Intro to Clinical Occlusion
On Occlusion
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.
Good articles to start with.
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