Inclined Plane

The inclined plane is an appliance that fully implements the principle of functional orthodontics. It is only by biting together that the force is produced to trigger remodeling processes. This is a special acrylic appliance that is placed on the mandibular teeth and contacts only individual teeth in the opposing jaw. The force during biting is vectorially distributed to the inclined plane so that the tooth being corrected is pushed in a labial direction.The corrective forces arise intermittently and only at a magnitude that is within the physiologic range of tolerance.

The indication for an inclined plane is the adjustment of maxillary incisors that are lingually tipped and caught behind the mandibular anterior teeth (Fig 10-68). To achieve stationary anchorage, the inclined plane at least embraces all four mandibular incisors without touching or irritating the gingiva.

Four incisors can be corrected effectively enough at the same time. During correction of the teeth, the periodontal tissues cannot be overloaded because the periodontium ensures that force is minimized in a reflex fashion.

If the distance to be spanned is very short, treatment success is quickly achieved.Therefore, correction of tooth position excluding antagonist contact is first undertaken with suitable active appliances, then adjustment is performed with an inclined plane within a very short treatment period.

A reverse articulation of individual teeth is often associated with crowding of teeth in that area. The teeth requiring correction overlap each other, and their movement is impeded. Therefore, the crowding must be rectified first.

Generally the inclined plane is firmly cemented. However, it can also be combined with a removable appliance that retrudes the mandibular teeth at the same time.The mandibular incisors need to bridge one half and the maxillary teeth the other half of the distance being corrected. This involves a mandibular active plate with a tightened labial bow to which the inclined plane for the maxillary incisors is fitted.

For retrusive movement, the plate must be reduced behind the mandibular incisors. With the removable plate, the occlusal pressure is transmitted via the inclined plane to the maxillary teeth and also to the mandibular teeth to the same extent. To achieve stationary anchorage for the maxillary teeth and for the mandibular active components, the plate is anchored by the usual retentive components.

The effect of the inclined plane is dependent not only on the angle of inclination but also on the number of teeth being corrected, the distance to be bridged, and the freedom of direction of movement. If only one tooth has to be corrected, the entire occlusal force will act on its periodontium and stimulate remodeling. With an increasing number of teeth to be adjusted, the force is spread, and so is the tensile and compressive effect in the periodontal tissues of the involved teeth, until the force falls below a threshold and any orthodontic effect is lost.

The treatment period with an inclined plane should not be longer than 6 weeks because chewing activity is considerably restricted. The dentition must be kept out of antagonist contact so that only the tooth or teeth being corrected are loaded and repositioned. This results in lengthening of the unloaded teeth, which may lead to an anterior open bite.The steeper the inclined plane, the faster the adjustment is achieved.

Fabrication of an inclined plane takes place in the laboratory on models. However, it can also be modeled directly in the mouth. The entire mandibular dentition is enclosed in a block with a splint to ensure stationary distribution of forces and prevent lengthening at least of the mandibular incisors. The acrylic is pulled up for the width of the tooth being adjusted so that only the affected tooth is touched by the acrylic block when biting together and all the other teeth are kept out of contact.

The acrylic bite plane is placed at an angle of 45 degrees to the occlusal plane. In the mouth, the surface of the bite plane can then be ground into the optimum angle of inclination. In several consecutive sessions (about every 3 days), the bite plane is then ground off until the incisal edge of the mandibular incisor can be seen.The posterior teeth should have no contact during the treatment period; otherwise the inclined plane will not work.