Written by E. Steve Senia, DDS, MS, and William L. Wildey, DDS Friday, 31 October 2003 19:00
In part 1 last month, we gave our reasons and supporting evidence for considering single-visit endodontics as a viable treatment option in many cases. We also listed our 5 exceptions to single-visit treatment. But, above all, we stressed that single visits could be justified only when certain criteria were met—namely, that canals be well cleaned, shaped, and obturated in the single appointment, and that additional visits would not improve the quality of treatment. In this article, we describe a technique for cleaning and shaping canals using a combination (“hybrid”) of 2 different types of instruments: tapered rotary instruments and nontapered rotary instruments.
A hybrid technique combines the desirable features of 2 different instrumentation systems. NiTi tapered rotary instruments are used in a crown-down fashion to prepare quickly and efficiently the coronal and midroot portions of the root canal, while nontapered, highly flexible NiTi rotary instruments are used for the final cleaning and shaping of the apical part of the canal. “Hybridization” is not a novel concept. Mixing and matching various instruments and techniques is commonly practiced because no single technique is suitable for every possible root canal configuration. The hybrid technique described in this article (including 3 case reports by 3 different clinicians) uses K3 tapered NiTi rotary instruments (Sybron Endo) and LightSpeed NiTi nontapered instruments (LightSpeed Endodontics).
SINGLE-VISIT ENDODONTICS: PART 1 REVISITED
It is widely accepted that bacteria (and their toxins) are the immediate cause of dental problems that often require root canal treatment, and that bacteria also are the cause of treatment failures. In part 1, we mentioned that the removal of all or most of the bacteria during the cleaning process was crucial for successful endodontics. The justification for single-visit endodontics depends upon the ability of the chosen instrumentation technique to render canals almost bacteria-free predictably in one appointment.
Recently, considerable evidence has surfaced that effective bacterial removal requires apical preparations larger than many would currently consider “normal.” We believe that sizes considered normal today (Nos. 20 to 35 range) will be considered small in the future. We anticipate an urgent interest by the research community in obtaining more information about apical canal diameters to support existing research indicating that “uninstrumented” apical diameters are not as small as we are led to believe. Fortunately, with the introduction of nickel-titanium technology approximately 10 years ago, the capability to prepare canals safely and effectively to larger sizes already exists. This paradigm shift will not occur overnight, but eventually apical preparation sizes of 45 and higher (for most molars) and 60 and higher (for most anteriors and premolars) will be considered normal to those willing to accept the scientific and clinical evidence.
STRAIGHT LINE ACCESS IS KEY
The hybrid technique, as with all other techniques, requires direct access into the apical third of canals—the area of the canal system considered most difficult to clean, shape, and fill. Better apical control is obtained with correct coronal and middle third shapes, manifested by more effective irrigation, improved visualization of the canal, removal of restrictive dentin, and improved tactile sense during instrumentation. As with our medical colleagues, we should never perform endodontic procedures without a clear and commanding visualization of the surgical site. Incorrect access and poor coronal management risks creating ledges and other serious iatrogenic events that compromise the prognosis.
TAPERED NITI ROTARY INSTRUMENTS
Crown-down instrumentation techniques are becoming more popular for the vast majority of teeth, regardless of the brand used. Crown- down instrumentation prepares the coronal third of the canal first, the middle third second, and apical third last. Orifice-shaping files with tapers of .12, .10, and .08 (all with a tip size of No. 25) appear to have the greatest universal applicability for attaining the ideal form in the most coronal part of the canal. Nonetheless, many clinicians still find that Gates Glidden Drills or Peeso Reamers further enhance the performance of the shaping files.
NONTAPERED NITI ROTARY INSTRUMENTS
When created judiciously and in proportion to the original canal sizes, larger apical sizes are desirable because more bacteria are removed from the canal and dentin tubules. However, as tapered instruments increase in size, they become more rigid, making the quality and safety of apical enlargement (cleaning) problematic. This is where nontapered rotary instruments become an essential part of the combined technique. Featuring a very short cutting blade and a smooth, nontapered, flexible shaft, they are well-suited for apical instrumentation, especially as tip sizes increase. The flexible shaft allows the cutting head to follow accurately the curves of the canal, and the short cutting head greatly reduces torsional stress on the instrument. Finally, the shortened cutting blade allows for enlarging the apical part of the canal without also over-enlarging the coronal aspect of the canal.
The nontapered design also provides very accurate tactile feedback so that apical gauging and correct apical preparation sizes can be achieved. Over-enlargement should be avoided since it weakens the root needlessly, while underpreparation does not achieve optimal canal cleaning. Precise preparation, particularly of the critical apical portion of the root canal, should be one of the objectives of instrumentation regardless of the technique or instruments used. Nontapered instruments help achieve this precise instrumentation.
In part 1, we discussed the role played by working length (WL). Working length is important from both a biological and mechanical (instrumentation) perspective. We caution against purposefully pushing the larger rotary instruments beyond the apical constriction (when present) or foramen. Many anatomical studies show that in most teeth the canal exits the tooth at an acute angle because the foramen is not at the apex in approximately 80% of teeth. It is these acute angles that lead to rapid instrument failure and ovaling of the foramen when an instrument with a large tip size is used.
Obtaining the perfect working length in all cases is not clinically possible, but a good apex (foramen) locator can help. Fortunately, the body’s powerful defense system gives us some tolerance to be a little short or a little long in the vast majority of cases.
Finally, canal patency is essential before using any rotary system. Most techniques require “exploring” the canal and making some initial canal preparation with hand files rather than with rotaries. Creating (and maintaining) a clear path to working length with hand files throughout the instrumentation process is a basic and important part of the hybrid technique.
THE HYBRID TECHNIQUE GUIDE
Instrumentation with Tapered Instruments
Before beginning this phase of instrumentation, be sure you are using the correct handpiece at the proper settings. For most tapered instruments, an rpm within the range of 150 to 350 is recommended. If a torque-controlled motor is used, set the torque as recommended by the manufacturer.
Step 1: Flare the coronal part of the canal. After locating the canal orifice, the largest appropriate shaper is used first. The shapers function as orifice openers and achieve coronal shape in a safe manner. The taper (T) used for enlargement depends on the original canal size: the .12T then .10T for large canals; the .10T then .08T for medium and small canals. Each shaper
is advanced apically until it meets a light resistance—usually about 3 to 4 mm down the canal. Sequentially smaller tapers follow in the same manner. Irrigation and recapitulation should be done frequently, ideally after every file used. EDTA is recommended.
Step 2: Clean and shape midroot. Depending on the size and shape of the canal, use .04 or .06 tapered instruments to prepare the midroot and gain access to the apical part of the canal. In most cases, the midroot shaping objective is achieved with the following recommended sequence of instrumentation: No. 35/.06, No. 30/.06, and No. 25/.06, used in that order. Narrower canals may require .04-tapered instruments and smaller sizes (Nos. 20 and 15) before the No. 25/.06 or No. 30/.04 can be taken to working length. Many advocate using .06T and .04T alternately in the same canal to minimize binding. Choosing the appropriate sequence will depend somewhat on experience, manufacturers’ recommendations, and an understanding of root and canal anatomy.
With the instrument rotating prior to entering the canal, advance it apically until resistance is met, give it 2 light pushes, then remove it from the canal. Irrigate and flood the canal between each instrument. Check for patency with a small hand file. Do not try to reach WL with all instruments. Only the No. 25/.06 or No. 30/.04 should be taken to working length unless the canal is very large.
Whichever instrumentation sequence you find best, remember that the shaping objective of this step will end when either a No. 30/.04T or No. 25/.06T instrument reaches WL.
Apical Instrumentation With Nontapered Instruments
|Table 1a and 1b. Estimated apical preparation sizes —maxillary and mandibular teeth based on research studies.|
Once the coronal and midroot portions of the canal are prepared, the superflexible, nontapered instruments are used to finish the apical preparation. Research has shown that the vast majority of teeth require instrumentation to sizes larger than a No. 25 or No. 30 for complete cleaning and canal disinfection (Tables 1a and 1b). By completing the apical part with instruments designed especially for this purpose, it relieves one from the discomfort of forcing large tapered instruments into the apical part of the canal.
Step 3: Apical gauging (sizing). The next step is to determine the approximate size of the apical part of the canal. This is done with a technique called apical gauging (sizing). Start the gauging process by hand with a LightSpeed (LS) No. 35. Advance the LS No. 35 apically without rotation. One of 3 things will occur:
(1) If the LS No. 35 reaches WL, it indicates the canal is larger than the No. 35 instrument (>0.35 mm). Continue gauging with sequentially larger LS sizes (still by hand) until reaching a size that does not go to WL (binds before reaching WL). We call this instrument the First LightSpeed Size to Bind (FLSB). This is your starting point—the instrument size to begin apical instrumentation using the handpiece. Go to step 4.
(2) If the LS No. 35 cannot reach WL (even when moderate force is applied), it indicates the canal is smaller than the No. 35 instrument (<0.35 mm). However, if it binds within 2 mm of WL, the No. 35 is the starting point (FLSB) for apical instrumentation using the handpiece. Go to step 4.
(3) If the LS No. 35 binds 2 mm or more short of WL (even when moderate force is applied), this indicates that the canal is smaller than the No. 35 (<0.35 mm) and also that the No. 35 is not the correct FLSB. Binding more than 2 mm from the WL means that the canal is not ready for apical instrumentation with the LS No. 35. This rarely occurs, but if it does, double check to be sure that a No. 30/.04 or No. 25/.06 does in fact reach WL as called for in step 2.
Note: LightSpeed instruments are available in sizes as small as No. 20. The smaller sizes can be very helpful when a No. 25/.06 or No. 30/.04 cannot be easily taken to working length or when canal anatomy makes it undesirable to do so. These small instruments also come in very handy when the LS No. 35 will not reach WL, even after coronal preparation with tapered instruments. It is a good idea to have these smaller instruments available in those instances when you need them.
Step 4: Begin nontapered rotary preparation. Before beginning apical instrumentation with LightSpeed, be sure you are using the correct handpiece at the proper settings. A speed range of 1,000 to 2,000 rpm is recommended. Most users prefer 2,000 rpm because instruments cut better, thus instrumentation time is shortened when the faster speed is selected. Forward rotation (clockwise) is critical.
A cordless handpiece is the best option. The newer models can be purchased with both 16:1 and 4:1 contra angles so that the motor speed can be easily and quickly changed from low rpm (tapered instruments) to the high rpm (nontapered instruments). Torque control and auto reverse are also now available on some models. When chair time is critical, many practitioners have found that using 2 cordless handpieces is the answer. This is because while the doctor is using one handpiece, the assistant can be getting the next one ready.
Instrumentation with the handpiece begins with the LS size (FLSB) determined by the gauging process described in step 3. Activate the handpiece before entering the canal, and with a slow, continuous motion, advance the instrument apically until feeling a slight resistance. Resistance indicates the cutting head is binding. At the first feeling of binding, stop apical advancement, pause momentarily, withdraw the instrument approximately 2 mm, then advance apically again, just past the previous point of binding. This is called a “pecking” motion. A peck is a down cut and a slight withdrawal of approximately 2 mm. Continue pecking until reaching WL. Once reaching WL, immediately remove the instrument (still rotating) from the canal. Do not linger at the WL because doing so will shorten the life of the instrument.
Step 5: Complete the apical preparation. Instrumentation continues with sequentially larger LS sizes (do not skip half-sizes) using the pecking motion as described in step 4.
When is Apical Instrumentation Complete?
|Table 2. Estimated apical preparation sizes—maxillary teeth based on clinical experiences.|
Clinical experience, research studies (see last month’s part 1 of this article), and the examination of many root cross-sections have shown that apical preparation is complete (thorough cleaning is achieved) when reaching a LS size that requires 12 or more pecks to instrument the apical third (the last 4 to 5 mm). This size LS instrument is known as the Master Apical Rotary (MAR). Table 2 gives the average MAR sizes for each tooth.
The nontapered design of the LightSpeed can bind only in one place (at the instrument’s tip), thus it provides the accurate tactile feedback necessary to indicate when a canal has been properly prepared with the appropriate instrument size. After using LightSpeed a few times, determining the correct final apical instrument size will become second nature.
Obturation can be accomplished in many different ways and plays an important role in successful single-visit endodontics. However, one must be aware that in the apical part of the canal (near WL), the obturation can only be as good as the preparation (as explained in “Another Look at Root Canal Obturation,” Dentistry Today, March 2002). If tissue or debris remains, obturating material cannot take its place and a good seal is less likely. Another advantage of cleaner and larger apical preparations is that they are much easier to fill with nearly any obturation technique you may choose to use.
CASE REPORT NO. 1
|Figure 1a. Pretreatment x-ray tooth No. 14.|
Figure 1a shows the pretreatment x-ray of a maxillary first molar (tooth No. 14). After a preoperative assessment was made and radiographs taken, access was made to establish a straight-line guide path to the midroot area. The MB2 canal was not patent to the foramen but blocked at about 12 mm. K3 (Sybron Endo) and LightSpeed NiTi rotary instruments (LightSpeed Endodontics) were used for canal preparation.
Crown-Down Preparation With Tapered K3 Instruments
The coronal third of all canals was instrumented with K3 orifice openers having .10 and .08 tapers respectively, both with tip sizes No. 25. The middle third was explored, patency was determined with hand files, and it was mechanically instrumented with the K3 No. 35/.06 to slightly beyond midroot. The apical third was then explored, WL was determined, and the canal instrumented to WL with a No. 20 hand K-file. This was followed by K3 files sizes Nos. 35/.06, 30/.06, and 25/.06 until the No. 25/.06 reached the working length of the canals. Each instrument was inserted to resistance, gently advanced apically 2 times, then removed from the canal. Canals were irrigated and patency was checked between each instrument. When the hybrid technique is used, coronal instrumentation is complete when WL is reached with either a No. 25/.06 or No. 30/.04.
Apical Preparation with Nontapered LightSpeed Instruments
Once the shaping objective was achieved with tapered instruments, the canals were gauged (by hand) with the LS No. 35. The LS No. 35 bound within 2 mm of WL in all canals. Therefore, it was the appropriate instrument to begin mechanical preparation of the apical part of the canal.
|Figure 1b. MARs: MB and DB LS No. 40; P = No. 50. Canals obturated with System B. (Courtesy of Dr. Richard Mounce, DDS, Portland, Ore.)|
Using a cordless handpiece rotating at approximately 2,000 rpm, apical instrumentation began with the LS No. 35. This instrument was taken to WL in all 3 canals using a pecking motion in the last 2 mm because the cutting of dentin walls was taking place. The LS No. 35 easily reached working length in all 3 canals (with just a few pecks required), so instrumentation continued with sequentially larger LS instruments, the No. 37.5 and the No. 40. The MAR size for the MB and DB canals was determined to be the LS No. 40, using the 12 pecks rule as a guide. The feedback from LightSpeed indicated that the larger palatal canal required further enlargement because the LS No. 40 reached WL easily (less than 12 pecks). In the P canal only, instrumentation continued with the LS Nos. 42.5, 45, and 47.5, all reaching WL with less than 12 pecks. Apical instrumentation was completed with the No. 50 because it took more than 12 pecks to reach WL. Note that the MARs closely approximate the average recommended sizes shown in Table 2. System B (Sybron Endo) was used for obturation (Figure 1b).
This case was treated using the recommended hybrid technique, and there were no surprises or deviations. Warm vertical obturation was accomplished quickly, easily, and effectively, even with the larger apical preparation sizes.
The next 2 hybrid cases show that on occasion exceptions and deviations may occur. As you will see, most of the time, rather easy solutions can be applied to deal with these exceptions.
CASE REPORT NO. 2
|Figure 2a. Pretreatment x-ray of tooth No. 4.|
Figure 2a shows the pretreatment x-ray of a maxillary right second premolar (tooth No. 4). After a straight-line access, K3 and LightSpeed instruments were used with the hybrid technique.
|Figure 2b. K3 No. 25/.04 to working length, completing the tapered phase of the hybrid technique.|
The coronal third of the canal was instrumented with K3 orifice shapers having .10 and .08 tapers and tip sizes of No. 25. After WL was determined, the canal was instrumented to WL with a No. 20 hand Flex-R file (Miltex). Then the middle and apical thirds of the canal were instrumented with the .06 and .04 K3 size Nos. 40, 35, 30, 25, 20, and 15, each progressing further down the canal. After this sequence, the No. 25/.04 reached the working length (23 mm) without being forced (Figure 2b). Clinical judgment indicated that neither shaping objective instrument, No. 25/.06 nor No. 30/.04, could reach working length without a significant amount of additional effort. Most likely, the rigidity of these instruments could not overcome the severe curve encountered.
|Figure 2c. LS No. 25 to working length (by hand). The canal was first gauged with the LS No. 35 by hand. It bound more than 2 mm from WL so smaller sizes were tried (to LS No. 25).||Figure 2d. The Master Apical Rotary (MAR) = LS No. 50.|
|Figure 2e. Post-treatment x-ray. The apical 5 mm of the canal was obturated with SimpliFill, and the middle and coronal thirds were backfilled with GP and Pac Mac. (Courtesy of Dr. Carlos Murgel, Brazil.)|
The canal was gauged with the LS No. 35 by hand. It bound more than 3 mm from WL, so smaller sizes were tried until it was found that the LS No. 25 went within 2 mm of WL (Figure 2c). The No. 25 was placed in the handpiece to begin rotary instrumentation. The MAR was a LS No. 50 (Figure 2d). The apical 5 mm of the canal was obturated with a size 50 SimpliFill obturator (LightSpeed Endodontics), and the middle and coronal thirds were backfilled with GP and Pac Mac (Sybron Endo, Figure 2e).
The severe curve did not allow for successful instrumentation with tapered instruments to the shaping objective. Therefore, apical gauging with the LS No. 35 was also not successful. Thus, apical gauging continued with smaller LS sizes (Nos. 30 and 25) until it was determined that the LS No. 25 was the appropriate instrument to begin rotary instrumentation. The canal was instrumented to the appropriate size with the LS No. 50 (12 pecks rule), which shows that even when the canal is severely curved and difficult to negotiate, the correct size for complete apical cleaning may still be quite large. Without the nontapered instruments, canal preparation would have ended at a No. 25 instead of a No. 50.
CASE REPORT NO. 3
|Figure 3a. Pretreatment x-ray of tooth No. 3.|
Figure 3a shows the pretreatment x-ray of a maxillary right first molar (tooth No. 3). K3 and LightSpeed instruments were used with the hybrid technique.
Crown-Down Preparation With Tapered K3 Instruments
The coronal third of all 4 canals was instrumented with K3 orifice openers having .10 and .08 tapers and tip sizes of No. 25. Working lengths were determined and the canals instrumented with a No. 20 hand K-file to WL. K3 instruments Nos. 35/.04, 30/.04, and 25/.04 were then used to prepare the middle third of the canals. The No. 25/.04 was able to reach working length comfortably in the palatal canal but was unable to do so in the MB1, MB2, and DB canals. Therefore, smaller K3s No. 15/.04 and then the No. 20/.04 were used and they went to WL in all 3 canals. Trying the No. 25/.04 again, the excessive resistance to apical advancement indicated that the No. 25/.04 was not going to reach WL comfortably without a significant amount of time and effort. Therefore, it was decided to end the tapered portion of the hybrid technique and proceed with nontapered instruments.
Apical Preparation With LightSpeed Nontapered Instruments
The palatal canal was gauged with the LightSpeed (LS) No. 35 by hand. Because it bound 2 mm short of WL (Step 3), rotary instrumentation with the cordless handpiece began with the LS No. 35 (FLSB) taking it to WL. Sequentially larger LightSpeeds were used to WL until it was determined that the final apical preparation size (MAR) for the palatal canal was a LS No. 60 (12 pecks rule).
The enlargement objective for tapered instruments requires either a No. 25/.06 or No. 30/.04 to reach working length (step 2). However, in this case, it was not possible in the MB1, MB2, and DB canals because of the severe curvatures encountered. Consequently, the usual gauging procedure of starting with LS No. 35 (step 3) was not used. Instead, rotary instrumentation was started with the smallest LS, a No. 20. Sequentially larger LightSpeed instruments were used until it was determined (using the 12 pecks rule) that the final apical preparation sizes (MAR) for the MB1 and MB2 was a LS No. 55 and for the DB a LS No. 50. The canals were irrigated with NaOCL and EDTA to complete the hybrid instrumentation technique.
|Figure 3b. Post-treatment x-ray. The palatal canal was instrumented to working length with a K3 No. 25/.04. The MB1, MB2, and DB canals were instrumented to working length with a K3 No. 20/.04, completing the tapered phase of the hybrid technique. The Master Apical Rotary sizes were as follows: MB1 and MB2 = LS No. 55; DB = LS No. 50; P = LS No. 60. All canals were obturated with SimpliFill Apical GP Plugs and backfilled according to the SimpliFill technique. (Courtesy of Dr. William L. Wildey, Hurst, Tex.)|
The apical 5 mm of each canal was obturated with a SimpliFill GP Plug (LightSpeed Endodontics) by using GP Plugs of the same size as each canal’s MAR (Nos. 55, 50, and 60). AH Plus (DENTSPLY DeTrey), an epoxy resin sealer, was used to coat the GP Plug and was also applied to the apical third of the canal. After obturating the apical 5 mm, the middle and coronal thirds were obturated by first injecting the sealer into the space with the SimpliFill syringe, then advancing a standardized cone, the same size as the GP Plug, through the sealer until it contacted the coronal top of the GP Plug. Additional nonstandardized cones were added to fill the remaining coronal space (Figure 3b).
This case is a good example of the variability of canal anatomy. All canals are “not created equal,” and in this situation, the shaping objective for the hybrid technique (No. 30/.04 or No. 25/.06 to WL) was not accomplished for the MB1, MB2, and DB canals. We should not be surprised, being mindful that any given technique does not work all of the time. This case also showed how the technique can be easily modified by using nontapered instruments smaller than No. 35 to gauge the canal when the shaping objective cannot be easily or safely achieved. By taking advantage of the nontapered instrument’s precise tactile feedback, LS determined that the preinstrumentation canal diameters required apical preparation sizes of Nos. 50, 55, and 60 in order to attain the cleaning objective. This avoided ending the preparation prematurely, which would result in under-prepared canals.
Single-visit endodontics is rapidly becoming the norm rather than the exception. The economics of single visits certainly encourage this strongly. (See last month’s part 1 of this article.) But it is science and not economics that should guide our treatment methods. Thorough canal cleaning (to larger apical sizes) is one of the key elements of scientifically based single-visit endodontics. With sensible exceptions noted, we encourage you to consider offering your patients single visits after you have embraced the concepts and put into practice a technique for thoroughly cleaning and obturating canals on the first visit.F
The authors want to thank Mr. Steven S. Senia, BSIE, MBA, and Richard Mounce, DDS, for their contributions to this article.
Dr. Senia has been published in national and international journals. He is a diplomate of the American Board of Endodontics, a former member of The Journal of Endodontics editorial board, and a consultant for the NASA space program. After receiving both his BS and DDS degrees from Marquette University in 1963, he re-entered the US Air Force (he had prior service as a pilot) to take a GPR residency program at Chanute Air Force Hospital. In 1969, he received a certificate in endodontics and a master of science degree from The Ohio State University. He retired from the US Air Force in 1981 as a colonel and as chairman of endodontics at Wilford Hall Medical Center, and accepted the position of director of the endodontic postdoctoral program at the University of Texas Dental School at San Antonio. He retired in 1992 as a professor and presently holds the title of clinical professor at the university.
Disclosure: Dr. Senia is the co-inventor of the LightSpeed root canal instrumentation and SimpliFill obturation systems.
Disclosure: Dr. Wildey is the co-inventor of the LightSpeed root canal instrumentation and SimpliFill obturation systems.
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