Increasing vertical dimension: when it is genuinely needed, and how to verify before becoming irreversible

Increasing the occlusal vertical dimension is among the most debated interventions in prosthodontics, and also one where theory and clinical practice took longest to reconcile.

For decades the prevailing conviction held that vertical dimension was a fixed value, that altering it caused joint disorders, and that it had to be restored with millimetric precision. Accumulated evidence has moderated that rigidity.

Studies of patients undergoing an increase in vertical dimension show adaptation in the great majority of cases, with transient symptoms resolving within a few weeks. Increases of up to 5 millimetres are generally well tolerated.

This does not mean the increase is without consequence, but that the margin of adaptability is wider than was taught. The question has shifted from how safe it is to the more useful one: is it actually needed.

There are three real indications. The first is lack of prosthetic space for restorative materials: if restoring correctly requires more thickness than is available, the alternative to increasing is endodontic treatment or accepting thin restorations destined to fracture.

The second is generalised wear with documented loss of vertical dimension, where the increase restores a previous condition rather than creating a new one. The third is the need to correct a severely altered intermaxillary relationship.

Outside these situations, increasing is often a shortcut avoiding crown lengthening or orthodontic treatment, and in those cases the bill arrives later as overload and fracture.

Assessment of vertical dimension has no single reference method, and this should be stated rather than presenting one technique as exact. Freeway space, phonetics, facial proportions and swallowing each give a partial indication.

The phonetic method remains the most practical: pronouncing the letter S, the teeth approach without contacting, leaving about a millimetre. If they contact, the vertical dimension is probably excessive.

But no measurement replaces the functional test. A provisional at the new dimension, worn for at least eight to twelve weeks, is the only way to know whether that particular patient tolerates that particular height.

The trial period should be used to gather information, not merely to wait. Muscular pain persisting beyond the first weeks, phonetic difficulty that does not resolve, or signs of overload on the provisional indicate the value must be revised.

A provisional that fractures repeatedly in the same area is signalling an occlusal problem that the definitive, being more rigid, will not resolve but will transfer to the underlying tooth.

In summary, increasing vertical dimension is safer than was feared but less necessary than is often proposed. It is justified by missing prosthetic space, verified with a provisional worn long enough, and confirmed by observed tolerance rather than a calculated figure.