Anterior Root and Alveolar Changes During Presurgical Decompensation: A Comparison of Fixed Appliances and Clear Aligners in Skeletal Class III Malocclusion

For many adults, the shape of their face and the way their teeth fit together are not just matters of appearance but of function. When the lower jaw grows significantly larger than the upper jaw, a condition known as skeletal Class III malocclusion, it can make chewing difficult and alter the profile of the face. Correcting this often requires a two-step approach: first, an orthodontist moves the teeth into a position that reveals the true size difference between the jaws, and then a surgeon repositions the jaws to match. This initial phase, called decompensation, is critical because the teeth have naturally tilted to compensate for the jaw mismatch over the years. To fix the bite, these teeth must be pushed back or pulled forward, often requiring them to move through the thin walls of bone that surround them. If the roots of the teeth are pushed too hard against these bony walls, the bone can thin out or disappear, and the roots themselves can shorten, a process known as resorption. The question facing modern dentistry is whether the tools used to move these teeth make a difference in how much damage occurs to the delicate bone and root structures during this intense phase of treatment.

Researchers at the Fourth Military Medical University set out to investigate this by looking at the internal structures of patients' jaws using a specialized 3D X-ray technique called cone-beam computed tomography, or CBCT. They studied forty adults who were preparing for jaw surgery, splitting them into two groups based on the method used to move their teeth before the operation. One group wore traditional fixed appliances, which are the metal brackets and wires commonly known as braces, attached directly to the teeth. The other group used clear aligners, which are a series of removable, transparent plastic trays that fit over the teeth. The team took detailed scans of the patients' mouths before treatment began and again after the decompensation phase was complete. They measured the length of the tooth roots, the thickness of the bone surrounding them, and the vertical height of the bone at various points along the front teeth in both the upper and lower jaws.

The results revealed a clear distinction in how the two methods affected the biological tissues. Patients treated with the fixed appliances experienced more significant shortening of their tooth roots compared to those who wore the clear aligners. This difference was particularly noticeable in the upper front teeth and the lower front teeth, where the root shortening was substantially greater in the group with braces. Similarly, the bone surrounding the teeth showed more signs of thinning and loss in the fixed appliance group. Specifically, the bone on the palate side of the upper central incisors and the bone on the tongue side of the lower incisors lost more thickness when treated with braces. In contrast, the clear aligner group maintained their root length and bone structure much better, with changes that were generally smaller and less widespread.

The study also examined whether the amount of tooth movement required influenced the amount of tissue damage. The researchers found that in the group using fixed appliances, the more the teeth had to be moved to correct the bite, the more root shortening and bone loss occurred, particularly in the lower jaw. This suggests a direct link between the intensity of the correction and the biological cost when using traditional braces. While the clear aligners also achieved the necessary tooth movements to prepare the patients for surgery, they did so with a gentler impact on the surrounding tissues. The data indicated that the plastic trays allowed for the required decompensation while preserving the roots and the alveolar bone more effectively than the metal brackets and wires.

These findings suggest that for adults with severe skeletal discrepancies who need presurgical orthodontics, the choice of appliance matters. The study indicates that clear aligners may offer a biological advantage by reducing the risk of root shortening and bone loss during the demanding decompensation phase. While both methods successfully prepared the teeth for surgery, the clear aligners achieved this goal with less collateral damage to the supporting structures of the teeth. This does not mean that one method is universally superior for every case, but it does highlight that the removable plastic trays can be a viable, and perhaps safer, alternative for preserving the health of the roots and bone in complex cases where large tooth movements are necessary.