Orthodontics: The Curve of Spee

The curve of Spee is the name given to describe the curvature in the jaw of the mandibular occlusal plane, which runs from the premolar to the terminal molar, following the buccal cusps of the posterior teeth. It can also be referred to as Spee’s curvature or von Spee’s curve.

It was named for Ferdinand Graf von Spee, who is credited with being the first person to characterise this part of the human anatomy in the sagittal plane. The curve of Spee is a naturally occurring phenomenon that has implications for restorative dentistry and orthodontics, although current knowledge understands little about why, how or when this develops.

Jonathan Alexander-Abt published a paper in 1992 from New York University’s Department of Orthodontics which discussed a pilot study investigating the relationship of the curve of Spee to skeletal pattern. Where dental malocclusions feature deep overbites, there is often exaggeration of the curve of Spee.

Muscle Imbalance

It has been observed that excessive curve of Spee can lead to improper functional occlusion by altering muscle imbalance. It is suggested that this type of imbalance, which occurs between the anterior and posterior occlusal force components, can cause overeruption of the lower incisors, infraeruption of the premolars, and mesial inclination of the lower molars. An orthodontic practitioner requires special skills to deal with this type of altered condition.

Graf von Spee

Graf von Spee first identified the curve of Spee in 1890, following a period of study of skulls with abraded teeth. Spee was able to make a series of predictions based on this curvature, viewing the skulls perpendicular to the midsagittal plane. Spee’s research contributed to the later spherical theory of Monson, which defines the ideal tooth arrangement within the dental arch. Spee’s original article from 1890 was re-presented in 1980.

Sloped Contact Points

In essence, the curve of Spee is a series of sloped contact points within the mouth. Ideal occlusion includes a flat or mild curve of Spee. Excessive curvature often contributes to an overbite. The curve of Spee is active in the process of mastication, with the masseter (the primary mastication muscle) sitting perpendicular with the curve for favourable loading of force.