The Next Level Of Mechanical Preparation By: A. Utku Ozan, DDS MS

The purpose of this article on endodontics is to utilize the advantages of the most popular and recent mechanical preparation techniques in root canal therapy with consideration of clinical analysis and research data. The goal is to implement these proven facts into the new techniques for better clinical results and efficiency.

After determination of working length followed by the localization of the orifices, the clinician’s focus is on mechanical preparation. The new techniques in rotary instrumentation indicates the usage of greater taper nickel-titanium files, starting from bigger numbers by using the crown down method. NiTi files are extremely flexible to access the curved portions of the canal. However the usage of these files is not the best way of establishing a decent coronal flaring. The file breakage due to working against resistance, leaving steps by changing the diameter size of the tapers, no irrigation while working, transportation of the original anatomy due to the metal memory are some of the clinical aspects to be reconsidered for two-thirds coronal flaring. On the other hand the cost of NiTi files is unacceptable for many clinicians. It is critical to refresh memories about some rotary systems in the past in order to compare recent ones and find some useful tips.

Fig 1. Anatomic Structures of Pulp Cavity (isthmus - lateral canals - apical deltas)

In the early 1970s the GiroMatic system was introduced to dentistry as an endodontic system using Headstrom, Reamers, Triocut and Rispi files as well as Spiral Fillers (stainless steel) on a 90 degree reciprocating contra angle. The files go back and forth with quarter turn, instead of a complete 360 degrees turn so that the stress is down to .25 on the file, while eliminating hand fatigue and giving better clinical results. Unfortunately, expecting complete success only from the change in the alloy of the files from stainless steel to NiTi is acting beyond physics rules.

The usage of sonic systems started in the mid 1980s. After years of clinical experience with ultrasonic endodontic systems, sonic devices were introduced to eliminate some disadvantages due to high frequency (in Hz) vibrations. In other terms, the ultrasonic devices were too aggressive for root canal therapy, sonic devices took place with less vibrations/second, more precise and controlled cutting with built-in irrigation. The Sonic device is an air driven handpiece, which is mountable to any highspeed outlet on every dental unit, offering a frequency adjustment. The unit has built in (internal) irrigation as well as a stopper for working length control. The acoustic waves (cycles per second) on the files were designed to follow the path of least resistance while going down towards the apical foramina. The principle of action around the files is pendulum movements––coming back after every strike. During this process the file’s direction is towards the apex, instead of an uncontrolled motion on harder dentin walls, working in the center’s softer pulp tissues, eliminating over filing one portion, perforations and transportations. In addition, the file’s direction keeps the original anatomy of the canal within the clinical values, if the agitation is being done under the existence of sodium hypochlorite, optimum debris removal is accomplished. Isthmus cleansing, smear layer removal, with desired cone shape, and keeping original anatomic form are a couple of the clinical advances with the use of sonic systems that were found in many clinical studies.

The following clinical studies approve the facts that were discussed in this article about the Sonic system: A) A Comparison Of Four Instrumentation Techniques On Apical Canal Transportation (Crown down and step-back technique with K-Files, sonic technique and NiTi) The results of the study comparing the four instrumentation techniques for canal transportation indicated that “no statistically significant differences were found for canal transportation.” “Sonic instrumentation significantly increased coronal flaring” than the other techniques.

Fig 2. Coronal flaring with sonic rispi files

Fig 3. Coronal flaring with niti greater tapers

Luiten DJ, Morgan LA, Baumgartner JC, Marshall J G. A comparison of four instrumentation techniques on apical canal transportation. J. Endod. 1995;21(1):26-32.

B) Endosonics in Curved Root Canals
“Canal curvatures were straightened in 3 of 51 cases. No measurable alteration occurred in 94% of the canals. The average length of time required to enlarge canals from size 15 to size 25 was 2.75 min. It appears that endosonics is efficient and may be used in curved root canals.”
Chenail BL, Teplitsky PE. Endosonics in Curved Root Canals. J. Endod. 1985;11(9):369-74.

C) The Efficacy of Step-Down Procedures during Endosonic Instrumentaion
“A log linear analysis showed that there was significantly less debris present with the step-down method using piezoelectric and sonic devices.”
Murgel C, Walmsley AD, Walton RE. The Efficacy of Step-Down Procedures during Endosonic Instrumentaion. J Endod. 1991;17(3):111-5.

D) Stereomicroscopic Evaluation of Canal Shape following Hand, Sonic, and Ultrasonic Instrumentation
“The comparisons between the sonic and ultrasonic techniques showed significantly better shapes were obtained with the Sonic Air MM 3000 instrument.”
Loushine RJ, Weller RN, Hartwell GR. Stereomicroscopic evaluation of canal shape following hand, sonic, and ultrasonic instrumentation. J Endod. 1989;15(9):417-21.

E) An In Vivo Comparison of the Step-back Technique versus a Step-back/Ultrasonic Technique in Human Mandibular Molars
“At the 3-mm level, there were no statistical differences in canal or isthmus cleanliness between the step-back group and the step-back/ultrasound group. At the 1-mm apical level, statistical analysis indicated that the step-back/ultrasonic technique was superior to the step-back technique in canal (99.6% versus 88%) and isthmus (86% versus 10%) cleanliness.”
Haidet J, Reader A, Beck M, Meyers W. An invivo comparison of the step-back technique versus a step-back/ultrasonic technique in human mandibular molars. J Endod. 1989;15(5):195-9.

F) Effects of Sonic Instrumentation on the Apical Preparation of Curved Canals
“Statistical analysis (chi-square test and analysis of variance) showed no significant difference (p>0.05) in the amount of apical transportation in canals prepared with the Kerr K-type, Rispi-Sonic, or Trio-Sonic files.”
Ehrlich AD, Boyer TJ, Hicks ML, Pelleu GB Jr. Effects of sonic instrumentation on the apical preparation of curved canals. J Endod. 1989;15(5):200-3.

G) Dentin Removal Efficiency of Six Endodontic Systems: A Quantitative Comparison
“The dentin removal efficiency of current endodontic systems, based on the amount of dentin removed in 1mm of canal axial length, was determined for working times of 1 and 2 min. Six endodontic systems were compared. For 1 min of instrumentation, the Mecasonic+Shaper was the most efficient system.”
Hennequin M, Andre JF, Botta G. Dentin removal efficiency of six endodontic systems: a quantitative comparison. J Endod. 1992;18(12):601

H) Effect of Precurving Endosonic Files on the Amount of Debris and Smear Layer Remaining in Curved Root Canals
“The root canals instrumented with the precurved files had a significantly lower debris score than those prepared with straight files. Precurving did not affect smear layer removal. In conclusion, precurving of files decreased the amount of debris but did not affect smear layer removal.”
Lumley PJ, Walmsley AD, Walton RE, Rippin JW. Effec of precurving endosonic files on the amount of debris and smear layer remaining in curved root canals. J Endod. 1992; 18(12): 616-9.

The adjunct use of Sonic systems with rotary NiTi files is the answer for an optimum mechanical preparation. Coronal two-thirds flaring, flushing, filing should be established by the help of Sonics while curved apical portion (one-third or even sometimes one-fifth apical portion) being shaped with NiTi files. (0.2 tapers / hand or rotary). As a result, clinicians seeking excellence using different techniques clinically for an optimum mechanical canal preparation.

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Dr. Ozan Dr. Ozan received his DDS, degree from the Gazi University Faculty of Dentistry where he completed his residential program on general dentistry in 1999. He lectured for endodontic residential programs in the USA as well as internationally. Dr. Ozan is the executive director of continuing education programs in Dental Forums and a product development consultant for the Medidenta International Group of Companies.