An Endodontic Evolution

August 28, 2010 at 5:37 pm · Filed under DENTAL PRODUCTS, Dental Technologies

“When men are easy in their circumstances, they are naturally enemies to innovations.” Joseph Addison

In This Week’s Issue
• An Endodontic Evolution, Welcome to the New World!

Note: This week’s issue is only focusing on one topic. Nothing like this has ever been seen. Endodontics has evolved!

An Endodontic Evolution, Welcome to the New World!……
Henry Ford invented the combustion engine in the early 1900’s. Since that time there have been many advances in the technology. It got bigger, more powerful & more efficient. We then created more sizes, mounted it sideways, in the center, in the rear. We adapted it for boats, trains and planes. However, the basics of the combustion system never changed. The fuel injects into the cylinders and causes an explosion that drives the piston.

The same theory has plagued endodontics since the file & reamer was tooled to fit the root canal of a tooth. We have seen hand files & reamers evolve into automation. Automation created debates between rotary & reciprocal techniques. Stainless steel gave way to nickel-titanium. Cutting edges changed to minimize separation and reduce procedure time. However, Files still separated and we were still trying to fit a round peg into a square hole, literally! The world has just changed!

The Science –watch?v=XIdqqmKDZvw

The Education – classroom.asp?x_classID=569

The Studies
The Self-adjusting File (SAF) – Canal Anatomy—A New Concept of Endodontic Files and Its Implementation

Zvi Metzger, DMD,*† Ehud Teperovich, DMD,† Raviv Zary, DMD,† Raphaela Cohen, DMD,† and Rafael Hof, MSc (Eng)†
Part 1: Respecting the Root
Abstract
Aim: To introduce a new concept, the self-adjusting file (SAF), and discuss its unique features compared with current rotary nickel-titanium file systems.

The New Concept:
The SAF file is hollow and designed as a thin cylindrical nickel-titanium lattice that adapts to the cross-section of the root canal. A single file is used throughout the procedure. It is inserted into a path initially prepared by a # 20 K-file and operated with a transline- (in-and-out) vibration. The resulting circumferential pressure allows the file’s abrasive surface to gradually remove a thin uniform hard-tissue layer from the entire root canal surface, resulting in a canal with a similar cross-section but of larger dimensions. This holds also for canals with an oval or flat cross-section, which will be enlarged to a flat or oval cross-section of larger dimensions. The straightening of curved canals is also reduced because of the high pliability of the file and the absence of a rigid metal core. Thus, the original shape of the root canal is respected both longitudinally and in cross-section. The hollow SAF file is operated with a constant flow of irrigant that enters the full length of the canal and that is activated by the vibration and is replaced continuously throughout the procedure. This results in effective cleaning even at the cul de sac apical part of the canal.

The SAF has high mechanical endurance; file separation does not occur; and mechanical failure, if it occurs, is limited to small tears in the lattice- work. Conclusion: The SAF represents a new step forward in endodontic file development that may over- come many of the shortcomings of current rotary nickel-titanium file systems.(J Endod 2010;36:679–690)

Design and Mode of Operation
The SAF is a hollow file designed as a compressible, thin-walled pointed cylinder either 1.5 or 2.0 mm in diameter composed of 120mm-thick nickel-titanium lattice. The 1.5-mm file may easily
be compressed to the extent of being inserted into any canal previously prepared or negotiated with a # 20 K-file. The 2.0-mm file will easily compress into a canal that was prepared with a #30 K-file. The file will then attempt to regain its original dimensions, thus applying a constant delicate pressure on the canal walls. When inserted into a root canal, it adapts itself to the canal’s shape, both longitudinally (as will any nickel titanium file) and along the cross-section. In a round canal, it will attain a round cross-section, whereas in an oval or flat canal it will attain a flat or oval cross-section, providing a three-dimensional adaptation. The surface of the lattice threads is lightly abrasive, which allows it to remove dentin with a back-and-forth grinding motion.

The SAF is operated with transline (in and out) vibrating handpieces with 3,000 to 5,000 vibrations per minute and an amplitude of 0.4 mm. Such a handpiece may be the Kavo GENTLEpower or equivalent combined with either a 3LDSY head (360free rotation; Kavo, Biberach Riss Germany) or MK-Dent head (360free rotation; MK-Dent, Bargteheide, Germany) or RDT3 head (80 rpm when free and stops rotating when engaging the canal walls, recently developed by Re- Dent-Nova, Ra’anana, Israel). The vibrating movement combined with intimate contact along the entire circumference and length of the canal removes a layer of dentin with a grinding motion (see later).

The hollow design allows for continuous irrigation throughout the procedure. A special irrigation device (VATEA, ReDent-Nova) is connected by a silicon tube to the irrigation hub on the file and and provides continuous flow of the irrigant of choice at a low rate. Micro-CT analysis of preparation of curved root canals using rotary
nickel-titanium files. Before, after, and three-dimensional analysis. Clear, prepared canal; green, affected surface; red, surface unchanged by the file. Reproduced with permission from Peters OA, Peters CI, Schonenberger K, et al. ProTaper rotary root canal preparation: effects of root canal anatomy on final shape analyzed by micro CT.

Int Endod J 2003;36:86-92. Basic Research—Technology 682 Metzger et al. JOE—Volume 36, Number 4, April 2010

Pressure at flow rates of 1 to 10 mL/min. Alternatively, any physiodispenser type of irrigation device (i.e., NSK Surgic XT Micro Motor System, Kanuma, Japan, or W&H ImplantMed, Burmoos, Austria) that is primarily designed for implantology may also be used.

The SAF is inserted into the canal while vibrating and is delicately pushed in until it reaches the predetermined working length. It is then operated with in-and-out manual motion and with continuous irrigation using two cycles of 2 minutes each for a total of 4 minutes per canal. This procedure will remove a uniform dentin layer 60- to 75-mm thick from the canal circumference. The SAF file is designed for single use.
An Self-adjusting File that Adapts Itself to the Three- Dimensional Anatomy of Root Canals

The SAF file is different from any current nickel-titanium rotary file. Most rotary file systems will find the widest part of the canal and gradually machine it, using several files of increasing diameter, to a wider canal with a round cross section. If the canal happens to be rela- tively narrow, the whole original canal may be included in the prepara- tion. However, if the canal is flat, oval, tear shaped, or simply large, this mode of preparation may leave untreated recesses, mainly buccally or lingually to the machined part of the canal.

The SAF is used as a single file (of either 1.5- or 2.0-mm diameter) that starts as a narrow, compressed, shape and gradually expands in the canal while removing a uniform layer of dentin from its walls. Because the file adapts itself to the cross-section of a given canal, a canal with a round cross-section is enlarged as a round canal, whereas an oval canal is enlarged as an oval canal of larger dimensions and. Even an extreme root canal anatomy, it lends itself to this mode of operation. High-resolution three-dimensional micro-CT analysis showed that high percentage (83.2%) of the canal wall is affected by the SAF file even in oval, flat root canals.
Uniform Removal of Dentin and Remaining Wall Thickness.

When operated in flat root canals, rotary nickel-titanium files may result in uneven thickness of the remaining dentin wall. In places in which the round bore has been created, the remaining dentin will be thinner in the mesial and distal aspects than in the untreated areas. When excessive apical preparations are used in an attempt to include as much of the irregular canal space in the preparation as possible, the uneven thickness may be even more pronounced. This uneven thickness of the remaining dentin wall may be The SAF Shank for attachment to a transline vibrating handpiece (in-and-out motion). Connector (hub) for the irrigation tube. Basic Research—Technology JOE—Volume 36, Number 4, April 2010
The Self-adjusting File. Part 1 – 683

The SAF file is extremely flexible and pliable. It does not impose its shape on the canal but rather complies with its original shape. This is true both circumferentially and longitudinally. The long axis of the apical part of curved canals is kept closer to its original place than re- ported for rotary files: a mean center-of-mass shift of 68.8Æ 7.7mm compared with the shift of 120 to 135mm previously reported by Peters et al with rotary files in similar canals(10) (Table 2 andFig. 8A). In curved canals, the thicker rotary nickel-titanium files have a tendency to transport the canal to the outer side of the curvature (Fig. 4)
(10). When the SAF is used to enlarge the canal to similar dimensions,
it tends to keep the apical part of curved canals closer to its original
location (Fig. 8A).

When rotary files accidentally pass the apical foramen of an apically curved canal, because of misleading length measurement or failure to maintain the marker in place, they may soon ‘‘zip’’ the apical foramen and form an oval opening. The SAF, on the other hand, may be operated in such conditions even for few minutes with no zipping what- so ever.

High Durability
The SAF file is extremely durable and may go through rather severe
abuse before a mechanical failure will occur. It does not have a core as
do other nickel-titanium instruments. Any strain applied to it is distributed along many of its delicate parts, and the total endurance is a function of the accumulated endurance of each of these individual parts.

Some of the tests used to compare the endurance of endodontic files are not directly relevant to this file’s mode of operation; nevertheless, they are indicative of its high durability(15). When torque durability was tested, the SAF can be turned 7Â 360before separation with a torque durability of 29.7 g/cm(15). These values are well beyond the ISO3630-1 requirement (1Â 360rotation and 18 g/cm in the torque durability test) and above that of many of the instruments compared in a recent American Dental Association Professional Product Review
(18).

When the American Dental Association cyclic fatigue test is
applied, SAF can be rotated for more than 150 hours at 900 rpm with a 5-mm deflection with no mechanical failure(15), whereas some of the nickel-titanium rotary instruments separated within the first hour or even within a few minutes(18). As mentioned previously, these tests are indicative of the SAF’s durability, even though the SAF’s mode of operation is a transline vibrating motion. A buckling test is more relevant to study the endurance of the SAF. The SAF can endure more than 600,500 consecutive 6-mm type I free buckling cycles before any mechanical damage could be observed(15). This represents an equivalent of$120 minutes of a rather abusive operation at 5,000 vibrations per minute.

A specially designed test apparatus allows the SAF to be continuously operated in simulated canals using the up and down motion of the handpiece, as used clinically. During this testing, the instruments were taken out and inspected every 1 minute. The SAF file was operated in this test for 29.1Æ 1.2 minute before any structural failure appeared.

After all this, the ultimate endurance test is the real-life test: operation in root canals. The SAF can be operated for 27 minutes in extracted human teeth before any structural failure appears. This represents more than 6 times the 4-minute operation time per canal, which is sufficient to achieve the desired results(15).

It is of particular importance to note that even when structural failure did occur, it was not of the separation type that is encountered with other nickel-titanium files. Detachment of one of the arches at one of its ends was the typical mechanical failure(15) (Fig. 9B). The damaged file could easily be retrieved from the canal, facing none of the challenges that a separated rotary nickel-titanium file presents

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