Palatal Shelf Anchorage

The frustration of poor cooperation and the possibility of litigation over eye damage from headgear provide sufficient cause to explore alternative methods of preserving maxillary anchorage. I have found the palatal shelf anchorage device works as well as, if not better than, headgear.

This appliance has no orthopedic effect, but it does accomplish what is required in the majority of extraction cases: it prevents treatment-induced mesial movement of maxillary posterior teeth without resorting to an extraoral appliance.

Appliance Features

The palatal shelf anchorage device is a removable appliance that uses vertical surfaces of the hard palate for anchorage. The acrylic body of the appliance is adapted to these surfaces and to the teeth distal to the extraction sites. When anterior teeth are retracted, they are pitted against the "V"-shaped wedge of the appliance, which is being pressed into a similar "V"-shaped wedge formed by the lateral shelves of the hard palate.

This "V into V" anchorage is particularly efficient because the depth and form of the lateral shelves provide resistance to anterior molar movement, and the area is further increased by incorporating the anterior slope of the hard palate into the anchorage unit. Before the anchor teeth could move mesially, the whole device would have to move anteriorly and displace the entire hard palate mesially and laterally.

The appliance is particularly valuable in steep-angle cases. These patients usually have high-vaulted palates and a more vertical component of the anterior slope of the hard palate. The bad news is that they have a tendency to lose anchorage quickly. The good news is that their extended, vertical palatal shelves are particularly amenable to resisting forward movement of the buccal segments when the appliance is in place.

Unlike headgear, the appliance is inconspicuous and therefore acceptable to socially aware adolescents and adults. Reducible pontics in the extraction sites conceal the edentulous areas that would be visible until the extraction spaces are closed (Fig. 1). This esthetic feature is a powerful inducement for cooperation. I have found that when the appliance is broken or a pontic breaks away, the patient asks that it be replaced immediately. I want my patients to wear the appliance to alleviate the complications of lost anchorage. They want to wear it because they have been assured it will simplify treatment, and because it makes them less self-conscious after extractions are performed.

The pontic, when it abuts the distal tooth in the extraction site, prevents the posterior tooth from tipping forward over the cervically placed clasp wire (Fig. 2). In addition, occlusal forces on the pontic from the opposing arch help keep the appliance in place.

A snug fit is maintained by the retention clasps snapping into place under the height of mesial contour of the teeth distal to the extraction sites. If the device does not click into place, the patient has not been wearing it as directed--a more immediate indication of cooperation than would be possible with headgear.

The palatal shelf anchorage appliance can be worn 24 hours a day, except for cleaning. There is no interference with the occlusion while eating.

Appliance Construction

Outline the body of the appliance on a stone cast. Adapt the clasps against the cervical margins and beneath the heights of contour of the tooth surfaces distal to the extraction sites (Fig. 3). Do not extend the clasps facially to the extent that they bind against the archwire when the patient removes the appliance for cleaning.

Adapt the acrylic firmly against the lingual surfaces of the molars. Do not include the horizontal part of the hard palate; this would not contribute to the anchorage unit, but would make the appliance more bulky and decrease tongue space. An anterior or posterior bite plane can be incorporated if necessary.

Do not place acrylic in the path of the teeth to be retracted or in the cervical area of the anterior teeth. This avoids bunching of the tissue between the incisors and the appliance during retraction. Anchorage will not be affected, because the vertical component of the anterior palate, not the incisors, is primarily responsible for buttressing the posterior teeth.

Build the appliance in two stages. First, construct the body of the appliance, including a thin layer of acrylic to form ridge laps over the edentulous areas (Fig. 4).

Second, adapt the pontics to these ridge laps. Prime the ridge laps and the bases of the pontics with acrylic monomer five minutes before bonding the pontics to the body of the appliance. A small hole can be drilled in the base of the pontic (Fig. 5); this is filled with acrylic to form a retention peg that rests against the ridge lap.

Clinical Use

Reduce the mesial surfaces of the pontics by 2mm before cuspid retraction (Fig. 6). If you prefer to retract the cuspids alone, rather than the entire anterior segment, use a closing loop archwire. Retract the cuspids 2mm, then activate the closing loop to retract the incisors into the new position; repeat until the extraction spaces are closed.

The principle is to sequentially reduce the mesial of the pontics, then retract anterior teeth into the spaces created. This procedure precludes unsightly gaps being created mesial to the cuspids during retraction.

Adjust the retention clasps periodically to insure a precise fit.

Conclusion

The advantages of palatal shelf anchorage are:

1. There is no occlusal interference with the opposing arch.

2. Except for cleaning, the device can be worn 24 hours a day.

3. Unattractive extraction spaces are eliminated, thereby providing a powerful esthetic inducement for patient cooperation.

4. The vertical surfaces and "V" shape of the palatal walls provide excellent anchorage potential.

5. Anterior or posterior bite planes can be incorporated into the appliance.