The Development of the Dentition in Class III Malocclusions
A Class III malocclusion is characterized by a ventral position of the mandibular dental arch in relation to the maxillary one. In comparison with the normal situation, the mandibular posterior teeth occlude too much mesially with the maxillary ones. In the incisor region, a reversed overjet exists with the incisal edges of the mandibular incisors ventrally to those of the maxillary ones. As has been explained before, the Angle Classification leaves undecided whether the primary factor that caused the malocclusion is located in the mandible, the maxilla, or in a combination of both. This etiological neutrality holds equally true for Class III as well as Class II malocclusions.
Theoretically, it could be stated that in Class III malocclusions as well as in Class II/1 malocclusions, the shape of the mandibular dental arch is basically normal as seen occlusally. However, this is not the case. In Class II/1 malocclusions, a normal though enlarged anteroposterior relation between the maxillary and mandibular incisors exists, resulting secondarily in an increased overjet and overbite. Viewed occlusally, the shape of the mandibular dental arch is not or only slightly influenced by the occlusion. This is not the case in the Class III malocclusions, as reversed anteroposterior relation of the incisors is accompanied by significantly deviating occlusal contacts. In the development of a Class III, the maxillary and mandibular incisors can become displaced reciprocally. These changes are not limited to the maxillary dental arch, but also involve alterations in the location of several teeth in the mandibular arch. Diastemata may develop in the mandible, particularly in cases with no shortage of space for the mandibular teeth.
As in the discussion of the development of the dentition in Class II/1 malocclusions, the discussion of Class III malocclusions starts with the situation in the deciduous dentition (Fig. 12-1), followed by the intertransitional period (Fig. 12-2), and the permanent dentition (Fig. 12-3). Subsequently, the eruption of the first permanent molars and the transition of the incisors is described (Fig. 12-4). Finally, the transition of the posterior teeth is treated (Fig. 12-5).
Fig. 12-1 Survey of a Class III malocclusion in the complete deciduous dentition (compare with Fig. 3-1).
A,B The mandibular dental arch is too far ventral in relation to the maxillary one. A good transverse relation exists between the mandibular and maxillary deciduous molars. The opposing four mandibular incisors and canines are situated in a reversed overjet (anterior cross bite).
C The mandibular incisors and canines are situated ventrally to the maxillary ones. A limited overbite is present.
D The mandibular deciduous molars occlude too far mesially to the maxillary ones. The terminal plane of the deciduous dentition shows an abnormally large mesial step.
Fig. 12-2 Survey of a Class III malocclusion in the intertransitional period. In comparison with the illustration in Figure 12-1 of the deciduous dentition, the malocclusion has aggravated considerably (see also Fig.5-1).
A,B Ventral position of the mandibular dental arch in relation to the maxillary one. Reversed overjet in the incisor-canine region. The individual position of the teeth is in accordance with the deviation in contacts and the crossing over of the occlusion in the canine region.
C The mandibular and maxillary incisors have erupted further. The incisal edges of the maxillary incisors contact the lingual surfaces of the mandibular incisors.
D The mandibular first permanent molar occludes too far mesially to the maxillary one. The contact surface between them is small.
Fig. 12-3 Survey of Class III malocclusion in the permanent dentition (compare with Fig. 7-1).
A,B Ventral position of the mandibular dental arch in relation to the maxillary one; reversed overjet in the anterior region. The position of the individual teeth is adapted to the deviations in occlusal relations.
C Also the mandibular permanent canines are positioned labially to the maxillary lateral incisors.
D All posteri/>