Because crowding is a common malocclusion, it’s important to look for its potential causes during every routine exam.

Arch form, arch width, and buccolingual inclination each play an important role in the development of proper occlusion. Understanding the dynamics of arch dimensions, especially of the mandibular arch, is important to identifying the need for orthodontia.

The size and shape of the arches are important for orthodontic diagnosis and treatment planning because they affect the space available, dental aesthetics, and stability of the dentition.^1,2

Improper arch form³

There is a close relationship between arch form and normal occlusion. Arch form is determined by the underlying bone and musculature. Proper arch form can help improve the occlusion and contribute to facial aesthetics.

Unless the teeth in both the mandibular and maxillary arches are properly aligned, the occlusion may be abnormal. While there are certain arch forms such as v-shape, square, and omega that are commonly seen in cases of crowding, arch form tends to vary from person to person.

Improper arch width

The distance between corresponding lingual points on the teeth in the same arch (e.g., transpalatal width between second molars) defines the arch width. An improper arch width (as shown below) can cause spacing or crowding. The ideal width is a McNamara measurement ranging from 35 to 39 mm between the linguals of the first molars.

When excess space exists between teeth, food particles and debris can get trapped and contribute to tooth erosion. When crowding is present, patients may find it difficult to keep their teeth clean, which can result in tooth decay and gum disease.

Look for improper arch form during exams and talk to patients about the problem, consequences, and solutions for their individual clinical situations.

Improper buccolingual inclination

The inward tilting of the teeth, especially the maxillary molars, is referred to as buccolingual inclination.

The force of chewing is directly transmitted from teeth to their roots. When teeth meet in a straight vertical direction, the force is minimal. If teeth tilt in one direction or the other, the lateral force is stronger and damage can occur to the enamel and tooth structure.

Improper buccolingual inclination can affect arch form and, therefore, cause crowding that may benefit from proper alignment. Failure to align teeth can negatively affect dental and systemic health.

1. Lee RT. Arch width and form: a review. Am J Orthod Dentofacial Orthop. 1999;115:305–313.
2. Radnzic D. Dental crowding and its relationship to mesiodistal crown diameters and arch dimensions. Am J Orthod Dentofacioal Orthop. 1988;94(1):50–56.
3. Shahroudi AS, Mirhashemi AH, Noroozi R, et al. An overview on dental arch form and different concepts on arch coordination in orthodontics. Indo-Iran J Ortho. 2011:6(1):46–57.