Place in the maxillofacial system
Teeth (dentes) are unique organs of the oral cavity constructed of exceptionally hard tissues. They are rigidly and securely anchored in special sockets of the upper and lower jaws. The maxillofacial apparatus functions as a single entity, where teeth work in close interaction with the jaws.
Incisors (dentes incisivi) occupy the anterior position in the dental arch. Their main functions are biting off food, as well as active participation in sound production and the formation of articulate speech. In each dental arch of an adult, which normally includes sixteen teeth, there are exactly four incisors. They are followed by two canines (dentes canini), four premolars (dentes premolares), and six molars (dentes molares).
Dental formulas and incisor position
The dental arch represents a specific sequence of tooth arrangement that directly depends on their functional purpose. A dental formula is used to record the quantitative ratio and order of arrangement of the teeth.
In the complete clinical dental formula, the location of each tooth is designated by a number corresponding to its ordinal number. The dental arches are divided into four quadrants (maxillary and mandibular, right and left) using horizontal and median planes. The recording order strictly corresponds to the physician's view of the patient sitting opposite. In this system, central incisors are designated by the number "1", and lateral incisors by the number "2".
The WHO dental formula is more detailed. It includes the numbering of jaw halves and the numbering of the tooth itself. According to this system:
- 1 — left half of the maxilla;
- 2 — right half of the maxilla;
- 3 — right half of the mandible;
- 4 — left half of the mandible.
Thus, the upper left central incisor is recorded as 11, and the lower right lateral incisor as 32.
Dental arch and antagonists
Incisors form the anterior segment of the dental arch—an imaginary line passing along the vestibular edges of the chewing surfaces and the cutting edges of the crowns. The upper dental arch (arcus dentalis superior) is normally somewhat wider than the lower dental arch (arcus dentalis inferior).
The biomechanics of the maxillofacial system is arranged so that, thanks to interdental contacts, pressure during biting and chewing is distributed to adjacent teeth. The load is distributed across the entire dental arch, which significantly reduces the mechanical impact on individual roots of the incisors.
When the jaws close, the teeth contact antagonist teeth—touching teeth of the opposite row. Normally, each tooth has two antagonists: a main one and an accessory one. However, incisor anatomy has an important exception: the mandibular medial (central) incisors have only one antagonist each. The only other exception in the oral cavity is the maxillary last molars.
Surgical instruments for incisors
When extraction of the upper incisors (both central and lateral) is necessary, specialized instruments are used. The design of dental forceps must always strictly correspond to the anatomical features of the tooth being extracted.
In oral surgery, forceps are classified by several features. Regarding jaw affiliation, instruments for the upper jaw differ in that the longitudinal axis of the beaks and the axis of the handles coincide, are parallel, or form an obtuse angle. For the lower jaw, these axes are located at a right angle (90 degrees) or close to it.
Straight forceps are used for upper incisors and canines. Their main anatomical feature (angle feature)—the longitudinal axes of the beaks and handles are in the same plane and completely coincide, forming a straight line.
Both beaks of straight forceps have the same shape (unlike, for example, forceps for upper molars, which have a side feature—a spike on one of the beaks). On the inner side, the beaks of straight forceps are equipped with a special recess (groove) for a better grip on the tooth, and their ends are rounded. Depending on the size of the incisor crown, the doctor can choose straight forceps with a larger or smaller beak width.
The crown preservation feature is also taken into account:
- Crown forceps are used for incisors with a preserved crown (when closing the instrument, their beaks do not meet).
- Root forceps are used for extracting incisor roots (when closing, their beaks meet).
To remember the exceptions among antagonists, use the edge rule: "The very first at the bottom and the very last at the top." Mandibular medial incisors (first) and maxillary last molars (last) have only one antagonist each.
Class and exam questions
How many incisors does an adult normally have?
In the complete dentition of an adult, there are 8 incisors: 4 each on the upper and lower jaws.
Which teeth have only one antagonist?
Normally, each tooth has two antagonists. The exceptions are the mandibular medial incisors and the maxillary last molars—they have only one antagonist each.
What instrument is used to extract upper incisors?
Straight forceps are used to extract the central and lateral incisors of the upper jaw. Their longitudinal axes of the beaks and handles coincide and are in the same plane.
How do crown forceps differ from root forceps during incisor extraction?
In crown forceps intended for teeth with a preserved crown, the beaks do not meet when closed. In root forceps used for root extraction, the beaks meet.
What else to study on this topic
- Anatomy and biomechanics of canines (dentes canini)
- Structure of premolars and molars
- S-shaped and bayonet forceps: indications for use
- Angle feature and side feature in surgical instruments
- Design features of mandibular forceps with limited mouth opening
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