In normal Class I occlusion, which mandibular tooth does tooth #5 (maxillary right first premolar) primarily occlude with?

In normal Class I occlusion, each maxillary tooth occludes with two mandibular teeth (shifted mesially by half a cusp width). The maxillary first premolar (#5) occludes primarily with the distal half of the mandibular first premolar (#28) and the mesial half of the mandibular second premolar (#29). The primary occlusal contact of #5 is with the distal of #28. This relationship follows the normal Angle Class I intercuspation where maxillary teeth are positioned one half-tooth width distal relative to the mandibular arch.