Significance of occlusal plane in orthodontics
Various analyses in orthodontics use reference planes for accurate diagnosis and treatment planning. The occlusal plane, as a reference, appears in different points plotted together. Its inclination predicts the growth pattern, function and stability of the maxilla, mandible and the temporomandibular joint. It affects the vertical dimension of the lower face through the continuous eruption of the molar during puberty and post puberty. It is also the basis how the occlusal surfaces of the teeth should relate to each other. A deviation of the occlusal plane will change the axial inclinations of the teeth, affecting stability. According to Sadao Sato, the occlusal function, rather than heredity, mostly influences the skeletal craniofacial growth.
The varied occlusal planes in different literature
Some of the different occlusal planes identified are listed in the table:
Occlusal plane | Reference points | Literature | Cephalometric Analysis |
Lower Incisor Occlusal Plane | Line drawn from bisection of distobuccal cusps of the first permanent molars to the tip of the lower incisor | Thayers 1990 | |
Posterior/ Functional Occlusal Plane | Posterior most occlusal contact of the last fully erupted mandibular molars extending anteriorly to the anterior most occlusal contact of the fully erupted premolars | Harvold, Thayers 1990 | Wits appraisal |
Conventional/ Bisected Occlusal Plane | One half of the cusp heights of the first permanent molars and one half of the overbite of the incisors in occlusion (a constructed point) Should the incisor be supraerupted or infraerupted, the occlusal plane is determined by the premolars | Okason, Sadao Sato, Thayers 1990 | Downs (in relation to FH plane), Steiners (in relation to SN plane) |
Upper Occlusal Plane | Connects the incisal edges of the upper central incisors with a point 0.2mm occlusal to the mesiobuccal cusp tip of the first permanent molar | Thayers 1990 | COGS analysis |
Lower Occlusal Plane | Connects the incisal edges of the lower central incisors with a point 0.5 occlusal to the mesiobuccal cusp tip of the first permanent molar | Thayers 1990 | COGS analysis |
In a study in 1990, Thayers noted that when used in Wits appraisal, the bisected occlusal plane showed a higher degree of affinity to dental values whereas the functional occlusal plane showed to be more related to variance with skeletal values. It was also concluded in this study that either occlusal planes may be used to calculate values in the Wits appraisal when aiming to diagnose the degree of anteroposterior jaw disharmony.
Relevance of each occlusal plane
A patient’s occlusion is influenced by alterations in the cant of the occlusal plane. Each degree of occlusal plane rotation leads in a 0.5mm change in dental occlusal relation. When the occlusal plane is steepened clockwise (downward backward), a Class II malocclusion will result to a Class I relation. In contrast, a flattening counterclockwise (upward forward) rotation of the occlusal plane will correct a Class II relation into Class I malocclusion. Among all the occlusal planes, the posterior occlusal plane, according to Sato, is most closely related to the position of the mandible.
The occlusal plane plays a pivotal role in orthodontic diagnosis and treatment planning upto securing a consistent progress of treatment, leading to a more stable finished occlusion.
References:
Beltrao P (2015). Class III High Angle Malocclusion Treated with Orthodontic Camouflage (MEAW Therapy) http://dx.doi.org/10.5772/59511. Issues in Contemporary Orthodontics Chapter 11: 219-240.
Chan CA (2007). A Review of the Clinical Significance of the Occlusal Plane: Its Variation and Effect on Head Posture. International College of Craniomandibular Orthopedics (ICCMO) Anthology VIII
Eliana Midori, Tanaka; Sadao, Sato (2008). Longitudinal alteration of the occlusal plane and development of different dentoskeletal frames during growth; AJODO, 134:602.e1-602.e11
Rong H, Long H, et al (2019). Clinical study on the posterior occlusal plane and morphology of the temporomandibular joint. Int J Morphol 37(4):1347-1352.
Sato Sadao (1994). Case Report: Developmental characterization of skeletal Class III malocclusion. The Angle Orthodontist 64(2): 105-111
Thayer T. A. (1990). Effects of functional versus bisected occlusal planes on the Wits appraisal. American journal of orthodontics and dentofacial orthopedics : official publication of the American Association of Orthodontists, its constituent societies, and the American Board of Orthodontics, 97(5), 422–426. https://doi.org/10.1016/0889-5406(90)70114-R