1. The euryprosopic facial form
The mongoloid has different characteristics to the Caucasoid or negroid, they are more common to have broad and flat facial profile with prominent zygomatic arches.15 Small nasal bones and a concave nasal profile are also common features for the mongoloid. To describe a face which is broad and not long, Franco et al1 pointed out that “euryprosopic” should be more specific and relevant than " brachyfacial". The authors indicated that the facial width is not considered in most classification system, and the terms related to cephalometric index such as dolicocephalic and brachycephalic are not able to describe the face. It was reported that the shape of face may not necessary relate to skull morphology, a dolichocephalic head may have euryprosopic facial pattern.16
Enlow17-19 proposed a concept in his counterpart analysis that the brachycephalic headform is more likely to have an upright orientation of the middle cranial fossa, which may cause the mandibular ramus and body to have a "protrusive effect", and the vertical dimension of the face is relatively reduced. Enlow reported normal variations in facial form as well as the anatomic basis of malocclusions and indicated that the backward rotation of the nasomaxillary complex concurrent with a well-developed nose contribute a tendency of Class II malocclusion with protrusive maxilla and retrusive mandible in facial development of dolichocephalic head.17-19 On the contrary, the oriental including Chinese and Japanese, have more common brachycephalic head form and strong mandible, retrusive maxilla and Class III tendency. The upward-turned nostrils in this patient was a sign of failing to have a backward rotation of the nasomaxillary complex.
Enlow also pointed out that the face is a composite of various imbalances and each malocclusion is the result of compensations on top of individual structures. Less backward but more downward growth of nasomaxillary complex could cause a compensatory growth of the mandible in transverse or/and sagittal dimensions.
In this case, small facial index, positive ANB value, small gonial angle and deep bite were detected. Because transverse growth completed before sagittal and vertical growth, after a broad transverse dimensional facial pattern was constructed, the growth potential of the other two dimensions became limited, which further hindered the forward movement of the teeth and the mandible. Therefore, the negation of mandibular prognathism in sagittal aspect was actually resulted from a euryprosopic facial composition. The Wylie's analysis confirmed that although the patient has a relative long mandibular corpus length, the net score of AP dysplasia is still a negative value and the mandible stayed in a posterior position to the maxilla (Figure 10).13
In patient's lower dentition, orthodontic mechanotherapy was designed to increase dentoalveolar compensation. In adult patients with increased corpus length of mandible and wide face, anterior flare of the lower incisors is required for their limited forward growth of the mandible.20
2. Midline diastema
The maxillary central diastema is prevalent in the oriental and midwestern people with high incident rate varied from 1.6 to 25.4%.21 After ruling out the developmental or pathological causal factors such as supernumerary teeth, high insertion of the labial frenum, odontomas, or cysts, conditions associated with the teeth size/ arch length discrepancies are known as the most common cause of the diastema in adults.22 This includes microdontia, hypodontia, or increased arch/ jaw dimensions as seen in this case. Another major factor for diastema is excessive anterior overbite. Any attempt to close the midline spacing without correcting the deep bite will lead to a speedy relapse of the condition.21-24 This patient had both of the above contributing factors, and avoiding relapse is a major concern. Long-term use of retainers or permanent bonded lingual retainers are necessary, especially in cases with large pretreatment diastema and the presence of at least one family member with a similar condition usually increases the risk of relapse.22
It is not recommended to close the upper central diastema only by reciprocal traction using elastomeric chains on an arch wire. Moving the roots of the central incisors apart can improve the stability of the treatment result.7 When both upper central incisors' roots are tipped distally, the vertical forces will produce functional moments to further tip the crown, which makes the crowns of the incisors only to stay in contact and not departing. If the space is already nearly closed, the crown portion cannot be tipped any more, clinicians can still diverge the roots to produce higher functional moments (Figure 12).
To have a stability test, remove all arch wires and elastic forces from the teeth for 6 months as suggested by Mulligan.7 If the space reopens, same arch wires are placed back into the bracket slots, and the roots are permitted to undergo additional divergence. The crown portions were tipped mesially, reshape the incisal edges is required (Figure 12B,13).
There was no evidence that long-term presence of bonded palatal surface retainer adversely affected the periodontal health of the maxillary central incisors.24 Fixed type wire retention at lingual surface of the anterior teeth was used in both arches on this case (Figure 14).
3. Class II elastic traction
The Class II elastics exerts a horizontal force on the lower dentition that will protract and extrude the lower posterior teeth. It could not only promote space closure and bite opening, but also increase the degree of the lower incisor flaring.25-26
The effects of Class II elastics include: (1) retract the upper anterior teeth, (2) protract the lower teeth forward, (3) extrude lower posterior teeth, (4) reduce overbite, (5) close the space, (6) reduce the excessive overjet. Upper anterior teeth extrusion and lower anterior teeth flaring are side effects. The characteristics of to achieve the treatment objectives of this patient could be achieved by the Class II elastics for bite opening, proper upper incisal show, no central diastema and not worsening the soft tissue profile.
The lower incisor changes did not compromise the esthetic expectation of the patient. This case finished with bilateral Class I canine and molar relationships with relatively improved facial profile. Initially, the patient had retrognathia and a horizontally long and wide mandible, the minor retraction of upper incisors and forward proclination of lower incisors corrected the deep bite and closed the diastema concomitantly.
4. Periodontal considerations
The periodontal care was provided with oral hygiene instruction and prophylactic scaling to eliminate periodontal inflammation before treatment. The dental papilla loss and gingival recession are more likely to occur in adult. The opening of gingival embrasures led to appearance of black triangles. In this case, tipping of 2 central incisors and increase the root divergence might change the level of the contact point coronally. Tarnow et al. pointed out that when the measurement from the contact point to the crest of bone was 5 mm or less, the papilla was present almost 100% of the time.27 If the distance increased, the higher chance of missing dental papilla. To avoid potential black triangle, inter-proximal enamel reduction could be applied and also favorable for anterior tooth retraction.
The gingival recession and apical displacement of the marginal bone level are often age-related, generalized reduction in marginal bone level is seen in patients with periodontal disease. Large overjet and overbite or lack of proper occlusal stops usually combined with tooth elongation. With a low bone level, the center of resistance of the tooth is displaced apically, functional forces acting on the crowns could generate moments to induce tooth migration, spacing, bite deepening and palatal gum impingement.28
In the present case, upper median diastema and deep overbite originated from jaw growth discrepancy and broad dental arches should be considered as predisposing factors for periodontal involvement. Orthodontic therapy on patients in the presence of periodontal problem will potentially intensify the tissue damages. Advanced periodontitis may disrupt the delicate balance of surrounding forces thereby resulting in pathologic tooth migration. The importance of a stable and healthy periodontium before, during and after orthodontic intervention should also be stressed.