Whenever dental reconstruction is planned as part of the resection and reconstruction procedure, virtual planning should be considered to assure that the maxillary reconstruction provides bone in the proper position to accept properly positioned dental implants.
Pre-operative staging in malignancies involving the maxilla includes preoperative 3D scanning. Whether the patient is dentate or not the reconstruction of the maxilla has to be backwards-planned prior to resection of the maxilla. There are different options for reconstruction (see section of postablative reconstruction) which can be applied primarily, delayed primarily (ie. within weeks) or secondarily (ie. after 6-12 months eg. following radiotherapy).
In the case of delayed reconstruction of the maxilla, temporary closure of the palatal defect can be performed with the help of a thermoplastic temporary splint.
Whatever reconstructive strategy is applied, a prosthodontic-driven backwards-planned digital workflow should be advocated. A stereolithographic (STL) model of an ideal reconstruction is made. This allows for preoperative adaptation of bone plates of to replace resected midfacial buttresses and reconstruct the original contours.
Furthermore, dental implant position can be virtually planned ensuring placement in sufficient bone stock (existent or to be reconstructed). A drill guide is then produced to ensure correct bone augmentation and simultaneously/secondary implant position.
The following clinical cases demonstrates examples of this digital workflow step by step.
A 3D-scan is made to diagnose the extent of the defect.
The Brown type II defect shown on the left will be used to illustrate the digital workflow for maxillary reconstruction.
This axial CT slice shows the right maxillary defect.
3. Case 1 - Virtual reconstruction
Ideal location of dental implants
In this case, the patient is partially dentate (3 teeth) on the contralateral side. Implant placement is simulated in red.
Note: In the case of a complete alveolar resection or an edentulous maxilla, the Atlas function of the software would be used to virtually reconstruct the ideal hard tissue anatomy based on the 3D-CT scan of a normal adult skull without any artifacts.
This virtual reconstruction would then serve as a base for the planning of dental implants without the need of any dental impressions or casts.
Bone stock needed for each implant
The red cylinders show the amount of vital bone needed around the dental implants.
Reconstruction volume needed
The shape and volume of the needed bone graft (yellow) is dictated by the shape of the bone necessary for successful insertion of implants (red cylinders).
4. Case 1 – Preparation of drill guide
A physical model of the maxilla is made and used to prefabricate a drill guide by a dental technician to define:
The position of the required bone graft
The position of the dental implants
Alternatively, the drill guide can be made virtually and fabricated with a 3D printer.
5. Case 1 - Reconstruction
Exposure of the defect
This picture show the right maxillary defect after the fasciocutaneous flap has been dissected.
The drill guide is inserted and used as an aid to place the bone grafts. Care is taken that adequate bone volume (red cylinders in the virtual planning) is added for each planned implant.
Each bone graft is adequately stabilized with either lag screws and/or plates.
Insertion of dental implants
After the bone has matured (min 12 weeks) the plates and screws are removed.
In the same surgery, the original drill guide is used to insert the dental implants.
Postoperative validation of the correct implant position by comparing the virtually-planned (red lower picture) and the final implant position (upper picture).
6. Case 2 – Diagnostic imaging
A 3D-CT scan is made to diagnose the extent of the defect.
In cases were the general health status of the patient does not allow for bony reconstruction of the maxillary defect, alternative techniques might help to rehabilitate the patient in terms of dentation, lip support and competence, speech etc.
The Brown type II defect shown on the left will be used to illustrate the digital workflow for maxillary reconstruction when bony reconstruction is not possible.
7. Case 2 – Virtual reconstruction
Ideal location of dental implants
If the malar bone provides sufficient bone stock, prosthodontic-driven backwards-planning helps to virtually position one or two zygomatic fixtures (blue and pink).
This picture shows the virtual position of the two implants to assure that the position meets prosthodontic requirements.
The exact trajectory of the drill is planned.
Intraoperative navigation is used to precisely position the implants.
Intraoral view after implant placement.
Postoperative cone beam scan in the coronal plane demonstrates the parallel position of the two zygomatic fixtures on the right side.
Three years follow up showing the screw-retained bar on the two zygomatic fixtures together with 5 conventional implants.