Importance of the occlusal plane in virtual treatment planning.

217 O diagnosis and treatment planning have recently moved into the digital realm, to the extent that virtual treatment projections have become commonplace. Several proprietary software platforms, including Invisalign ClinCheck,* OrthoCAD iQ,** and Ormco Insignia,*** allow clinicians to modify virtual models that are suspended in space on their computer screens. But there is a significant shortcoming in the basic design of the most commonly used programs: improper orientation of the occlusal plane. That is the fundamental flaw in the current process of virtual smile design. For many years, when an orthodontist trimmed diagnostic study models, the bases of the models were trimmed parallel to the Frankfort horizontal plane, and the resulting occlusal plane was thus oriented to be a true representation of the patient’s actual occlusal plane angle relative to Frankfort horizontal (Fig. 1). According to Downs, that angle ranges from 2° to 17°, with a mean of about 9° (Fig. 2).2-7 At some point, however, the standard changed so that study models were trimmed with the occlusal plane parallel to the floor (or desktop). That was because the upper model would frequently fall off the lower model and break if they were trimmed in the original manner. The new