Year : 2009 | Volume
: 27 | Issue : 2 | Page : 85--89
A scanning electron microscope study of prevalence of accessory canals on the pulpal floor of deciduous molars
Department of Pedodontics and Preventive Dentistry, V. S. Dental College and Hospital, Bangalore, Karnataka, India
V D Kumar
Department of Pedodontics and Preventive Dentistry, V. S. Dental College and Hospital, V. V. Puram, K. R. Road, Bangalore, Karnataka
The present in vitro study was carried out on 60 extracted human maxillary and mandibular, first and second primary molars, which were distributed equally into four groups to determine the prevalence, size, shape, location, and number of accessory canals in the pulpal floor of primary molars. The specimens were observed under scanning electron microscope. Out of 60, 34 teeth showed accessory canals with 97 patent canals. It was observed that maxillary molars showed a greater number of accessory canals when compared to mandibular molars, but mandibular molars showed a greater dimension in the size of the accessory canals. Round and oval accessory canals were seen, with round being more predominant.
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Kumar V D. A scanning electron microscope study of prevalence of accessory canals on the pulpal floor of deciduous molars.J Indian Soc Pedod Prev Dent 2009;27:85-89
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Kumar V D. A scanning electron microscope study of prevalence of accessory canals on the pulpal floor of deciduous molars. J Indian Soc Pedod Prev Dent [serial online] 2009 [cited 2021 May 8 ];27:85-89
Available from: https://www.jisppd.com/text.asp?2009/27/2/85/55332
The furcation area of deciduous molars is of special significance due to its close anatomical relationship with the follicle of the permanent successor. Moreover, in primary molars, pathological bone changes following pulpal necrosis are not likely to be found at the apices, but rather in the interradicular region. ,,,,, There seems to be a general consensus that a direct interrelationship exists between the pulp and the periodontal tissue. Many a times, failure of endodontic treatment has been attributed to the presence of accessory and lateral canals in both primary and permanent teeth, which makes a definitive communication between the pulp and supporting structures. 
Accessory canals, defined as a communication between the pulp tissue and the periodontal ligament other than through the root apex, are the result of a localized failure in the formation of Hertwig's sheath during embryonic stages of tooth formation. , This leads to a failure in odontoblastic differentiation and dentine formation and eventually to the formation of the accessory canal. Bacteria and toxins or products of the pulp tissue decomposition may diffuse through them to periodontal tissues. ,,
Much information on this anatomic relationship originates from studies of permanent dentition.  The documentation of accessory canals in furcation areas of primary molars is scanty. Their presence having been established, the question remains as to the frequency of their occurrence in primary molars.
The present study was undertaken with the aim to investigate the prevalence of patent accessory canals and to determine the number, size, and shape of these accessory canals in the pulpal floor of primary human molars.
Materials and Methods
Sixty extracted, human primary first and second, maxillary and mandibular molars, which were indicated for extraction due to extensive caries, periapical pathology, were collected. Caries involving the pulpal floor and root resorption, which was close to the external furcation area, were not included in the study. The teeth obtained were cleaned of surface debris and calculus, and stored in normal saline until further use.
Access cavity was prepared on each tooth using Airotor hand piece and diamond point with water coolant, and the pulp extirpation was done using a barbed broach. The crowns were separated from roots using a diamond disk in such a way that the crowns were sectioned about 2 mm above the cemento-enamel junction, so as to expose the internal furcation area. Roots were sectioned transversely about 2 mm coronal to the external furcation area. For further debridement of the specimen, they were subjected to ultrasonic cleaning for 3 minutes and it was then immersed in a 3% sodium hypochlorite solution for 5 minutes followed by rinsing under running water for 2 minutes and finally placed in saline solution.
The specimens were then mounted on aluminum stubs and were placed in a vacuum chamber of ion sputter gold coating unit model [JOEL-JFC 110 E]. A thin layer of approximately 200 A of gold, under vacuum was sputtered on to the entire internal surface of the specimen. The sample stubs were then inserted on a model [JOEL-JSM-840A] to the vacuum chamber of the scanning electron microscope (SEM) and were observed for accessory canals at a minimum magnification of 120× to a maximum magnification 1200 to determine the size, shape, location, and prevalence of accessory canals along with the main canals. Each specimen was rechecked twice at the same time and variations were noted down. Only those accessory canals which were patent were taken into consideration and those accessory canals where there was calcification or which ended into the dentin were not included; along with these few accessory canals which were observed in the pulpal floor, accessory canals found between the mesiobuccal and mesiolingual canals were excluded from the study, because they occurred on the root and not directly on the pulpal floor.
The size and shape of the accessory canals were measured at a minimum magnification of 120× at which they were visible initially. Finally findings were noted, tabulated, and analyzed for significance.
The present in vitro study was carried out on 60 extracted human maxillary and mandibular, first and second primary molars, which were distributed equally into four groups (15 teeth in each group) to determine the prevalence, size, shape, location, and number of accessory canals in the pulpal floor of primary molars.
[Table 1] shows the distribution of accessory canals in the primary maxillary first molar group where the prevalence rate was noted to be 60% with the diameter of the canal ranging from 10 µm to 100 µm, with the most common being 30 µm. The shape of the canal ranged from round to oval, with round being most prevalent.
[Table 2] shows the prevalence of accessory canals in the primary maxillary second molar group as 53.33% with the canal diameter ranging from 10 µm to 70 µm and the most common size being 20 µm and 30 µm. The shape of the canals ranged from round to oval with round being the most common.
[Table 3] shows the distribution of accessory canals in the primary mandibular first molar group where the prevalence rate was noted to be 60% with the diameter of the canal ranging from 20 µm to 100 µm, with the most common being 20 µm. The shape of the canal ranged from round to oval, with oval being most prevalent.
[Table 4] shows the prevalence of accessory canals in the primary mandibular second molar group to be 53.33% with the size ranging from 10 µm to 180 µm in diameter, with the most prevalent size being 30 µm. This group showed equal number of round and oval accessory canals.
[Table 5] shows the prevalence of patent accessory canals in all the four groups. The total number of teeth showing patent accessory canals was found to be similar to the total number of teeth showing the presence of accessory canals, but the number of accessory canals varied in all four groups.
The present study was done to investigate the prevalence of accessory canals, its size, shape, and location in the pulpal floor on 60 deciduous primary molars using SEM. A variety of techniques have been used to demonstrate the presence of accessory canals both in permanent and deciduous teeth, including radiopaque dye penetration method in conjunction with the radiograph, , topographical studies,  SEM studies, , and vulcanite perfusion technique.  Of all various methods mentioned above, SEM was preferred in the present study because it required less preparation of the specimen.  It also enhanced the inspection of the hard tissue surfaces due to high magnification provided, thus reducing the possibility of missing the accessory canals present.  With the use of SEM, a rapid survey of the structure of the foramina of the accessory canals and the dimension are possible. 
Out of 60 teeth studied under SEM, 34 teeth showed the presence of accessory canals with a prevalence of 56.66%. First primary maxillary and mandibular molars showed 60% and second primary maxillary and mandibular molars showed 53.33% of accessory canals, with variation in the number of patent accessory canals. Difference between the groups are found to be statistically non-significant P >0.05, whereas the study done by Winter et al.  found 29% of prevalence of accessory canals and a study done by Moss et al  showed 20% prevalence of accessory canals in primary molars.
The results of these two studies were very much less, when compared to the results of the present study that were high at 56.66%. This difference in the prevalence can be attributed to the difference in the methodology used. As Winter et al.  and Moss et al.  have done a histological evaluation, where there is possibility that during the sectioning and staining a few accessory canals could have been lost. Karl et al  showed 77.5% of accessory canals of the 40 deciduous second maxillary and mandibular molars with an individual prevalence of 80% in maxillary molars and 75% in mandibular molars. The results of both the studies were much higher when compared to the present study, which could be possibly attributed to the difference in the sample size . Decalcification procedure carried out before microscopic examination might have opened more accessory canals and dentinal tubules thus making their presence more evident, and in the present study only patent accessory canals were taken into consideration.
In the present study, the location and shape of the accessory canals were also evaluated. It was found that most of the accessory canals were located in the center of the furcation region. Both round- and oval-shaped canals were seen, with the round shape being more predominant. These accessory canals were smooth walled and traveled through the dentin. The similar findings were noted by Morabito et al .  and Paras et al  .
Along with this, the dimensions of the accessory canals were calculated at the least magnification at which they were visible. Most of the accessory canals were visible at 120× magnification where as the dentinal tubules were visible at a much higher magnification of 1200× [Figure 1],[Figure 2],[Figure 3]. The diameter of the accessory canals showed a wide variation among them, with the range of 10-180 µm, the prevalent diameter being 20-30 µm. Only one accessory canal measuring 180 µm and 4 canals showed 100 µm in the present study, whereas the study done by Paras  showed a diameter ranging from 6 to 43µm and 4 to 300 µm at the internal and the external furcation areas, respectively.
The diameter of the accessory canals were generally greater in the mandibular deciduous molar when compared with the first and second deciduous maxillary molars studied. In the present study, more number of accessory canals were found in the maxillary molars when compared with the mandibular molars which were similar to the studies done by Konings et al . 
Accessory canals can assume a variety of positions and locations that have been described by Yoshida et al.  who has classified these accessory canals as True, Blind, Looping and Enclosed accessory canals. It is important to know the termination of the accessory canals and the nature of the accessory canals, which is quite difficult to evaluate using SEM. Further studies are required to determine the termination of these canals.
Form the present study the following conclusions were derived:
Out of 60 teeth studied, 34 teeth (56.66%) showed accessory canals with 97 patent canals.First maxillary and mandibular primary molars showed 60%, whereas second maxillary and mandibular primary molars showed 53.33% prevalence of accessory canals in which variation in the number of patent accessory canals in individual teeth were seen.Maxillary molars showed a greater number of accessory canals when compared to mandibular molars, but mandibular molars showed a greater dimension in the size of the accessory canals.Round and oval accessory canals were seen, with round being more predominant.The size of the canals varied from a least of 10 µm to a highest of 180 µm in size, with the most prevalent size being 20 µm and 30 µm in diameter.Most of the accessory canals were located in the central region of the pulpal floor.
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