The term “shark teeth” in humans is a common description for a specific dental situation known as retained primary teeth. This occurs when a permanent tooth begins to emerge before the corresponding baby tooth has naturally fallen out, creating a temporary double row of teeth. This condition is relatively common, affecting an estimated 3% to 10% of children during their transition to adult dentition, and warrants attention to ensure the new teeth erupt into their correct positions.
The Biological Mechanism Behind Dual Rows
The appearance of a second row of teeth is primarily caused by a disruption in the normal process of root resorption. Normally, the developing permanent tooth pushes directly against the root of the primary (baby) tooth positioned above it. This pressure triggers specialized cells, called odontoclasts, to dissolve the primary tooth’s root structure, a process known as physiological root resorption.
The progressive dissolution of the root causes the baby tooth to loosen and eventually exfoliate, creating a path for the permanent successor to erupt. However, in cases of “shark teeth,” the permanent tooth bud takes a slightly altered eruption path, often moving to the tongue side of the primary tooth. Because the adult tooth is not directly under the baby tooth, it fails to exert the necessary pressure to stimulate complete root resorption.
The baby tooth remains firmly seated in the jawbone because its root is intact, even as the permanent tooth begins to emerge behind it. This misalignment results in the characteristic double-row appearance. This failure of the primary root to dissolve properly is the core mechanism allowing the temporary co-existence of both tooth sets.
Typical Ages and Locations of Appearance
This dental occurrence is most frequently observed during two distinct phases of a child’s dental development. The first phase, and the most common presentation, happens around the ages of five to seven. During this time, the lower central incisors—the front bottom teeth—are usually the first permanent teeth to emerge.
These lower incisors often erupt on the lingual side, or the side closest to the tongue, creating the visible double-row effect. A second, less common phase occurs later, around ages 11 or 12, often involving the upper canines or the permanent molars in the back of the mouth. The lower front teeth are the most common site because they are the first to transition.
Treatment and Management
The initial management for retained primary teeth is often a “wait and watch” approach, especially if the baby tooth has some mobility. Encouraging the child to gently wiggle the baby tooth can help speed up the natural exfoliation process. The tongue naturally pushes the newly erupted permanent tooth forward, and a loose baby tooth allows this pressure to guide the adult tooth into its proper position once the primary tooth is shed.
Intervention by a dentist becomes necessary when the primary tooth shows no signs of loosening after several weeks, or if the permanent tooth has erupted significantly, perhaps more than half of its crown height. A dentist will take X-rays to assess the condition of the primary tooth’s root and the position of the permanent tooth. If the primary tooth is firmly retained and shows minimal root resorption, a simple extraction is often recommended.
This procedure is typically quick and straightforward, performed under local anesthesia in a pediatric dental office. Removing the firm primary tooth eliminates the physical obstruction. This allows the continuous pressure from the tongue and lips to naturally move the permanent tooth into the correct alignment within the dental arch. Timely extraction helps prevent future complications, such as crowding or significant misalignment, that would require more extensive orthodontic correction later.