 ± 0.316 in Group IV, and 2.90 ± 1.297 in total. In apical, mean debris layer scoring was 4.40 ± 0.699 in Group I, 3.70 ± 0.823 in Group II, 3.10 ± 1.197 in Group III, 2.20 ± 0.422 in Group IV, and 3.35 ± 1.145 in total.

In control, mean debris layer scoring was 3.70 ± 0.949 in cervical, 4.20 ± 0.789 in middle, 4.40 ± 0.699 in apical, and 4.30 ± 0.1.201 in total. Difference of mean in four groups was statistically not significant. In PTU, mean debris layer scoring was 3.50 ± 0.963 in cervical, 3.30 ± 1.494 in middle, 3.70 ± 0.823 in apical, and 3.50 ± 1.109 in total. Difference of mean in four groups was statistically significant. In TF, mean debris layer scoring was 3.30 ± 1.160 in cervical, 2.20 ± 0.789 in middle, 3.10 ± 1.197 in apical, and 2.83 ± 1.238 in total. Difference of mean in four groups was statistically significant. In XP Endo, mean debris layer scoring was 1.80 ± 0.422 in cervical, 1.90 ± 0.316 in middle, 2.20 ± 0.422 in apical, and 2.65 ± 1.122 in total. Difference of mean in four groups was statistically significant.

In cervical, mean smear layer scoring was 1.00±0.000 in Group I, 3.20 ± 0.789 in Group II, 2.60 ± 0.516 in Group III, 2.40 ± 0.516 in Group IV, and 2.40 ± 1.033 in total. In middle, mean smear layer scoring was 1.00 ± 0.000 in Group I, 3.30 ± 0.823 in Group II, 2.80 ± 0.422 in Group III, 1.80 ± 0.422 in Group IV, and 2.23 ± 1.025 in total. In apical, mean smear layer scoring was 1.00 ± 0.000 in Group I, 3.60 ± 0.516 in Group II, 3.10 ± 0.316 in Group III, 2.50 ± 0.707 in Group IV, and 2.45 ± 1.037 in total. In apical, mean smear layer scoring was 4.30 ± 1.201 in Group I, 3.50 ± 1.109 in Group II, 2.83 ± 1.238 in Group III, 2.65±0.177 in Group IV.

In control, mean smear layer scoring was 1.00 ± 0.000 in cervical, 1.00 ± 0.000 in middle, 1.00 ± 0.000 in apical, and 1.00 ± 0.000 in total. In PTU, mean smear layer scoring was 3.20 ± 0.789 in cervical, 3.30 ± 0.823 in middle, 3.60 ± 0.516 in apical, and 2.75 ± 1.149 in total. In TF, mean smear layer was 2.60 ± 0.516 in cervical, 2.80 ± 0.422 in middle, 3.10 ± 0.316 in apical, and 2.40 ± 0.982 in total. In XP Endo, mean smear layer scoring was 2.40 ± 0.516 in cervical, 1.80 ± 0.422 in middle, 2.50 ± 0.707 in apical, and 2.10 ± 0.841 in total.

Highest amount of debris layer detected in Group I (control group), followed by Group II, Group III, and least amount of debris layer seen in Group IV and they are statistically significant (P < 0.05).

In case of smear layer formation highest amount of smear layer seen in Group II followed by Group III, Group IV, and least amount of smear layer seen in Group I (control group) and they are statistically significant (P < 0.05).

DISCUSSION

Chemomechanical preparation is a very important step in root canal treatment. Various kinds of chemicals and instruments are used for this purpose. However, vigorously using harsh chemicals can weaken tooth structure.[12] Debris and smear layer production during root canal treatment is unavoidable, every instrument whether hand, rotary or reciprocal some amount of debris and smear layer will produce during instrumentation. It is very important factor to keep in mind that if we cannot completely avoid the formation of debris and smear layer, we should choose the file system which produces minimum amount of debris and smear layer. Hence, in the present study, the amount of debris and smear layer produced by these newer Ni-Ti instruments with different configuration has been compared with ProTaper Universal which commonly used file system in clinical scenario [Tables 1-9].

Table 1

Armamentarium used in this study

Armamentarium	Manufacturer
ProTaper Universal file (rotary)	Dentsply Maillefer, Switzerland
Twisted file	SybronEndo (orange, CA, USA)
Xp-endo Shaper and Finisher	FKG
Endomotor Measuring Scale	Dentsply, Maillefer, CA, USA
Micromotor	Marathon
Straight hand piece	Marathon
Scanning electron microscope	S 3400N (Hitachi), Tokyo
Diamond disk with mandrill	Local dealer
Ultrasonic Scaler	WoodPecker, China
X ray machine	Satelec X MIND DC

Table 9

Comparison of smear layer removal between different groups

ANOVA (smear layer)
	Sum of squares	df	Mean square	F	Significance
PTU
Between groups	12.600	3	1.523	1.284	0.0265
Within groups	40.000	32	1.194
Total	38.600	39
TF
Between groups	17.100	3	5.367	5.655	0.002
Within groups	31.000	37	0.915
Total	47.100	39
XP Endo
Between groups	24.600	3	7.210	22.000	0.000
Within groups	12.800	34	0.300
Total	31.400	39

ANOVA: Analysis of variance, PTU: Protaper Universal, TF: Twisted File

SEM is been used by several researchers to evaluate smear layer formation by various instruments after use in root canal.[1314] We have used ×5000 and ×1500 magnification to evaluate the presence of debris and smear layer; this is in consensus with the previous study conducted by Bidar et al. and obtained good result.[15]

Normal saline was used as irrigating agent in this study because normal saline has only flushing action on debris and smear layer not have any active action like organic tissue dissolving capacity or chelating action.

ProTaper endodontic files are designed with progressive taper over the length of their cutting blades, allowing each instrument to prepare a specific area of the canal (i.e., each file engages a smaller zone of dentin). We have selected this file system in our study because it is the most commonly used file system till now and giving satisfactory result.

Twisted File is manufactured from a proprietary process of heating, cooling, and twisting of nickel titanium in the rhombohedral crystalline phase configuration (an intermediate phase between austenite – the phase at rest and martensite – the phase present during function). Twisted and XP Endo file system are newly introduced in the field of dentistry very little literatures are available regarding its debris and smear layer formation during instrumentation so we have compared these newly introduced file system with the mostly used file system ProTaper Universal.

XP Endo Shaper is available in one size 30, 0.01 taper which is produced from NiTi MaxWire alloy. MaxWire alloy enables the instruments to react to changes in temperature and take a predetermined shape inside the root canal at body temperature. According to the manufacturer, it's booster tip design allows the file to start shaping after a glide path of at least ISO 15 and to steadily increase its working field to accomplish an ISO 30 with only one instrument.[16] In addition, the file will contact and clean the dentine but not change the original shape of the canal. With XP Endo Finisher, we get an optimal cleaning of the root canal while preserving dentine.

Control group in which (no instrumentation was done) showed maximum amount of debris and least amount of smear layer which is similar to the result of the study conducted by Yang et al.[17]

Among all the file systems, ProTaper Universal rotary file system showed maximum amount of debris (3.50 ± 1.109) followed twisted file (2.83 ± 1.238) and least amount showed by XP Endo file system (2.65 ± 1.122) at all levels (cervical, middle, and apical third) and were statistically significant (P < 0.05).

Among all the file systems, ProTaper Universal rotary file system showed maximum amount of smear layer (2.75 ± 1.149) followed twisted file (2.40 ± 0.982) and least amount showed by XP Endo file system 2.10 ± 0.841 at all levels (cervical, middle, and apical third) and were statistically significant (P < 0.05) which is accordance to various previous studies like Sharma et al., Reddy et al. stated that ProTaper files produced statistically significant (P < 0.05) maximum smear layer scores overall in the coronal, middle, and apical portions.[1819]

The ability of rotary instruments to remove dentine and debris during shaping is obviously connected to the flute and cross-sectional design of the file.[20] Twisted File and ProTaper files possess similar design in following aspects, such as continuously changing pitches and helical angles, the flute width and depth becoming larger moving from the tip to the handpiece end of the file and nonlanded triangular cross-section designs with positive rake angles.[21] Hence, in the present study, the different operating technique plays a dominant role for cleanliness difference. In this study, XP Endo showed least amount of debris and smear layer at all the levels (cervical, middle, apical third) and were statistically significant (P < 0.05) which was accordance with various studies like Desai et al. found that maximum cleaning efficacy was obtained with XP Endo finisher.[22]

CONCLUSIONS

At all the levels (cervical third, middle third, and apical third), among all the experimental groups, highest amount of debris and smear layer formed by ProTaper Universal rotary file system group followed by Twisted file system group and least amount showed by XP Endo file system group and they are statistically significant. The samples of all the experimental groups showed some amount of debris and smear layer irrespective of the file system or area of the root surface. Control group showed highest amount of debris layer and least amount of smear layer among all the groups.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

Table 2

Mean debris removal

Debris layer	n	Mean±SD	Minimum	Maximum
Cervical
Group I	10	3.70±0.949	2	5
Group II	10	3.50±0.963	2	5
Group III	10	3.30±1.160	2	5
Group IV	10	1.80±0.422	1	2
Total	40	2.73±1.109	1	5
Middle
Group I	10	4.20±0.789	3	5
Group II	10	3.30±1.494	2	5
Group III	10	2.20±0.789	1	4
Group IV	10	1.90±0.316	1	2
Total	40	2.90±1.297	1	5
Apical
Group I	10	4.40±0.699	3	5
Group II	10	3.70±0.823	2	5
Group III	10	3.10±1.197	2	5
Group IV	10	2.20±0.422	2	3
Total	40	3.35±1.145	2	5

SD: Standard deviation

Table 3

Comparison of debris layer in different groups

Debris layer	n	Mean±SD	Minimum	Maximum
Control
Cervical	10	3.70±0.949	2	5
Middle	10	4.20±0.789	3	5
Apical	10	4.40±0.699	3	5
Total	30	4.30±1.201	3	5
ProTaper Universal
Cervical	10	3.50±0.963	2	5
Middle	10	3.30±1.494	2	5
Apical	10	3.70±0.823	2	5
Total	30	3.50±1.109	2	5
Twisted file
Cervical	10	3.30±1.160	2	5
Middle	10	2.20±0.789	1	4
Apical	10	3.10±1.197	2	5
Total	30	2.83±1.238	1	5
XP Endo
Cervical	10	1.80±0.422	1	2
Middle	10	1.90±0.316	1	2
Apical	10	2.20±0.422	2	3
Total	30	2.65±1.122	1	3

SD: Standard deviation

Table 4

Comparison of smear layer removal

Smear layer	n	Mean±SD	Minimum	Maximum
Cervical
Group I	10	1.00±0.000	1	1
Group II	10	3.20±0.789	2	4
Group III	10	2.60±0.516	2	3
Group IV	10	2.40±0.516	2	3
Total	40	2.40±1.033	1	4
Middle
Group I	10	1.00±0.000	1	1
Group II	10	3.30±0.823	2	4
Group III	10	2.80±0.422	2	3
Group IV	10	1.80±0.422	1	2
Total	40	2.23±1.025	1	4
Apical
Group I	10	1.00±0.000	1	1
Group II	10	3.60±0.516	3	4
Group III	10	3.10±0.316	3	4
Group IV	10	2.50±0.707	2	4
Total	40	2.45±1.037	1	4

SD: Standard deviation

Table 5

Comparison in different groups for smear layer removal

Smear layer	n	Mean±SD	Minimum	Maximum
Control
Cervical	10	1.00±0.000	1	1
Middle	10	1.00±0.000	1	1
Apical	10	1.00±0.000	1	1
Total	30	1.00±0.000	1	1
ProTaper Universal
Cervical	10	3.20±0.789	2	4
Middle	10	3.30±0.823	2	4
Apical	10	3.60±0.516	3	4
Total	30	2.75±1.149	2	4
Twisted file
Cervical	10	2.60±0.516	2	3
Middle	10	2.80±0.422	2	3
Apical	10	3.10±0.316	3	4
Total	30	2.40±0.982	2	4
XP Endo
Cervical	10	2.40±0.516	2	3
Middle	10	1.80±0.422	1	2
Apical	10	2.50±0.707	2	4
Total	30	2.10±0.841	2	4

SD: Standard deviation

Table 6

ANOVA done for comparison of debris layer between different areas i.e cervical, middle and apical third

ANOVA (debris)
	Sum of squares	df	Mean square	F	Significance
Cervical
Between groups	21.475	3	7.158	11.556	0.000
Within groups	22.300	36	0.619
Total	43.775	39
Middle
Between groups	18.500	3	6.167	6.727	0.001
Within groups	33.000	36	0.917
Total	51.500	39
Apical
Between groups	12.275	3	4.092	4.676	0.007
Within groups	31.500	36	0.875
Total	43.775	39

ANOVA: Analysis of variance

Table 7

Comparison of debris layer removal between different groups

ANOVA (debris)
	Sum of squares	df	Mean square	F	Significance
PTU
Between groups	4.600	3	1.533	1.284	0.0295
Within groups	43.000	36	1.194
Total	47.600	39
TF
Between groups	16.100	3	5.367	5.855	0.002
Within groups	33.000	36	0.917
Total	49.100	39
XP Endo
Between groups	21.600	3	7.200	24.000	0.000
Within groups	10.800	36	0.300
Total	32.400	39

ANOVA: Analysis of variance, PTU: Protaper Universal, TF: Twisted File

Table 8

ANOVA done for comparison of smear layer between different areas i.e cervical, middle and apical third

ANOVA (smear layer)
	Sum of squares	df	Mean square	F	Significance
Cervical
Between groups	24.475	3	7.162	11.546	0.000
Within groups	22.300	32	0.617
Total	43.775	31
Middle
Between groups	17.500	3	6.170	6.735	0.001
Within groups	34.000	32	0.912
Total	51.500	38
Apical
Between groups	12.275	2	4.092	4.646	0.004
Within groups	37.500	34	0.874
Total	41.775	39

ANOVA: Analysis of variance