Skeletofacial Objectives

These objectives rely on understanding the growth status of the patient and often on the ability to predict the amount, direction, and rate of remaining growth. Due to the great variability in growth, it is difficult to define specific skeletofacial objectives. Perhaps this inability to accurately predict growth is the reason why many clinicians do not believe that specific objectives can be set in treatment planning for growing patients. This is not an issue in adult patients for whom skeletal objectives can be defined adequately, although for them a similar problem is encountered in determining the soft tissue objectives (see below).

Even though there is great variability in predicting growth, this objective is important and cannot be disregarded. A good approach is to underestimate future growth in skeletal Class II patients and overestimate growth in Class III patients. In this manner any additional growth (in a Class II patient) or limited growth (in a Class III patient) relative to the prediction would be favorable. Of course this is not always easy, especially in patients with moderate-to-severe dentofacial deformities, since growth can be the deciding factor between a surgical and nonsurgical approach to treatment.

Useful growth information is best obtained with a series of lateral cephalometric radiographs taken at 6-month to 1-year intervals. These radiographs provide important information since growth patterns are usually maintained in the majority of patients.⁷ Unfortunately, serial cephalograms are often unavailable when a patient initially presents for treatment. Therefore an assessment of growth potential (amount of growth left in relation to puberty) and evaluation of craniofacial morphology (Bjork indicators)⁸ may aid in the prediction.

It is important to note, however, that even if growth cannot be modified extensively at the level of the apical bases, significant skeletofacial changes can be achieved by affecting the dentoalveolar apparatus. This is especially evident in the vertical control of the molar, where favorable skeletofacial vertical and anteroposterior changes can be obtained with carefully selected mechanics.

In a nongrowing patient, surgery can substantially affect the skeletofacial objectives. As mentioned, the specific soft tissue component here directly relates to skeletal movements and can still be difficult to predict in these cases. However, pure skeletal changes, such as reducing mandibular prognathy in a Class III patient with a mandibular setback procedure, can be estimated and visualized with a VTO.

Soft Tissue Objectives

As mentioned above, soft tissue objectives are very much related to the skeletofacial objectives. The only aspect not covered in the skeletofacial objectives is the soft tissue changes due to dentoalveolar movement. The most remarkable changes in this area relate to the lips: reduction of interlabial gap and lip protrusion or retrusion. Direct effects on the soft tissue drape are seen with dentoalveolar movement in the vertical dimension at the molar level and in the anteroposterior dimension at the incisor level.

Anteroposterior incisor movement can result in changes at the lip level, at least to some degree.^9–11 Accurate prediction of soft tissue response to incisor movement is difficult. Therefore the soft tissue objectives should be set in terms of direction (more predictable) rather than magnitude of change.

Occlusal Plane Objectives

Occlusal plane objectives are often overlooked in treatment planning. Occlusal plane goals should be considered from a frontal and lateral perspective and in conjunction with skeletal and soft tissue objectives.¹² In the lateral view, anterior and posterior occlusal planes should be coincident. For example, in open-bite and deep overbite patients, the anterior and posterior occlusal planes are often at different levels. When determining specific objectives for a patient, it is a good idea to predetermine the level of the occlusal plane in order to apply proper mechanics during treatment. In deep bite patients it may be desirable to intrude anterior teeth to the level of the posterior teeth or vice versa. A straight wire ligated into all brackets has no ability to selectively intrude or extrude teeth. These mechanics are not optimal; the wire rather than the clinician ultimately controls the occlusal plane objectives. Similarly, in open-bite patients placement of a straight wire can have very undesirable results. The best option in this situation may be to treat the posterior and anterior segments separately.

Specific occlusal plane objectives in the frontal view should also be determined carefully. Often a cant in the anterior occlusal plane is associated with a midline deviation. This can be treated effectively by selective ligation of an intrusion arch or use of a cantilever to rotate the anterior teeth as a whole.¹³

Treatment objectives should outline not only the level of the occlusal plane, but also the cant. The term level refers to a parallel vertical movement, whereas the term cant refers to angular movement of the occlusal plane. A level change can be achieved, for example, by using an anterior bite plane, which allows eruption of posterior teeth. In addition, the application of box elastics to the posterior teeth aids in the occlusal plane leveling of the buccal segments by extrusion.¹⁴ Indiscriminate use of Class II elastics for a prolonged period of time will invariably cant (steepen) the occlusal plane, whether or not this is a desired part of the treatment plan.

Arch Width Objectives

Arch width objectives relate mainly to the intercanine and inter-molar width. The lower intercanine width has been considered to be almost unalterable, as changes in this distance yield unstable results.¹⁵ Any significant increase in the mandibular intercanine width may indicate a need for long-term fixed retention.¹⁶ More leeway has been given to the alteration of the upper canine and molar width. Increasing the arch width depends largely on the occlusal and esthetic objectives.

For occlusal correction, a definitive indicator for expansion of the maxillary arch width occurs in a case with skeletal crossbite. However, from an esthetic perspective, some cli­nicians may expand the maxillary arch to fill the buccal corridors and approach treatment with a nonextraction, expansion treatment.

Midline Objectives

The midline is an important occlusal and esthetic objective. This topic is discussed extensively in this book. Needless to say, the facial and dental midlines should coincide. The planning of this objective becomes more elaborate when a surgical correction due to apical base midline problems is considered. In these patients the desired dental movement must be determined in conjunction with the apical base movement.¹⁷ This is illustrated in Case 3 in this chapter, wherein an apical base discrepancy exists in the absence of a dental midline discrepancy. In this case, with the maxillary osteotomy performed, the maxilla is rotated such that the apical base deviation is corrected while the dental midline position is maintained.

Anteroposterior Objectives

Vertical Incisor and Molar Objectives

As mentioned above, the final vertical position of the upper and lower incisors is influenced by the occlusion (overbite) and esthetics (incisor display). The vertical incisor position, together with the anteroposterior position, are good starting reference points for treatment planning. The vertical position of the incisors can be easily defined by boundaries determined by the incisor display and overbite.

The influence of the molar vertical position on the skeletofacial objectives makes these teeth a key factor in the vertical and anteroposterior dimensions. The molars can be held against growth (relative intrusion) or absolutely intruded with the use of implants. They can also be extruded for overbite correction, although the long-term stability of this type of extrusion in adults is questionable. Furthermore, extrusion of molars should be considered carefully due to the resultant clockwise rotation of the mandible, which may negate any positive changes that occur during adolescent mandibular growth.