Additive manufacturing can be easily integrated with digital imaging technologies to build and design complex physical models and prototype parts. The various technologies used in additive manufacturing are liquid-based processes (ex. Inkjet printing), powder-based printing (ex. 3D printing), and solid-based manufacturing (ex. Laminated object manufacturing) [10, 11]. These technologies can reproduce craniofacial structures and have been used to treat craniomaxillofacial bone defects [12,13,14,15]. Stereolithography is the most commonly used additive manufacturing technology application in oral and maxillofacial surgery. It creates medical models for diagnosis, treatment planning, and surgical simulation [16].

Meanwhile, the customized titanium implants and reconstruction plates are manufactured by direct metal laser sintering fabrication technology. In this, the implants are fabricated by applying a focused laser beam to fuse thin layers of powder and metal in a layered manner in a localized region [10, 17]. The 3D VSP, along with additive manufacturing, can be used to plan surgical resections, fabricate the surgical guide, and simultaneously plan and manufacture the implants to reconstruct the ablative defects.

The conventional obturator is the simplest and easiest form of reconstruction in the reconstruction ladder of mid-face defects. Despite being simplistic in approach, these obturators have disadvantages like improper oro-nasal seal leading to regurgitation, inadequate masticatory efficiency, and need for repeated adjustment [6]. On the other hand, reconstruction with flaps or free tissue transfer provides the most physiologic outcomes with respect to speech, deglutition, and formation of an oro-nasal seal. However, they still pose a significant challenge in dental rehabilitation as placement of dental implants in this reconstructed bone requires meticulous planning. The placement of the dental implants is guided by the eventual location of the vascularized bone flap used to reconstruct the alveolus. If this is not planned by VSP, it might lead to placement of dental implants which is not prosthodontically suited [18, 19].

The zygomatic implants have provided an acceptable non-grafting solution for rehabilitation of atrophic maxilla. They can be used in patients with maxillary alveolar defects but with good bone quality in the body of the zygoma region. The long-term functional and esthetic outcomes of zygomatic implant supported rehabilitation has been excellent [20]. However, some of the complications associated with zygomatic implants include risk of orbital injury, speech problems with palatal emergence, post-operative sinusitis, and oro-antral fistula [21]. Further, a lower survival rate of zygomatic implants has been reported in patients with maxillary resection [22]. In our experience, the cost of the patient-specific implants rehabilitation was equivalent to the zygomatic implant supported rehabilitation.

In the current case series, the authors used the out-sourced services of the software ‘Geomagic freeform with haptic’ for the VSP. The use of VSP helps the surgeon plan the overall treatment guided by the placement of the final prosthesis. With 3D VSP, the surgeon can precisely mark out the resection margins and replicate it by manufacturing the cutting guides, which is used intra-operatively. After creating this residual defect on the VSP, the surgeon can now plan the prosthetic-driven reconstruction and prevent any compromise in the dental prosthesis. The additive manufacturing technology uses this prosthetic-driven VSP to print the customized framework. (Fig. 5).

Proposed algorithm for flow of VSP using the prosthetic-driven plan for rehabilitation of maxillary defects by customized implants

This precise guided implant placement carried out during tumor resection offers a huge advantage for patients requiring radiotherapy by hastening the process of dental rehabilitation [23]. Also, owing to the high accuracy of VSP, good control over tumor margins can be achieved by using cutting guides during ablative surgery [24]. Reconstruction of mid-face defect with free-tissue transfer is best suited when extensive soft tissue reconstruction is required. However, customized implant-supported rehabilitation offers significant advantages over free tissue transfer, such as the absence of donor-site morbidity, reduced operating time, and faster recovery for the reconstruction of alveolar defects and low-level maxillectomies. In addition, this prosthesis over customized implants can be made in a semi-fixed manner by incorporating ball-and-socket like attachments, which offers the advantage of disease surveillance.

Recently in the COVID-19 pandemic, there has been an increased incidence of maxillofacial mucormycosis. By June 2021, over 40,000 cases of mucormycosis were reported in India [25, 26]. The standard treatment for these maxillofacial mucormycosis is surgical debridement depending on the extent of infection, leading to various types of maxillectomy defects. This has led to a massive burden of cases requiring rehabilitation of these defects. As with any other maxillectomy defect, the reconstruction option remains the same, which ranges from hollow bulb obturator to free flap reconstruction [27,28,29]. The option of VSP and additive manufacturing offers a suitable alternative for the rehabilitation of such patients.

Even with all its benefits, VSP can potentially be challenging and have pitfalls of their own [30]. There has to be proper communication between the engineers and the surgeon during the planning, to minimize incorporation of any error. Additionally, the simulation of occlusion in centric relation during the virtual planning can be challenging. For pathology resection planning, the resection margins can vary intra-operatively from the one as determined during the VSP. These modifications intra-operatively can be detrimental to the PSI fixation, if a simultaneous resection and rehabilitation had been planned. It is important to understand that the VSP can work as a useful adjunct and should always be preceded by clinical examination and judgment.