How does the mesio-distal length of the second deciduous molar compare to the second permanent molar?

The second deciduous molar is actually shorter in mesio-distal length compared to the second permanent molar. This is because the permanent molars are designed to accommodate the larger size and increased functionality required for adult teeth, which include more complex occlusal surfaces and greater room for multiple cusps. The second permanent molar typically exhibits a greater mesio-distal width to support the full masticatory function of adult dentition.

In the case of deciduous molars, while they are designed to serve the child's masticatory needs effectively, they are naturally smaller to fit the developing jaw structure of a child. As the jaw grows, the permanent molars emerge and take up more space within the arch, leading to the differences in size. Thus, the mesio-distal length of the second deciduous molar is shorter, making this the correct comparison.