The transition from primary (baby) teeth to the permanent adult set is a universal developmental stage for children. This period is known as mixed dentition, named for the presence of both primary and permanent teeth in the mouth simultaneously. Mixed dentition typically begins around age six with the eruption of the first permanent molars and the shedding of the front primary teeth. This phase continues until approximately age twelve, ending when the last primary tooth is naturally lost, allowing the child’s jaw to develop and accommodate the larger adult teeth.
The Three Phases of Mixed Dentition
The process of mixed dentition is an organized progression, generally divided into three distinct phases to track the sequence of tooth eruption and jaw growth. The first transitional period, starting around age six, is marked by the eruption of the first permanent molars, often called the “six-year molars,” which come in behind the last baby teeth. During this same phase, the primary central and lateral incisors begin to shed, making way for their permanent replacements in the front of the mouth.
Following this initial burst of change is the inter-transitional period, which usually lasts for one to two years. This stable phase allows the newly established permanent incisors and molars to settle into their positions and is characterized by significant jaw growth. The root formation of these new permanent teeth continues during this period, preparing the mouth for the next major changes.
The mixed dentition culminates in the second transitional period, which begins around ages ten to twelve. This final phase involves the replacement of the remaining primary teeth: the canines and the first and second primary molars. These baby teeth are replaced by the permanent canines and premolars, often referred to as bicuspids, marking the last major eruption sequence before the full permanent dentition is achieved.
Common Issues During the Transition Period
The co-existence of teeth of different sizes often leads to several aesthetic and physical challenges during the mixed dentition phase. A frequent observation is temporary crowding or spacing, as the permanent teeth are noticeably wider than the primary teeth they replace, creating a temporary space discrepancy called “incisor liability.” This can result in the front teeth appearing crowded or slightly rotated until the jaw completes its growth and other permanent teeth erupt to fill the arch.
Parents may also notice a temporary, wide space between the two upper front teeth, a condition informally called the “Ugly Duckling Stage.” This spacing is caused by the developing permanent canines pressing on the roots of the lateral incisors, causing them to flare out, but the gap usually self-corrects as the canines eventually erupt. Another concern is a retained primary tooth, which occurs when a permanent tooth erupts before the baby tooth has fallen out, leading to the permanent tooth erupting on the tongue side, commonly described as “shark teeth.”
The uneven surfaces created by erupting and loose teeth introduce difficulties in maintaining oral hygiene. The newly erupted permanent molars, in particular, often have deep grooves that are hard to clean, increasing the risk of plaque accumulation and the onset of gingivitis. This transitional period can also be uncomfortable for children, as the constant process of teeth loosening and erupting makes brushing challenging.
Essential Dental Care for Mixed Dentition
Because of the structural changes occurring, this stage requires proactive care from both parents and dental professionals to ensure optimal oral health. Brushing requires increased focus, particularly around the gum line of newly erupted and partially emerged teeth, to disrupt plaque before it can cause decay or inflammation. Using a soft-bristled brush and a pea-sized amount of fluoridated toothpaste twice a day remains the standard recommendation.
One of the most effective preventive measures during this period is the application of dental sealants, which are thin, protective plastic coatings. Sealants are painted onto the chewing surfaces of the newly erupted permanent molars and premolars to fill the deep grooves and pits where food particles and bacteria often get trapped. Since the first permanent molars are particularly susceptible to decay soon after they erupt, sealants act as a barrier against cavities.
Orthodontic evaluation is a prudent step, typically recommended around the age of seven, even if the child’s teeth appear straight. An early evaluation allows a professional to identify potential underlying skeletal or spacing issues that may require early intervention, sometimes called Phase I orthodontics. Regular checkups with the dentist are necessary to monitor the sequence of tooth eruption and to address any retained primary teeth that need professional removal.