a computerized method for evaluating root canal morphology

6
0099-2399/86/1201-0002/$02.00/0 JOURNAL OF ENDODONTICS Copyright 1986 by The American Associationof Endodontists Printed in U.S.A. VOL. 12, NO. 1, JANUARY1986 SCIENTIFIC ARTICLES A Computerized Method for Evaluating Root Canal Morphology C. Vaughn Mayo, DMD, Steve Montgomery, DDS, and Carlos del Rio, DDS Access was performed on nine extracted single- rooted permanent human premolars. Complete de- bridement of the root canal system was accom- plished by running high volumes of NaOCI through them for 90 min. Volumes of the root canal system and access preparation were calculated for each specimen by weighing the teeth, filling them with contrast medium at a known density, and reweighing them. Radiographs were taken of each tooth at known angles with the contrast medium in place. Then each tooth was cross-sectioned at known dis- tances from the anatomical apex. Microscopic measurements were made of canal diameter on each cross-section. The radiographs of each tooth were evaluated by a computerized digital image processing program. Computerized calculations of canal volume and diameter were made and com- pared with the actual measurements taken from each tooth. The data were analyzed by paired t tests. Results indicate this computerized method for evaluating diameter of root canals to be accurate within 0.1 mm of actual measurements. The volu- metric data differed significantly. The difference was probably due to voids in the contrast medium. Overall, this technique appears to be very accurate in determining the anatomy of root canal systems. REVIEW OF THE LITERATURE For years clinicians have realized the role a thorough knowledge of root canal anatomy plays in successful endodontic therapy. The Washington Study reflects this significance by attributing more than 58% of all endo- dontic failures to incomplete obturation of the root canal system (1). Endodontics involves cleaning, shaping, and obtura- tion of the root canal system. To improve our success in endodontics, each of these steps should be evalu- ated and improved. To accomplish this, a tooth with a known anatomy should be evaluated throughout treat- ment to determine the effects of each stage of therapy. Work by many researchers expanded our understand- ing of the intricacies of root canals (2-8). To gather this knowledge techniques were used which either de- stroyed or altered the tooth structure, thus precluding further studies on the same teeth. In the past, investigators have studied the effects of instrumentation by working on clear resin blocks (9, 10). This technique allowed observation of the effects of instrumentation on canal morphology, but it had the disadvantage of physical differences between the resin and dentin. Other investigators have studied posten- dodontic canal morphology by clearing the teeth chem- ically to observe canal morphology three-dimensionally (11). The disadvantage here was a lack of knowledge about the pretreatment root canal anatomy. Even with such disadvantages, each of these techniques provided valuable information to the endodontic profession. To overcome some of these disadvantages, endodontics needs a model for studying canal morphology before, during, or after endodontic therapy on actual teeth. In 1967, G. N. Hounsfield applied pattern recognition techniques to X-ray images of objects taken from mul- tiple projections (12). This information was stored and analyzed by computers. The computers were pro- grammed to calculate the values of transmission read- ings through an object at many angles of scan. Com- bined, these individual images from each angle of scan were assimilated by the computer into a three-dimen- sional representation of the area scanned. With this technology computer-assisted tomography, or CAT scans, were introduced. The purpose of this study was to develop a tech- nique, utilizing computer image processing, that would allow three-dimensional imaging of root canals. MATERIALS AND METHODS Nine extracted single-rooted permanent human pre- molars with mature apices and single canals were used in this study. All teeth were stored in 10% formalin after extraction and between each phase of the experiment.

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0099-2399/86/1201-0002/$02.00/0 JOURNAL OF ENDODONTICS Copyright �9 1986 by The American Association of Endodontists

Printed in U.S.A. VOL. 12, NO. 1, JANUARY 1986

SCIENTIFIC ARTICLES

A Computerized Method for Evaluating Root Canal Morphology

C. Vaughn Mayo, DMD, Steve Montgomery, DDS, and Carlos del Rio, DDS

Access was performed on nine extracted single- rooted permanent human premolars. Complete de- bridement of the root canal system was accom- plished by running high volumes of NaOCI through them for 90 min. Volumes of the root canal system and access preparation were calculated for each specimen by weighing the teeth, filling them with contrast medium at a known density, and reweighing them. Radiographs were taken of each tooth at known angles with the contrast medium in place. Then each tooth was cross-sectioned at known dis- tances from the anatomical apex. Microscopic measurements were made of canal diameter on each cross-section. The radiographs of each tooth were evaluated by a computerized digital image processing program. Computerized calculations of canal volume and diameter were made and com- pared with the actual measurements taken from each tooth. The data were analyzed by paired t tests. Results indicate this computerized method for evaluating diameter of root canals to be accurate within 0.1 mm of actual measurements. The volu- metric data differed significantly. The difference was probably due to voids in the contrast medium. Overall, this technique appears to be very accurate in determining the anatomy of root canal systems.

REVIEW OF THE LITERATURE

For years clinicians have realized the role a thorough knowledge of root canal anatomy plays in successful endodontic therapy. The Washington Study reflects this significance by attributing more than 58% of all endo- dontic failures to incomplete obturation of the root canal system (1).

Endodontics involves cleaning, shaping, and obtura- tion of the root canal system. To improve our success in endodontics, each of these steps should be evalu- ated and improved. To accomplish this, a tooth with a known anatomy should be evaluated throughout treat-

ment to determine the effects of each stage of therapy. Work by many researchers expanded our understand- ing of the intricacies of root canals (2-8). To gather this knowledge techniques were used which either de- stroyed or altered the tooth structure, thus precluding further studies on the same teeth.

In the past, investigators have studied the effects of instrumentation by working on clear resin blocks (9, 10). This technique allowed observation of the effects of instrumentation on canal morphology, but it had the disadvantage of physical differences between the resin and dentin. Other investigators have studied posten- dodontic canal morphology by clearing the teeth chem- ically to observe canal morphology three-dimensionally (11). The disadvantage here was a lack of knowledge about the pretreatment root canal anatomy. Even with such disadvantages, each of these techniques provided valuable information to the endodontic profession. To overcome some of these disadvantages, endodontics needs a model for studying canal morphology before, during, or after endodontic therapy on actual teeth.

In 1967, G. N. Hounsfield applied pattern recognition techniques to X-ray images of objects taken from mul- tiple projections (12). This information was stored and analyzed by computers. The computers were pro- grammed to calculate the values of transmission read- ings through an object at many angles of scan. Com- bined, these individual images from each angle of scan were assimilated by the computer into a three-dimen- sional representation of the area scanned. With this technology computer-assisted tomography, or CAT scans, were introduced.

The purpose of this study was to develop a tech- nique, utilizing computer image processing, that would allow three-dimensional imaging of root canals.

MATERIALS AND METHODS

Nine extracted single-rooted permanent human pre- molars with mature apices and single canals were used in this study. All teeth were stored in 10% formalin after extraction and between each phase of the experiment.

Vol. 12, No. 1, January 1986

Coronal access was prepared in each tooth with a high-speed #557 bur and a low-speed #2 round bur. The occlusal surface of each tooth was flattened with a high-speed #557 bur to remove the occlusal anat- omy. The canals were gently broached to remove most of the soft tissue, A #10 file was placed into the canal and advanced through the apical foramen to ensure its patency. To completely debride the canal system of soft tissue, the teeth were inserted into a section of rubber tubing connected to a filtration flask assembly. A total of 3000 ml of 5.25% NaOCI was drawn through each tooth with alternating apical and coronal suction at a pressure of 300 mm Hg (Fig. 1). The total time each canal was exposed to NaOCI was 11/2 h. After this procedure the teeth were flushed with 30 ml of tap water to remove any salt accretions. A tenth tooth was debrided using the same technique. It was grooved on its long axis buccally and lingually with a high-speed #330 bur and cracked with a chisel and mallet. The halves were examined for the presence of soft tissue at x32 using a stereomicroscope (Carl Zeiss, Inc., Oberkochen, West Germany). The split halves were photographed at 1:1 using a 35-mm camera (Nikon, Inc., Garden City, NY) with a 90-mm Panagor lens (Jaca Corp., Tokyo, Japan) and a point flash (Lester A. Dine, Inc., Farmingdale, NY).

The volume of each root canal system was deter- mined in the laboratory. Each tooth was dried with apical suction and coronal air spray for 30 s. After being dried, each tooth was weighed to the nearest micro- gram with a Mettler H54AR scale (Mettler Instrument Corp., Hightstown, N J). The root canal systems and access preparations of the teeth were then filled with contrast medium. It was made by mixing 6 ml of Ethio- dol (Savage Laboratories, Missouri City, TX), one level teaspoon of barium sulfate, and the amalgam powder from 10 double spill Phasealloy capsules (Phasealloy, Inc., El Cajon, CA). The suspension was drawn through the canal system, from occlusal opening to the apical foramen, by applying apical suction while syringing it

Root Canal Morphology 3

into the access. A lentulo spiral was used to aid in the placement of the medium. When a few drops passed through the apical foramen, the tooth was disconnected from the vacuum. The excess medium was removed from the external surface of each tooth, and they were reweighed with the contrast medium in place. A known volume of medium was weighed to determine its den- sity. The volume of each tooth was calculated by sub- tracting the weight of the empty tooth from the weight of the tooth filled with contrast medium, then dividing this weight by the medium density.

Accurate radiographs taken at various angles were then made. Proper orientation of the specimens was ensured by grooving each tooth on its long axis on the facial and mesial surfaces. The mesial groove was painted with red fingernail polish and allowed to dry. A wooden stick 3 inches long was secured to the occlusal surface of each tooth with sticky wax so it pointed facially. Each tooth was positioned on an Everett Fixott grid (13) with a no. 2 periapical film directly under it. Six radiographs were exposed of each tooth. By using a protractor and the facial indexing stick, the teeth were positioned to allow the following exposures: facial, 30 deg mesial; 45 deg mesial, 90 deg mesial; 30 deg distal, and 45 deg distal (Fig. 2). All radiographs were exposed at 70 kVp, 15 ma, and 19 impulses using a long cone technique and Kodak D speed film (Eastman Kodak Co., Rochester, NY). The source to object and object to film distances were kept constant for each exposure. All films were processed in a Philips 810 automatic processor (Philips Medical Systems, Inc., Stamford, CT).

The radiographs were then analyzed by a comput- erized video image processing program, which was developed specifically for this purpose. They were pro- jected from a special viewer to a computer display monitor. The viewing area of the monitor consisted of small dots of light called pixels. There were 512 pixels per line and 480 lines on the screen. The computer program was developed to measure the gray level being

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FIG 1. Each tooth was debrided by drawing 5.25% NaOCl through its root canal system until all soft tissue was removed.

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FIG 2. A protractor was placed at the coronal end of each tooth. By utilizing the facial indexing stick, the teeth were positioned at known angles for radiographic exposure.

4 Mayo et al.

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Joumal of Endodontics

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FiG 4. Every cross-section from each tooth was oriented on a template for microscopic measurement of canal diameters.

FIG 3. The contrast medium clearly delineates the walls of the root canal system in this facial radiograph of tooth 3.

emitted from each pixel on a scale from 0 to 255. By utilizing the contrast medium in the canal, the walls were clearly demarcated (Fig. 3). The computer pro- gram selected only those gray values representing the medium and stored this information. By combining all six views, a mathematically determined three-dimen- sional representation of the canal was obtained (14, 15). From this data the diameters of each root canal system and access preparation were determined at various distances from the anatomical apex. Commonly employed mathematical procedures for calculating the volume of irregular three-dimensional objects were used. The computer divided the root canal system of each tooth into 1-mm sections from the apical foramen to the flattened occlusal surface. The mean of the apical and coronal cross-sectional area for each section was multiplied by the height (1 mm). The volumes of all of the 1-mm sections of each tooth were added together to get the total canal system volume.

Next, the teeth were dissected and the actual canal diameters were measured. Each tooth was embedded in self-curing acrylic. After curing, cross-sections were made in 1.5-mm increments from the anatomical apex with an Isomet 11-1180 low-speed saw (Buehler Ltd., Lake Bluff, IL). Eight sections were prepared for each tooth. Allowances were made for blade thickness to ensure that the cut surface corresponded to the desired

level. Each cross-section was positioned on a template using the facial and mesial orientation grooves. The canal diameters corresponding to each radiographic view were measured for each angle at each level (Fig. 4). These measurements were made at x32 using a screw micrometer ocular (Carl Zeiss, Inc.) in a Zeiss SR stereomicroscope. Photographs were taken of each cross-section at x5 with the same stereomicroscope.

The volumetric and canal diameter data collected from the teeth in the laboratory were statistically com- pared with the corresponding data collected from the radiographs by the computer program. This analysis utilized multiple paired t tests. An alpha level of p < 0.05 was set to determine significance.

RESULTS

The through-and-through irrigation of each tooth with 5.25% NaOCI successfully debdded the root canal system. Examination of the split halves of the longitu- dinally cracked tooth revealed a canal system free of debris (Fig. 5). Examination of each cross-section was made at x32 during the actual measurement of canal diameters. In every section the contrast medium closely approximated the canal wall and no soft tissue debris was seen.

The volumetric data collected in the laboratory were statistically compared with the computer calculated value using a paired t test. Results of this analysis showed a statistically significant difference at p = 0.0149 (Table 1). Based on these results, the accuracy of the laboratory technique, the computer program, or both in determining the volume of root canal systems and access preparations is questionable.

The diametric data collected in the laboratory were statistically compared with the diameters calculated by the computer program. The data were grouped by angle and level and each group was analyzed with a paired t test. Results of these tests detected no statis- tically significant difference among the 432 (6 angles x 8 levels x 9 teeth) paired measurements (Table 2). Based on these results, the program accurately meas-

Vol. 12, No. 1, January 1986

ures canal diameter to within 0.1 mm more than 95% of the time. The diametric data were further analyzed by comparing one angle to another in all possible com- binations. This additional analysis consisted of 15

FiG 5. No soft tissue is evident in the root canal system of this tooth which was cracked longitudinally following debridement.

TABLE 1. Laboratory volume versus computer volume

Laboratory Computer Volume Tooth Volume Volume Difference

(ml) (ml) (ram) 2 0.023 0,024 -0.001 3 0.023 0.023 0 4 0.029 0.037 -0.008 5 0.025 0.032 -0.007 6 0.034 0,037 -0.003 7 0.041 0,039 0.002 8 0.035 0.038 -0.003 9 0.026 0.032 -0.006

10 0.032 0.040 -0.008

Root Canal Morphology 5

paired t tests. Results of these tests detected no sta- tistically significant differences (Table 3). In other words, the diameters obtained by the computer program for any one angle were as accurate as those from any other angle.

The standard deviations and means for the residual canal diameter values (computer-laboratory data) for six angles and eight levels were plotted. Results show the mean discrepancy to be less than 0.1 mm in 100% of the cases (Fig. 6).

DISCUSSION

The introduction of a new technique usually raises many questions. Some questions about this computer

TABLE 3. Probability value of residual diameters for each angle versus every other angle*

Angles M90 M45 M30 F D30 D45

M90 0.007 0 ,011 0.004 0.096 0,011 M45 0,788 0,772 0.214 0.375 M30 0.600 0.267 0.477 F 0.082 0.230 D30 0.507 D45

�9 Significance level is p < 0.05 and with alpha adjustment p < 0.003.

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FiG 6. The data derived in the laboratory was subtracted from the corresponding computer data. This residual value for each angle and each level was plotted. Each group of eight lines represents one angle. Each individual line represents the range of values at one level. The left line in each group is level 1 and the r ight line is level 8.

TABLE 2. Probability values of computer versus lab diametric data at each level for each angle*

Angles Levels

1 2 3 4 5 6 7 8

M90 0.438 0.169 0.169 0.351 0.195 0.104 0,121 0.347 M45 0.347 0,095 1.000 1.000 0.081 0.214 0.195 0.325 M30 1.000 0.104 0.272 0.598 0,347 0.195 0,195 0.681 F 0.035 0,594 0.594 0,598 1.000 0.594 1.000 0.272 D30 1,000 0,081 0.512 0,087 0,512 0.782 0,397 0,512 D45 0.594 0.447 0.792 0,170 1.000 1.000 0,139 0,594

* Significance level is p < 0.05 and wi th alpha adjustment p < 0.001.

6 Mayo et al.

technique can be answered with logic and some may require technique modification to address them. An obvious question is, how accurately does the computer program calculate canal volume? In all but one instance the calculated volume was greater than the volume measured in the laboratory. In five of nine teeth, the volumes were within 8% of each other. In the remaining teeth the differences were greater. In every case in which a large difference occurred, the 90-deg mesial radiograph showed large and obvious voids in the contrast medium (Fig. 7). The laboratory volume was determined by dividing the weight of the contrast me- dium in the root canal system by the density of the medium. Therefore, any void in the medium would result in measured volumes being less than calculated vol- umes. A better contrast medium or a better method of inserting it into the canal needs to be developed, and this portion of the study needs to be repeated.

Root canal diameter measurements from the radi- ographs were actual measurements made by the com- puter program. The monitor of the video imaging sys- tem was divided into small dots or pixels. There were 512 pixels per line and 480 lines on the screen. This pixel density determined the resolution capacity of the video imaging system. With this system the resolution capacity was between 0.06 and 0.1 mm. Possible sources of error between laboratory measurements and computer measurements include: failure to position

FIG 7. Voids are obvious in this 90-deg mesial radiograph of tooth 4.

Journal of Endodontics

each cross-section so it accurately corresponded to its angled radiograph; failure to section each specimen so the cut surface accurately corresponded to the level being measured by the computer; or failure of the contrast medium to demarcate adequately the walls of the root canal system. Because of the lack of statisti- cally significant differences between the laboratory and computer data, these sources of error were apparently well controlled.

The diametric data were analyzed with multiple paired t tests. When they are performed at an estab- lished significance level, the probability value must be corrected by dividing the selected probability value by the number of multiples. This statistical technique is an example of alpha adjustment which is done to reduce the chance of committing a type I (false positive) error. The probability values are listed for multiple paired t tests in Tables 2 and 3. The corrected probability values for each of these tables would be 0.001 (0.05 of 48) for Table 2 and 0.003 (0.05 of 15) for Table 3. Although some probability values approach the adjusted alpha level, none are significant statistically.

Ongoing research will attempt to reduce sources of error inherent in this technique. Higher quality cameras and monitors will enable the video imaging system to produce better resolution. Xeroradiography may pro- duce more suitable images due to superior edge en- hancement when compared with conventional radi- ographs. These improvements should allow the use of a less opaque contrast medium and one with better handling properties. Successful resolution of these ob- stacles may result in a technique that can determine root canal system anatomy at anytime before, during, or after an endodontic procedure.

Digital image processing could also be adapted for educational purposes. Efforts have already been made to incorporate computer graphics into dental school endodontic courses (16). This attempt was limited to teaching root canal anatomy. Developed to its full po- tential, digital image processing could provide a subjec- tive method for evaluating student performance in pre- clinical endodontics.

There are many areas in research where such a technique would be useful. The digital image processing system is capable of producing graphic information in addition to the data output. The program allows cross- sectioning of the tooth at any level and produces line drawings representing the cut surface (Fig. 8). These drawings are produced using curve smoothing tech- niques to connect the points input from the radiographs. Instrumentation studies could be performed by overlay- ing preoperative and postoperative line drawings of each tooth. This would allow researchers to follow sequentially the changes in canal shape with each instrument introduced into the root canal system. Ob- serving procedural accidents such as zipping, trans- portation of the apical foramen, or strip perforations as

Vol. 12, No. 1, January 1986

3 6

5

,4

9

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7

FtG 8. Line drawings representing the tooth and canal outl ines were generated from the computer program. This display represents eight cross-sect ions taken at 1.5-mm increments from the apex of tooth 3.

they occur would allow elimination of any particular size or type of instrument, or any instrumentation technique found to be causing these problems. In this manner digital image processing could be very useful in devel- oping and studying instrumentation techniques and in- strument design.

CONCLUSIONS

1. The debridement technique used in this study appears to remove all soft tissue from the root canal system visible at x32.

2. Overall, this technique appears to be very accu-

Root Canal Morphology 7

rate in determining the anatomy of root canal systems. 3. The development of this new technique will allow

observation of the changes in the root canal system produced by root canal therapy. Possible applications of this technique in the fields of research and education are very promising. Additional studies are planned to investigate these applications.

We wish to thank Bill Rogers for developing the computer program and Robert Wood for the statistical analysis.

Dr. Mayo is now in private practice in Virginia Beach, VA. Drs. Montgomery and del Rio are affiliated with the Department of Endodontics, University of Texas Health Science Center, San Antonio, San Antonio, TX.

References

1. Ingle JI, Beaveridge EE. Endodontics. 2nd ed. Philadelphia: Lea & Febiger, 1976:43.

2. Hess W. Anatomy of the root canals of teeth of the permanent dentition. London: John Bale, Sons and Danielson, Ltd., 1925.

3. Green D. Morphology of the pulp cavity of the permanent teeth. Oral Surg 1955;8:743-59.

4. Kuttler Y. Microscopic investigation of root apexes. J Am Dent Assoc 1955;50:544-52.

5. Vertucci F, Seelig A, Gillis R. Root canal morphology of the human maxillary second premolar. Oral Surg 1974;38:456-64.

6. Vertucci F, Williams R. Furcation canals in the human mandibular first molar. Oral Surg 1974;38:308-14.

7. Vertucci F. Root canal morphology of mandibular premolars. J Am Dent Assoc 1978;97:47-50,

8. Vertucci F. Root canal morphology of the maxillary first premolar. J Am Dent Assoc 1979;99:194.

9. Weine F, Kelly R, Lio P. The effect of preparation procedures on original canal shape and on apical foramen shape. J Endodon 1975;1:255-62.

10. Weine F, Kelly R, Bray K. Effect of preparation with endodontic hand- pieces on original canal shape. J Endodon 1976;2:298-303.

11. Robertson D, Leeb J. The evaluation of a transparent tooth model system for the evaluation of endodontically filled teeth. J Endedon 1982;8:317- 21.

12. New P. Computer-assisted tomography. J Am Med Assoc 1975;232:941-3.

13. Everett F, Fixott H. Use of an incorporated grid in the diagnosis of oral roentgenograms. Oral Surg 1963;16:1061-4.

14. Gonzalez R. Digital image processing. Reading: Addison-Wesley, 1982:1-23.

15. Castleman K. Digital image processing. Englewood Cliffs, NJ: Prentice- Hall, 1979:1-16.

16. Pao YC, Reinhardt RA, Krejei RF, Taylor DT. Computer graphics aided instruction of three-dimensional dental anatomy. J Dent Educ 1984;48:315-7.