Dental Education Lecture: Space Maintenance

When a child loses a front tooth, we usually do not have to do anything.  We have to place a special device called space maintenance if a back tooth (baby) is lost.  What are front and back teeth?

Normally there are 20 baby teeth and 32 adult teeth.  Our mouth is divided into 4 quadrants.  Each quadrant has 5 baby teeth and 8 adult teeth as shown in Fig.1.  The first five adult teeth (#1-5) replace their corresponding baby teeth (indicated by 5 short arrows), whereas the last 3 adult teeth (molars, #6-8) come into the mouth without substitution (3 long arrows).  The first 3 teeth in either baby (A-C) or adult (1-3) dentition are named front teeth, the rest (D, E, 4-8) back teeth. As mentioned above, if D or E is lost prematurely (earlier than expected), we need to do something to keep the space.  If a baby front tooth (A, B or C) is lost prematurely, do nothing and watch. Although there is a minor cosmetic issue losing one or several front teeth, it is temporary.

Let us take a look at Eruption Age in Fig.1.  The tooth #6 (first adult molar) erupts at the age of 6.  The tooth next to it (#5, 2nd adult premolar) comes in the mouth at the age of 11.  There is 5 year difference between #5 and #6 in eruption.  

As mentioned above, the last 3 adult teeth (including #6) erupt without substitution in the back of the mouth.  Fig.2 shows that #6 erupts (arrow) along the back surface of E around 6 years old.  Exfoliation of a baby tooth is due to natural process of root shortening (resorption).  As shown in Fig.2, the root of D is shorter than that of E.  The shortening of root is in turn related to development of underlying adult teeth.  The tooth #5 has formed its crown, whereas #4 has formed its crown and initial root.  The growth of adult teeth place pressure their overlying baby teeth, causing root shortening.

As time passes by, the tooth #6 comes into its right place (Fig3) due to the presence of the neighboring tooth E.  With further development of the roots of #4 and 5, the roots of D and E have become shorter and shorter.  Finally D is exfoliated (comes out, as indicated by arrow). 

Fig. 2, 3, 6 and 7 show the side view of adult teeth #4-6, whereas Fig. 4 and 5 show the occlusal (biting) view of them.  Natural exfoliation of baby teeth helps formation of normal alignment of adult teeth (Fig.4).  When the 2nd baby molar (E) is prematurely pulled out (Fig.6 thick arrow), the tooth #6 loses guidance during its eruption (short vertical arrow).  It may shift forward as indicated the horizontal arrow and block the eruption of the tooth #5.  The latter is unable to erupt in its normal position.  It may be positioned either inside or outside of the dental arch (Fig.5 as compared to Fig.4).  It is difficult to clean the crooked area (arrow, Fig.5).  It is prone to get cavities and gum disease in this area.

It appears from above that one of purposes to keep baby teeth is to keep space for adult teeth to come out normally.  If a baby back tooth is lost prematurely, we have to make space maintenance (Fig.7 gray area).  It will prevent forward movement of the tooth #6 (X in front of the horizontal arrow).  There will be enough space for #5 to erupt normally.  The space maintenance will stay in child mouth until the tooth it rests upon (D) is falling out or the tooth #5 erupts and touches the bar of the space maintenance.  The space maintenance is easy to make and usually covered by insurance 100%.  We can avoid orthodontic treatment (braces) if space maintenance is used properly.  We are going to use a real case to show that we will lose space fairly quickly if space maintenance is not installed in timely manner in next lecture.

Xin Wei, DDS, PhD, MS 1st edition 01/17/2009, last revision 03/20/2010