0099-2399/90/1603-0109/$02.00[0 JOURNAL OF ENDODONTICS Copyright 9 1990 by The American Association of Endodontists
Printed in U.S.A. VOL. 16, NO. 3, MARCH 1990
SCIENTIFIC ARTICLES Remaining Dentin/Cementum Thickness after Hand or Ultrasonic Instrumentation John T. McCann, DMD, David L. Keller, DMD, MSEd, MS, and Gary L. LaBounty, DDS, MS
surface with the anticurvature filing technique. In addition, round bur flaring in an anticurvature manner was as safe as flaring with Gates Glidden burs. It was also demonstrated that the area 4- to 6-mm apical to the coronal orifice was the most susceptible to the risk of perforation during instrumentation. Lim and Stock (7) compared anticurvature and step-back filing. They found a statistically significant reduction in the risk of perforation with anticurvature filing. Martin et al. (8) demonstrated that ultrasonically energized files removed a significantly greater amount of dentin in a fixed time period than did hand instrumentation. Other authors (9-11) compared the efficacy o f these two instrumentation methods in removing debris from canals with variable results. Pedicord et al. (12) compared step-back hand filing to ultrasonic instrumentation in the mesial roots of mandibular molars. Their study confirmed that both techniques transported the canals toward the furcation. In contrast, Chenail and Teplitsky (13) found little or no straightening of canal curvature with ultrasonic canal preparation. The purpose of this study was to compare the degree of encroachment upon the furcation area in mesial roots of mandibular molars during hand or ultrasonic instrumentation. A new model system was used that enabled the evaluation of the same canal pre- and postoperatively.
A quantitative study was undertaken to measure remaining dentin/cementum thickness after using step-down, step-back hand instrumentation or ultrasonically energized instrumentation techniques. A model system was used which enabled the same canal system of extracted human mandibular molars to be accurately evaluated and measured before and after instrumentation. Although no statistical difference was demonstrated in the encroachment upon the furcal aspect of mesial roots of mandibular molars, both techniques came dangerously close to creating stripping and perforations in a high percentage of cases.
Proper cleaning and shaping of the root canal system encompasses the removal of all necrotic tissues, including pulpal tissue as well as dentin, to eliminate microorganisms and their toxic by-products. The unique features of the finely curved canals of mandibular molars often make instrumentation of these canals difficult. These features, which include curvature in two dimensions, a lack of natural taper, irregularities in shape, and the presence of calcifications, cause procedural errors such as loss of working length, apical transportation, instrument breakage, and strip perforations (1-3). Weine (1) states that the preparation of canals in mandibular molars can be consistently accomplished provided a flaring technique is used to compensate for the canal curvature and lack of natural taper. Weine et al. (3) further advocated the use of a step-back flared preparation to prevent procedural errors. Abou-Rass et al. (4) postulated that an anticurvature filing technique, which selectively removes more dentin from the outer wall, would reduce the incidence of stripping the inner (furcal) root surface. Further modifications to the stepback flaring technique have been proposed. Goerig et al. (5) proposed a step-down technique whereby the coronal portion of the canal is flared before the apical step-back procedure is performed. Kessler et al. (6) evaluated standard step-back filing techniques and coronal flaring with Gates Glidden burs or small round burs. Their results showed less risk to the furcal root
MATERIALS AND METHODS Forty extracted human mandibular first and second molars were selected for this study and stored in a 10% buffered formalin solution before use. Teeth that had incompletely formed apices, unusual root morphology, or damage from extraction were excluded from the sample. Tissue and debris were removed from external root surfaces with hand curettes. Standard access openings were made as described by Cohen and Burns (14). Internal canal morphology, apical patency, and working lengths of the canals of the mesial roots were determined with #08 and #10 K-type files. Working lengths were established by measuring the #10 file at the point it first became visible at the apex and subtracting 0.5 m m from that length. Teeth were randomly placed into two groups. The model system used for instrumentation was a modification of the method presented by Bramante et al. (15). By fabricating muffles of ticonium instead of stone and using
109
110
McCann et al.
Journal of Endodontics
these as molds for the preparation of the acrylic resin-tooth blocks, fewer muffles were required. After modifying a technique of Kessler et al. (6), sectioning of the tooth-containing acrylic resin blocks was performed as depicted in Fig. 1 using an Isomet circular diamond saw (Buehler, Ltd., Lake Bludd, I L Before instrumentation, photographs o f all sections were made with a Zeiss binocular photomicroscope (Wild HeerHeerbrugg, Heerbrugg, Switzerland) at original magnification
x 6 and x 12. The least thickness from the canal to the external root surface was recorded with a measuring reticle in 0.1-mm intervals (Figs. 2A, 3A, 4A, and 5A).
Group 1 In this group of 20 teeth, a hand instrumentation technique was used as described by Goerig et al. (5) except that Flex R files (Union Broach Corp., Long Island City, NY) were substituted for K-type files. Canals were filed to a #25 at the working length. Each canal was irrigated with 2.0 ml of 2.5% sodium hypochlorite solution between each instrument size. The final rinse consisted of sequentially flushing each canal with 5.0 ml each of 15% EDTA, 2.5% sodium hypochlorite solution, and 70% isopropyl alcohol.
Group 2
CUT
SECTION 9 FURCATION
|
'
-
~
-IKImm~
9.0 mm
F=G 1. Sectioning technique. Initial cut at furcation level with subsequent cuts progressing apically in 3.0-mm increments. Kerr of blade equals 0.3 mm.
Ultrasonic (endosonic) instrumentation was performed on 20 teeth according to the directions of the manufacturer (L. D. Caulk Dentsply, Milford, DE). The final instrument used at the working length was an ultrasonic #25 file. Each file was used in an anticurvature (4) manner for 1 min with continuous irrigation of 2.5% sodium hypochlorite solution at a rate of 20 ml per min. To complete the ultrasonic group an endosonic #35 diamond file was used to coronally flare the canal. The final rinse was identical to that described for teeth in group I. After instrumentation, the tooth sections, embedded in acrylic, were photographed again at x 6 and • 12 magnification and the least remaining thickness of dentin/cementum
FtG 2. Representative horizontal section of root at furcation level (original magnification x12). A, Preinstrumentation. Distance from canal to periphery is 2.1 mm. B, Postinstrumentation. Distance from canal to periphery is 1.5 mm.
FIG 3. Representative horizontal section of root 3.0-mm apical to furcation (original magnification • A, Preinstrumentation. Distance from canal to periphery is 1.4 mm. B, Postinstrumentation. Distance from canal to periphery is 0.9 to 1.0 mm.
Vol. 16, No. 3, March 1990
Remaining Root Thickness
111
FIG 4, Representative horizontal section of root 6.0-mm apical to furcation (original magnification x12). Arrow indicates cementodentinal junction. Note relative thicknesses of dentin and cementum. A, preinstrumentation. Distance from canal to periphery is 1.0 to 1.1 mm. B, Postinstrumentation. Distance from canal to periphery is 0.6 mm.
FIG 5. Representative horizontal section of root 9.0-ram apical to furcation (original magnification x12). A, Preinstrumentation. Distance from canar to periphery is 0_7 to 0.8 mm. B, Postinstrumentafion. Distance from cana~ to periphery is 0.7 to 0.8 mm.
was recorded (Figs. 2B, 3B, 4B, and 5B). All results were then submitted for statistical analysis. Paired t tests were used to evaluate the measured distances from the canals to the root surfaces and the percentages of original dentin/cementum thickness data. RESULTS The mean values of the least remaining root thickness at each level before and after instrumentation are shown in Tables 1 and 2, respectively. Statistical comparison of the two groups, using Student's t test, demonstrated that the differences were not significant (p > 0.05) at any of the levels. In only one instance did a perforation occur and this was in a hand-instrumented tooth 3-mm apical to the furcation (Fig. 6). Table 3 compares the two groups in the distribution of remaining root thicknesses from all measured levels. Chisquare analysis of this data showed no difference at a p of 0.05. The number of sections in each group at each level with a remaining thickness of dentin/cementum less than 0.5 m m is presented in Table 4. Similarly, Table 5 compares the two techniques at each level for the number of sections in which more than 50% of the original thickness of dentin was removed during instrumentation. Again, chi-square analysis failed to show a significant difference between the two groups (p > 0.05). Finally, after hand or ultrasonic instrumentation, the least remaining thickness of dentin/cementum 3.0- and 6.0-mm apical to the furcation was toward the distal (furcal) surface of the mesial root.
DISCUSSION The results of this study corroborate those of Pedicord et al. (12) with regard to no significant difference between the two instrumentation methods. This study and that of Pedicord et al. demonstrate a tendency to transport the canal toward the distal surface of the root. Tables 1 and 2 demonstrate that in the areas of the canals where no rotary instruments were used, the ultrasonic instrumentation technique removed a slightly greater amount of dentin. Also evident in Tables 1 and 2 was the removal of a greater a m o u n t of dentin with rotary instruments at the level 3.0-mm apical to the furcation. The area 4.0-mm apical from the canal orifice has been identified by Abou-Rass et al. (16) as especially prone to perforations in the mesial roots secondary to use of rotary instruments. Bower (17) referred to the area 2.0-mm apical to the furcation in mesial roots of mandibular molars as being concave 100% of the time. The concavity of mesial roots which has a mean value of 0.7 m m is greater than the concavity in distal roots which has a mean value of 0.5 mm. Bower (17) also stated that with greater root concavities an increased a m o u n t of cementum is found. The roles attributed to cementum are repair of damaged root surfaces and periodontal attachment (19) and not structural integrity of the root. Reduced thickness of tooth structure as measured in this and other studies (5, 12, 18) might not necessarily provide a valid indication of root integrity or resistance to obturationinduced fractures since these measurements included both cementum and dentin. A great advantage of this model system is the ability to
112
McCann et al.
Journal of Endodontics TABLE 1. Results of hand instrumentation (n = 20)
Least Dentin/Cementum Thickness from Canal to Root Surface (mm)
Level Apical from Furcation (mm)
Preinstrumented (mean -+ SD)
Postinstrumented (mean +_ SD)
(2,) 0.0 3.0 6.0 9.0
1.4 0.8 0.8 0.5
Tooth Structure Removed
Final Dentin/Cementum
(mm) (X, - X2)
as % of Original
0.4 0.3 0.1 0.1
71.4 62.5 87.5 80.0
(22)
___0.4 • 0.2 + 0.2 • 0.3
1.0 • 0.5 • 0.7 • 0.4 •
0.4 0.2 0.2 0.2
TABLE 2. Results of ultrasonic instrumentation (n = 20)
Least Dentin/Cementum Thickness from Canal to Root Surface (mm)
Level Apical from Furcation (mm)
Preinstrumented (mean • SD)
Postinstrumented (mean • SD)
(2~) 0.0 3.0 6.0 9.0
1.5 0.7 0.8 0.5
Tooth Structure Removed
Final Dentin/Cementum
(mm) 22)
as % of Original
(21 --
(22)
--- 0.3 _+ 0.1 - 0.2 - 0.3
1.1 0.5 0.7 0.4
__+0.4 ___0.2 _ 0.1 _+ 0.2
0.4 0.2 0.1 0.1
73.3 71.4 87.5 80.0
FIG 6. Horizontal section of root 3.0-mm apical to furcation showing perforation produced by hand instrumentation (original magnification x l 2). A, Preinstrumentation. Distance from canal to periphery is 0.6 mm. B, Postinstrumentation. Perforation is noted.
TABLE 3. Frequency distribution of postinstrumented dentin/cementum thicknesses (mm)
Post-instrumented Thickness Group
of Dentin/Cementum
Hand instrumented (n = 67) Ultrasonically instrumented (n = 72)
>0.5
Printed in U.S.A. VOL. 16, NO. 3, MARCH 1990
SCIENTIFIC ARTICLES Remaining Dentin/Cementum Thickness after Hand or Ultrasonic Instrumentation John T. McCann, DMD, David L. Keller, DMD, MSEd, MS, and Gary L. LaBounty, DDS, MS
surface with the anticurvature filing technique. In addition, round bur flaring in an anticurvature manner was as safe as flaring with Gates Glidden burs. It was also demonstrated that the area 4- to 6-mm apical to the coronal orifice was the most susceptible to the risk of perforation during instrumentation. Lim and Stock (7) compared anticurvature and step-back filing. They found a statistically significant reduction in the risk of perforation with anticurvature filing. Martin et al. (8) demonstrated that ultrasonically energized files removed a significantly greater amount of dentin in a fixed time period than did hand instrumentation. Other authors (9-11) compared the efficacy o f these two instrumentation methods in removing debris from canals with variable results. Pedicord et al. (12) compared step-back hand filing to ultrasonic instrumentation in the mesial roots of mandibular molars. Their study confirmed that both techniques transported the canals toward the furcation. In contrast, Chenail and Teplitsky (13) found little or no straightening of canal curvature with ultrasonic canal preparation. The purpose of this study was to compare the degree of encroachment upon the furcation area in mesial roots of mandibular molars during hand or ultrasonic instrumentation. A new model system was used that enabled the evaluation of the same canal pre- and postoperatively.
A quantitative study was undertaken to measure remaining dentin/cementum thickness after using step-down, step-back hand instrumentation or ultrasonically energized instrumentation techniques. A model system was used which enabled the same canal system of extracted human mandibular molars to be accurately evaluated and measured before and after instrumentation. Although no statistical difference was demonstrated in the encroachment upon the furcal aspect of mesial roots of mandibular molars, both techniques came dangerously close to creating stripping and perforations in a high percentage of cases.
Proper cleaning and shaping of the root canal system encompasses the removal of all necrotic tissues, including pulpal tissue as well as dentin, to eliminate microorganisms and their toxic by-products. The unique features of the finely curved canals of mandibular molars often make instrumentation of these canals difficult. These features, which include curvature in two dimensions, a lack of natural taper, irregularities in shape, and the presence of calcifications, cause procedural errors such as loss of working length, apical transportation, instrument breakage, and strip perforations (1-3). Weine (1) states that the preparation of canals in mandibular molars can be consistently accomplished provided a flaring technique is used to compensate for the canal curvature and lack of natural taper. Weine et al. (3) further advocated the use of a step-back flared preparation to prevent procedural errors. Abou-Rass et al. (4) postulated that an anticurvature filing technique, which selectively removes more dentin from the outer wall, would reduce the incidence of stripping the inner (furcal) root surface. Further modifications to the stepback flaring technique have been proposed. Goerig et al. (5) proposed a step-down technique whereby the coronal portion of the canal is flared before the apical step-back procedure is performed. Kessler et al. (6) evaluated standard step-back filing techniques and coronal flaring with Gates Glidden burs or small round burs. Their results showed less risk to the furcal root
MATERIALS AND METHODS Forty extracted human mandibular first and second molars were selected for this study and stored in a 10% buffered formalin solution before use. Teeth that had incompletely formed apices, unusual root morphology, or damage from extraction were excluded from the sample. Tissue and debris were removed from external root surfaces with hand curettes. Standard access openings were made as described by Cohen and Burns (14). Internal canal morphology, apical patency, and working lengths of the canals of the mesial roots were determined with #08 and #10 K-type files. Working lengths were established by measuring the #10 file at the point it first became visible at the apex and subtracting 0.5 m m from that length. Teeth were randomly placed into two groups. The model system used for instrumentation was a modification of the method presented by Bramante et al. (15). By fabricating muffles of ticonium instead of stone and using
109
110
McCann et al.
Journal of Endodontics
these as molds for the preparation of the acrylic resin-tooth blocks, fewer muffles were required. After modifying a technique of Kessler et al. (6), sectioning of the tooth-containing acrylic resin blocks was performed as depicted in Fig. 1 using an Isomet circular diamond saw (Buehler, Ltd., Lake Bludd, I L Before instrumentation, photographs o f all sections were made with a Zeiss binocular photomicroscope (Wild HeerHeerbrugg, Heerbrugg, Switzerland) at original magnification
x 6 and x 12. The least thickness from the canal to the external root surface was recorded with a measuring reticle in 0.1-mm intervals (Figs. 2A, 3A, 4A, and 5A).
Group 1 In this group of 20 teeth, a hand instrumentation technique was used as described by Goerig et al. (5) except that Flex R files (Union Broach Corp., Long Island City, NY) were substituted for K-type files. Canals were filed to a #25 at the working length. Each canal was irrigated with 2.0 ml of 2.5% sodium hypochlorite solution between each instrument size. The final rinse consisted of sequentially flushing each canal with 5.0 ml each of 15% EDTA, 2.5% sodium hypochlorite solution, and 70% isopropyl alcohol.
Group 2
CUT
SECTION 9 FURCATION
|
'
-
~
-IKImm~
9.0 mm
F=G 1. Sectioning technique. Initial cut at furcation level with subsequent cuts progressing apically in 3.0-mm increments. Kerr of blade equals 0.3 mm.
Ultrasonic (endosonic) instrumentation was performed on 20 teeth according to the directions of the manufacturer (L. D. Caulk Dentsply, Milford, DE). The final instrument used at the working length was an ultrasonic #25 file. Each file was used in an anticurvature (4) manner for 1 min with continuous irrigation of 2.5% sodium hypochlorite solution at a rate of 20 ml per min. To complete the ultrasonic group an endosonic #35 diamond file was used to coronally flare the canal. The final rinse was identical to that described for teeth in group I. After instrumentation, the tooth sections, embedded in acrylic, were photographed again at x 6 and • 12 magnification and the least remaining thickness of dentin/cementum
FtG 2. Representative horizontal section of root at furcation level (original magnification x12). A, Preinstrumentation. Distance from canal to periphery is 2.1 mm. B, Postinstrumentation. Distance from canal to periphery is 1.5 mm.
FIG 3. Representative horizontal section of root 3.0-mm apical to furcation (original magnification • A, Preinstrumentation. Distance from canal to periphery is 1.4 mm. B, Postinstrumentation. Distance from canal to periphery is 0.9 to 1.0 mm.
Vol. 16, No. 3, March 1990
Remaining Root Thickness
111
FIG 4, Representative horizontal section of root 6.0-mm apical to furcation (original magnification x12). Arrow indicates cementodentinal junction. Note relative thicknesses of dentin and cementum. A, preinstrumentation. Distance from canal to periphery is 1.0 to 1.1 mm. B, Postinstrumentation. Distance from canal to periphery is 0.6 mm.
FIG 5. Representative horizontal section of root 9.0-ram apical to furcation (original magnification x12). A, Preinstrumentation. Distance from canar to periphery is 0_7 to 0.8 mm. B, Postinstrumentafion. Distance from cana~ to periphery is 0.7 to 0.8 mm.
was recorded (Figs. 2B, 3B, 4B, and 5B). All results were then submitted for statistical analysis. Paired t tests were used to evaluate the measured distances from the canals to the root surfaces and the percentages of original dentin/cementum thickness data. RESULTS The mean values of the least remaining root thickness at each level before and after instrumentation are shown in Tables 1 and 2, respectively. Statistical comparison of the two groups, using Student's t test, demonstrated that the differences were not significant (p > 0.05) at any of the levels. In only one instance did a perforation occur and this was in a hand-instrumented tooth 3-mm apical to the furcation (Fig. 6). Table 3 compares the two groups in the distribution of remaining root thicknesses from all measured levels. Chisquare analysis of this data showed no difference at a p of 0.05. The number of sections in each group at each level with a remaining thickness of dentin/cementum less than 0.5 m m is presented in Table 4. Similarly, Table 5 compares the two techniques at each level for the number of sections in which more than 50% of the original thickness of dentin was removed during instrumentation. Again, chi-square analysis failed to show a significant difference between the two groups (p > 0.05). Finally, after hand or ultrasonic instrumentation, the least remaining thickness of dentin/cementum 3.0- and 6.0-mm apical to the furcation was toward the distal (furcal) surface of the mesial root.
DISCUSSION The results of this study corroborate those of Pedicord et al. (12) with regard to no significant difference between the two instrumentation methods. This study and that of Pedicord et al. demonstrate a tendency to transport the canal toward the distal surface of the root. Tables 1 and 2 demonstrate that in the areas of the canals where no rotary instruments were used, the ultrasonic instrumentation technique removed a slightly greater amount of dentin. Also evident in Tables 1 and 2 was the removal of a greater a m o u n t of dentin with rotary instruments at the level 3.0-mm apical to the furcation. The area 4.0-mm apical from the canal orifice has been identified by Abou-Rass et al. (16) as especially prone to perforations in the mesial roots secondary to use of rotary instruments. Bower (17) referred to the area 2.0-mm apical to the furcation in mesial roots of mandibular molars as being concave 100% of the time. The concavity of mesial roots which has a mean value of 0.7 m m is greater than the concavity in distal roots which has a mean value of 0.5 mm. Bower (17) also stated that with greater root concavities an increased a m o u n t of cementum is found. The roles attributed to cementum are repair of damaged root surfaces and periodontal attachment (19) and not structural integrity of the root. Reduced thickness of tooth structure as measured in this and other studies (5, 12, 18) might not necessarily provide a valid indication of root integrity or resistance to obturationinduced fractures since these measurements included both cementum and dentin. A great advantage of this model system is the ability to
112
McCann et al.
Journal of Endodontics TABLE 1. Results of hand instrumentation (n = 20)
Least Dentin/Cementum Thickness from Canal to Root Surface (mm)
Level Apical from Furcation (mm)
Preinstrumented (mean -+ SD)
Postinstrumented (mean +_ SD)
(2,) 0.0 3.0 6.0 9.0
1.4 0.8 0.8 0.5
Tooth Structure Removed
Final Dentin/Cementum
(mm) (X, - X2)
as % of Original
0.4 0.3 0.1 0.1
71.4 62.5 87.5 80.0
(22)
___0.4 • 0.2 + 0.2 • 0.3
1.0 • 0.5 • 0.7 • 0.4 •
0.4 0.2 0.2 0.2
TABLE 2. Results of ultrasonic instrumentation (n = 20)
Least Dentin/Cementum Thickness from Canal to Root Surface (mm)
Level Apical from Furcation (mm)
Preinstrumented (mean • SD)
Postinstrumented (mean • SD)
(2~) 0.0 3.0 6.0 9.0
1.5 0.7 0.8 0.5
Tooth Structure Removed
Final Dentin/Cementum
(mm) 22)
as % of Original
(21 --
(22)
--- 0.3 _+ 0.1 - 0.2 - 0.3
1.1 0.5 0.7 0.4
__+0.4 ___0.2 _ 0.1 _+ 0.2
0.4 0.2 0.1 0.1
73.3 71.4 87.5 80.0
FIG 6. Horizontal section of root 3.0-mm apical to furcation showing perforation produced by hand instrumentation (original magnification x l 2). A, Preinstrumentation. Distance from canal to periphery is 0.6 mm. B, Postinstrumentation. Perforation is noted.
TABLE 3. Frequency distribution of postinstrumented dentin/cementum thicknesses (mm)
Post-instrumented Thickness Group
of Dentin/Cementum
Hand instrumented (n = 67) Ultrasonically instrumented (n = 72)
>0.5
