.archivetempcanal And Isthmus Morphology In Mandibular.pdf

Canal and isthmus morphology in mandibular incisors – An in vitro study Uma Ch.* Ramachandran S** Indira R*** and Shankar P****

ABSTRACT The aim of the study was to evaluate the canal anatomy and the presence of isthmus in mandibular incisors encountered during routine endodontic treatment and apical surgery. Fifty randomly selected extracted mandibular incisors were examined to assess root canal anatomy and presence of the isthmus. A combination method of radiography (mesiodistal and buccolingual views) and sectioning of apical 3mm (1, 2 and 3mm from the apex ) simulating a surgical resection method was followed. Radiographic study showed that 98% (49 teeth) had single portal of exit. One tooth had double portal of exit. Sectioning study showed that canal shapes varied from round to oval, long oval and ribbon shaped. Surgical microscopy and ultrasonic root end preparation enables the clinician to have better visualization for root end resection. Greater knowledge of canal anatomy in the apical 3rd of the root will help clinicians in better preparation and sealing the root canal system in this critical area. Keywords : Canal morphology, isthmus, mandibular incisors

Introduction

The prevalence of two canals in mandibular incisors has been reported to be from 11.5 – 44.1%, although many merge into one canal in the apical 1-3 mm of the root3,4,5.

For the success of endodontic treatment, awareness of normal configuration of pulp space, together with aberrations of canal anatomy is critical. In reviewing the literature, one finds a divergence of opinion concerning the anatomic configuration of the pulp cavity of mandibular incisors1. One of the reasons for endodontic failure of lower incisors is the presence of an undetected lingual canal or the presence of an untreated isthmus2. * ** *** ****

Bifurcation of the root canal in mandibular incisors may result in complications or in operative failure during endodontic therapy4. Authors studying roots with two canals commonly report an isthmus, fin or corridor, which may be present between the two canals. Green3 described this corridor as a “ribbon shaped passage”. He found this ribbon shaped passage in 22% of mandibular central and lateral incisors. Non-surgical root canal therapy failure has been attributed to an inability to debride this area adequately. In some roots with two canals, periapical surgery is required to facilitate cleaning and sealing the root apex3.

Post graduate student Professor & Principal Professor & Head of the Department Assoc. Professor Dept. of Conservative Dentistry & Endodontics. Ragas Dental College & Hospital Chennai.

7

Endodontology, Vol. 16, 2004

Historically, a steep facial bevel is required during surgical endodontics to visualize the canal space –due to the lingual inclination of mandibular incisors3. Root end resection may expose the second canal or an isthmus. Surgical microscopy and ultrasonic root end preparation enables the clinician to have better visualization for root end resection. Greater knowledge of canal anatomy in the apical third of the root will help the clinician in preparing this area and sealing the root canal system3.

Replication techniques, Ground sections Clearing techniques and Radiography. There appears to be a great disparity between different studies in the number of canals, canal exits and variations in anatomy. These differences may be due to dissimilarities in examination methods6. In the present study a combination method of radiography (mesiodistal and buccolingual radiographs) and sectioning of apical 3 mm (at 1, 2, & 3 mm from the apex), simulating a 200 surgical resection method (200 facial bevel) on mandibular incisors was followed3.

The purpose of this study was to evaluate the canal anatomy and the presence of isthmus in mandibular incisors encountered during routine endodontic treatment and apical surgery.

Fifty mandibular caries free incisors were randomly collected and stored in 10% formalin. The teeth were placed in 5.25% NaOCI for fifteen minutes after which any remaining external tissue debris was removed by scaling. Each tooth was radiographed from both facial and proximal views using intra oral Kodak E speed super polysoft size 2 periapical films exposed

Material and Methods The endodontic morphology of mandibular incisors has been studied by many investigators. Methods of study have included-

Fig. 1. Section at 1mm with single oval canal.

Fig. 2. Section at 1mm with double canals (long oval) with Type I isthmus.

Fig. 3. Section at 3mm with double canals (round shaped) with Type I isthmus

Fig. 4. Section at 3mm with double canals (ribbon shaped) with Type I isthmus

8

Uma Ch. et al.

Canal and isthmus morphology...

Table 1 : Radiographic interpretation (n-50) Canal Morphology (based on Vertucci’s classification) Type I (1)

Type II (2-1)

Type III (1-2-1)

Type IV (2)

Type V (1-2)

22 (44%)

1 (2%)

26 (52%)

–

–

Portal of Exit

Type VI Type VII Type VIII (2-1-2) (1-2-1-2) (3) –

1 (2%)

–

Single

Double

49

1

with a dental x-ray unit (Satellec at 70 Kvp, 8ma). The samples were mounted on the xray films with the help of wax in the required position and exposed, such that the cone of the x-ray machine was at 900 angle, at 16-inch object-source distance to the periapical film. All the periapical films were developed, fixed and dried by the manual method and mounted.

and evaluated for number of canals, canal shape and presence of an isthmus. Photographs were made for recording and evaluation.

Radiographs were evaluated with the help of a magnifying lens and X-ray viewer for the number of canals in the apical third and type of canal morphology. All the teeth were stored separately until sectioning was done. Angulation of 200 was marked on a wax sheet and with the help of this, it was transferred on the apical third of the root of each tooth at 1, 2, 3 mm from the apex with a pencil. The root portion of each tooth was embedded in self cure clear acrylic resin and cut over the pencil markings visible through the resin at 1, 2, 3 mm level from the apex with the help of a diamond disc mounted on a dental lathe. The sectioned specimens were placed in 5.25% NaOCI for 45 minutes to remove organic material remaining in the canal space and stored separately in vials containing saline. They were viewed under a stereomicroscope at 16X magnification from the coronal aspect

Radiographic study showed that Type III (1-2-1) morphology was seen in majority of teeth. Type I (1-1) was the next common seen. Tendency for bifurcation occurred at various levels .

Results Results of the study are tabulated in tables 1, 2, 3, 4

Sectioning study showed that canal shapes varied from round, oval, long oval and ribbon shaped at 1, 2 & 3 mm from apex. Table 2: Sectioning study (n=50) Levels of section from apex

No. of teeth Single

Double

1 mm

49

1

2 mm

50

0

3 mm

46

4

Table 3: Type of Isthmus (n = 50) Level of section from apex

Type of Isthmus

No. of teeth with isthmus

I

II

III

IV

V

1 mm

1

-

-

-

2

47

2 mm

-

-

-

-

1

49

3 mm

4

-

-

-

5

41

9

Endodontology, Vol. 16, 2004

Table 4: Shape of canals (n=50) Level of section from apex

Canal shape Round

Oval

Long Oval

Ribbon Shaped

1 mm

5

39

6

–

2 mm

7

39

3

1

3 mm

3

37

4

6

Type I, Type V isthmus was seen at 1, 2 & 3 mm sections.

The mesio-distal radiograph revealed greater width of the pulp canal, that is never visualized by routine intra oral roentgenograms, which allows room for two separate canals or one wide canal with an island of dentin in the middle. Ribbon shaped canals are common enough to be considered normal and demands special attention in cleaning and shaping10.

Discussion One of the main reasons for endodontic failure of lower incisors is the presence of an undetected lingual canal or the presence of an untreated isthmus2. In terms of success of treatment, awareness of normal configuration of the pulp space, together with aberrations of canal anatomy is critical. Mandibular incisors have been reported presenting two canals within a single root. Rankine-Wilson and Henry in 1965 observed that two canals were present in 40% of the incisors studied. These teeth presented with two foramina in 87% of the cases. Benjamin and Dowson in 1974 reported that 41% of mandibular incisors contained two canals, whereas only 1.3% presented two foramina.7

On examination of sectioned specimens, 49 of 50 teeth examined had one single canal and only one had double canals at one mm level. At two mm level, all the teeth exhibited one single canal. At three mm level of section from the apex, 46 teeth had single canal and 4 teeth had double canals. The type of isthmus was determined based on Yeung Yi Hsu classification7, which is as follows:

In the present study, radiographs were taken in both buccolingual and mesiodistal direction, as it helps in three dimensional view of a two dimensional object. Pucci and Reigh8 stated that root canals exhibit the largest number of variants in the buccolingual plane. In this study, canal morphology was determined based on Vertucci’s 9 classification. It was found that Type III (1-2-1) morphology was seen in majority of the teeth (52%). Type I (1-1) was the next common seen in mandibular incisors (44%) .The present radiographic study has shown that Type III morphology is commonly seen than usually thought. Tendency for bifurcation occurs in the middle third of the root. Bifurcation of a single canal into two canals occurred at various levels and the distance of bifurcation varied. 10

Type I

Two or Three canals with no notable communication.

Type II

Two canals that posses a definite connection between the two main canals.

Type III

Three canals that are present with a definite connection. (incomplete "C" shaped canals with three canals are also included).

Type IV

Canals extended into the isthmus area.

Type V

True connections or corriodor was present throughout the section.

Uma Ch. et al.

Canal and isthmus morphology...

The isthmus connection can be observed between any two root canal systems that occur within one root. The actual formation of the isthmus is embryonic in origin, through the epithelial root sheath. An isthmus is formed when an individual root projection is unable to close itself off. Partial fusion of root projections results in formation of two root canals with an isthmus formed in between, such as the mesial root of the mandibular first molar. No fusion leads to a large ribbon shaped canal that also forms an isthmus throughout the entire root7.

and correct interpretation of x rays and modification of the access opening where required, will assist the clinician for a more thorough assessment. Standard instrumentation techniques alone cannot clean the narrow ribbon shaped canals. Additional methods like use of NaOCl and ultrasonics should be used to clean these areas – not reachable by instruments. An isthmus opened during surgery needs to be included in the root end preparation. Surgical operating microscope should be used in critical cases as it provides better illumination with enhanced magnification for locating additional canals and identifying the isthmus in surgical procedures.

In the present study, canals that were long oval and ribbon shaped were characterized as having Type V isthmus (a true connection or corridor was present throughout the section). The canal shape did not remain constant. It generally was more ribbon or long oval shaped in 3 mm sections. However in some teeth, the apical area of the root canal was larger than the more coronal area. Four long oval and four ribbon shaped canals were characterized as having Type V isthmus (combined 1mm, 2 mm and 3 mm level sections from root apex).

References 1. Vertucci FJ. – Root canal anatomy of the mandibular anterior teeth. J. Am. Dent Assoc,1974; 89, 369-371. 2. Surgical Endodontics in Harty’s Endodontics in Clinical Practice-4th ed. 1997 pp.179. 3. Mauger MJ, Schindler WG and Walker WA. An evaluation of canal morphology at different levels of root resection in mandibular incisors. J. Endod 1998; 24:607-609.

Cleaning the apical portions of canals having oval, long oval or ribbon shape is more difficult. Generally, the canals were round or oval, closer to the apex and tended to elongate to a long oval or ribbon shape more coronally. Instrumenting the larger buccolingual dimension of the canal in these teeth is impossible with pure rotary motion. Use of NaOCl irrigation or ultrasonics is necessary along with mechanical instrumentation.

4. Madeira MC and Hetem S. Incidence of bifurcations in mandibular incisors. Oral Surg. 1973:36;589-591. 5. Kartal N and Yanikoglu FC. Root canal morphology of mandibular incisors. J. Endod 1992;18:62-564. 6. Walker RT. The root canal anatomy of mandibular incisors in a southern Chinese population. Int. Endod J 1988;21: 218-223. 7. Yi-Hsu Y, Kim S. The resected root surface. The issue of canal isthmuses. Dent Clin N Amer. 1997;41:529-540. 8. Pineda F and Kuttler Y. Mesiodistal and buccolingual roentgenographic investigation of 7,275 root canals. Oral Surg. 1972; 33:101-110.

Conclusion From the present study, it can be concluded that pulp space anatomy of mandibular incisors show high incidence of complexity which includes variations in canal configuration, number of canals and presence of isthmus. Additional radiographs taken at different angles

9. Caliskan MK, Pehlivan Y, Sepetcioglu F, Turkun M and Tuncer SS. Root canal morphology of human permanent teeth in a Turkish population. J. Endod, 1995; 21:200-204. 10. Weine FS. Endodontic Therapy 1996 5 th edn. Harcourt Brace & Co. Asia Pvt. Ltd.

11