Which of the following is true regarding Applegate's Rules for applying the Kennedy Classification?

The true statement regarding Applegate's Rules for applying the Kennedy Classification is that the extent of the modification is only considered by the number of areas. In the Kennedy classification system, the primary classification is determined by the most posterior edentulous area. When modifications are present, they are indicated by the number of additional edentulous spaces that exist alongside the primary classification. Therefore, this statement accurately reflects that modifications are designated based solely on the count of these areas rather than their extent or other factors.

In contrast, the essence of the other statements helps to clarify why they do not align with Applegate's Rules. For instance, while the classification does focus on the most posterior edentulous area, it does consider other factors like the presence of spaces, thus making the claim that a first molar's absence does not factor into the classification inaccurate. Moreover, modifications in the classification system indeed can occur for areas that extend beyond the main edentulous space, so the characterization that there cannot be modifications in Class IV arches is misleading.