Reverse Engineering for Post-Treatment Analysis of a Surgical-Orthodontic Case

Treatment objectives were to improve the facial appearance, achieve normal overbite and overjet, correct the upper and lower crowding, improve the chin projection, obtain lip competence, reduce the proclination of the lower incisors, procline the upper incisors, and establish a stable and functional occlusion. Considering the patient’s convex profile and Class II malocclusion, we recommended surgical-orthodontic treatment. The first option for the orthodontic phase was a nonextraction approach in which the dental arches would be leveled and aligned while the crowding, lower curve of Spee, and upper-incisor inclination were corrected. The second option involved extraction of the lower first premolars to allow retraction of the canines and incisors without loss of anchorage, thus providing enough overjet for the mandibular advancement surgery. The crowding, curve of Spee, and upper- and lower-incisor inclination would also be resolved. A third alternative was to extract the upper second premolars as well and to close the spaces with loss of anchorage, adding labial torque to the upper incisors to improve their inclination. This third option was selected.

Treatment Progress

After extraction of the upper second and lower first premolars, .022" Roth-prescription brackets and a lower lingual arch were placed. Wires in both arches progressed from .014" to .016" × .022" nickel titanium, followed by .017" × .025" stainless steel. In the upper arch, the spaces were closed with anchorage loss and labial torque of the upper incisors. Anterior retraction was finished with the insertion of nickel titanium closed-coil springs on a three-piece .017" × .025" stainless steel archwire. Posterior miniplates were inserted on both sides of the mandibular body and tied to the lower molars for anchorage control.^11,12 The lower canines and incisors were intruded with three-piece mechanics, while side effects in the anchorage unit were controlled by the miniplates. 

After 19 months, all spaces were closed and leveling and alignment were complete, resulting in a 13.9mm positive overjet (Fig. 2A). At this time, the .021" × .025" stainless steel surgical archwires were inserted. Spaces were left between the upper incisors for later cosmetic correction of a 4.23mm anterior tooth-size discrepancy. Comparison of the pretreatment and presurgical lateral cephalograms confirmed the upper and lower incisor decompensation.

A three-piece Le Fort I maxillary osteotomy was then performed to simultaneously correct the transverse, vertical, and sagittal discrepancies. Bilateral sagittal split osteotomies were used to provide mandibular advancement and counterclockwise rotation. The segments were fixated by rigid bone plates and screws.

Immediately after surgery, bilateral Class I molar and canine relationships and a normal overbite and overjet could be observed (Fig. 2B). During the postoperative orthodontic phase, the occlusion was maintained using intermaxillary vertical elastics.

Seven months after surgery, the fixed appliances were removed. An .018" lingual 3-3 retainer wire was bonded, and an upper Hawley retainer was delivered.

Treatment Results

Post-treatment records showed an improvement in the facial profile (Fig. 3). The lip incompetence was corrected, and the upper-incisor display was adequate. A good occlusion was produced, with Class I molar and canine relationships on both sides. Normal overbite and overjet were achieved, and the upper and lower midlines remained coincident. Cephalometric assessment confirmed maxillomandibular advancement with counterclockwise rotation of the occlusal plane and an improvement in the incisor inclination (Table 1).

Fifteen years after treatment, the facial profile and the Class I molar and canine relationships remained stable (Fig. 4). Some relapse of the overbite and incisor crowding could be observed in the lower arch. Cephalometric assessment confirmed the maxillomandibular stability and increased overbite.

Virtual Treatment Simulation

After the 15-year follow-up records were taken, the original orthodontic plan was reanalyzed using a virtual setup. The original upper and lower presurgical plaster casts were scanned with Identica Light Scanner,^* saved as STL files, and exported to 3D Slicer^** version CMF 4.0. The patient’s initial pretreatment casts were also scanned, and a virtual presurgical orthodontic setup of the STL files was performed using SureSmile Elemetrix^*** software and exported to 3D Slicer. The actual presurgical casts and the virtual setups were then superimposed using landmarks at the upper right canine, incisal papilla, and left canine and the mesial cusps of the lower first and second molars (Fig. 5).

The superimpositions showed minor differences between the presurgical casts and the virtual setup. The upper right molars were more extruded and the upper arch was narrower on the original model. The lower arches differed in arch width (more constricted in the virtual setup) and in the vertical position of the canines and incisors (more extruded on the original model).

The three original treatment options were analyzed with SureSmile Elemetrix using the STL files of the patient’s pretreatment casts. The nonextraction simulation resulted in satisfactory leveling and alignment of both arches, as well as a curve of Spee correction due to incisor intrusion and proclination (Fig. 6A). The second approach, involving extraction of only the two lower first premolars, resulted in a larger overjet, which would have allowed more significant mandibular advancement than the nonextraction option (Fig. 6B). This simulation also showed, however, that the upper second molars would have had no opposing teeth after orthognathic surgery, which could have
led to their overeruption. The four-premolar extraction plan was clearly the most appropriate for this case because it allowed for correction of the curve of Spee, inclination of the incisors, and adequate mandibular advancement, and it established a stable and functional occlusion (Fig. 6C).

Discussion

Reverse engineering involves steps such as data acquisition, preprocessing (noise filtering and merging), triangulation, feature extraction, segmentation, and surface fitting.¹³ Already well established in the medical field, it has a number of potential applications for dentistry and orthodontics, including 3D model scanning and superimposition, digital diagnostic setups, volumetric evaluation of tooth wear, 3D soft-tissue facial analysis, and smile assessment.^13,14

Digital setups are as useful and accurate as manual setups and can be reliably reproduced.⁶ There is a significant difference, however, in inter- and intraexaminer reliability of digital orthodontic setups.¹⁵ The virtual setups in the present report were performed by a single orthodontist.

Among the many advantages of digital models is the possibility of adding spatial registration at different points in time.^16,17 The stability of the palatal rugae as a reference point has been confirmed using dental casts.¹⁸ Since neither external cranial references nor palatal rugae were visible in our setup models created with SureSmile Elemetrix, we had to devise a landmark method.