IMPORTANCE OF OCCLUSION

 The 3 GOLDEN RULES OF OCCLUSION

The 3 Golden Rules of Occlusion can apply to any occlusal philosophy because they are sound physiological and mechanical principles that have been proven by both scientific research and common sense. Nevertheless, when the patient requires occlusal therapy, or when there is a need to reconstruct a bite, the most practical, anatomical, and physiological sound place to position the condyle is into the centric relation position. 

The first Golden Rule is to have bilateral and even occlusal contact. The masticatory muscles can generate huge forces, often several hundred pounds of force per square inch.⁵ For this reason, bilaterally even contacts throughout the dentition are mechanically sound, allowing for proper load distribution and a stable occlusion. When a tooth interferes with full closure, it will trigger deflective interferences^6-8 and cause any of the 7 signs and symptoms of occlusal disease such as hypersensitivity, abfractions, mobility, excessive wear or fractures, and muscle or temporomandibular (TM) pain. Posterior teeth deflections may create an occlusal avoidance pattern leading to excessive anterior tooth wear (Figures 1 and 2). Also, in order for muscles to function in coordination, teeth need to contact evenly. It is possible to induce muscle incoordination by introducing an occlusal interferences as shown by Sheikholeslam and Riise.⁹ Additionally, although controversial in the scientific literature, clinical experience shows that occlusal interferences in centric can trigger muscle or TM discomfort, and that removing them will bring about improvement of the symptoms.¹⁰ 

The second Golden Rule is posterior teeth disclusion, or anterior and canine guidance. Anterior and canine guidance allows for the immediate disclusion of molars and premolars when making lateral or protrusive movements, such as in chewing. This immediate posterior disclusion provides some important mechanical benefits, in that masticatory muscles significantly decrease activity and the amount of force applied to the anterior guiding teeth is greatly decreased.^11,12 Williamson and Lundquist¹³ found that when posterior teeth touch, the muscles can function with full force. On the other hand, when only anterior teeth touch, the forces decrease significantly. An additional mechanical benefit is that since the mandible works as a Class III lever, the further a tooth is from the fulcrum (joint), the less force is applied to it. When a patient lacks this mechanical benefit, during lateral movements, the posterior teeth grind over each other with full muscular force, and it is typical to see these patients with severe signs and symptoms of occlusal disease (Figures 3 and 4). 

Finally, the third Golden Rule of Occlusion is an unobstructed envelope of function.¹⁴During the chewing motion, the mandible does not only swing laterally, it swings forward (protrusively) during the closure movement, returning back into the centric stop. This is called the envelope of function. It varies from patient to patient, but Lundeen and Gibbs15 found that the average was 0.37 mm. The correct amount of overjet allows the space for this protrusive movement to occur without interference (Figure 5). When the overjet is insufficient, or the lingual morphology of the anterior teeth is not concave enough, interference to the anterior path of closure will occur. The consequences of violating this principle while restoring anterior teeth are that patients may complain that their bite feels high or locked in. This often triggers parafunction activity. Also, this interference in the path of closure may cause a scraping of the anterior teeth, resulting in the typical wear pattern, severe “thinning” of incisal edges, or wear of the lingual surface of the maxillary anterior teeth with wear of the facial of mandibular anterior teeth (Figure 6). It can also cause other problems, including mobility, chipping, and fracture of the teeth.