Digital Radiographic Evaluation of Primary Molar Obturation Following Use of Lentulo Spiral and Endodontic Pressure Syringe in Root Canals Prepared with Rotary Ni-Ti Files and Manual Files: An In Vivo Study

INTRODUCTION

Endodontic treatment of primary teeth is demanding and arduous. The primary objective of cleaning and shaping the root canal system is to remove necrotic tissue containing bacteria, provide access for irrigants to the apical third, and make space available for medicaments and the obturation. The tortuous and irregular root canal walls of primary molars require to be carefully shaped to avoid perforation of canals. The conventional hand instrumentation technique for primary teeth is time-consuming.^1,2 The root canal preparation can be done faster with the use of rotary files, and so would be suitable for use in pediatric patients as children cannot cooperate for lengthy appointments.^3-5 The design and flexibility of rotatory files reduce procedural errors.

An ideal obturation technique is a complete filling of the canal without over-fill and with minimal gaps or spaces. The method of mixing an obturating material as well as the technique of obturation significantly influences the success rate of root canal treatment of primary teeth.^6-9 Lentulo spiral,^8,10,11 endoplugger,¹² and premixed syringe¹³ have been utilized in the obturation of root canals of primary teeth. Previous studies assessing the quality of obturation were limited to the preparation of root canals in primary teeth using conventional hand files and ex vivo conditions.^6,12,14

Hence, this clinical study was undertaken to evaluate and compare the quality of root canal filling in primary molars following the use of lentulo spiral and endodontic pressure syringe in canals prepared with rotary Nickel-Titanium files and manual files.

MATERIALS AND METHODS

Normal, healthy, and cooperative children for the study were recruited from patients visiting the Department of Pediatric Dentistry.

Radiographic Evaluation

Preoperative and postoperative digital radiographic images of all the primary molars were taken using sensors that were exposed with a dental X-ray unit operating at 60 kvp, 6 mA, 0.3 seconds, and 15 mm. Radiographic images obtained with Digora PSP plates were scanned immediately after exposure (Digoraoptime, Helsinki, Finland) and stored. Radiographs were evaluated for quality of obturation by two examiners, one of them blinded for the study groups. If there was a disagreement a lower ranking was given. Evaluation of root canal obturation was done for the quality of filling as per the following criteria:¹⁹

1 = Less than or equal to half the root canal length was filled.

2 = More than half the root canal length was filled but the filling was not optimal.

3 = Optimal filling (canal filled to within 0–1.5 mm of the apex).

4 = Filling material extruding from the apex (overfilling).

The presence or absence of voids, number and location of voids in each root canal (coronal, middle, apical) was also evaluated.¹⁹

The data obtained were subjected to statistical analysis using a Student’s t-test (two-tailed, independent) was used to find the significance of study parameters on a continuous scale between the groups. ANOVA and Chi-square were used to find the significance of study parameters and correlation of study parameters on a categorical scale between two or more groups, respectively. The p value (p ≤ 0.05) was considered as significant, p < 0.001 was taken as highly significant. Data were analyzed using Statistical Package of Social Sciences (SPSS) software 19.0 using windows.

RESULTS

In both the groups, none of the root canals showed obturation that was less than or equal to half the root canal length.

Following preparation with rotary files, all palatal canals were optimally filled using an endodontic pressure syringe, and overfilling was seen only in 10% of distal canals. The use of lentulo spiral gave optimal filling in 83.3% of DB canals; and overfilling was observed in 10.5% of distal, MB (5.6%), and 25% of ML canals. In mandibular molars, 80–90% of root canals were optimally filled following obturation with the endodontic pressure syringe and 58–71% using the lentulo spiral. In maxillary molars, 92–100% of root canals showed optimal filling with the endodontic pressure syringe and 83–89% using lentulo spiral (Table 1).

Root canals prepared with manual files and obturated using an endodontic pressure syringe showed optimal filling in all DB and palatal canals. With lentulo spiral, all mesial and palatal were optimally filled. In mandibular molars, 70–75% of root canals were optimally filled using the endodontic pressure syringe and 77–100% using lentulo spiral technique. Whereas, in maxillary molars, 93–100% of root canals showed optimal filling with the endodontic pressure syringe and 33–100% using lentulo spiral (Table 2).

A higher number of root canals obturated using lentulo spiral showed voids. In comparison to the endodontic pressure syringe, a significant difference was seen in ML canals prepared with rotary files and filled using lentulo spiral (33.3%) (p = 0.04) (Tables 3 and 4). The use of an endodontic pressure syringe resulted in a higher distribution of voids in the middle third of the canals; whereas, voids were present in the middle and apical third of canals obturated using lentulo spiral. There was no significant difference (Tables 5 and 6).

DISCUSSION

In this study, the HERO shaper files (Micro-Mega) were used which have high flexibility and a constant taper. These files have a non-cutting tip and better access due to the short handle. They have a cross-section of triple helix design which reduces threading²⁰ and prevents, by a screw-like action, the instrument from binding in the root canal.¹⁸ Anthogyr handpiece, (gear reduction of 1:64) was used in this study, which is more convenient to use in children due to its small head and simplicity.²¹

In the present study, a Pulpdent root canal sealer, which has a similar composition as zinc oxide eugenol cement was used for obturation using the endodontic pressure syringe. It is biocompatible, bacteriostatic, and radiopaque.^22,23 Earlier studies have used conventional intraoral radiographs to assess the quality of root canal fillings.^6,11,12 In this study, an indirect type of digital radiography using photostimulated phosphor-imaging (PSP) sensors were used.^24,25 Children may not tolerate wired sensors, and may chew on the cable, or maybe more fearful of the appearance of a wired system. To better assess filled canals, computerized enhancements of the digitized image can be used to alter image contrast, measure the distance of root canal filling materials from the apex, and detect voids in the filling material. Individual canals can be more accurately evaluated.¹⁹

In the present study, root canals prepared by rotary files resulted in a better quality of obturation as compared to manual files, which may be due to a more conical form of canal preparation achieved with rotary files.^3,26 Tables 1 and 2 show the comparison between the quality of obturation following preparation with manual and rotary files. This was based on radiographic criteria to evaluate the quality of obturation according to Memarpour et al.¹⁹ Although there was no significant difference, the teeth prepared by rotary files and obturated using an endodontic pressure syringe showed more number of optimally filled canals. A recent in vivo study concluded that the lentulo spiral and modified disposable syringe technique were equally effective in the obturation of primary molar root canals in terms of quality of root canal obturation.²⁷

The higher viscosity and consistency of the material used with the endodontic pressure syringe makes the material flow under its own weight, once the needle is introduced in the canal. There could have been a tendency for the operator to have applied excessive pressure while extruding the material into the canal. Whereas with the lentulo spiral, a relatively high number of canals showed less than optimal filling. A probable reason could be that the correct root canal length was not maintained while fitting the rubber stop on the instrument. The frequency of overfilling was also higher following obturation using the lentulo spiral technique. Extrusion of filling material was seen to be more in the fine, narrow mesio-lingual canals of primary mandibular molars. The orifices of these canals may have been sufficiently enlarged with rotary files, thus providing better access to the lentulo spiral instrument. The lentulo spiral allows the less viscous zinc oxide material to be carried further apically, during rotation of the instrument inside the canal. It may also be related to the reduction in operator “feel” during the filling procedure, with resultant overfilling.

Possible consequences of overfilling are foreign body reaction or deflection of the underlying permanent tooth when zinc oxide eugenol is used.¹⁰

Certain studies have recommended the use of the endodontic pressure syringe technique for straight canals and the lentulo spiral technique for curved canals.^12,14 However, with the use of Endoflare together with rotary files, better access to the apical portion of the canals was achieved in our study. Khubchandani et al. assessed the quality of obturation in primary molars using two techniques—lentulo spiral and a pressure syringe (NaviTip). Lentulo spiral technique produced the best results in terms of length of obturation, while the NaviTip syringe was efficient enough in controlling voids and produced the best apical seal.²⁸

Interestingly, preparation using manual files showed a higher number of under-filled mesial canals, when the endodontic pressure syringe was used. These canals may have remained narrow and the highly viscous material may not have flowed adequately. Conversely, a higher number of manually prepared canals were optimally filled using the lentulo spiral technique; wherein the low viscosity material was able to flow into the relatively narrow canals.

A uniform and dense obturation was seen when obturation was done using the endodontic pressure syringe. Also, the greater viscosity of the zinc oxide eugenol sealer makes it extrude with a thick rope-like consistency into the canal, resulting in a more homogeneous, dense filling and therefore, lesser voids.

In the present study, the distribution of voids was higher in the middle and apical thirds of root canals prepared with either technique of root canal preparation, and irrespective of the technique of obturation.¹⁹ Pre-enlarging the coronal third of the canal with the Endoflare instrument could have resulted in a lesser number of voids and better quality of obturation, especially in the coronal third of root canals.^20,21 Endodontic pressure syringe technique of obturation following preparation with rotary files can be considered a good option for the root canal filling in primary teeth. Knowledge of rotary systems, as well as experience in handling the endodontic pressure syringe, is essential.

CONCLUSION

• Root canals of primary molars prepared by rotary files and obturated using endodontic pressure syringe technique resulted in a better quality of obturation than that obtained with lentulo spiral.
• In root canals prepared by manual files, there was no difference in the quality of obturation between endodontic pressure syringe and lentulo spiral techniques.
• More number of voids were observed in canals obturated using the lentulo spiral technique compared to that of the pressure syringe technique. In root canals prepared by rotary files, voids were found to be significantly higher in the mesiolingual canals.

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