The Development of the Dentition in Class II/2 Malocclusions
The Class II/2 malocclusion is characterized by a Class II occlusion of the posterior teeth, a distinct retroinclination of two or more maxillary incisors, and a retrusion of the mandibular incisors. However, the most important characteristic of the Class II/2 malocclusion is the high position of the lip line in the median plane (stomion) in relation to the maxillary incisors. Normally the lower and the upper lip contact at a level of one to three millimeters superiorly to the incisal edges of the maxillary centrals. In Class II/2 malocclusions, the lip line is more superiorly located in the median plane and often at the level of the cervical region of the maxillary centrals.
The Class II/2 malocclusion deviates clearly from the Class II/1, not only in its appearance, but also in its development. Furthermore, the dental characteristics of the Class II/2 malocclusion appear in a relatively late phase of the development. Soon after emergence of the maxillary permanent incisors, it becomes obvious in Class II/1 malocclusions that these teeth will protrude too much and that the adequate lip closure may be jeopardized. In Class II/2 malocclusions, the lip closure does not incur a risk.
In Class II/2 malocclusions, three types (A, B, and C) can be distinguished based on differences in the spatial conditions in the maxillary dental arch. In this discussion it is assumed that only in the development of Type A no deviations are originally present in both dental arches.
A Class II/2 malocclusion initially develops as a Class II/1. In the deciduous dentition and in the first transitional period, the normally shaped and sized mandibular dental arch is situated too much dorsally in relation to the maxillary one. The transverse relation between opposing posterior teeth is the same in Class II/2 as in Class II/1 malocclusions. The most important difference in the early developmental stages between the two malocclusions indicated above is formed by the superior location of the lip line. In Class II/2 malocclusions, stomion is often situated at the junction of the maxillary central deciduous incisor crowns and the labial gingival tissue (Figs. 11-1A and B). In Class II/1 malocclusions, stomion is usually located near the incisal edge of the maxillary central deciduous incisors (Fig. 10-4). In Class II/2 the lower lip covers the labial surfaces of the maxillary deciduous incisors. These teeth are more vertically oriented in the jaw than in a Class II/1 malocclusion. They are also, although slightly, more vertically oriented than in patients with normal development of the dentition (Fig. 4-3).
Fig. 11-1 Survey of the changes in the incisor and molar regions in a Class II/2 malocclusion, from the complete deciduous dentition to the adult situation. The drawings are composed of cross sections through the right molars, the right central incisors and surrounding bony structures, and the profile (compare with Figs. 4-3 and 10-4).
A In the complete deciduous dentition, the maxillary deciduous incisors are slightly less labially inclined than normal. The overjet is somewhat enlarged. Both features differ from the picture in the Class II/1 malocclusion, in which the deciduous incisors are usually somewhat abnormally inclined labially and the overjet is considerably larger than normal. In the Class II/2 malocclusion, the lips are often rather voluminous and the lip line in the median plane (stomion) is situated at the level of the cervical border of the maxillary central deciduous incisors.
B The mandibular permanent incisor has emerged normally; the maxillary one continues to erupt within the jaw. Prior to emergence, the position of the latter may be normal or slightly more upright. The high lip line relation to the maxillary deciduous incisors is maintained.
C The maxillary central permanent incisor has emerged according to its previous orientation within the jaw. In accordance with the superior lip line position, the upper lip has only limited effect on the inclination and further eruption of the maxillary centrals. In this stage of development, the lower lip may lead to a limited lingual tipping of the mandibular incisors.
D The mandibular and maxillary central permanent incisors erupt further. The maxillary central gradually becomes more affected by the lower lip. With continuing eruption of the maxillary central, the size of the contacting area between its crown and the lower lip increases leading to a further lingual tipping of that tooth.
E Because of the Class II relation between the two dental arches, no sagittal or vertical contact existed between the mandibular and maxillary incisors prior to this stage. The eruption of the incisors has continued until vertical contact has been attained. As a result, the mandibular as well as the maxillary incisors have overerupted. The inclination of the palatally tipped maxillary incisor is unfavorable for supporting the mandibular incisor vertically. Upon the attainment of sagittal contact between the mandibular and maxillary central incisors, the pressure of the lower lip will also lead to a lingual tipping of the mandibular teeth as the force is transmitted through the maxillary teeth, which continue to tip palatally.
F In the adult situation, the maxillary central incisor is tipped severely palatally and its labial surface is completely covered by the lower lip. The lower lip does not, or only in a very limited way, support the maxillary central incisor vertically. The maxillary incisors may contact the gingiva labially to the mandibular ones. In a comparable way, the maxillary central incisor received little or no support vertically from the mandibular incisors, which in turn usually contact the palatal mucosa.
Upon emergence, two or more maxillary permanent incisors tip palatally under influence of the abnormal lip position and the forces exerted by the lower lip on the maxillary incisors (Fig. 11-1;31, 36, 37, 47, 60