Crown and Root Landmarks, Division into Thirds, Line Angles and Point Angles.

Aims and Objectives An introduction to the main parts of the tooth. Understanding the nomenclature of the tooth landmarks. Knowledge of the division of teeth into thirds for a better description of teeth. Familiarity with the line angles and point angles.

The Crown and Root The crown. The root(s). Anatomically, each tooth is divided into 2 main parts: The crown. The root(s).

Tooth Structure .A tooth has a crown and root(s) with a pulp chamber and root canal(s). Enamel, dentine, pulp tissue and cementum make up a tooth. The crown and root join at the cementoenamel junction (CEJ), the cervical line.

Dental tissues A. Enamel. The protective outer surface of the anatomic crown. It is 96% mineral and is the hardest tissue in the body. B. Dentin. Located in both the crown and root, it makes up the bulk of the tooth beneath the enamel and cementum. It lines the pulp cavity. C. Cementum. This substance covers the surface of the anatomic root. D. Pulp. The central, innermost portion of the tooth. It has formative, sensory, nutritive, and functions during the life of the tooth.

Tooth Structure Incisor teeth (central and lateral) have incisal edges. Canines have single cusps. Premolars and molars have two or more cusps.

Tooth Structure A Apex of the root. R Root. CL Cervical line. C Crown. IE A Apex of the root. R Root. CL Cervical line. C Crown. IE Incisal edge.

Tooth Structure The root is fixed in the bony process of the jaw called the alveolar process.

Tooth Structure The bone of the tooth socket is called the alveolus.

Tooth Structure The fully erupted crown is partly covered at the cervical third in young adults by the gingiva or gums.

Parts of the Tooth A. Crown. The term can be defined in two ways. The anatomical crown is covered with enamel. The clinical crown is the portion of the anatomical crown that is visible clinically. It is what you see when you look in the mouth.

Parts of the Tooth B. Root. The term can be defined in two ways. - The anatomical root is the portion of the tooth that is covered with cementum, a bone-like substance that facilitates anchorage of the tooth in its bony socket (the alveolus). - The clinical root is that part of the anatomical root that is actually embedded in the jaw. In a patient with advanced bone loss, the clinical root may be reduced in size.

Parts of the Tooth C. Cervical line. This is the line that separates the anatomic crown from the anatomic root. It is the junction between two tissues--the enamel and the cementum. It is also called the cemento-enamel junction or simply the CEJ. This region of the tooth is also called the cervix of the tooth. The cervical line is important in your laboratory drawings. D. Pulp cavity. This is the space in the tooth that in life contains the pulp or 'nerve' of the tooth. In your specimens, the pulp will be withered or absent. It has a coronal (crown) portion and a radicular (root) portion, usually called the root canal.

Surfaces and Ridges - Incisors and canines have four surfaces and a ridge. - Premolars and molars have five surfaces. - Surfaces are named according to their positions and uses .

Surfaces and Ridges - In anterior teeth (Incisors and canines) the surfaces toward the lips are called labial surfaces. - In premolars and molars surfaces facing the cheek are called buccal surfaces. - Collectively, labial and buccal surfaces are called Facial Surfaces.

Surfaces and Ridges - Surfaces facing the tongue are called lingual surfaces. - Surfaces of premolars and molars that come in contact with those in the opposite jaw are called occlusal surfaces. - These are called incisal surfaces in the anterior teeth.

Surfaces and Ridges - Surfaces facing adjacent teeth in the same dental arch are called proximal surfaces. Proximal surfaces are either mesial or distal. Proximal surfaces facing the median line are called mesial surfaces and those distant from the median line are called distal surfaces.

Surfaces and Ridges The area of the mesial or distal surface of a tooth that touches its neighbour in the arch is called the contact area.

Tooth Landmarks A cusp is an elevation on the crown portion of a tooth making up a divisional part of the occlusal surface. (or a peak on the occlusal surface of molar and premolar teeth and on the incisal edges of canines)

Tooth Landmarks Tubercle is a smaller elevation (than a cusp) on some portion of the crown produced by an extra formation of enamel. These occur on the marginal ridges of posterior teeth or on the cingulum of anterior teeth. These are deviations from the typical form.

Tooth Landmarks Cingulum: a bulge or elevation on the lingual surface of incisors or canines. It is the lingual lobe of an anterior tooth and makes up the bulk of the cervical third of the lingual surface. Its convexity mesiodistally resembles a girdle encircling the lingual surface at the cervical third.

CL Cervical Line CI Cingulum MR Marginal Ridge LF Lingual Fossa IR Incisal Ridge

Tooth Landmarks - Ridge: Any linear elevation on the surface of a tooth. It is named according to its location or form (e.g., buccal, incisal, or marginal ridge).

CL Cervical Line CI Cingulum MR Marginal Ridge LF Lingual Fossa IR Incisal Ridge

Tooth Landmarks - Marginal ridges are those rounded borders of the enamel that form the mesial and distal margins of the occlusal surfaces of premolars and molars and the mesial and distal margins of the lingual surfaces of the incisors and canines.

CL Cervical Line CI Cingulum MR Marginal Ridge LF Lingual Fossa IR Incisal Ridge

Tooth Landmarks -Triangular ridges descend from the tips of the cusps of molars and premolars toward the central part of the occlusal surfaces. The slopes of each side of the ridge are inclined to resemble two sides of a triangle. They are named after the cusps to which they belong (e.g., the triangular ridge of the buccal cusp).

Triangular Ridge http://www.tpub.com/content/medical/14274/css/14274_80.htm

Tooth Landmarks Transverse ridges are created when a buccal and lingual triangular ridges join. It is the union of two triangular ridges crossing transversely across the surface of a posterior tooth.

Transverse Ridge http://www.tpub.com/content/medical/14274/css/14274_80.htm

Tooth Landmarks -The oblique ridge is a ridge obliquely crossing the occlusal surfaces of maxillary molars and formed by the union of the triangular ridge of the distobuccal cusp and the distal cusp ridge of the mesiolingual cusp. They are a companion to the distal oblique groove.

Oblique Ridge http://www.tpub.com/content/medical/14274/css/14274_80.htm

Tooth Landmarks - Cervical ridges are the height of contour at the gingival, on certain deciduous and permanent teeth.

Tooth Landmarks Fossa: An irregular, rounded depression or concavity found on the surface of a tooth. Lingual fossae are found on the lingual surface of incisors.

Central fossae are on the occlusal surface of molars Central fossae are on the occlusal surface of molars. They are formed by the convergence of ridges terminating at a central point in the bottom of the depression where a junction of grooves occurs. http://www.tpub.com/content/medical/14274/css/14274_78.htm

Tooth Landmarks -Triangular fossae are found on posterior teeth on the occlusal surfaces mesial or distal to marginal ridges.

Tooth Landmarks -A sulcus is a long depression or valley in the surface of a tooth between ridges and cusps, the inclines of which meet at an angle. A sulcus has a developmental groove at the junction of its inclines.

Sulcus http://www.tpub.com/content/medical/14274/css/14274_80.htm

Tooth Landmarks A developmental groove is a sharply defined, narrow and linear depression formed during tooth development and usually separating lobes or major portions of a tooth. Major grooves are named according to their location. http://www.tpub.com/content/medical/14274/css/14274_78.htm

Tooth Landmarks -A supplemental groove is a shallower linear depression on the surface of a tooth, but it is but it is usually less distinct and is more variable than a developmental groove and does not mark the junction of primary parts of a tooth

Tooth Landmarks -Buccal and lingual grooves are developmental grooves found on the buccal and lingual surfaces of posterior teeth.

Tooth Landmarks -Pits are small pinpoint depressions located at the junction of developmental grooves or at terminals of those grooves. A central pit is found in the central fossa on the occlusal surfaces of molars where developmental grooves join. A pit is often the site of the onset of dental caries.

Tooth Landmarks -A lobe is one of the primary sections of formation in the development of the crown (cusps and mamelons). A mamelon is any one of the three rounded protuberances found on the incisal ridges of newly erupted incisor teeth.

Maxillary First Molar CF Central Fossa DBC Distobuccal Cusp DMR Distal Marginal Ridge OR Oblique Ridge DLC Distolingual Cusp DG Developmental Grooves BCR Buccocervical Ridge BG Buccal Groove MBC Mesiobuccal cusp SG Supplemental Groove TF Triangular Fossa MLC Mesiolingual Cusp Maxillary First Molar

Mandibular First Molar TRR Transverse Ridge DLC Distolingual Cusp TR Triangular Ridge DC Distal Cusp DBC Distobuccal cusp DBG Distovuccal Groove CF Central Fossa MLC Mesiolingual Cusp MMR Mesial Marginal Ridge MBC Mesiobuccal cusp MBG Mesiobuccal Groove BCR Buccocervcal Ridge Mandibular First Molar

Division into Thirds -.The crown is divided into an incisal or occlusal third, a middle third, and a cervical third. The root is divided into a cervical third, a middle third, and an apical third.

Line Angles -. A line angle is formed by the junction of two surfaces and derives its name from the combination of the two surfaces that join

Point Angles -A point angle is formed by the junction of three surfaces. The point angle also derives its name from the combination of the names of the surfaces forming it. For example, the junction of the mesial, buccal, and occlusal surfaces of a molar is called the mesiobuccoocclusal point angle.