May 1, 2006
by A. Utku Ozan, DDS, MS
This article provides the clinicians a higher success ratio in endodontic treatment by focusing on advanced mechanical preparation. The protocol of advanced technique is not only increasing quality of prognosis but also the efficiency.
Since the introduction of Giromatic (90 degrees reciprocating contra angle) in late ’60s;
Techniques and equipment to perform automated root canal therapy improved through out the years. Clinical efficiency and easiness of using contra angles to file canals gained a large acceptance in the dental world in last 40 years. The reciprocation technique was offering a step back protocol, with a series of various styles of files and reamers negotiating canal walls that are made out of stainless steel. The increasing numbers of follower clinicians indicated that dentists who use a controlled mechanical force and a protocol of quarter turns (eliminating some stress on these stainless steel files) feel more comfortable performing endodontic treatment. There was a big need for progress in automated root canal therapy.
In early ’80s, the term “acoustic streaming” came out with a new concept of “Sonic filing with vibration while irrigating” and found great acceptance by clinicians that preferred automated root canal therapy. The protocol was considered step back since it started using a smaller size of file to next larger one, till an acceptable amount of enlargement is accomplished from crown to apex. There was a major difference in the number of files needed in this protocol versus hand filing and Giromatic techniques. Now 3-4 files performed the enlargement that the earlier techniques accomplished additionally offering much cleaner canals with the help of irrigation.1 Files needed to be pre-curved where extreme curves were being negotiated.2 The technique was safe and superior to previous ones in terms of establishing a selective straight line access (avoiding danger zones), smear layer removal, coronal flaring, debris removal.3,4 Ultrasonic units came out before the sonic system, using inserts, most of them with cutting tips leading to transportation and ledges. The biggest disadvantage was they were too aggressive to be used in every step of Endodontic therapy where Sonic technique was found to be safer (less aggressive) yet more efficient.5
The introduction of Sonic hand piece (MM 1500) in late ’80s helped the progress of results due to much less aggressiveness and safe (non-cutting tips) files. Irrigation still remains a definite principle to be followed and to perform such cleanliness in the canal systems, while help of vibration (Figs.1 & 2) is undeniable particularly in the cavitation effect of Sodium Hypo – Chlorite.6,7
Having lateral components of movement while the file is traveling towards the apical area (vertical) is what the Sonic technique offers to Endodontic treatment. This brings the efficiency in all steps of the treatment, filing with irrigation (to eliminate debris packing and blockage), distributing disinfecting agents into lateral canals, isthmus, delta formation and most importantly into fins (Figs.1 & 2) and also while distribution of canal sealers where the lateral canals need to be accessed.8
In early 90s Nickel Titanium rotary files were introduced with a new protocol called “Crown down technique”. The protocol was starting from the orifice by using larger files then going to smaller sizes as approaching the working length so that the stress on the files; which leads to ledges, perforation and file breakage could be decreased.9 The alloy of NiTi, offers greater flexibility, metal memory — higher re-usage but more expense. The rotary technique alone is not “the answer” to the removal of all infected tissue since any rotational file will perform only enlargement as far as their radius reaches. On the contrary; the anatomy of many roots will have fins and lateral components (accessory canals), some of them with C shaped anatomy (oval roots) which require unique approach as a combination to rotary.10 To be able to penetrate such lateral extensions of the canal system, that radius of the file has to be very large when canals will not allow, even a #10 hand file during the first penetration.
There was a lot of room for progress in rotary systems. The breakage of files, transportation, leaving steps that will become voids after obturation are common problems that occur with some rotary techniques.11 Also a secondary factor, expense should not be forgotten. The less number of files used to accomplish the procedure and the more re-usage clinicians get out of every file the less expense occurs.
Coronal flaring is necessary with every rotary system. The orifice enlarging components of every rotary system are also rotational (like gates gliddens, Peezo reamers, orifice burs, Endodontic burs, S1 – S2 etc.). Establishing straight line access with rotary components does not offer a safe approach towards danger zones (bifurcation and trifurcation areas where minimal contact is needed) (Fig. 3). Clinicians end up weakening the root by enlarging danger zones of the orifice where it might lead to a crack or even perforation. Also use of rotary components while establishing the coronal flaring leads to many problems like, apical extrusion, losing the patency, use of more of the expensive NiTi files (much greater tapers like 12-10 or 8) which may lead to breakage or steps in the preparation.
There is a need for a second device; which has lateral components of filing not only rotational, that also is irrigating and cleansing to the rest 2/3 of the canals, where the fins are continuing through out the whole canal system. Many clinicians use the MM 1500 Sonic hand piece as a conjunct tool to their rotary system where they could initially penetrate and establish SELECTIVE straight line access (enlarging away from the danger zones) (Figs. 3 & 4), for coronal flaring and also utilize the irrigation and clean the canal walls (Figs. 5 & 6) before shaping with NiTi files.
The desired file system for rotary users should;
1. Avoid breakage
2. Avoid transportation (preserve original anatomy)
3. Avoid screwing in effect
4. Cut efficiently with less files
5. Allow circumferential filing
6. Unwind prior to breakage as a safety factor (indication of discarding)
7. Be usable in multiple cases
Currently HERO Shapers are being introduced to Canadian dentists. This file series is the next generation of HERO family. The first was Hero 642 file system which has a large acceptance in the world dentistry. There are more than 15 studies in the dental literature in many languages on Hero file systems, comparing the results clinically to the others. Hero Shapers are more flexible and resistant to breakage compared to Hero 642 series.
Hero Shapers’ design is uniquely different from the current NiTi rotary files: offering a longer pitch. The engagement and pulling down feeling (screw in effects) that is being experienced in many file systems is not a part of Hero protocol due to design.11 As a result less breakage, less failure and elimination of stress on the performer is being established among Hero users.12 The design of these files enables the clinician circumferential filing offering more flexibility and less stress. On top of such advantages the file design also offers a bigger inner core but not stiffness, a positive rake angle for better debris removal and constant gradual enlargement from the passive file tip to the shank that enables less breakage.9,13,14
Hero Shaper files offer a new pitch which varies according to the taper size. As known the more tapered an instrument is the longer is its pitch which can be described as “Adapted pitch” leading to increase of instrument performance also avoiding screwing effects.
The protocol that is going to be discussed in this article is self explanatory, which has been accepted by many clinicians around the world. Combining advantages of multiple techniques and utilization of right file and technique in the right po
rtion of the canals is essential. Sonic cleansing (especially in apical 1/3 portion that shows significantly more pulpal and inorganic debris, smear layer and a high number of surface profile irregularities)15 + NiTi rotary shaping can be used in every case. Focusing on a difficult molar case is more critical than an average easier anterior, so this protocol below is for a molar root that is large enough to negotiate #15 hand file for patency and initial working length determination. (If the canal is tighter, #10 Rispi-Sonic file can be used as initial file.)
In this protocol; a combination of Sonic, step back and Crown down techniques are used to eliminate disadvantages present in other protocols by utilizing right equipment and techniques.
Dr. Ozan received his DDS degree from Gazi University where he completed his residential program in 1999. He operates multiple practices in Europe and USA. Dr. Ozan is also a consultant for product development and manufacturing in endodontics as well as general dentistry.
Oral Health welcomes this original article.
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