Dahl Appliance and the Dahl Concept: Localised Bite Raising

A Dahl appliance lets you restore worn anterior teeth when wear and dento-alveolar compensation have left no room for restorative material. Instead of cutting the damaged teeth further or reorganising the whole occlusion, you raise the bite locally and let axial tooth movement create the space. This article explains the difference between the appliance and the concept, how the space actually forms, which patients are suitable, how Dr Hajtó designs and places the build-ups, and how strong the evidence really is.

Dahl appliance versus Dahl concept

The two terms are often used interchangeably, but they describe different things.

• The Dahl appliance is the device that holds the bite open in one part of the mouth. In its original form it was a removable cobalt-chromium bite platform on the palatal surfaces of the upper anterior teeth. Today it is usually a set of bonded composite build-ups or definitive restorations placed in supra-occlusion.
• The Dahl concept is the biological response. Poyser et al. (2005) define it as the relative axial tooth movement that follows when a localised appliance or localised restorations are placed in supra-occlusion and the occlusion re-establishes full-arch contacts over time.

Ray-Chaudhuri et al. (2023) describe the same response as a triad of tooth intrusion, tooth extrusion and mandibular distalisation, and note that it is now used well beyond tooth wear, for example in the Hall technique and for resin-bonded bridges cemented in supra-occlusion. They also observe that general practitioners remain far more cautious with it than specialists.

Where it came from: the Dahl and Krogstad studies

In 1975 Dahl, Krogstad and Karlsen described a combined orthodontic and prosthetic approach to advanced localised attrition. Their patient, an 18-year-old, wore a removable cobalt-chromium clasp appliance in the maxilla 24 hours a day. Tantalum markers in the basal bone of both jaws and lateral cephalograms made the tooth movement measurable. After twelve months there was enough space for palatal gold pinlays on the upper incisors.

The group then followed a larger cohort:

Poyser et al. point out that this implant-cephalometric work is still the only data giving a mechanistic explanation, and that the repeated radiographic exposures would hardly be approved by an ethics committee today.

How the space is created

According to the review by Poyser et al. (2005), the space comes roughly 40% from intrusion of the anterior teeth under the appliance and 60% from eruption of the discluded posterior teeth. Contact usually returns first on the last molars and then progressively further forwards. On average the occlusion closes after about six months, but it can take 18 to 24 months.

A three-dimensional analysis of superimposed casts by Bhai et al. (2023) in 26 patients found the same pattern: 56.9% extrusive posterior movement and 43.1% intrusive anterior movement, at rates of 0.13 and 0.11 mm per month. Re-establishment took 3.9 to 28.2 months and occurred regardless of age and sex. The movement was three-dimensional, with all teeth moving more mesially than distally.

In Dr Hajtó's cases, posterior extrusion dominates and the second molars move fastest, while the anterior teeth also intrude. The canine acts as the anchor point and does not change position. Bone and gingiva follow the moving teeth, and the younger the patient, the faster the bite closes.

Not every report shows this balance. In a small trial of 3D-printed Dahl restorations, Derakhshani et al. (2026) measured posterior extrusion of 0.37 mm at six months and 0.31 mm at 24 months, while anterior intrusion was clinically absent. The proportions vary between patients, so plan the case around the space you need, not around a fixed ratio.

Case selection

Good indications

• localised anterior wear with a stable posterior occlusion, typically palatal erosion or attrition of the maxillary incisors in a deep bite
• worn mandibular incisors, where Poyser et al. regard direct composite as the material of choice because crown preparation of these small teeth is particularly damaging
• over-erupted teeth after loss of the antagonist, and lost space after a crown has decemented
• resin-bonded bridge retainers that need occlusal clearance without removing enamel

For localised posterior wear, a case series by Hoekstra-van Hout et al. (2023) describes a posterior Dahl approach with supra-occluding direct restorations on molars. Eight of nine patients were very satisfied, but one showed no compensatory movement in the untreated areas and kept a vertical open bite.

When to avoid it

Dr Hajtó does not use the Dahl concept in patients with:

• temporomandibular joint problems, which are diagnosed and treated reversibly first
• tongue dysfunction
• a need for more than about 2 mm in one step, because a tongue resting between the separated posterior teeth can hinder their eruption

Ray-Chaudhuri et al. (2023) list further general factors to weigh: age, occlusal adaptability, skeletal and incisal pattern, a history of temporomandibular disorders, parafunction and altered bone metabolism. Local factors include retainers and splints, implants and fixed prostheses, periodontal status, and the choice, material and thickness of the restoration. Implants in the discluded segments will not erupt. Poyser et al. advise delaying treatment in patients with active periodontal disease until it is stable.

Designing the Dahl appliance

Poyser et al. (2005) set out what any Dahl appliance should do, whatever the material:

• place material only on the incisal or occlusal aspect of the teeth where space is needed, with no mucosa-borne component
• match the thickness to the interocclusal space you need
• direct occlusal forces along the long axes of the teeth, ideally through a bite platform
• provide stable interocclusal contacts
• leave the movement of the discluded teeth unimpeded

Dr Hajtó adds two practical rules. First, do not build a dorsal vector into the build-ups: their contact surfaces must not push the mandible backwards. Second, check the proximal contacts of the posterior teeth before you start, so that erupting teeth do not lock against each other.

Removable, cemented or bonded

Dahl's removable splint depended on the patient wearing it. In his original cohort, two of 30 patients withdrew because they disliked its appearance, and Poyser et al. identify poor compliance as the main reason space creation fails with removable designs. Gough and Setchell (1999) already used mostly cemented appliances in their series of 50 treatments in 45 patients aged 19 to 69. Bonded composite removes the compliance problem, looks better and can be adjusted chairside; Poyser et al. call it the ideal material for an interim Dahl appliance.

Clinical sequence

1. Baseline records. Photographs including palatal views, periodontal pocket charting, a panoramic radiograph, a T-Scan recording and 3D scans or study casts; a lateral cephalogram where indicated. You will compare against these at the end.
2. Function and joint check. Joints, muscles and tongue function must be unremarkable before any change in jaw relation. Where a reproducible reference position is needed, register it with an anterior jig.
3. Plan the build-ups. Define the increase from the restorative space required, at most about 2 mm in one step, and design palatal contact areas without a dorsal vector.
4. Bond the build-ups. Use direct composite or laboratory-made build-ups. Protect the adjacent teeth with PTFE tape or a metal matrix during bonding.
5. Inform the patient. Expect an unfamiliar bite, difficulty with fine chewing and temporary lisping. Poyser et al. stress that an uninformed patient may find the immediate change distressing.
6. Monitor. Track which posterior teeth have regained contact with articulating paper and shimstock, and compare scans with the baseline.
7. Finalise the guidance. Once the occlusion has closed, check anterior and canine guidance and refine the build-ups. The palatal plateaus are left in place as part of the restoration.

One-stage or two-stage?

In a one-stage procedure you cement definitive laboratory restorations in supra-occlusion. Because the final contacts cannot be predicted, you may need to adjust them afterwards, which can weaken or perforate the restoration. Poyser et al. therefore recommend a two-stage approach whenever tooth preparation or laboratory restorations are planned: create the space with direct composite first, then make the definitive restorations for the settled occlusion. In many patients the composite can simply stay as a medium-term definitive restoration.

What the evidence shows

Clinical follow-up of composite Dahl restorations is reasonably consistent:

• Redman et al. (2003): 225 restorations in 31 patients, median survival of 4 years 9 months when all failures were counted; major failure was uncommon within the first five years.
• Poyser et al. (2007): 168 restorations in 18 patients; posterior contacts returned after a mean of 6.2 months in 14 of 15 Dahl patients; complete failure in 6% at 2.5 years.
• Fan et al. (2026), a meta-analysis of 11 studies: complete occlusal re-establishment in 86.9%, partial in 10.0% and none in 0.6%, unaffected by age; annual failure rates of 0 to 8.7% for direct and 0 to 0.7% for indirect materials.

Poyser et al. (2005) summarise the adverse events as rare and mostly transient: occasional pulpal symptoms, short-lived periodontal tenderness after placement in 3 to 10% of patients, and no reports of apical root resorption.

The weak point is the quality of evidence. Goldstein and Campbell (2022) concluded that low-level case series show the space can be gained, but that there is no compelling evidence for how it is gained or for the long-term stability of the result, and that negative outcomes have been reported. Composite build-ups also wear, chip and discolour, so maintenance is part of the plan. Warn patients that full closure is likely but not guaranteed, and know in advance how you would add contacts if some teeth stay apart.

When wear is generalised rather than localised, a local appliance is not enough. You then plan an increase in the vertical dimension of occlusion for the whole arch, as described for the full mouth rehabilitation of the worn dentition.

Summary

A Dahl appliance raises the bite locally so that intrusion of the anterior teeth and eruption of the posterior teeth create space for restorations without sacrificing tooth structure. It works best for localised anterior wear in patients with healthy joints and normal tongue function, with increases of no more than about 2 mm at a time, bonded build-ups without a dorsal vector and careful monitoring. Planning localised and generalised bite raising is taught with clinical cases in our VDO dental training course.

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