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A Reevaluation of Hanau’s Laws of Articulation and the Hanau Quint.

INDIAN DENTAL ACADEMY Leader in continuing dental education

Hanau’s Laws of articulation and the Hanau Quint have been great contributions to field of prosthodontics. As described by Hanau, they seem very confusing and unnecessarily complicated. Hanau was not a dentist, but an engineer and a great researcher. He believed articulation of artificial teeth was related to 9 factors.

1. Horizontal condyle inclination. 2. Compensating curve 3. Protrusive incisal guidance 4. Plane of orientation 5. Bucco-lingual inclination of tooth axes 6. Sagittal condylar pathway 7. Sagittal incisal guidance 8. Tooth alignment 9. Relative cusp height He mathematically charted 9 factors and listed the laws of balanced articulation in a series of 44 statements.

Hanau combined the original 9 factors and reduced them to 5. 1. Condylar guidance 2. Compensating curve 3. Relative cusp height 4. Incisal guidance and 5. Plane of orientation. He showed how they affected one other with a clever diagram called The Articulation Quint.

Trapozzano Concept Trapozzano reviewed Hanau's 5 factors and decided that only 3 factors were concerned in obtaining balanced occlusion. He eliminated the plane of orientation “ since its location is highly variable with in the available inner ridge space” and also suggested that the occlusal plane can be located at various heights to favour a weaker ridge. He saw no need for compensating curve as it is “redundant – when the cuspal angulation which will produce a balanced occlusion has been determined, we are automatically confronted with a compensating concavity or convexity. Thus establishing the prominence of the compensating curve is a passive factorshould be omitted”. Trapozzano presented “ TRIAD OF OCCLUSION” which is simpler than Hanau’s Quint but eliminates the important compensating curve.

Boucher Concept He disagreed with Trapozzano’s concept that the occlusal plane could be located at various heights to favour a weaker ridge and he recommended that the occlusal plane “be oriented exactly as it was when the natural teeth are present.” He believed that this must be done conform to anatomic and functional needs. Boucher felt there was a need for compensating curve and stated “the value of the compensating curve is that it permits an alteration of cusp height without changing the form of manufactured teeth…if the teeth themselves do not have cusp the equivalence of cusp can be produced by using a compensating curve.”

Boucher’s concept is that 1. There are 3 fixed factors. Orientation occlusal plane. Incisal guidance and Condylar guidance. 2.Angulation of cusp is more important than the height of cusp. 3.Compensatiing curve enables one to increase the effective height of the cusps without changing the form of the teeth.

Lott’s concept Lott clarified the Hanau’s laws of occlusion by relating them to the posterior separation that is the resultant of the guiding factors. He stated the laws as follows. 1. Greater the angle of the condylar path, greater is the posterior separation. 2. Greater the angle of overbite, greater is the separation in the anterior and the posterior regions regardless of the angle of the condylar path. 3. Greater the separation of the posterior teeth, greater or higher must be the compensation curve. 4. Posterior separation beyond the ability of a compensation curve to balance the occlusion requires plane of orientation. 5. Greater the separation of teeth, greater must be the cusps of the posterior teeth.

Levin’s concept Similar to Lott’s concept but eliminates plane of orientation. It agrees the need for compensating curve that the occlusal plane should be included only in its correct anatomic position that is in the position that conforms to the patients anatomy , esthetics and function. It concur with Trapozzano and Boucher that the plane of orientation is a fixed factor and believe that it should not be included at all, because for practical purposes it cannot be used. The laws of articulation are used as an aid in understanding the balancing of occlusion for complete dentures. As explained by Lott, the guiding factor produce the separation of posterior teeth which must be prevented by the controlling factors that occurs in both protrusive and lateral movements.

He made a diagram similar to Hanau’s Quint but eliminates unnecessary plane of orientation and shows how the 4 factors of articulation are related in protrusive and lateral movements and named it as QUAD. 1. Condylar guidance is fixed and is recorded from the patient. The balancing condylar guidance includes the working condyle Bennet movement which may or may not affect lateral balance. 2. Incisal guidance is obtained from patient’s esthetic and phonetic requirements. 3. Compensating curve is important factor for obtaining balance. Monoplane or low cusp teeth must employ the use of this curve. 4. Cusped teeth have inclines necessary for obtaining balance occlusion but are used with a compensating curve. The concept of controlling posterior separation is an important goal for achieving a bilaterally balanced denture occlusion.


Conclusion Gysi stated “our understanding of the problem of articulation now is such that the dental profession can safely accept it and by doing so may obtain marvelous results. Of course we should not dream of a panacea for all prosthetic ills.�

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