|Year : 2017 | Volume
| Issue : 2 | Page : 92-96
Unevenness of apical constriction of maxillary incisors and canines: An in vitro study
Siddarth Suthar, Rupal Vaidya, Shraddha Chokshi, Zarna Sanghvi, Pruthvi Patel, Purav Mehta
Department of Conservative Dentistry and Endodontics, Ahmedabad Dental College and Hospital, Ahmedabad, Gujarat, India
|Date of Web Publication||25-Apr-2017|
Ahmedabad Dental College and Hospital, Bhadaj.Ranchhodpura Road, Santej, P. O. Rancharda, Kalol, Ahmedabad, Gujarat
Source of Support: None, Conflict of Interest: None
Aim: To examine and measure a possible skew in the longitudinal position of the apical constriction in human maxillary central incisors, lateral incisors, and canines around the circumference of the canal.
Materials and Methods: Twenty-five human maxillary central incisors, lateral incisors, and canines were split and imaged with ×25 magnification. The most apical and coronal limits of the apical constriction were identified and measured.
Results: Analysis of the data indicates that a majority (>64%) of maxillary central incisors, (>69.6%) lateral incisors, and (>70%) of canines exhibit an unevenness or “skew” of the apical constriction of >100 μ m in the incisoapical dimension. A statistically significant (P < 0.05) variation in the longitudinal position of the apical constriction around its circumference was confirmed in maxillary central incisors.
Conclusion: The termination of working length is more likely to end in an apical constriction zone rather than at an apical constriction point or plane.
Keywords: Apical constriction, apical foramen, root apex, skew
|How to cite this article:|
Suthar S, Vaidya R, Chokshi S, Sanghvi Z, Patel P, Mehta P. Unevenness of apical constriction of maxillary incisors and canines: An in vitro study. Saudi Endod J 2017;7:92-6
|How to cite this URL:|
Suthar S, Vaidya R, Chokshi S, Sanghvi Z, Patel P, Mehta P. Unevenness of apical constriction of maxillary incisors and canines: An in vitro study. Saudi Endod J [serial online] 2017 [cited 2018 May 25];7:92-6. Available from: http://www.saudiendodj.com/text.asp?2017/7/2/92/205125
| Introduction|| |
Successful and predictable root canal therapy requires an in-depth knowledge of root anatomy and an appreciation of the microanatomy of the root apex. Kuttler  remarked that a hermetic seal beyond the apical constriction was not possible, unless overfilled with cement, because of the funnel-shaped widening of the canal beyond this point. The primary objective of nonsurgical endodontic therapy is a thorough cleaning, shaping, and obturation of the total length of the root canal system  up to apical constriction. Ending instrumentation and obturation at this point creates the smallest wound area between pulpal and periapical tissues and minimizes the tissue surface area exposed to toxic irrigants and obturation materials. Achieving this objective will maximally reduce the number of microorganisms and pathologic debris, resulting in an increased chance for healing of the periapical tissues, and a successful outcome of nonsurgical root canal therapy.
A hallmark of the apical region is its variability and unpredictability. Because of the tremendous variation in canal shapes and diameters, there is concern about a clinician's ability to shape and clean canals in all dimensions. However, it is worth noting that the apical constriction may not always be present or easily identifiable.,
The location of the apical constriction can be highly variable in the longitudinal aspect of the canal., In one study, it was found that 92.5% of constrictions were between 0.5 and 1.0 mm from the apex. The pulp canal, also, does not always terminate at the anatomic apex of the root.
The apical constriction has also been shown to deviate from a purely circular shape in the cross-sectional dimension. Horizontal sections of the apical 5 mm of root apices revealed that 25% of apical canals had diameters two times larger in the long canal diameter than in the short canal diameter, creating a long oval shape.
Various studies have been conducted that describe the shape and diameter of the apical constriction in the horizontal dimension and its position in the longitudinal direction in relation to anatomic apex, major foramen, and cemento-dentinal junction. None of these studies, however, examined the extent of the apical constriction in the vertical or longitudinal dimension of the canal. In the past, only a few studies have considered that the apical constriction is not flat but is actually uneven, skewed, or undulating in a coronal to apical dimension as it traces a path around the circumference of the apical canal. Dummer et al. classified the apical constriction into four types: Traditional single constriction, the tapering constriction, the multiconstricted, and the parallel constriction. However, the study did not measure the unevenness of the apical constriction. Olson et al. examined the longitudinal position of the apical constriction in human maxillary central incisors. They found that over 70% of teeth deviated more than 0.1 mm in the longitudinal extent of the apical constriction. They concluded that when using the apical constriction as a reference point, the working length does not end in an apical constriction point but in an apical constriction zone. The study conducted by Olson et al. was the first study in which longitudinal skew of apical constriction was studied. This is the second study to date that examines this third dimension of the apical constriction for maxillary central incisor and the first study that examines this same dimension for maxillary lateral incisor and canine.
The purpose of this study, therefore, was to examine and measure a possible skew in the longitudinal position of the apical constriction in human maxillary central incisors, lateral incisors, and canines around the circumference of the canal. This has implications in determining optimal working lengths because the apical constriction might not be of uniform depth (longitudinal position) at all points around its circumference.
| Materials and Methods|| |
Twenty-five extracted human maxillary central incisors, lateral incisors, and canines for a periodontal reason each were selected for this study. Criteria for teeth included in this study were those with a mature and intact apical root without signs of resorption or fracture. All teeth were sectioned under a dental operating microscope (Labomed-Labo America Inc., CA, USA) at ×10 magnification by using a diamond disk in an electric handpiece (NSK EX 6-BM-Buffalo Dental, Syosset, NY, USA) under running water. Two longitudinal slits were made in the root apex on opposite sides of the major foramen but without involving it in the cut. These slits were made as close to the center of the major foramen as possible in an effort to create two equal halves when split. Roots were sectioned horizontally approximately 8 mm from the apex to separate them from the coronal tooth segment. By using a thin chisel and avoiding transecting the apical 2–3 mm, only slight pressure was required to separate the sectioned roots into opposite halves. The separated root halves were immersed in 3% sodium hypochlorite (Vishal Dentocare Private Limited, Ahmedabad, Gujarat, India) to remove all pulp tissue remnants and debris from the now exposed canal space. Samples were stored in separately numbered vials containing deionized water. Hematoxylin staining was used to add definition and contrast to the samples before imaging. Each root sample was imaged at ×25 magnification using a dissecting microscope (Olympus SZX 7, Pennsylvania, USA) and a color imaging camera (Olympus E-330, Pennsylvania, USA). An eyepiece micrometer was used for roughly measuring the constriction.
Final measurements were made with Image J software from the National Institutes of Health. Images were sharpened by this software for further clarity before measurement. For avoiding subjective errors related to the observer while recording the distance in the software, observation was taken by two observers and analyzed for correlation between the observations. The most incisal and most apical limits of each apical constriction sample were identified, and the distance between these limits was measured and recorded for each sample [Figure 1]. This represents the skew of the apical constriction in the longitudinal dimension of the canal. To more closely represent the limitations of clinical measurement and instrumentation, a skew measurement up to and including 100 μ m was arbitrarily considered to still represent a “flat” apical constriction. Teeth were evaluated for skew of the apical constriction beyond 100 μ m with the Chi-square test (P < 0.05).
|Figure 1: Digital image of a sectioned root half showing distortion of the apical constriction in the longitudinal dimension of the canal. Bold arrows identify the coronal and apical limits of this apical constriction. The distance between these limits (black double arrow) is the longitudinal skew that was measured|
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| Results|| |
The correlation between the data obtained from the two observers
The correlation between the observations of the two observers was tested by Karl Pearson's correlation test, and it was found that the correlation value was very near to 1 (0.999) in all the three tooth groups signifying perfect positive correlation and reproducibility of the result with two different observers. Finally we consider initial observer 1 as a final observer for this study.
Comparison of the obtained values with the hypothesized value (the null hypothesis)
The null hypothesis formulated for this study was that there is no significant difference between hypothetical incisoapical distance value (100 μ m) and obtained sample mean (level of significance 0.05 considered for this study). The comparison was done using one sample t-test [Table 1],[Table 2],[Table 3]. It was found that there was a statistically significant difference between the obtained incisoapical dimension of the apical constriction and the value hypothesized that is 100 μ m. Thus, the null hypothesis is rejected.
|Table 1: One sample statistics of maxillary central incisor group obtained by performing t-test|
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|Table 2: One sample statistics of maxillary lateral incisor group obtained by performing t-test|
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|Table 3: One sample statistics of maxillary canine group obtained by performing t-test|
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Statistical comparison of the incisoapical distance of apical constriction of each tooth group with the other
Independent t-test was performed to check the difference between the obtained mean values incisoapical extent of the apical constriction of three tooth group [Table 4],[Table 5],[Table 6]. In this study, the difference in the mean values obtained for each tooth group was found to be insignificant (>0.05). The results of the analysis showed no significant difference in the skewing of apical constriction of all the three tooth groups and there was the only minor difference in the relative unevenness of the three tooth group.
|Table 4: Group statistics showing the comparison of the central incisor and lateral incisor group using independent t-test|
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|Table 5: Group statistics showing the comparison of the central incisor and canine group using independent t-test|
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|Table 6: Group statistics showing the comparison of the lateral incisor and canine group using independent t-test|
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The results of the study are summarized as follows:
- The overall average of skew in the longitudinal position of the apical constriction around the canal for maxillary central incisor group was 162.68 μ m. The maximum and minimum skews measured were 581 and 0 μ m, respectively. Sixty-four percent of the evaluated teeth had skew more than 100 μ m of the skew
- The overall average of skew in the longitudinal position of the apical constriction around the canal for maxillary lateral incisor group was 172.87 μ m. The maximum and minimum skews measured were 355 and 0 μ m, respectively. Nearly 69.56% of the evaluated teeth had skew more than 100 μ m of the skew
- The overall average of skew in the longitudinal position of the apical constriction around the canal for the maxillary canine group was 166.65 μ m. The maximum and minimum skews measured were 338 and 9 μ m, respectively. Seventy percent of the evaluated teeth had skew more than 100 μ m of the skew
- Statistical analysis of this data shows that a significantly greater number of apical constrictions were skewed or showed a measured variation beyond 100 μ m in all the three tooth groups in longitudinal position around the canal circumference relative to chance
- There appeared to be no significant difference between the skew in the longitudinal position of the apical constriction around the canal between all the three tooth groups studied.
| Discussion|| |
In this study, we examined and measured the apical constriction along the longitudinal axis of the canal. Our goal was not to measure the location of the apical constriction from the anatomic apex but rather to determine whether the constriction itself is on a level plane, or whether it is uneven as it traces a path around the circumference of the canal. This unevenness was evaluated by measuring the distance between the most coronal and apical limits of the apical constriction as identified on a magnified image of a longitudinal cross section of the root apex.
The measurement was made in relation to the projected path; an endodontic file would take as it negotiates the canal and apical constriction.
Despite delicate and careful handling of specimens during the processing, two canine specimens and two lateral incisor specimens failed because of fracture of the apical segment of the sectioned half.
In the previous study conducted by Olson et al., only one tooth type was examined, that is, maxillary central incisor. The results obtained in this study were in accordance with Olson's study. The mean unevenness of the three groups of teeth was also compared with each other statistically, but no significant difference was found between the three groups.
To more closely represent the limitations of clinical measurement and instrumentation, a significant skew of the apical constriction was defined as a measurement exceeding 100 μ m between the incisal and apical limits of apical constriction. In other words, unevenness of the apical constriction up to and including 100 μ m was still considered to be a flat ring or a flat constriction that an endodontic instrument would meet at the same level at all points around its circumference. Our results show that the apical constriction of more than 64% of human maxillary central incisors examined was not planar but was actually uneven or skewed by more than 100 μ m. In a study performed by Olson et al., 70% of human maxillary central incisors examined had nonplanar apical constriction skewed more than 100 μ m. Similarly, for maxillary lateral incisors, 69.6% specimens had nonplanar constriction skewed more than 100 μ m and for canines, 70% specimen studied had nonplanar constriction skewed more than 100 μ m.
When adjusting working lengths to the level of the apical constriction, it is a common clinical practice to adjust measurements to an accuracy of 0.5 mm. The maximum amount of apical constriction unevenness observed in this study, however, was 0.581 mm for maxillary central incisor, 0.355 mm for lateral incisor, and 0.338 mm for canines. However, the observation of 0.581 mm incisoapical unevenness of apical constriction was a single isolated reading exceeding the accuracy limit of 0.5 mm for working length adjustment. In this regard, our measurements of constriction unevenness, while significant within the parameters of this study, might or might not significantly affect the clinical working lengths. However, these results might be important in interpreting the measurements obtained by newer, more accurate electronic apex locators.
In a study of the accuracy of the Root ZX electronic apex locator, Pagavino et al. found that when the Root ZX indicated the file tip was at the apical foramen, it was actually, on average, 0.395 mm beyond it. On the basis of these findings, they recommended withdrawal of the instrument by 0.5–1.0 mm to avoid over instrumentation. These results could be interpreted differently with an uneven apical constriction. One might be 0.395 mm beyond the constriction at one point on the canal wall while exactly at or near the constriction at another point around the circumference of the canal. This could produce working lengths that are simultaneously short and long when ending working lengths at an uneven apical constriction. The apical anatomy of the root canal can be very unique from apex to apex. In addition to the unevenness of the apical constriction found in this study, other apical landmarks have shown variance as well. Ponce and Vilar Fernández  found the cemento-dentino-canal junction to have great variability in depth within the apical portion of the canal, depending on which point was examined on the canal wall. It is also important to keep in mind the comparisons and limitations between the dynamic variations found in the apical portion of the canal and the unvaried or rigid dimensions of our endodontic armamentarium. Matching our instruments and materials to the varied anatomy of the apical canal might be much like the common phrase, “making a square peg fit in a round hole."
| Conclusion|| |
In determining accurate working length to the level of apical constriction, our finding indicates the termination of working length is more likely to end in an apical constriction zone rather than at an apical constriction point or plane.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6]