Dahl effect

The Dahl effect or Dahl concept is used in dentistry where changes are planned in the dental occlusion. Dahl first described this phenomenon as the use of a Dahl appliance or anterior bite plane to increase the available interocclusal space available for restorations.

The Dahl concept is commonly used when an increase in the interocclusal space is required together with an increase in occlusal vertical dimension ; for example when restoring a case of severe anterior tooth surface loss.

Typically, restoring the worn anterior teeth with dental composite to the original proportions will result in an increase in OVD, with the posterior dentition held apart out of the occlusion.

Adaptation occurs over a period of some months: compensatory eruption of the posterior teeth will occur, together with some intrusion of the anterior teeth and potential growth of the alveolar bone. This will allow the posterior occlusion to reestablish at the new increased OVD, stabilizing the increased interocclusal space.

The advantages of this approach are:

• minimal removal of tooth substance is required to create the interocclusal space
• lost OVD can be restored
• minimisation of facial aging by restoring facial height
• safety
• relative simplicity
• relatively reversible
• relatively cost effective approach

Dentoalveolar tissues tend to compensate by remodelling when incisal/occlusal tooth surface loss has occurred to allow the teeth to regain a functional occlusion. A subsequent increase in the OVD with the Dahl approach could exceed the patient's tolerance and adaptive capacity. If the patient is unhappy with the height of their teeth and a Dahl approach cannot be tolerated then crown lengthening may be appropriate.

Planned occlusal changes can be tested using a removable appliance prior to permanent treatment. Dental composite based approaches to tooth surface loss allow for easy adjustment or removal if required. One study published in the British Dental Journal, 2011 found that patient satisfaction was high when composite restorations were used in the Dahl approach and that the median survival time was between 4.75 and 5.8 years. Survival analysis of composite Dahl restorations provided to manage localised anterior tooth wear (ten year follow-up)http://www.nature.com/bdj/journal/v211/n4/full/sj.bdj.2011.683.html.

References

• Smith BGN (1998). Planning and making crowns and bridges (3rd ed.). London: Routledge. p. 71. ISBN 978-0-203-41955-7. OCLC 60311365. 
• Poyser NJ; Porter RW; Briggs PF; Chana HS; Kelleher MG (June 2005). "The Dahl Concept: past, present and future". British Dental Journal. 198 (11): 669–76; quiz 720. doi:10.1038/sj.bdj.4812371. PMID 15951771.