In-house precision bracket placement with the indirect bonding technique

In the era of the fully banded standard edgewise orthodontic appliances, orthodontists most skilled at wire bending generally achieved the best results; several wire bends were unavoidable. The advent of the straight-wire appliance ushered in a new era in orthodontic practice. Orthodontists could choose from a variety of bracket prescriptions to achieve optimum esthetics and functions with the least chair time, fewest appointments, and greatest patient comfort. The theoretical ideal of treating a patient from start to finish with no archwire bends was within reach at last. Also, with the introduction of bondable brackets, appliance placement could be rapid for the orthodontist and pain-free for the patient, with no residual band spaces to close at the end of treatment.

Unfortunately, the promise of rapid, efficient, and comfortable orthodontic treatment with these precision bracket systems has been less than fully realized for most orthodontists because of improper bracket placement. Many orthodontists still spend considerable time detailing, particularly near the end of treatment, to compensate for bracket-positioning errors.

One of Andrews’ 6 keys to occlusion is the achievement of even marginal ridges on the posterior teeth. It could be argued that this goal is more easily reached by orthodontists who still routinely band, rather than bond, posterior teeth with straight-wire attachments welded to the bands. It is relatively easy to visualize and properly seat molar and premolar bands relative to marginal ridges and with the occlusal edge of each band parallel to the occlusal surface of the tooth. As long as the manufacturer welds all the bracket slots or tubes the same distance from the occlusal edge of the band, the marginal ridges of the teeth should be even with each other with full-sized archwires in place. Additionally, this generally places the slot in (or near) the occlusogingival center of the anatomic crown of the tooth, where most appliance systems require it to be placed for proper torque expression.

Yet, with the widespread availability of chemical conditioning agents and procedures to allow strong bonding of brackets to porcelain, metal, and enamel, many orthodontists now routinely bond brackets to most or all posterior teeth. Unfortunately, proper placement of direct-bonded brackets is challenging on the posterior teeth, because they can be difficult to visualize in the best of circumstances. The penalty for poor placement, especially on posterior teeth, can be great because these teeth tend to more readily extrude rather than intrude as an archwire levels out, potentially propping open the bite and creating a fulcrum from which recovery can be difficult.

Indirect bonding, although used routinely by a relatively few orthodontists, allows excellent visualization of all teeth; this is a great advantage, according to its proponents. Perfect bracket placement on the stone model should be simple, and, as long as the transfer trays are properly made and seated, each bracket should end up in its ideal position, right? Well, no. The problem is that the teeth start out crooked, and getting the brackets in just the right place on all of these crooked teeth, even when you can hold the model in your hand and look at the teeth from all directions, is still difficult. This is especially so when it comes to the vertical (occlusogingival) position of each bracket. Where is the vertical center of the crown? A bracket-positioning gauge, used by many orthodontists, is not of great help because it assumes average-sized teeth and unworn cusps. Also, it is difficult or impossible to use on molar tubes. Besides, what we really want to see is even, level marginal ridges, not necessarily level buccal cusps. We need a means to place the bracket slots relative to the marginal ridges of the posterior teeth so that all marginal ridges line up. If the cusps are unworn, and tip and torque are properly expressed, this automatically places the functional cusps on a level plane. Ideally, bonded brackets would be positioned so that, if a molar band is placed later, the marginal ridges of the banded teeth are even with those of the bonded teeth. Even better, we would like a simple means of placing anterior brackets so that, whether the patient has small or large teeth, long or short posterior cusps, the brackets are placed approximately in the center of the crown on all teeth; this is something no bracket-positioning gauge can accomplish.

The goal of placing brackets perfectly so that few, if any, archwire bends are needed was greatly furthered for me after I began using a modified version of the indirect bonding technique promoted by Kalange. His technique of bracket placement on models requires drawing a line on each posterior tooth to connect the mesial and distal marginal ridges. A second, parallel line is drawn approximately 2 mm gingival to the marginal ridge line; this is the slot line, where the vertical center of the bracket slot should be placed.

What I found potentially inaccurate with Kalange’s technique was the drawing of the marginal ridge line; if I could cut all the teeth out first, it would be easy, but usually the adjacent teeth made proper visualization and placement of this line on each tooth difficult. Subsequent drawing of the slot line 2 mm gingival to the marginal ridge line could introduce additional inaccuracy.

Described here is a modification of Kalange’s technique that I believe improves accuracy and repeatability. It does not use advanced computer technology and might be a disappointment to those accustomed to seeing such things in the “Techno Bytes” section of this journal. But the simplest, least-expensive technologies are often the most easily attempted and, ultimately, accepted.

Material and methods

The tools of this bracket placement technique are simple: 2 bow compasses (model 508, Alvin, Boston, Mass) and 3 mechanical pencils (Draft/Matic, Alvin) ( Fig 1 , A ). In Figure 1 , B , the compass in the center (compass 1) is adjusted with the aid of a millimeter ruler ( Fig 2 , A ) so that the tip of the lead in the pencil is approximately 2 mm longer than the long axis of the compass (with the steel leg of the compass representing the long axis). For a patient with large teeth, this distance can be set a little longer than 2 mm; for a patient with small or short teeth, it should be a little shorter than 2 mm. This ensures that the slots or tubes are in the center of the anatomic crowns, regardless of tooth size. If bands are to be placed alongside bonded brackets, then this measurement should perhaps be exactly the same as the vertical distance from the occlusal edge of the band to the center of the slot or tube; this is usually about 2 mm but can vary depending on the manufacturer. The exact distance can be measured with a caliper or Boley gauge ( Fig 2 , B ). Another way of looking at this is to adjust the distance between the marginal ridge and the slot line based on tooth size, and any bands should be seated more or less relative to the marginal ridges. Compass 2 ( Fig 1 , B ; left ) has its steel stylus set considerably longer than the pencil; the exact amount is not important, as long as the side of the steel stylus can rest on the cusp tip of the first premolar perpendicular to the long axis of the tooth, before the pencil lead touches the buccal surface.

Apr 14, 2017 | Posted by in Orthodontics | Comments Off on In-house precision bracket placement with the indirect bonding technique
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