Occlusion is one of the fundamental aspects of dentistry, influencing nearly every clinical procedure performed in restorative, prosthodontic, orthodontic, and periodontal practice. Understanding occlusion allows clinicians to maintain the functional harmony of the masticatory system, which includes the teeth, temporomandibular joints (TMJs), and the associated musculature. Improper occlusal relationships can contribute to discomfort, tooth wear, fracture of restorations, and even temporomandibular disorders (TMDs).
Definitions and Fundamental Concepts
Ideal Occlusion
Ideal occlusion refers to an anatomically perfect relationship between the maxillary and mandibular teeth when the jaws are in centric relation. This theoretical condition ensures even distribution of occlusal forces and perfect intercuspation. However, such perfection is rarely found in natural dentitions. Instead, clinicians focus on achieving a functional occlusion, which is free of interferences and pathology.
Functional Occlusion
A functional occlusion is defined as an occlusal relationship that permits smooth, unhindered movements of the mandible during all functional activities, without causing trauma or discomfort to the teeth, supporting tissues, or TMJs. The goal of restorative dentistry is to reproduce or restore this functional harmony after treatment.
Balanced Occlusion
Balanced occlusion describes simultaneous bilateral contacts of the upper and lower teeth during all mandibular movements. This concept is primarily applied to complete denture prosthodontics to provide stability and prevent tipping of the denture bases. In natural dentition, balanced occlusion is neither necessary nor desirable, as it could lead to excessive tooth wear and muscle strain.
Group Function
In group function, multiple teeth on the working side make simultaneous contact during lateral excursions of the mandible. There are no contacts on the non-working side. This occlusal scheme helps distribute occlusal forces over several teeth, reducing the load on any single tooth, and is often seen in natural dentitions or restored posterior regions.
Canine-Guided Occlusion
In this scheme, the canines disclude all posterior teeth during lateral movements. The canines, being robust and well-supported by long roots and dense alveolar bone, are ideally suited to bear lateral forces. Canine guidance is often considered desirable because it minimizes potentially damaging forces on posterior teeth and provides proprioceptive feedback to the muscles of mastication.
Mandibular Movement and Axes
Hinge Axis and Terminal Hinge Axis
The hinge axis refers to the imaginary line passing through both condyles around which the mandible rotates during the initial phase of mouth opening. The terminal hinge axis represents the position when the condyles are in their most superior, unstrained position within the glenoid fossae. Understanding these axes is essential when recording centric relation or mounting casts on an articulator.
Retruded Arc of Closure
This is the arc along which the mandible closes when rotating around the terminal hinge axis. It terminates when the first tooth contact occurs, known as the retruded contact position (RCP). The retruded arc of closure provides a reproducible reference position, crucial for full-mouth rehabilitation and prosthodontic planning.
Occlusal Relationships and Key Positions
Anterior Guidance
Anterior guidance is the dynamic relationship between the maxillary and mandibular anterior teeth during mandibular movements. It is characterized by two components:
- Overjet: The horizontal overlap of the anterior teeth.
- Overbite: The vertical overlap of the anterior teeth.
Together, they guide mandibular movements and protect posterior teeth from excessive lateral forces. Restoration of anterior guidance is a vital component of any anterior restorative or prosthodontic procedure.
Intercuspal Position (ICP) or Centric Occlusion
The intercuspal position is the position of maximum intercuspation between the upper and lower teeth, regardless of condylar position. It is the position most patients naturally adopt when they close their mouths. In restorative dentistry, this is often the reference position for single-tooth restorations or small prostheses.
Retruded Contact Position (RCP) or Centric Relation
Centric relation is a bone-determined position, representing the relationship of the mandible to the maxilla when the condyles are in their most anterior-superior position within the glenoid fossae, with the articular discs properly interposed. The initial tooth contact in this position defines the RCP. In about 10% of patients, RCP coincides with ICP; in most, a small slide forward occurs between the two. This relationship is crucial for establishing stable occlusion in full-mouth reconstructions.
Rest Position and Freeway Space
The rest position is the habitual postural position of the mandible when the patient is relaxed and the teeth are apart. The vertical distance between the rest position and ICP is called the freeway space, typically 2–4 mm. Maintenance of an appropriate freeway space is important for comfort and masticatory efficiency.
Supporting and Non-Supporting Cusps
Supporting (or functional) cusps are those that occlude in centric stops, maintaining vertical dimension. They are palatal cusps in the maxilla and buccal cusps in the mandible.
Non-supporting (or guiding) cusps do not contact opposing teeth in centric occlusion but assist in guiding mandibular movements. They are buccal cusps of the maxilla and lingual cusps of the mandible.
Occlusal Contacts, Interferences, and the Occlusal Vertical Dimension
Centric Stops
Centric stops are precise points on the occlusal surfaces where opposing teeth make contact in ICP. Preservation or accurate reproduction of these stops is essential during restorative work to ensure stability of the occlusion.
Deflective Contacts and Interferences
Deflective contacts alter the natural path of mandibular closure, potentially diverting the mandible from its ideal position. Interferences are undesirable contacts that hinder smooth gliding movements during protrusion or lateral excursions. Eliminating interferences is a key part of occlusal adjustment and polishing of restorations.
Occlusal Vertical Dimension (OVD)
OVD represents the vertical relationship between the maxilla and mandible when the teeth are in ICP. It essentially defines facial height and plays a major role in aesthetics and function. Inappropriate alteration of OVD can lead to esthetic disharmony, speech difficulty, and TMJ discomfort.
Occlusal Factors and Temporomandibular Disorders (TMDs)
Temporomandibular disorders (TMDs) have a multifactorial aetiology, involving occlusal, neuromuscular, and psychological factors.
While occlusal discrepancies alone rarely cause TMDs, they can contribute in susceptible individuals by inducing abnormal muscle activity or joint loading.
Stress and parafunctional habits such as bruxism often lower the patient’s adaptive capacity, allowing minor occlusal interferences to manifest as symptoms.
Thus, restorative procedures must aim to prevent the introduction of iatrogenic occlusal interferences.
Occlusal Examination in Clinical Practice
Before any restorative procedure, a careful occlusal examination is vital. The clinician should assess:
- The number and distribution of occluding teeth
- Over-eruption, tilting, or rotation
- Presence or absence of centric stops
- RCP–ICP relationship and any slide between them
- Nature of anterior guidance
- Presence of group function or canine guidance
- TMJ function and muscle tenderness
Thin articulating paper (20 µm) or Shimstock foil (8 µm) can be used to identify occlusal contacts. The examination provides baseline information to guide treatment planning.
For complex restorative cases or patients with suspected occlusal dysfunction, a more detailed analysis—termed diagnostic mounting—is performed using mounted study models on a semi-adjustable articulator.
Occlusal Considerations for Restorative Procedures
The Conformative Approach
In most restorative cases, the goal is to reproduce the patient’s existing occlusion. The conformative approach ensures that new restorations blend harmoniously with the patient’s established occlusal pattern, thereby avoiding the introduction of new interferences.
This approach is suitable for single or small multiple restorations, where existing occlusion is stable and satisfactory.
The Reorganized Approach
When extensive crown or bridgework is planned and the existing occlusion is unsatisfactory, a new occlusal scheme must be established. This is termed the reorganized approach.
The mandible is positioned in centric relation (RCP), the only reproducible jaw relationship, and the new occlusal scheme is designed around it.
This approach is essential in full-mouth rehabilitations, severe wear cases, or when the existing occlusal stability is lost.
Clinical Steps and Practical Guidance
Marking and Preserving Centric Stops
Before tooth preparation, centric stops should be marked using articulating paper and preserved if possible. After restoration placement, occlusion must be checked to ensure that these stops are accurately recreated.
Checking Intercuspal Position
Restorations should be verified in ICP to confirm they are not high and that they re-establish proper centric contacts. A restoration left out of occlusion may result in over-eruption of opposing teeth, while one left high can cause trauma or discomfort.
Excursive Movements
The restoration should also be checked during lateral and protrusive excursions to confirm that no interferences have been introduced. This ensures smooth functional movement and patient comfort.
Extracoronal and Intracoronal Restorations
Simple intracoronal restorations usually require minimal occlusal adjustment if proper attention is paid during carving or finishing. For extracoronal restorations, laboratory stages must replicate the patient’s occlusion accurately. Errors are common in distal-most restorations; therefore, use of occlusal records and articulators is often advisable.
Articulators and Mounting Procedures
An articulator is a mechanical device that simulates mandibular movements and holds dental casts in a defined relationship. Semi-adjustable articulators, such as the Denar® Mark II, are commonly used for restorative work.
To ensure accuracy, casts are mounted using a facebow record, which transfers the spatial relationship of the maxillary arch to the TMJs.
In the conformative approach, casts are mounted in ICP, whereas in the reorganized approach, they are mounted in RCP (centric relation). This distinction ensures appropriate control over the occlusal scheme depending on the case complexity.
Occlusal Records
Accurate occlusal records are crucial for mounting casts. The two principal reference positions are ICP and RCP.
ICP Records
A wax “squash bite” is traditionally used, but it is often inaccurate due to mandibular deviation during closure. For single restorations, it is often best to mount casts manually in the position of best fit.
RCP Records
To record the retruded position, the mandible is guided along the retruded arc of closure before tooth contact occurs. This pre-centric record is made using hard waxes such as Moyco® Dental Wax or silicone-based materials like TempBond®.
The record should capture the relationship of the mandible just before occlusal contact to allow accurate mounting.
Transfer Coping Technique
When multiple preparations have been made, the working dies may not easily relate to the opposing arch. The transfer coping technique, using materials like Duralay®, allows intraoral registration of occlusal relationships by creating precise imprints of opposing teeth. This ensures accurate articulation in the laboratory.
Clinical Relevance and Common Pitfalls
Occlusal errors are a leading cause of restoration failure, postoperative sensitivity, and patient discomfort.
- High restorations may lead to tooth mobility or fracture.
- Loss of occlusal contact may cause over-eruption or drifting of opposing teeth.
- Improper guidance can result in excessive wear or TMJ strain.
Therefore, every restoration, from a small filling to a full arch reconstruction, should be evaluated for occlusal harmony in both static and dynamic functions.
Conclusion
A thorough understanding of occlusion is fundamental to successful restorative dentistry. It bridges the gap between form and function, ensuring that restorations integrate seamlessly within the stomatognathic system.
Dental students and clinicians must develop the ability to recognize normal occlusal patterns, identify potential interferences, and restore teeth in a manner that maintains functional equilibrium.
The key to clinical success lies in the careful examination of occlusion, precise recording and replication of mandibular relationships, and a meticulous approach during restorative procedures to prevent iatrogenic problems.
By adhering to these principles, dentists can ensure restorations that are not only durable and aesthetic but also physiologically harmonious.
References
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