Dental Education Lecture: Congenital Missing Tooth
Congenital (inborn) missing tooth can happen in baby and adult dentitions. The most common missing tooth is the third molar (#8 in Fig.1). The 2nd most common missing tooth is the 2nd premolar (adult) (#5 in Fig.1). In Lecture Space Maintenance, we have discussed that the 1st 5 adult teeth (#1 to 5)replace their overlying baby teeth (A to E; 5 short arrows), whereas the last 3 adult teeth erupt directly without substitution (3 long arrows).
How do baby teeth fall out naturally? Development of underlying adult teeth puts pressure on the roots of baby teeth, causing them to become shorter (compare Fig.2 and 3). With congenital missing of #5, the roots of E are hardly shortening (compare Fig.4, 5, and 6). After eruption, the adult teeth (#4 and 6) keep growing (arrows in Fig.6). By contrast, the retained baby tooth E fuses with surrounding bone (ankylosed) and stays at the same level. Gradually the ankylosed E becomes shorter than its neighboring teeth (submersion, Fig.7). The roots of retained baby tooth E may keep becoming shortening albeit at slower pace (Fig.8). The baby tooth may finally fall out (arrow, Fig.8). The best treatment for missing tooth is implant.
Before the retained E becomes sunk down (submerged), the relationship of upper and lower teeth is pretty normal (Fig.9). With sinking of E, the upper corresponding tooth (arrow in Fig.10) has no opposing (stop), keeping growing downward. This can cause severe bite disturbance. The best treatment is to raise the biting surface (shaded area in Fig.11) after E sinking before overgrowth of the opposing tooth. To correct overgrown tooth is a complicated procedure requiring braces and minimplant. Some of retained baby teeth may function for a long time. We need to prevent associated complication before their final exfoliation.
Xin Wei, DDS, PhD, MS1st edition 01/17/2009, last revision 06/07/2010