Lingual Orthodontics: A Status Report, Part 5: Lingual Mechanotherapy

In the preceding articles, we have presented the development history, rationale, bonding procedures, and some general guidelines on patient selection for lingual orthodontics. These were offered as building blocks, providing the basis for this report and the case presentations to follow.

While we all know a "cookbook" approach cannot routinely be applied to a biological situation, we have found it necessary at this early stage of lingual development to attempt to categorize our diverse mechanotherapy approaches into a set of guidelines that the lingual practitioner must modify to meet the specific requirements of the case at hand.

These treatment guidelines are the result of two or more years of lingual experience compiled from seven practitioners of varying backgrounds and philosophies of treatment. Differences of opinion are presented along with concurrences. We present a few of the many avenues in lingual mechanotherapy that can lead to a unifying goal of excellence. Certainly, as we all continue to learn, these approaches will be modified and some discarded, for it would be presumptuous to imply that in our limited exposure to lingual mechanics there is no further improvement required.

Treatment Sequence-- General

For convenience of discussion, we have defined four primary phases of edgewise lingual mechanics:

These phases are generally characterized by a progressive increase in wire stiffness. A wire selection guide (Fig. 1), utilizing the work by Burstone1 in quantifying wire stiffness, may provide some general guidelines in the archwire progressions by phase of treatment and degree of malocclusion.

The decisions on which teeth to bond or band and on the use of lingual and buccal brackets are dictated by:

Whenever possible, the patient should be encouraged to accept conventional labial appliance treatment on the lower arch. In a great many cases, this will satisfy the patient's needs and simplify the treatment. The bonding or banding of maxillary bicuspids is also an esthetic decision. Placement of buccal and lingual brackets on maxillary second bicuspids can be tolerated by many lingual patients and can add considerably to the stability of the buccal segments, particularly on extraction cases.

Short lingual crowns on mandibular bicuspids frequently preclude the bonding of lingual brackets. These teeth may be bypassed on the lingual arch in favor of buccal segments, or banded with buccal and lingual attachments. The latter would certainly be preferred in cases requiring the additional stability and control of arch form afforded by combined buccal/lingual mechanics.

Lingual archwire form and the necessary first and second order bends require some discussion. Compensating bends should be made in the very first wire placed. First order bends between cuspids and bicuspids should be made at right angles, with a generous step to allow for the differences in labiolingual thickness between cuspids and premolars. First order bends contacting the mesiolingual of bicuspids or first molars can also act as archwire stops. These can provide an advancing or expansive force to the arch (Fig. 2A). While this can be used to advantage when advancement is indicated, one must be cautious to allow room between wire bends and lingual brackets and teeth for retraction or consolidation mechanics, and to avoid undesirable anterior expansion (Fig. 2B).

The lingual appliance can be expansive in nature. Much of the expansion force can be attributed to insufficient constriction of archwire form in the anterior segments. As rotations are corrected and the anteriors align, archwire length is gained. If the anterior arch form is just slightly oversize, the gain in archwire can produce an advancing force. Contouring a small-diameter, dead-soft brass wire into the bracket slots cuspid to cuspid and measuring the resulting archwire length may be helpful in determining arch form and necessary wire length.

A tendency to induce an anterior maxillary open bite should also be recognized. While all the cause-and-effect relations are not fully understood at present, this tendency seems to occur more often in nonextraction cases and in moderate-to-high mandibular plane angle cases. Advancement of maxillary anteriors on resilient round wires, coupled with posterior extrusion, may permit the tongue to open the anterior bite further. This tendency is difficult to control, but its prevention is of paramount importance. Prevention includes:

Leveling, Aligning, Rotational Control, and Bite Opening

The objectives of this initial phase of therapy are to:

Typically, these objectives have been met using lingual archwires having a wire stiffness of less than 200, combined with complete seating of the archwire within the bracket slot and a degree of patience in permitting these resilient wires to express their control.

A common problem in lingual therapy, infrequently encountered with labial brackets, is the inability to place a lingual bracket or to achieve wire engagement with moderate-to-severe crowding. A common problem with lingual edgewise brackets that have a horizontal slot is the additional difficulty in obtaining complete archwire engagement and the tendency for the archwire to be pulled out of the bracket slot. Neither of these concerns occurs with labial mechanics, and both are a function of the high bracket-slot torque angles and lingual directional forces (Fig. 3).

A ligation method termed the double-over tie has been effective with both metal and elastic ligatures in directing the ligating force more directly along the bracket-slot angle (Fig. 4). This ligating technique has greatly improved the ability to eliminate rotations and maintain archwire engagement throughout treatment. Several auxiliary devices have been tried for rotational control. Thus far, round elastomeric tubing with .009" ligature wire passing through the tubing and ligated in place has been most effective in correcting rotations (Fig. 5).

Lingual archwires that have proven effective for initial leveling and alignment have been the multistrand spiral wires-- .0155" and .0175" Respond, .014" Nitinol, .016" TMA, and where early torque control is required, .016" X .022" D-Rect.

While the immediate bite opening can present some additional difficulties, e.g., vertical and A-P changes, it is certainly beneficial in deep bite correction and can be used to advantage in other instances. The immediate posterior disclusion provides an excellent opportunity for molar uprighting, any mesial posterior movement desired, and crossbite corrections; and, if distal movement via headgear is expected, it will be facilitated by the absence of interference of the posterior occlusion. If preparation for any of these corrections is required prior to opening the bite, bonding of the maxillary lingual brackets can be delayed.

These cases are best treated by initiating alignment with as many teeth as possible, while obtaining space for further alignment. On severely crowded extraction cases, initial cuspid retraction should not be attempted until the case is into a lingual arch having a wire stiffness factor of 200 or more, e.g., .016" round stainless steel. Once space is gained, any remaining rotations are bonded and continued alignment is achieved with lighter wires, i.e., Respond, Nitinol, TMA, or D-Rect (Fig. 6). Initial cuspid retraction for high or blocked-out cuspids can be achieved with light buccal elastics placed to a distogingivally, labially bonded plastic button or Elastilug (Fig. 7). Where maxillary crowding involves the centrals or laterals, high-pull headgear with J-hooks to the lingual of the cuspids has been utilized effectively for gaining space by cuspid retraction (Fig. 8). Open coil springs and initial cuspid retraction with elastic chain have worked well in preparation for further alignment (Fig. 9).

Retraction/Consolidation Mechanics

Lingual mechanotherapy techniques for retraction and consolidation have followed conventional appliance procedures, using either sliding mechanics, closing loop arches, or combinations.

Proper anchorage preparation should receive additional attention, with the initial loss of posterior occlusion resulting from the bite plane opening. It has become standard practice to place a transpalatal arch and/or headgear on all extraction cases. As described in Part 4 (JCO, January 1983), this has eliminated earlier problems of transverse arch bowing and excessive mesiobuccal molar rotation due to retraction forces (Fig. 10).

Buccal segments should be leveled and aligned prior to initiating retractions. Buccal segment archwire stiffness should routinely be greater than lingual archwire stiffness by at least 400 stiffness numbers, e.g., .016" round stainless steel (Ws 256) or .0175" X .0175" TMA (Ws 292) lingual retraction arch, with buccal segments of .017" X .025" TMA (Ws 740/342) or .016" X .022" stainless steel (Ws 1130/598). On brachyfacial cases with more critical anchorage, consideration might be given to establishing a firm posterior occlusion prior to retraction mechanics.

Retraction of the maxillary anterior segment as a unit has become more frequent, as the cosmetically conscious lingual patient may object to the spacing with cuspid retraction. This, of course, gives additional import to anchorage units and torque control during retraction.

Retraction mechanics should not be initiated until wires of sufficient stiffness (Ws greater than

250-300) can be utilized. Typically, the lingual archwires used for retraction have been .016" round stainless steel (Ws 256), .0175" X .0175" TMA (Ws 292), and .016" X .016" stainless steel (Ws 434). As mentioned previously, alignment of the anterior segment, prior to retraction, may require initial unraveling on heavier wires (e.g., .016" stainless steel), returning to the more resilient Respond, TMA, or D-Rect for complete engagement and alignment, followed again by the lingual retraction archwires. Retraction technique option considerations are: (1) anchorage needs, (2) patient desires and cooperation, and (3) the operator's preference, based on prior experience and expertise.

Where anchorage is of concern or maxillary anterior intrusion is desired, high-pull anterior headgear may be considered. This extraoral traction method has been successful with J-hooks to the lingual of the cuspids and the anteriors ligated together. A lingual closing archwire can be used in conjunction with the extraoral retraction (Fig. 11). Another effective method that may offer additional torque control is the use of high-pull headgear to an acrylic plate (Fig. 12).

Cuspid retraction, when indicated and permitted by the patient, has most often been accomplished on .016" stainless steel or .016" X .022" stainless steel. Posterior segments should be ligated as a unit and the cuspids firmly ligated with double-over steel ligatures. The maxillary anteriors may be ligated lateral to lateral with either steel ligature or elastic chain. A three-unit elastic chain is then placed from the ball hook on the cuspids to the most mesial tooth in the posterior unit. Once cuspid retraction is complete, the cuspids are ligated as part of the posterior unit and anterior retraction is initiated on rectangular wire (e.g., .017" X .025" TMA) with closing loops (Fig. 13). The anteriors must be firmly ligated with a double-over tie at this time. One method used to insure complete seating of the retraction archwire and to unify the anterior segment is to place both metal and elastic ligatures. Steel ligature wire (.009") is first figure-eight tied to the segment. The archwire is then placed and secured with double-over tie elastic ligatures (Fig. 14).

Retraction of the entire anterior segment, following any initial cuspid retraction and anterior alignment, should be performed on a rectangular wire with a relatively high stiffness factor, e.g., .016" X .022" stainless steel (Ws 1130/598) or .017" X .025" stainless steel (Ws 1761/815). Anodic reduction of the posterior wire will facilitate sliding mechanics while maintaining anterior torque control. Class I retraction force with closing loops (Fig. 15), sliding mechanics and elastics (Fig. 16), or J-hook headgear (Fig. 11) have all been effective options. Following retraction, any additional arch consolidation, torque control, and arch leveling can be accomplished with .016" X .022" stainless steel or .017" X .025" TMA and elastic chain or closing loops.

Midline corrections are difficult to make after arch consolidation, and every effort should be made to correct midline discrepancies by intra-arch shifting, i.e., unilateral retraction or coil springs.

Torque Control

Fortunately, with the rectangular wire selections available (Fig. 1) and following Burstone's principles of variable modulus orthodontics,1 we can now initiate torque control early in treatment using .016" X .022" D-Rect (Ws 68/36) or .017" X .025" D-Rect (Ws 106/49) and maintain it in all

phases of treatment when torque control is required.

The amount of desired torque is obtained by varying the size of the square or rectangular archwires used. More torque has been built into the lingual brackets than is normally required to compensate for the many variables such as variable tooth morphology, bracket height vs. torque change, mode of treatment, and wire selection. It is, therefore, left to the practitioner to select the amount of torque and degree of control via his wire selection. Typically, lingual archwires used in finishing and torque control have been .016" X .022" stainless steel for moderate torque and .017" X .025" TMA for full torque.

Class II Correction and Detailing/Finishing

Whenever possible, utilization of intermaxillary elastics should be reserved for finishing arches with sufficient wire stiffness (greater than 700) to resist any arch deformation. Lingually placed Class II elastics, from the lower first molars to the maxillary cuspids, have not proven to be very effective. This is perhaps due to the more vertical vector component of the shorter span. Debnam cleats or Elastilugs bonded labially on maxillary cuspids are relatively esthetic, and elastics from the lower second molars to these cleats are functional and easier for the patient to apply and remove (Fig. 17). Additional Class II correction can also be accomplished with a gnathological positioner. Finishing archwires have been .016" X .022" stainless steel, .017" X .025" TMA, or .016" and .018" TMA when additional detailing of the occlusion is required.

Summary

As a number of our initial lingual cases reach completion and the earlier problems of accurate bracket placement are resolved, it becomes more and more apparent that lingual mechanotherapy should follow well-established conventional therapy principles. Additional archwire changes are often required, but with time and further refinements in appliance design, the system will be improved and simplified.

The cautious optimism of two years ago has been reinforced as our cases progress. Numerous mistakes have been made, but the trials and tribulations have resulted in positive developments. Continued research, perseverance, and patience will undoubtedly make this mode of treatment a viable alternative.

The suggested guidelines, with modification for the individual biological situation and with proper case selection, can yield treatment results with the same excellence that we strive to attain in all modes of orthodontic care.

(Examples of typical lingual mechanotherapy sequences are following)

Clinician: Dr. John SmithCase Type: Class I Crowding, Four Bicuspid Extraction

Clinician: Dr. John SmithCase Type: Nonextraction Class I or II

Clinician: Dr. R.G. Alexander Case Type: Extraction

bond lower incisors and cuspids with lingual brackets, band lower second bicuspids and first molars with buccal and lingual brackets, and bond lower second molars with buccal tubes

Clinician: Dr. R.G. Alexander Case Type: Nonextraction

Clinician: Dr. John C. GormanCase Type: Class II Division 1, Upper First Bicuspid Extraction

Clinician: Dr. John C. GormanCase Type: Class II Division 1, Four Bicuspid Extraction

Class II correction

Clinician: Dr. John C. GormanCase Type: Class I Bimaxillary Protrusion With Severe Crowding (cuspids blocked out), Four Bicuspid Extraction

Clinician: Dr. James J. HilgersCase Type: Class I Bimaxillary Protrusion, Extraction

Clinician: Dr. James J. HilgersCase Type: Class II Division 2 Nonextraction, TMJ Tx

Clinician: Dr. James J. HilgersCase Type: Class I Crowded, Nonextraction

Clinician: Dr. Craven KurzCase Type: Class I Deep Bite, Consolidation

Clinician: Dr. Craven KurzCase Type: Class I or II, Extraction