others use it at later stages of the cleaning process to remove the smear layer before disinfection and/or obturation of the root canal. For decalciÞcation of dentin by EDTA, the dentin must Þrst be exposed to sodium hypochlorite [6, 31, 33, 61]. Therefore, in areas of the canal that were not effectively exposed to active sodium hypochlorite, the effect of EDTA may be limited. As any mechanical device, the SAF generates a smear layer [54]. Nevertheless, the subsequent use of EDTA and its activation by the vibrations of the SAF effectively remove the smear layer, even in the apical cul-de-sac area. The frequent appearance of lateral canals in SAF-treated cases (Fig. 11.9) may be the result of the removal of the smear layer plugs that otherwise block the lateral canal entrance [83].

a

b

Fig. 11.9 Lateral canals in SAF-treated clinical cases. Lateral canals frequently appear when SAF-treated cases are obturated. (a) Courtesy of Dr. Ajinkia Pawar, Mumbai, India; (b) Adapted from Solomonov [82]

Mode of Cleaning with the SAF System

When the SAF system is used, the process of delivering fresh, fully active sodium hypochlorite is continuous. The SAF protocol requires a glide path that allows the compressed SAF to reach WL at the beginning stages of the procedure. This is different from other instrumentation concepts in which reaching WL represents the end of the procedure. The SAF system is then used for 4 min using pecking motions that reach the WL with a simultaneous continuous replenishing ßow of fresh, fully active sodium hypochlorite. This may explain the effective cleaning of the apical part of the canal [2, 54, 55, 101] and the cleaning of the canalÕs recesses and Þns [23, 45].

Another important cleaning feature of the SAF system is the scrubbing of the canal walls. If pulp tissue or a bacterial bioÞlm is left in the canal, sodium hypochlorite is commonly expected to dissolve them. However, one should consider the volume and three-dimensional structure of these substances. When the outer layer of the target material is attacked, the inner layers may still be protected from the actions of the sodium hypochlorite. Furthermore, when attacking the outer layers, sodium hypochlorite is inactivated and becomes less potent. The deeper the Þn or recess, the more difÞcult it is to simply dissolve the pulp tissue or bioÞlm that it may contain.

If the pulp tissue or bacterial bioÞlm were loosely attached to the canal wall, they could potentially be detached by the ßow of irrigant. However, both substances are closely and Þrmly attached to the canal wall (Fig. 11.10) [59]. Direct mechanical action is often required to remove them from the canal wall [57].

The SAF consists of a metal mesh, which closely adapts around the canal walls, even in oval canals. Continuous movements of this metal mesh over the surface have a scrubbing effect, which is a more effective method of cleaning (Fig. 11.11).

This dual cleaning action of the SAF system, continuous replacement of fresh, fully active sodium hypochlorite, all the way to WL

Fig. 11.10 A bacterial bioÞlm tightly attached to the root canal wall. The mesial root of a mandibular molar was clinically treated, resulting in a satisfactory radiographic result. The apical tip of the root was removed surgically after the procedure and subjected to transmission electron microscopy. The intact bioÞlm that remained in the isthmus was tightly attached to the dentin wall and was not affected by the copious irrigation with sodium hypochlorite used during the endodontic treatment (Adapted from Nair et al. [59]). BA Bacteria, D Dentin

throughout the procedure, and the continuous scrubbing of the canal walls may explain the unique cleaning efÞcacy of the SAF system [54, 56, 57].

When using the SAF system, EDTA may be applied in the canal with a syringe and needle and then agitated for 30 s by the SAF with the irrigation pump turned off. Alternatively, the pump may be turned off and EDTA applied through a special ÒyÓ connector that is attached to the irrigation tube close to its connector to the SAF (Fig. 11.12). In such a case, the continuous ßow of EDTA is manually controlled by the person holding the syringe.

Cleaning Efficacy of the SAF System

The ultimate tool for evaluating the cleaning efÞcacy of a root canal is scanning electron microscopy (SEM). Many studies have used this tool to evaluate the cleaning of a root canal [4, 17, 28, 40, 51, 62, 70, 94].

In the majority of these studies, while the coronal and middle parts of the root canal may be effectively cleaned by rotary Þles and syringe and needle irrigation, the apical part of the canal, with its cul-de-sac shape, presented a greater challenge. In most of these studies, the apical part of the canal contained large amounts of debris and was covered with a smear layer, even after EDTA irrigation [4, 17, 28, 40, 51, 62, 70, 94].

When the SAF system was used, alternating between sodium hypochlorite and EDTA, the apical part of the canal was clean of debris in all of the samples, and in 65 % of the cases, no smear layer was present (Fig. 11.13) [2, 54, 101]. This was likely due to the dual action described above.

Lin et al. recently used a unique model to study the ability of different Þles and irrigation systems to remove the bacterial bioÞlm from grooves that were placed in the wall of the root canals, representing Þns or other recesses [45]. They found that when hand Þles were used with copious sodium hypochlorite irrigation applied with syringe and needle, 27 % of the groove area was still covered with bioÞlm. Rotary Þles with similar irrigation reduced the area of the groove covered by bioÞlm to 19 %, while the SAF system with its scrubbing effect and continuous sodium hypochlorite irrigation left only 3 % of the groove area covered with bioÞlm [45].

Histology is another effective tool to evaluate the efÞcacy of cleaning root canals. De-Deus et al. used this tool on pair-matched, ßat-oval canals of canines with vital pulp, to study the cleaning efÞcacy of rotary Þles and syringe and needle irrigation, and compared them to the SAF system [23]. They found that while rotary Þles left large amounts of pulp tissue in the canal Þns (Fig. 11.14), the SAF system was more effective in cleaning and removing the pulp tissue [23].

Both above methods of study involved the interpretation of the observer and can potentially

Fig. 11.11 Irrigation vs. scrubbing. An illustration of the efÞcacy of cleaning by scrubbing. (a) Burnt forage on the bottom of the pot represents the bacterial bioÞlm or pulp tissue that is tightly attached to the canal walls. (b)

Fig. 11.12 ÒYÓ connector with a syringe containing EDTA. A ÒYÓ connector in the irrigation tube (arrow) allows for the attachment of a syringe containing EDTA that may be applied into the SAF during its operation while the irrigation pump is turned off. The tube connecting the ÒyÓ connector to the EDTA syringe may be longer, to allow comfortable operation by the dental assistant

Irrigation alone, with no mechanical action, is unlikely to remove such bound material. (c) A metal scrubbing cushion, representing the SAF, is much more effective in cleaning off a tightly bound material (d)

c

Fig. 11.13 SEM of a root canal treated with the SAF system, alterating between sodium hypochlorite and EDTA. (a) Coronal part of the canal. (b) Middle part of the canal. (c) Apical part of the canal. All of these images are at ×500 times magniÞcation. All of the coronal and mid-root surfaces were clean of debris and of a smear layer. In a study by Metzger et al. [54], all of the apical parts of the canals were free of debris, and in 65 % of the cases, they were also free of a smear layer

Fig. 11.14 Intact pulp that remained in the ÒÞnÓ of an oval canal treated with rotary Þles. (a) A rotary Þle was used in an oval canal with syringe and needle irrigation (3 % sodium hypochlorite). The pulp in the deeper part of the ÒÞnlikeÓ recess remained intact. Dentin particles that were packed into the ÒÞnÓ by the rotating Þle can be observed (arrow). (b) Similar oval canal that was treated with the SAF system with a continuous ßow of 3 % sodium hypochlorite. Both cases were pair-matched canines, which were vital before extraction (Adapted from De-Deus et al. [24])

be subjected to Þeld selection or section-level selection bias.

MicroCT is a tool that cannot directly evaluate the soft tissue or bioÞlm remaining in the canal. Nevertheless, it allows an indirect evaluation of the whole canal walls with complete computerized analysis. One may assume that if a layer of dentin was removed from all the root canal surfaces, any material attached to this dentin surface is likely to be removed from these walls [56, 57]. Under this assumption, the efÞcacy of cleaning root canals may be evaluated three-dimensionally by the microCT tool. When rotary Þles were used in oval or curved canals, a large percent of the canal wall was unaffected by the procedure. This reached 70 % in oval canals [65] and up to 45Ð50 % in the curved canal of maxillary molars [71]. When