Simple hinge and semiadjustable articulators in orthognathic surgery.

Model surgery, an integral part of the planning of orthognathic surgical cases, can in some cases be performed on a simple hinge articulator, while in other cases a face-bow and semiadjustable articulator is required. Careful geometric and mathematic analyses of both simple hinge (for example, the Galetti) and semiadjustable articulators (for example, a Hanau) will yield definite indications for their use. The purpose of this article is fourfold: to discuss the theoretic errors inherent in the use of the face-bow record, to derive error formulas that calculate the errors inherent in the use of all articulators, to determine the indications for the use of simple vs. adjustable articulators, and to describe the use of a semiadjustable articulator and intermediate splint in two-jaw surgery. The error formulas show that, although a simple hinge articulator can be used in many cases, its use should be restricted to mandibular surgery, anterior subapical surgery, and transverse maxillary surgery. However, to err on the side of overuse of a semiadjustable articulator will not create difficulties in any orthognathic surgery case.