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Evaluation of cracks associated with ultrasonic root-end preparation
0099-2399/96/2204-0157503.00/0 JOURNALOF ENDODONTICS Copyright©1996 by The American Association of Endodontists
Printed in U.S.A. VOL. 22, NO. 4, APRIL1996
SCIENTIFIC ARTICLES Evaluation of Cracks Associated with Ultrasonic Root-End Preparation Carol A. Layton, DDS, J. Gordon Marshall, DMD, Leslie A. Morgan, DMD, and J. Craig Baumgartner, DDS, PhD
The purpose of this study was to evaluate the integrity of resected root-end surfaces of extracted human teeth after using ultrasonic tips at low or high frequencies for root-end preparation. Thirty bilaterally matched pairs of single-rooted human teeth had root-end resections using a low-speed diamond saw and were examined for root-end cracks. The matched pairs of teeth were then divided into two experimental groups, with one member of each pair being placed in each group. In group 1, root-end preparations were made with an ultrasonic tip on the lowest frequency setting. The preparations in group 2 were done on the highest power setting. Two investigators again examined the resected root-ends using a stereomicroscope at x20 to x63 and recorded the numbers, types, and location of the cracks. Three types of cracks were observed: canal cracks, intradentin cracks, and cemental cracks. There were significantly more root-ends with cracks after ultrasonic rootend preparation than after root-end resection only. In root-ends that had any cracks, significantly more canal cracks per root occurred when the ultrasonic tip was used on the high-frequency setting for root-end preparation than when the ultrasonic tip was used on the low power setting.
on the cut surfaces of resected roots. They found an average of 13,000 tubules/ram 2 at the dentin-cementum junction at a level 3 mm from the anatomic apex. They recommended that a minimal bevel be placed with a root-end filling extending deeper than the most coronal aspect of the bevel. Gilheany et al. (3) noted that resecting the root apex perpendicular to the long axis of the root minimized the amount of apical leakage. Root-end resection has traditionally been accomplished using a high-speed handpiece with surgical length burs followed by a root-end preparation with a high-speed or micro contra-angle slowspeed handpiece (4). Nedderman et al. (5) evaluated the surface properties of resected roots obturated with gutta-percha that had been sectioned by different bur configurations with high- and low-speed handpieces. A low-speed diamond saw was used for control resections. Their scanning electron microscopy showed that a cross-cut fissure, high-speed bur produced the roughest surface with characteristic parallel grooves. The smoothest surface was produced by the plain fissure bur in the low-speed handpiece. Although they noted that both burs produced shredding and tearing of the gutta-percha, no cracks were reported on the resected rootends. Parsons and Stanek (6) also used scanning electron microscopy to evaluate surface topography of resected root-ends. They found that a multifluted finishing bur produced a significantly smoother surface than did a coarse or fine diamond or a cross-cut fissure bur. Pannkuk (7) suggests that a shorter bevel will allow access while keeping the root-end surface area to a minimum so that optimal attachment of periodontal ligament fibers will be maintained. Short ultrasonic tips allow root-end preparations to be placed down the long axis of a root canal when the root resections are almost perpendicular to the long axis of the root. This may decrease the risk of perforation and enhance cleaning and shaping of the apical section of the root canal (8). In a recent study evaluating microleakage of root-end fillings, Saunders et al. (9) noted the presence of dentin cracks in resected root-ends prepared with ultrasonics. In a study comparing incomplete root fractures associated with obturation techniques, Onnick et al. (10) used a stereomicroscope at ><40 magnification and observed dentin fractures in teeth with no canal preparation. No studies have specifically evaluated whether ultrasonic root-end preparation can produce cracks or fissures in root-end surfaces. The purpose of this study was to evaluate resected root-end surfaces of
Endodontic surgery often includes root-end resection, preparation, and placement of a root-end filling. Mattison et al. (1) stated that the depth of the root-end filling is a critical factor in achieving an apical seal. They stated that a preparation depth of 3 mm with subsequent placement of varnish and an amalgam restoration can significantly reduce apical leakage and potential failure of the root-end restoration. Tidmarsh and Arrowsmith (2) demonstrated the existence of large numbers of exposed dentinal tubule orifices
157
158
Journal of Endodontics
Layton et al.
bilaterally matched human teeth for cracks before and after root-end preparation using ultrasonic tips at low or high frequencies.
M A T E R I A L S AND M E T H O D S Thirty bilaterally matched pairs of single-rooted human teeth extracted for periodontal or prosthodontic reasons were stored in 0.9% NaCI with 0.2% sodium azide to inhibit microbial growth (11). Some of the single-rooted teeth were bicuspids with two canals connected by an isthmus. All teeth were initially evaluated using ×2.6 magnification (Oroscoptic Research, Inc.,' Madison, WI) to ensure that there were no pre-existing fractures or cracks in the roots. A 3-ram root-end resection was made on each tooth perpendicular to the long axis of the root using a low-speed diamond wafering saw (4 inches × 0.012 inch) (Isomet; Buehler Ltd., Lake Bluff, IL) with continuous water spray. Following root resection, the teeth were immediately placed in 20-ml scintillation vials (Wheaton, Millville, NJ) and stored in a solution of 0.004% aqueous methylene blue dye in distilled water adjusted to a pH of 7. Forty-eight h following emersion, two investigators independently examined the resected root-ends using a stereomicroscope (Nikon SMZ-2T, Melville, NY) at X20 to × 6 3 using a fiberoptic transilluminating light source (Quality Aspirators, Duncanville, TX) held at least one-half inch from the root surface. A timer was used to ensure that the observation time for each tooth did not exceed 2 min. The presence, location, and number of cracks, or aberrant surface configurations were recorded. Following examination, the teeth were placed back in their individual scintillations vials with methylene blue dye solution. Disagreements between the two evaluators were subsequently discussed, and a consensus was reached. A member of each matched pair was placed in one of two groups. The root canals of the teeth used in the study were uninstrumented and unobturated. The root-end preparations were made using an Excellence in Endodontics (EIE) ultrasonic unit with ultrasonic tips (Excellence In Endodontics, San Diego, CA). A class l root-end preparation was made in the resected root-ends of the 30 teeth in group 1 using the EIE on the lowest frequency setting. The 30 teeth in group 2 received a similar root-end preparation using the EIE on the highest frequency setting. Cutting with the ultrasonic tips was done using a feather-like back and forth motion with the tip enveloped in water spray (12). Root-end preparation was done in hand with the tooth surrounded by gauze soaked in distilled water. The root tip was kept moist throughout the procedure. The CT-5 ultrasonic tip was used to start the preparation and include isthmuses. The CT-1 ultrasonic tip was then used to increase the depth and size of the preparation to 3 mm from the root-end surface (1, 12). The tooth was then immediately returned to the scintillation vial and immersed in fresh 0.004% methylene blue solution. The total preparation time for each root was < 2 min. Following root-end preparation, the investigators who previously evaluated the resected teeth, and who were unaware of the technique used, re-examined the root surfaces and recorded their findings. Root surfaces selected as representative of the different configurations observed were photographed at ×20. Differences in the numbers and types of cracks observed after root resection and after root-end preparation using the ultrasonic technique at low and high frequencies were statistically analyzed using the Student t test for percentages at the 95% significance level.
FIG 1. Low-frequency ultrasonic preparation. Original magnification ×20. Multiple cracks are seen: canal cracks (black arrows) and intradentin crack (curved white arrow). A defect (white arrow) in the dentin produced by the ultrasonic tip is shown at the margin of the root-end preparation.
FIG 2. High-frequency ultrasonic preparation. Original magnification x20. Branching cracks (white arrow) and cemental cracks (black
arrowheads). RESULTS Three types of cracks were observed on the resected root-ends: canal cracks, intradentin cracks, and cemental cracks (Fig. 1 and 2). Canal cracks were those cracks that originated within the canal and radiated into the dentin. Canal cracks may branch and can be subdivided into complete and incomplete canal cracks. Complete canal cracks extended from the c a n a l s p a c e to the external root surface. Incomplete canal cracks extended from the canal space for a variable distance into the dentin, but ended short of the external root surface. Intradentin cracks were confined to dentin and seemed to run in a faciolingual direction either mesial or distal to the canal. Cemental cracks were observed radiating from the cemental surface to the cementodentinal junction (Figs. l and 2). Cemental cracks were not seen in all teeth, but when present were too numerous to count. Cracks were observed in some of the teeth in the experimental groups after root resection and before ultrasonic root-end preparation (Table 1). Additional cracks occurred after root-end preparation. Many of the teeth in the experimental groups had no visible cracks of any type at any time. A significantly greater number of teeth had canal cracks after ultrasonic root-end preparation than
Ultrasonic Root-End Preparation
Vol. 22, No. 4, April 1996 TABLE 1 NO. of root-ends with cracks Low-Frequency Group
Canal cracks tntradentin cracks
Resection Only
Root-End Preparation
5 1
10* 2
High-Frequency Group Resection Root-End Only Preparation 3 2
13" t
* Significance level, p <- 0.05 (n - 30 teeth in each group).
TABLE 2 Total no. of observed cracks
Canal cracks Intradentin cracks *
Low-Frequency Group
High-Frequency Group
Resection Only
Root-End Preparation
Resection Only
Root-End Preparation
9 3
14 2
3 3
23* 3
Significance level, p -~ 0.001.
after root resection only (p < 0.05) (Table 1). Considering canal cracks only, no significant differences were observed in the n u m b e r of teeth with cracks when comparing low-frequency with high-frequency ultrasonic preparation. However, when cracking did occur in a tooth, high-frequency ultrasonic root-end preparation resulted in a significantly greater number of canal cracks per tooth than did a low-frequency preparation technique (p --< 0.001) (Table 2).
DISCUSSION To standardize the root-end resection, it was decided to use a low-speed diamond saw with water spray (5). Root-end preparations were made using the EIE ultrasonic tip on the lowest frequency for one tooth of each matched pair (30 teeth) and on the highest frequency setting for the other tooth of the matched pair (30 teeth) with the tip constantly enveloped in water. Although not reported in the literature, the manufacturers of the EIE unit have stated in a personal communication that the ultrasonic tips operate at a frequency of 40,000 mHz. They state that changing the power from the lowest to the highest setting only alters the frequency of the tip by a maximum of 100 to 200 mHz, but that the highest power setting has a greater amplitude of directional movement. Canal and intradentin cracks have been described by Onnick et al. (10) in instrnmented and uninstrumented roots. They did not find any complete canal cracks. Although both complete and incomplete canal cracks were seen in the present study, they were considered as a group in the observations. It is interesting to speculate whether incomplete cracks might be complete cracks if sectioned in successive planes. It is also interesting to speculate as to whether incomplete cracks can become complete cracks over time. Neither of these possibilities were addressed in this study. Cemental cracks were observed radiating from the cemental surface to the cementodentinal junction (Fig. 2). Because these cracks did not extend past the cementodentinal junction, it seems unlikely that they would be produced by root-end resection or preparation. They are likely already present before resection and are related to extraction or aging processes.
159
Methylene blue was used in this study as it has been shown by Cambruzzi et al. (13) to be an aid in the detection of fractures. The teeth were stored in 0.004% methylene blue to decrease the optical activity of dentin and to stain cracks for easier microscopic identification. Transillumination was a valuable aid in observing cracks stained with methylene blue. To avoid heating and dessication of the roots, a surgical fiberoptic light source was used for transillumination at a distance of at least one-half inch from the root surface for a time period of < 2 rain. The air temperature around the root was 28°C when it was transilluminated using this light source. Cracks observed in the dentin after root resection alone may be produced by the sectioning procedure or may have been previously present. Root-end preparation using ultrasonic tips activated at both frequencies increased the number of canal cracks. Defects were occasionally noted at the canal cavosurface margin that were likely the result of the ultrasonic tips cutting against the canal walls (Fig. 1). Canal cracks were often found emanating from these defects. However, one resected root (Table 2) had a canal crack present after resection that was removed by root-end preparation. This is not surprising, because canal cracks of limited length may be eliminated in the process of enlarging the canal space with the ultrasonic tip. Saunders et al. (9) found significantly more cracking of teeth than reported herein when the root-end had been prepared with the ENAC ultrasonic instrument. Experimental design may be a factor in the formation of these cracks, as Saunders et al. (9) demineralized and sequentially dehydrated the teeth in isopropyl alcohol. This dehydration process could result in crack development. Although it was impossible to determine the depth of the cracks using this experimental design, cracks were observed extending longitudinally down the canal wall when evaluated with the stereomicroscope. Cracks extending down the canal wall were observed with both low- and high-frequency ultrasonic root-end preparations. If ultrasonic root-end preparation causes significantly more cracks on the resected root surface, one could speculate that the prognosis for success is reduced. However, based on the data reported herein, it is impossible to hypothesize on the success rate for surgical endodontic therapy using the ultrasonic root-end preparation technique. In addition, there are no comparable studies evaluating resected root-ends following root-end preparation with burs or sonic devices. Further research is needed to evaluate the depth of the cracks to assess their impact on other variables such as leakage. Similar studies should be done to assess and compare whether similar types and numbers of cracks develop following root-end preparation with high- and low-speed burs, sonic instrumentation, and other ultrasonic systems. The forces needed to generate cracks should be studied, as well as whether the periodontal ligament and surrounding bone attenuate the effects of ultrasonic preparation on crack formation.
Dr. Layton is a former endodontic postgraduate student, Oregon Health Sciences University, School of Dentistry, and is currently in private endodontic practice in Edmonton, Alberta, Canada. Dr. Marshall is assistant professor, Dr. Morgan is assistant professor, and Dr. Baumgartner is associate professor and chairman, Department of Endodontology, Oregon Health Sciences University School of Dentistry, Portland OR. Address requests for reprints to Dr. J. Gordon Marshall, Department of Endodontology, Oregon Health Sciences University School of Dentistry, 611 SW Campus Drive, Portland, OR 97201.
160
Journal of Endodontics
Layton et al. References
1. Mattison GD, Von Frauhofer JA, Delivanis PD, Anderson AN. Microleakage of retrograde amalgams. J Endodon 1985;11:340-5. 2. Tidmarsh BG, Arrowsmith MG. Dentinal tubules at the root-ends of apicected teeth: a scanning electron microscopic study. Int Endod J 1989; 22:184-9. 3. Gilheany PA, Figdor D, Tyas MJ. Apical dentin permeability and microleakage associated with root-end resection and retrograde filling. J Endodon 1994;20:22-5. 4. Nicholls F. Retrograde filling of the root canal. Oral Surg 1962;15:46373. 5. Nedderman TA, Hartwell GR, Portell FR. A comparison of root surfaces following apical root resection with various burs: scanning electron microscopic evaluation. J Endodon 1988;14:423-7. 6. Parsons MD, Stanek AH. A qualitative SEM evaluation of root-end resections. J Endodon (in press).
7. Pannkuk TF. Endodontic surgery: the treatment phase and wound healing. Part 2. Endod Rept 1992;7:14-9. 8. Carr GB. Advanced techniques and visual enhancement for endodontic surgery. Endod Rept 1992;7:6-9. 9. Saunders WP, Saunders EM, Gutmann JL. Ultrasonic root-end preparation. Part 2. Microleakage of EBA root-end fillings. Int Endod J 1994;27: 325-9. 10. Onnick PA, Davis RD, Wayman BE. An in vitro comparison of incomplete root fractures associated with three obturation techniques. J Endodon 1994;20:32-7. 11. Fogel HM, Pashley DH. Dentin permeability; effects of endodontic procedures on root slabs. J Endodon 1990;16:442-5. 12. Carr GB. Microsurgical techniques in endodontics: an introduction (instruction manual). San Diego: Pacific Endodontic Research Foundation, 1993. 13. Cambruzzi JV, Marshall FJ, Pappin JB. Methylene blue dye: an aid to endodontic surgery. J Endodon 1985;11:311-4.
You Might Be Interested Many persons use small--100 mg daily--doses of aspirin prophylactically against cardiovascular disease. Chronic ingestions of daily aspirin doses of 300 mg or greater have been related to greatly increased risk of bleeding peptic ulcer. A recent study concludes (BMJ 310:827, 1995) that "the overall benefits of 'aspirin usage' are likely to considerably outweigh possible risks." John Willow
Printed in U.S.A. VOL. 22, NO. 4, APRIL1996
SCIENTIFIC ARTICLES Evaluation of Cracks Associated with Ultrasonic Root-End Preparation Carol A. Layton, DDS, J. Gordon Marshall, DMD, Leslie A. Morgan, DMD, and J. Craig Baumgartner, DDS, PhD
The purpose of this study was to evaluate the integrity of resected root-end surfaces of extracted human teeth after using ultrasonic tips at low or high frequencies for root-end preparation. Thirty bilaterally matched pairs of single-rooted human teeth had root-end resections using a low-speed diamond saw and were examined for root-end cracks. The matched pairs of teeth were then divided into two experimental groups, with one member of each pair being placed in each group. In group 1, root-end preparations were made with an ultrasonic tip on the lowest frequency setting. The preparations in group 2 were done on the highest power setting. Two investigators again examined the resected root-ends using a stereomicroscope at x20 to x63 and recorded the numbers, types, and location of the cracks. Three types of cracks were observed: canal cracks, intradentin cracks, and cemental cracks. There were significantly more root-ends with cracks after ultrasonic rootend preparation than after root-end resection only. In root-ends that had any cracks, significantly more canal cracks per root occurred when the ultrasonic tip was used on the high-frequency setting for root-end preparation than when the ultrasonic tip was used on the low power setting.
on the cut surfaces of resected roots. They found an average of 13,000 tubules/ram 2 at the dentin-cementum junction at a level 3 mm from the anatomic apex. They recommended that a minimal bevel be placed with a root-end filling extending deeper than the most coronal aspect of the bevel. Gilheany et al. (3) noted that resecting the root apex perpendicular to the long axis of the root minimized the amount of apical leakage. Root-end resection has traditionally been accomplished using a high-speed handpiece with surgical length burs followed by a root-end preparation with a high-speed or micro contra-angle slowspeed handpiece (4). Nedderman et al. (5) evaluated the surface properties of resected roots obturated with gutta-percha that had been sectioned by different bur configurations with high- and low-speed handpieces. A low-speed diamond saw was used for control resections. Their scanning electron microscopy showed that a cross-cut fissure, high-speed bur produced the roughest surface with characteristic parallel grooves. The smoothest surface was produced by the plain fissure bur in the low-speed handpiece. Although they noted that both burs produced shredding and tearing of the gutta-percha, no cracks were reported on the resected rootends. Parsons and Stanek (6) also used scanning electron microscopy to evaluate surface topography of resected root-ends. They found that a multifluted finishing bur produced a significantly smoother surface than did a coarse or fine diamond or a cross-cut fissure bur. Pannkuk (7) suggests that a shorter bevel will allow access while keeping the root-end surface area to a minimum so that optimal attachment of periodontal ligament fibers will be maintained. Short ultrasonic tips allow root-end preparations to be placed down the long axis of a root canal when the root resections are almost perpendicular to the long axis of the root. This may decrease the risk of perforation and enhance cleaning and shaping of the apical section of the root canal (8). In a recent study evaluating microleakage of root-end fillings, Saunders et al. (9) noted the presence of dentin cracks in resected root-ends prepared with ultrasonics. In a study comparing incomplete root fractures associated with obturation techniques, Onnick et al. (10) used a stereomicroscope at ><40 magnification and observed dentin fractures in teeth with no canal preparation. No studies have specifically evaluated whether ultrasonic root-end preparation can produce cracks or fissures in root-end surfaces. The purpose of this study was to evaluate resected root-end surfaces of
Endodontic surgery often includes root-end resection, preparation, and placement of a root-end filling. Mattison et al. (1) stated that the depth of the root-end filling is a critical factor in achieving an apical seal. They stated that a preparation depth of 3 mm with subsequent placement of varnish and an amalgam restoration can significantly reduce apical leakage and potential failure of the root-end restoration. Tidmarsh and Arrowsmith (2) demonstrated the existence of large numbers of exposed dentinal tubule orifices
157
158
Journal of Endodontics
Layton et al.
bilaterally matched human teeth for cracks before and after root-end preparation using ultrasonic tips at low or high frequencies.
M A T E R I A L S AND M E T H O D S Thirty bilaterally matched pairs of single-rooted human teeth extracted for periodontal or prosthodontic reasons were stored in 0.9% NaCI with 0.2% sodium azide to inhibit microbial growth (11). Some of the single-rooted teeth were bicuspids with two canals connected by an isthmus. All teeth were initially evaluated using ×2.6 magnification (Oroscoptic Research, Inc.,' Madison, WI) to ensure that there were no pre-existing fractures or cracks in the roots. A 3-ram root-end resection was made on each tooth perpendicular to the long axis of the root using a low-speed diamond wafering saw (4 inches × 0.012 inch) (Isomet; Buehler Ltd., Lake Bluff, IL) with continuous water spray. Following root resection, the teeth were immediately placed in 20-ml scintillation vials (Wheaton, Millville, NJ) and stored in a solution of 0.004% aqueous methylene blue dye in distilled water adjusted to a pH of 7. Forty-eight h following emersion, two investigators independently examined the resected root-ends using a stereomicroscope (Nikon SMZ-2T, Melville, NY) at X20 to × 6 3 using a fiberoptic transilluminating light source (Quality Aspirators, Duncanville, TX) held at least one-half inch from the root surface. A timer was used to ensure that the observation time for each tooth did not exceed 2 min. The presence, location, and number of cracks, or aberrant surface configurations were recorded. Following examination, the teeth were placed back in their individual scintillations vials with methylene blue dye solution. Disagreements between the two evaluators were subsequently discussed, and a consensus was reached. A member of each matched pair was placed in one of two groups. The root canals of the teeth used in the study were uninstrumented and unobturated. The root-end preparations were made using an Excellence in Endodontics (EIE) ultrasonic unit with ultrasonic tips (Excellence In Endodontics, San Diego, CA). A class l root-end preparation was made in the resected root-ends of the 30 teeth in group 1 using the EIE on the lowest frequency setting. The 30 teeth in group 2 received a similar root-end preparation using the EIE on the highest frequency setting. Cutting with the ultrasonic tips was done using a feather-like back and forth motion with the tip enveloped in water spray (12). Root-end preparation was done in hand with the tooth surrounded by gauze soaked in distilled water. The root tip was kept moist throughout the procedure. The CT-5 ultrasonic tip was used to start the preparation and include isthmuses. The CT-1 ultrasonic tip was then used to increase the depth and size of the preparation to 3 mm from the root-end surface (1, 12). The tooth was then immediately returned to the scintillation vial and immersed in fresh 0.004% methylene blue solution. The total preparation time for each root was < 2 min. Following root-end preparation, the investigators who previously evaluated the resected teeth, and who were unaware of the technique used, re-examined the root surfaces and recorded their findings. Root surfaces selected as representative of the different configurations observed were photographed at ×20. Differences in the numbers and types of cracks observed after root resection and after root-end preparation using the ultrasonic technique at low and high frequencies were statistically analyzed using the Student t test for percentages at the 95% significance level.
FIG 1. Low-frequency ultrasonic preparation. Original magnification ×20. Multiple cracks are seen: canal cracks (black arrows) and intradentin crack (curved white arrow). A defect (white arrow) in the dentin produced by the ultrasonic tip is shown at the margin of the root-end preparation.
FIG 2. High-frequency ultrasonic preparation. Original magnification x20. Branching cracks (white arrow) and cemental cracks (black
arrowheads). RESULTS Three types of cracks were observed on the resected root-ends: canal cracks, intradentin cracks, and cemental cracks (Fig. 1 and 2). Canal cracks were those cracks that originated within the canal and radiated into the dentin. Canal cracks may branch and can be subdivided into complete and incomplete canal cracks. Complete canal cracks extended from the c a n a l s p a c e to the external root surface. Incomplete canal cracks extended from the canal space for a variable distance into the dentin, but ended short of the external root surface. Intradentin cracks were confined to dentin and seemed to run in a faciolingual direction either mesial or distal to the canal. Cemental cracks were observed radiating from the cemental surface to the cementodentinal junction (Figs. l and 2). Cemental cracks were not seen in all teeth, but when present were too numerous to count. Cracks were observed in some of the teeth in the experimental groups after root resection and before ultrasonic root-end preparation (Table 1). Additional cracks occurred after root-end preparation. Many of the teeth in the experimental groups had no visible cracks of any type at any time. A significantly greater number of teeth had canal cracks after ultrasonic root-end preparation than
Ultrasonic Root-End Preparation
Vol. 22, No. 4, April 1996 TABLE 1 NO. of root-ends with cracks Low-Frequency Group
Canal cracks tntradentin cracks
Resection Only
Root-End Preparation
5 1
10* 2
High-Frequency Group Resection Root-End Only Preparation 3 2
13" t
* Significance level, p <- 0.05 (n - 30 teeth in each group).
TABLE 2 Total no. of observed cracks
Canal cracks Intradentin cracks *
Low-Frequency Group
High-Frequency Group
Resection Only
Root-End Preparation
Resection Only
Root-End Preparation
9 3
14 2
3 3
23* 3
Significance level, p -~ 0.001.
after root resection only (p < 0.05) (Table 1). Considering canal cracks only, no significant differences were observed in the n u m b e r of teeth with cracks when comparing low-frequency with high-frequency ultrasonic preparation. However, when cracking did occur in a tooth, high-frequency ultrasonic root-end preparation resulted in a significantly greater number of canal cracks per tooth than did a low-frequency preparation technique (p --< 0.001) (Table 2).
DISCUSSION To standardize the root-end resection, it was decided to use a low-speed diamond saw with water spray (5). Root-end preparations were made using the EIE ultrasonic tip on the lowest frequency for one tooth of each matched pair (30 teeth) and on the highest frequency setting for the other tooth of the matched pair (30 teeth) with the tip constantly enveloped in water. Although not reported in the literature, the manufacturers of the EIE unit have stated in a personal communication that the ultrasonic tips operate at a frequency of 40,000 mHz. They state that changing the power from the lowest to the highest setting only alters the frequency of the tip by a maximum of 100 to 200 mHz, but that the highest power setting has a greater amplitude of directional movement. Canal and intradentin cracks have been described by Onnick et al. (10) in instrnmented and uninstrumented roots. They did not find any complete canal cracks. Although both complete and incomplete canal cracks were seen in the present study, they were considered as a group in the observations. It is interesting to speculate whether incomplete cracks might be complete cracks if sectioned in successive planes. It is also interesting to speculate as to whether incomplete cracks can become complete cracks over time. Neither of these possibilities were addressed in this study. Cemental cracks were observed radiating from the cemental surface to the cementodentinal junction (Fig. 2). Because these cracks did not extend past the cementodentinal junction, it seems unlikely that they would be produced by root-end resection or preparation. They are likely already present before resection and are related to extraction or aging processes.
159
Methylene blue was used in this study as it has been shown by Cambruzzi et al. (13) to be an aid in the detection of fractures. The teeth were stored in 0.004% methylene blue to decrease the optical activity of dentin and to stain cracks for easier microscopic identification. Transillumination was a valuable aid in observing cracks stained with methylene blue. To avoid heating and dessication of the roots, a surgical fiberoptic light source was used for transillumination at a distance of at least one-half inch from the root surface for a time period of < 2 rain. The air temperature around the root was 28°C when it was transilluminated using this light source. Cracks observed in the dentin after root resection alone may be produced by the sectioning procedure or may have been previously present. Root-end preparation using ultrasonic tips activated at both frequencies increased the number of canal cracks. Defects were occasionally noted at the canal cavosurface margin that were likely the result of the ultrasonic tips cutting against the canal walls (Fig. 1). Canal cracks were often found emanating from these defects. However, one resected root (Table 2) had a canal crack present after resection that was removed by root-end preparation. This is not surprising, because canal cracks of limited length may be eliminated in the process of enlarging the canal space with the ultrasonic tip. Saunders et al. (9) found significantly more cracking of teeth than reported herein when the root-end had been prepared with the ENAC ultrasonic instrument. Experimental design may be a factor in the formation of these cracks, as Saunders et al. (9) demineralized and sequentially dehydrated the teeth in isopropyl alcohol. This dehydration process could result in crack development. Although it was impossible to determine the depth of the cracks using this experimental design, cracks were observed extending longitudinally down the canal wall when evaluated with the stereomicroscope. Cracks extending down the canal wall were observed with both low- and high-frequency ultrasonic root-end preparations. If ultrasonic root-end preparation causes significantly more cracks on the resected root surface, one could speculate that the prognosis for success is reduced. However, based on the data reported herein, it is impossible to hypothesize on the success rate for surgical endodontic therapy using the ultrasonic root-end preparation technique. In addition, there are no comparable studies evaluating resected root-ends following root-end preparation with burs or sonic devices. Further research is needed to evaluate the depth of the cracks to assess their impact on other variables such as leakage. Similar studies should be done to assess and compare whether similar types and numbers of cracks develop following root-end preparation with high- and low-speed burs, sonic instrumentation, and other ultrasonic systems. The forces needed to generate cracks should be studied, as well as whether the periodontal ligament and surrounding bone attenuate the effects of ultrasonic preparation on crack formation.
Dr. Layton is a former endodontic postgraduate student, Oregon Health Sciences University, School of Dentistry, and is currently in private endodontic practice in Edmonton, Alberta, Canada. Dr. Marshall is assistant professor, Dr. Morgan is assistant professor, and Dr. Baumgartner is associate professor and chairman, Department of Endodontology, Oregon Health Sciences University School of Dentistry, Portland OR. Address requests for reprints to Dr. J. Gordon Marshall, Department of Endodontology, Oregon Health Sciences University School of Dentistry, 611 SW Campus Drive, Portland, OR 97201.
160
Journal of Endodontics
Layton et al. References
1. Mattison GD, Von Frauhofer JA, Delivanis PD, Anderson AN. Microleakage of retrograde amalgams. J Endodon 1985;11:340-5. 2. Tidmarsh BG, Arrowsmith MG. Dentinal tubules at the root-ends of apicected teeth: a scanning electron microscopic study. Int Endod J 1989; 22:184-9. 3. Gilheany PA, Figdor D, Tyas MJ. Apical dentin permeability and microleakage associated with root-end resection and retrograde filling. J Endodon 1994;20:22-5. 4. Nicholls F. Retrograde filling of the root canal. Oral Surg 1962;15:46373. 5. Nedderman TA, Hartwell GR, Portell FR. A comparison of root surfaces following apical root resection with various burs: scanning electron microscopic evaluation. J Endodon 1988;14:423-7. 6. Parsons MD, Stanek AH. A qualitative SEM evaluation of root-end resections. J Endodon (in press).
7. Pannkuk TF. Endodontic surgery: the treatment phase and wound healing. Part 2. Endod Rept 1992;7:14-9. 8. Carr GB. Advanced techniques and visual enhancement for endodontic surgery. Endod Rept 1992;7:6-9. 9. Saunders WP, Saunders EM, Gutmann JL. Ultrasonic root-end preparation. Part 2. Microleakage of EBA root-end fillings. Int Endod J 1994;27: 325-9. 10. Onnick PA, Davis RD, Wayman BE. An in vitro comparison of incomplete root fractures associated with three obturation techniques. J Endodon 1994;20:32-7. 11. Fogel HM, Pashley DH. Dentin permeability; effects of endodontic procedures on root slabs. J Endodon 1990;16:442-5. 12. Carr GB. Microsurgical techniques in endodontics: an introduction (instruction manual). San Diego: Pacific Endodontic Research Foundation, 1993. 13. Cambruzzi JV, Marshall FJ, Pappin JB. Methylene blue dye: an aid to endodontic surgery. J Endodon 1985;11:311-4.
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