SLJO

Sri Lankan Journal of Orthodontics

CONTEMPORARY TECHNIQUES USED TO PLAN ORTHOGNATHIC SURGERY IN A UK TEACHING HOSPITAL

Renuka Priyadarshanie1, Muhanad Hatamleh2, Giovanna Grados2, Gavin Mack1

  1. Orthodontic Department, King’s College Hospital NHS Foundation Trust, London, UK, 
  2. Cranial and Maxillofacial Department, King’s College Hospital NHS Foundation Trust, London, UK

The objective of this case series is to demonstrate different approaches carried out in a UK teaching hospital for orthognathic surgical planning.

Correction of dentofacial deformity is always challenging. For optimal aesthetic, functional and stable results, combined orthodontic and orthognathic surgical treatments are often required. Some deformities require facial reconstruction for the correction of the deformity. Careful pre-surgical planning with model surgery and fabrication of accurate surgical splints are the fundamentals in achieving a successful outcome in orthognathic surgery. For reconstructive surgery, bone grafts together with reconstructive plates are the gold standard for treatment. While the traditional technique of orthognathic surgical planning is still being carried out in many centres in the world, 3D planning for orthognathic and reconstructive surgery has increasingly become popularized among many clinicians over the last decade.

Three cases are presented in this paper, using the conventional orthognathic technique, 3D planning with printed wafers and 3D planning with customized reconstruction plates for orthognathic and mandibular reconstruction surgeries respectively.

Case 1

This patient had a class II skeletal deformity with mandibular retrognathism. The orthognathic surgery was mandibular advancement with bilateral sagittal split osteotomy. A conventional technique was used for orthognathic surgical planning.

Case 2

This patient presented with a class III malocclusion on a class III skeletal base with mandibular asymmetry, anterior open bite and maxillary cant. A 3D virtual planning was undertaken. The surgical splints were constructed using CAD/CAM technology.

Case 3

A patient presented with a deficient left side of the mandible. He had a reconstruction with iliac crest bone graft and printed titanium implant using selective laser sintering technology. In addition, simultaneous bimaxillary surgery to achieve class I occlusion was performed with the aid of 3D planning and printed surgical wafers.

The reported cases show the importance of careful planning in orthognathic surgery for achieving a successful outcome. They also demonstrate the versatility of different techniques used, depending on the nature of the jaw deformity and the type of the surgery.

Introduction

Treating dentofacial deformity is one of the challenging aspects in orthodontics and in maxillofacial surgery. Successful orthognathic surgery equally depends on surgical technique and surgical plan. The surgical plan involves diagnosis of skeletal and dental deformity and presurgical prediction of jaw movements. It is followed by a three-dimensional representation of intended movements, which are then transferred to surgical splints. These splints are used to replace the maxilla and mandible in the predetermined position intra-operatively.

In conventional orthognathic surgical planning technique, surgical movements are quantitatively determined by redirection of maxilla and mandible into the desired position on the lateral cephalogram. This can be achieved manually using paper templates or using computer software. Then, the mock surgery is performed on the mounted casts followed by the construction of surgical wafers to represent the new occlusion. These splints are placed on the relocated dentition intra-operatively in order to confirm the actual surgery matches the model surgry1. The drawbacks of conventional technique includes multiple steps with excessive time consumption, diagnostic limitations of using lateral cephalograms for surgical planning in maxillofacial region, and possible errors in mounting casts.

Over the past few years, the development of 3-dimensional (3D) virtual surgical planning (VSP) has become more important for planning orthognathic surgery2.

It involves the acquisition of a CBCT image and 3D reconstruction, virtual diagnosis and 3D virtual planning of orthognathic surgery 3. Then, printed surgical wafers are used during the surgery to transfer the plan to actual surgery. More detailed visualization of the dentofacial anatomy 3, less laboratory time consumption and less labor work are the main advantages of this new technique 2.

Computer-aided planning and navigation is a useful adjunct for surgeons in maxillofacial reconstruction. Such systems specifically focus on enhanced visualization tools and 3D modeling to give the surgeon the ability for precise preoperative surgical planning and designing patient specific implants preoperatively4. Advances in manufacturing technology and material science has led to the possibility of turning such virtual model or design into reality as physical replica models, surgical guides or cutting jigs, splints and patient specific implants for intraoperative use 4.

In this paper three cases are presented which used (1) conventional orthognathic surgical planning (2) 3D orthognathic surgical planning with printed surgical wafers and (3) 3D planning with customized surgical plates for mandibular reconstruction in a UK teaching hospital.

Case 1

A 24-year-old female patient presented complaining of a small lower jaw. Clinical examination revealed a Class II division 1 incisor relationship on a Class II skeletal base with retrognathic mandible and increased Frankfort Mandibular Plane (FMPA). There was no significant facial asymmetry. Her upper and lower dental arches were mildly crowded and LR6 had been extracted previously. The overjet was 9 mm and overbite was reduced. Upper and lower dental midlines coincided with each other and with the facial midline. Canine relationships were a full unit Class II bilaterally (Figure 1).

Figure 1. Patient’s initial presentation

Based on clinical examination and radiographic findings, the necessity of both orthodontic treatment and orthognathic surgery to attend her malocclusion was clear. The ideal surgical treatment was a Le-Fort1 maxillary impaction to attend her increased vertical proportions and a BSSO (bilateral sagittal split osteotomy) to advance mandible. Since the patient’s only concern was the small lower jaw, the eventual orthognathic surgical plan was only BSSO to bring the mandible forward.

Upper second premolars were extracted to relieve upper arch crowding. LL6 with root canal treatment was also extracted to balance the extraction of LR6. Presurgical treatment was carried out with fixed appliance (0.022” x 0.028” slot, MBT prescription). Lower first molar extraction spaces were utilized for lower arch alignment and decompensation. At the end of 16 months of orthodontic treatment, alignment of upper and lower dental arches, decompensation and arch coordination were satisfactory. Orthognathic surgical planning was done on lateral cephalogram manually, using a mandibular paper template. The template was moved forward until a good posterior teeth interdigitation and an overjet of 1mm were achieved. Molar relationship could not be determined since her lower first molars have been extracted. The amount of mandibular forward movement was measured and recorded as 7mm.

Two sets of impressions were taken with irreversible hydrocolloid. One was to analyze the pre-operative occlusion, and the other one was to perform mock surgery. Orthodontic brackets were blocked out with wax to prevent tearing and distortion of the impression during removal. Wax bite registration in centric occlusion was done in order to determine the patient’s occlusion for mounting the models on the articulator.

Impressions were poured with type IV dental stone. The models were mounted in a semi adjustable articulator using the patient’s wax bite. Face bow registration was not necessary in the mounting because, (1) anteroposterior and vertical position of the maxilla was determined by clinically and cephalometrically, (2) tripod occlusal stability existed between the maxillary and mandibular models, (3) no maxillary occlusal cant was present5.

A horizontal line was drawn on the mandibular cast just below the roots of the teeth. Then a second line was drawn   10mm below the first line. A digital caliper was used to measure the vertical distance between base of the lower cast and (1) lower incisal edge, (2) tip of canines, (3) buccal cusp tip of first premolars (4) distobuccal cup tip of upper second molars.  Horizontal distances were also measured from the articulator pin to the above reference points on teeth.

After taking the measurements, the mandibular cast was separated from the base between the two horizontal lines. Then the mandible was brought into Class I occlusion with the maxillary cast and fixed with soft wax. Then mandibular cast was sealed to its base with sticky wax. The same horizontal and vertical distances were remeasured. The difference between first and second measurements was equal to the amount and the direction of mandibular movement. The difference of +7 mm in the horizontal plane at the incisal edge of lower central incisors showed that mandible has moved forward by 7mm.  Splints were fabricated with auto polymerizing resin. The upper and lower casts were coated with a layer of separating medium (cold mold seal) and left to dry. The undercuts were blocked with putty.  Acrylic is rolled into a cylindrical shape at dough stage and adapted to the lower teeth. Then the upper cast was closed into occlusion. Excess acrylic was trimmed with scissors and left for curing. All the external surfaces were sandpapered, pumiced, and polished (Figure2).

Figure 2. Mounted casts in centric occlusion (left). Mandibular cast is fixed after mock surgery (middle) and the surgical wafer (left)

The wafer was used to position the mandible during the surgery. There were no intraoperative and post-operative complications. After combined orthodontic and surgical treatment, there was a marked improvement in jaw relationship and occlusion. The patient was extremely happy with new appearance and the bite (Figure 3).

Figure 3. Post-operative facial, cephalometric and intraoral views

Case 2

A 28-year-old female patient reported with a chief complaint of a shifted lower jaw towards the right side. She had a Class III incisor relationship on a Class III skeletal base with average FMPA. Her malocclusion was complicated by marked facial asymmetry and negative 2mm overjet measured on right side central incisors. She also had an upper and lower dental midline discrepancy by 3mm. Her upper dental midline was coincident with her facial midline. Lower dental midline was shifted 3mm from upper centerline, but coincident with the chin point (Figure 4).

Figure.4 Patient initial presentation

Following diagnosis with the aid of clinical examination and radiographs, it was planned to perform both orthodontic and bimaxillary orthognathic surgical treatments to correct her malocclusion.

Presurgical orthodontics were carried out with fixed orthodontic appliance (MBT prescription, 0.022”x0.028” slot). After 18 months of presurgical orthodontic treatment, the alignment, decompensation and arch coordination were satisfactory. The required orthognathic surgery was a Le Fort 1 maxillary osteotomy for differential impaction of maxilla and a BSSO to bring the mandible into class I occlusion. 3D planning was performed in the preparation for the orthognathic surgery.

A CBCT scan was obtained using an i-CATTM device. It was processed and 3D virtual model of patient skull and mandible was constructed using CMF Pro. Plan software (v 3.0; Materialise). Upper and lower impressions of the patient’s mouth were taken and poured with dental stone to produce upper and lower dental casts.  The CBCT did not show accurate occlusal anatomy due to noise and scatter around the teeth secondary to patient’s metallic fixed orthodontic appliance. This prevents accurate upper and lower teeth intercuspation to determine the planned new occlusion and construction of surgical wafers. To overcome this, both the upper and lower dental casts were scanned (3 Shape R700) separately and in the final occlusion to produce e-casts. Then, the e-teeth were amalgamated with CBCT to create enhanced reconstruction of upper and lower dental arches (Figure 5).

Figure 5.  CBCT showing noise and scatter around teeth (top left). Scanned upper and dental casts in final occlusion (top right).

CBCT image amalgamated with e-teeth (bottom left). CBCT soft tissue image (bottom right)

Virtual Le Fort 1 and BSSO were performed to the maxillary and mandibular composite models respectively.  The maxilla was advanced 6mm and impacted 1mm anteriorly. Differential impaction was done on left (3mm on UL6) and right (1mm on UR6) hand sides to correct the occlusal cant. The mandible moved backward by 1mm and to the right side by 3mm for the scanned final occlusion.

The final surgical plan with simulation of both soft and hard tissue relationships was shown to the patient and discussed (Figure 6). Then, the working files were imported into 3-matic software (Materialise, Leuven, Belgium) to design the intermediate and final splints. These were 3D printed in biocompatible resin using a 3D printer (object 250, Stratasys)

The actual bimaxillary surgery was done using the splints. After combined orthodontic and surgical treatment, there was a marked improvement in jaw relationship and occlusion. The patient was highly contented with the result (Figure 7)

Figure 6. CBCT images of hard tissues (left) soft tissues (right) after virtual bimaxillary surgery

Figure 7. Post-operative facial, cephalometric and intraoral views

Case 3

A 21 year old male reported complaining of a deviated lower jaw. He had Class II division 1 incisor relationship with average vertical proportions. The malocclusion was complicated by severe facial asymmetry with deficiency of left side mandible and chin shifted to the same side (Figure 8). He had multiple missing teeth posterior to the lower left canine and severely proclined lower labial segment. The mandibular deficiency was secondary to facial trauma during his childhood. His temporomandibular joint function was satisfactory.

Figure 8. Pre-treatment facial views

Based on the clinical examination and radiographic findings it was decided that the patient would benefit from combined orthodontics, orthognathic surgery and reconstruction of deficient left side of the mandible. The orthodontic treatment plan included fixed appliance treatment for alignment of teeth and coordination of dental arches for final occlusion. The orthognathic surgical plan was Le Fort I osteotomy of maxilla and bilateral sagittal split osteotomy of the mandible

Treatment proceeded with fixed orthodontic appliance (MBT prescription, slot size 0.022”x0.028”) which resulted in good alignment and arch coordination in 13 months.

CBCT of the head was obtained and converted into 3D virtual model as previously described. Upper and lower e teeth were amalgamated with the 3D images (Figure 9).

Figure 9. CBCT showing deficient left side of the mandible and noise and scatter around teeth (top). Scanned upper and dental casts (bottom left) and CBCT images amalgamated with e-teeth (bottom right)

Virtual Le Fort 1 (3 mm maxillary advancement, 3 mm rotation of upper centreline to the left and 1.5mm anterior down fracture) and BSSO (6.5 mm advancement and 2 mm rotation of lower midline to the right) were performed as previously described . The final maxillary and mandibular positions were imported into design software (3-Matic; Materialise), and intermediate and final wafers were designed and printed in biocompatible resin.

Following bimaxillary virtual planning of orthognathic surgery, reconstruction of the deficient left side of the mandible was planned virtually. The mirror image of the normal right side of the mandible was moved to match the remaining left side of the mandible until maximum symmetry was achieved. Then, the virtual designing of reconstruction plate and guides for screw placement were carried out using the same software. Finally, the plate and the guides were printed with titanium and resin respectively (Figure 10).

Figure 10. 3D reconstruction of mandibular deficiency; Mandible after virtual BSSO (top left), mirror imaging of normal side to deficient side (Top right), symmetry achieved (bottom left) and virtually reconstructed plate (bottom right)

Bimaxillary surgery was done as planned using the splints. The titanium plate was fixed to body and the condyle of the deficient side of the mandible. The fixation screw guides were used for accurate positioning of the plate. Then, a bone was graft harvested from iliac crest and secured to the titanium plate with titanium screws at the body of the mandible. This was for future dental rehabilitation with osseointegrated implants.

There were no intraoperative or post-operative complications. The patient was satisfied with the aesthetic and functional outcome (Figure11).

Figure 11. Post-treatment facial views

Discussion

Conventional planning has been the most commonly used method of orthognathic surgical planning before development of the virtual planning.  It has been used for more than 50 years with good and reliable outcomes6. However, this requires an extensive radiographic analysis, dental model fabrication and surgical splint preparation which require an extensive time commitment, and a firm grasp of dental material7.

The lateral cephalometric radiograph used in this technique is a 2D (two-dimensional) representation of a 3D object and therefore has diagnostic limitations. When using semi adjustable articulators, models are articulated using a face bow recording to determine position of maxilla to condyle hinge axis. It is also an aid for vertical positioning of the maxilla with respect to a chosen horizontal plane of reference5.  However, customary use of semi-adjustable articulators and a facebow in orthognathic surgical planning has been debated 8. The mandibular rotational axis is not located in the mid-condylar head (and hence the articulator condylar axis), but is typically more than 2 cm posterior and 1–2 cm inferior to this site9,10. This variation in the location of the centre of mandibular rotation causes clinically significant errors in the horizontal maxillary position with simulated maxillary impaction movements11. Such articulator errors are compounded by errors in the facebow recording due to inaccurate orientation of the maxillary model relative to the Frankfort (horizontal reference) plane12. This results in inaccurate splint fabrication leading to incorrect surgical movements compromising the outcome 12.

Furthermore Mock surgery on dental casts is only a partial view of the actual surgery and is a repositioning of the dentition to the desired position to make a splint. Therefore, in conventional orthognathic surgical planning, positioning of craniofacial complex is loosely made through an estimation of the casts to the lateral cephalometric radiograph1.

The first case described here is a good example to describe conventional planning. Since surgical movement is only in anteroposterior direction and is relatively straightforward, there was no need for 3D planning. In an academic institution with trainees and maxillofacial technicians, the traditional method is neither time or cost restrictive. In fact, it is found to be highly educational and informative. It allows the new surgeon to have an outstanding spatial relationship of the 3-dimensional movements necessary to perform successful orthognathic surgery, which will facilitate their true intraoperative experience7.

Recent advances in CBCT as well as CAD/CAM technology have led to an emergence of several computer-assisted surgical simulation software programs with a wide range of applications13. One of the main advantages of 3D planning over conventional planning is the ability of the clinician to visualize the dental arch, bony skeleton, and the soft tissues and thereby obtain more information of the anatomy of the area of interests. It enables practitioners to focus more on facial harmonization in all 3 planes rather than on the facial profile3. It can also quantify dental cant, yaw deformities, and other facial asymmetries that would have been otherwise undetected in physical examination, 2D lateral cephalometric analysis, and in conventional orthognathic planning.3, 13,14. The assessment of the deviation of dental midlines from facial midlines and the position of the chin are much more difficult clinically in the presence of facial asymmetry or occlusal plane tilting3. This can be fulfilled easily and more accurately with 3D planning3. This technique has shown similar precision to surgical planning in a semi-adjustable articulator 6 and significantly less laboratory time involvement than conventional planning2. Due to the complete digitization of the treatment plan, virtual planning offers many other important advantages over conventional treatment planning. Treatment plans can be stored online and save the space normally taken up by materials used in conventional technique. The virtual treatment plan can easily be visualized and conferred with treating team members anywhere in the world via the internet. It also offers an excellent communication tool to teach contemporary treatment of maxillofacial deformities to residents in orthodontics and oral and maxillofacial surgery3. In addition, virtual planning also holds the possibility of extracting knowledge from surgeries performed in different centres all around the world, which makes it possible to review the treatment plan of rare and difficult maxillofacial deformities previously performed by other surgeons, and to evaluate the postoperative outcome in both hard and soft tissues3.

The second case described in this paper is benefitted with virtual planning sine the patient’s skeletal deformity is in all three planes, required bimaxillary surgery and intended surgical movements are in all three directions. The good outcome of this case demonstrates the usefulness of the novel technique for complex cases.

One of the main limitations of 3D virtual surgical planning is exposure to increased radiation due to the need for a CBCT scan. Although, CBCT scans significantly reduce the radiation exposure compared to multi-slice CT scans, they still increase the exposure compared to conventional panoramic and cephalometric imaging15. Although the cost of the software for orthognathic planning has come down considerably they are still expensive. Updating of the software is required each year, which is an additional expense. 3D model scanners and 3D printers and milling devices are also expensive.

The aims for maxillofacial reconstruction are the maintenance of proper esthetics and symmetry of the face and the achievement of a good functional occlusal result, thus preserving the form and the strength of the jaw and allowing future dental rehabilitation16. Current reconstruction procedures combine mandible reconstruction plate fixation and use of micro vascular flaps. Currently, the use of computer-assisted techniques for mandibular reconstruction has increased, leading to a decrease in the surgical duration and complication rate and improved aesthetic and functional outcomes 17,18. The last case described here is a typical example for satisfactory outcome of using 3D virtual reconstruction and preshaped printed fixation plate and fixation guides.

Conclusion

The three cases in this paper demonstrate a range of orthognathic surgical planning using conventional and 3D techniques appreciated in a large teaching hospital in the UK.

  1. Tucker S, Cevidanes L, Styner M, Kim H, Reyes M, Proffit W, Turvey T. Comparison of Actual Surgical Outcomes and 3D Surgical Simulations.Oral Maxillofac Surg. 2010; October; 68(10): 2412–2421.
  2. Steinhuber T, Brunold S, Gartner C, Offermanns V, Ulmer H, Ploder O. Is Virtual Surgical Planning in Orthognathic Surgery Faster Than Conventional Planning? A Time and Workflow Analysis of an Office-Based Workflow for Single- and Double-Jaw Surgery. J Oral Maxillofac Surg 2017: in press. 6666666666mmmmAM (AM J ORTHOD DE
  3. Swennen GRJ, Mollemans W, Schutyser F. Three- Dimensional treatment planning of orthognathic surgery in the era of virtual imaging. J Oral Maxillofac Surg 2009;67:2080-2092.
  4. Parthasarathy J. 3D modeling, custom implants and its future perspectives in craniofacial surgery. Ann Maxillofac Surg 2014 Jan-June; 4(1): 9–18
  5. Marko JV. Simple hinge and semiadjustable articulators in orthognathic surgery. Am J Orthod Dentofacial Orthop. 1986;90:37–44.
  6. Ritto FG, Schmitt ARM, Pimentel T, Canellas JV, Medeiros PJ. Comparison of the accuracy of maxillary position between conventional model surgery and virtual surgical planning. Int J Oral Maxillofac Surg 2017: in press
  7. Hammoudeh JA, Howell LK, Boutros S, Scott MA, Urata MM. Current Status of Surgical Planning for Orthognathic Surgery: Traditional Methods versus 3D Surgical Planning.  Plast Reconstr Surg. Global Open 2015;3(2):e307 doi:10.1097/GOX.0000000000000184.
  8. Richard RJ, Cousleya, Bainbridgea M, Rossouwb The accuracy of maxillary positioning using digital model planning and 3D printed wafers in bimaxillary orthognathic surgery. Journal of orthodontics. 2017:44(4):256-267
  9. Nattestad A, Vedtofte P. Mandibular autorotation in orthognathic surgery: a new method of locating the centre of mandibular rotation and determining its consequence in orthognathic surgery. J Craniomaxillofac Surg. 1992 May-June; 20(4):163–170.
  10. Lindauer SJ, Sabol G, Isaacson RJ, Davidovitch M. 1995. Condylar movement and mandibular rotation during jaw opening. Am J Orthod Dentofac Orthop. 1995 June;107(6):573–577.
  11. Nattestad A, Vedtofte P, Mosekilde E. 1991. The significance of an erroneous recording of the centre of mandibular rotation in orthognathic surgery. J Cranioxaxillofac Surg. 1991 Aug;19(6):254–259.
  12. Barbenel JC, Paul PE, Khambay BS, Walker FS, Moos KF, Ayoub AF Errors in orthognathic surgery planning: the effect of inaccurate study model orientation. Int J Oral Maxillofac Surg. 2010 Nov;39(11):1103-1108
  13. Ellis E. Accuracy of model surgery: evaluation of an old technique and introduction of a new one. J Oral Maxillofac Surg. 1990 Nov;48(11): 1161–7.
  14. Baker SB, Goldstein JA, Seruya M. Outcomes in computer-assisted surgical simulation for orthognathic surgery. J Craniofac Surg. 2012 Mar;23(2):509-13
  15. Silva MA, Wolf U, Heinicke F, Bumann A, Visser H, Hirsch E. Cone- beam computed tomography for routine orthodontic treatment planning: a radiation dose evaluation. Am J Orthod Dentofac 2008 May; 133(5):640
  16. Cohen A, Laviv A, Berman P, Nashef R, Abu-Tair J. Mandibular reconstruction using stereolithographic 3-dimensional printing modeling technology. Oral Surg Oral Med Oral Pathol Oral Radiol Endod.2009 Nov;108(5):661-6
  17. Modabber A, Ayoub N, Möhlhenrich SC, Goloborodko E, Sönmez TT, Ghassemi M, Loberg C, Lethaus B, Ghassemi A, Hölzle F. The accuracy of computer-assisted primary mandibular reconstruction with vascularized bone flaps: iliac crest bone flap versus osteomyocutaneous fibula flap. Med Devices (Auckl).2014 Jun;16(7):211-7.
  18. Paleologos TS, Wadley JP, Kitchen ND, Thomas DG. Clinical utility and cost-effectiveness of interactive image-guided craniotomy: Clinical comparison between conventional and image-guided meningioma surgery. Neurosurgery. 2000 Jul;47(1):40-7