ORTHO NORMAL OCCLUSION

• Occlusion is the medium that brings all branches of dentistry together
• Occlusion is the act of closure or being closed
• Occlusion is the contact relationship of the teeth in function or parafunction
• Dental occlusion is the static, closed contacting position of the upper teeth to lower teeth
• Occlusion is the relationship between all components of the masticatory system in normal function, parafunction, and dysfunction
• Occlusion includes the morphology and functional features of the contacting surface of the opposing teeth and restoration
• In the fictional period:

  • Pioneers like Fuller, Clark, and Imrie talked about antagonism, meeting, or gliding of teeth
  • Kingley in 1880 described the standard of normality of the dental arch as a curved line expanding towards the ends, with all teeth standing on that line
• In the hypothetical period:

  • E.H. Angle in 1897 defined occlusion as the normal relation of the occlusal inclined planes of the teeth when the jaws are closed
  • Angle's postulate stated that the upper first molars were key to occlusion and that the mesiobuccal cusp of the upper molar occludes in the buccal groove of the lower molar
• In the factual period:

  • Broadbent introduced roentgenographic cephalometry in 1930 to follow longitudinally the orofacial developmental pattern
  • Splanner in 1925 emphasized the efficacy of the masticatory system in occlusion
  • The temporomandibular joint became a significant element in occlusion
  • Andrews in 1972 provided six keys to occlusion for exact positioning of each tooth in all 3 planes of space
  • Roth in 1981 added to the static occlusion keys, relating occlusal function and orthodontic mechanics
• Intraarch tooth alignment:

  • Refers to the relationship of the teeth to each other
  • The plane of occlusion touches the incisal edges of the incisors and the tips of the occluding surfaces of the posterior teeth
• Mesiodistal axial inclination:

  • Angulation of the teeth with respect to the alveolar bone can be observed when lines are extended through the crowns
  • In the mandibular arch, both anterior and posterior teeth are mesially inclined, with molars more inclined than premolars
  • In the maxillary arch, anterior teeth are generally mesially inclined, with the most posterior molars being distally inclined
• Curve of Spee:

  • Refers to the anteroposterior curvature of the occlusal surfaces, following a curve from the lower cuspid to the anterior border of the ramus
• Buccolingual axial inclination:

  • In the maxillary arch, posterior teeth have a slightly buccal inclination
  • In the mandibular arch, posterior teeth have a slightly lingual inclination
• Curve of Wilson:

  • Mesiolateral curve that contacts the buccal and lingual cusp tips on each side of the arch, resulting from the inward inclination of the lower posterior teeth, making the lingual cusps lower than buccal cusp in mandibular arch
• Masticatory function:

  • Lower occlusal table is desined for direct access of food from the lingual side
  • Upper occlusal table provides acces from the buccal for the food to be tossed directly onto the occlusal table by the action of buccinator muscle
• Bonwill Triangle:

  • Describes an equilateral triangle between the centers of the condyles and the mesial contact areas of the mandibular central incisor
• Curve of Monson:

  • Proposed a theory of a sphere with a radius of 4 inches, center equidistant from occlusal surfaces of posterior teeth and from the center of the condyles
• Interarch tooth alignment:

  • Refers to the relationship of the teeth in one arch to those in the other when the two arches come into contact during mandibular closure
• Arch length:

  • In normal interarch relation, both arches have approximately the same length, with the mandibular arch slightly smaller than the maxillary arch
• Arch width:

  • Mandibular arch is slightly less than the maxillary arch, protecting soft tissues during mastication
• Buccolingual occlusal contact relationship:

  • Mandibular teeth's buccal cusp tips align with the central fossa line of maxillary teeth
  • Maxillary teeth's lingual cusps align with the central fossa line of mandibular teeth
• Mesiodistal occlusal contacts relationship:

  • The proximal contact areas are placed slightly buccal to the central fossa line
• Occlusal contacts occur when the centric cusps contact the opposing central fossa line
• Cusp-fossa occlusion:

  • Stamp cusp of one tooth occludes in a single fossa of a single opponent
  • Upper stamp cusps fit into all the fossae of the lower teeth while the lower stamp cusps fit into the upper fossae except the distal ones of bicuspids
• Cusp-embrasure occlusion:

  • Each tooth occludes with two opposing teeth
• Advantages of cusp-fossa relationship:

  • Forces are directed along the long axis of the tooth
  • Greater stability to the entire arch of teeth and less tendency toward tooth movement
  • Less chance of food impactions between embrasures
• Centric stops:

  • When in centric occlusion, teeth should have maximal interdigitation with locking of the two arch positions
  • Centric contacts occur at height of cusp contour, marginal ridges, and central fossae
  • Cusps that function during occlusion are called supporting cusps
• Centric relation:

  • Positional relationship of the temporomandibular joints
  • Axial position where joints can rotate to open or close the jaw without moving off the centric relation position
  • Mandible can be in centric relation even when teeth are separated
• Centric occlusion:

  • Voluntary position of the dentition that allows maximum contact when teeth occlude
  • Related to the functioning of the dentition
  • Individuals with occlusal interferences on posterior teeth may experience centric slide
• • Class III Malocclusion:
  • Mandibular first molar situated in embrasure between maxillary second premolar and first molar
  • Maxillary first molar situated over embrasure between mandibular first and second molar
• Common occlusal relations of posterior teeth:

  • Class I Malocclusion:
  • Mandibular first molar occludes in the embrasure area between maxillary second premolar and first molar
  • Maxillary first molar aligned directly over buccal groove of mandibular first molar
  • Each mandibular tooth occludes with its counterpart and adjacent mesial tooth
  • Class II Malocclusion:
  • Mandibular first molar occludes in central fossa area of maxillary first molar
  • Maxillary first molar aligned with buccal groove of mandibular first molar
  • Full occlusal load shifts to most posterior teeth
• Pseudo Class III Malocclusion:

  • Mandible shifts anteriorly due to premature contact of teeth or other reasons in centric occlusion
• Factors and forces determining tooth position:

  • Musculature, proximal contacts, and occlusal contacts play a role in tooth alignment within dental arches
  • Neutral space is where labiolingual and buccolingual forces are in equilibrium
  • Proximal contacts help maintain normal arch alignment
  • Occlusal contacts prevent extrusion or supraeruption of teeth, maintaining arch stability