The question of whether upper and lower teeth should sit directly on top of one another is common, and the simple answer is no. When the jaws close, the relationship where the teeth meet is called occlusion, and a healthy bite involves a precise, slight overlap, not a direct meeting. Teeth that sit perfectly edge-to-edge are actually considered a form of poor alignment, known as malocclusion, which can lead to dental problems over time.
The Ideal Relationship Between Upper and Lower Teeth
The proper alignment of teeth is defined by a highly specific arrangement known as Class I occlusion, which serves as the benchmark for a balanced bite. This ideal relationship ensures that the teeth and jaw joints function together without excessive strain. It is characterized by a specific horizontal and vertical overlap of the front teeth.
The upper front teeth should extend slightly over the lower front teeth in both dimensions. The vertical overlap, referred to as overbite, is typically around 20%, meaning the upper teeth cover about one-fifth of the lower teeth’s height. The horizontal overlap, or overjet, is a small gap of approximately 1 to 2 millimeters between the front surfaces of the lower incisors and the back surfaces of the upper incisors.
In the back of the mouth, the cusps of the upper teeth should precisely interlock with the grooves of the lower teeth. This ideal molar relationship dictates that the prominent mesiobuccal cusp of the upper first molar fits into the central buccal groove of the lower first molar. This precise interdigitation ensures maximum chewing efficiency and distributes force evenly across the dental arches.
Common Deviations from Normal Alignment
Any deviation from the defined parameters of Class I occlusion is classified as a malocclusion, and these variations are numerous. A condition known as a deep bite, or excessive overbite, occurs when the upper front teeth cover too much of the lower teeth, sometimes completely obscuring them. This is often associated with a Class II malocclusion, where the upper jaw or teeth are positioned too far forward relative to the lower jaw.
Conversely, an underbite, or Class III malocclusion, is defined by the lower front teeth protruding out in front of the upper teeth, creating a reversed horizontal overlap. Another deviation is the edge-to-edge bite, where the upper and lower incisors meet directly at their biting surfaces, resulting in zero overbite and zero overjet. This specific alignment is considered an unstable bite that can be highly destructive to tooth structure.
A crossbite is a misalignment where one or more upper teeth sit inside the lower teeth when the mouth is closed. This can occur in the front (anterior crossbite) or in the back (posterior crossbite). An open bite occurs when the upper and lower teeth do not overlap vertically, leaving a gap between the biting surfaces when the jaw is closed.
Why Proper Alignment is Important for Function and Health
The precise alignment of teeth is necessary for the long-term health and function of the entire chewing system. When teeth meet improperly, such as in an edge-to-edge or deep bite, the enamel surfaces wear down unevenly. This excessive tooth wear can lead to sensitivity, chipping, and eventual fracture, requiring restorative dental work.
Poor alignment also significantly impacts chewing efficiency, which can affect the initial stages of digestion. Teeth that are crooked, crowded, or severely overlapped create areas difficult to clean effectively with a toothbrush and floss. This compromised hygiene increases the risk of developing periodontal disease and tooth decay.
Malocclusion can also place stress on the temporomandibular joints (TMJ). This strain can manifest as chronic jaw pain, headaches, or difficulty opening and closing the mouth. Maintaining proper occlusion helps ensure that the jaw muscles and joints operate smoothly.
Addressing Alignment Issues
If a malocclusion is identified, a dental professional, often an orthodontist, can recommend treatment to correct the alignment. For most patients, the primary treatment involves orthodontic appliances like traditional braces or clear aligners. These methods apply controlled forces to gradually shift the teeth into their correct positions over a period of months or years.
In cases where the alignment issue is mild, a less comprehensive approach, such as minor reshaping or the application of restorative materials, may be an option. For severe discrepancies involving the jawbones, such as a severe underbite or overbite, a combination of orthodontics and orthognathic surgery may be necessary to reposition the jaws themselves.
Following active tooth movement, a retainer is necessary to hold the teeth in their newly corrected positions. Retainers, which can be removable or permanently bonded, prevent the teeth from shifting back toward their original misalignment. Early assessment is helpful, as interceptive orthodontics in children can sometimes guide jaw growth and simplify later treatment.