Alignment and Occlusion of the Dentition, Part I

Department of Endodontics, Prosthodontics, and Operative Dentistry

University of Maryland, Baltimore

Pauline Hayes Garrett, D.D.S.

This material is taken from: Okeson, J.P. Management of Temporomandibular Disorders and Occlusion, St.

Louis, MO: Mosby, Chapter 3

Wheeler’s Dental Anatomy, Physiology and Occlusion, Ash, Chapter 16

Video Clips Ash, Nelson. Wheeler’s Dental Anatomy, Physiology, and Occlusion. St. Louis,MO: Saunders CD

Objectives!

• Identify, compare, contrast and describe the clinical significance of axial alignment.

• Identify, compare, contrast and describe the clinical significance of basic static occlusal relationships.

Factors and Forces that Determine Tooth Position

• Lips and cheeks

• Tongue

• Tooth size

• Proximal contact

• Occlusal contact

• Arch width

Occlusal Plane (Plane of Occlusion)

• An imaginary surface, related anatomically to the cranium, which theoretically touches the incisal edges of the incisors and the tips of the cusps of the posterior teeth

• Not a flat surface

• Curved due to the varying degrees of inclinations of the teeth

Bonwill’s Triangle

• 4 inches between the center of the condyles = base of the triangle

• 4 inches from each condyle to the mesial contact area between the mandibular central incisors-sides of the triangle

The Spherical Theory of the 1930’s: Monson’s Sphere

• A sphere exists with a radius of 4 inches

• The center of the sphere is equi-distant from the occlusal surfaces of the posterior teeth and from the centers of the condyle

-- Center of Monson’s Sphere ( located in the gabella area of the brain above the condyles)

Harmony

• Theoretically, a relationship is believed to exist between Bonwell’s Triangle* and Monson’s Sphere*.

*Note: These simplistic theories do not apply to all cases. They are oversimplifications and they sparked controversy which led dentistry to the current theories on occlusion used today.

1. From Sagittal plane it is known as the Curve of Spee

2. From Frontal plane it is called the Curve of Wilson

Spherical Theory of the 1930’s

Curve of Spee

• Alignment of the cusp tips of posterior teeth

produces a relatively linear curve in an anteroposterior direction

• This curve exists only in the saggital plane, whether it be from a slightly superior view or at the same level of the plane. Remember the curve is “a view of the 3-D sphere”

• Curve of the mandibular arch is concave from the level of occlusion.

• Curve of the maxillary arch is convex.

• Note: if looking down from a slightly superior view, the Curve of Spee relative to the maxillary teeth appears concave. ie. The maxillary teeth fit into the cuped shape of the Curve of Spee

Curve of Wilson

• The curve formed by an imaginary line touching the buccal and lingual cusp tips of similar teeth on each side of the mandibular arch

• Typically, viewed in the frontal plane (However, to improve visibility, this image is viewed from the posterior)

Harmony

Form follows function: • The arches fit a three

dimensional plane

• Not a flat surface

• Note the angulation of the maxillary teeth and how they relate to the curvature of the occlusal plane. (See Chapter 3 of the Okeson text.)

Angulation, Harmony continued

Angulation: (Harmony continued)

Maxillary posterior teeth are inclined facially Mandibular posterior teeth are inclined lingually Note how the angulations teeth relate to the Curve of Wilson

Intraarch Alignment

Anatomy of Posterior Surfaces

• Lingual cusps of maxillary teeth

• Buccal cusps of mandibular teeth

**Note: The loss of a occluding

centric supporting cusps could lead to the super eruption of the opposing tooth.

Supporting Cusps (centric

cusps)

Anatomy of Posterior Surfaces

• The inner aspect of a posterior tooth is the area between the cusp tips

• Also called the occlusal table

Inner Aspect

Anatomy of Posterior Surfaces

• Buccal cusps of maxillary teeth

• Lingual cusps of mandibular teeth

• Generally sharper (tip) than supporting cusp, they are not generally in function

• Inner aspects has potential for functional contact

• “Guiding cusp”=because in group function the inner aspect has a functional contact

Non-Supporting Cusps (Non-centric cusps):

Anatomy of Posterior Surfaces

• The occlusal area outside the cusp tips

• Functional Outer Aspect

• Small area of the centric cusp (about 1 mm) is the only area in which an outer aspect has any functional significance. This small area functions against the inner incline of the non-centric cusp or non-supporting cusp. This area assist in shearing of food during mastication.

Outer Aspect

Note: Where function occurs, wear occurs. As teeth wear they remain in contact due to the mesial drift and super eruption of adjacent teeth.

Maximum Intercuspation

• The relationship between the maxillary and mandibular teeth which produces the maximal contact between their respective occlusal surfaces

Angle’s Classification of Occlusion • Based on the position of the mandibular first molar

Angle’s Class I Angle’s Class II

Angle’s Class III

Angle’s Class I

• The mesiobuccal cusp of the mandibular first molar occludes in the embrasure area between the maxillary second premolar and first molar

• The mesiobuccal cusp of the maxillary first molar is aligned directly over the buccal groove of the mandibular first molar

Angle’s Class I

• The mesiolingual cusp of the maxillary first molar is situated in the central fossa area of the mandibular first molar

• In Angle’s Class I each mandibular tooth occludes with it’s counterpart and the adjacent tooth mesial to it.

Class I Occlusal Contacts

• The contacts on premolars occur between cusp tips and opposing marginal ridges

• The contacts on molars occur on both cusp tip and fossae and cusp tip and marginal ridges

Occlusal Contacts, Angles Class I

• Centric cusps contact in central fossa areas and marginal ridge areas.

Angles Class I

Note Cusp Tips:

• Mandibular cones in maximum intercuspation

Positive Wax Addition Technique:

(Technique originally developed by Dr. Everett Payne and then modified by Dr. Peter K. Thomas

Waxing Completed (Lingual view)

• Mandibular teeth are waxed to completion utilizing a positive waxing technique to allow the various area of the occlusal table to be viewed.

Occlusal Contacts

• Contacts shown with Zinc Stearate

• When properly waxed, the occlusion is supported harmoniously by including contacts in three main areas.

• Central Fossa, Marginal Ridge and Centric Supporting Cusps

Occlusal Contacts, Class I

• Each tooth contacts two teeth in the opposing arch except the mandibular central incisors and the maxillary third molars

• Each tooth occludes with its namesake in the opposing arch and an adjacent tooth

Angle’s Class II

Angles Class II

• The mesiobuccal cusp of the mandibular first molar occludes in the central fossa of the maxillary first molar

Class II

Angle’s Class III

• The distobuccal cusp of the mandibular first molar occludes with the embrasure between the maxillary first molar and the maxillary second premolar

• The mesiobuccal cusp of the maxillary first molar is situated over the embrasure between the mandibular first and second molar

• The mesiolingual cusp of the maxillary first molar occludes with the mesial pit of the mandibular second molar

Class III Occlusion

Alignment

Video Clips Ash, Nelson.(2003) Wheeler’s Dental Anatomy, Physiology, and Occlusion 8th ED. St. Louis,MO: Saunders CD

Buccoocclusal Line (B-O line)

• An imaginary line extended through all the buccal cusp tips of the mandibular posterior teeth

• Represents the general arch form

• Demarcation between the inner and outer aspects of the buccal cusps

Linguoocclusal Line (L-O Line)

• An imaginary line extended through the lingual cusp tips of maxillary posterior teeth

• Represents the general arch form

• Demarcation between outer and inner aspects of lingual cusps

Central Fossa Line (C-F Line)

• An imaginary line extended through the central developmental grooves of the maxillary and mandibular posterior teeth

• Represents the general arch form

• Proximal contact areas are generally located slightly buccal to the C-F line

• Allows food to be shunted

toward the tongue

Landmarks of Occlusion: Class 1 Occlusion

Common Occlusal Relationships of Anterior Teeth

• The maxillary anterior teeth are normally positioned labial to mandibular anterior teeth

• The maxillary anterior teeth overlap the mandibular anterior teeth almost ½ the length of the mandibular crowns

•Both maxillary and

mandibular teeth are inclined labially

Common Inter arch Relationships of Anterior Teeth

• Incisal edges of mandibular incisors contact the lingual surfaces of maxillary incisors in the lingual fossa

• Normally the maxillary anterior teeth overlap the mandibular anterior teeth almost 1/2 the length of the mandibular crowns

• Contacts are lighter as anterior teeth are not designed for heavy occlusal function

Two Types of Overlap

Horizontal Overlap= Overjet Vertical Overlap= Overbite

Functional Purposes of Anterior Teeth

• To guide the mandible through eccentric or lateral movements-called anterior guidance

• To incise food

• Speech, lip support and esthetics

Anterior Guidance

• The anterior tooth contacts that provide guidance of the mandible

• affected by horizontal overlap and vertical overlap or overbite

Anterior Guidance

Posterior

disocclusion

Posterior

disocclusion

Anterior guiding contacts

To Be Continued!!!!!!