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

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.

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 Incisal edge.

A

R

CL

C

IE

Tooth Structure

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

The bone of the tooth socket is called the alveolus.

Tooth Structure

Tooth Structure

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

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 neighbor 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.

Tooth Landmarks

●A tubercle is a smaller elevation (than a cusp) on some portion of the crown produced by an extra formation of enamel.

Tooth Landmarks

●A cingulum 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

-A ridge is any linear elevation on the surface of a tooth and is named according to its location (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 Ridgehttp://www.tpub.com/content/medical/14274/css/14274_80.htm

Tooth Landmarks

-When a buccal and lingual triangular ridge joins, they form a transverse ridge. A transverse ridge is transversely crossing the surface of a posterior tooth.

Transverse Ridgehttp://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.

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

Tooth Landmarks

A fossa is an irregular depression.

Lingual fossae are on the lingual surface of incisors.

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.

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

http://www.tpub.com/content/medical/14274/css/14274_78.htm

Tooth Landmarks

A developmental groove is a shallow groove or line between the primary parts of the crown or root

Tooth Landmarks

-A supplemental groove is a shallower linear depression on the surface of a tooth, but it is supplemental to a developmental groove and does not mark the junction of primary parts

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 (e.g. central pit is a term describes a landmark in the central fossa of molars where developmental grooves join).

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.

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

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.