Melker's occlusion part 1: Idealised occlusion

Occlusion can be studied to try and improve success or reduce failures. Occlusion isn't a goal but it is a tool that we can use to achieve our goal. Everything fails if given enough time but we are aiming to slow the progress of this down so that the failure occurs as far away as possible. Patients need to understand this risk before agreeing to any treatment. Dental materials excepting fracture from trauma tend to break after repeated cyclic fatigue. The management of occlusion aims to reduce the force on teeth and restorations to reduce cyclic fatigue failure. This aim is independent of the materials used.

Be it LiSi, zirconia, gold, base metal, composite, amalgam, enamel or dentine they will all fail if loaded enough for enough time. Materials that claim extrordinary strength such as some zirconias have the trade off of being very brittle. On the other hand, materials that are softer such as gold will burnish under high load, adapt to the conditions and therefore is less likely to fail under cyclic fatigue.

The aim of managing occlusion according to Dr. Melkers is "Distribution in load, reduction of resistance in shear". As a concept this means that when the patient bites down lightly into MIP, all the posterior teeth should contact evenly with the force through the long axis of the tooth (without deflection). When the patient clenches on their posterior teeth the anterior teeth should come lightly into contact. If designing a full mouth rehabilitation, all the teeth should touch at the apex of force (also known as the position of the jaws when the masticatory muscles are activated to their maximum, also known as centric relation). Centric relation in this sense is not a magical or special position but can simply be thought of as the position where the jaw moves when muscle activity is the highest. Therefore it would be ideal to ensure that the load is spread out amongst as many teeth as possible when the patient moves into this position. As the patient undergoes excursion, the aim is to separate the posterior teeth by providing anterior guidance. This will reduce the muscle activity of the elevator muscles and reduce the shear forces on the posterior teeth which aren't designed to take non axial forces.

The illustration of this concept is represented in Figure 1 which is based of Dr. Peter Dawson's work. Dr. Melkers simplifies these occlusal concepts into "dots" and lines" where dots represent point occlusal contacts on anterior and posterior teeth in MIP and lines represent excursive movements from MIP. When designing occlusion, these dots ideally go in flat axially loaded areas i.e cusp tips and in the centre of the tooth (marginal ridges and fossa) for posterior teeth and marginal ridges or cingulums for anterior teeth because they are the thickest parts of the teeth most readily able to accept force form loading and will transmit this force axially through the tooth

Figure 1: An idealised occlusion. "Dots in the back, lines in the front". Simultaneous, even contacts in MIP and immediate disocclusion of posterior teeth by anterior teeth on excursion.