Dahl effect

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The Dahl effect is a dental method used to create extra space between the upper and lower teeth (interocclusal space) so restorations can be placed without grinding down healthy teeth.

How it works
- A localized bite-raising appliance or restoration is placed on the front teeth that sit too high (in supra-occlusion). This moves the bite out of full contact.
- Over time, the back teeth lose contact (posterior disclusion) and the jaw adjusts. The front teeth may intrude a little, and the back teeth may erupt slightly to re-establish a new, stable bite with more vertical height (occlusal vertical dimension, or OVD).
- This creates the needed space for restorations, often reducing how much tooth structure must be removed.

History and origin
- The idea of creating interocclusal space was proposed in 1962 by D.J. Andersen, who studied over-eruption and bite-raising caps.
- In 1975, Dahl and colleagues described using a bite-raising appliance on worn upper front teeth to create space for restorations. They found that space developed after months due to a mix of anterior intrusion (about 40%) and posterior eruption (about 60%).

Current approach and applications
- Today, adhesive dentistry and provisional restorations can achieve similar space.
- The Dahl concept is commonly used when you need more interocclusal space and a higher bite, especially in cases of severe anterior wear from factors like bulimia or GERD.
- Without it, you might have to further reduce the height of worn teeth, which can weaken retention and risk pulp damage. Dahl allows space with less tooth preparation.

What happens during treatment
- An appliance is placed to create space between the jaws. The back teeth disengage and, over months, adaptation occurs: posterior teeth erupt slightly and anterior teeth may intrude.
- Once the posterior teeth recontact at the new height, restorations can be placed on the front teeth without removing excessive healthy tooth structure.
- The appliance can also help restore facial height that was lost due to tooth wear.

Materials and methods
- The original Dahl appliance was a removable cobalt-chromium bite platform. Now, various materials can be used, including composite resin appliances that sit on worn front teeth to separate and stimulate eruption of the back teeth.
- Composite or adhesive approaches offer easy adjustment or removal if needed.

Advantages and considerations
- You can test planned occlusal changes with a removable appliance before permanent treatment.
- Composite approaches allow easy adjustment and reversible treatment.
- Often results in less tooth reduction and preserves pulp health.

Evidence
- A 2011 study in the British Dental Journal found high patient satisfaction with composite Dahl approaches and a median restoration survival of about 4.8 to 5.8 years.