Melker's occlusion 2: Variations in ideal occlusion

Class 1 occlusions are the ideal occlusions discussed in the textbooks but they aren't always present. In fact, the majority of people in the community will be class 2. The occlusal contacts represented as dots and lines in the diagram of the previous part is based on a class 1 occlusion. Class 2 and class 3 occlusions will show different relationships and achieving a class 1 occlusion post treatment is not always possible or desirable when considering the goals of the patient. It is important to know why we do what we do and why the goals of treatment is what they are so that we can bend the rules as needed.

The main change with Class 2 and 3 occlusions is the anterior guidance component of the occlusion. distribution of occlusal contacts is possible in any occlusion as the reason why we aim to do this is to reduce the non axial loads through teeth when the muscles are at their highest force. The position of these contacts may change with different positions on the occlusal surface but as long as you keep in mind the aim is to have them on flat, axial receiving areas e.g cusp tips , fossae, marginal rides.

Class 2 div 1 patients have larger overjet so the anterior teeth technically have reduced resistance in excursions. However, large overjets mean that the incisors may not be able to achieve guidance in protrusion. Therefore if designed improperly this may increase the shear forces on posterior teeth. In severe cases it may be required to use canines in protrusion and pick up the central incisors as the mandible moves further forwards. This still achieves the goal of reducing the muscle forces from 100% to 70% to 30% on protrusion and achieves disclusion of the posterior teeth on excursion.

Class 2 div 2 patients have increased resistance in shear due to the increase in overbite and overjet. these patients may show increased wear on anterior teeth due to the high shear forces on excursion. They may exhibit higher levels of destruction on posterior teeth due to resistance to excursions prevents effective disclusion of posterior teeth and may cause more of the bite force to transmit through the teeth. If the goal of treatment is to mitigate destructive forces, the aim may be to reduce the overbite and/or increasing the overjet through orthodontics or raising the VD

As Class 3 occlusions increase in severity the patient moves further towards and then past edge to edge position. As they go closer to edge to edge, resistance is reduced as the overbite decreases. At edge to edge MIP bites, they are already in excursions at MIP position i.e MIP has is axial force through the anterior teeth and there is already reduction in shear stress at MIP. Therefore when the occlusion is checked, we won't see dots and lines but will see smudges all around.