Abstract
In these endodontic case reports we present a root canal preparation protocol using the M
A hybrid
References
‘Simultaneous technique’ and a hybrid microseal/pacmac obturation
From Volume 38, Issue 7, September 2011 | Pages 477-484
Article
Root canal preparation involves cleaning and shaping of the root canal system1 in order to eliminate infection and necrotic or inflamed pulp tissue2 and to prepare the root canal to receive a specific root-filling material.1 Because of their ability to shape root canals with fewer procedural errors, Nickel-Titanium (Ni-Ti) rotary instruments enhance the predictability of root canal preparation.2
Mtwo instruments have the following properties:
Their cross-sectional design is therefore comparable to the Quantec LX series.2
It is suggested that the standard Mtwo Ni-Ti rotary files (Sweden and Martina, Due Carrare, Padua, Italy and VDW, Munich, Germany) are used according to the ‘simultaneous technique’.4 This is a ‘crown-down’ preparation characterized by the fact that each instrument should be used to the full working length (WL),3,4 from smaller to larger size.4,5 Light pressure in an apical direction is required during instrumentation; if a binding sensation is experienced the instrument should be used 1–2 mm shorter than the maximum depth reached, in an anti-curvature brushing motion with an amplitude of around 5mm, to remove coronal interferences on the outstroke, prior to further progression. The standard sequence can be followed by the Mtwo apical finishing files (Mtwo A), if the proposed hybrid Microseal/PacMac obturation technique is chosen.
A root canal filling aims to obliterate the empty spaces inside the root canal and, in association with the coronal restoration, to provide a barrier to possible re-contamination.6 The Microseal/PacMac (SybronEndo Amersfoort, The Netherlands) obturation technique is based on the combination of gutta-percha of different phases and involves three stages: master cone compaction, backfill with plasticized (heated) gutta-percha and vertical compaction. Traditionally, the main cone matches the size and shape of the last instrument that was used in the apical region or is adjusted until achieving ‘tug back’, and the cone is compacted with a spreader (1 mm short from the WL).7 However, in the hybrid technique presented, a gutta-percha point larger than the apical preparation is placed short from the full working length and is compacted to fill the previously prepared ‘apical stop’. A final vertical compaction stage is included to reduce the risk of mid-root and coronal voids (taking into account the volume changes that occur as the material returns to body temperature), and to increase the amount of gutta-percha in the final obturation.
This paper reports clinical cases treated following the ‘simultaneous technique’ using the Mtwo Ni-Ti files basic sequence, followed by apical preparation using the Mtwo A files and a hybrid Microseal/PacMac obturation method.
Presentation of the protocols
The files were operated at 250 rpm.
Mtwo standard sequence (Figure 2)
Apical preparation
To obtain the required ‘apical stop’, three different Mtwo apical finishing files (Figure 3) can be used:
The working length was determined with the use of an apex locator (Root ZX, J Morita, Japan).
Copious irrigation (5 ml circa) using 5% sodium hypochlorite (Teepol Bleach, Teepol, Orpington, UK), as well as 17% liquid EDTA (EDTA solution, Pulpdent, Watertown, MA, USA) is suggested as an irrigant between files, with a 27 gauge Monoject syringe (Kendall, Tyco, Mansfield, MA, USA) in an up-and-down motion.
Root canal obturation was carried out with a modification of the original Microseal technique (SybronEndo) consisting of three stages:
First a MicroFlow gutta-percha cone 0.02 tapered (SybronEndo) was chosen according to the final Mtwo A finishing file used. For an A1 a size 35 point, for an A2 a size 40 point, and for the A3 a size 45 point was selected. The master cone tip was coated with a small amount of sealer (Pulp Canal sealer, SybronEndo) fitting 1 mm shorter than the working length; at this stage the gutta-percha point was condensed using a Ni-Ti Microseal spreader (SybronEndo) – normally a size 25 0.04 – brought 2–3 mm shorter than the working length, at approximately 300 rpm rotation.
Subsequently, a MicroFlow gutta-percha cartridge (SybronEndo) is heated in the Microseal oven (SybronEndo) according to the manufacturer's instructions; a thin and uniform layer of plasticized gutta-percha is applied on a ISO 25 0.04 taper PacMac (Sybron Endo) and introduced 2–3mm from the apex, without motion, into the space left by the previous compaction. Once introduced, rotation was started (6.000–7.000 rpm), holding the instrument at this position for one to two seconds. The rotating PacMac (SybronEndo) was then allowed to exit coronally from the canal, pushed by the pressure caused by the flow of gutta-percha, keeping the instrument in light contact with the root canal wall.
Finally, a non-rotating engine spreader (SybronEndo) was used as plugger to a mid-root position, to compact vertically the middle and apical parts of the root-filling material.
Coronal voids were normally present after this procedure; therefore a further heated gutta-percha backfill using the PacMac (SybronEndo) was required.
Discussion
The purpose of this paper is to present endodontic cases (Figures 4–8) treated using the ‘simultaneous technique’ with Mtwo rotary instruments and a hybrid Microseal/PacMac filling method.
Considering a ‘crown-down’ approach is suggested for most Ni-Ti rotary files sequences,8 taking into account that Ni-Ti rotary instruments are used in a continuous full 360° rotation,9 there is a need to prevent excessive torque against the root canal wall to reduce the risk of instrument fracture.10 In traditional ‘crown-down’ rotary Ni-Ti systems, larger instruments are first used in the coronal region of the canal, followed sequentially by smaller instruments deeper in the canal until the root apex is reached;2,9 the Mtwo instruments are designed to cut in the coronal part of the root first, to obtain a straight line access, before progressing apically to the full working length, without the need for coronal preparation using drills such as Gates-Glidden, Peeso or similar.
Moreover, the creation of a ‘glide path’ prior to the use of rotary Ni-Ti files has been recommended to reduce the incidence of instrument fracture10 although, depending on canal size and the first instrument that enters the length of the canal through to the apex, this is often achieved by using stainless steel ISO 0.02 tapered files matching the tip size of the first rotary file that will work apically, in order to reduce torsion-related stress.11
The first instrument of the Mtwo series (Mtwo 1) has a 0.10 mm apical diameter and a 0.04 taper. It was designed to create the glide path mechanically prior to using larger, and therefore stiffer, Ni-Ti files. In vitro investigations suggest that preflaring using Ni-Ti rotary files (Pathfile, Dentsply Maillefer, Baillegues, Switzerland) causes fewer curvature modifications and fewer canal aberrations, when compared to hand stainless steel files.12
It is worth noting that the manufacturer of Pathfile (Dentsply Maillefer, Baillegues, Switzerland) suggests scouting the canal with hand k-files prior to usage of the rotary sequence.12 Though the Mtwo files may be used to create a glide path, it is suggested that stainless steel files, up to size ISO 10, be used for this purpose to reduce the risk of iatrogenic errors, particularly file separation.
The Microseal technique requires a root canal preparation with a regular taper to allow for the flow of the thermoplasticized gutta-percha, as well as an ‘apical stop’.13 The Mtwo apical finishing instruments appears to be suitable for this obturation technique as they provide a predictable and consistent apical preparation after the coronal preparation has been achieved. The creation of a ‘stop’ using the Mtwo apical finishing files creates a space where the master cone can adapt and subsequently engage under the condensor pressure, providing sufficient space for this instrument to reach a depth close to the working length. Thanks to the use of flowable gutta-percha and to the creation of this stop, it is possible to control the obturation length while maintaining all the benefits associated with warm gutta-percha obturation techniques, including the presence of favourable hydraulics that would allow for the obturation of apical deltas, as well as other accessory anatomy.
The vertical compaction stage aims to control the gutta-percha contraction during its cooling phase and to reduce the risk of sealer pooling in the root filling; sealer has been associated with risk of leakage due to dissolution or through interfaces with the dentine, gutta-percha points or around the material itself.13 An in vitro investigation suggested that the MicroSeal technique produced a heterogeneous fill consisting of the MicroFlow Master cone and gutta-percha from the MicroFlow cartridge mixed with sealer, especially at the mid root and coronal levels.13 Further investigations, however, will be required to assess if the suggested modification would address the problem.
During the final vertical compaction, the engine spreader (flat-tipped) is used as a plugger and is often able to reach mid root level, however, this can vary according to the flow characteristics of the filling material. This depends on multiple factors, including quality differences amongst the gutta-percha batches provided by the manufacturer, the temperature of the gutta-percha, the sealer mix consistency, as well as the sealer/gutta-percha ratio. Microseal protocols previously described suggest the use of a vertical plugger for this final stage and penetration of the instrument is limited to the canal entrance.13,14
Conclusion
The ‘simultaneous technique’, as well as the hybrid Microseal/PacMac filling method may both be valid alternatives for the preparation and obturation of root canals.