Occlusion Terminologies 
By Dr Yasser el Hadari, MFDS, MPros RCSEd 

Dental occlusion is an important science in dentistry. Any manipulation of dental tissues involves occlusion. Occlusion basically means the contacts between the teeth. To study occlusion is to learn the dynamic biological relationship of the teeth, periodontium and the articulator system. These are the components of the masticatory system that determine tooth relationships. 

Analysis of occlusion 

The occlusal relations when the mandible is stationary is the static occlusion, and those relations when the mandible is moving relative to the maxilla are the dynamic occlusion. 

Static occlusion : 

Centric Occlusion (CO) can be described as the occlusion the patients make when they fit their teeth together in maximum intercuspation. Also Known as Intercuspation Position (ICP), Bite of Convenience or Habitual Bite. It is the occlusion the patient makes on being told to bite. Unarticulated models close together in this way, guided by the anatomy of the occlusal surfaces of the teeth. To avoid confusion with Centric Relation and other definitions of centric occlusion, the term Intercuspation Position (ICP) is used instead. 

Retruded jaw position (RP) is the guided jaw position with the condyles in a physiologically acceptable position for recording transfer records. The ‘most retruded position’ is not physiologically acceptable and isn’t a centric relation position as will be explained later. 

Retruded contact position or point (RCP) is the tooth contact position when the jaw is in RP.

Centric Relation (CR) describes the relation between maxillary and mandibular skeletal bases independent of the teeth. It is reproducible with or without teeth present. It can be described anatomically, conceptionally and geometrically. 
  • Anatomical : The position of the mandible to the maxilla, with the intraarticular disc in place, when the head of the condyle is against the most superior part of the distal facing incline of the glenoid fossa. It is not acceptable to understand it as the ‘uppermost and rearmost’ position. In this case RP and CR are describing similar clinical anatomical relationships. It is the condylar position at RP or CR that is used for clinical recording of the jaw relationship for transfer to an articulator. 
  • Conceptual : The position of the mandible relative to the maxilla, with the articular disc in place, when the muscles that support the mandible are at their most relaxed and least strained position. This description is pertinent to an understanding of ‘ideal occlusion’. This definition supports the concept of a ‘qualitative’ relationship between a jaw position and another element of the articulatory system. 
  • Geometrical : The position of the mandible relative to the maxilla, with the intra-articular disc in place, when the head of the condyle is in terminal hinge axis. 

Postural jaw position (PJP) is the position of the jaw when an individual is sitting or standing upright when relaxed and alert. The height of the lower face in this position is the Vertical Dimension at Rest. 

Occlusal vertical dimension (OVD) is the vertical height of the lower third of the face when the teeth contact in ICP. The lower third of the face is an important component of facial aesthetics and is an essential element of treatment planning in conjunction with PJP. 

Freeway Space is the variable space between maxillary and mandibular teeth, termed 'free-way' or speaking space. It is an important determinant of speech communication. Dental restorations may have a significant influence on speech in both dentate and edentulous treatment. 

Freedom in centric , also known as ‘long centric,’ is when the mandible is able to move 0.5-1.5mm anteriorly for a short distance in the same horizontal and sagittal plane while maintaining ICP. 

Dynamic Occlusion :

The dynamic occlusion refers to the occlusal contacts that are made whilst the mandible is moving relative to the maxilla. The mandible is moved by the muscles of mastication and the pathways along which it moves are determined not only by these muscles but also by two guidance systems: 

The Posterior guidance system consists of six determinants. The first three cannot be modified clinically but the final three can ;

1. The intercondylar distance. 
2. The Condylar Angle, which is the angle between the Frankfort horizontal plane and the downwards trajectory of the condyle during translation.
3. The Bennett Angle, which is the angle of medial movement between the non-working side condyle and the sagittal plane.
4. Curve of Spee, the anteroposterior curve from the tip of the lower canine, following the buccal cusps of the natural premolars and molars and continuing to the anterior border of the ramus. 
5. Curve of Wilson, the mediolateral curve created by the curvature of the cusps as projected on the frontal plane expressed in both arches; the curve in the mandibular arch being concave and the one in the maxillary arch being convex. 
6. Occlusal Plane. The average plane established by the incisal and occlusal surfaces of the teeth; generally, it is not a plane but represents the planar mean of the curvature of these surfaces 

The Anterior guidance is provided by the anatomy of the functional surfaces of whichever teeth touch during excentric movements of the mandible. The overjet and overbite between the teeth will determine the dimensions of the anterior guidance. Anterior guidance may be further classified : 
  • Protrusive guidance. Contacts between teeth in the anterior excursive direction by the cuspids and incisors, often referred to as incisal guidance. Any area of a tooth that contacts an opposing tooth during protrusive movement is considered to be protrusive contact. 
  • Canine guidance refers to a dynamic occlusion that occurs on the canines during a lateral excursion of the mandible. A canine protected occlusion refers to the fact that the canine guidance is the only dynamic occlusal contact during this excursive movement. 
  • In Group function the contacts are shared between several teeth on the working side during a lateral excursion. Previously including the molars was mandatory, but o qualify for the term ‘group function’, the contacts would be towards the front of the mouth and the most anterior of the group would be the earliest and hardest contacts. 

Interferences are contacts during excursive movement which interrupt the smooth movement of the mandible: 

Working side interference : which infers a heavy or early occlusal contact towards the back of the mouth during an excursive movement. The working side is the side of the mandible towards which the mandible is moving during a lateral excursion 

Balancing side interference : is an anterior guidance on the back teeth on the non working side during lateral excursion. The non working side is the side of the mandible away from which the mandible is moving. 

Posterior interference : Anterior guidance on back teeth 

Centric Interference : Initial tooth contact when mandible is closed in centric. 

Definition of ideal occlusion This is described on the tooth level, the articulatory system level and the patient level 

On the tooth level ideal occlusion requires ;
Multiple simultaneous contacts 
No incline contacts
Angulations which allow occlusal forces to go down the long axis of the tooth.

On the articulatory system level ideal occlusion is ;
1. The coincidence of Intercuspation Position in Centric Relation (ICP=CR) 
2. When there is Freedom in Centric. 
3. When the mandible moves there is immediate and lasting posterior disclusion (anterior guidance on front teeth) .

On the patient level the ideal occlusion is one which is tolerated well by the patient on the neuromuscular level at that time in their life. 

FURTHER READING Applied Occlusion by Robert Wassel BDJ Series on Occlusion

Good articles to start with.