THE EDITOR'S CORNER

The management of most orthodontic cases can be divided into six distinct but overlapping stages of treatment: anchorage control, leveling and aligning, overbite control, overjet reduction, space closure, and finishing. These stages are sequential, with the effective management of one stage being a prerequisite for the successful completion of the next.

For example, overbite control is a direct result of leveling and aligning procedures. Overjet reduction and space closure cannot be properly completed without prior management of overbite. This is particularly true when preadjusted appliances are used with sliding mechanics.

We have previously presented an overview of the six stages of treatment with a preadjusted appliance system1 and a detailed discussion of space closure.2 This article will examine the diagnosis and clinical management of overbite control.

Diagnosis and Treatment Planning

Correction of a deep overbite can involve any combination of these tooth movements, depending on the individual case (Fig. 1):

1. Extrusion of posterior teeth.

2. Uprighting of posterior teeth.

3. Increasing the inclination of anterior teeth.

4. Intrusion of anterior teeth.

Whether to extract teeth is a significant decision in treatment planning. The following are the main factors to be evaluated.

Vertical Skeletal and Dental Pattern

We use the maxillary (palatal) plane to mandibular plane (MM) angle as a key diagnostic measurement, with the average being 28º at 12 years of age. This measurement is supplemented with the FM angle (average 26º) and the GoGnSN angle (average 32º).3

A nonextraction approach seems to be most effective for controlling deep overbite in low-angle cases (MM angle less than 25º). In such cases, leveling and subsequent bite opening occur primarily as a result of the uprighting and slight extrusion of posterior teeth. The anterior teeth are usually upright or retroclined in these patients; when the incisors are slightly advanced or inclined forward, bite opening is enhanced and facial esthetics are often improved. Intrusion of anterior teeth is normally unnecessary, because lower facial height is being increased rather than maintained. The exception would be a case with retroclined and extruded incisors, in which an intrusion arch can be used to intrude the incisors before they are advanced.

If teeth are extracted in low-angle cases, overbite control becomes difficult because strong muscle forces impede the ability of the posterior teeth to move forward. As the extraction sites are closed, the anterior teeth then tend to upright and move posteriorly, which leads to further bite deepening and undesirable profile changes. In the few low-angle cases where extractions are indicated (such as severe crowding or protrusion), the leveling and aligning and space closure must be done slowly, with light forces, to control the overbite.

High-angle cases (MM angle greater than 31º) present a different set of challenges and a more difficult extraction decision. Extrusion of posterior teeth must be resisted to avoid further increase in the MM angle and downward and backward rotation of the mandible. This is best accomplished with light forces, supplemented if necessary with anterior intrusion mechanics. Evaluation of incisor position and crowding becomes critical in these cases, and extractions should be considered more strongly than in low-angle cases.

Horizontal Skeletal and Dental Pattern

In a Class II deep bite case, it is usually the forward positioning of the maxillary dentition that has led to the extrusion of anterior teeth and subsequent development of the overbite. If the lower incisors can be slightly advanced, it minimizes the need for over-retraction of the upper incisors (with negative profile changes) and also initiates the bite-opening process.

Nonextraction treatment is more conducive to such lower incisor movement, because extractions tend to maintain or upright the incisors, thus working against bite opening. In the maxilla, the more the upper incisors need to be retracted, the more they tend to be uprighted and the more difficult it is to correct the deep overbite.

With this nonextraction approach, the advantage of a growing patient is obvious. If upper teeth must be extracted in a Class II deep bite case (as with an uncooperative or adult patient), great care must be taken to maintain torque as the upper incisors are retracted, and intrusion mechanics to the incisors are sometimes necessary to allow for bite opening. In severe cases, surgery may be the only satisfactory option.

Incisor Position

The evaluation of incisor position is critical, as shown with the two preceding factors. If the incisors are retrusive and can be advanced, bite opening is significantly enhanced. If they are protrusive and must be retracted, the bite tends to deepen and overbite control becomes more difficult.

Crowding

Evaluation of crowding is important, but unless it is severe it does not take precedence over considerations of vertical pattern, horizontal pattern, and incisor position.4 If these three factors all favor nonextraction treatment, then all but severely crowded cases can be treated without extractions using space-gaining procedures, including uprighting and retraction of molars, expansion and uprighting of buccal segments, advancement of incisors, and judicious interproximal stripping. If the other three factors favor extraction treatment, then even minimally crowded cases can be successfully managed with extractions.

Nonextraction Treatment

Leveling and Aligning

Most of the treatment procedures normally used in deep bite nonextraction cases encourage bite opening. For example, during leveling and aligning with a complete arch system, the posterior segments are uprighted and slightly extruded while the anterior segments are inclined forward.

In the initial stages of moderate-to-low-angle cases, an upper anterior bite plate can relieve posterior muscle forces, thus encouraging the uprighting and extrusion of the posterior teeth (Fig. 2). The bite plate also allows for early lower incisor bracket placement, which might otherwise be impossible due to the interference of the upper incisors. The earliest possible banding of the second molars (especially in the lower arch) is highly beneficial in these cases; we have observed that complete leveling of the lower curve of Spee is virtually impossible without the inclusion of the lower second molars (Fig. 3).

In high-angle cases, the bite plate is contraindicated because extrusion of the posterior teeth is undesirable. The lower anterior segment is therefore not bracketed until the bite has opened sufficiently. The upper second molars are usually omitted from the arch to avoid their extrusion. If they must be banded for improved positioning or torque control, the archwire can be stepped up behind the upper first molars to the level of the second molars.

The leveling and aligning process is often thought of as a round-wire procedure that is completed in the first months of treatment, but it is actually not concluded until rectangular wires have been in place for one to three months. It is sometimes even necessary to place slight biteopening curves in the upper and lower rectangular archwires to complete leveling and aligning (Fig. 4).

We find an .019"X.025" archwire in an .022" slot more effective in arch leveling and bite opening than an .017"X.025" archwire in an .018" slot.

Anchorage Control

In the early stages of treatment with a preadjusted appliance system, the tip built into the anterior brackets can cause these teeth to incline anteriorly. Although this enhances bite opening, it may be undesirable for other reasons. Headgear and Class III elastics can help control this anterior tipping if necessary.

Class III elastic forces should be very light if used with light leveling wires, to avoid extrusion of the lower incisors and further bite deepening. Therefore, we usually wait until at least an .016" round wire is in place before initiating Class III elastics.

If anchorage control is needed for Class II molar correction, and headgear or Class II elastics are applied to the upper molars, the distalization of these teeth is usually accompanied by some extrusion, which is helpful in bite opening.

Overjet Reduction

Bite-opening procedures should be virtually completed before proceeding with overjet reduction. The premature use of Class II elastics-- for instance, in the round-wire leveling stage--can lead to bite deepening and to excessive interference between the advancing lower incisors and the retracting upper incisors. This, in turn, can lead to periodontal breakdown, tooth wear or root resorption of the incisors, a tendency toward distal displacement of the mandible, and potentially damaging forces on the temporomandibular joints (Fig. 5).

Once the overbite has been adequately controlled, overjet reduction can be accomplished with headgear or Class II elastics. Class II elastics are particularly effective in moderate-to-low-angle cases, since the extrusive force applied to the lower posterior segment encourages the completion and maintenance of bite opening (Fig. 6). In high-angle cases, Class II elastics should be used sparingly and with light force to avoid the extrusion of the posterior teeth.

Space Closure

Spaces are not usually of great concern in nonextraction treatment of deep bite cases. If minimal spacing does occur, the clinician will not usually be inclined to attempt space closure prematurely (as can happen in extraction cases). Spaces can easily be closed after leveling and bite-opening procedures have been completed.

Case Report

Figures 7A-D and 7E-H demonstrate proper bite-opening procedures in a typical nonextraction case.

Extraction Treatment

Most of the treatment considerations for deep bite nonextraction cases also apply to extraction cases. These include the use of bite plates, banding of second molars, the .022" slot vs. the .018" slot, the use of headgear and Class III elastics for anchorage control and their effect on overbite control, and the importance of proper overbite control before initiating Class II mechanics for overjet reduction.

There are two additional significant factors that must be taken into account in extraction treatment. First, in an extraction case the incisors are usually maintained or uprighted, which makes bite opening more difficult than in a nonextraction case, where the incisors are usually maintained or advanced. Second, if space closure is attempted before completion of leveling and overbite control, this can lead to further bite deepening.

One of the great advantages of a preadjusted appliance system is the ability to use effective sliding mechanics. This was not possible with the standard edgewise appliance because of the need for archwire loops and posterior bends. However, if the rectangular archwire is to slide effectively through the posterior bracket slots, they must be free of friction. Archwires that are deflected because of incomplete leveling and overbite control will not be friction-free during space closure.

We have found that effective correction of deep overbite in extraction cases depends on the use of light force levels during both leveling and aligning and space closure.

Leveling and Aligning

Bicuspids are usually extracted in deep bite cases to reduce anterior protrusion, to eliminate anterior crowding, or both. In any case, management of the cuspids is vitally important. If there is anterior protrusion without crowding, a decision must be made whether to retract the anterior segment en masse or to retract the cuspids and then the incisors. We prefer to use en masse retraction with a rectangular wire after arch leveling has been completed and the bite opened. If there is anterior crowding, we prefer to retract the canines during the leveling process only enough to allow adequate space for incisor alignment, and later to retract the anterior segment en masse.

Some contend that initial retraction of the canines followed by retraction of the incisors helps to maintain anchorage, but we have seen little evidence to support this hypothesis. Such an approach lengthens treatment time and creates a second major area of gingival tissue and alveolar bone between the lateral incisors and cuspids. Also, extreme care must be taken to avoid tipping the cuspids distally.

With a preadjusted appliance system, the tip built into the cuspid and incisor brackets causes these teeth to tip anteriorly upon initial archwire placement. When this tendency is counteracted by the early application of even the lightest elastic forces, the cuspids are tipped distally, the overbite deepens, and the posterior bite opens.1 This "roller coaster" effect invariably results in extended treatment time (Fig. 8).

To prevent anterior tipping of the cuspids and to retract them without distal tipping, we use "lacebacks"--.010" figure-8 ligature wires from first molars to cuspids (Fig. 9). These wires at first compress the periodontal ligament space distal to the cuspids, resulting in slight tipping. However, there is adequate time for uprighting because of the absence of elastic force on the cuspids and because of the leveling effect of the archwire.

If the cuspids are initially upright or tipped distally, then the preadjusted appliance system can make overbite control more complicated by exerting an extrusive force on the incisors when initial archwires are placed (Fig. 10). We normally prefer to include as many incisors as possible in the initial archwires to provide greater stability of arch form and better tip control of the canines. However, if the cuspids are unfavorably positioned, we do not include the incisors in the archwires until the cuspid roots have been retracted enough to provide a more level cuspid slot angulation.

There are many factors that can lead to bite deepening, rather than effective overbite control, in the initial leveling stage of extraction treatment. The use of light forces with minimal activation lengths, such as the "lacebacks", has proven most efficient in controlling cuspid position and movement, and therefore overbite.

Space Closure

The same tendency for the bite to deepen can occur during space closure with rectangular wires if forces are excessive. The cuspids can tip into the extraction sites, causing archwire deflection and binding, ineffective sliding mechanics, and resultant bite deepening. Also, excessive forces can overpower the torque control of the rectangular wire on the incisors (especially upper incisors), which leads to distal tipping or uprighting of the incisors and deepening of the bite (Fig. 11) .

In addition to the use of light forces, a small amount of torque added to the upper archwire in the incisor region can be helpful in minimizing these bite-deepening factors. We find that forces of 50-150g are most effective and can be delivered by small elastic modules, attached to anterior archwire hooks with ligature wires extended forward from the molars2 (Fig. 12).

Case Report

Figures 13A-D, 13E-I, and 13J show the clinical management of a deep bite extraction case.

Conclusion

Deep overbites can be effectively controlled with preadjusted appliances when the following principles are observed:

1. Avoid extractions in low-angle cases whenever possible.

2. Use .022" slots with .019"X.025" working archwires.

3. Use anterior bite plates at the beginning of treatment in moderate-to-low-angle cases.

4. Use light initial forces to avoid deepening the bite.

5. Avoid elastic retraction of cuspid brackets.

6. Band or bracket second molars as early as possible.

7. Use Class II elastics selectively.

8. Do not hurry final leveling of the arches; use flat rectangular wires at first, then add biteopening curves as needed.

9. Use gentle forces for space closure in extraction cases. [show_img]End.gif[/show_img]