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The Effect of Mesio-Distal Chamber Dimension on Access Preparation in Mandibular Incisors
Clinical Research
The Effect of Mesio-Distal Chamber Dimension on Access Preparation in Mandibular Incisors Christen John Nielsen DMD, MS, and Kianor Shahmohammadi, BS Abstract Because the pulp chamber of a young mandibular incisor flares coronally in a mesio-distal dimension, the access form pictured by a number of authors is triangular in shape. As a person ages, the chamber recedes and the access shape becomes oval in form consistent with a canal system that is primarily bucco-lingual in orientation. Endodontic literature generally recommends either the triangular or oval access shape without acknowledging that both are appropriate at a given time in the life of the individual. The question addressed by this study is when does the pulp chamber loose its coronal flare to become primarily oval in shape, and as a consequence of this change, when should the access form go from triangular to oval. It was concluded that by the age of 40 the canal has decreased in size sufficiently to justify in routine cases an oval preparation of less than 2 mm mesio-distal width.
From the Southern Illinois School of Dental Medicine, Southern Illinois School of Dental Medicine, Glen Carbon, IL. Address request for reprints to Christen J. Nielsen, 108 Kingsbrooke Blvd, Glen Carbon, IL 62034; E-mail address: [email protected]. Copyright © 2005 by the American Association of Endodontists
P
roper access form in gaining entrance to a tooth’s chamber and canal system has long been a goal in achieving adequate cleaning, shaping, and obturation. In the case of mandibular incisors, considerable attention has been given to what constitutes an appropriate inciso-gingival access dimension. Mauger et al. and others point out that to achieve optimal straight-line access to an oval canal and to better facilitate locating a lingual canal, the operator must extend the access incisally (1– 4). Indeed, the suggestion is made that with the current state of restorative materials, the old taboo of not weakening the incisal edge by having the access encroach upon it be disregarded in a case where a lingual canal was suspected, but not found. Considerably less discussion has involved the appropriate mesio-distal dimension of the access preparation. Because the preparation is dictated by the tooth’s internal anatomy, most authors concede that it is appropriate in the young tooth to flare the preparation slightly mesio-distally towards the incisal to accommodate the flared pulp horns seen in younger teeth. This typically results in a triangular preparation. But as a tooth ages, the flared nature of the chamber recedes, and an oval access preparation is recommended (5, 6, 11). However, other than looking at a preoperative radiograph, which often does not allow for adequate visualization of the chamber, the clinician does not really know when a chamber goes from being flared mesio-distally to primarily oval bucco-lingually. The purpose of this study was to investigate the mesio-distal narrowing of the chamber with age and to suggest when the triangular access preparation might be considered no longer appropriate.
Materials and Methods The first 30 noncarious mandibular incisors requiring extraction from patients presenting to the Southern Illinois School of Dental Medicine were collected. Patients ranged in age from 40 to 78 yr of age. Teeth were stored in a 50:50 NaOCl/water solution until ready for study. All teeth were individually mounted on acrylic jigs with adjacent millimeter rulers on each side. Roots were removed 2 mm apical to the buccal cementoenamel junction to confirm the existence of a canal at this level (Fig. 1). Using a high-speed handpiece with a #57 bur, coronal segments were then shaved off in a coronal direction in 0.5 mm increments, allowing the investigator to measure the remaining canal’s/chamber’s mesio-distal dimension using a Unitron measuring microscope. Increments were removed until the chamber was seen to no longer exist for three repeated sections, after which all more coronal sections were assumed to be without a chamber. The widest mesio-distal dimension of each tooth beginning at the cemento-enamal junction was recorded and graphed in relation to age. All points were used to compute a regression line with a Pearson’s r value, mean, and SD.
Results The raw data generated by the sectioning of each tooth is presented in Table 1. All but four of the 30 teeth had chambers whose widest mesio-distal dimension was less than 1.00 mm. All but one tooth was seen to have a detectable canal at the ⫺2.0 mm section. The widest mesio-distal dimension of each tooth (bold number in Table 1) was plotted in relation to the age of the patient (Fig. 2). From these points a regression line y ⫽ 1.941 ⫺ 0.023x) was plotted with a Pearson’s r value of ⫺0.6. The mean value of all 30 teeth was 0.628 mm with a SD of 0.392.
88
Nielsen and Shahmohammadi
JOE — Volume 31, Number 2, February 2005
Clinical Research
Fig 1. Tooth having been sectioned at the ⫺2.0 mm mark.
Discussion The suggested widest coronal extent of the mesio-distal dimension in triangular access preparations from four different literature sources varies from 1.781 to 2.28 mm (5, 7–9), with an average of the four being 2.04 mm (based on an average mesio-distal crown width of 5.25 mm (10). These dimensions are assumed to reflect the widest mesiodistal dimension of the tooth’s chamber, presumably where the pulp horns are most flared incisally. As the tooth matures, the pulp horns
recede and at some time during the life of the tooth, if endodontic therapy is required, it would seem reasonable that an oval preparation might be better suited for a tooth whose canal system is primarily oriented in a bucco-lingual dimension. In fact this is recognized by texts that advocate this oval design (5, 6, 11). While the correlation coefficient seen in this study of ⫺0.6 is borderline strong, it is none-the-less obvious that the negatively sloped regression line is in harmony with the clinical observation that the mesio-distal dimension of the mandibular incisor’s chamber does decrease with age. Furthermore, it would appear that over the age range studied, the greatest mesio-distal dimension of the chamber is generally going to be smaller than the smallest recommended access dimension (1.78 mm) cited (7). In fact, the results predict a greatest mesio-distal dimension equal to about 1.0 mm in a 40-yr-old individual. The results of this study might suggest that the mesio-distal dimension of the access preparation in a 40-yr-old need be no larger than the equivalent of a number 57 or 2 bur, both of whose diameters average 1 mm. However, proper access form ultimately depends on more than anatomy alone and in the case of the mandibular incisor, considerable attention must be given to preparing an access adequate for locating two canals and subsequent cleaning, shaping, and obturation. For this reason, it is thought that enlarging an access beyond 1 mm width is justifiable if necessary to allow for adequate visualization and canal instrumentation. However, to routinely widen an access beyond 2 mm, except in extenuating circumstances, would seem excessive. Based on the results of this study, it would appear that the suggested dimensions seen in past literature of between 1.78 and 2.28 mm would appear to be unnecessarily large in the case of patients greater than 40 yr of age. Because of the decreasing flare of the coronal chamber, it is recommended that normal endodontic access of mandibular incisors of patients older than
TABLE 1. Mesio-distal dimensions of chambers (millimeters). Teeth 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30
Section (0.0 taken at cementoenamal junction) 0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
0.000 0.123 0.468 0.728 0.608 0.569 0.635 0.513 0.464 0.499 0.391 0.667 0.654 0.000 0.000 0.000 0.174 0.283 0.372 0.182 0.254 0.583 0.605 0.217 0.355 0.000 1.302 0.240 0.720 0.706
0.000 0.000 0.000 0.803 0.627 0.658 0.724 0.271 0.589 0.421 0.579 0.828 0.721 0.000 0.000 0.000 0.163 0.290 0.251 0.000 0.239 0.546 0.535 0.000 0.346 0.000 0.834 0.000 0.598 0.652
0.000 0.000 0.000 0.704 0.482 0.503 0.558 0.234 0.597 0.403 0.622 0.883 0.817 0.000 0.000 0.000 0.133 0.216 0.183 0.000 0.109 0.709 0.945 0.000 0.117 0.000 1.047 0.000 0.861 0.765
0.000 0.000 0.000 0.871 0.593 0.659 0.767 0.387 0.433 0.672 0.698 0.871 0.723 0.104 0.126 0.000 0.117 0.000 0.186 0.000 0.000 0.765 0.969 0.000 0.187 0.000 1.128 0.000 0.822 0.732
0.000 0.000 0.000 0.308 0.362 0.000 0.581 0.447 0.000 0.532 1.080 0.868 0.574 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.795 0.924 0.000 0.315 0.000 1.161 0.000 0.956 0.760
0.000 0.000 0.000 0.000 0.000 0.000 0.410 0.418 0.000 0.885 1.135 1.076 0.941 0.000 0.137 0.000 0.000 0.000 0.000 0.000 0.000 0.806 0.837 0.000 0.000 0.000 0.202 0.000 1.003 0.727
0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.890 1.065 0.782 0.684 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.528 0.000 0.000 0.000 0.186 0.000 1.000 0.000
0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 1.293 0.691 1.420 1.310 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.135 0.000 0.000 0.000 0.962 0.000 0.000 0.000
0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 1.347 0.000 1.380 1.206 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.141 0.000 0.000 0.000 0.207 0.000 0.000 0.000
JOE — Volume 31, Number 2, February 2005
Access Preparation in Mandibular Incisors
89
Clinical Research References
Fig 2. Greatest Mesio-distal dimension related to age.
40 yr of age be limited to an oval preparation of less than 2 mm mesiodistal width.
90
Nielsen and Shahmohammadi
1. Mauger MJ, Waite RM, Alexander JB, Schindler WG. Ideal endodontic access in mandibular incisors. J Endod 1999;25:206 –7. 2. LaTurno SA, Zillich RM. Straight-line endodontic access to anterior teeth. Oral Surg Oral Med Oral Pathol 1985;59:418 –9. 3. Clements RE, Gilboe DB. Labial endodontic access opening for mandibular incisors: endodontic and restorative considerations. J Can Dent Assoc 1991;57:587–9. 4. Madjar D, Kusner W, Shifman A. The labial endodontic access: a rational treatment approach in anterior teeth. J Prosthet Dent 1989;61:317–20. 5. Ingle JI, Mullaney TA, Russell A, Grandich RA, Taintor JF, Fahid A. Endodontic cavity preparation. In: Ingle J, Taintor JF, eds. Endodontics, 3rd ed. Philadelphia: Lea and Febiger, 1985;128. 6. Luks S. Practical endodontics, 1st ed. Philadelphia: JB Lippincott, 1974;42. 7. Wilcox L. Pulpal anatomy and access preparations. In: Walter RE, Torabinejad M, eds. Principles and practice of endodontics, 3rd ed. Philadelphia: WB Saunders, 2002; 568. 8. Morse D. Clinical endodontology, 1st ed. Springfield: Williams & Wilkins, 1974;454. 9. Streiff JT, Gerstein H. Access cavity preparation. In: Gerstein H, ed. Techniques in clinical endodontics, 1st ed. Philadelphia: WB Saunders, 1983;25. 10. Ash MM. Wheeler’s dental anatomy, physiology and occlusion, 7th ed. Philadelphia: WB Saunders, 1993;151,163. 11. Burns RC, Herbranson EJ. Tooth morphology and cavity preparation. In: Cohen S, Burns RC, eds. Pathways of the pulp, 8th ed. St. Louis: Mosby, 2002;203.
JOE — Volume 31, Number 2, February 2005
The Effect of Mesio-Distal Chamber Dimension on Access Preparation in Mandibular Incisors Christen John Nielsen DMD, MS, and Kianor Shahmohammadi, BS Abstract Because the pulp chamber of a young mandibular incisor flares coronally in a mesio-distal dimension, the access form pictured by a number of authors is triangular in shape. As a person ages, the chamber recedes and the access shape becomes oval in form consistent with a canal system that is primarily bucco-lingual in orientation. Endodontic literature generally recommends either the triangular or oval access shape without acknowledging that both are appropriate at a given time in the life of the individual. The question addressed by this study is when does the pulp chamber loose its coronal flare to become primarily oval in shape, and as a consequence of this change, when should the access form go from triangular to oval. It was concluded that by the age of 40 the canal has decreased in size sufficiently to justify in routine cases an oval preparation of less than 2 mm mesio-distal width.
From the Southern Illinois School of Dental Medicine, Southern Illinois School of Dental Medicine, Glen Carbon, IL. Address request for reprints to Christen J. Nielsen, 108 Kingsbrooke Blvd, Glen Carbon, IL 62034; E-mail address: [email protected]. Copyright © 2005 by the American Association of Endodontists
P
roper access form in gaining entrance to a tooth’s chamber and canal system has long been a goal in achieving adequate cleaning, shaping, and obturation. In the case of mandibular incisors, considerable attention has been given to what constitutes an appropriate inciso-gingival access dimension. Mauger et al. and others point out that to achieve optimal straight-line access to an oval canal and to better facilitate locating a lingual canal, the operator must extend the access incisally (1– 4). Indeed, the suggestion is made that with the current state of restorative materials, the old taboo of not weakening the incisal edge by having the access encroach upon it be disregarded in a case where a lingual canal was suspected, but not found. Considerably less discussion has involved the appropriate mesio-distal dimension of the access preparation. Because the preparation is dictated by the tooth’s internal anatomy, most authors concede that it is appropriate in the young tooth to flare the preparation slightly mesio-distally towards the incisal to accommodate the flared pulp horns seen in younger teeth. This typically results in a triangular preparation. But as a tooth ages, the flared nature of the chamber recedes, and an oval access preparation is recommended (5, 6, 11). However, other than looking at a preoperative radiograph, which often does not allow for adequate visualization of the chamber, the clinician does not really know when a chamber goes from being flared mesio-distally to primarily oval bucco-lingually. The purpose of this study was to investigate the mesio-distal narrowing of the chamber with age and to suggest when the triangular access preparation might be considered no longer appropriate.
Materials and Methods The first 30 noncarious mandibular incisors requiring extraction from patients presenting to the Southern Illinois School of Dental Medicine were collected. Patients ranged in age from 40 to 78 yr of age. Teeth were stored in a 50:50 NaOCl/water solution until ready for study. All teeth were individually mounted on acrylic jigs with adjacent millimeter rulers on each side. Roots were removed 2 mm apical to the buccal cementoenamel junction to confirm the existence of a canal at this level (Fig. 1). Using a high-speed handpiece with a #57 bur, coronal segments were then shaved off in a coronal direction in 0.5 mm increments, allowing the investigator to measure the remaining canal’s/chamber’s mesio-distal dimension using a Unitron measuring microscope. Increments were removed until the chamber was seen to no longer exist for three repeated sections, after which all more coronal sections were assumed to be without a chamber. The widest mesio-distal dimension of each tooth beginning at the cemento-enamal junction was recorded and graphed in relation to age. All points were used to compute a regression line with a Pearson’s r value, mean, and SD.
Results The raw data generated by the sectioning of each tooth is presented in Table 1. All but four of the 30 teeth had chambers whose widest mesio-distal dimension was less than 1.00 mm. All but one tooth was seen to have a detectable canal at the ⫺2.0 mm section. The widest mesio-distal dimension of each tooth (bold number in Table 1) was plotted in relation to the age of the patient (Fig. 2). From these points a regression line y ⫽ 1.941 ⫺ 0.023x) was plotted with a Pearson’s r value of ⫺0.6. The mean value of all 30 teeth was 0.628 mm with a SD of 0.392.
88
Nielsen and Shahmohammadi
JOE — Volume 31, Number 2, February 2005
Clinical Research
Fig 1. Tooth having been sectioned at the ⫺2.0 mm mark.
Discussion The suggested widest coronal extent of the mesio-distal dimension in triangular access preparations from four different literature sources varies from 1.781 to 2.28 mm (5, 7–9), with an average of the four being 2.04 mm (based on an average mesio-distal crown width of 5.25 mm (10). These dimensions are assumed to reflect the widest mesiodistal dimension of the tooth’s chamber, presumably where the pulp horns are most flared incisally. As the tooth matures, the pulp horns
recede and at some time during the life of the tooth, if endodontic therapy is required, it would seem reasonable that an oval preparation might be better suited for a tooth whose canal system is primarily oriented in a bucco-lingual dimension. In fact this is recognized by texts that advocate this oval design (5, 6, 11). While the correlation coefficient seen in this study of ⫺0.6 is borderline strong, it is none-the-less obvious that the negatively sloped regression line is in harmony with the clinical observation that the mesio-distal dimension of the mandibular incisor’s chamber does decrease with age. Furthermore, it would appear that over the age range studied, the greatest mesio-distal dimension of the chamber is generally going to be smaller than the smallest recommended access dimension (1.78 mm) cited (7). In fact, the results predict a greatest mesio-distal dimension equal to about 1.0 mm in a 40-yr-old individual. The results of this study might suggest that the mesio-distal dimension of the access preparation in a 40-yr-old need be no larger than the equivalent of a number 57 or 2 bur, both of whose diameters average 1 mm. However, proper access form ultimately depends on more than anatomy alone and in the case of the mandibular incisor, considerable attention must be given to preparing an access adequate for locating two canals and subsequent cleaning, shaping, and obturation. For this reason, it is thought that enlarging an access beyond 1 mm width is justifiable if necessary to allow for adequate visualization and canal instrumentation. However, to routinely widen an access beyond 2 mm, except in extenuating circumstances, would seem excessive. Based on the results of this study, it would appear that the suggested dimensions seen in past literature of between 1.78 and 2.28 mm would appear to be unnecessarily large in the case of patients greater than 40 yr of age. Because of the decreasing flare of the coronal chamber, it is recommended that normal endodontic access of mandibular incisors of patients older than
TABLE 1. Mesio-distal dimensions of chambers (millimeters). Teeth 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30
Section (0.0 taken at cementoenamal junction) 0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
0.000 0.123 0.468 0.728 0.608 0.569 0.635 0.513 0.464 0.499 0.391 0.667 0.654 0.000 0.000 0.000 0.174 0.283 0.372 0.182 0.254 0.583 0.605 0.217 0.355 0.000 1.302 0.240 0.720 0.706
0.000 0.000 0.000 0.803 0.627 0.658 0.724 0.271 0.589 0.421 0.579 0.828 0.721 0.000 0.000 0.000 0.163 0.290 0.251 0.000 0.239 0.546 0.535 0.000 0.346 0.000 0.834 0.000 0.598 0.652
0.000 0.000 0.000 0.704 0.482 0.503 0.558 0.234 0.597 0.403 0.622 0.883 0.817 0.000 0.000 0.000 0.133 0.216 0.183 0.000 0.109 0.709 0.945 0.000 0.117 0.000 1.047 0.000 0.861 0.765
0.000 0.000 0.000 0.871 0.593 0.659 0.767 0.387 0.433 0.672 0.698 0.871 0.723 0.104 0.126 0.000 0.117 0.000 0.186 0.000 0.000 0.765 0.969 0.000 0.187 0.000 1.128 0.000 0.822 0.732
0.000 0.000 0.000 0.308 0.362 0.000 0.581 0.447 0.000 0.532 1.080 0.868 0.574 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.795 0.924 0.000 0.315 0.000 1.161 0.000 0.956 0.760
0.000 0.000 0.000 0.000 0.000 0.000 0.410 0.418 0.000 0.885 1.135 1.076 0.941 0.000 0.137 0.000 0.000 0.000 0.000 0.000 0.000 0.806 0.837 0.000 0.000 0.000 0.202 0.000 1.003 0.727
0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.890 1.065 0.782 0.684 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.528 0.000 0.000 0.000 0.186 0.000 1.000 0.000
0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 1.293 0.691 1.420 1.310 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.135 0.000 0.000 0.000 0.962 0.000 0.000 0.000
0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 1.347 0.000 1.380 1.206 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.141 0.000 0.000 0.000 0.207 0.000 0.000 0.000
JOE — Volume 31, Number 2, February 2005
Access Preparation in Mandibular Incisors
89
Clinical Research References
Fig 2. Greatest Mesio-distal dimension related to age.
40 yr of age be limited to an oval preparation of less than 2 mm mesiodistal width.
90
Nielsen and Shahmohammadi
1. Mauger MJ, Waite RM, Alexander JB, Schindler WG. Ideal endodontic access in mandibular incisors. J Endod 1999;25:206 –7. 2. LaTurno SA, Zillich RM. Straight-line endodontic access to anterior teeth. Oral Surg Oral Med Oral Pathol 1985;59:418 –9. 3. Clements RE, Gilboe DB. Labial endodontic access opening for mandibular incisors: endodontic and restorative considerations. J Can Dent Assoc 1991;57:587–9. 4. Madjar D, Kusner W, Shifman A. The labial endodontic access: a rational treatment approach in anterior teeth. J Prosthet Dent 1989;61:317–20. 5. Ingle JI, Mullaney TA, Russell A, Grandich RA, Taintor JF, Fahid A. Endodontic cavity preparation. In: Ingle J, Taintor JF, eds. Endodontics, 3rd ed. Philadelphia: Lea and Febiger, 1985;128. 6. Luks S. Practical endodontics, 1st ed. Philadelphia: JB Lippincott, 1974;42. 7. Wilcox L. Pulpal anatomy and access preparations. In: Walter RE, Torabinejad M, eds. Principles and practice of endodontics, 3rd ed. Philadelphia: WB Saunders, 2002; 568. 8. Morse D. Clinical endodontology, 1st ed. Springfield: Williams & Wilkins, 1974;454. 9. Streiff JT, Gerstein H. Access cavity preparation. In: Gerstein H, ed. Techniques in clinical endodontics, 1st ed. Philadelphia: WB Saunders, 1983;25. 10. Ash MM. Wheeler’s dental anatomy, physiology and occlusion, 7th ed. Philadelphia: WB Saunders, 1993;151,163. 11. Burns RC, Herbranson EJ. Tooth morphology and cavity preparation. In: Cohen S, Burns RC, eds. Pathways of the pulp, 8th ed. St. Louis: Mosby, 2002;203.
JOE — Volume 31, Number 2, February 2005