Arrangement of Posterior Teeth PDF

Arrangement of posterior teeth By Dr. Mohammed A. El-Sawy BDS, MSc, PhD Factors affecting setting-up of posterior teeth:  1-The position of the posterior teeth in relation to the alveolar ridge As a general principle the most acceptable position for the...

Arrangement of posterior teeth By Dr. Mohammed A. El-Sawy BDS, MSc, PhD Factors affecting setting-up of posterior teeth:  1-The position of the posterior teeth in relation to the alveolar ridge As a general principle the most acceptable position for the teeth is usually over the crest of the ridge. The mandibular teeth are positioned in the wax occlusion rim over the crest of the residual ridge in their ideal buccolingual relationship. The maxillary teeth are set in a tight centric occlusal arrangement regardless of their buccolingual positions 2- The neutral zone  3- Balanced occlusion To achieve balanced occlusion, the posterior teeth are arranged so that their cusps present anteroposterior and lateral curves. These curves correspond to the curve of Spee and curve of Monson (compensating curves). In anatomy, the Curve of Spee (also called von Spee's curve or Spee's curvature) is defined as the curvature of the mandibular occlusal plane beginning at the canine and following the buccal cusps of the posterior teeth, continuing to the terminal molar. According to another definition the curve of Spee is an anatomic curvature of the occlusal alignment of the teeth, beginning at the tip of the lower incisor, following the buccal cusps of the natural premolars, and molars and continuing to the anterior border of the ramus. It is named for the German embryologist Ferdinand Graf von Spee (1855–1937), who was first to describe the anatomic relations of human teeth in the sagittal plane. The curve of Wilson is the across arch curvature or posterior occlusal plane. Arc of the curve, which is concave for mandibular teeth and convex for maxillary teeth The curve of Wilson is defined by a line drawn from left mandibular first molar to right mandibular first molar. 1- Monson’s articulator: based on spherical theory of occlusion. (lower teeth move against upper teeth in part of sphere its center at glabella The maxillary posterior teeth Side view  Arrangement of upper first and second premolars: 1-Its long axis is parallel to the vertical axis when viewed from the front or the side. 2-For the first preomolar tooth, the buccal cusp only touch the occlusal plane, the palatal cusp raised 0.5mm from the occlusal plane.while in the second premolar, both buccal and palatal cusp toutch the occlusal plane. 3- The central sulcus lies directly over the lower ridge crest.  The upper first molar: 1-Its long axis inclined slightly upward mesially when viewed from the front. 2- Its long axis inclined slightly downward and buccally when viewed from the side. 3- Only its mesiopalatal cusp is in contact with the horizontal plane. 4- The central sulcus lies directly over the lower ridge crest.  The upper second molar: 1- Its long axis slopes as the first molar but steeper. 2- All four cusps are short of the horizontal planer but the mesiopalatal cusp is always nearest to it. The mandibular posterior teeth  The lower first molar: 1- The mesiobuccal cusp of maxillary first molar lies in the mesiobuccal groove of the lower first molar. 2- The lingual cusps of the maxillary first molar in contact with the central fossae of the lower first molar  The lower second molar: The same inclinations and relation to the maxillary teeth as in the first molar. However, the long axis inclination is more prominent. The mandibular posterior teeth  The lower second premolar 1- The buccal cusp touches distal marginal ridge of first premolar and mesial marginal ridge of second premolar. 2- Lingual cusp rest lingually between the maxillary first and second premolars.  The lower first premolars If the maxillary posterior teeth were set first, space available to lower first premolar may be small and its mesiodistal width may require reduction from the mesial contact point. In the other hand, if the mandibular posteriors were set first, a spacing (1/4 to ½ mm) of the maxillary posteriors will be required to achieve the proper intercuspation. The buccal cusp of the lower first premolar touches the mesial marginal ridge of upper first premolar.  The buccal cusps of the upper posterior teeth overlap those of the lower. Every tooth except the two lower central incisors and the two upper last molars occlude with two teeth in the opposite jaw. Thank you