Virtual Planning and 3D Printing in Contemporary Orthognathic Surgery

Abstract

Orthognathic surgery is a powerful tool to improve facial balance, form, and function. Virtual planning and three-dimensional printing has improved our ability to visualize complex anatomy, consider various iterations and execute complex movements, and create accurate splints, plates, and cutting guides. This article will outline the distinct advantages of the use of virtual surgical planning over traditional planning, and it will explore the utility of computer-aided design and technology within contemporary orthognathic surgery, including its expanded applications and limitations.

Orthognathic Surgery and Computer-Aided Design/Computer-Aided Manufacturing

Orthognathic surgery is a versatile and powerful tool to address dentofacial anomalies, treat tongue-based airway obstruction and sleep apnea, and optimize overall facial balance and profile aesthetics. ¹ As the indications for orthognathic surgery continue to expand, it behooves the surgeon to be able to effectively communicate objectives and outcomes with the patient and their orthodontist, plan and perform surgery with precision and efficiency, and critically evaluate their postoperative results.

Virtual surgical planning (VSP) and computer-aided design/computer-aided manufacturing (CAD/CAM) technology have revolutionized our ability to visualize, plan, and execute surgical treatment within craniofacial surgery, and this is no more evident than within the scope of orthognathic surgery, with its emphasis on facial balance and symmetry. CAD/CAM and three-dimensional (3D) analysis not only allow for custom device and cutting guide fabrication, but also for assessment of dysmorphology, quantitative and diagnostic confirmation, treatment planning, and vector selection (in distraction osteogenesis cases). ^{2 3} This provides a distinct advantage over traditional planning for orthognathic surgery, an otherwise tedious process involving two-dimensional (2D) cephalometric analysis and splint fabrication using facebow mounting and bite registration. ^{4 5} Conventional orthognathic planning with its numerous steps and transfers introduces the potential for compound error, and its multiplatform medium can obfuscate subtleties of the overall craniofacial skeleton. ⁶ Difficulty in identifying facial reference planes based on the overlap of the different bony structures on posteroanterior radiographs, transfers of the plane from mounted models to articulator, and the complex movements required of the jaw in the treatment of asymmetry all introduce the potential for inaccuracy. ⁷ Additionally, stone model surgery depicts only the teeth and alveolar arches, failing to capture the entire bony anatomy which can be the most important surface structure to be considered in the surgically planned movements and outcome. This complicates the planning of adjunctive aesthetic treatments (e.g., custom malar or angle implants) and presents challenges to educating patients on the nuances of a surgical plan.

Almost two decades of research comparing traditional planning and VSP in terms of accuracy, time, and cost have been reported. ^{8 9 10 11} Patient-reported outcomes data comparing conventional 2D and 3D modeling demonstrate at least equivalent satisfaction between the two techniques by 4 months postsurgery. ¹² In a systematic review, Nilsson et al reported that the computer-assisted design demonstrated shorter surgical and ischemia times for maxillofacial reconstruction and decreased preoperative planning time for orthognathic surgery compared with traditional planning. ¹³ Furthermore, it has been shown that stereolithographic intermediate and final splints have at least an equivalent, if not higher degree of fidelity and accuracy, compared with those generated from traditional plaster models. ¹⁴

3D planning integrates dental and skeletal parameters onto one platform, which improves diagnostic recognition, planning and correction of bodily movement, yaw, cant, and pitch, and assessment and modification of occlusal plane, nerve position, and bony gap sizes ⁵ ( Fig. 1 ). Furthermore, VSP permits simulation and evaluation of multiple surgical plans, with special consideration given to soft tissue simulation. ¹⁵ After occlusal correction with osseous movements, facial asymmetries and volume discrepancies can be accounted for and adjunctive procedures such as implant placement, fat grafting, or bony contouring can be planned.

Fig. 1.

( A ) Preoperative and final virtual surgical plan for a patient with facial asymmetry and malocclusion, with three-dimensional (3D)-printed titanium right angle implant in addition to custom genioplasty and bilateral sagittal split osteotomy (BSSO) plate. ( B ) Preoperative and postoperative cone-beam computed tomography (CT) scans demonstrating correction of facial asymmetry and high fidelity to the virtual plan. ( C ) Preoperative photographs showing facial asymmetry, chin deviation, and deficient right mandibular angle. ( D ) Postoperative images showing improvement in facial balance and symmetry.

3D Planning Steps

If traditional wire braces are anticipated as part of a patient's presurgical orthodontics (vs. clear tray aligners), imaging and dental models should be obtained with wire braces in place. High-resolution, low-radiation computed tomographic (CT) imaging, such as a cone-beam CT, should be obtained relatively close to the anticipated date of surgery so that orthodontic movement can be accounted for in virtual planning and custom splint fabrication. Casts or molds of the patients' teeth are then captured either digitally using a 3D dental scanner or via conventional dental impressions and stone pour-up. These molds of the teeth should not be obtained in the setting of active orthodontic tooth movement. The teeth should be in their final preoperative position and not moving, as splints will be fabricated to fit these surfaces. The casts of the patient's passive presurgical bite are then articulated into the final goal occlusion—either digitally (for 3D models), or by hand if with plaster casts. This goal occlusion is then digitally merged with the CT for surgical planning. If a transverse maxillary width discrepancy is to be addressed at the time of orthognathic surgery, the models require digital or hand segmentation to achieve the final idealized occlusion. This segmented model as well as a model of the preoperative occlusion can then be digitized and fused with CT data. The segmented model can then be used to create a 3D-printed palatal splint with wiring holes, in addition to the usual intermediate and final occlusal splints. Following digital data aggregation, the virtual planning session should be conducted with the surgeon and technician, with input from the orthodontist. Preoperative photographs, measurements, and cephalometrics are useful to address occlusal, functional, and aesthetic goals. Based on this plan, intermediate and final splints can be 3D printed. In addition, custom genioplasty or maxillary cutting guides and plates can be fashioned.

The maxillary movements should be planned first, regardless of intraoperative steps, in the following fashion ¹⁶ ( Fig. 2A–D ):

1. Design the maxillary osteotomy, with consideration for the maxillary tooth roots.

2. Centralize maxillary midline to the face.

3. Correct yaw and arch form.

4. Correct cant, typically rotating around the canine of the contralateral or down-canted side.

5. Alter pitch and occlusal plane, which may steepen or flatten around central incisors.

6. Sagittal repositioning, determined based on soft tissue envelope and tooth-lip position.

7. Check bony architecture and support at piriform.

Fig. 2.

Sequence of three-dimensional (3D) planning. ( A ) Yaw correction after centralizing maxillary midline to face. ( B ) Cant correction. ( C ) Maxillary sagittal adjustment and pitch correction. ( D ) Step-off at pyriform noted. ( E ) Bilateral sagittal split osteotomy (BSSO) designed and mandible moved according to maxillary movements, proximal segments rotated into distal segment. ( F ) Amount of sagittal advancement noted and yaw corrected to midline reference. ( G ) Genioplasty designed based on length of lower facial third (top left). Osteotomy design and advancement (bottom right and left). Genioplasty yaw and symmetry correction (top right).

Next, the mandible can be virtually positioned ( Fig. 2E, F ):

1. Design the mandibular osteotomy.

2. Place mandible to maxilla in idealized occlusion.

3. Rotate proximal mandibular segments up and into distal segment.

4. Check condylar seating within the fossa.

5. Check overlap or advancement gap to determine need for custom mandible plates for large advancements.

6. Check for symmetry (yaw, transverse, vertical).

Finally, the chin can be addressed, as outlined below ( Fig. 2G ):

1. Measure vertical length of the lower facial third.

2. Design osteotomy, with consideration for the mental nerve and foramen.

3. Plan advancement and lengthening of chin segment.

4. Correct symmetry (wedge and/or rotation differential movement).

Anatomic and Technical Considerations

Patient Selection

The principal goals of orthognathic surgery are to optimize functional Class I occlusion and overall aesthetic facial balance. To this end, ideal candidates for orthognathic surgery are those skeletally mature patients with healthy teeth and periodontal support for whom orthodontic treatment alone would be inadequate to achieve these principal goals.

Patients presenting for evaluation for orthognathic surgery should first be assessed for skeletal maturity. Adolescent patients should be evaluated for active growth, and definitive surgery is typically delayed until growth is completed, except in cases of Class II deformity or vertical maxillary excess (VME), where earlier intervention may yield more stable surgical results compared with Class III deformities. ¹⁷ Age at menarche for women and changes in shoe size and height can guide the clinician in decisions of surgical timing, though if ambiguity exists, a hand-wrist radiograph, serial lateral cephalograms, or cervical spine imaging may provide more concrete direction. For patients presenting with new onset or progressive occlusal asymmetry, particularly those with new or worsening temporomandibular joint (TMJ) pathology, condylar growth discrepancy should be considered as a possible culprit. This will be explored later in this article, but as far as surgical timing and planning is concerned, the TMJ should be stabilized prior to or as the first step in any orthognathic procedure, either through awaiting condylar growth cessation or performing a growth-arresting procedure (e.g., high condylectomy).

Finally, a thorough understanding of the patient's orthodontic and dental history and occlusal exam should be obtained. Prior dental extractions, restorations, and orthodontic interventions may yield an overall dentally compensated Class I molar or canine relationship in spite of significant jaw discrepancies. Recognition of dental compensation preoperatively can inform the surgeon in expectations for presurgical orthodontics to decompensate and upright the dentition and level the curve of Spee in addition to anticipating jaw movements during surgical planning.

Single- versus Double-Jaw Surgery

Since the introduction of the bilateral sagittal split osteotomy, skeletal stability of single-jaw versus double-jaw surgery has been studied. Proffit et al reported that the postoperative relapse after double-jaw surgery is no more significant than the changes seen in a single-jaw procedure after maxillary advancement or mandibular setback alone. ¹⁸ However, in an analysis of patients with skeletal Class III deformities undergoing single-jaw or double-jaw procedures, Al-Delayme et al reported a significant increase in horizontal mandibular skeletal relapse in the single-jaw cohort compared with those undergoing double-jaw procedures. ¹⁹ Data suggests that relapse is highly dependent on the magnitude of the sagittal discrepancy, and the rotational component of double-jaw surgery helps to mitigate those forces contributing to relapse by optimizing projection without creating larger sagittal movements and bony gaps.

Regardless, the decision to perform single-jaw versus double- or triple-jaw surgery should ultimately be determined by the type and severity of the dentofacial deformity as well as the patient's aesthetic concerns. Single-jaw surgery may be indicated in some patients with isolated smaller sagittal discrepancies, but larger or more complex movements to modify the occlusal plane and correct vertical asymmetries require both maxillary and mandibular repositioning. In these circumstances, double-jaw or triple-jaw surgery allows for more freedom to establish the spatial relationship of the maxilla-mandibular complex with consideration given to the rest of the craniofacial skeleton and soft tissue.

Class II Sagittal Discrepancies

A convex facial profile with mandibular hypoplasia is typical of a Class II skeletal relationship, the most common dentofacial anomaly. ²⁰ Patient may present with excessive overjet, retrognathia, mentalis strain, lower lip incompetence, a shortened facial lower third, and a decreased submental distance with an obtuse cervicomental angle. While classic intraoral findings demonstrate the mesiobuccal cusp of the maxillary first molar anterior to the buccal groove of the mandibular first molar, not infrequently, patients with a Class II skeletal relationship have a history of orthodontic intervention and dental camouflage to accommodate lower arch crowding and flared mandibular incisors to compensate for excessive overjet. Patients may also have a history of prior genioplasty to counterbalance their retrognathism.

When planning orthognathic surgery in the Class II patient, the main objective is to establish normo-occlusion by advancing the mandible. ²¹ In doing so, lower lip incompetence can be improved, the jawline sharpened, and chin projection optimized. Additionally, an understanding of the patient's occlusal relationship and vertical height of the mandible should also guide anticipated movements in surgical planning. While Class II patients with good vertical height may benefit from counterclockwise (CCW) rotation of the maxillomandibular complex to maximize mandibular advancement and pogonion position, patients with a deep bite and decreased vertical height may benefit from clockwise (CW) rotation to steepen their occlusal plane ( Fig. 3 ). Class II patients with VME and an open bite require differential maxillary impaction (often posteriorly) with possible advancement in addition to the expected mandibular advancement with CCW rotation. In Class II patients with an open bite from anterior maxillary deficiency, the maxilla must also be advanced and repositioned along with mandibular advancement with CCW rotation. For patients who present with a shortened ramus-condyle unit as a result of condylar hypoplasia or resorption, flattening the occlusal plane while advancing the mandible is still indicated, though joint reconstruction may be of consideration to restore the loss of posterior vertical height ²² ( Fig. 4 ).

Fig. 3.

Preoperative and final plan of a patient with Class II skeletal relationship with deep bite and shortened face. Final plan demonstrates mandibular advancement, clockwise (CW) rotation of the maxillary-mandibular complex, and advancement genioplasty to correct microgenia.

Fig. 4.

Preoperative and final plan of patient with Class II skeletal relationship with shortened ramus-condyle unit from condylar resorption. Bilateral condylectomy for temporomandibular joint (TMJ) reconstruction planned (bottom row). Note the counterclockwise (CCW) rotation of the maxillary-mandibular complex.

Because microgenia is commonly seen in the setting of mandibular hypoplasia, genioplasty can be considered to further augment the chin and address residual asymmetry, and this will be discussed separately in greater depth. For Class II patients with a history of alloplastic chin augmentation, it may be advisable to perform a first-stage implant removal prior to orthognathic surgery to more precisely plan the movements necessary during osseous genioplasty. Finally, soft tissue interventions such as submental liposuction, lower face- or neck-lift, and platysmaplasty are all useful adjuncts to optimize facial aesthetics and better define the jawline in Class II patients. ²³

Class III Sagittal Discrepancies

A concave facial profile with mandibular prognathism is emblematic of a Class III skeletal relationship. Intraorally for these patients, the mesiobuccal cusp of the maxillary first molar lies posterior to the buccal groove of the mandibular first molar. An anterior crossbite or edge-to-edge occlusion may be present, often with retroclination of the mandibular incisors. Patients may present with decreased maxillary tooth show on smile, mentalis strain, and poor upper lip support in addition to a prominent, long chin. Goals of dental decompensation are to upright flared maxillary incisors and retroclined mandibular incisors to facilitate appropriate orthognathic movements. ²⁴

Unlike Class II patients, in whom mandibular hypoplasia is almost always present, the etiology of the Class III relationship may be result of mandibular hyperplasia or maxillary hypoplasia, or, often, a combination of the two. ²⁵ The occlusal plane and vertical growth of the Class III patient contributes to malocclusion and overall facial profile, wherein a steep occlusal plane may disguise a prognathic appearance and concave profile, while a flattened one may enhance it. For this reason, a mandibular setback or Le Fort I advancement alone may not be sufficient for correction. ²⁶

Repositioning the maxilla and modifying the occlusal plane to optimize occlusion and tooth-lip position is a primary objective in treating the Class III skeletal relationship ( Fig. 5 ). Treatment of the facial skeleton should generally favor expansion over contraction whenever possible to optimize aesthetics, soft tissue support, and airway patency. ²⁷ Therefore, large mandibular setbacks to correct Class III occlusion are generally discouraged. Instead, advancing the maxilla, altering its pitch to a more favorable occlusal plane depending on the vertical deficiency or excess, and performing a smaller mandibular setback is a better approach to optimizing the profile, nasolabial soft tissue, and airway. A modest reduction genioplasty may further enhance the overall profile if a residual prognathic appearance persists.

Fig. 5.

Class III skeletal relationship. ( A ) Preoperative plan. ( B ) Planned bilateral sagittal split osteotomy (BSSO) with anticipated overlap. ( C ) Postoperative plan including Le Fort 1 advancement, BSSO setback, and genioplasty. SNA, SNB, and ANB noted in final plan. SNA, sella nasion a-point; SNB, sella nasion B-point; ANB, apoint - nasion, b-point.

Vertical Maxillary Excess

Upper incisor display and 1 to 2 mm of gingival display on smile is considered youthful and aesthetic. Patients with VME may demonstrate excess gingival show at rest, which is only exacerbated on broad smile (“gummy smile”). While VME is considered the most common cause of facial vertical excess, potential other causes of gummy smile include a short or hyperactive upper lip, short clinical crown, altered dental eruption, dentoalveolar extrusion, and gingival hyperplasia. ²⁸ These soft tissue and dental considerations should be accounted for in orthodontic and orthognathic planning.

If the maxillary excess extends posteriorly, an anterior open bite is usually present, often accompanied by mentalis strain and lower lip incompetence. In these patients, the mandible is often forced to rotate CW. The primary objective in these patients is to level the maxillary occlusal plane. Differential maxillary impaction should be planned in these cases with anticipated CCW rotation of the mandible to close the open bite. ²⁹

Genioplasty

Osseous genioplasty is a versatile adjunctive procedure that can address chin asymmetry and correct sagittal and vertical deficiency or excess. ³⁰ Chin malposition and disproportion detracts from overall facial aesthetics and exacerbates the appearance of sagittal discrepancies. Chin projection is a significant determinant of lower facial aesthetics by influencing lower lip competence, mentalis strain, and submental support. Furthermore, chin prominence and morphology can impart a masculinizing or feminizing effect, with typical male chins often being wider and squarer while female chins are narrower and more pointed. ³¹ While the chin may not have occlusal consequence, chin advancement can facilitate functional upper airway expansion by pulling the genioglossus and geniohyoid muscles anteriorly.

A systematic approach to assessing the soft tissue relationships of the lower face is fundamental to planning osseous genioplasty movements. A vertical plumb line extending from the soft-tissue nasion to intersect the Frankfurt horizontal serves as a sagittal reference for the soft-tissue pogonion and labiomental sulcus, which should lie 2 and 4 mm behind, respectively. Similarly, the Ricketts E-line is drawn from the tip of the nose to the soft-tissue pogonion. The upper lip should be 4 mm and the lower lip should be 2 mm behind this tangent. Riedel's plane connects the most prominent points of the upper and lower lips. The soft tissue menton should ideally intersect this line. ³²

Correspondingly, the bony support and diagnosis of microgenia, macrogenia, and chin asymmetry should be analyzed. When planning osseous genioplasty, sagittal discrepancies should be managed with advancement or setback with wedge removal. Vertical discrepancies can be addressed with either lengthening or shortening with a wedge reduction. Chin asymmetry may require wedge reduction or rotation. Changing the angulation of the osteotomy will facilitate lengthening or shortening on advancement as indicated.

VSP allows the surgeon to visualize chin position following orthognathic movements to reposition or rotate the maxillary-mandibular complex. By modeling the anticipated chin position and projection, complex genioplasty movements can be virtually planned and then performed at the time of orthognathic surgery (“triple-jaw” surgery). The use of custom cutting guides and 3D-printed plates in this regard greatly enhances both surgical efficiency, accuracy, and aesthetic outcomes. Importantly, VSP facilitates visualization of the mental nerve and allows for cutting guide fabrication for safe and precise osteotomy creation ( Fig. 6 ).

Fig. 6.

( A ) Genioplasty three-dimensional (3D)-printed cutting guide. ( B ) Custom 3D-printed titanium plate.

Condylar Asymmetry and TMJ Dysfunction

The TMJ is a sine qua non of mandibular stability, and it should be critically evaluated and stabilized prior to virtual planning and orthognathic surgery. ³³ Analysis of condylar asymmetry, which can easily go unaccounted for in conventional planning, is an important consideration in orthognathic surgery. Often, clinical exam and history is key to recognizing the diagnosis preoperatively. Patients with significant and progressive chin deviation, worsening crossbite, cant, midline shift, vertical height difference in angles, or ramus-condyle units should raise suspicion for condylar growth discrepancy or condylar resorption. In cases of condylar hyperplasia, simultaneous high condylectomy is indicated and can be considered simultaneously to orthognathic surgery ³⁴ ( Fig. 7 ). Similarly, for patients with TMJ degeneration with severe trismus, bilateral TMJ replacements can be considered concurrent to orthognathic intervention. ³⁵ 3D planning in both these instances permits a more sophisticated surgical plan and is beneficial in designing condylar osteotomies, predicting the new TMJ position, and setting the foundation for jaw movements. ³⁶ For virtual planning of these cases, condylectomy should be performed as the first step in operative planning, before the steps outlined above.

Fig. 7.

A left high condylectomy planned for condylar hyperplasia.

Facial Asymmetry

The inferior mandibular border, chin point, and malar eminences are key determinants of facial asymmetry. But because these anatomic structures reside outside the occlusal surface, they are not accounted for in traditional 2D orthognathic planning. ³⁷ 3D planning permits the surgeon to evaluate and correct yaw rotation or bodily movement in the mandible, assess asymmetries in the mandible or midface, and plan bony contouring or design biocompatible implants to address deficiencies ³⁸ ( Figs. 8 and 9 ). While doing so, bony interferences and collisions can be analyzed and anticipated. Differential bony gaps at the piriform rim can also be appraised, to plan more sophisticated rotational movements of the maxillomandibular complex without sacrificing mandibular projection. ³⁹

Fig. 8.

Orthognathic treatment of complex facial asymmetry. ( A ) Preoperative plan demonstrating large cant and significant mandibular asymmetry. ( B ) Cant correction and with counterclockwise (CCW) rotation to flatten the occlusal plane, open the posterior airway space, and limit large step-offs at the pyriform. ( C ) Final plan following triple-jaw procedure including left high condylectomy (not pictured). Note significant differential advancement of the mandible to correct mandibular asymmetry.

Fig. 9.

Three-dimensional planning of custom titanium malar implants in a patient undergoing concomitant segmental Le Fort 1, bilateral sagittal split osteotomy (BSSO), and genioplasty.

Revision and Redo Orthognathic Surgery

The challenge of revision or redo orthognathic surgery should not be underestimated. Beyond the need for improvement in occlusion and asymmetry, the presence of hardware, prior osteotomies, scarring, and soft-tissue asymmetries—not to mention, an already dissatisfied patient—can add to the complexity of an already nuanced, multistep surgery. ⁴⁰ In these instances, accuracy is paramount. VSP enables better visualization of hardware, altered anatomy, and prior osteotomies. Virtual planning facilitates custom fabrication of cutting guides, splints, as well as preoperative and idealized mandible or midface models for intraoperative use. ² In our experience, VSP is particularly helpful in visualizing the amount of space and bone stock available for new hardware placement and to avoid potential interferences with prior screw holes or any preexisting implants that do not require removal.

Distraction Osteogenesis

The gradual and controlled elongation during distraction osteogenesis allows for tissue regeneration and repair to occur within the skeleton and the soft tissue associated with it, including the muscles, subcutaneous tissue, and skin. ⁴¹ Especially in the case of severe midface hypoplasia and/or upper airway obstruction ⁴² often seen in cleft patients, orthognathic surgery may be planned with the use of internal or external distractors. The reasons for the use of distraction within orthognathic surgery are manifold but may include concern for the increased risk of bony relapse with anticipated large maxillary or mandibular advancements, a deficient or nonpliable soft tissue envelope, or the need to provide additional functional or aesthetic benefit beyond the maxillary-mandibular relationship (e.g., exophthalmos due to shallow orbits, central midface deficiency with shortened nasal bones, etc.). ⁴³ In these patients, Le Fort 1, 2, or 3 distraction procedures may be indicated depending on the deformity and goals ( Fig. 10 ). To this end, the effect of orthognathic surgery or distraction on the upper airway and speech should not be overlooked. In a study of cleft patients, Bradley et al demonstrated that Le Fort I internal distraction for severe maxillary deficiency led to better occlusion and better speech outcomes compared with conventional orthognathic surgery. ⁴⁴ While hypernasality developed postoperatively for most of these patients as a result of the anterior displacement of the soft palate, this was usually self-limited and resolved after 6 months with speech therapy. For this reason, cleft lip-cleft palate patients treated with a large maxillary advancement with either orthognathic surgery or Le Fort distraction should be counseled that velopharyngeal insufficiency may develop or worsen, even if only temporarily.

Fig. 10.

Severe syndromic midface hypoplasia with planned Le Fort 3 distraction. ( A ) Preoperative plan with osteotomy design. ( B ) Internal midface distractor. ( C ) Final plan with 13 mm planned distraction.

In addition to sagittal discrepancies, maxillary and mandibular width discrepancies should also be appropriately evaluated prior to orthognathic surgery, and distraction osteogenesis considered. Patients with transverse deficiencies may present with a narrowed arch form, posterior crossbites, dental crowding, slit-like nares, deepened nasolabial folds, and wide black buccal corridors with smile. Conventional approaches for correction include dental extraction, dentoalveolar expansion, and interproximal enamel reduction. ⁴⁵ While these approaches may be adequate in some patients, treatment of larger transverse discrepancies with dentoalveolar expansion or incisor protrusion has been shown to be unpredictable and could result in relapse and undesirable side effects in the long term. ^{46 47} Distraction osteogenesis, either with tooth-borne, bone-borne, or a hybrid-anchored device, has been suggested as the treatment of choice for mandibular arch expansion without affecting bigonial width. ^{48 49} Correspondingly, for those transverse maxillary deficiencies too large to be treated with segmental Le Fort 1 (> 7–8 mm), surgically assisted maxillary expansion (SAME) may be indicated to widened the maxillary arch in a horizontal plane. Depending on the degree of maxillary constriction, asymmetry, and anteroposterior discrepancy, SAME or mandibular expansion can be recommended as a definitive occlusal treatment or as a first-stage procedure in anticipation of future orthognathic surgery. ⁵⁰

VSP based on patient-specific CT data aids in the establishment of a target endpoint for distraction. Whether derived from a skeletal, occlusal, or airway endpoint, virtual planning facilitates estimation of the end of the activation phase. Foreknowledge of this endpoint can inform a multidisciplinary care team of important postdistraction studies that confirm clinical success of skeletal and airway expansion, and these in turn can be used to determine the need for additional distraction in the early consolidation phase. Second, an understated feature of VSP is the ability to simulate soft tissue changes that occur from virtual surgery, including external soft-tissue elements such as facial contours and airway simulation. ^{51 52} Though some limitations in VSP software exist in terms of soft-tissue modeling, the ability to compare simulated and postoperative airway volumes and external soft tissue drape can be used as a modicum of quality control.

Limitations

Despite the many advantages of VSP, drawbacks do exist. The nature of VSP warrants different preoperative logistical demands including obtaining and uploading cone-beam CT and 3D or physical dental cast models, securing and obtaining any prefabricated plates, guides, or models, and coordination of associated interventions including orthodontic treatment and adjunctive imaging and work up. ⁵³ Indeed, virtual planning and implant prefabrication are costly, although studies have demonstrated that despite the initial fixed-cost investment, significant cost is recouped through reduced operative time, particularly with the use of precise CAD/CAM splints. ⁵⁴ As 3D printing becomes more efficient and available, 3D-printed splints and guides are likely to become more cost-effective over time.

One challenge of virtual planning remains accurate simulation of the effects of the overlying soft tissue. Soft-tissue movement as a result of bony changes can be unpredictable and is therefore more challenging to model virtually. ^{55 56} That said, conventional planning also has a similar disadvantage, though advances in 3D stereophotogrammetry and postoperative CT data may soon address this issue. For this reason, standardized photography in orthognathic surgery should remain a mainstay of operative planning.

While any number of custom guides, plates, and repositioning aids can be fashioned using CAD/CAM, a thoughtful approach to their use is fundamental. In our experience, it is not always necessary to use prefabricated plates and guides for every step, though we have found it very helpful to use VSP to assess spatial relationships between future custom or stock plates. Rustemeyer et al have reported that a 2D cephalometric analysis and 3D planning without custom plate fabrication are sufficient for accurate planning and will ensure good results for experienced surgeons. ⁵⁷ In our own practice, we frequently prefer mandible-first surgery to account for inaccuracies in bite registration and provide increased intraoperative control of centric relation. After sagittal split osteotomies are created, we use a custom intermediate splint to position the jaw for fixation with stock miniplates. Once maxillary osteotomies are created and a final splint is secured, stock plates are used to secure the midface after careful assessment of tooth-lip position, soft tissue drape, and overall facial balance. However, for osseous genioplasty specifically, we have found that the use of custom plates and cutting guides greatly decreases operative time for this portion of the procedure, eliminating the aesthetic “guesswork” and the need to bend plates intraoperatively. In our practice, a discerning approach to the use of custom implants and guides is an essential factor in improving efficiency, accuracy, and cost.

Conclusion

3D planning and virtual surgery enhance efficiency, accuracy, and reproducibility in orthognathic surgery. ⁵⁸ Despite differences in logistical constraints and cost, VSP and 3D printing provide a degree of versatility that allow the surgeon to visualize and execute more sophisticated, complex, and comprehensive plans that would be challenging or even impossible to account for with traditional 2D planning. While clinical judgment and technical ability are irreplaceable, by implementing a thoughtful approach to the use of CAD/CAM technology within orthognathic surgery, patient occlusion, function, and facial balance can be optimized in a safe, effective, and creative manner.