18.2 Developmental & Acquired Occlusal Problems
Key Takeaways
- Centric relation is a maxillomandibular relationship determined by condylar position and is independent of tooth contact, whereas maximum intercuspation is defined by tooth contact alone
- Primary occlusal trauma acts on a normal periodontium, while secondary occlusal trauma acts on a periodontium already reduced by attachment loss
- Occlusal trauma alone does not initiate periodontitis, but it can accelerate attachment loss where inflammation is already present
- Attrition is tooth-to-tooth wear, abrasion is wear from a foreign object, erosion is chemical dissolution, and abfraction is proposed cervical loss from occlusal flexure
- Occlusal adjustment is irreversible and should follow reversible therapy and a definitive diagnosis, never precede them
Developmental & Acquired Occlusal Problems
Why this matters on the INBDE: Occlusion connects restorative, prosthodontic, periodontal, orthodontic, and temporomandibular content. Items in this area typically test definitions precisely — the examination distinguishes centric relation from maximum intercuspation, and primary from secondary occlusal trauma, without leniency.
Reference Positions and Terminology
| Term | Definition | Key point |
|---|---|---|
| Centric relation (CR) | Maxillomandibular relationship in which the condyles articulate with the thinnest avascular portion of their discs, with the complex in the anterosuperior position against the articular eminences | A condylar, ligament-determined position; independent of tooth contact; reproducible, which is why it is the reference for full-mouth reconstruction |
| Maximum intercuspation (MIP / centric occlusion) | The complete intercuspation of opposing teeth irrespective of condylar position | Defined only by teeth |
| CR–MIP discrepancy ("slide") | Distance and direction the mandible shifts from initial contact in CR into MIP | A small slide is common and physiologic; a large or laterally deviating slide can be pathologic |
| Vertical dimension of occlusion (VDO) | Face height with teeth in MIP | Lost with severe attrition; restored deliberately, never guessed |
| Vertical dimension at rest | Face height at physiologic rest position | Interocclusal rest space is typically 2–4 mm |
| Freeway space | Rest vertical dimension minus occlusal vertical dimension | Encroachment causes soreness and clicking of teeth in speech |
| Canine guidance (mutually protected occlusion) | Canines disclude posterior teeth in lateral excursion; anterior teeth disclude posteriors in protrusion; posterior teeth protect anteriors in MIP | The most commonly restored scheme |
| Group function | Multiple teeth on the working side share lateral contact | Acceptable, especially where canine support is compromised |
| Working / non-working (balancing) side | Side toward which / away from which the mandible moves | Non-working interferences are the most destructive, because they act as a fulcrum with the strongest elevator muscle force |
| Curve of Spee / curve of Wilson | Anteroposterior / mediolateral compensating curves | Relevant to restorative plane and complete-denture balance |
| Balanced occlusion | Simultaneous bilateral contact in all excursions | Desirable for complete dentures; not a goal for the natural dentition |
Occlusal Trauma
Trauma from occlusion is injury to the attachment apparatus from occlusal forces.
| Type | Definition | Periodontium |
|---|---|---|
| Primary occlusal trauma | Excessive force on a tooth with normal attachment | Normal bone support; the force is the problem |
| Secondary occlusal trauma | Normal or excessive force on a tooth with reduced attachment | The support is the problem; even physiologic force is now excessive |
Clinical and radiographic signs: increasing mobility, fremitus (perceptible movement on function), widened periodontal ligament space with an intact lamina dura, thickened lamina dura in some cases, wear facets, tooth migration, cervical sensitivity, and sometimes root resorption.
The critical concept the examination tests: occlusal trauma does not initiate periodontitis and does not cause gingivitis or pocket formation by itself. It is a co-destructive factor — in the presence of plaque-induced inflammation, it can accelerate attachment loss. The primary therapy for periodontitis is therefore always inflammation control, with occlusal management as an adjunct.
Tooth Wear: Four Distinct Mechanisms
| Mechanism | Definition | Typical appearance |
|---|---|---|
| Attrition | Tooth-to-tooth contact | Flat, shiny, matching wear facets on opposing teeth; incisal and occlusal |
| Abrasion | Wear by a foreign object | Toothbrush and dentifrice: horizontal V-shaped cervical notches, often on canines and premolars, worse on the side opposite the dominant hand; pipe stem or hairpin notches |
| Erosion | Chemical dissolution, non-bacterial | Broad, smooth, glossy concavities; restorations standing proud; palatal in reflux/vomiting, facial in dietary acid |
| Abfraction | Proposed cervical loss from occlusal flexure stressing the cervical enamel | Wedge-shaped, sharp-angled cervical defect; the mechanism remains debated and most cervical lesions are multifactorial |
Most real wear is multifactorial — an eroded surface abrades and attrites far faster than sound enamel. Management identifies each contributing factor and addresses it, and restoring worn teeth without stopping the cause guarantees failure of the restorations.
Bruxism and Parafunction
Bruxism is repetitive masticatory muscle activity — clenching or grinding — classified as sleep bruxism or awake bruxism. Contemporary understanding places its origin centrally, driven by sleep arousals, stress and anxiety, certain medications (SSRIs, stimulants), tobacco, alcohol, and caffeine, with obstructive sleep apnea an important association. Occlusal interferences are not the primary cause, a change from older teaching that the examination reflects.
Consequences: attrition, restoration and porcelain fracture, implant overload, cervical abfraction-type lesions, masticatory muscle hypertrophy and pain, morning jaw stiffness, headache, and tooth hypersensitivity.
Management:
- Address contributing factors — sleep quality, stress, medications, alcohol and caffeine; screen for sleep apnea and refer where indicated. A full-coverage occlusal appliance can worsen untreated obstructive sleep apnea in some patients, which is why screening precedes appliance therapy.
- Occlusal appliance — a full-coverage, hard acrylic maxillary or mandibular stabilization appliance, adjusted to even simultaneous contacts in centric with canine guidance in excursions. Its role is to protect teeth and restorations and reduce muscle symptoms, not to cure bruxism.
- Avoid partial-coverage appliances for long-term use — anterior-only appliances can allow posterior over-eruption and occlusal change.
- Restorative protection — materials selected for the load, cusp coverage on compromised teeth, avoidance of thin unsupported porcelain.
- Behavioral measures — awareness training for awake clenching, sleep hygiene.
Managing Occlusal Problems: The Correct Sequence
- Diagnose first. Identify whether the presenting problem is muscular, joint-related, periodontal, restorative, or a combination. Mounted diagnostic casts and a deprogramming record clarify the CR–MIP relationship.
- Reversible therapy before irreversible therapy. Occlusal appliances, physical therapy, behavioral change, and analgesia come before any tooth structure is removed.
- Control inflammation — periodontal therapy precedes occlusal adjustment where periodontitis is present.
- Occlusal adjustment is irreversible. Legitimate indications include removing a demonstrable non-working interference producing fremitus or mobility, eliminating a single high restoration, and refining occlusion after orthodontics or restorative treatment. It is not an appropriate first-line treatment for temporomandibular disorders or for generalized tooth wear.
- Restore at the correct vertical dimension. Where wear has been slow, alveolar compensation usually preserves vertical dimension, and the restorative space must be created — by orthodontic intrusion, crown lengthening, or a deliberate and carefully tested increase in vertical dimension validated with a provisional phase before definitive restorations.
A defensible principle for the exam: when an option offers occlusal adjustment as the first treatment for pain or wear, it is almost always wrong. Reversible therapy and a definitive diagnosis come first.
A tooth with 60 percent bone loss shows increasing mobility under normal masticatory forces. How is this best classified?
Which statement about the relationship between occlusal trauma and periodontitis is correct?
A patient shows broad glossy concavities on the occlusal surfaces of the mandibular molars with amalgam restorations standing proud of the surrounding tooth structure. Which wear mechanism is dominant?
A patient with sleep bruxism, morning headaches, loud snoring, and daytime sleepiness requests an occlusal appliance. What should precede appliance fabrication?