The first classification system employs a description of the angulation of the long axis of the impacted third molar _vith respect to the 19n9 axis of the second molar. Because teeth at certain inclinations have ready-made
pathways for withdrawal, whereas pathways for teeth of other inclinations require the removal of substantial amounts of bone, this classification system provides an initial evaluation of the difficulty of extractions.
The mesioangular impactlon is generally acknowledged as the least difficult impaction toremove (Fig. 9-16). The mesioangular-impacted tooth is tilted toward the second molar in a mesial direction. This type of impaction is also the most commonly seen and comprises approximately’ 43% of all impacted teeth. In a severe mesial inclination the impacted tooth is
horizontal (Fig. 9-17). This type of impaction is usually considered ‘110re difficult to remove than the mesioangular impaction. Horizontal impactions occur I~s frequently and are only seen in approximately 3% of all mandibular impactions.
FIG. 9-16 A, Mesioangular impaction-most common and easiest impaction to remove. 8, Mesioc
angular impaction is usually in close proximity to second molar
FIG. 9-17 A, Horizontal impaction-uncommon and more difficult to remove than me~ioangular impaction. 8, Occlusal surface of horizontal impacted third molar is usually immediately adjacent to root of second molar, which often produces early severe periodontal disease In the vertical impaction the long axis of the impacted toorn runs in the same direction as the long axis of the second molar. This impaction occurs with the second greatest frequency, accounts for approximately 38% of all impact” and is t rd in difficulty of removal (Fig.9-18). Finally, the istoangular impaction is the tooth. with the mo t difficult angulation for removal (Fig. 9-19). In the distoangular impaction the long axis of the third molar is distally or posteriorly angled away from second molar. This impaction is the most difficult to remove because the tooth has a ithdrawal pathway that runs into the mandibular ramus, and its removal requires greater surgical int~rvention. Distoangular impactions occur uncommonly and account for- only approximately 6’Yo) of all impacted third molars. Erupted third molars may be in a distoanguli\r position. When this occurs, they are extremely difficult to remove routinely, compared with the removal of other erupted teeth.
A, Vertical impaction-second most common impaction and second most difficult to
remove. B, Vertical impaction is frequently covered on its posterior aspect with bone of anterior ramus
A, Distoangular impaction-uncommon and most difficult of the four types to remove. B, Occlusal surface of distoangular impaction is usually mbedded in ramus of mandible and requires significant bone removal for extraction. In addition to the relationship between the angulation of the long axes of the second and third molars, the teeth . can also be angled in a buccal or lingual direction. As is noted earlier, the linguocortical plate of the mandible becomes thinner as it progresses posteriorly. Therefore most mandibular third molars are angled toward the lingual direction orin lingual version. Occasionally, a tooth is angled toward the buccal aspect of he mandible or in bucca I version.; Itt[ciy a tooth is a transverse impaction, that is, in an absoluiotv horizontal position in a buccolingual direction. The OCclusal surface of the tooth can face either the buccal or lingual direction. To determine buccal or lin- . gual version accurately, the dentist must take a perpen
occlusal film. However, this determination is usually not necessary, because the surgeon can make this identification early in the operation, and the buccal or lingual position of the tooth does not greatly influence
the difficulty of the surgery