Indirect Bonding: A Closer Look by Clark D. Colville, DDS, MS

Drawbacks and limitations
In all fairness to direct bonding, the indirect system has some limitations, as well.

There are multiple opportunities for error to be introduced into the system. Ultimately, any error can result in a suboptimal bracket position at best, and at worst a failure to bond the bracket to the tooth at all. The latter often results in the need to resort to direct bonding to place the bracket.

The inability to place the bracket in the ideal position due to gingival interference is common. Short clinical crowns are especially prone to this. When this happens, the gum tissue has to be relieved on the stone model, or the bracket pad has to be altered. Both of these require additional time to finalize the bracket placement, which is often done by the orthodontist. Many times the orthodontist won’t take the additional time and accepts a less-than-ideal bracket position, which defeats the original purpose altogether.

The difficulty of including second molars in the bonding trays. Often, the upper second molars are difficult to access and don’t allow the bonding tray to be placed without moving the jaw to one side or the other, which leads to poor and inaccurate bonding. The mandibular second molars are hard to isolate and keep dry, and many times the tongue will quickly become the enemy of an otherwise perfect bonding routine. As a result, many orthodontists will direct bond some or all of the first and second molars.

By far the biggest obstacle to achieving ideal bracket position is the inability to project the final position of the teeth once the straight wire has done its magic. Any “static” indirect bonding setup is relying on our ability to visualize the resultant tooth movement once the brackets have been applied to the model.

In the 23 years that I’ve been using indirect bonding as my preferred technique, I have rarely if ever had a case that did not require some bracket repositioning during treatment. While frustrating to say the least, there are new innovations that may turn this disadvantage into a decided advantage for indirect bonding.

Virtual treatment planning
Current imaging, including CBCT and intraoral scanning, are changing the indirect bonding from “static” to a virtual 3-D CAD platform. Scanning technology that produces generic .STL files is used to create printed models that are close to flawless.

As major orthodontic laboratories move their business models toward a digital world, many now accept these .STL files and can digitally print models to fabricate a variety of appliances. Indirect bonding can be outsourced to some of these labs using a static model and provide indirect bonding setups, much the way we’ve been doing in-house for years. Orthodontists look at 3-D virtual models and confirm the final placement of the brackets. Transfer trays are fabricated and shipped to the office.

While this eliminates some of the errors associated with the impressions, model preparation and tray fabrication, the key element of examining the final tooth position after the teeth are aligned with a straight wire is still missing.

More recently, proprietary software applications have been introduced that allow visualization of tooth position after bracket placement, simulating tooth movement achieved after placing a straight wire (Figs. 1 and 2).

Elemetrix, Insignia, Orchestrate 3D and ArcadLab are just a few proprietary systems that allow either brackets or teeth to be repositioned digitally before visualizing the “final” results. Final tooth position can be modified, which is then reversed back to the initial bracket position in the CAD simulations. This provides a more ideal setup from the start of treatment.

Challenges and changes
There are some drawbacks to early adoption of this technology.

• As with all new technology, there’s a learning curve to become efficient with the software. Most of what I’ve seen isn’t intuitive and doesn’t provide a simplified workflow to obtain the ideal setup. An average setup requires 10–30 minutes to finalize, which is all nonpatient time.
• In addition, the patient’s roots aren’t visible—or the roots shown are simulated ones that often don’t match the actual root position when compared to panoramic X-rays or CBCTs.
• The simulations aren’t completely realistic, primarily because of the way torque is expressed in the final setup. Rotation, leveling and arch-form simulation are much more reliable at this stage of software development.

Over time, the software should improve so a dedicated staff member can be trained to prepare digital setups to the point that the doctor time required will be minimal. In addition, as 3-D printers continue to drop in price, more orthodontists may choose to print indirect bonding trays directly in their offices. This capability already exists and the early adopters are working out the kinks for the rest of us.

The digital era of orthodontics is upon us and it may be time to investigate these new technologies. It’s worth taking a closer look.

Clark D. Colville, DDS, MS, maintains private practices in Seguin and San Marcos, Texas. Colville is a diplomate of the American Board of Orthodontics and is active in the American Association of Orthodontists and the Southwestern Society of Orthodontists. He is an assistant clinical professor in the graduate orthodontic department at the University of Texas Health Science Center at Houston, School of Dentistry, where his primary responsibility is teaching clear-aligner treatment to orthodontic residents.