With the advent of the surgical operating microscope in endodontics in the 1990s came the evolution of microendodontic instruments. Ultrasonic instruments found increasing use in preparing retrograde endodontic cavities, removal of root canal obstructions, and refinement of access preparations. The ultrasonic technique is a nonrotary method of cutting dental hard tissue and restorative materials using piezo electric oscillations. The use of high magnification and proper illumination is essential with these instruments. A combination of ultrasonic instruments with the microscope has been termed microultrasonics.
|Figure 1. CPR tips 1 to 5 are diamond-coated with built-in water ports that allow wet or dry cutting. (Courtesy of Dr. Sujung Shin.)|
In order to improve efficiency, ultrasonic instruments are being manufactured with a diamond coating. Presumably, the diamond coating makes the tips more durable and more cutting efficient. CPR ultrasonic instruments (Obtura Spartan) are diamond-coated, have built-in water ports (Figure 1), and at the time of this writing are the only instruments available with these features. This article will discuss the clinical applications of microultrasonics using the CPR system of instruments.
|Figure 2. Titanium CPR ultrasonic tips 6 to 8. (Courtesy of Dr. Sujung Shin.)|
|Figure 3. BUC Access Refinement tips 1 to 3. (Courtesy of Dr. Sujung Shin.)|
The CPR system of instruments is designed to function on Spartan piezo electric units. This system is also accompanied by a set of slender and long tips made from titanium alloys (Figure 2). More recently, a set of BUC (Figure 3) access refinement tips (Obtura Spartan) has been introduced. These tips are also diamond-coated and have built-in waters ports that constantly bathe the activated tip.
Both the CPR and BUC systems provide the option for using in a wet or dry field. The advantages of a wet field include easier rinsing of the field and a cooling effect. However, the area must be dried to allow the clinician a clearer view. A Stropko Surgical Irrigator (EIE/Analytic Technology) may be used to continuously work in a dry field. This device attaches to a standard or quick-change air-water syringe and can be used for blowing air on the field to maintain visibility throughout the procedure.
Ultrasonic tips most often break because they are not operated at their recommended frequencies. Therefore, one must follow the manufacturer's recommendations regarding ultrasonic intensity for a particular tip. Generally speaking, thicker and shorter tips are operated at higher intensities, while longer and thinner tips are operated at lower intensities. The slender and long tips with small cross-sectional diameters (ie, CPR 6 to 8) will easily fracture if used at high intensity. On the other hand, short and sturdy tips (ie, CPR 1, CPR 2D, or BUC 1) are operated at a higher intensity. The tips that are primarily designed for cutting dentin can easily break if inadvertently brought into contact with metals. The shanks of ultrasonic instruments come in different lengths, ranging from 15 to 27 mm. The instruments are selected according to the depth they will be required to operate inside the root canal.
Each of the instrument systems usually comes with its own ultrasonic engine, which is capable of generating ultrasonic frequencies in the range of 20 to 30 kHz. The oscillation of the ultrasonic tip is stalled if it is introduced into narrow canals or forcefully applied against dentin or restorative material. If the instrument is stalling, contact with the cutting surface should be removed to allow the tip to regain its oscillations. Also, in order to experience the full range of power, one should use a wrench to tighten the tips. At the present time, the use of these instruments in patients with cardiac pacemakers is not recommended.
ENDODONTIC INDICATIONS FOR MICROULTRASONICS
Access Cavity Preparation
Access cavity preparation is the most important phase of endodontic therapy. There are many advantages of using ultrasonic tips rather than burs to refine the access cavity. The ultrasonic instruments provide an unobstructed view of the operative field under magnification. Therefore, the clinician is no longer working blindly, and can maintain visual contact with the operating field at all times during ultrasonic procedures. In order to find a canal, the clinician can dig blindly with a small round bur while the head of the handpiece completely blocks his or her view, or use a CPR 2D tip and dig precisely by keeping visual contact with the operating field at all times.
|Figure 4a. Mandibular molar requiring re-treatment shows presence of gutta-percha in 2 mesial and one distal canal. Note remnants of sealer cement and necrotic tissue on the chamber floor.|
|4b. Removal of gutta-percha and use of ultrasonic instruments reveal presence of an untreated fourth canal.|
|4c. Refinement of the access cavity and root canal orifices with ultrasonic tips gives the washed appearance of the field.|
The size of ultrasonic tips is smaller than the smallest burs; therefore, the dentin can be brushed off in smaller increments until the road map's on the floor of the pulp chamber is completely uncovered. Another advantage of ultrasonic instruments is that they produce bubbles in the water that bathe the tips. This action generates enough shock waves to cause disruption of remnants of necrotic pulp tissue and calcific deposits. Therefore, access cavities refined with ultrasonic instruments with water ports have a thoroughly washed and clean appearance (Figures 4a, 4b, 4c).
|Figure 5a. The use of ultrasonic energy led to shattering of pulp stones located at the floor of the pulp chamber.|
A number of tips are available to refine the access cavity. The unroofing of the pulp chamber can be accomplished with the help of CPR 2D or BUC 1. If pulp stones are encountered, then they can be vibrated out by the CPR 2D or BUC 1 tips or planed with the help of the BUC 2 tip (Figure 5a). The tip of the BUC 2 instrument is designed with a planed surface, and it can grind the floor until the dark colored dentin becomes visible.
|Figure 5b. Deepening the bucco-lingual groove overlying the mesio-buccal root with ultrasonic instruments exposes the presence of MB2 canal.|
The second mesiobuccal canal (MB2) is reported to occur in more than 90% of maxillary molars.1 A protocol involving deepening of the bucco-lingual groove overlying the mesiobuccal root is essential for locating the MB2.2 A CPR 2D or BUC 1 can be used to deepen the groove in a controlled manner until the MB2 orifice is located (Figure 5b).
|Figure 6a. Preoperative radiograph shows a calcified maxillary left central incisor with a periapical rarefaction.|
|Figure 6b. A check radiograph of the calcified central incisor showing ultrasonically prepared test site filled with radiopaque gutta-percha. The ultrasonic tip was aligned parallel to the long axis of the tooth.|
|Figure 6c. Continued digging with ultrasonic instruments at the site led to location of the calcified root canal.|
The refining tips are also used for moving the mesial marginal ridges mesially in order to have a direct lineaccess to the MB2 canal.3 In addition, the tips can be used for clearing root canal orifices by removing overhanging dentin deposits. This step helps to guide the hand instruments easily in and out of the canals and sometimes leads to discovery of 2 canals in a single orifice. The ultrasonic tips can also be used to dig and follow the sclerosed canals until patency is achieved. However, this procedure must be accomplished by a number of radiographic checks and restricted to the coronal aspect of the canal. To check the progress, an ultrasonic tip is used to dig a test hole at the most probable site of the sclerosed canal. The test site is filled with thermoplastisized gutta-percha, and an orientation radiograph is taken (Figures 6a, 6b, 6c). If the test site is found centered in the root and pointing correctly, then cutting is continued to enter the canal; otherwise the direction of the cutting is modified according to information gathered from the radiograph.
Ultrasonics have provided the clinician with an important adjunct for removing posts. A number of studies have shown that the use of ultrasonic vibration significantly reduces the amount of tensile force required to dislodge both the cast and prefabricated posts.4-7 The tip of the CPR 1 instrument is spherical in shape and is placed against the post to transmit vibration. It is activated at the maximum intensity and moved circumferentially until the post loosens or dislodges. If this step does not loosen and free the post, then alternate methods must be used. The tip should not be directly placed on ceramics since it may cause chipping.
The inability to remove posts by vibration alone is dependent on many factors, such as the type of luting agent, the length and type of the post, and the type of core buildup. It has been reported that posts luted with zinc phosphate cement can be readily dislodged by ultrasonics because of microcrack formation in the cement. However, posts luted with resin cements such as Panavia (J. Morita) fail to dislodge by ultrasonic vibration, probably because of lack of the microfracture propagation in these materials.8
Ultrasonic tips can also be used to remove dentin and core material quickly and expeditiously before subjecting the root canal obstruction to vibratory or troughing procedures. BUC 1 and CPR 2D are examples of tips that can be used for the bulk removal of dentin and restorative materials.
In retreating cast posts and cores, the core portion is reduced and sculpted until it becomes an extension of the post itself.9 This gives the clinician a purchase point to apply extraction devices if normal vibratory motions fail to dislodge the post completely. The controlled and incremental cutting with ultrasonic instruments and the use of magnification allow the clinician to differentiate clearly between the core materials, especially composites, and the underlying dentinal structure. Therefore, the chances of inadvertently perforating are greatly reduced.
A number of ultrasonic tips are available that can be used to trough around posts and separated instruments. These tips are used to create a sufficiently deep trough around a post to maximize the benefits of subsequently applied vibratory or extraction forces.
|Figure 7. The initial troughing around a post can be carried out with shorter tips such as diamond-coated CRP 2D or 3D.|
The initial troughing is carried out with instruments such as CPR 3D, 4D, and 5D, which are 15, 20, and 25 mm in length, respectively (Figure 7). These instruments are diamond-coated and aggressively cut dentin along their lateral sides. The BUC 3 tip can also be used for troughing purposes, and must be used at low intensity.
The titanium CPR tips 6 (red), 7 (blue), and 8 (green), which are 20, 24, and 27 mm in length, respectively, are utilized if the obstruction is located in the deeper part of a straight canal. These instruments are quite slender, long, and parallel-sided in order to cut deep into the root without taking away too much dentin while at the same time providing maximum visibility under the microscope. These instruments are especially useful when removing long and thick prefabricated post systems. The instruments should be used with a light touch (pressure that would not break the lead tip of a pencil). Unlike CPR 3D to 5D, which are diamond-coated and active along the sides of their tips, the CPR 6 to 8 are end-cutting and only active at their tips. Therefore, prior to troughing with these tips, a collar of dentin must be exposed around obstructions that are embedded in root canals.
|Figure 8. The root canal is sequentially enlarged with the help of modified LightSpeed instruments until a platform (a) is created abutting the separated instrument (b). The CPR 6 to 8 tips can then be used to create a trough around the separated instrument.|
|Figure 9a. Preoperative radiograph of a maxillary left first premolar shows a separated instrument in the palatal canal.|
|Figure 9b. Post-obturation radiograph. The instrument was easily removed with ultrasonic vibration. (Courtesy of Dr. Bekir Karabucak, Philadelphia.)|
The collar or shelf of dentin can be prepared around the obstructions with the help of LightSpeed instruments (LightSpeed). The tips of these instruments are flattened with the help of a grinding stone, allowing them to cut dentin as close to the obstruction as possible. The instruments are sequentially used to the coronal extent of the obstruction until the canal is sufficiently enlarged and a shelf of dentin is prepared around the obstruction (Figure 8). Retreatment becomes difficult if the coronal end of the separated instrument lies apical to the elbow of the curvature and cannot be seen with the help of a microscope. Once the shelf of dentin is prepared, CPR 6 to 8 tips can be used to create a trough around the instrument. The tips are moved counterclockwise around the fractured instrument to disengage it from the surrounding dentin.10 Once loosened, the instrument usually moves coronally and jumps out from the root canal (Figures 9a, 9b). In other instances the exposed part of the separated instrument can be grasped and pulled out with one of the currently available extraction devices.
Removing Hard Paste Materials
In addition to trephining around posts and removal of broken instruments and other intracanal obstructions, ultra-sonic instrumentation can also be used for eliminating brick-hard paste type materials.11 The procedure can be accomplished with CPR 3D to 5D or BUC 3 tips under the microscope so that the paste can be differentiated easily from the surrounding root canal dentin. Under the microscope, the paste, depending on its color, appears as a white or pinkish dot. The CPR tips are used to eliminate it by following the dot to its apical extent. However, no attempt should be made to remove paste materials around curves, be-cause the ultrasonic files are unable to negotiate curvatures and may lead to perforation of the root surface.
Ultrasonic instruments have multiple uses and have become an integral part of endodontic armamentarium. However, it must be realized that their use demands specialized knowledge and development of certain skills that may require additional training prior to incorporating them into everyday practice.
1. Kulild JC, Peters DD. Incidence and configuration of canal systems in the mesiobuccal root of maxillary first and second molars. J Endod. 1990;16:311-317.
2. Weller RN, Hartwell GR. The impact of improved access and searching techniques on detection of the mesiolingual canal in maxillary molars. J Endod. 1989;15:82-83.
3. Spartan Marketing Group. Instructions for Use: BUC Non-Surgical Ultrasonic Endodontic Instruments. Fenton, Mo: Spartan Marketing Group; 2004. Available at: http://www.obtura.com/bucinstruments.pdf. Accessed July 15, 2004.
4. Buoncristiani J, Seto BG, Caputo AA. Evaluation of ultrasonic and sonic instruments for intraradicular post removal. J Endod. 1994;20:486-489.
5. Berbert A, Filho MT, Ueno AH, et al. The influence of ultrasound in removing intraradicular posts. Int Endod J. 1995;28:100-102.
6. Johnson WT, Leary JM, Boyer DB. Effect of ultrasonic vibration on post removal in extracted human premolar teeth. J Endod. 1996;22:487-488.
7. Yoshida T, Gomyo S, Itoh T, et al. An experimental study of the removal of cemented dowel-retained cast cores by ultrasonic vibration. J Endod. 1997;23:239-241.
8. Bergeron BE, Murchison DF, Schindler WG, et al. Effect of ultrasonic vibration and various sealer and cement combinations on titanium post removal. J Endod. 2001;27:13-17.
9. Ruddle CJ. Micro-endodontic nonsurgical retreatment. Dent Clin North Am. 1997;41:429-454.
10. Ruddle C. Microendodontics. Eliminating intracanal obstructions. Oral Health. Aug 1997;87:19-24.
11. Jeng HW, ElDeeb ME. Removal of hard paste fillings from the root canal by ultrasonic instrumentation [published correction appears in J Endod. 1987;13:565]. J Endod. 1987;13:295-298.
Dr. Kratchman is clinical assistant professor of endodontics and assistant director of postgraduate endodontics at the University of Pennsylvania School of Dental Medicine. He has been in private practice since 1991, limited to endodontics. Dr. Kratchman lectures on several endodontics topics, both nationally and internationally. He can be reached at (215) 898-4927.