shaped master cone. The irrigant is thus expected to clean the rest of the canal space by its tissue or bioÞlm-dissolving action [27, 35, 78, 89]. The distance from this simplistic idea to practically reducing the whole endodontic treatment to preparing a space to accommodate a master cone may be small.

Studies indicate that the effective cleaning of oval canals is a challenge that is beyond the ability of syringe and needle irrigation. The action of rotary Þles in such canals not only fails to clean the buccal and/or lingual ÒÞnsÓ or the isthmus between canals but also actively packs these recesses with dentin particles [63, 66, 67] that are difÞcult to remove, even with passive ultrasonic irrigation [66].

Such Þndings led De-Deus et al. to conclude that Òthe notion that Ôthe Þle shapes; the irrigant cleansÕ represents wishful thinking rather than an established scientiÞc fact, at least in the case of oval canalsÓ [23].

These limitations of syringe and needle irrigation led to a search for and introduction of new irrigation methods that are designed to overcome this barrier, by either (a) affecting the ßow or motion of the irrigant at given time points of the procedure or by (b) adding a scrubbing effect to a continuous ßow of the irrigant. The Þrst group included negative pressure irrigation systems [36, 60, 69, 81] and sonic and ultrasonic irrigant activation systems [9, 25, 43]. The new self-adjusting Þle system represents the second approach.

The Self-Adjusting File (SAF) System

The self-adjusting Þle system is a shaping and cleaning system designed for minimally invasive endodontic treatment. The system consists of a self-adjusting Þle that is operated with a special RDT handpiece head and an irrigation pump that delivers a continuous ßow of irrigant through the hollow Þle [39, 53Ð57].

The Self-Adjusting File (SAF)

The SAF is the Þrst Þle that does not have a solid metal core. The Þle is designed as a hollow tube, in which the walls are made from a thin nickel-

titanium lattice with a rough outer surface. The tube has an asymmetrically positioned tip (Fig. 11.1). The tip is located at the wall of the tube, as opposed to the symmetrically centered tips that may be found in all conventional nickeltitanium rotary Þles. The Þle is extremely compressible, such that a 1.5 mm SAF diameter may be compressed into a root canal that only a #20 K Þle can be inserted into (Fig. 11.2). This compressibility also enables the Þle to adapt to the shape of the cross section of the canal [39, 53Ð 56]. When inserted into an oval canal with a 0.2 mm mesiodistal diameter, a 1.5 mm SAF will be compressed mesiodistally and thus spread buccolingually, reaching a buccolingual diameter of 2.4 mm [39, 53Ð57]. This will occur even if the operator is not aware that the canal is oval, hence the name Òself-adjusting Þle.Ó Naturally, such a ßattened Þle cannot rotate while it is in the canal and is operated with in-and-out vibrations that are created by the RDT handpiece head.

The RDT Handpiece Head

The RDT handpiece head (Fig. 11.3) has a dual mechanical function. It transforms the rotation of the micromotor into a trans-line in-and-out vibration with an amplitude of 0.4 mm and contains a clutch mechanism that allows the SAF to rotate slowly when not engaged in the canal but that completely stops the rotation once the Þle is engaged with the canal walls. The micromotor is operated at 5,000 rpm, which results in 5,000 vibrations/min, and the operator uses pecking motions when using the SAF. Free rotation of the Þle should occur at the outbound portion of every pecking stroke, when the SAF is disengaged from the canal walls. When the SAF enters the canal during the inbound pecking motion, it should do so at random, with different circular positions, thus ensuring uniform treatment of the canal walls [53Ð56, 68, 73, 74, 95]. This random circular position also allows the asymmetrical tip of the Þle to negotiate curvatures that may be found in the root canal. RDT heads may be adapted to a large variety of endodontic motors (Fig. 11.3).

Fig. 11.1 The SAF. (a) The SAF. (b) Structure of the Þle: two longitudinal beams, connected by a series of arches that are designed to allow maximal compressibility. The arches are harnessed to each other with thin struts that pre-

vent pulling the arches out of the cylinder. (c) The asymmetrically located tip of the Þle. (d) Extreme ßexibility of the SAF. This should be compared to that of the last rotary Þle that is used in the canal

EndoStation/VATEA Irrigation Pumps

The SAF is provided with a freely rotating hub to which a polyethylene tube is connected (Fig. 11.4), thus allowing the irrigant to ßow through the hollow Þle into the root canal. The irrigant is delivered into the tube by either

EndoStation or VATEA irrigation pumps (Fig. 11.5).

The VATEA is a self-contained pump that has a built-in irrigant reservoir of 500 mL and is powered by a rechargeable battery (Fig. 11.1a). The EndoStation is a compound all-in-one machine that can be operated in either rotary or reciprocat-

Fig. 11.2 SAF compressed into a narrow canal. Left: the SAF in its relaxed form.

(a) The same SAF inserted into a narrow canal, which was prepared with a # 20 K Þle. (b) A #20 K Þle that Þts into the same canal

a

b

Fig. 11.4 Rotating hub on the SAF for connecting the irrigation tube. The SAF is equipped with a rotating hub that allows it to attach to the irrigation tube, which allows the irrigant to ßow from the irrigation pump to the hollow Þle

Fig. 11.3 RDT handpiece heads. (a) RDT3 handpiece head that may Þt into various handpieces. (b) RDT3-NX handpiece head attached to an X-smart endomotor through a 1:1 NSK gear/adaptor

ing Þle modes, using a regular handpiece, or in the SAF mode, which enables continuous irrigation when using a special separate handpiece with an RDT head. The irrigant container of the EndoStation is an external bottle from which a peristaltic pump draws the irrigant into the tube and into the attached Þle (Fig. 11.5b).

Either irrigation pump delivers the irrigant at an adjustable ßow rate of 1Ð10 mL/min. Because the Þle is built as a lattice-walled cylinder, no

a

b

Fig. 11.5 EndoStation and a VATEA pump. (a) A VATEA peristaltic pump with irrigant container within the unit. (b) EndoStation is an all-in-one endodontic motor that can be operated in either the ASF mode with irrigation using a handpiece with an RDT head or in rotary mode or reciprocating modes using a regular E-type handpiece. The built-in peristaltic pump draws the irrigant from the external bottle container

pressure is generated within the Þle: any small pressure that is generated by the pump to deliver the irrigant through the tube is eliminated when the irrigant enters the Þle.

Minimally Invasive Shaping

and Cleaning

The concept of minimally invasive shaping and cleaning uses a different method of achieving the same aims as the conventional, traditional shaping and cleaning procedures. Conventional shap-

ing and cleaning, which uses rotary Þles, involves

(a) the removal of large amounts of sound dentin in attempt to include as much as possible the canal wall within the preparation and to allow effective irrigation at the apical end of the canal and (b) the creation of unnoticeable micro-cracks in the remaining dentin by the rotary Þles [3, 8, 13, 37, 46, 85, 102]. Both these damaging effects were either accepted so far or ignored, as there was no other effective means to thoroughly clean the root canal.

The minimally invasive concept is aimed at achieving the effective cleaning of a root canal by

(a) removing a uniform thin layer of dentin around the entire root canal without the unnecessary excessive removal of sound dentin and without causing micro-cracks and (b) providing a continuous ßow of fresh, fully active irrigant that is applied with a scrubbing motion of the walls, all the way to the apical part of the canal.

Conventional shaping procedures involve machining the root canal into a desired shape, with either a sequence of rotary instruments or one reciprocating tool. Such process is used (a) to enable irrigation in the apical part of the canal and (b) to facilitate obturation by using a master cone that has the shape of the machined canal. If the canal is straight and narrow with a round cross section, this concept may work well as it may allow the removal of all the inner layers of dentin with anything that was attached to it, be it pulp tissue or bacterial bioÞlm. The debris are carried coronally by the ßutes or compacted into the ßutes, and the subsequent irrigation may remove the leftover debris from the canal.

Nevertheless, if this simplistic view of the process is applied to all canals, it may often be considered as treating imaginary canals while ignoring the 3D reality of root canals. MicroCT studies have shown that in oval and curved canals, rotary Þles fail to remove the inner layer of dentin from all around the canal wall [66, 71]. Furthermore, the discrepancy between the size of the tip of many rotary Þles (i.e., #25) and the known dimensions and shape of the apical parts of root canals led to the suggestion that a larger apical preparation should be used to include all the apical canal surfaces within the perimeter of the instrumented