Ideal Position of the Central Incisor

Facially Generated Treatment Planning: What is the ideal position of the central incisor in three planes of space?

Goals are critical in interdisciplinary treatment planning. As a team, how do we determine the ideal position of the central incisor? What are the important parameters? Do we look at the teeth relative to one another? Relative to the bone and soft tissue? Relative to the base of the skull? Relative to the face? Why are certain parameters important? This article will outline the ideal position of the central incisor in three planes of space: vertical, anterior/posterior and angulation.

Historically, we have always considered the ideal central incisor position with respect to incisal edge display at repose. A classic article written by Vig and Brundo in 1978 outlined that a certain amount of tooth display shows below the lip line when a patient's lips are in a relaxed and gently parted position (repose). This amount of tooth display reduces as we age and lose elasticity in our upper lip.

Arnett, in his classic article on parameters of facial aesthetics, further defined the ideal vertical position of the central incisor. He demonstrated that the center of the clinical crown in a patient with an unworn dentition should be positioned vertically at the wet-dry line of the upper lip when the lips are relaxed and parted.

Once the vertical position of the maxillary central incisor is determined, we must consider the anterior/posterior position of the tooth. A central incisor may be in the ideal vertical orientation, but it may be retrusive or protrusive relative to the patient's skeletal base, leading to an un-esthetic final outcome. What skeletal and facial landmarks can we use to determine if the central incisors are too far back or too far forward relative to the face?

When we view our patients from a lateral perspective and the lips are together, we can often misdiagnose the anterior/posterior position of the central incisors. Therefore, Andrews, et al in 2008 gave the simple solution of examining our smiling patients from a lateral perspective. As you can see in the above photos from their paper, the diagnosis and treatment plan changes when we can see the teeth relative to the smile.

The forehead is a fixed skeletal landmark and is easy to identify in our patients. Drs. Larry and Will Andrews, as well as Dr. Arnett, have all identified the ideal anterior/posterior position of the central incisor relative to the skeletal base. They all independently identified that the ideal a/p position of the central incisor should be in approximately the same vertical plane as the forehead, or slightly back from the forehead. These concepts are illustrated in the following drawings. As you can see, when teeth are proclined or retroclined relative to the forehead, smile esthetics are compromised. 

An unfavorable angle of the maxillary central incisors can negatively influence esthetics. Proclined and retroclined incisors reflect light differently. (Ciucchi) Furthermore, retrusive maxillary incisor positions are significantly less desirable esthetically. (Schlosser)

The anterior/posterior position of the maxillary central incisor is critical to predicting airway health. In the absence of obesity, the odds of having moderate to severe sleep disturbed breathing (SDB) increase threefold to sevenfold when the central incisor (premaxilla) is retrusive.

The retrusive position of the maxilla decreases the horizontal cross section of the posterior pharyngeal airway space. A constricted maxilla puts the patient at risk for pharyngeal wall collapse with loss of muscle tone. (Dempsey) The ideal anterior/posterior position of the central incisor is critical not only for esthetics, but also for airway health in our patients.

Upright or retrusive incisors contribute to excessive wear and can lead to a restricted envelope of occlusal function. Retrusive maxillary incisors restrict the movement of the mandible as they guide the arc of mandibular closure posteriorly. Additionally, as the mandible moves anteriorly, the facial surfaces and incisal edges lower incisors will run into the palatal aspects of the maxillary incisors, leading to loss of enamel and dental destruction on these opposing surfaces. Creating the ideal inter-incisal angle allows for proper disclusion of both arches and protects the incisors from excessive wear. 

What is the ideal incisor angle for function as well as esthetics? Dr. Arnett defined the ideal incisor angle as approximately 57 degrees from the functional occlusal plane. This ideal angle allows for anterior guidance, does not restrict mandibular movement in a chewing cycle and allows for proper phonetics as well as esthetics.

In summary, three-dimensional placement of the maxillary central incisor is critical to comprehensive treatment planning. Vertically, the center of the maxillary central incisor should fall at the same height as the wet-dry line of the upper lip when the lips are relaxed and gently parted. This allows for a youthful appearance.

In the anterior/posterior dimension, the center of the crown of the maxillary central incisor should be in the same vertical plane as the most prominent part of the forehead when the patient is in a natural head position. This allows for maximum esthetics and is key to airway health.

Finally, the root angulation of the central incisor is key to proper function and to preventing future wear. The maxillary central incisor should be angled at approximately 57 degrees from the functional occlusal plane.

Rebecca Bockow, D.D.S., M.S. SeattleSmileDesigns.com 

References:

1. Arnett GW, Jelic JS, Kim J, Cummings DR, Beress A, Worley CM, Chung B, Bergman R. Soft tissue cephalometric analysis: Diagnosis and treatment planning of dentofacial deformity. AM J Orthod Dentofacial Orthop. 1999;116:239-53.

2. Arnett GW, Bergman RT. Facial keys to orthodontic diagnosis and treatment planning  - part I. Am J Orthod Dentofacial Orthop. 1993;Vol 103, Issue 4.

3. Arnett GW, Bergman RT. Facial keys to orthodontic diagnosis and treatment planning  - part II. Am J Orthod Dentofacial Orthop. 1993;Vol 103, Issue 5.

4. Andrews WA. AP relationship of the maxillary central incisors to the forehead in adult white females. Angle Ortho. Jul 2008. Vol. 78, No. 4. pp. 662-669

5. Ciucchi P, Kiliaridis S. Incisor inclination and perceived tooth colour changes. Eur J Orthod. 2017 Jan 25.  

6. Schlosser JB, Preston B, Lampasso J. The effects of computer-aided anteroposterior maxillary incisor movement on ratings of facial attractiveness. AJODO 2005;127:17-24.