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In-house precision bracket placement with the indirect bonding technique

2010; Elsevier BV; Volume: 137; Issue: 6 Linguagem: Inglês

10.1016/j.ajodo.2009.04.023

1097-6752

Mark W. Joiner,

Dental materials and restorations

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 occlusion1Andrews L.F. The six keys to normal occlusion.Am J Orthod. 1972; 62: 296-309Abstract Full Text PDF PubMed Scopus (731) Google Scholar 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.2Kalange J.T. Ideal appliance placement with APC brackets and indirect bonding.J Clin Orthod. 1999; 33: 516-526PubMed Google Scholar 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. 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.Fig 2A, Millimeter rule to measure the lead tip in the pencil; B, caliper or Boley gauge to measure vertical distance from occlusal edge of band to the center of the slot or tube.View Large Image Figure ViewerDownload Hi-res image Download (PPT) Accurate bracket placement begins with drawing the long axis of each crown. A point source of light shining on the side of the teeth illuminates developmental lobes or grooves on the labial surface and will help you locate the long axis (Fig 3). To construct the slot line, place the steel stylus of compass 1 on the marginal ridge of a posterior tooth, with the long axis of the compass parallel to the long axis of the crown, and then rotate the compass slightly to make a pencil mark on the buccal surface (Fig 4, A). Place these dots on the mesial and distal aspects of each posterior tooth. You can use the adjustment wheel of the compass to move its legs as close to each other as practical to allow the 2 dots on each tooth to be widely separated (Fig 4, B). For buccally or lingually tipped teeth, the long axis of the compass should be tipped accordingly.Fig 4Construct the slot line for each tooth: A, place the stylus of compass 1 on the marginal ridge of a posterior tooth, with the long axis of the compass parallel to the long axis of the crown; B, rotate the compass slightly to make a pencil mark on the buccal surface; C, connect the dots.View Large Image Figure ViewerDownload Hi-res image Download (PPT) It is a simple matter then to connect the dots on each tooth with the pencil (Fig 4, C). This establishes the slot line. Some orthodontists may prefer to deviate from precisely connecting the dots on some teeth; for instance, slanting the line on the maxillary second molar so that it is slightly more occlusal on the distal aspect of the crown will aid in creating a slight curve of Spee and avoiding overuption of this tooth. Next, mark the anterior teeth so that the anterior slot lines are properly placed relative to the posterior teeth. For both arches, I use the first premolar as the reference tooth by transferring the distance between its cusp tip and its slot line to the lateral incisor. To accomplish this, place the steel stylus of compass 2 on the cusp tip of the first bicuspid, parallel to the occlusal plane, and rotate the adjustment wheel until the tip of the pencil is resting on the slot line in the center of the crown (Fig 5, A).Transfer this distance to the lateral incisors by placing the side of the steel stylus on the incisal edge, again parallel to the occlusal plane, and draw a short line on the crown long axis line (Fig 5, B). In the mandibular arch, mark the central incisors in the same manner, by using the same distance obtained from the mandibular first premolar. Rotate the compass adjustment wheel to add 0.5 to 0.75 mm to the distance between the side of the steel stylus and the pencil tip, and mark the canines in a like manner. For the maxillary arch, rotate the compass adjustment wheel to add about 0.5 mm to the distance used for the lateral incisor, and mark the canines; mark the central incisors after opening the compass legs slightly farther. Attrition to the first premolars or anterior teeth must be accounted for when using compass 2; hold the steel stylus away from the cusp tip or incisal edge by an amount equal to the amount of attrition that you estimate has occurred. Similar adjustments should be made for unusual teeth, such as peg-shaped lateral incisors or unusually long, pointed canines. The placements suggested for the anterior tooth slot lines relative to the first premolars are suggestions only. Other orthodontists might prefer more or less distance from the cusp tip or incisal edge to the slot line, depending on the preferred overbite, the amount of step between the maxillary central and lateral incisors, and so on. The placements I suggest differ from those of Kalange.1Andrews L.F. The six keys to normal occlusion.Am J Orthod. 1972; 62: 296-309Abstract Full Text PDF PubMed Scopus (731) Google Scholar He instructed that, in the maxillary arch, the premolar cusp tip to slot line distance should be transferred to the central incisor, with a reduction of 0.5 mm to the lateral incisors and an addition of 1.0 mm to the canines; in the mandibular arch, he suggested the same settings as I do to the incisors, but added 1 mm rather than 0.5 to 0.75 mm to the canines. Next, lengthen the short slot line so that it is visible mesially and distally after the bracket is placed (Fig 6, A). Knowledge of the degrees of mesiodistal tip built into each bracket is important so that the crown long-axis line and the slot line align with both the slot and mesiodistal tip of the bracket. Placing the brackets on the models is then a straightforward matter of lining up each bracket with the slot line and crown long-axis line drawn on each tooth. For actual placement of brackets, you can use a light-cured composite; this allows placement of brackets to the models by a laboratory technician for further checking and adjustment by the orthodontist. Error can be introduced at this point if you are not sighting exactly into the slot of the bracket, perpendicular to the base of the slot. Placing the exact center of the slot of each bracket over the slot line drawn on the model is aided by a point light source behind and slightly to the side of the head of the technician, so that the light is reflected off the bottom of the slot of the bracket (Fig 6, B). Place the models in a light-curing oven for 6 minutes to harden the composite, and then fabricate the transfer trays. Many techniques and materials have been promoted over the years for construction of the transfer trays, and it is not the intent of this article to provide highly detailed instructions on my technique. I use a clear double tray and light-cure the brackets onto the patient's teeth. The soft layer enveloping the brackets is a transparent 2-part polyvinyl siloxane material (RM bond Inner Tray Material, Rocky Mountain Orthodontics, Denver, Colo), which is syringed around the brackets and over the occlusal surfaces and incisal edges. The more rigid outer tray is .040-in thick A+ plastic (GAC International, Bohemia, NY), formed over the inner tray and teeth on a Biostar unit (Great Lakes Orthodontics, Tonawanda, NY). After the models are soaked in water and the trays and brackets are removed and the trays trimmed, the composite on the bracket bases is lightly microetched, and Enhance (Reliance Orthodontics, Itasca, Ill), a 2-part adhesion booster, is mixed and painted on each bracket base. At the chair, after a thin layer of light-curable sealant is painted on the etched enamel, a small line of flowable composite (Flow-Tain, Reliance) is syringed onto the gingival aspect of each bracket base, and the tray is placed onto the teeth. Each bracket is cured for 10 seconds, and then the trays are removed, and each bracket is cured for an additional 10 seconds. The advantages of indirect bonding relative to direct bonding are numerous, and I believe they outweigh the perceived disadvantages of increased laboratory time and technique sensitivity.3Kalange J.T. Indirect bonding: a comprehensive review of the advantages.World J Orthod. 2004; 5: 301-307PubMed Google Scholar However, the expected advantage of increased accuracy in bracket placement has been questioned.4Koo B.C. Chung C. Vanarsdall R.L. Comparison of the accuracy of bracket placement between direct and indirect bonding techniques.Am J Orthod Dentofacial Orthop. 1999; 116: 346-351Abstract Full Text Full Text PDF PubMed Scopus (79) Google Scholar, 5Hodge T.M. Dhopatkar A.A. Rock W.P. A randomized clinical trial comparing the accuracy of direct versus indirect bracket placement.J Orthod. 2004; 31: 132-137Crossref PubMed Scopus (48) Google Scholar This is not really surprising, because most orthodontists who try indirect bonding still use a gauge, or they "eyeball" bracket position.