How many teeth do an adult and a child have?

Preface

The goal of root canal therapy is to remove the contents of the root canal space and then fill it. Proper treatment requires knowledge of both the external and internal anatomy of the tooth to reduce the risk of failure and the possibility of iatrogenic biological damage.

Understanding the coronal morphology of the tooth allows us to make endodontic access in the most conservative manner; The shape of the access cavity is described for all teeth. Studying the morphology of the root canal system and its several variations makes it obvious why there are operational difficulties during instrumentation, as shown in the iconographic part. From the morphological and histological tables of Hess, the complexity of the entire root canal system is visible, which confirms the difficulty of completely removing pulp tissue from the endodontic space and encourages the search for new methods and technologies in endodontics.

The microscopic anatomy section summarizes the interaction of the root dentin wall structure with mechanical (files, ultrasound), chemical (irrigants) and physical (lasers) factors during therapy. In particular, in order to understand the different effects of lasers on tissue depending on the wavelength, it is very important to carefully study the ultrastructure and histology of dentin in the canal.

Why do you need teeth numbering?

The modern tooth numbering system successfully copes with several tasks at once. Firstly, it allows you to effectively systematize knowledge about the masticatory organs. Thanks to some formulas, scientists can study in detail the structure of the oral apparatus not only of humans, but also of animals.

Secondly, with the help of numbers it is much easier for the attending physician to tell the patient which teeth have been affected by pathology. Based on generally accepted diagrams, the dentist also enters the necessary information into the dental chart without wasting time on a verbal description of the type, structure and position of each unit.

In addition, numerical designations are indispensable when prescribing treatment procedures and transmitting detailed instructions to other specialists. In the same way, data on the condition of the teeth and the treatment already performed is recorded.

Anatomy of primary teeth

The macroscopic anatomy of primary teeth is very similar to that of permanent teeth, with some differences between them outlined in this section.

Ernst Zurcher (1922), Walter Hess school in Zurich, carried out the first scientific work on pulp morphology in primary teeth.

The endodontic morphology of primary teeth is very similar to the endodontic morphology of permanent teeth, but is smaller in size. Primary teeth are usually shorter and smaller than permanent teeth; the roots are narrow, while the roots of permanent teeth are thicker, especially in the cervical third. However, the width of the crowns of primary teeth is more pronounced compared to their height. The roots of temporary molars, in addition to being thinner than permanent roots, diverge to the sides to ensure the eruption of permanent premolars, first of all during their formation, and then during eruption.

Primary upper and lower molars often have a fourth canal in the mesiobuccal root of the upper molar and in the distal root of the lower molar.

As the child grows, the length of the roots of primary teeth decreases due to physiological resorption (exfoliation) (Fig. 1.1 and 1.2). Sometimes resorption of the floor of the pulp chamber at the furcation precedes apical root resorption (Fig. 1.3ad).

Rice. 1.1 Primary upper molar: root resorption starting in the apical region (arrows)

Rice. 1.2. Primary lower molar: root resorption affecting all parts of the root from apex to crown

Rice. 1.3. Primary upper molar: radicular resorption is more obvious at the floor of the pulp chamber in the area of ​​the furcation, which in this case precedes apical resorption; (a) root apices are intact; (b) resorption in the area of ​​the furcation of the pulp chamber; (c) palatal root resorption (arrows); (d) mesial view of furation resorption (arrows)

Unlike permanent teeth, the loss of primary teeth explains why canal filling at the end of endodontic treatment requires the use of resorbable materials that allow gradual root resorption.

On what basis are teeth numbered according to different classification systems?

In addition to the Latin names of teeth, digital designations are used in dentistry. The numbering of teeth is based on the order in which they erupt. It starts from the front incisors (from the middle of the jaw) and runs to the left and right of them.

There are several generally accepted systems for numbering human teeth.

Universal system

Most often, dentists name teeth not by the Latin alphabet, but according to their location in the oral cavity (ordinal number). Moreover, using not Roman, but familiar Arabic numerals.

Names of teeth according to the universal classification system:

• two central incisors are located at number 1 and are called ones;
• the second incisors are numbered 2;
• the fangs are called triplets;
• chewing teeth or premolars are called fours and fives;
• molars are called sixes, sevens and eights.

According to the universal system of classification of dental units, the jaw is divided into 4 segments:

• top left;
• top right;
• bottom right:
• bottom left.

The further name indicates not only the serial number, but also the location of the dental unit in the human oral cavity.

The universal dental numbering system is the most popular and frequently used. It is used by dental therapists and surgeons in various countries.

The picture shows a diagram of the designation of teeth in the oral cavity of an adult according to the universal numbering system:

European system

The European Viola system is one of the newest and most advanced methods for naming human teeth. It is characterized by the division of the jaw into segments (two at the bottom and two at the top). Each segment is numbered (from 1 to 4).

Based on these numbers, each tooth receives a two-digit number. The first digit indicates the segment, and the second is the actual sequence number.

The Viola system is recognized internationally and is therefore popular all over the world. It is used in radiography, making panoramic images and allows dentists from different countries to exchange information about patients, overcoming the language barrier.

Haderup system

To designate dental units according to the Haderup system, Arabic numerals are used and segmentation into the lower and upper jaws is used:

• the “+” sign indicates that it belongs to the upper jaw;
• the “–” sign indicates the lower jaw.

The only disadvantage of such numbering is that it is necessary to additionally indicate whether the dental unit belongs to the left or right side of the jaw.

Zsigmond-Palmer system

The Zsigmond-Palmer system is considered the most imperfect, since it only indicates the numbers of teeth without their location. Standard Arabic numerals are used for numbering.

This tooth numbering system is practically not used in therapeutic and diagnostic procedures. It is used only by orthodontists and maxillofacial surgeons.

Permanent teeth

Macroscopic anatomy

Human permanent teeth consist of a crown and one or more roots. The endodontic space, created by the dentin of the root and pulp chamber, is very complex and is classified differently depending on the crown-root relationship and canal morphology.

Weine (1996) classified the root canal system into four types when considering the relationships between the pulp chamber, root canals and their apical termination (Fig. 1.4).

Rice. 1.4. Weine's classification of the root canal system takes into account the relationship between the pulp chamber, root canals and their apical termination.

Vertucci (1984) identified eight main types. Later, the Vertucci classification was expanded to include other morphological classifications by Gulabivala et al. (2001 and 2002) and Sert and Bayirili (2004) (Figures 1.5, 1.6 and 1.7).

Rice. 1.5 and 1.6 Graphic display of the morphological classification of Gulabivala endodontic system

Rice. 1.7 Graphic display of the morphological classification of Sert and Bayirili endodontic system

Schneider analyzed single-rooted human teeth and classified them according to the degree of root curvature as straight, with a curvature less than or equal to 5°, with a moderate curvature between 10° and 20°, and with a strong curvature between 25° and 70°. Lautrou [1987] also described and classified various morphologies of root cross sections (Fig. 1.8).

Rice. 1.8 Graphical representation of Lautrou classification of morphology in root cross sections

Zidell (1985) and Ingle and Taintor (1985), in addition to the degree of root and apical curvature, also considered the complexity of the anatomy, including the presence of bifurcations, the presence of accessory canals, and the presence of lateral and accessory canals.

Various studies and texts later described the anatomy and morphology of permanent human teeth and their countless possible shapes.

In paragraphs about a particular tooth, the age of eruption considered is according to Logan and Kronfeld, slightly modified by Schour and included in the text by Ash. The dimensions of human teeth described in this textbook are instead taken from various texts.

What does the dental formula look like in a medical record?

The dental formula of an adult, as well as a child, in the medical record of a dental patient looks in the form of a schematic table (Fig. 5), which will reflect only the serial numbers of permanent or baby teeth.
Directly in this formula, the doctor will mark the missing teeth (in this case, the number is crossed out with a cross), which teeth are affected by caries, pulpitis or periodontitis, as well as which of them have crowns or bridges. Dental formula in the form of a table in the medical record –

Upper incisors

Central upper incisor

The central upper incisor erupts (one per quadrant) between the ages of six and seven years, and the complete formation of the apical third occurs after 2 or 3 years. The average tooth length is 22-23 mm.

The crown has a triangular shape, about 10.5 mm long, the base extends in the mesial-distal direction, corresponding to the anterior edge of the tooth, up to 9 mm in size, and its buccal-palatal size is 7 mm (Fig. 1.9).

Rice. 1.9 Upper central incisors: palatal view of the crown

The root is usually straight (75%), but according to Ingle, a slight curvature may be present in a small percentage of cases. Lateral canals may be present in more than 20% of cases, and an apical delta is also common (35%).

The coronal pulp space also has a triangular shape, especially in the region of the cervical radicular third, with the base facing the vestibular wall and the apex located palatally, after which it gradually becomes a round canal until the apex.

The access cavity is triangular and follows the shape of the pulp space (Fig. 1.10).

Rice. 1.10 Upper central incisor: graphical representation of the access cavity

Lateral upper incisor

The eruption of the upper lateral incisor (one in the quadrant) occurs 1 year after the central one, and its complete formation takes approximately 3 years.

It is approximately 1 or 2 mm shorter than the central incisor, its mesial-distal size is smaller - about 7 mm, and the vestibular-palatal size is only 5.5-6 mm (Fig. 1.11).

Rice. 1.11 Upper lateral incisor: palatal view of the crown

Normally there is only one root canal, straight in 30% of cases, and often it is curved distally (53%), in a small percentage of cases there is curvature in other directions. The shape of the canal is ovoid in the cervical region, with a tendency to become more rounded in the apical region; the access cavity has a similar structure (Fig. 1.12).

Rice. 1.12 Upper lateral incisor: graphical representation of the access cavity

Histological structure of the tooth

The special hardness of teeth is due to their structure. The outside of the crown is covered with enamel, the basis of which is hydroxyapatite crystals. 96% of the enamel consists of inorganic substances, which is why it is so hard (which, however, does not mean that experiments can be carried out on teeth, testing their strength). But dentin, which is located under the enamel, has much less inorganic substances - about 70%. It is softer, and therefore is destroyed by caries more than enamel. Inside the tooth there is a cavity filled with a neurovascular bundle, or pulp. The entire rich spectrum of pain during the deepening of the carious process is associated with it. In addition to nerve fibers, the pulp also contains a large number of blood vessels, through which infection from the affected tooth spreads throughout the body. This is why it is so dangerous to leave dental diseases untreated.

Lower incisors

The lower incisors, two per quadrant, are very similar to each other, with some peculiarity retained.

Lower central incisors

The lower central incisors are the first permanent teeth to emerge in children's mouths, usually between 6 and 7 years of age, and are fully formed by 9 or 10 years of age. The lower central incisor is approximately 21.5 mm long. The apical third of the root is straight in 60% of cases and curves distally in 23% of cases.

The crown has a trapezoidal shape with a large base corresponding to the cutting edge and a smaller base that continues into the cervical third of the root. Its mesio-distal size is 5.5 mm at the greatest width of the incisal edge and gradually decreases to 3 mm at the cervical level (Fig. 1.13).

Rice. 1.13 Lower incisors: lingual view of crowns

The lower central incisor has a buccal inclination. In the root, it is possible to have a second canal located lingually in relation to the main canal in 18-23% of cases (Fig. 1.14).

Fig 1.14 Lower central incisor: graphical representation of the access cavity

Lower lateral incisor

The lower lateral incisor is similar to the central incisor, but slightly larger - about 1 mm, usually erupts 1 year after the lower central incisor and completes its formation after 3 years.

Root examination confirms the presence of two canals in 15% of cases.

The access cavity of the lower incisors is formed in a buccal-lingual direction to search for a second canal located lingually (Fig. 1.15a-c).

Rice. 1.15 (a - c) Lower central incisor: buccal, lingual and proximal views

Fangs

Upper canine

The upper canine, one per quadrant, erupts at approximately 11-12 years of age and completes its formation after 3-4 years.

This is the longest tooth in the arch (about 27 mm or more).

The crown has a diamond shape with a peculiar sharp cusp, which on the vestibular side divides the mesial and distal sides of the crown. The crown is 10 mm high (length) and has a maximum mesial-distal diameter of 7.5 mm at the point of proximal contact and decreases to 5.5 mm cervically. The buccal-palatal diameter is wider (8 mm), and it remains up to 7 mm at the cervical level due to the presence of a prominent marginal ridge (Fig. 1.16).

Rice. 1.16. Upper canine: palatal view

The long root, like the crown, is narrow in the mesial-distal direction and more pronounced in the buccal-palatal direction. There is almost always only one root canal with lateral canals at different levels in 24% of cases. The apical third is straight in 40% of cases, and is often curved distally (32%) and/or vestibularly (13%) (Fig. 1.17).

Rice. 1.17 Upper canine: graphical representation of the access cavity

The pulp space at the level of the cervical third and the root middle third has an oval shape in the buccal-palatal direction; often two canals are present with a tendency to merge into one common round canal in the apical third (Fig. 1.18a, b).

Rice. 1.18 (a, b) Upper canine: buccal and proximal view

The endodontic access cavity is oval-shaped, extending from the cusp to the marginal ridge of the coronal cervical third to gain access to the radicular space without obstruction that could cause instruments to create steps or transposition of the apical foramen (see Fig. 1.19).

Rice. 1.19. Anatomical pictures from Hess and Keller: the endodontic space of the upper canine at the level of the cervical third of the canal is represented by one oval canal, and in the middle third it is divided into two different canals and often merges into one round canal in the apical third

Lower canine

The lower canine, one per quadrant, erupts approximately 8-10 months before the upper one and completes its formation after 3-4 years.

The crown has a length of 11 mm, and its mesiodistal diameter is narrower than the upper one (7 mm), and decreases to 5.5 mm at the cervical level. The maximum buccolingual diameter is 7.5 mm wide and decreases to a minimum at the cervical level. The cervical lingual marginal ridge is less pronounced than that of the upper canine (Fig. 1.20).

Rice. 1.20 Lower canine: lingual view of the crown

The lower canine is about 27 mm long, and has two separate roots in 6% of cases, or two canals in one root, connected by isthmuses, with a common or two separate apexes (Fig. 1.21). In 20% of cases, the apical third has a distal slope (Fig. 1.22).

Rice. 1.21 Lower canine: graphical representation of the access cavity

Rice. 1.22. Anatomical pictures from Hess and Keller: the endodontic space of the lower canine has two separate canals connected by an isthmus in the coronal third; the canals merge into one opening in the apical third

The endodontic space is oval in shape in the bucco-lingual direction for two-thirds of the root, and then gradually becomes rounded.

The endodontic access cavity should be oval in shape in a buccolingual direction, from the cusp to the marginal ridge (Fig. 1.23a, b).

Rice. 1.23 (a, b) Lower canine: buccal and proximal view

Anatomical structure of the tooth

We figured out the order of the teeth. Further - more interesting! After all, a tooth is a unique organ, designed by nature to perform very important functions, primarily chewing. To be firmly held in the jaw bone, you need a root. The longest root is at the canine. Teeth can be single-rooted or multi-rooted. The structure of the upper teeth (molars) is somewhat more complex than that of the lower ones, since they have 3 roots. There are especially many variations in the number and type of roots in “wisdom teeth.” But the visible part of the tooth protruding above the gum is called the crown. It has different shapes in the incisors, canines and molars to perform the functions of biting, crushing or chewing food. The boundary between the crown and the root is the neck of the tooth. It is usually not visible, but it can become exposed due to certain diseases (periodontal disease, etc.). An x-ray is a kind of photo of the structure of the tooth and will give you an idea of ​​​​what the state of affairs is in the oral cavity.

Upper premolars

Two per quadrant, premolars erupt between 10 and 12 years of age, and root formation is completed after 3 years. They replace temporary molars.

The first and second premolars have a similar crown but different morphology.

Upper first premolar

The first upper premolar erupts when the child is about 10-11 years old. It has a length of about 21-22 mm, and its buccal-palatal dimensions are 9 mm and mesial-distal dimensions are 7 mm. It has two cusps, buccal and palatine, which are slightly shorter (about 1 mm). The pulp space is determined by the shape and size of the outer crown (Fig. 1.24). In approximately 72% of cases, two roots with two different apical foramina are present (Fig. 1.25). Premolars may also have only one root with two canals (13%) (Fig. 1.26a, b), and in some cases three roots (6%) (Fig. 1.27). In addition, in 37% of cases we found a distal root bend in the apical third.

Rice. 1.24 First upper premolar: occlusal view

Rice. 1.25 Upper premolars: graphical representation of the access cavity; note the mesial position of the second premolar access cavity (right in the figure) to facilitate passage of the distally curved canal

Rice. 1.26 (a, b) Upper single-root premolar: buccal and proximal view

Rice. 1.27 Anatomical pictures from Hess and Keller: complex pulp space of an upper single-rooted premolar; two different channels have multiple messages along the root and two separate outputs

The access cavity to the pulp chamber should have an oval shape in the buccal-palatal direction, from one tubercle to another Fig. 1.28.

Rice. 1.28 Anatomical pictures from Hess and Keller: an upper premolar with three roots, two buccal and one longer palatal

Upper second premolar

The second upper premolar erupts between the ages of 10 and 12 years. It is very similar to the upper first premolar, both in size and crown shape. But there are some main differences between the roots, presented in three versions:

One root with one canal in 75% of cases (Fig. 1.29a, b)

Rice. 1.29 (a, b) Upper first premolar: mesial and distal view

One root with two canals and one or two separate apical foramina (12%) (Fig. 1.30 and 1.31)

Rice. 1.30. Anatomical pictures from Hess and Keller: an upper single-rooted premolar having two canals merging into one exit; lateral canals are also present in the apical and middle third of the canal

Rice. 1.31 Anatomical pictures from Hess and Keller: upper single-rooted premolars have two canals with separate exits, apical and lateral

Two separate roots and canals (12%)

Three separate roots (usually two of them buccal) with three canals (1%)

On the buccal side, the roots have a distal curvature in 27% of cases, and a vestibular curvature in 12% of cases, and in 20% of cases they have two sharp curvatures.

The endodontic access cavity to the pulp chamber has an oval shape in the buccal-palatal direction. If there is significant distal apical curvature, the approach should be moved closer to the mesial marginal ridge, maintaining an oval shape (Fig. 1.28).

TOOTH CEMENT

The cementum of the tooth covers the root and is divided into primary and secondary. Primary (cell-free) cement is adjacent directly to dentin, covering the lateral surfaces of the tooth root. Secondary (cellular) contains cementocides, covers a layer of primary cement, is localized only in the area of ​​the root apex and on the interroot surfaces of premolars and molars.

The main substance of cement is represented by collagen fibers running in different directions, most of which run in the radial direction. In some pathological conditions, hypercementosis is observed (excessive deposition of layers of cement on the surface of the tooth root). Cement consists of 68% inorganic and 32% organic substances.

Lower premolars

Two in each quadrant, they erupt between 10 and 12 years of age, with full root formation after about 3 years. They replace primary molars. In contrast, the upper premolars are distinct from each other (Fig. 1.32).

Fig 1.32 Lower premolars: occlusal view

Lower first premolar

The lower premolar erupts sometimes several months before and sometimes after the lower canine and is the smallest of all premolars. The crown has two cusps, one very large and similar to the cusp of a canine tooth. The other is shorter by about 2 mm, similar to the lingual marginal ridge of the canine (Fig. 1.33).

Figure 1.33 Lower premolars: graphical representation of the access cavity

Length is about 21-22 mm, usually has one root with one canal (73-74%). Sometimes one root with two canals is possible (19%) (Fig. 1.34a, b), two roots with two canals (6%) (Fig. 1.35a, b) or three canals (1-2%).

Rice. 1.34 (a, b) First lower premolar: occlusal and proximal view

Rice. 1.35 (a, b) Second lower premolar: (a) coronal view; (b) Proximal view showing the presence of a single root

The root is often distally curved in 35% of cases and with a sharp curve in 7% of cases. The shape of the access cavity to the pulp chamber is oval, extending from the main tubercle to the tip of the minor lingual tubercle (Fig. 1.36).

Figure 1.36 Anatomical pictures from Hess and Keller: a mandibular premolar with a complex canal system that has two main canals connected by several fins and two separate exits

Lower second premolar

The second lower premolar erupts at the age of 11-12 years and is larger than the first premolar by 1 or 2 mm. The crown has two cusps (a larger buccal and a smaller lingual), but the lingual cusp is often divided into two parts (Fig. 1.37).

Rice. 1.37 Anatomical pictures from Hess and Keller: lower premolar with two roots and two canals; several short lateral canals present in the apical third

It has only one root with one canal in 85% of cases, but we can also find two separate canals in one root (11.5%) or two canals that merge into one apical foramen (1.5%) (Fig. 1.37 ). Rarely three channels are possible (0.5-1%). In approximately 40% of cases the root is straight, while in approximately 40% the apical third is distally curved. Severe curvature (7%) and vestibular curvature (10%) are possible.

The access cavity has an oval shape, also in the buccal-lingual direction, located in the center of the occlusal surface (Fig. 1.36).

Teeth of ancient people

The dentofacial apparatus of prehistoric and modern humans differs significantly. Ancient people had more than 36 teeth, protruding fangs and a massive jaw. This was explained by the need to chew rough food and raw meat. With the addition of thermally processed foods to the diet, the dentition began to change. The canines were the first to transform, becoming aligned with the bite line. Then the jaw arch narrowed, the interdental spaces disappeared, and the teeth themselves decreased in size. Currently, 32 teeth in humans are the norm, but third molars are considered to be an atavism.

Interesting fact!

The teeth of ancient man cannot be called aesthetic, but they were healthy. According to scientists, cavemen never suffered from caries and other oral diseases.

Upper molars

Three molars in a quadrant without corresponding primary teeth.

Upper first molar

It erupts between 6 and 7 years behind the second primary molar. The formation of the apex is completed between the ages of 9 and 10 years.

The crown has four cusps on the occlusal surface and three roots, one palatal and two vestibular (Fig. 1.38).

Rice. 1.38 First upper molar: occlusal view

The length of the tooth is about 21-22 mm and there is one canal in the palatal and disto-buccal roots

The mesiobuccal root has two separate canals in 60-70% of cases (MB1 and MB2). The second canal in the distobuccal root (DB2) is quite rare (2-3%) (Figs. 1.39, 1.40 and 1.41).

The access cavity to the pulp chamber has a triangular shape with the base facing the buccal side and the apex facing the mesial-palatal tubercle; the cavity is always located mesial (in front) of the transverse ridge, which unites the mesiopalatine tubercle with the distal buccal tubercle. The mouths of the canals are located at the vertices of the triangle, which form the access cavity (Fig. 1.42); if we combine the orifice of the MB1 canal with the palatal orifice, we can find a second mesiobuccal root canal (MB2), which is often closed by calcification (Fig. 1.43).

Rice. 1.39 Anatomical pictures from Hess and Keller: the upper molar has a very complex canal anatomy

Rice. 1.40 Anatomical pictures from Hess and Keller: the upper molar has a very complex canal anatomy; MB1 and MB2 visible in the mesiobuccal root

Rice. 1.41 Anatomical pictures from Hess and Keller: the upper molar has a very complex canal anatomy; MB1 and MB2 visible in the mesiobuccal root

Rice. 1.42 Upper first molar: triangular access cavity with three canals

Rice. 1.43 Upper first molar: access cavity extended to the mesial ridge to locate the MB2 canal on the line connecting the mesiobuccal and palatal canal

Second upper molar

Eruption occurs at the age of 12 years with the completion of the apical third at approximately 14 years.

It is smaller and shorter than the first molar by about 1-2 mm, is about 19-20 mm high and has four occlusal cusps. There are three roots and three canals, just like the first molar, and the MB root also has a second canal (37-42%). The shape of the pulp chamber is rhomboidal rather than triangular (see Figs. 1.42 and 1.43).

Upper third molar

This tooth erupts after age 17. It has a very unique anatomical morphology; the crown has three or five tubercles (Fig. 144). The average height of the third molar is about 18 mm. There may be one root or more often than one - three or four roots, usually curved distally (Figs. 1.45, 1.46, 1.47 and 1.48).

Figure 1.44. The upper third molars have a very distinctive occlusal morphology with three or four cusps

Rice. 1.45. Upper single root third molar

Rice. 1.46. Upper third molar with four distally curved canals

Rice. 1.47. Upper third molar with atypical anatomy

Rice. 1.48. Upper third molar with strong 3D root curvature

Lower molars

Three molars in a quadrant without corresponding primary teeth.

First lower molar

This is the first permanent tooth that erupts at the age of 6 years and completes its formation at approximately 9-10 years. The crown has five cusps, two lingual and three buccal (Fig. 1.49). 22-23 mm long. There are usually two roots, one mesial and one distal (97%), and we rarely find a third distolingual root (3%). In the mesial root we find two canals in 65% of cases: they may have only one apical foramen (40%) or two separate ones (60%). The distal root has one canal (70%) or two canals (30%); there may also be two separate apical foramina (38%) or only one (62%) (Figs. 1.50, 1.51 and 1.52) (Figs. 1.53 and 1.54).

Rice. 1.49. Lower first molar: occlusal view

Rice. 1.50 Anatomical pictures from Hess and Keller: lower molar with very complex canal anatomy

Rice. 1.51 Anatomical pictures from Hess and Keller: lower molar with very complex canal anatomy

Rice. 1.52 Anatomical pictures from Hess and Keller: lower molar with very complex canal anatomy

Rice. 1.53. Micro-computed tomography scan of the roots of lower molars: note the complex morphology of the pulp space

Rice. 1.54. Micro-computed tomography scan of the roots of lower molars: modern digital techniques reproduce the subtle and complex morphology of the pulp space previously illustrated by Hess histological images

All roots on the buccal side have a moderate distal slope. The pulp chamber is triangular or square, depending on the number of canals (3 or 4), located in the center of the crown in the mesial-lingual area. Because of this feature, during the formation of the pulp chamber access cavity, it is important to be careful not to remove precious tooth structure in the distal area.

The shape of the access cavity should be triangular or trapezoidal with the larger base facing the mesial ridge and the smaller (or triangular apex if there is only one distal canal) slightly distal to the central occlusal fossa (Figs. 1.55 and 1.56).

Rice. 1.55 Lower molar: access cavity to three canals

Rice. 1.56 Lower molar: trapezoidal access cavity to four canals

If there is a third root, its mouth can be found along the bottom of the pulp chamber in the corners of the base of the trapezium.

Second lower molar

The tooth erupts at the age of 11 years and is very similar to the lower first molar with some differences.

It is smaller than the first molar by 1-2 mm in each direction. It has four cusps on the occlusal surface and usually two roots, one mesial and one distal. The mesial root has only one canal in 13% of cases; most often there are two channels that end in only one opening (49%), or there are two channels with two independent openings (38%). The distal root has only one canal in 92% of cases. Rarely there are two canals with one apical foramen (5%) or two separate foramina (3%).

The access cavity to the pulp chamber is located in the middle of the mesial-lingual region and has a trapezoidal shape. Due to the size of the pulp chamber and its proximity to the mesial-lingual wall, we advise careful design of the access cavity to avoid unnecessary excision of tooth structure (see Figures 1.55 and 1.56).

Third lower molar

Erupts after 17 years, usually at the age of 25. Also called "wisdom teeth", they have an atypical and varied morphology. It can have from three to five tubercles (Fig. 1.57). Often there is a fusion of roots from two or three roots. And, as a consequence, the anatomy of the canals cannot be schematized, as with the upper molar. Experience in root canal treatment will help the clinician perform the endodontic procedure correctly (Figs. 1.58, 1.59, and 1.60).

Rice. 1.57. The varied occlusal morphology of mandibular third molars may have four to five cusps

Rice. 1.58 (a) Lower third molar with a curved mesial root fused to the distal one. (b) Lower third molar: distal root

Rice. 1.59 (a) Lower third molar with four roots, two mesial and two distal: the mesiobuccal root is a very curved canal in the middle third. (b) Lower third molar: distal view showing graceful curvature of the distolingual root

Rice. 1.60 (a) Lower third molar: on the buccal side, two separate mesial roots are visible with extremely severe curvature, according to Schneider. The distal root has a moderate 3D curvature in the mesial and lingual direction. (b) Lower third molar: from the distal side, a 3D curvature of the distal root is visible in the lingual as well as mesial direction

Igor Lukinykh