when determining occlusal classifications a class one occlusion what you want to look for is the center or buccal groove of the mandibular molar including with the mesial buccal cusp of the maxillary molar what i like to do is find the buccal groove place my probe on the buccal groove of the mandibular molar and then look to see where it's at in relation to the mesial buccal cusp of the maxillary first molar so in this case you can see they're right in line that is a class 1 occlusion now if that position shifts then again i'll bring my probe to the buccal groove of the mandibular molar and i'll say where am i in relation to the mesial buccal cusp of the maxillary molar now i can say that i am mesial to that cusp because i am mesial this is mesio occlusion or class 3. then the next thing that i need to ask myself is how far am i into mesial occlusion because i have to be at least the width of a premolar to be a true class iii so if i come here and i measure the premolar i say i have about a seven millimeter width of the premolar now i'm going to place my probe on the mesia buckle cusp and say am i at least seven millimeters from the mesial buccal clasp to the buccal groove of the mandibular molar and i am so this is a true class 3. now if that distance were less than the width of a premolar so here i am still mesioclusion i'm mesial buccal groove mandibular first smaller mesial to the mesia buccal cusp of the first molar however i am only about four millimeters mesial so this is a tendency towards a class three occlusion the same is true of a class two occlusion if i come here the jaws are positioned this way and again i'm always going to go buccal groove of the mandibular first molar i'm going to place my probe in the center and i'm going to say where am i in relation to the mesial buccal cusp of the maxillary first molar and i am now distal to the mesia buccal cusp of the maxillary first molar so this is distoclusion class 2 occlusion and then i must do the same thing is it a true class 2 and the way that i do that again i would measure the width of the premolar we've already done that and determined it's about eight and so i come to the buccal groove and i say am i separating those two surfaces the buccal groove of the max or the mandibular molar and the mesial buccal cusp of the maxillary molar are those apart at least the width of a premolar and in this case yes they are so this is a true class two but if i have a relationship that looks something like this then again i come here say where am i in relationship to the mesial buccal cusp i'm still distal but i am less than the width of a premolar and so this is a tendency towards a class 2 occlusion the trickiest part of occlusion is remembering the surfaces that must occlude for a class one so if you always remember buccal groove of the mandibular molar mandibular first molar and mesial buccal clasp of the maxillary first molar should occlude then wherever the teeth are positioned just always come to the buccal groove of the mandibular first molar and then ask yourself where am i in relation to the mesial buccal cusp of the maxillary first molar and answer mesial or distal here again i am distal to that cusp so this is disto and the only other thing you have to remember is that distal occlusion is class 2 and mesioclusion is class 3.