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1 These authors (Sungsu Heo and Jae Hyun Park) contributed equally to this work.
Jae Hyun Park
Footnotes
1 These authors (Sungsu Heo and Jae Hyun Park) contributed equally to this work.
Affiliations
Postgraduate Orthodontic Program, Arizona School of Dentistry & Oral Health, A.T. Still University, Mesa, Ariz; International Scholar, Graduate School of Dentistry, Kyung Hee University, Seoul, South Korea
2 Visiting Scholar, Postgraduate Orthodontic Program, Arizona School of Dentistry & Oral Health, A. T. Still University, Mesa, Ariz
Affiliations
Department of Orthodontics, School of Dentistry, University of Wonkwang, Wonkwang Dental Research Institute, Daejeon Dental Hospital, 77 Doonsan–ro, Seo-Gu, Daejeon 35233, South Korea
1 These authors (Sungsu Heo and Jae Hyun Park) contributed equally to this work. 2 Visiting Scholar, Postgraduate Orthodontic Program, Arizona School of Dentistry & Oral Health, A. T. Still University, Mesa, Ariz
Traditionally, orthodontic diagnosis and treatment have primarily involved the assessment of skeletodental relationships, with a particular focus on the mandibular dentition. Recently the focus has shifted towards the maxillary incisors as a starting point for facial esthetics with growing demands for facial esthetics. Three-dimensional maxillary incisor position (MIP) plays a pivotal role in improving facial esthetics in smiling and resting positions. With the advent of miniscrews, biomechanical force application in orthodontic treatment has become simpler due to absolute anchorage. Miniscrews allow clinicians to move teeth more precisely and easily in three dimensions according to the treatment plan, which was challenging or impossible with conventional biomechanics. Therefore, MIP using miniscrews should be a starting point for esthetic treatment planning.
Introduction
Improving facial and smile esthetics has gained popularity with the introduction of the soft tissue paradigm and has become a principal goal in orthodontic treatment.
Importantly, the center of resistance (CR) of the total or segmental dentition must be considered to achieve a desired biomechanical tooth movement with miniscrews (Fig. 1).
Fig. 2The influence of the steepness of the maxillary occlusal plane (OP) on the smile arc and projection of the chin point. (A) Steep OP; (B) Normal OP; (C) Flat OP. The steeper OP tends to lead to a more curved smile arc and a more posterior position of the chin point. The flatter OPA tends to lead to a less curved or reversed arc curve and a more forward position of the mandible.
Maxillary incisor position (MIP) plays an important role in esthetics with smiling and resting states and in supporting the lower lip and functional occlusion.
proposed that the amount of maxillary incisor display when smiling and speaking is one of the most decisive components in esthetic judgment.
Therefore, in this article, we will present the maxillary incisor-based diagnosis and treatment planning with miniscrews and illustrate clinical cases where appropriate biomechanics was used to achieve optimal facial balance and smile esthetics.
MIP is one of the most important factors in the enhancement of smile esthetics. The ideal vertical MIP should be determined by establishing 2-4 mm of incisal show at a relaxed lip position,
Of these, maxillary incisor exposure at rest position is the most important factor in determining the vertical MIP and the amount of vertical movement of the maxillary incisors. The maxillary incisors should also have the proper inclination and be positioned favorably in horizontal and vertical relationships to all facial structures to ensure maximum facial harmony.
It has been defined as the relationship of the curvature of the maxillary incisal and canine edges to the curvature of the lower lip during a posed smile. Factors that contribute to an ideal smile arc relationship may include the lengths of the maxillary teeth, the inclination of the maxillary incisors, arch width, arch form, the curvature of the lower lip, and the occlusal plane angle (OPA). Hulsey
reported that one-third of orthodontically treated patients had flatter smile arcs compared to control patients who were not orthodontically treated. Smile arc flattening during orthodontic treatment can occur in several ways due to formulated bracket positioning and injudicious intrusion of the maxillary incisors with miniscrews. Standardized bracket positioning and palatal expansion in the maxillary arch may result in a loss of the maxillary incisor curvature relative to the lower lip curvature.
Vertical MIP relative to the upper lip should be examined to evaluate the amount of maxillary incisor exposure not only on smiling but also with lips in the resting position. When a patient displays a gummy smile even though this is the normal maxillary incisor exposure at rest,
The OPA slope can affect smile arc and chin projection. When the maxillary OP is flattened with Class III elastics, the maxillary incisal display might decrease, resulting in a flat smile arc.
On the contrary, Class II elastics may steepen the OP, which might increase the curve of the smile arc, but this could also make the smile less attractive.
Therefore, OP control should be carefully considered to improve the smile arc and facial profile.
MIP-based treatment planning
There are five steps in the cephalometric treatment process to optimize facial and smile esthetics and occlusal results with the use of miniscrews (Fig. 3):
1.
Evaluate the vertical position, inclination, and symmetry of the maxillary incisors and maxillary incisor exposure when smiling and at rest. Plan to control the 3-dimensional (3D) position of the maxillary incisors based on the facial and smile esthetics.
2.
Evaluate the OP in both arches. Plan to control the OP by vertical movement of the anterior and posterior segments in both arches.
3.
Evaluate for lip incompetency, chin deficiency, and anterior facial height. Plan to control the vertical and horizontal dimensions with extraction or total dentition movement.
4.
Evaluate the vertical and horizontal position of the chin. Plan to control the mandibular autorotation to achieve a proper overbite and a favorable facial profile by vertical control of the dentition with miniscrews.
5.
Evaluate the vertical position, inclination, and symmetry of the mandibular incisors and their relationship with the maxillary incisors. Plan to control the 3D position of the mandibular incisors to achieve an optimal relationship and to avoid premature contact with the maxillary incisors during autorotation of the mandible.
Fig. 3Five steps for cephalometric treatment planning to optimize facial and occlusal traits. (1) Determine the three-dimensional position of the maxillary incisors; (2) Determine the occlusal plane angle; (3) Assess lip incompetency and chin projection; (4) Determine the autorotation of the mandible; (5) Determine the position of the mandibular incisors.
Additionally, vertical change of the upper lip should be evaluated depending on the vertical control of the maxillary incisors, anterior facial height, and facial pattern because it could affect the maxillary incisor exposure on smiling and at rest.
And in some cases, during the maxillary anterior teeth retraction with conventional biomechanics, they are prone to extrude and upright, causing premature contact with the mandibular anterior teeth and deteriorating smile esthetics and facial profile. Therefore, vertical and torque control of the maxillary incisors is of utmost importance to improve and maintain an esthetic smile. Assuming that the center of the mandibular rotation is located around the condyle, even though a large individual variation was found locating the center of rotation, the amount of incisal movement should be greater than that of the molar movement.
Types of maxillary incisor tooth movement for an esthetic smile
Orthodontic maxillary incisor tooth movement should be determined from esthetical and functional occlusal standpoints. Additionally, the OPA should be changed depending on the MIP. Four types of maxillary incisal tooth movement are illustrated in Figure 4. The resultant tooth movement pattern of the maxillary incisors largely depends on the relationship between the line of force and the CR. Therefore, localization of the target segments’ CR is crucial when predicting and interpreting the displacement pattern of the dental arch in response to the lines of force from the miniscrews.
Fig. 4Required types of tooth movement of the maxillary incisors. With Class II malocclusion: (A) Intrusive retraction with controlled tipping; (B) Bodily retraction along the occlusal plane. With Class III malocclusion: (C) Extrusive decompensation with uncontrolled tipping; (D) Bodily protraction along the occlusal plane.
In clinical situations, the line of force is confined by anatomical limitations. Sometimes, it is recommended to use an equivalent force system to achieve the desired displacement of an active unit. According to recent finite element studies, we can identify the estimated location of the active unit's CR and simulate displacement of the dentition depending on the force angulations (FAs) and develop a theoretical basis for 3D tooth movement patterns (Fig. 1).
Therefore, the treatment objectives must be clarified prior to the construction of a force system.
Case reports
We present four cases illustrating MIP-based treatment planning to achieve optimal facial balance and smile esthetics in Class II or III patients with hyper- or hypodivergency (Fig. 5).
Fig. 5Autorotation of the mandible with extrusion and intrusion of the dentition considering maxillary incisor position (MIP)-based treatment planning. (A) Upward and forward mandibular spatial change (forward rotation of the mandible) with intrusive mechanics in the Class II hyperdivergent patient. (B) Downward and backward mandibular spatial change (backward rotation of the mandible) by extrusive mechanics in the Class III hypodivergent patient.
Case 1: Total intrusion and distalization of the maxillary dentition with miniscrews in a Class II hyperdivergent adult patient with lip incompetency
A 22-year-old male patient presented with complaints of severe lip protrusion and chin deficiency. The patient showed lip incompetency even though he had been treated orthodontically with four premolar extractions. He displayed a hyperdivergent facial pattern with a Class II dental relationship and a large overjet. The maxillary incisor exposure when smiling was normal (Fig. 6). Total intrusion and distalization of the maxillary dentition were achieved using maxillary posterior and anterior buccal, and midpalatal miniscrews (Fig. 7). A Class I dental relationship and favorable facial profile were accomplished with distalization and intrusion of the maxillary dentition, mesialization of the mandibular dentition, backward rotation of the OP, and forward autorotation of the mandible. A good smile arc with appropriate gum exposure when smiling was obtained by vertical and torque control of the maxillary incisors using miniscrews (Fig. 8). The overall treatment time was 29 months.
Fig. 6Case 1: Pretreatment photographs and radiographs.
Case 2: Total intrusion of the maxillary and mandibular dentitions and anterior teeth intrusive retraction with miniscrews in a severe hyperdivergent adult patient
A 30-year-old female patient presented with lip protrusion and chin deficiency. She showed moderate crowding, unilateral scissors bite on the left side, and slight left-up canting of the upper lip and maxillary anterior teeth. She displayed a hyperdivergent facial pattern with a Class I dental relationship and anterior edge-to-edge bite (Fig. 9). The total intrusion of the maxillary and mandibular dentitions and intrusive anterior teeth retraction were achieved using each maxillary and mandibular four buccal miniscrews (Fig. 10). A favorable facial profile was accomplished with the total intrusion of dentition and retraction of the anterior teeth in both arches with no rotation of OP, correction of the scissors bite, reduction of the anterior facial height, and forward autorotation of the mandible. A consonant smile arc with proper gingival exposure when smiling was obtained by vertical and torque control of the maxillary incisors using miniscrews (Fig. 11). The overall treatment time was 30 months.
Fig. 9Case 2: Pretreatment photographs and lateral cephalogram.
Fig. 10Case 2: Total intrusion of the maxillary and mandibular dentitions, and anterior teeth retraction with each maxillary and mandibular four buccal miniscrews. Red circles are the center of resistances of the maxillary and mandibular dentition with extraction of the maxillary first premolars and mandibular second premolars. Violet circles are the center of resistances of the maxillary and mandibular six anterior teeth.
Case 3: Backward rotation of OP with miniscrews in a hypodivergent adolescent patient with a reverse smile arc
A 15-year-old female patient presented with a severe proclination of her maxillary incisors and a reverse smile arc. The diagnostic records revealed a dental Class II with transverse deficiency of the premaxilla, labioversion of the maxillary incisors, minor crowding in both arches, and mandibular dental midline deviation to the left side. She displayed a hypodivergent facial pattern and insufficient maxillary incisor exposure when smiling (Fig. 12). Miniscrew-assisted rapid palatal expansion (MARPE) was applied for expansion of her maxilla and to gain space for the uprighting of her maxillary incisors. Interradicular miniscrews in both arches were used for distalization of the maxillary dentition and backward rotation of the OP (Fig. 13). A favorable facial profile and Class I dental relationship was accomplished with backward rotation of OP (intrusion of the maxillary posterior and mandibular anterior teeth and extrusion of the maxillary anterior and mandibular posterior teeth), distalization of the maxillary dentition, and increased anterior facial height. A consonant smile arc with an appropriate maxillary incisor exposure when smiling was obtained by extrusion and uprighting of the maxillary incisors and intrusion of the mandibular incisors using miniscrews (Fig. 14). The overall treatment time was 19 months.
Fig. 12Case 3: Pretreatment photographs and radiographs.
Fig. 13Case 3: Total distalization of the maxillary dentition and backward rotation of the occlusal plane with maxillary and mandibular interradicular miniscrews. Brackets with MBT prescription were bonded upside down to give lingual crown torque on the maxillary incisors.
Case 4: MARPE and total distalization of the mandibular dentition in a skeletal Class III normovergent adolescent patient with mandibular asymmetry
A 13-year-old female patient complained of mandibular prognathism and asymmetry. She showed lower lip protrusion, a slight concave profile, and 3.5 mm chin deviation and 2.5 mm mandibular dental midline deviation to the right side. She displayed Class III dental relationship with transverse discrepancy and insufficient maxillary incisor exposure when smiling (Fig. 15). MARPE was applied for expansion and slight forward movement of the maxilla after maxillary expansion
and total distalization of the mandibular dentition with interradicular miniscrews in the mandible for camouflage treatment. During distalization of the mandibular dentition, lingual root torque (approximately 20°) was applied on the mandibular incisors for bodily and intrusive movement (Fig. 16). A favorable facial profile and Class I dental relationship was accomplished with protraction and extrusion of the maxillary dentition, and total distalization of the mandibular dentition. The maxillary incisor exposure increased with elastics and intrusion of the mandibular anterior teeth using miniscrews, which improved smile esthetics (Fig. 17). The overall treatment time was 16 months.
Fig. 15Case 4: Pretreatment photographs and radiographs.
Fig. 16Case 4: Miniscrew-assisted rapid palatal expansion (MARPE), total distalization of the mandibular dentition with mandibular interradicular miniscrews, and elastics.
MIP should be carefully considered to achieve favorable facial and smile esthetics. Consequently, MIP-based orthodontic treatment with proper biomechanics using miniscrews is essential to obtain an esthetic smile and facial balance.
Patient consent
Consent to publish the case report was obtained.
Funding
No funding or grant support.
Author contributions
All authors attest that they meet the current ICMJE criteria for Authorship.
Declaration of competing interest
The authors reported no competing financial interests or personal relationships that could appear to influence the work reported in this paper.
References
Ackerman JL
Proffit WR
Sarver DM.
The emerging soft tissue paradigm in orthodontic diagnosis and treatment planning.
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