Which of the following statements regarding the developing primary dentition is INCORRECT?

The statement that spaced primary arches produce favorable alignment of permanent incisors is incorrect. In dental development, spaced primary arches refer to an arrangement in which there are spaces between the primary teeth. This spacing is generally beneficial as it allows adequate space for the larger permanent incisors that are set to erupt. However, if the primary teeth are not appropriately spaced, it can lead to crowding or misalignment of the permanent incisors as they emerge.

In contrast, the other statements correctly reflect principles of dental occlusion and development. A straight terminal plane helps in achieving a Class I relationship for permanent molars, providing a neutral basis for occlusion as the molars erupt. The mesial step indicates that the primary second molar is positioned more mesially compared to its counterpart, which typically supports a Class I molar relationship, suggesting a favorable relationship for proper occlusion of permanent molars. Lastly, a distal step in primary dentition typically indicates a potential for Class II malocclusion since the primary molars in this configuration would lead to a more retruded position of the first permanent molars upon eruption.

Understanding these relationships is crucial for predicting and managing the alignment of permanent teeth as the primary dentition transitions into the mixed dentition phase.