Chapter 7
Digital Workflow in Oral and Maxillofacial Surgery

Daniel Negrelle, Alexandre M. Borba, Isabella Romão Candido, Shaban M. Burgoa, Luiz F. Palma, and Arthur R.G. Cortes

7.1 Image‐Guided Surgical Removal of Impacted Teeth

With current technology in digital dentistry, different types of surgical guides can be designed. CAD software enables the digital planning of the entire surgical procedure and then the digital design of guides that can be printed or milled in order to orientate the procedures. Surgical planning of procedures involving osteotomies allows for designing surgical guides to provide precise access to the anatomical location and for calculating the amount of bone to be removed. This is particularly useful in cases of retrieval of foreign bodies or impacted teeth. In addition, digital workflow allows for sharing treatment plan data immediately with a network of other professionals, enhancing communication among patients and professionals [1].

Among the most important requirements for planning an image‐guided surgery is the combination of STL files from intraoral scans (IOS) and DICOM files from cone beam computed tomography (CBCT). Such combination allows for considering conditions of hard and soft tissues during virtual surgical planning [2]. In cases involving oral rehabilitation following surgery, prosthetically driven virtual implant planning can also be carried out [3]. Furthermore, digital workflow methodologies have also been described for orientating bone grafting procedures [4, 5]. However, despite new types of surgical guides which have recently been designed and used in dentistry [4, 6], it was not possible to find any article in the literature describing the use of a sleeveless surgical guide for orientating surgical removal of supernumerary tooth impacted between adjacent roots.

A surgical technique using a CAD‐CAM surgical guide for removal or retrieval of impacted objects in the maxilla is presented and illustrated with the following clinical case: an 18‐year‐old male patient who presented for orthodontic treatment was referred for surgical removal of a supernumerary tooth. The patient signed an informed consent to present his treatment data in this report.

7.2 Surgical Planning of Orthognathic Surgeries

Accurate presurgical planning is essential for the treatment of dentofacial deformities, especially in orthognathic surgeries. Virtual surgical planning is the current gold standard method to achieve greater precision for bone and dental movements as well as to gain a reliable perspective of postsurgical changes to facial soft tissues.

7.2.1 Virtual Skull Construction

All virtual planning software programs, regardless of their particularities, are based on the same steps (image importation; virtual skull composition and orientation; osteotomy design; cephalometric landmarks definition; bone segment movement;splint construction). Case Report 7.3 will show these steps using Dolphin 3D v12.0 software.

Case Report 7.1 Image‐Guided Surgical Retrieval of Impacted Supernumerary Tooth

(Clinical case and technique by Dr Shaban Burgoa)

Figure 7.1 Superimposed IOS and CBCT scans used to locate the tooth in a 2D cross‐sectional (left) and a 3D reconstructed model (right). The purple circular area corresponds to the site volume planned to receive synthetic bone grafts (150 mm³ or 0.15 cc).

In the initial clinical appointment, clinical profile, frontal and facial photographs of the patient were taken. A clinical examination was then performed to confirm satisfactory conditions of the soft tissues (e.g., amount of keratinized tissue, low levels of gingival inflammation, and normal periodontal probing depth). In the same appointment, both maxillary and mandibular dental arches, as well as the occlusion of the patient were scanned using an IOS (TRIOS 3, 3Shape). In addition, a CBCT (OP 300, Instrumentarium) was taken with the patient using a lip retractor to facilitate alignment with the IOS images.

All CBCT DICOM and IOS STL files obtained were imported to the same CAD software (NemoStudio^®, Nemotec SL). Multiplanar and three‐dimensional (3D) reconstructions were then used for location and segmentation of the supernumerary tooth in an independent 3D mesh. The impacted supernumerary tooth was positioned in the right anterior maxilla between the roots of canine and lateral incisors (Figure 7.1).

Virtual planning of the supernumerary surgical removal was performed by first using 2D cross‐sectional images (Figure 7.2) and then rendering a 3D reconstructed model to digitally design a tooth‐supported surgical guide to orientate the access to the supernumerary tooth through the maxillary anterior bone wall (Figure 7.3).

Figure 7.2 Axial view of 2D measurements performed during surgical planning and surgical guide digital design.

This surgical guide was designed in two parts: the first was the support of the guide which was designed to be on the teeth shown in the IOS mesh (teeth‐supported guide). The second part was designed over the bone of the CBCT mesh to generate the osteotomy access on the bone window created at the level of the supernumerary tooth. Then both parts were fused with a boolean operation tool of the software. The resulting surgical guide (Figure 7.4a) was then exported as a STL file and 3D printed (Hunter®, Flashforge) with light‐curing resin specific for surgical guides (Makertech Labs). The volume of the remaining site planned to receive synthetic bone grafts were measured using the same software in cubic millimeters.

Figure 7.3 Digitally designed tooth‐supported surgical guide used to orientate surgical removal of the impacted supernumerary tooth.

A full‐thickness flap was opened with the Partsch’s incision, performed 3 mm below the area of surgical access. Surgical removal was then conducted by performing osteotomy of the anterior maxillary wall through the opening of the surgical guide using a piezoelectric surgical device (DentSurg Pro‐CVDentus®, Clorovale Diamantes) (Figure 7.4b) with osteotomy tips that were compatible with the hexagonal shape of the surgical guide opening. The supernumerary tooth and its dental follicular tissue were removed using different curettes and tweezers.

Figure 7.4 Use of the CAD‐CAM surgical guide. (a) Surgical guide in position. (b) Surgical osteotomy performed with a piezoelectric device orientated by the surgical guide.

The remaining site was then grafted using synthetic bone substitutes (Blue Bone^®, Regener) [7]. The number of packages required to achieve the grafting volume was the same as estimated during surgical planning. A bovine collagen membrane (Green Membrane®) was then used to close the osteotomy window. Vicryl sutures were used to secure the surgical site with primary closure. Healing was uneventful and there were no intra‐ or postoperative complications associated with the procedure.

This case used a digital workflow for image‐guided surgical removal of an impacted tooth. Despite the excessive proximity with adjacent roots of maxillary teeth, the procedure was uneventful. Such findings suggest the CAD‐CAM technique used herein could also be useful for other related situations, such as retrieval of impacted or displaced objects or foreign bodies in the maxillofacial area. Among the most common related situations that could be treated using this technique is the accidental dislocation of a tooth into the maxillary sinus during extractions [8], or due to trauma [9].

As shown in the present case, aligning superimposing intraoral and CBCT scans in a CAD software allows the professional to plan an image‐guided surgery by choosing and editing the desired shape of the surgical guide used to orientate the procedure. As described in the literature, the present digital workflow provides advantages compared with conventional surgical planning, such as fewer patient visits and shorter chairside times [10].

This technique also enabled adequate volumetric calculation of synthetic material required to graft the site of the impacted supernumerary teeth after its removal. This finding is in agreement with previous studies using similar techniques of graft volumetric estimation for alveolar socket grafting [11]. Furthermore, as observed in the present findings, the synthetic material used here (Blue Bone) has been proven to provide adequate new bone formation and osteoconduction without significant levels of cytotoxicity [7].

Case Report 7.2 Digital Workflow in Orthognathic Surgery

(Clinical technique by Dr Alexandre M. Borba)

Virtual surgical planning starts with the acquisition of imaging exams, generally a CBCT. Besides allowing more comfortable positioning (sitting patient), CBCT provides better soft tissue reproducibility and reduces image distortion in comparison to conventional tomographic scans (Figures 7.5 and 7.6). Moreover, digitalization of plaster models and, more recently, intraoral scanning have become important factors in reducing possible artifacts that may alter dental anatomy, reproducing faithfully the patient’s dental characteristics (Figure 7.7).

Figure 7.5 CT scan, initial aspect (coronal, sagittal, and axial views, and a 3D reconstruction).

There is a lot of software available for virtual surgical planning nowadays, such as Dolphin® 3D (Dolphin Imaging & Management Solutions). Considering this diversity and all the opportunities of 3D manipulation that allow oral and maxillofacial surgeons to make diagnoses and surgical decisions from this digital workflow, other dentistry areas such as implantology and orthodontics might also benefit.

Figure 7.6 CT scan slices reconstructed into a volume of the craniofacial region (frontal, lateral, and inferior views).

Figure 7.7 Upper and lower dental arches digitally reproduced (frontal, lateral, and occlusal views).

The first step of the workflow is the creation of the virtual patient based on data acquisition from CT scans (DICOM files), intraoral scanning (commonly STL or OBJ files, including isolated dental arches and occlusion), and facial photographs. Head orientation is paramount to determine the axes of rotation, so that pitch, yaw, and roll planes should be determined according to clinical referential frames. Then, a facial soft tissue mask, as well as upper airway volume, can be created from the CBTC data. The composite skull model will be finally obtained from the fusion of dental anatomy obtained from intraoral scanning and the CBCT dental anatomy, an essential stage for the execution of surgical planning (Figure 7.8).

The following phase consists of the design of the jaw osteotomies to be used (most commonly LeFort I and bilateral sagittal split ramus) (Figure 7.9). The surgical movements can then be finally simulated, reproduced, and shown to the patient (Figures 7.10 and 7.11). The end of the planning takes place with the impression of the 3D guides.

Figure 7.8 Composite skull model creation by the superimposition of dental anatomy from the digitalization of the dental arches, volume of the upper airway space, and 3D photography, providing robust information for diagnostic and planning purposes.

Figure 7.9 Maxillary and mandibular osteotomies designed on bone surfaces, allowing surgical movements to be performed.

Figure 7.10 Lateral view of the preoperative status (left) compared to the postoperative simulation of changes predicted to facial soft tissues (right).

Figure 7.11 Frontal view of the preoperative status (left) compared to the postoperative simulation of changes predicted for facial soft tissues (right).

Case Report 7.3 Image‐Guided Orthognathic Surgery

(Clinical technique by Dr Daniel Negrelle)

Image Acquisition

Computed tomography and dental scanning are the main imagining exams used to carry out virtual planning.

Computed Tomography

For a reliable virtual replication of the skull, a CT scan should be obtained with the head in the natural position, the mandible in centric relationship, and with no soft tissue deformations and contractions of the facial muscles. A common error results from deformation originating from forced lip sealing.

If the occlusion leads to a mandibular position in which the mandibular heads will not remain centralized into the mandibular fossae, an occlusal splint guide is suggested. This appliance should be adjusted by removing excess material that would cause deformation of the lips or skin in the oral region.

The CT scan can be performed by a cone beam device, allowing upright positioning of the patient’s head. On the other hand, a fan beam device can also be used, which has a larger field of view, higher resolution, and better image quality, but the patient is positioned in a lying position, causing some soft tissue deformation at times.

The ideal field of view should comprise all the patient’s head and the beginning of the neck. It is also important to include the ears and the entire skull for precise virtual orientation.

Dental Scanning

Due to CT limitations such as artifact generation by metallic objects (dental restorations and orthodontic appliances) and low resolution of dental anatomy, dental scan files should be incorporated into the virtual skull. They can be generated using an intraoral scanner or by scanning plaster models.

Additional, Optional Imagining Exams: 3D Photography or 3D Facial Scanning

Although it is not considered an essential exam for virtual planning and is subject to acquisition errors, resulting in minor distortions, 3D photography or 3D facial scanning is interesting because of texturing and colorization of the soft tissue mesh. Therefore, a more realistic view is obtained, making the patient’s clinical understanding easier as well.

Obtaining 3D photography from devices that project vertical and horizontal lines of reference to the patient’s face is also valuable since the virtual skull can be better positioned by replicating the patient’s natural head positioning (Figure 7.12).

Figure 7.12 3D photography or 3D facial scanning.

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Tags: Digital Dentistry

Nov 13, 2022 | Posted by mrzezo in General Dentistry | Comments Off

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Digital Workflow in Oral and Maxillofacial Surgery

Chapter 7
Digital Workflow in Oral and Maxillofacial Surgery

7.1 Image‐Guided Surgical Removal of Impacted Teeth

7.2 Surgical Planning of Orthognathic Surgeries

7.2.1 Virtual Skull Construction

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