There are over 62,000 combinations of edentulous space possible when patient lose their tooth/teeth so it is important to communicate with the laboratory or other dentists as to what general spacing is present with a case.
There are 4 categories of missing teeth.
1. Class-I: Free-end saddle on both sides. Bilateral edentulous area present posterior to remaining natural teeth. These cause the most difficulty in providing dentures as there is no help from any distal teeth for retention and stability.
2. Class-II: Free-end saddle on one side only. Unilateral edentulous area present posterior to remaining natural teeth. These also cause the difficulty in providing dentures as there is no help from any distal teeth on that side for retention and stability.
3. Class-III: This is most common. Unilateral edentulous area with natural teeth both anterior and posterior to it.
4. Class-IV: Single but bilateral edentulous area present anterior to remaining natural teeth. Usually occurs when patient has had an accident or trauma to their anterior teeth. These are the most demanding from aesthetics point of view. (i) If the gap has closed to any degree, the missing teeth have to be somehow accommodated into a reduced space. (ii) The teeth especially if uppers are the most aesthetically demanding as this is immediately noticed during function and at rest. (iii) The resorption of the alveolar ridge has now to be compensated both vertically and labio-lingually. (iii) where clasps are required, these are difficult to camouflage. Using gingival approaching clasps can also cause food to entangle. (iv) If the patient has a high lip line, these issues are magnified further.
There are 8 additional rules to help apply the classification. They are called Applegate Modifications.
RULE 1: Classification should follow rather than precede any extractions of teeth that might alter the original classification. So if immediate extractions are envisaged, the classification should reflect this.
RULE 2: If a third molar is missing and not to be replaced, it is not considered in the classification. It is rare that a 3rd molar is ever replaced.
RULE 3: If a third molar is present and is to be used as an abutment, it is considered in the classification. If it happens to be replaced on its own or with a 2nd molar, then it will come as a Kennedy Classification 1 or 2.
RULE 4: If a second molar is missing and is not to be replaced, it is not considered in the classification (for example, if the opposing second molar is likewise missing and is not to be replaced).
RULE 5: The most posterior edentulous area (or areas) always determines the classification.
RULE 6: Edentulous areas other than those determining the classification are referred to as modifications and are designated by their number.
RULE 7: The extent of the modification is not considered, only the number of additional edentulous areas.
RULE 8: There can be no modification areas in Class IV arches. (Another edentulous area lying posterior to the “single bilateral area crossing the midline” would instead determine the classification).