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Precision measurement control in endodontics
Precision measurementcontrol in endodontics Leslie B. Hardy, Jr., Major, DC, USA, * and Frederick L. Cox, Colonel, DC, USA** FORT RILEY,
KANSAS, AND FORT SAM HOUSTON,
TEXAS
A technique for measurement control in endodontic therapy is presented. The technique, which involves the use of a 10 mm. segment of plastic ruler mounted on the end of a mirror handle, eliminates the inaccuracies associated with rubber stops and other devices used for measurement control. It gives the dentist precision control of instrumentation, which is vital to the development of a dentinal matrix at an optimum position.
easurementcontrol is a subject that is given very M little emphasisduring the discussionof endodontic procedures. Successful endodontic treatment is related to maximum canal debridement and complete obturation of the root canal which effectively eliminates the portal of entry for bacteria, their toxins, and necrotic tissuebreakdown products. Studieshave shown that complete canal debridement is rarely accomplished.l--3 Therefore, maximum emphasis must be placed on elimination of the portal of entry. To eliminate the portal of entry effectively, an apical seal must be achieved, preferably by filling the root canal with a plastic filling material under pressure. In order to confine the filling material to the root canal, it is necessaryto develop a dentinal matrix (apical constriction, apical seat, apical fixation) during the debridement phase of treatment.4 Precisely locating this constriction as close as possible to the apical foramen demandsan exacting technique of measurementcontrol. A popular endodontic text recommendsthat rubber or silicone discs be placed at a measureddistanceon the instrument shaft as devices for measurementcontrol5 The shortcomingsof theseparticular devices are (1) the instability of the stop with its potential to move up and down the instrument shaft; (2) difficulty in repeatedly placing the stop perpendicular to the long axis of the shaft of the instrument; (3) difficulty in placing more than one instrument at a time in a premolar or molar; and (4) the fact that placement is usually done by an assistant, which introduces a potential source of inaccuracy. *Chief, Endodontic Service, Fort Riley, Kan. **Chief, Endodontic Service, Fort Sam Houston, Texas; formerly Director of the Army Endodontic Residency at Fort Benning, Ga.
538
Fig. 1. A
10mm. segmentof plasticruler mountedon theend of a mirror handle.
The purpose of this article is to present an easy, precise technique for measurementcontrol in endodontic therapy which provides accurate control of instrument penetration and eliminates many of the inaccuracies associatedwith rubber stops and other devices for measurementcontrol. TECHNIQUE
The initial component of the armamentariumnecessary to implement the technique consists of a 10 mm. segmentof plastic ruler. By cutting a slot in the end of a mirror handle with a No. 557 bur, one can mount the ruler segment in the groove with epoxy cement (Pig. 1). It is suggestedthat the ruler be mounted at an angle to facilitate placement in the posterior portion of the mouth. The ruler segmentshould be prepared with extreme care, so that it is precisely 10 mm. in width. The secondcomponent of the armamentariumis a device to premeasureeach instrument prior to placement into the tooth. Premeasuring is necessary because “standardized” 25 mm. files and reamerscan vary in length plus or minus 1 mm. Such a device can be madeby cutting a
Volume 49 Number 6
Precision
measurement
control
539
Fig. 2. Finger ruler used to premeasureinstruments.
Fig. 4. Millimeter ruler measuring the amount of instrument
out of the tooth. This instrumentprotrudes2 mm.
Fig. 3. Premeasuringan instrument prior to placementinto the canal. This instrument measures25 mm.
40 mm. section from a plastic ruler or, preferably, by purchasing a finger ruler* which can be worn as a ring, making premeasuring more convenient (Fig. 2). The initial step in instrumentation is determination of the exact tooth length. To determine the exact tooth length with this concept of measurementcontrol, one should first premeasure the length of the instrument (Fig. 3) and then insert that instrument into the root to a depth based on an estimate of the tooth length made from a radiograph, averagetooth length values, and/or clinical “feel. ” The instrument must bind at this length, so that there will be less chance for accidental displacement in a coronal or apical direction. If a radiograph shows that the instrument is too long, it should be backed out of the canal an appropriate distance. If the instrument is too short, it should be advanced further into the tooth. Radiographs as needed should be taken to verify the position of the instrument in the tooth. Once the instrument is at the radiographic apex, one should measure the amount of instrument protruding from the tooth with the millimeter ruler (Fig. 4). By taking the premeasuredinstrument length and subtract*Union Broach Co., Long Island City, N. Y.
ing the amount of instrument protruding from the tooth, one arrives at the amount of instrument in the tooth, or an exact tooth length measurement.For example, if a premeasuredNo. 15 file is 25.0 mm. and the amount of file measuredout of the tooth is 2.0 mm., then 25.0 mm. minus 2.0 mm. equals 23.0 mm., which is the exact tooth length (Fig. 5). Once this measurementis obtained, one should proceed with the instrumentation technique of choice. If a serial preparation technique is used, the sequentialdrop back can be controlled in 0.25 mm. incrementsbecauseof the extreme accuracyof the millimeter ruler. If a - 1 working length is employed, then the out-of-tooth measurement will always be the original instrument length minus the measurementat which the operator wants the instrument to penetrate. Two important factors must be considered to eliminate sources of error in the technique. The first is establishment of a definite reference point to place the ruler. Standard reference points are incisal edges for anterior teeth, cusp tips for canines and premolars, and buccal grooves for maxillary and mandibular molars. If for some reason these landmarks cannot be used, then one should write on the patient’s record the location of the referencepoint used or artifically createa reference point with a bur. The second point to remember is to keep the proper ruler orientation to the instrument. This will be more of a concern in the molar area where the instruments exit the tooth at different angles. The objective is to keep the edge of the ruler parallel with the instrument shaft (Fig. 6). It must be kept parallel in a buccolingual direction as well as in a mesiodistal direction. When
540 Hardy and Cox
Oral Slug. June, 1980
6. Millimeter ruler parallelto theinstrumentshaft.This is necessaryto ensurerepeatabilityof the measurement.
Fig.
Fig. 5. Schematicdrawingillustratingtheconceptthatout-oftoothmeasurement minusthetotal instrumentlengthwill give the amountof instrumentin the tooth.
parallelism between ruler and instrument is maintained, the measurement becomes precisely repeatable from instrument to instrument becausethe ruler returns to a definite orientation in relation to the instrument shaft. DISCUSSION
The technique of using a millimeter ruler to control instrumentation has the following advantages:(1) The dentist is in complete control of instrument penetration and the possibility of nonoperator influence is eliminated. (2) The depth of instrument penetration is precisely controlled; it is possible to interpolate and subdivide the millimeter segmentsinto quarter millimeters. (3) The measurementis extremely stable in that there is no movable component which may change position on the instrument shaft. (4) The measurementis repeatable from visit to visit. A millimeter today will measurea millimeter tomorrow and is not under the influence of variable positioning, as is the rubber stop. (5) Multiple instruments can be placed in multirooted teeth at the sametime with no interference with measurementdetermination. (6) The technique is easy to employ and inexpensive to implement. A difficult adjustment to mastering the technique is thinking in terms of amount of instrument our of the tooth during the initial stagesof use. Repeateduse of
the technique will breed familiarity with the numbers, so that this problem is rapidly eliminated. One way to keep the mathematics straight at first is to write down the numbers on a piece of paper. This gives an easy visual reference to what the out-of-tooth measurement should be. SUMMARY
A technique for measurementcontrol in endodontic therapy using a 10 mm. segment of plastic ruler mounted on the end of a mirror handle is presented. The technique eliminates the inaccuracies associated with rubber stops and other devices used for measurement control. The technique gives the dentist precision control of instrumentation, which is vital to the development of a dentinal matrix in an optimum position. REFERENCES
I. Matsumiya, S., and Kitamura, M.: Histopathological and His-
2. 3. 4. 5.
tobiological Studies of the Relation Between the Condition of Sterilization of the Interior of the Root Canal and the Healing Process of Periapical Tissues in Experimentally Infected Root Canal Treatment, Bull. Tokyo Dent. Coil. 1: 1, 1960. Mizrahi, S. J., Tucker, J. W., and Seltzer, S.: A ScanningElectron Microscopic Study of the Efficacy of Various Endodontic Instruments, J. Endod. 1: 324, 1975. Moodnik, R. M., et al.: Efficacy of Biomechanical Instrumentation: A Scanning Electron Microscopic Study, J. Endod. 2: 261, 1976. Weine, F. S.: Endodontic Therapy, St. Louis, 1972, The C. V. Mosby Company, p. 194. Ingle, J. I., and Beveridge, E. E.: Endodontics, ed. 2, Philadelphia, 1976, Lea & Febiger, pp. 188-189.
Reprint requeststo: Major Leslie B. Hardy, Jr. DENTAC Fort Riley, Kansas 66442
KANSAS, AND FORT SAM HOUSTON,
TEXAS
A technique for measurement control in endodontic therapy is presented. The technique, which involves the use of a 10 mm. segment of plastic ruler mounted on the end of a mirror handle, eliminates the inaccuracies associated with rubber stops and other devices used for measurement control. It gives the dentist precision control of instrumentation, which is vital to the development of a dentinal matrix at an optimum position.
easurementcontrol is a subject that is given very M little emphasisduring the discussionof endodontic procedures. Successful endodontic treatment is related to maximum canal debridement and complete obturation of the root canal which effectively eliminates the portal of entry for bacteria, their toxins, and necrotic tissuebreakdown products. Studieshave shown that complete canal debridement is rarely accomplished.l--3 Therefore, maximum emphasis must be placed on elimination of the portal of entry. To eliminate the portal of entry effectively, an apical seal must be achieved, preferably by filling the root canal with a plastic filling material under pressure. In order to confine the filling material to the root canal, it is necessaryto develop a dentinal matrix (apical constriction, apical seat, apical fixation) during the debridement phase of treatment.4 Precisely locating this constriction as close as possible to the apical foramen demandsan exacting technique of measurementcontrol. A popular endodontic text recommendsthat rubber or silicone discs be placed at a measureddistanceon the instrument shaft as devices for measurementcontrol5 The shortcomingsof theseparticular devices are (1) the instability of the stop with its potential to move up and down the instrument shaft; (2) difficulty in repeatedly placing the stop perpendicular to the long axis of the shaft of the instrument; (3) difficulty in placing more than one instrument at a time in a premolar or molar; and (4) the fact that placement is usually done by an assistant, which introduces a potential source of inaccuracy. *Chief, Endodontic Service, Fort Riley, Kan. **Chief, Endodontic Service, Fort Sam Houston, Texas; formerly Director of the Army Endodontic Residency at Fort Benning, Ga.
538
Fig. 1. A
10mm. segmentof plasticruler mountedon theend of a mirror handle.
The purpose of this article is to present an easy, precise technique for measurementcontrol in endodontic therapy which provides accurate control of instrument penetration and eliminates many of the inaccuracies associatedwith rubber stops and other devices for measurementcontrol. TECHNIQUE
The initial component of the armamentariumnecessary to implement the technique consists of a 10 mm. segmentof plastic ruler. By cutting a slot in the end of a mirror handle with a No. 557 bur, one can mount the ruler segment in the groove with epoxy cement (Pig. 1). It is suggestedthat the ruler be mounted at an angle to facilitate placement in the posterior portion of the mouth. The ruler segmentshould be prepared with extreme care, so that it is precisely 10 mm. in width. The secondcomponent of the armamentariumis a device to premeasureeach instrument prior to placement into the tooth. Premeasuring is necessary because “standardized” 25 mm. files and reamerscan vary in length plus or minus 1 mm. Such a device can be madeby cutting a
Volume 49 Number 6
Precision
measurement
control
539
Fig. 2. Finger ruler used to premeasureinstruments.
Fig. 4. Millimeter ruler measuring the amount of instrument
out of the tooth. This instrumentprotrudes2 mm.
Fig. 3. Premeasuringan instrument prior to placementinto the canal. This instrument measures25 mm.
40 mm. section from a plastic ruler or, preferably, by purchasing a finger ruler* which can be worn as a ring, making premeasuring more convenient (Fig. 2). The initial step in instrumentation is determination of the exact tooth length. To determine the exact tooth length with this concept of measurementcontrol, one should first premeasure the length of the instrument (Fig. 3) and then insert that instrument into the root to a depth based on an estimate of the tooth length made from a radiograph, averagetooth length values, and/or clinical “feel. ” The instrument must bind at this length, so that there will be less chance for accidental displacement in a coronal or apical direction. If a radiograph shows that the instrument is too long, it should be backed out of the canal an appropriate distance. If the instrument is too short, it should be advanced further into the tooth. Radiographs as needed should be taken to verify the position of the instrument in the tooth. Once the instrument is at the radiographic apex, one should measure the amount of instrument protruding from the tooth with the millimeter ruler (Fig. 4). By taking the premeasuredinstrument length and subtract*Union Broach Co., Long Island City, N. Y.
ing the amount of instrument protruding from the tooth, one arrives at the amount of instrument in the tooth, or an exact tooth length measurement.For example, if a premeasuredNo. 15 file is 25.0 mm. and the amount of file measuredout of the tooth is 2.0 mm., then 25.0 mm. minus 2.0 mm. equals 23.0 mm., which is the exact tooth length (Fig. 5). Once this measurementis obtained, one should proceed with the instrumentation technique of choice. If a serial preparation technique is used, the sequentialdrop back can be controlled in 0.25 mm. incrementsbecauseof the extreme accuracyof the millimeter ruler. If a - 1 working length is employed, then the out-of-tooth measurement will always be the original instrument length minus the measurementat which the operator wants the instrument to penetrate. Two important factors must be considered to eliminate sources of error in the technique. The first is establishment of a definite reference point to place the ruler. Standard reference points are incisal edges for anterior teeth, cusp tips for canines and premolars, and buccal grooves for maxillary and mandibular molars. If for some reason these landmarks cannot be used, then one should write on the patient’s record the location of the referencepoint used or artifically createa reference point with a bur. The second point to remember is to keep the proper ruler orientation to the instrument. This will be more of a concern in the molar area where the instruments exit the tooth at different angles. The objective is to keep the edge of the ruler parallel with the instrument shaft (Fig. 6). It must be kept parallel in a buccolingual direction as well as in a mesiodistal direction. When
540 Hardy and Cox
Oral Slug. June, 1980
6. Millimeter ruler parallelto theinstrumentshaft.This is necessaryto ensurerepeatabilityof the measurement.
Fig.
Fig. 5. Schematicdrawingillustratingtheconceptthatout-oftoothmeasurement minusthetotal instrumentlengthwill give the amountof instrumentin the tooth.
parallelism between ruler and instrument is maintained, the measurement becomes precisely repeatable from instrument to instrument becausethe ruler returns to a definite orientation in relation to the instrument shaft. DISCUSSION
The technique of using a millimeter ruler to control instrumentation has the following advantages:(1) The dentist is in complete control of instrument penetration and the possibility of nonoperator influence is eliminated. (2) The depth of instrument penetration is precisely controlled; it is possible to interpolate and subdivide the millimeter segmentsinto quarter millimeters. (3) The measurementis extremely stable in that there is no movable component which may change position on the instrument shaft. (4) The measurementis repeatable from visit to visit. A millimeter today will measurea millimeter tomorrow and is not under the influence of variable positioning, as is the rubber stop. (5) Multiple instruments can be placed in multirooted teeth at the sametime with no interference with measurementdetermination. (6) The technique is easy to employ and inexpensive to implement. A difficult adjustment to mastering the technique is thinking in terms of amount of instrument our of the tooth during the initial stagesof use. Repeateduse of
the technique will breed familiarity with the numbers, so that this problem is rapidly eliminated. One way to keep the mathematics straight at first is to write down the numbers on a piece of paper. This gives an easy visual reference to what the out-of-tooth measurement should be. SUMMARY
A technique for measurementcontrol in endodontic therapy using a 10 mm. segment of plastic ruler mounted on the end of a mirror handle is presented. The technique eliminates the inaccuracies associated with rubber stops and other devices used for measurement control. The technique gives the dentist precision control of instrumentation, which is vital to the development of a dentinal matrix in an optimum position. REFERENCES
I. Matsumiya, S., and Kitamura, M.: Histopathological and His-
2. 3. 4. 5.
tobiological Studies of the Relation Between the Condition of Sterilization of the Interior of the Root Canal and the Healing Process of Periapical Tissues in Experimentally Infected Root Canal Treatment, Bull. Tokyo Dent. Coil. 1: 1, 1960. Mizrahi, S. J., Tucker, J. W., and Seltzer, S.: A ScanningElectron Microscopic Study of the Efficacy of Various Endodontic Instruments, J. Endod. 1: 324, 1975. Moodnik, R. M., et al.: Efficacy of Biomechanical Instrumentation: A Scanning Electron Microscopic Study, J. Endod. 2: 261, 1976. Weine, F. S.: Endodontic Therapy, St. Louis, 1972, The C. V. Mosby Company, p. 194. Ingle, J. I., and Beveridge, E. E.: Endodontics, ed. 2, Philadelphia, 1976, Lea & Febiger, pp. 188-189.
Reprint requeststo: Major Leslie B. Hardy, Jr. DENTAC Fort Riley, Kansas 66442