Mixed dentition

How the AAO, the ADA and the AAPD define mixed dentition

The American Association of Orthodontists (AAO) defines mixed dentition in its Glossary of Orthodontic Terms as a dental developmental stage in children, approximately ages 6 to 12, “when they have a mix of primary (baby) and permanent teeth.”

The American Dental Association (ADA) files the same stage under transitional dentition in its glossary of dental terms, where the entry “Refers to a mixed dentition; begins with the appearance of the permanent first molars and ends with the exfoliation of the deciduous teeth.” In plain words, the stage starts when the first permanent molars come in and ends when the last baby tooth is shed.

The American Academy of Pediatric Dentistry (AAPD) adds that the stage “can be divided further into early mixed and late mixed dentition.”

The primary dentition, the stage before the mix

The primary dentition comes before the mixed dentition, and in it every tooth in the mouth is a baby tooth. The AAPD describes the primary dentition as “beginning in infancy with the eruption of the first tooth, usually about 6 months of age, and complete from approximately 2 to 6 years of age when all primary teeth are erupted.”

Primary teeth go by more than one name, and the AAO glossary’s entry for them reads “Baby teeth. Also called deciduous or milk teeth.”

Where the mixed dentition comes up in orthodontic care

The mixed dentition is the stage in which the AAO places the start of early treatment, on its page about two-phase treatment: “Phase One usually begins when a child still has a mix of baby and permanent teeth, and Phase Two generally begins later when most or all permanent teeth are in.”

The AAPD names a problem common in the early part of the stage: “Inadequate arch length with resulting incisor crowding is a common occurrence, particularly in the early mixed dentition.” Crowding, which that sentence ties to the stage, is defined in the orthodontic glossary.

We start seeing kids at age 7 to watch their growth. What that first look covers is walked through on the page about a child’s first orthodontic check-up.