Therootcanalmorphology 140311093051 Phpapp02(1)

8/11/2019 Therootcanalmorphology 140311093051 Phpapp02(1)

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MANDIBULAR CENTRAL INCISOR

#41. The mandibular central incisor always has one root, but often (20 %) has tworoot canals. Usually (75 %), the two canals join before the apical foramen. Thecanal(s) is very flattened: wide in the bucco-lingual dimension and narrow in themesio-distal dimension. Only the most apical part of the canal is more round. Thelong axis of the canal traverses the incisal edge or the labial surface of the crown.Because the access opening is made, for aesthetic reasons, in the lingual surface, thereis always a risk that the lingual canal is missed unless it is specifically looked for witha pre-curved file. For the same reason there is a risk of unsymmetrical preparation ofthe labial side of the root canal. The canal(s) of the lower central incisor is almostalways straight unlike in the lower lateral incisor, where the root tip and canal oftencurve sharply distally.


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MANDIBULAR LATERAL INCISOR

#42. The lower lateral incisor is quite similar to the lower central incisor. However,the lateral incisor is approximately 2 mm longer and the apical root and canal oftencurve distally, which must be taken into consideration during instrumentation.


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MAXILLARY CANINE

#13. The upper canine is the longest tooth, and occasionally longer files of 28 or 31mm lengths are needed for the root canal treatment. It always has only one root canal,which usually has an oval cross-section. The root canal is typically quite large, butoften the few most apical millimeters before the foramen are much narrower. Thismay lead to incorrect working length if the position of the apical constriction isdetermined only with tactile sensation with the file and fingertips. Like the upperlateral incisor, the apical canal in the upper canine may have a pronounced curve,usually either distally or labially, although not quite so frequently. Awareness of the

possibility of apical curvatures and careful assessment of root canal anatomy areessential in order to avoid complications in therapy.


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MAXILLARY FIRST PREMOLAR

#14. The upper first premolar normally has two roots and two root canals.Occasionally only one root is present, but even then two canals are still often found.The root tips are very fine which may result in perforation even in a straight canal if alarge apical open size is attempted. The roots are often equally long but 1 - 2 mmdifferences may occur. The root tips and apical canals may curve in the mesio-distalor bucco-palatal dimensions. Rarely, the upper first premolar has three roots and threeroot canals (= molarization) as with upper molars, although the roots are much finerand smaller.


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MANDIBULAR FIRST PREMOLAR

#44. All teeth in the lower jaw can have more than one root canal. Double canals are particularly frequent in the mandibular first premolars, with approximately 30% ofthese teeth having two root canals. First premolars with one canal are quite easy toinstrument, the canal is oval in cross-section and seldom curves severely. When thereare two canals, the files usually easily find the buccal canal, while the lingual canaloften requires bending of the instrument tip. Molarization in the lower first premolaris very rare.


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MANDIBULAR SECOND PREMOLAR

#45. The mandibular second premolar resembles the first premolar, but the lingualcanal is present only occasionally. Instead, molarization is more frequent than in thefirst premolar, yet still quite rare. The root canal is oval in cross-section and ratherstraight with only a slight distal curvature in some canals.


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MAXILLARY FIRST MOLAR

#16. Maxillary molars have from one to three roots and from two to four root canals.From an occlusal view the pulp chamber is situated rather mesially, which has to betaken into account when cutting the access cavity.The upper first molar is perhaps the most variable tooth when it comes to root canalmorphology, and provides quite a challenge in endodontics. There are usually threeroots with three or four root canals. Dentists are quite familiar with the mesiobuccal,distobuccal and palatal canals, but not with the fourth canal, which is known as themesiocentric or mesiopalatal, mb2 or accessory mesiobuccal canal. This fourth canalis usually difficult to find just by clinical inspection and is not apparent in theradiograph. However, finding all canals is necessary for successful therapy.The distobuccal canal is often easy to locate and instrument. It is typically ratherstraight or curves only slightly mesially, or sometimes distally.The palatal canal always looks straight radiographically but often has a buccalcurvature. If this curvature is not identified by careful exploration with files it canlead to perforation 2 - 4 mm before the apex. Moreover, in radiographs a file will stillappear to be in the canal but in reality it is only superimposed onto the canal. The

palatal canal is often 1 - 2 mm longer than the buccal canals. Two palatal roots in theupper first molar have been reported in the literature.The mesiobuccal root is the most challenging to treat. The root is usually curved all

the way to the apex, which increases the risk of tip perforation and strip perforation.The distal surface of the root is concave which increases the risk of strip perforation.


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The mesiopalatal canal is present in well over half of cases, with some authorsreporting over 90% incidence. The canal orifice is difficult to find because it istypically situated near the mesial wall of the pulp chamber. While the other threecanals can readily be found, the fourth canal must always be actively looked for withsuitable instruments. The orifice is usually located 1 - 3 mm palatally from the

mesiobuccal canal. In most cases the mesiopalatal canal joins the mesiobuccal canal before the apex.

MANDIBULAR FIRST MOLAR#46. The mandibular first molar is perhaps the most frequently endodontically treatedmolar. It is, however, often quite difficult to treat because of its root canal anatomy. Itusually has 3 - 4 canals, two in the mesial root and one or two in the distal root. TheDistal canal(s) is normally straight all the way to the apex, oval or flattened in cross-section, but quite large, which makes instrumentation easy. Often the most apical 1 - 2mm of this canal curves up to 90 degrees distally, but this is seldom a clinical

problem. The distal canal may also curve mesially, but the curvature is not sharp andusually remains easy to instrument. The mesial canals in the first molar are often achallenge for the dentist. Both the mesiobuccal and mesiolingual canals are usuallycurved along their whole length, and the curvature is typically greatest in the apicalregion. The canals curve distally, but they also curve buccally or lingually at the same


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time. Bucco-lingual curvatures are not readily seen in the radiograph, whichemphasizes the importance of the dentist's knowledge of possible variations in canalmorphology. One must routinely search for four canals in the lower first molar. Thedistal canals often start together and separate a few millimeters below the pulpchamber floor. Both distal and mesial canals can join before the apex. This is

important to detect before obturation, to gain optimal results. Mandibular first molarswith two canals are rare. Usually, finding only two canals indicates that themesiobuccal canal has not yet been located.

MAXILLARY SECOND MOLAR

#17. The maxillary second molar closely resembles the first molar. However, thenumber of canals is usually three, sometimes two, but also four canals can be found(two canals in the mb root). A typical upper second molar resembles the first molar,the difference being that the orifices of the mb and db canals are closer together;sometimes almost forming a line (mb - db - pal). Sometimes the two buccal canals areside by side in the mesio-distal dimension. The apical part of the palatal and themesiobuccal canals is not as curved as in the first molar.


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MANDIBULAR SECOND MOLAR

#47. The lower second molar is much like the first molar but generally easier toinstrument because the curvatures are milder. The occurrence of four canals in thesecond molar is more rare than in the first molar, and only two canals is a morefrequent possibility than in the first molar. A small percentage of lower second molarshave a special root canal anatomy; two or more of the canal openings in the pulpchamber floor join to form a C-shaped groove. This has occasioned the name "C-shaped canals". Usually the mb or ml canal joins the distal canal, sometimes bothmesial canals join the distal canal. Deeper in the root there sometimes are furtherramifications.


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MAXILLARY THIRD MOLAR

#18. The upper third molar is often a "reduced version" of the second molar. Thereare usually two or three root canals, and the orifices of the buccal canals may be veryclose to each other. Some upper third molars have a root canal anatomy similar to firstmolars. Sometimes the buccal canals share the same orifice in the pulp chamber butthen separate 1 - 4 mm below the chamber floor (this may also occur in the secondmolar). Some upper third molars have additional roots and/or root canals.


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MANDIBULAR THIRD MOLAR

#48. The lower third molar resembles the first and second molars, but the probabilityof teeth with four canals is again less and of teeth with two canals greater. Thirdmolars are shorter than the other molars, which makes instrumentation easier.However, many third molars have very curved canals and may be difficult toinstrument.


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SPECIAL MORPHOLOGY FOR

ROOT CANALS


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Dentine structure

Evaginations

Evaginations are morphological anomalies where the pulp has made an extensiontowards the tooth surface. Dentine and enamel follow the pulpal extension which may

be seen as an extra cusp or enamel pearl on the tooth surface. Evaginations are rare,and are usually seen in lower premolars. They typically cause occlusal interference. Ifeliminated by grinding in one appointment, pulpal exposure and damage will follow.Gradual grinding of 0.1 mm per month before occlusal contact is established may helpto avoid pulpal inflammation.


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Invaginations

Invaginations are shallow or deep developmental cavities in tooth crowns, covered partly or totally by enamel walls. Their frequency has been reported to be between 0.1and 10%. They are most frequent in upper lateral incisors, but can be found in anytooth. Invaginations are divided into four main types (see drawing). Invaginationsoften increase the risk of pulp infection, and they should be well sealed with a

permanent filling whenever found, in order to reduce the risk of infection in the pulpor in the periodontal tissues. Deeper invaginations (type 2) should be cleanedmechanically and by irrigation, and they should be filled to their whole depth if

possible. Type 3 and 4 invaginations are problematic to treat if the infection penetrates to the tissues.

Pulp stones

Pulp stones are calcified structures that may form within vital pulpal tissue They areoften oval or round, but they may also have an irregular shape. Sometimes pulpstone(s) may diffusely fill a major part of the pulpal chamber.


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Size and morphological features have been used for classification of intrapulpalcalcifications, but classifications have little significance in endodontics.

Previously, pulp stones were thought to be a sign of pulpal pathosis, but evidence forthis is lacking. Nowadays pulp stones are not regarded as an indication for endodontic

therapy.

If endodontic treatment is, however, started for other reasons, pulp stones maycomplicate gaining access to the root canals or obtaining correct working length. Useof ultrasound often helps to remove pulp stones during root canal preparation.

TABLES

Table 1

The average length of teeth in the upper jaw varies from 19mm to 26 mm. The canineis the longest tooth in the upper jaw followed by the central incisor.

The central incisor is the only tooth that is regularly straight to the root tip. The lateralincisor typically has a distal or buccal apical curvature. Upper canines may be straight

but may also curve buccally or distally. Most teeth in the premolar and molar regionshave curved roots.

Double canals are practically never found in upper incisors or canines. Single-rooted premolars and mesiobuccal roots of upper molars often have double canals. As in thelower jaw, double canals are located in the bucco-lingual dimension.


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Table 2

The average length of teeth in the lower jaw varies from 19mm to 25 mm. The canineis the longest tooth in the lower jaw and only slightly shorter than the upper canine.

The central incisor is usually straight, down to the root tip. Most lower premolars andcanines are also quite straight, while lateral incisors and molars typically have curved

roots.All teeth in the lower jaw can have double canals. Double canals are located in the

bucco-lingual direction. In the molars, double canals are typically found in mesialcanals, but may be also found in distal canals, particularly in the first molar.

Terminology


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Apical canal

Apical preparation assumes a key role in successful therapy of apical periodontitis, because it is the bacteria, particularly in this area of the root canal, that are responsiblefor the development of the periapical lesion. The technical goal of treatment of apical

periodontitis is to reach the apical constriction and all regions of the root canal systemwith preparation instruments, intracanal medicaments and the root filling. If this can

be done successfully, prognosis of the therapy is good. Variations in apical root canalmorphology, however, may complicate treatment, as in the case of an apical delta,which may offer areas of concealment for micro-organisms. Details of apical rootcanal morphology often cannot be seen in radiographs.

Changes in morphology

Ageing and various irritants, such as deep caries lesions, cause several changes inteeth. Pulp chambers and root canals become narrow and more obliterated because ofsecondary dentine produced by odontoblast cells in the pulp. Also the crown becomesshorter because of occlusal wear. It is important to understand the effects of thesechanges on endodontic treatment.


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Canal cross-sections

Thorough knowledge and understanding of the cross-sectional shape of root canals indifferent teeth and tooth groups is essential for successful endodontic treatment.Optimally, the canal should be round or only slightly oval to allow easy access for

preparation instruments to all parts of the root canal system. In practice, however,many root canals are flattened and asymmetric in shape.

The cross-sectional shape of the root canal also changes during its course from the pulp chamber towards the apex. In the apical 1 - 4mm, most canals become oval or

round. This again facilitates cleaning of the apical canal, which is essential for controlof the infection and helps to give the canal a shape that can be tightly filled with a rootfilling.


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Curved canals

Up to 90% of all root canals are curved to some degree. Canal curvatures are achallenge to preparation and can cause different kinds of technical complications(preparation of curved canals). Canals that curve in the mesio-distal dimension areusually easily detected in radiographs. However, many canals also curve in the bucco-lingual dimension, which can only occasionally be detected in radiographs. Foroptimal clinical results it is important to detect all curvatures in order to select thecorrect instruments and avoid complications.

The type of curvature dictates the ease or difficulty of instrumentation. Evencurvatures with a long radius are easy to prepare with the right choice of instrumentsand techniques. Sharp curves with a short radius and S-shaped curvatures are always

very demanding and easily result in transportation, ledges and even perforations.

Even up to 90% of all root canals are more or less curved. Canal curvatures are achallenge to preparation and can cause different kinds of technical complications (see

preparation of curved canals). Canals that curve in the mesio-distal direction areusually easily detected in radiographic pictures. However, many canals curve also inthe bucco-lingual direction, which can only occasionally be detected in radiographs.For optimal clinical results it is important to detect all curvatures in order to select thecorrect instruments and avoid complications.

The type of curvature dictates the ease or difficulty of instrumentation: evencurvatures with a long radius are easy to prepare with the right choice of instrumentsand techniques, sharp curves with a short radius and S-shaped curvatures are alwaysvery demanding and easily result in transportation, steps and even perforations.


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Double canals

Double canals means two canals in one root. Double canals can be separate from the pulp chamber down to the apex, both having their own apical foramen. However, thecanal may also begin as one canal, divide into two canals, and join again before theapex.

Double canals are almost always situated as buccal and lingual canals in the root,which makes their detection in radiographs difficult. However, knowing the

possibility of their existence together with careful analysis of radiographs and clinical

examination helps to find double canals. From the clinical point of view it isimportant to be aware of the possibility of double canals.

Double canals can be present in most roots. Maxillary incisors and canines are theonly teeth where double canals are practically never found. Also the palatal anddistobuccal roots of upper molars usually have only one root canal.

Double canals are most frequent in mesial roots of mandibular molars, followed bythe mesiobuccal root of the maxillary first molar, upper second premolar and lowerfirst premolar. Roughly one fifth of lower incisors and canines also have doublecanals, but most of these join shortly before the apex.

Analysis of radiographs


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C-shaped canals

The C-shaped canal is a special feature of some lower second molars. Approximately1% of lower second molars have C-shaped canals. The name comes from theappearance of the pulp chamber floor when viewed from above. Some or all of thecanal orifices are joined in the form of a groove or isthmus with a shape of the letterC. In teeth with three canals the mesiobuccal canal usually joins the distal canal. Insome teeth both mesial canals join the distal canal at the cervical area near the pulpchamber floor. The canals may later, closer to apex, separate again to leave the toothvia separate foramina.

Taurodontism


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Molarization may occur in all front teeth and premolars

Maxillary "molarization" premolars have two buccal roots and one palatal root

The roots in three-rooted maxillary premolars are easy to detect in the radiographs

Maxillary second premolar with two root canals has one mesial and one distal canal

Two root canals in maxillary second premolar usually join 1 - 5 mm before apex

Maxillary first molar has usually three (3) root canals

Maxillary second molar has usually three (3) root canals

MB1 and MB2 canals of upper molars often join before apex

Sometimes maxillary second molar has only one root canal

MB2 canal is located in the distobuccal root

The openings of MB1 and MB2 canals in the same root are of same size and equallyeasy/difficult to find

MB2 canal in first maxillary molar is located on the straight line between MB1 and palatal canal

MB2 canal in first maxillary molar is located mesially to the straight line between MB1and palatal canal

There is always only one palatal canal in maxillary molars

Palatal canal in maxillary molars is the narrowest canal

Mesiobuccal root of maxillary molars in flattened mesio-distally

Palatal canal of maxillary molars often curves palatally at the apical end

Palatal canal of maxillary molars often curves buccally at the apical end

The apical curvature of maxillary molar palatal canal is readily visible in the radiographs


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Mandibular teethTrue False

Mandibular incisors and canines have always one root canal

20 % of mandibular incisors have two canals in the same root (= double canals)

Double canals in mandibular incisors usually join 1 - 5 mm before apex

The root tip of lower lateral incisor often curves distally

Lower incisors of the same patient are always equally long

Lower central incisor is usually longer than the lateral incisor

Mandibular canine has always only one root

Mandibular canine may have two root canals that often join before apex

First mandibular premolar can have one canal

First mandibular premolar can have two canals

First mandibular premolar can have three canals

Two canals are more usual in lower second than in lower first premolar

When two canals are present in lower premolars, the files typically have easier access tothe lingual canal

Molarization is more frequent in second than in first lower premolar

First mandibular molar has usually three or four root canals

First mandibular molar can have five root canals

Double canals in molar roots (except upper palatal roots) are always buccal and lingual


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Curved root canals in lower molars curve only in mesio-distal direction

When an extra root is present in lower molars, it is usually mesial

Double canals in molar roots typically have anastomoses

Lower third molar can have up to four root canals

EvaginationTrue False

Evaginations are more frequent than invaginations

Evagination can increase the risk for pulpal infection

InvaginationTrue False

Invagination can increase the risk for pulpal infection

Invaginations occur only in maxillary lateral incisors

Invagination has always a connection to the root canal

A tooth with an invagination cannot be saved from pulpal necrosis

Invaginations cannot occur in mandibular teeth

Type III (three) invagination opens into periodontal tissue in mid-root

Type I invagination is the deepest of the four invaginations

Pulp stoneTrue False

A pulp stone is not an indication for endodontic treatment

Pulp stones are found only in the pulp chamber

Pulp stones are found only in the root canal


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Pulp stones are not always round

Once diagnosed, pulp stones are always easy to remove

Pulp stones are much softer than dentine

ApexTrue False

Apical foramen can be located at the radiographical apex

Apical foramen can be located at the lateral root surface

One root canal has always only one apical foramen

Lateral canals end at the dentine-cement border

Root surface cement can be found a few micrometers inside the apical canal

Changes in morphology True False Reduction of pulpal space is always a consequence of a pathological phenomenon

Calcification/obliteration of the pulp is an indication for endodontic treatment

Pulp chamber space reduction occurs mainly by the floor "growing up"

Pulp chamber space reduction occurs mainly by the roof "growing down"

In the apical 1 - 4 mm most canals are oval or round in cross section

Curved canalsTrue False

Ca. 10% of the canals are curved

Canals curve only in mesio-distal direction


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Normal radiographs can detect mesio-distal and bucco-lingual curvatures equally easily

Sharp curves with a short radius are more difficult to instrument than even curveswith long radius

S-shaped canal curves two times to the same direction

Palatal canal of upper molars often curves buccally

Double canalsTrue False

Double canals can join and separate again before apex

Double canals always join before apex

Difficulty to see double canals in radiographs is because they are located bucco-lingual

Sudden disappearance of canal shadow in mid-root in the radiograph in a strongindication of a double canal

Depending on the angulation, periodontal ligament space can cause canal-resemblingvertical shadows on the root in the radiograph

MolarizationTrue False

Is equally common/rare in all premolars

The frequency of molarization is ca 1%

Maxillary "molarization" premolars have two buccal and one palatal root

C-shaped canalsTrue False

C-shaped canal is a special feature of lower second molar

In C-shaped canals the mesial canals join forming a C-shaped orifice in the pulpchamber

Ca. 5 % of lower second molars have a C-shaped canal system

Taurodontism


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True False

In taurodontism, the pulp chamber is exceptionally deep

Taurodontic teeth are generally difficult to instrument

Taurodontic teeth are easier to root fill than normal teeth

Therootcanalmorphology 140311093051 Phpapp02(1)

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