Dental Anatomy is a subject in which, through the knowledge of basic sciences, a practical skill may be obtained for a dental practitioner. Morphology of teeth helps and guides us to identify developmental anomalies, which may be one of the features of clinical condition and also helps to provide skills for restoring a tooth or replacing a tooth.
An attempt is made to simplify the morphology of teeth and carving technique. A simpler carving technique is provided in this textbook for dental students.
PRINCIPLES OF CARVING TECHNIQUE
- A modified pen grasp should be used to hold a lecron carver (Fig. 1.1)
- Wax block should be smoothened before carving is proceeded.
- Direction of carving should be in one direction only.
- Uniform pressure should be applied during carving.
- Finishing is done by removing the excess wax and also by carving the surface uniform.
- After finishing, polishing should be done by using a pellet of cotton or a piece of soft cloth. A pellet of cotton is preferable to polish the minor details of teeth. Polishing should also follow the carving, otherwise the carved features will be lost.
Modified pen grasp used in carving: the right thumb and index finger will hold the carver, the middle finger placed near the carving edge which will control the carving. The ring finger and little finger will support the wax block (Fig. 1.1).
NOMENCLATURE
Certain terms should be known to understand dental anatomy. The term maxillary means upper jaw, mandibular means lower jaw. Primary means belonging to the first stage of any process. The term deciduous means not permanent, transitory.2
Fig. 1.2: Photograph showing crown and root of various permanent mandibular teeth(Courtesy: Department of Oral Pathology, Vydehi Institute of Dental Sciences, Bangalore)
Deciduous teeth commonly called as milk tooth is defined as “One of the temporary teeth of a mammal that are replaced by permanent teeth.”
The term succedaneous can be used to describe a successor dentition. The term permanent dentition suggests it is permanent (Fig. 1.2).
Each tooth has a crown and root portion. The crown is covered with enamel and the root portion is covered with cementum. The junction of crown and root is cervical line. The hard tissues of a tooth are enamel, dentin and cementum. The soft tissue of a tooth is pulp.3
Fig. 1.3: Crown and root(Courtesy: Department of Oral Pathology, Vydehi Institute of Dental Sciences, Bangalore)
SURFACE
Anterior teeth are incisors and canines. Posterior teeth are premolars and molars. Surfaces of anterior teeth are:
- Labial surface: Surface toward the lips
- Mesial surface: Surface toward the midline
- Distal surface: Surface away from the midline
- Lingual surface: Surface toward the tongue
- Palatal surface: Surface toward the palate
Surfaces of posterior teeth are:
- Buccal/facial surface: Surface toward the cheek
- Mesial surface: Surface toward the midline
- Distal surface: Surface away from the midline
- Lingual surface: Surface toward the tongue
- Palatal surface: Surface toward the palate
Cusp: A cusp is an elevation or mound on the crown portion of a tooth making up a divisional part of the occlusal surface (Fig. 1.5).
Tubercle: A tubercle is a smaller elevation on some portion of the crown produced by an extra formation of enamel.4
Fig. 1.4: Cingulum, ridge and fossa(Courtesy: Department of Oral Pathology, Vydehi Institute of Dental Sciences, Bangalore)
Fig. 1.5: Ridges and cusp(Courtesy: Department of Oral Pathology, Vydehi Institute of Dental Sciences, Bangalore)
Cingulum: A cingulum or girdle, is the lingual lobe of an anterior tooth and makes up the bulk of the cervical third of the lingual surface (Fig. 1.4).
Ridge: A ridge is any linear elevation on the surface of a tooth and is named according to its location (e.g. buccal, incisal, marginal, etc.) (Figs 1.4 and 1.5).
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 mesial and distal margins of the lingual surfaces of the incisors and canine.
Triangular ridges descend from tips of the cusps of molars and premolars toward the central part of the occlusal surface. They are named after the cusps to which they belong. When a buccal and lingual triangular ridge join, they form a transverse ridge. A transverse ridge is the union of two triangular ridges transversely crossing the surface of a posterior tooth.
Oblique ridge: The oblique ridge is a ridge obliquely crossing the occlusal surfaces of maxillary molars and formed by the union of triangular ridge of distobuccal cusp and distal cusp ridge of mesiolingual cusp.5
Fig. 1.6: Sulcus(Courtesy: Department of Oral Pathology, Vydehi Institute of Dental Sciences, Bangalore)
Fig. 1.7: Photograph showing grooves and pits(Courtesy: Department of Oral Pathology, Vydehi Institute of Dental Sciences, Bangalore)
Fossa (Fig. 1.4): A fossa is an irregular depression or concavity; they are named according to the location. Lingual fossae are seen on lingual surface of incisors and central fossae on occlusal surface of molars. Triangular fossae are found on premolars and molars on the occlusal surface, mesial or distal to marginal ridges.
Sulcus: A sulcus is a long depression or valley on the surface of a tooth between ridges and cusps, the inclines of which meet at an angle. Sulcus has a developmental groove at the junction of its inclines (Fig. 1.6).
Groove (Fig. 1.7): A developmental groove is a shallow groove or line between the primary parts of the crown or root. A supplementary groove is also a shallow linear depression on surface of a tooth, radiating from the developmental groove, but does not mark the junction of primary parts.
Different types of developmental grooves are seen such as: central develop-mental groove, mesial developmental groove, distal developmental groove, buccal developmental groove, lingual developmental groove, etc.
Pits (Fig. 1.7): Pit is a small pinpoint depression located at the junction of develop-mental grooves or at terminals of these grooves. Types are—central pit, distal pit and mesial pit.6
Lobe: A lobe is one of the primary sections of formation in the development of crown. Cusps and mamelons are representative of lobes. A mamelon is any one of the three rounded protuberances found on the incisal ridges of newly erupted incisor teeth.
Division into thirds of crown and root for descriptive purpose and easy understanding.1,2 The crown and root are divided into thirds. Cervical third, middle third and incisal/occlusal third of crown. Cervical third, middle third and apical third of root (Fig. 1.8).
A line angle is formed by the junction of two surfaces. The line angles of anterior teeth are (Fig. 1.9):
- Mesiolabial
- Distolabial
- Mesiolingual
- Distolingual
- Labioincisal
- Linguoincisal
The line angles of posterior teeth are (Fig. 1.10):
- Mesiobuccal
- Distobuccal
- Mesiolingual
- Distolingual
- Labio occlusal
- Linguo occlusal
A point angle is formed by the junction of three surfaces. The point angles of anterior teeth are (Fig. 1.11):
- Mesiolabio incisal
- Distolabio incisal
- Mesiolingual incisal
- Distolingual incisal
The point angles of posterior teeth are (Fig. 1.11):
- Mesiobucco occlusal
- Distobucco occlusal
- Mesiolingual occlusal
- Distolingual occlusal
Fig. 1.9: The ink marking is to represent line angles on the crown as well as on the root of a anterior tooth(Courtesy: Department of Oral Pathology, Vydehi Institute of Dental Sciences, Bangalore)
Fig. 1.10: Photograph showing mesiolingual and distolingual line angles of posterior tooth (ink markings)(Courtesy: Department of Oral Pathology, Vydehi Institute of Dental Sciences, Bangalore)
Fig. 1.11: The ink dot markings in the picture showing point angles described in text(Courtesy: Department of Oral Pathology, Vydehi Institute of Dental Sciences, Bangalore)
CHRONOLOGIES OF HUMAN DENTITION2
Many early labels and charts disagreed on timing of chronological events. One of the altered and widely used table by Schour and Massler and presents a long history of subsequent development and compilations (Table 1.1).
REFERENCES
- Woelfel JB, Scheid RC. Dental Anatomy. Williams & Wilkins. 1997.
- Ash, Nelson. Wheelers Dental Anatomy, Physiology & Occlusion. 8th edition. Elsevier. 2003.