The sight of a new permanent tooth emerging before the primary (baby) tooth has fallen out can be concerning for parents. This common scenario usually occurs in children aged six to eight years old as their permanent teeth begin to replace the primary set. Instead of the baby tooth loosening and making way, the adult tooth appears to erupt directly behind it, creating a crowded appearance.
The Specific Names for This Phenomenon
The phenomenon of a permanent tooth emerging behind a primary tooth has both clinical and popular names. Dentists often call this specific presentation lingual eruption, which describes the permanent tooth following a path toward the tongue (lingual side) instead of directly underneath the primary tooth. If the position is significantly off the normal path, it may be broadly categorized as ectopic eruption, meaning the tooth is developing or erupting in an abnormal location.
The common term for this dual-row appearance is “shark teeth,” which vividly describes the temporary look of having two sets of teeth, similar to the multiple rows found in a sharkâs mouth. This condition is observed most frequently with the mandibular central incisors (the lower front teeth).
Why This Eruption Pattern Occurs
The standard process of dental replacement requires the developing permanent tooth to move upward and apply pressure directly onto the primary tooth’s root. This pressure triggers a natural biological process called root resorption, where specialized cells gradually dissolve the primary root structure. As the root resorbs, the baby tooth loosens and falls out, clearing the path for the permanent tooth.
Failure of Resorption
When a tooth grows behind another, the normal resorptive pathway is interrupted. The permanent tooth bud develops along an incorrect trajectory, most often lingually (toward the tongue side). Because the successor tooth is not positioned directly beneath the primary tooth, it fails to exert the necessary mechanical force against the primary root. This lack of sustained pressure means the specialized cells are not activated efficiently, and the primary root remains firmly anchored. The permanent tooth is then forced to erupt through the path of least resistance, typically the soft tissue behind the still-present primary tooth.
Necessary Steps and Treatment
The initial course of action depends entirely on the stability of the primary tooth. If the baby tooth is already noticeably loose, a period of observation for a few weeks is often recommended. The pressure from the erupting permanent tooth may provide the final push needed for the primary tooth to detach naturally, resolving the situation without intervention.
If the primary tooth remains firmly seated, it acts as a physical barrier preventing the permanent tooth from migrating into correct alignment. In these cases, a dentist must perform a simple extraction to remove the obstruction. Once the primary tooth is extracted, the tongue plays a beneficial role in guiding the permanent tooth into its proper position. The constant, gentle pressure exerted by the tongue naturally encourages the newly erupted tooth to shift toward the front of the dental arch, often correcting the alignment completely.