System that describes dental occlusion. Class 1 (normal), mesiobuccal cusp of 1st maxillary molar fits into mesiobuccal groove of 1st mandibular molar; class 2, mesiobuccal cusp of 1st maxillary molar is closer to dental midline than mesiobuccal groove of 1st mandibular molar; class 3, mesiobuccal cusp of 1st maxillary molar is distal to mesiobuccal groove of 1st mandibular molar.