Case Study: Jaw Surgery and 3-D Imaging
Case Study: “C” Shaped Facial Asymmetries
Facial asymmetry is a relatively common maxillofacial skeletal deformity. All patients have some degree of asymmetry, but minor discrepancies from one side to the other are not perceived by the average layperson and have no functional clinical significance. Marked facial imbalances, however, can cause functional issues with mastication and overloading problems with the masticatory system. While some skeletal asymmetries can be masked orthodontically, many cannot and, as interest in facial aesthetics increases, more patients are seeking orthognathic surgeons for treatment. More orthodontists are referring patients for treatment of facial asymmetries as complaints of crooked smiles and deviated chins are voiced by their patients. This is especially true among dental patients undergoing “smile aesthetics”.
Midface and mandibular skeletal asymmetries are complicated deformities involving all three planes of space and encompass yaw, pitch, and roll of the jaw bones. Understanding the movement of the jaws in three planes of space is very important because success is dependent upon removing all bony interferences at the time of surgery to ensure a stable outcome.
Cone beam CT scanning along with three-dimensional virtual surgical planning has been a game-changer in this regard. Through these advanced technologies, orthognathic surgeons have the ability to see the midfacial and mandibular skeletal deformity clearly and from all angles. Figure 1 shows a patient preoperatively and the extent of the skeletal facial asymmetry.
Facial asymmetries can be categorized into four distinct groups with the simplest asymmetry being confined to the body of one side of the mandible and the most complicated asymmetries being what is termed a “C” shaped asymmetrical skeletal pattern because it involves both the upper and lower jaw. With this type of deformity, as demonstrated in Figure 2, the condyle, mandibular body and symphysis of the mandible is affected in combination with maxillary canting and yaw.
The patient in Figure 1 is a 22-year-old male with a facial asymmetry involving both the maxilla and mandible in a classic “C” shaped pattern. There is a definite cant to both the midface and mandible with a severe deviation of the lower jaw to the left and a corresponding shift of the mandibular midline to the left side. Canting of the maxilla follows the cant of the mandible with a midline shift to the left as well.
Virtual surgical treatment planning allows for a three-dimensional view of both the maxilla and mandible to better evaluate yaw of both jaws. Evaluating and correcting this yaw has plagued orthognathic surgeons until virtual surgical treatment planning became available five years ago. Figure 3 demonstrates the pre-surgical and post-surgical rotation of the jaws and correction of the yaw.
In Figure 4, it is easy to see the extent of the maxillary cant after the mandible has been corrected for cant and deviation.
Note the sagittal advancement on the left side of the mandible (Figure 5), compared to the right side that actually went backward as the asymmetry to the left was corrected and the midline of the mandible was placed on the midline of the upper jaw.
Leveling the maxilla requires raising it on the right side almost 2mm and lowering it on the left by just as much (Figure 6).
Advancement of the maxilla by 6mm corrected the anterior posterior position of the midface and corrected the Class III pseudoprognathism (Figure 7).
Figures 8 and 9 compare the pre-operative and post-operative result. Good aesthetics is accomplished along with re-establishment of normal function. The chin is still asymmetrical as was noted in the virtual surgical planning. A genioplasty procedure was declined by the patient.
“C” shaped facial asymmetries are the most difficult to diagnose and treat. Postoperatively they require close follow-up by both the orthodontist and the oral surgeon because shifting can occur from muscle function and the complexity of the skeletal move. Three-dimensional virtual surgical planning has lessened relapse dramatically by exposing bony interferences that prevent passive movements of the mandibular segments. This can be seen in a close-up of the left sagittal split osteotomy site. Virtual surgical treatment planning identifies these interferences so they can be removed at the time of surgery. (Figure 10)
I thank orthodontist, Jay Parekh, DDS, for referring this most-complicated case and having confidence in our ability to diagnose and treat complex deformities of the midface and mandible.