University of São Paulo, Faculty of Odontology of Ribeirão Preto,
Department of Restorative Dentistry

ENDODONTIC RESEARCH LABORATORY

External and Internal Anatomy of Mandibular Canines with two roots

Anatomia interna e externa dos caninos inferiores com duas raízes

Ranjna Sharma

 

An elective study presented to the Faculty of Dentistry-University of Birmingham for the Degree of Bachelor of Dental Surgery.

Advisor in Brazil: Prof. Dr. Jesus Djalma Pécora
Advisor in England: Dr. Adrian Damian Walmsley
Ribeirão Preto SP and Birminghan UK, 1994, 43p.


SUMMARY | RESUMO | INTRODUÇÃO | REVISÃOPROPOSIÇÃOMATERIAL E MÉTODO | RESULTADOS | DISCUSSÃO | CONCLUSÕES | REFERÊNCIAS



 

INTRODUCTION

     As early as 1844 researchers were beginning to investigate tooth anatomy, at which time Carabelli employed simple methods of direct observation to study human teeth. He provided the most detailed description of the root canals (i.e. number and course) prior to 1891. In 1902 GV Black emphasized the importance of the acquirement of knowledge of the details of specific forms of human teeth. Since Blacks time extensive research has been ` carried out in the field of dental anatomy. In 1901 novel methods were being utilized to investigate internal tooth anatomy. Preiswerk injected molten Wood's metal into root canals to analyze the presence of lateral canals and anastomoses in mesio-buccal roots of upper molars and mesial roots of lower molars.

Fisher (1907) used celluloid acetone instead of molten Wood´s metal followed by decalcification.

 Grove (1916) injected vulcanite into the canals and decalcified using 5 % nitric acid and rendered the teeth transparent using glycerin.

Callahan (1916) reiterated the importance of knowledge of internal anatomy and in 1917 Hess used the decalcification and diaphanization technique to study internal anatomy and drew several conclusions from his findings. He found that 1.6% of mandibular canines examined, presented with two roots.

 Interestingly enough in 1993 Matzer found in his research concerning the anatomy of teeth of Maiz Indians of Guatemala Republic, that the incidence of two rooted canines was as much as 4.1%.

 Pineda and Kutler (1972) categorized the methods used by various researchers as follows: Direct observation with the aid of a microscope, macroscopic section, microscopic section, transverse sections and micrometric measurements, examination of intraoral radiographs, filling and decalcification, filling and clearing and finally grinding and radiography.
 And so the number of methods possible for the study of tooth anatomy increases as researchers continually investigate new techniques and modify the old.  We now recognize that for each group of teeth numerous variations of external and internal anatomy may be observed. It has become evident that the internal anatomy of root canals does not reproduce the simplicity of the external anatomy of the tooth.

 Why has it become so important to scrutinize the macroscopic appearance of individual teeth Black (1902) believed it necessary to provide a systematized nomenclature of the several parts of the tooth in detail.

 However, since the advent of endodontic therapy it has become mandatory to recognize the possible permutations of internal canular morphology in order to provide road maps to successful endodontics. The main objective of endodontic therapy is the thorough mechanical and chemical cleaning of the entire pulp cavity and its complete obtrusion with an inert filling material.

 In todays climate of affairs the medico-legal consequences of poor endodontics must be bourne in the forefront of the proffessionals mind. It has become increasingly more important to prolong the life of the natural dentition using conservative methods to retain the correct occluso-vertical dimension for preservation of pleasing facial aesthetics.

 Several researchers have investigated failure of root canal therapy due to lack of knowledge of both external and internal tooth anatomy.

 In 1982 Robertson and Leeb described the use of the diaphanization method to determine the quality of obtrusion based on the physical appearance of the fill. His experimental method was aimed at being able to visualise the result of instrumentation and obtrusion, in-situ, to provide a mechanism to evaluate endodontic filling techniques, and also to allow a critical self evaluation of practical ability. These methods also provide an insight into possible deviations from the norm which must always be anticipated. For example, Pécora et al (1993) presented a case of endodontic conservative treatment of a maxillary incisor with an atypical crown and type III dens invaginatus. It was found that the root canals were difficult to locate due to the atypical internal anatomy and thus similarly, a tooth with a normal crown appearance may present with aberrations in root morphology.

 Ferraz and Pécora (1992) also investigated racial variations in root anatomy which can lead to therapeutic failure if not recognised. Racial anatomic variations have also been demonstrated by Souza-Freitas et al (1971) and Trope et al (1986).

 Hence it follows that the use of transparent teeth is indicated in the study of canal anatomy, the teaching of instrumentation and obtrusion techniques and facilitates the learning of endodontic methods, clarifying technical errors not evident clinically.

Glass tubes have been used as transparent root canals, however there is no similarity between the surface of the tubes and the contours of the prepared teeth. The clearing technique gives a three dimensional view of the pulp cavity in relation to the exterior of the tooth. Pao et al (1984) explored the use of computer graphics as an aid to teaching dental anatomy, particularly with respect to the relationship between the pulp and the external tooth morphology in various planes.

 A knowledge of the variations in the anatomy of two rooted mandibular canines as observed in this investigation, will assist the dentist in reaching conclusions when diagnosing and treating endodontic cases of these teeth.


REVIEW OF LITERATURE

Maxillary Molars

 Weine (1982) has stated that the frequent failure of endodontic treatment of maxillary molars is likely due to failure to locate and fill the second mesiobuccal root canal, principally in the first permanent maxillary molar.

 Hess (1925), Okumura (1927), Pucci and Reig (1944), Pineda (1973), De Oeus (1986); Silveira and Soares (1983), Neaverth et al (1987) have reported the existence of two canals in the mesiobuccal root.

 Pécora et al (1992) studied the internal anatomy of three hundred and seventy (370) decalcified and cleared human maxillary molars. The authors observed that 25% of first molars, 42% of the second molars and 36% of third molars studied, presented with four root canals. They observed that the incidence of two root canals in the mesiobnccal root was higher in second maxillary molars than in first molars.

Maxillary Premolars
First

 In order to perform endodontic treatment skillfully and effectively, It is imperative tl; the dentist know tooth anatomy, particularly the internal anatomy.

 A lack of knowledge of internal anatomy and its variations will undoubtedly lead to an error in localization, instrumentation and obtrusion of root canals.

 Before initiating endodontic treatment, the dentist ought to routinely take two or three radiographs, each at a different angle, to show the exact anatomic variations.

 The internal anatomy of the maxillary premolars is particulary complex due to their variation in number of roots and canal configurations.

 Several researchers have reported a low incidence of maxillary first premolars with a single canal (Okumura, 1927; Green, 1973; Vertucci and Gegauf, 1979; Bellizzi and Hartwell, 1985).

 Hess (1925), Barrett (1925), Pineda and Kutler (1972) and Walker (1987) observed an incidence of a single canal above 10%.

 The presence of three canals in the first premolars is relatively low; 35 were found by Bellizzi and Hartwell (1985), none were found by Okumura (1927), Green (1973) and Walker and Quackenbush (1985).

 Pécora et al (1991) studied the external and internal anatomy of 240 extracted maxillary first premolars. The external anatomy was studied by measuring each tooth and by observing the direction of the root curvature from the facial and proximal aspects. The internal anatomy of the pulp cavity was studied by a method of making the teeth transparent. A total of 55.8% of the teeth had a single root, 41.7% had two roots and 2.5% had three roots. Consíderíng all of the first premolars studied, the authors found 17.1% had one canal, 80.4% had two canals and 2.5% had three canals.

 The discrepancy in a larger number of multiple canals that are found could be due to  Various factors, such as; great antomical variation of these teeth, methods used and racial differences.

In the past, many dentists have treated maxillary first premolars assuming them to have just two canals. This should change because we now know that between 0.5% and 7.5% of these teeth have three canals ( Hess, 1925; Barrett, 1925; Pucci and Reig, 1944; Pineda and Kutler, 1972; Carns and Skidmore, 1973; Vertucci and Gegauf, 1979; Bellizzi and Hartwell, 1985; De Deus, 1986; Pécora et al, 1991).  Despite the low incidence of three canals, the possibility cannot be overlooked.

Maxillary Premolars
Second

Pineda and Kutler (1972), Green (1973) did not fmd maxillary second premolars with three canals, however; Hess (1925), Vertucci and Gegauff (1979), Bellizzi and Hartwell (1985), De Deus (1986) and Pécora et al. (1992), all did.

 Pécora et al (1992) studied "in vitro" the internal anatomy of 300 maxillary second premolars and observed that one canal was found ín 67.3% two canals in 32.4% and three canals in 0.3%. A total of 90.3% had one root and 9.7% two roots. The direction of curvature was predominantly distal in maxillary sccond premolars with both one or two roots.

MaxiIlary Anterior Teeth.

 Maxillary canínes are the largest teeth of the human dentition. ln spite of theìr measurements these teeth present difficulties in radiographic examination. The maxillar canines frequently present with a single root.

 The region of the maxillary incisors corresponds to an area of embryological risk, presenting a variety of malformations: Cleft lips, supernumerary teeth, peg shaped teeth, shovel shaped teeth, dens invaginatus and talon cusps.

 Pécora et al (1992) published a case report about dens invaginatus in a maxillary canine and Pécora et al (1993) related a case of endodontic conservative treatment ~f a maxillary central incisor with an atypical crown and type III dens invaginatus..

 Pécora and Cruz Filho (1992) investigated the incidence of radicular grooves in the upper incisors of 642 patients. Radicular grooves present in 3.9% of the patients, were found mainly on the lingual surface of the maxillary lateral incisor (3.0%). The maxillary central incisor showed radicular grooves on both the buccal and lingual surfàces with an incidence of 0.9%. It was not possible to relate the incidence of these grooves with race (white and negro) or sex.

 Pécora et al (1993) presented a case report of a maxillary lateral incisors as teeth with one root and one root canal in 100% of cases (Pucci and Reig, 1944; Ingle and Beveridge, 1976; Weine, 1982; De Deus, 1992). However, this is not always true as several authors have published cases of maxillary lateral incisors with two roots (Swazey, 1888; Madeira, 1973; Christie et al, 1981; Moraes, 1983; Zillich et al. 1983: Thompson et al 19R5: Fahra-Campos, 1990; Pécora and Santana, 1 991).

Mandibular Molars

 Three-rooted mandibular molars may be observed in patients of mongolian, caucasian and negro origin. Pucci and Reig (1944) verified an incidence of 5.5% of mandibular molars with three roots in a sample of teeth &om the population of Uruguay.

 De Deus (1960) reports an incidence of 2.5% of molars with three roots in a sample of teeth from patients in the Southeast of Brazil. Teixeira (1963), citing an incidence of 10%, reported this extra-root to be smaller than normal roots in the disto-lingual position.

 Souza-Freitas et al (1971) using radiographic examination, observed a presence of 17.8% of mandibular first molars with three roots in patients of Japanese descent and only 4.3% in patients of European descent.

 Ferraz and Pécora (1992) using radiographic examination of 105 patients of mongolian origin, 106 of negro origin and 117 of caucasian origin observed that the mongolian race showed a greater incidence of three rooted mandibular molars ( 1. mongolian patients, 7.5% of the negro patients and 6.8% of caucasian patients).

 The authors did not fmd a statistically significant difference with respect to sex and incidence of this extra-root.

 According to literature reviews, a high incidence of mandibular molars with three roots was found in people of mongolian origin (Japanese, Malaysian, Chinese, Thai, Eskimo, Aleutan, American indian) Tratman (1938), Reichart and Metath (1981), Walker and Quakenbush (1985).

 Several researchers have studied the internal anatomy of mandibular premolars (Pineda and Kutler, 1972; Green, 1973; Vertucci, 1984; DeDeus, 1986; Pécora et al, 1991). Pécora et al (1991) studied the internal anatomy of mandibular premolars by the decalcification-diaphanization technique, and it was observed that 27.45% of the first mandibular premolars presented with two canals (22.3% with two canals and two foramina and 5.12% with two canals and one foramina). Only 9.7% of second mandibular premolars analysed, presented with two canals (5.3% with two canals and two foramina and 4.4% with two canals and one foramina). The incidence of three canals with three foramina was significantly low (0.46%) in both first and second premolars. With respect to mandibular premolar length, the first premolars presented a maximum value of 26.8 millimetres, a minimum of 18.1 millimetres and an average of 21.5 millimetres. The second mandibular premolars presented a maximum value of 27.7 millimetres, a minimum value of 16.1 millimetres and an average of 22.0 millimetres.
 Pécora et al (1990) studied, in vitro, the incidence of two root canals in the human permanent mandibular incisors. A total of 634 teeth were analysed, 300 of which were lower central incisors and 334 lower lateral incisors. The internal anatomy of the root canal was complex because of the high &equency of double canals with 29.7% in the central incisor and 90.9% in the lateral incisor. The presence of two canals and two foramina was 2.3% in the lower central incisor and 1.5% in the lower lateral incisor.

 The internal anatomy of roots often does not reproduce the simplicity of the external anatomy of the tooth and human mandibular canines do not escape from the rule. They do not present an internal anatomy as simple as could be expected, as demonstrated in cases in which a single root and two canals are present (Barrett, 1925; Pucci and Reig, 1944; Madeira et al, 1973; De Deus, 1992). Cases in which there are two roots have been related (Vanwter, 1886; Taylor, 1886; Koskins, 1923; Hetem et al, 1965; Madeira et al, 1973; DeDeus, 1992; Pécora et al 1993).

 Clinicians and endodontists ought to be aware of the existence of mandibular canines with more than one root canal in order to avoid failure during treatment. In fact, failure to localize a possibly existant second canal in mandibular canines generally leads to therapeutic failure due to lack of instrumentation and sealing.

 Pécora et al (1993) studied the internal anatomy, direction, number of roots and size of 830 extracted human mandibular canines. The internal anatomy was studied using the methyl salicylate clearing method which showed that 98.3% of these teeth presented with a single root, 92.2% presenting with one canal and one foramina, 4.9% with two canals and one foramen, and 1.2% with two canals and two foramina. The incidence of two-rooted canines was as low as 1.7%. As for the direction of the roots, 5.1 % were straight, 14.6% were mesial, 25.5% distal, 1.0% lingual, 3.2% buccal and 4.4% had sigmoid curvatures. The mean length of the teeth was 25.5 millimetres, with lengths ranging from 20.3 to 32.8 millimetres.

 This literary review shows that mandibular canines with two roots have a low incidence. The purpose of this research is to investigate the external and internal anatomy of extracted human mandibular canines with two roots.



 

OBJECTIVES

 Detailed studies have been conducted on all teeth of the maxillary and mandibular arches, however, only a brief review of two rooted mandibular canines has been provided by several workers between 1886 and 1993. Hence in this study the author proposes to investigate only those extracted human mandibular canines that have two roots.

 The following items will be observed:

1° External anaton of teeth. 2° Length of teeth
3° Root size
4° Direction of roots
4° Position of bifurcation
6° Internal anatomy with particu -ence to the presence of lateral canals
 
 



 

MATERIAL AND METHODS

 A total of 65 mandibular canines with two roots where studied. The teeth had becn extracted for various reasons and no note was made of patients age, sex or race. Fifty-eight teeth were collected over a period of five years in Ribeirão Preto, Brazil and seven in Birmingham,U.K.

 The teeth were cleaned using a curette to remove all traces of hard and solt tissue and then placed in a solution of 5% sodium hypochlorite for approximately one day. Following the cleaning procedure. the topographic dimensions of the teeth were observed and recorded.

 The teeth were measured using a digital pakimeter (Tesa, Switzerland) from the cusp tip to the apex of the buccal root and from the cusp tip to the apex of the lingual root (Figure 1 ).

 The direction of root curvature, region of root bifurcation and root size were observed.

 The internal anatomy was studied as follows: The mandibular canines were prepared for surgical access to the pulp chamber according to established endodontic procedures. A round diamond bur with a size proportional to the crown was used in the high speed hand piece. Buccal and lingual canals were located using a Maillefer Kerr file (size 10).

 The teeth were then immersed in a 5% sodium hypochlorite solution and submitted to a vacuum of 27Kg/cm for 1 hour. The teeth were kept in this solution for three days, thus the remaining pulp tissue was dissolved by a chemical action.

The teeth were then washed in running water for 6 hours after which time they were
placed in a container of 5% hydrochloric acid. A magnetic agitator provided constant agitation until decalcification was complete (Figure 2).

 After decalcitication, the teeth were washed in rurmïng water fór 12 hours to remove all of the remaing acid.

 The teeth were then dehydrated for 4 hours in successive solutions of alcohol in an ascending sequence of concentrations (75, 85, 96 and 1 00° GL).

 After this, the teeth were injected with gelatin coloured with black India Ink via the pulp chamber, until the gelatin flowed out from the apex. To prepare the darkened gelatin 12g of colourless gelatin was dissolved in 200m1 of cold water. The suspension was warmed until total dissolution was achieved, and then 20m1 of india ink was added. Thc resulting product was stored in the refrigerator to gelatinise.

 A carpule syringe with fine needle was used to inject the ink into the teeth, taking care not to mark the exterior surface of the tooth. Any excess was scraped off using a scalpel.

 The teeth were then placed in absolute alcohol for 4 hours and forty-nine teeth were immersed in methyl salicylate for diaphanization.

 Using this method to make each tooth transpa~ent, the internal anatomy (Shown by the coloured gelatin) was easily observed and studied with minute details of canal configurations being made visible. This method was first described by Pécora et al. (1991).

 Following decalcification, dehydration and ink injection, twelve teeth were placed in a jar containing 100m1 of Resapol T 208 resin. This jar was then put into a pressure cooker that had been modified specifically for the experiment (Figure 3).

 Compressed air was introduced into the pressiuc cooker until a prcssure of 25Lbs per square inch was observed on the manometer. The teeth were maintained in this condition until they were completely diaphanized. Next, two drops of Peroxol catalyst were added to SOmI of the same resin and this solution was placed in each compartment of an ice-cube tray (Figure 4).

 A base was thus prepared by allowing the resin to partially polymcrise in the pressure cooker again at 25Lbs per square inch of pressure for 12 hours. The tray was then removed and the teeth were placed on the base. The resin containing catalyst was added to completely immerse the teeth and the whole thing placed for the final time into the pressure cooker until the process of polymerisation was complete i.e. when the resin had changed from the gelatinous phase to the solid phase. The process was observed at regular intervals to avoid the formation of bubbles. Any that were formed were immediately removed using a ball-ended probe. On completion of this process the blocks of resin were removed from the mould and the transparent teeth observed at leisure (Pécora et al 1993).



 

RESULTS

 The lengths of the buccal and lingual roots of each tooth was measured and the results tabulated as shown in Table I.

 The average length of mandibular canines with two roots as mcasured from the highest point of the crown to the apex of the buccal root and the apex of the lingual root were 22.99 mm and 22.66 mm respectively.

 The maximum buccal length was 26.67 mm and the minimum value was 17.85 mm. d the maximuxn lingual length was 27.24 mm and the minimum value was 17.03 mm.

 Table I. Canine Root Lengths (millimetres).

 Figure 5 demonstrates the diversity in mandibular canine ,,gest tooth set against the shortest tooth for comparative purposes.

 Table II shows root curvatures of the 65 mandibular canines as observed from proximal and facial views. In the former it was found that the majority of the buccal and lingual roots curved buccally, 49.2% and 69.2% respectively.

 Straight roots were observed in 38.5% of the buccal roots and 29.2% of the lingual roots, and only a small proportion of the roots exhibited a lingual curvature when viewed proximally with 12.3% of the buccal roots and 1.5% of the lingual roots presenting thus.

 When viewed from a buccal direction it was found that the least common curvature was the sigmoid 'S' curve. Only 6.2% of the buccal roots and 7.7% of the lingual roots exhibited this variation.The frequency of occurrence of straight, distal or mesial curvatures of both buccal and lingual roots seemed somewhat arbitrary with 43.1 % of the buccal roots tending towards the distal, 10.8% mesially and the remaining 26% were straight. The lingual root showed only a 1.5% difference in the relative frequencies of curvatures in straight, distal and mesial directions. The actual percentages were 29.2%, 30.8% and 32.3% respectively.

Table II. Direction of root curvatures of 65 mandibular canines with two roots

 There was found to be a relatively noticeable variation in region of bifurcation of the two rooted canines. An apical bifurcation was seen in 56.9% of teeth, 40% presented with a bifixrcation in the middle third and only 3.1 % in the cervical third (Table III).

Table III. Position of the bifurcation in mandibular canines with two roots.

Figure 6 shows the teeth with root bifurcations in each third, namely; cervical, middle and apical.

 On examination of the size of each root it was observed that the buccal root was the larger of the two in 47.7% of the teeth, and 43.1% had equal sized roots. A larger lingual root was uncommon with as few as 9.2% presenting as such (Table IV).

Table IV. Comparison of root sizes Large buccal root . 47.7% (31), Large lingual root : 9.2% (6) Equal sized roots . 43.1% (28)

The results of the above table may be better illustrated in the form of a pie chart
(Figure 7)

 The internal antomy of 61 two rooted mamdibular canines was studied. 1'hc tccth were categorised according to the region of the bifurcation and the frequency of occturence of various features within each group was recorded as shown in Table V.

 All teeth examined presented with two root canals. None were observed to have three canals. A number of teeth presented with more than one of the listed anatomical features.

 Lateral canals were seen in a total of 68.9% of the teeth whether they extended from the lingual canal, buccal canal or occurred at the bifucation. Only 11.5% of the teeth presented with an apical delta with the majority occurring in those teeth with an apical bifurcation, and 11.5% of teeth presented with secondary canals, however, in contrast to the apical delta, the majority of the secondary canals occurred in teeth with a middle bifurcation.

 Table V. Number of teeth showing anatomical variations in canal morphology.

Figure 9 Tooth diaphanized using methyl-salicylate showing lateral canals at bifurcation and the buccL root.

Figure 10 illustration of different locations of lateral canals



 

DISCUSSION
 

 Although the existence of two rooted canines has been recognised since 1886, a detailed study of the anatomy has not been conducted. It has now become necessary to investigate the internal anatomy of such anomalies since working with poor anatomic data reduces endodontic success, and thus increases the risk of subsequent extraction. It is important to maintain mandibular canines within the arch not only for aesthetic purposes, but also because of their involvement in lateral excursive movements which, in many individuals, is achieved primarily by canine guidance as opposed to group function.

 This study shows both lingual and buccal roots of the two rooted canines to be of approximately equal lengths, with the lingual root being only fractionally shorter. In 1902 Black measured the average length of single rooted canines to be 25.6 mm. It follows that two rooted canines are, on average, shorter than single rooted canines. Operators should be familiar with the average length of teeth so that the correct length of instrument may be selected, and the expected working length known if apical perforation is to be avoided.

 In 1972 Grondahl and Mithon suggested that, generally speaking, information on the anatomy of the root(s) and the pulp chamber of individual teeth can be obtained by radiographic examination; however, it is important to know which projections are most informative. Because of the position of the teeth in the jaws, the choice of projections and, therefore, the possibilities of obtaining complete information about the anatomy of the teeth are limited.

 There was a significant variation in root curvatures which would inevitably undermine the value of clinical radiographic examination. The buccal and lingual curvatures of both buccal and lingual roots would not be identifiable radiographically.

What is seen on intra-oral radiographs is a poor image of the canals because root canals have three-dimensions. This image is deficient since it is impossible to see buccal or lingual curvatures in the bucco-lingual (proximal) aspect and, according to Pucci and Reig (1944), it is in this plane that root canals exhibit the largest number of variants. Fortunately the percentage of teeth with a lingual curvature in this view was relatively low (1.5%). However, it is evident that a significant proportion of the teeth presented with a buccal curvature (49.2%); therefore, this should be anticipated in endodontic therapy.

 Generally only cervical and middle thirds of the teeth are clearly visible r radiographically. However, a well defined view of middle and apical thirds of the root is required since bifurcations were seen to occur most commonly in these regions.

Numerous variations in internal anatomy were also observed here. Therefore if this is made apparent radiographically, two rooted canines may be recognised more easily. In 1979 Slowey suggested that a two rooted mandibular canine may be detected by a change in radiographic density.

 Following the study of the external anatomy, access was gained to the canals. In 1975 Rankine-Wilson stated that the dentist must always be aware of the possibility of a bifurcated root canal in the lower anterior teeth. Single rooted mandibular canines are moderately narrow mesio-distally but very broad bucco-lingually, and a comparable anatomy is observed of two rooted canines. However, the opening must be modified to allow access to the lingual root and canal for adequate instrumentation of the lingual aspect. This is achieved by cutting an "inverted pear" shaped cavity with sufficient lingual extension. The lingual shoulder was removed in a number teeth to gain access to the lingual wall of the root canal. This modification of the conventional access cavity for mandibular canines contraindicates the conservation of the crown substance if failure is to be avoided as a result of insufficient access (Figure 11). Once adequate access had been achieved it was found that curving the instrument slightly allowed the lingual canal to be engaged.

 If the access cavity is not prepared correctly then root canal therapy can be frustrating and may be an unsuccessful procedure.

 The buccal canal was the one most continuous with the large main passage and therefore was the easiest to instrument. Instrumentation of lingual roots (the narrower of the two in a large proportion of the teeth (see Table IV) and apically bifurcated teeth was decidedly more difficult. With time and patience all teeth were eventually instrumented.

 Figure 12 shows that both buccal and lingual canals have been located and the radiographic appearance of the instrumented tooth.

 An operator who is oblivious to the presence of a second canal, only enlarges and fills the one most amenable to treatment.

The other is left unfilled. This would explain some of the endodontic failures associated with teeth even though radiographically and clinically the canal systems appear to be obturated.

Figure 13 provides a clear illustration of such a case. A gutta-percha point can be seen in the buccal canal. However, the dentist has failed to observe and hence obturate the lingual canal which has therefore been filled by the ink.

 Immersion in 5% soditun hypochlorite solution provides a quick and effective cleaning method. A vacuum is passed through the solution to evacuate the canals of pulp and debris creating patent channels. This method allows preservation of the original mould as emphasised by Prinz in 1913, and is superior to the methods previously used by researchers which involved root canal preparation, obtrusion and finally decalcification.

 Decalcification was originally carried out using 5% Nitric acid, however it has since been recognised that the discolouration caused by this acid may be avoided by using a similar concentration of hydrochloric acid. The process is quick, only taking approximately 8-12 hours for each tooth to achieve complete decalcification, with each tooth decalcifying at a different rate.

The teeth may be viewed more clearly using this acid. It is necessary to observe the teeth hourly to avoid total degradation.

Four teeth were lost in this way. The acid is mechanically agitated to avoid incomplete or uneven decalcification. The determination of the end point of this stage of the experiment was simply by examining the flexability of each tooth and listening to the sound when dropped against a laminated surface together with a calcified tooth. Decalcified teeth were flexible and made a dull sound on impact as compared to the sharper sound of the calcified tooth. The teeth were then washed in running water primarily to neutralise the acid.

 It is necessary to dehydrate the teeth using ascending concentrations of alcohol so that the process is gradual, and the organic material becomes fixed. Complete dehydration is achieved by keeping the teeth in a solution of alcohol at a concentration of 100%. Opaque patches at sites of incomplete decalcification are thus avoided when teeth are diaphanized.

 In 1975 Hasselgren and Tronstad used a contrast medium of water and lndia ink to identify the canals. He found that the ink adhered tenaceously to the root canal walls and was difficult to remove. Incorporation of the ink into gelatin is therefore the optimum method of controlling it. The coloured gelatin flows into all aspects of the canular tree where it is fixed by the alcohol, thus providing a three-dimensional reconstruction of the internal anatomy of root canals.

 In 1980 Robertson et al used a method in which the injected ink was drawn through the canal system by applying a negative pressure to the apical end of the tooth with the use of a central suction system. Pécora et al (1993) and the principles adopted in this study utilise no such technique. A positive pressure applied at the pulp chamber automatically forces the gelatin through the canal system. The appearance of a pearl of gelatin at the apex of each canal is a good indicator that the canals have been filled. The lingual canal was difficult to fill in most cases because its narrow diameter offered a greater resistance to the flow of fluid. A similar problem was observed in teeth with apical bifurcations.

 Previous authors have used other methods to clarify canal anatomy as mentioned carlier. In 1901 Preiswerk used molten Woods metal but this would not flow into the finer canals and foramina.

 In 1907 Fisher used celluloid acetone. This penetrated all foramina of the pulp canals but was brittle and therefore the fine projections or casts of the foramina were easily broken.

 In 1925 Hess forced vulcanite rubber into the pulp canals and exposed the casts by dccalcification. Most of the valuable data was gathered using this method.

 Two techniques of diaphanisation and preservation have been presented. The conventional method involves immersion of the prepared teeth in methyl salycilate. The mandibular canines were rendered totally transparent within five hours. Prinz (1913) described the mechanism of action of this chemical in the diaphanization process. Although very quick and effective, methyl salycilate is potentially toxic and is known to cause nausea, vomiting, acidosis, pulmonary oedema, pneumonia and death. An injection of 30m1 in an adult and lOml in a child is enough to cause death (Merek 1983). The teeth must be kept in a securely closed container, and exposure to the fumes must be minimal, and then only in a well ventilated room. It is vital that the teeth remain in the methyl salicylate solution at all times otherwise the transparency will be permanently reversed and the teeth will become opaque. Hence the time available to carry out a detailed study is limited.

Figure 14 shows the results of this diaphanization technique.

 After a period of extensive research, Pécora et al (1993) described a simplified technique for preparing transparent teeth for the study of internal anatomy and their inclusion in resin blocks for permanent transparency. This procedure, although simple, requires more laboratory time because the teeth must be observed at regular intervals to remove newly formed bubbles. In this experiment, only two drops of the catalyst were used (cf three drops used by Pécora et al 1993). This prolonged the polymerisation time with blocks taking at least one week to solidify. However, regardless of the time, this proved to be a more successful method of reducing bubble formation. It was not necessary to polish the blocks which is a very laborious and time consuming process. The blocks may then be manipulated without toxic effects.

Figure 15 show s a tooth diaphanized by this process.

 In 1927 Okumura claimed that the trmsparcnt tooth model was the best method because: 1) the original form of the root may be retained; 2) the form of the canal, even its minute structure, can be shown clearly; 3) failure in preparation of the specimen is rare; 4) the specimen can be preserved for a long time (i.e. long shelf life).

 This and other methods have produced a mass of statistics illustrating the complexity of the canal system. De Deus (1975) defined a lateral canal as that structure which extends from the main canal to the periodontal ligament, and the secondary canal as the structttre extending from the main canal to the periodontal ligament in the apical region. It was observed that more than 50% of the teeth examined, had lateral canals. This is of some clinical significance since lateral radicular lesions may arise from lateral branchings of'the root canal. In 1963 Nicholls investigated the presence of a lateral radicular lesion associated with a lateral canal and found an association in 4.4% of teeth. The results of this study show that lateral canals occur most frequently in the lingual root. According to Nicholls, successful treatment of the lesion may be achieved by non-sttrgical root canal therapy. However, as stated earlier, the lingual canal was more difficult to instrument. This therefore highlights the clinical implications of endodontic treatment of two rooted mandibular canines. The overall incidence of this anomaly may be very small, but for an operator faced with the treatment of a two-rooted canine, the incidence becomes 100%.

 Research such as this raises many questions and opens the door for future work. The author believes that it would be of general interest to investigate the following:

l. A comparative anthropological study of internal and external anatomy of teeth from caucasian and asian populations.
2. An investigative study of cavity design for teeth presenting with anatomical variations in crown or root morphology.

 The results of the former study would be invaluable to the dentist because of the rapid growth of ethnic groups in England.

The latter investigation would help to increase the frequency of successful endodontic treatment of anomalous teeth.


CONCLUSION

 Following the study of the external anatomy of 65 two rooted mandibular canines and internal anatomy of 61 two rootcd mandibular canines, several conclusions may be drawn;

External anatomy:

1 . Two rooted mandibular canines have average buccal and lingual lengths of 22.99 mm and 22.66 mm respectively.
2. When viewed proximally, a buccal curvature is most frequently observed in both buccal and lingual roots
3. When viewed facially, straight roots arc most frequently observed in the buccal root and a mesial curvature in the lingual root.
4. An apical bifurcation is observed most commonly, with a frequency of occurrence of 56.9%.
5. The buccal root is the larger of the two in 31 out of 61 teeth (47,&%).

Internal anatomy:

1. All two rooted mandibular canines have two root canals.
2. Lateral canals are observed in 68.7% of teeth of which 1 1.5% are furcation canals.
3. Furcation canals occur most commonly in teeth in which the root bifurcates in the middle.
4. Secondary canals and apical deltas are equally uncommon.



 

SUMMARY

The author studied the external and internal anatomy of human mandibular canine with two roots.

The results of the external anatomy showed that the average buccal root length was 22.99 mm and the average lingual root length was 22.66 mm.

The maximum buccal length was 26.67 mm and the minimiun value was 17.85 mm and the maximum lingual length was 27.24 mm and the minimum was 17.05 mm.

The buccal root was the larger of the two in 47.7% of teeth and 43.1% had equal size roots. The lingual root was larger than the buccal root in 9.2% of cases.

The internal anatomy was studied by decalcification in 5% hydrochloric acid and diaphanization was carried out using methyl salicylate. For identification of the internal anatomy, each tooth was injected with gelatin coloured with India ink.

Diaphanization was also carried out using resin for the construction of resin blocks, allowing permanent preservation.

All mandibular canines with two roots had two root canals. Lateral canals were found in 68.9% of teeth and 19.7% had lateral canals at the bifurcation .

RESUMO

 Estudaram-se a anatomia extema e interna de caninos inferiores com duas raízes:.

 Os resultados mostraram que o tamanho médio pela vestibular dos caninos foi de 22,99 mm e, por lingual foi de 22.66 mm.

 O valor máximo obtido pela face vestibular foi de 26,67 mm, o mínimo foi de 17.85 mm e o valor máximo obtido pela face lingual foi de 27.24 mm e o mínimo foi de 17,03 mm.

 O comprimento obtido pela face vestibular foi maior do que o obtido pela lingual em 47,7% dos dentes e, em 43,1% apresentavam-se com valores iguais. O comprimento obtido pela lingual foi maior do que o obtido pela vestibular em 9,2% dos casos.

 A anatomia interna foi estudada pelo método da descalcificação em ácido clorídrico a 5% e a diafanização foi realizada com salicilato de metila. Para a identificação da anatomia interna utilizou-se gelatina com tinta da India de cor preta. Usou-se, também, neste trabalho a diafanização com resina para se construir blocos transparentes.

 Todos os caninos inferiores com duas raízes apresentaram-se com dois canais. A incidência de canais laterais foi de 68,9% e, na região, da bifurcação encontraram-se canais laterais em 19,7% dos casos.


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