Figure 8-53 Comparison of effectiveness of various endodontic instruments for machining. Substrate removal was measured in square millimeters. Hedström files generally are much more efficient than K-type instruments. For details see Stenman and Spångberg.2881, Trio-Cut; 2, Miltex; 3, Brasseler; 4, Brasseler; 5, Healthco Delux; 6, J.S. Dental; 7, Aristocrat; 8, Antaeos; 9, K-Flex; 10, Dentsply Maillefer 11, Flex-R; 12, Union Broach; 13, Dentsply Maillefer 14, Miltex; 15, J.S. Dental; 16, Healthco Delux; 17, Hygenic Corp.; 18, S-File; 19, Aristocrat; 20, Zipperer; 21, Antaeos.
Radiographs, tactile sensation, the presence of homebody fluids on paper points, and a knowledge of root morphology have been used to determine the length of root canal systems. Custer63 described the first device used for this purpose in 1918. In 1942 Suzuki297 studied the use of direct current to measure canal lengths. Sunada295 suggested that the apical foramen could be localized using a direct electrical current. Currently the apex locator is considered an accurate tool for determining working length.87,89,90,92 One study reported that the use of electronic apex locators in a dental student clinic resulted in a higher quality of obturation length control and an overall reduction in the number of radiographs taken.91 However, these devices must not be considered flawless, because several variables are known to affect their accuracy. For example, immature roots can present problems. One study found errors when the electronic devices were used in immature teeth.133 Once the roots had matured (i.e., formed a narrow apical foramen) and the instruments were able to contact the canal walls, the electronic apex locator's accuracy greatly improved. These instruments apparently can be used to assess apical closure in teeth undergoing apexification procedures. Apical resorption may not have a significant effect on the accuracy of electronic measurement of canal lengths. Some investigators have found no statistical difference between roots with vital and necrotic tissue.104,184 Because apical root resorption is prevalent in necrotic cases with long-standing apical lesions, these researchers concluded that apical resorption does not have a significant effect on the accuracy of electronic apex locators.
Recently some clinicians have advocated the use of the electronically determined working length in place of radiographs with a file at the estimated length. However, joint use of the two techniques has resulted in greater accuracy.74 This was further demonstrated in a case study in which radiographs were not used, and the condition did not heal because of a missed canal.256
The first two generations of electronic apex locators were sensitive to the contents of the canal and irrigants used during treatment. The development of an algorithm called the ratio measurement method distinguished the third generation of apex locators.160 To arrive at this method, the impedance of the canal was measured with two current sources of different frequencies, and a quotient was determined using the electrical potentials proportional to each impedance.160 This study found that electrolytes did not have a significant effect on the accuracy of the unit. Some third-generation apex locators are the Endex Plus, or Apit, (Osada, Los Angeles),110 the Root ZX (J. Morita, Kyoto),90,166 and the Neosono Ultima EZ (Satelec, Mount Laurel, NJ). The Endex device uses 1 and 5 kHz and provides apex location based on subtraction. The Root ZX emits currents at frequencies of 8 and 0.4 kHz and provides apex location based on the resulting quotient.
A fourth-generation apex locator was introduced with the Elements Diagnostic Unit and the Apex Locator (SybronEndo) and the Bingo 1020/Ray-X4 (Forum Engineering Technologies, Rishon Lezion, Israel). The Bingo uses only one of its two frequencies at a time (8 Hz or 400 Hz). According to the manufacturer, the Elements unit (which operates at frequencies of 0.5 and 4 kHz) compares the resistance and capacitance information to a data base to determine the distance between the file and the apex. When the file tip reaches the area of the apical foramen, the apex locator emits a signal.
An apex locator typically has four parts: (1) the lip clip, (2) the file clip, (3) the instrument itself, and (4) a cord connecting the other three parts. A display indicates the advancement of the file toward the apex (Fig. 8-55).
These electrical instruments are generally safe. However, manufacturers' instructions state that they should not be used on patients with pacemakers without consulting the patient's cardiologist.25,88 When connected directly to cardiac pacemakers in vitro, four of five electronic apex locators did not interfere with the function of the pacemaker.97 One case report demonstrates the importance of paying attention to details: the patient swallowed the lip clip, which lodged in the oropharynx and had to be removed with the aid of a laryngoscope and forceps.85 Safety can be improved by not leaving the clip in place for the entire appointment and by checking that the clip is fully inserted into the cord.
Instruments for Root Canal Obturation
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Figure 8-55 Root ZX apex locator with lip clip and file holder. (Courtesy J. Morita USA, Irvine, CA.)
After the root canal has been properly cleaned and enlarged, the space is obturated with a manufactured material. A number of obturation methods are practiced, but lateral and vertical compactions are the two most common. Many specialized instruments are available for every type of method. Spreaders and pluggers are the significant instruments for obturation. The spreader is a tapered, pointed instrument intended to displace gutta-percha laterally for insertion of additional accessory gutta-percha cones. The plugger is similar but has a blunt end. In smaller sizes the spreader and plugger are often used interchangeably. These instruments are available with handles or as finger-held instruments (Fig. 8-56). The instruments with handles are potentially dangerous, because the tips of the working ends are offset from the long axes of the handles. This results in strong lateral wedging forces on the working ends if the instruments are not operated carefully.
The risk of vertical damage to the root is greatly reduced with finger spreaders and pluggers. Each clinician must choose the appropriate spreader and plugger according to personal working preferences. Standardized instruments are available with the same taper as the files (e.g., #.02). Considering the greater taper of standardized accessory gutta-percha cones (Table 8-2), nonstandardized spreaders with a larger taper sometimes may be used to better accommodate the gutta-percha. In recent years spreaders and pluggers have become available in nickel-titanium (Fig. 8-57). Nickel-titanium spreaders have been shown to reach deeper into canals than the stainless steel type when #.02 tapered gutta-percha is used in canals with a curvature of more than 20 degrees. When #.04 taper gutta-percha was used, the nickel-titanium spreaders were more effective regardless of the degree of curvature.32
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Figure 8-56 Sets of finger spreaders (A) and pluggers (B).(Courtesy Sybron Endo, Orange, CA.)
Table 8-2. Size Designations for Auxiliary Gutta-Percha Cones*
*The cones are pointed. The diameters 3 mm (D3) and 16 mm (D16) from the tip are prescribed. Tolerance is ±0.05 mm, and length is ≥30 mm ±2 mm.
Heat carriers are used for vertical compaction obturation techniques. Traditionally, heat carriers are handled similar to pluggers. They are used to transfer heat to the gutta-percha in the root canal, allowing apical and lateral displacement of the gutta-percha. Electrical heat carriers include Endotec (Caulk/Dentsply), Touch 'N Heat and System B (Analytic Endodontics). With these devices, heat carriers can be heated to controlled levels. Some also have different tips for various endodontic uses (Fig. 8-58).
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Figure 8-57 HyFlex NiTi finger spreader and plugger. Note the very smooth surfaces.
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Figure 8-58 Touch 'N Heat device for heating endodontic instruments for obturation or gutta-percha removal. (Courtesy SybronEndo, Orange, CA.)
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Figure 8-59 Lentulo spiral.
A lentulo spiral (Fig. 8-59) may be used for placement of the sealer, cement, and calcium hydroxide dressings. The lentulo spiral is a safe instrument if used correctly. It must be operated clockwise in the handpiece and started or stopped outside the root canal. If started in the canal, it may cut into the wall of the root canal and break. This instrument effectively drives the paste into the root canal. However, for optimal effect the spiral must be as large as possible so that the paste is forced forward as the material is squeezed between the canal walls and the spiral. Endodontic files, paper points, and syringes also are commonly used to place sealer in the root canal system.
Devices for Removing Root Canal Obstructions
Please see Chapter 25 for details on these devices.