Crown curvature sign
This criterion is based on the pronounced asymmetry of the convexities of the buccal and labial surfaces of the tooth crown. The evaluation of curvature depends on the tooth group:
- For the anterior tooth group: the maximum convexity is always shifted closer to the midline. Consequently, the medial part of the crown is more convex, while its lateral part is flattened and significantly less prominent.
- For the posterior tooth group: a similar asymmetry is observed, but in a different projection. The anterior part of the vestibular surface has greater convexity, while the posterior part is less convex.
Crown angle sign
This sign consists in evaluating the angles formed by the convergence of various crown surfaces. The rule states that certain surfaces form a sharper angle, whereas the opposite crown angles are always more obtuse.
- For anterior teeth: the sharpest angle is formed at the junction of the medial surface and the incisal edge.
- For the posterior group: the sharper angle is the one formed by the intersection of the anterior and occlusal (masticatory) surfaces.
Root sign
The third most important criterion for tooth lateralization is the characteristic spatial deviation of its root part.
- Anterior tooth group: the roots of these teeth tend to deviate from the midline strictly in a lateral direction.
- Posterior tooth group: the roots demonstrate a deviation in the posterior direction relative to the main longitudinal axis of the tooth root.
Permanent teeth (Dentes permanentes)
In dental practice, permanent teeth of an adult are classified into groups. According to the universally accepted digital designation, the following categories are distinguished:
- Incisors — designated by numbers 1 and 2.
- Canines — designated by number 3.
- Premolars — designated by numbers 4 and 5.
- Molars — designated by numbers 6, 7 and 8.
Briefly: answers to topical questions
Which muscles belong to the group of muscles of mastication?
The group of muscles of mastication includes four main paired muscles that attach to the mandible and perform the act of chewing. According to the anatomical classification, this group includes:
- Masseter muscle
- Temporalis muscle
- Medial pterygoid muscle
- Lateral pterygoid muscle
What is the innervation of the muscles of mastication?
The muscles of mastication are innervated by motor fibers of the mandibular nerve (n. mandibularis), which is the third branch of the trigeminal nerve (V3). Specifically, the masseter muscle is supplied predominantly by the motor masseteric nerve (n. massetericus), branching off from the main trunk of the mandibular nerve and penetrating the muscle through the mandibular notch.
Where does the temporalis muscle originate and insert?
The temporalis muscle is located in the subaponeurotic space of the temporal region beneath the temporal fascia and attaches to the anterior pointed coronoid process (Processus coronoideus) of the mandible. The exact origin of this muscle is not specified in the provided materials, however, it is known that during trauma, the powerful temporalis muscle is capable of avulsing the thin coronoid process.
What functions does the lateral pterygoid muscle perform?
The lateral pterygoid muscle participates in the depression of the mandible and mouth opening. It has two heads — upper and lower.
Where does the medial pterygoid muscle originate and insert?
The medial pterygoid muscle attaches to the pterygoid tuberosity (Tuberositas pterygoidea) on the inner surface of the angle of the mandible. Its exact origin is not specified in the provided materials. It belongs to the muscles that elevate the mandible.
Which muscles depress the mandible?
Depression of the mandible and mouth opening are performed by the following muscles of the anterior group:
- Mylohyoid muscle (forms the floor of the oral cavity)
- Geniohyoid muscle
- Digastric muscle (anterior and posterior bellies)
- Lateral pterygoid muscle
- Stylohyoid muscle
For their effective biomechanical action, the hyoid bone must be rigidly fixed by the underlying musculature.
Which arteries supply blood to the muscles of mastication?
Blood supply to the masseter muscle is provided from branches of the external carotid artery. Directly approaching it are:
- Transverse facial artery (a. transversa faciei) — a branch of the superficial temporal artery.
- Masseteric artery (a. masseterica) — a branch of the maxillary artery.
Information on the blood supply to the remaining muscles of mastication (temporalis, lateral and medial pterygoids) is not presented in the sources.
The rule of three "C"s for the tooth side: Curvature (convexity anteriorly/medially), Corner (sharp angle anteriorly/medially), and Root (deviated posteriorly/laterally).
Class and exam questions
Which surfaces form a sharp angle in posterior teeth?
In posterior teeth, the anterior and occlusal surfaces form a sharper angle.
How do the roots of the anterior group of teeth deviate?
In anterior teeth, the roots are specifically deviated from the midline in a lateral direction.
What is the sign of crown curvature for anterior teeth?
The convexity of the labial surface is shifted toward the midline: closer to the medial surface, crowns are more convex, while their lateral part is less convex.
What else to study on this topic
- Anatomical structure of incisors (teeth 1, 2)
- Morphological features of canines (tooth 3)
- Structure of premolars (teeth 4, 5)
- Specifics of molar structure (teeth 6, 7, 8)
- Comparison of lateralization signs between the upper and lower jaws
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Other topics in the section "Chapter 4. Structure of the Dentoalveolar System"
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