By Dr C. Sharath Babu
Prosthodontist and Implantologist
Published on 12/08/2022
Patients have suffered greatly as a result of post-covid mucormycosis. Mucormycosis is a fungal infection that mainly affects immunocompromised individuals. Long-term corticosteroid treatments in such vulnerable patients, combined with high fungal spore counts in the hospital setting, creates an environment conducive to fungal infections.
Inhalation of fungal spores causes infection in the nose and paranasal sinuses. It can spread to orbital and intracranial structures directly or through blood vessels. The fungus infiltrates arteries, causing thrombosis and necrosis of hard and soft tissue.
When the maxilla is involved, surgical removal and debridement of the affected areas causes extensive defects in the maxilla. The defect could be a small opening that allows communication from the oral cavity into the maxillary sinus, or it could include a portion of the palate, alveolar ridge, and nasal cavity floor. In patients with extensive removal of the maxilla, facial disproportion, speech and masticatory difficulties, leakage of fluid through the nose and along with acute and chronic episodes of sinusitis.
1. Patients should be evaluated with a full history and physical examination to ensure they are an appropriate candidate for the procedure
2. Cone-beam computed tomography (CBCT) is recommended for preoperative evaluation.
(A)To evaluate the distance from the alveolar ridge to the zygoma body to obtain an estimate for implant sizes.
(B)To evaluate the quality and quantity of the zygomatic bone available.
3. A minimum of 7 mm of anchorage into the zygoma is required for stability of zygomatic implants, with a greater amount required if 2 implants are to be placed.
The types of prosthesis are:
The quad zygoma concept uses four Zygoma implants to treat severely atrophic maxilla. Two implants are placed bilaterally with the appropriate front and back portion of the jaw spread equally and inclined for prosthetic rehabilitation. Typically, a fixed prosthesis is provided although this implant solution may also be used to retain an overdenture.
Complete removable dentures are used to rehabilitate completely edentulous patients regardless of degree of atrophy. However, this approach may not meet each individual's functional, psychological, and social needs.
Over time options evolved:
1. Jaw reconstruction surgery involving bone grafting and secondary implant placement.
2. Using tilted implants to eliminate the need for bone grafting and engage available bone where possible with appropriate implant distribution for prosthetic rehabilitation.
3. Using an alternative source of bone for implant anchorage, such as the zygoma or pterygoids.
The quad zygoma combined with prosthetic reconstruction can address patients’ needs for esthetics and function similar to conventional treatments. Zygoma implants obtained better outcomes and constituted a much faster means of rehabilitation.
Zygomatic implants are developed to help patients who had extensive bone loss due to trauma, neoplasms, or congenital pathologies. These implants can be used in conjunction with intra-alveolar implants or on their own to support a prosthesis.
Nonalveolar implants offer a predictable alternative to bone augmentation techniques in situations of severe alveolar atrophy. The placement of implants in bone of a different embryologic origin favours high survival rates derived from the absence of bone resorption and atrophy.
It includes severe atrophy of maxilla, in particular insufficient bone volume for the placement of even a single dental implant in both front and back part of the jaw. In these patients, the quad zygoma is the first option of treatment. It may also be used as a rescue implant in patients who have previously undergone bone grafting or had implants fail.
Sinusitis is the most common complication associated with zygomatic implants. Appropriate pre-surgical diagnostics and sinus evaluation, as well as using the extra-sinus surgical approach and immediate implant loading, appear to reduce or even eliminate this complication.
Other complications reported during and after zygoma implant insertion include infraorbital nerve paresthesia, oronasal fistula, and orbital perforation.
Removable prosthesis :
Obturator or removable prosthesis
A maxillectomy or palatectomy prosthesis, also known as an "obturator," is used to restore the surgical defect and helps with swallowing, speaking and chewing. It fills the surgical void and artificially replaces lost tissues and teeth
Obturator fabrication is typically completed in three stages:
A temporary prosthesis is used to restore the continuity of the hard palate immediately after surgery.
When surgical dressings or surgical prostheses are removed 10-14 days after surgery, this phase begins. The interim prosthesis is fitted and adjusted until the healing process is complete. This stage can last anywhere from 2 to 24 months.
Definitive phase is initiated when healing is complete and involves the fabrication of long-term prostheses. Fixed prosthesis such as crowns or removable prosthesis may be used in definitive treatment.
Mucormycosis rehabs with PSI (patient specific implants)
Prosthetic rehabilitation has been advised for the rehabilitation of defects of the hard and soft palate due to mucormycosis. There are maxillary obturators for hard palate defects, pharyngeal obturators for soft palate defects, and maxilla-pharyngeal obturators for defects that include both structures. In general, prosthetic intervention leads to a rehabilitation of dentition, reduction of hypernasality and subsequent restoration of speech and also limit nasal leakage of liquids and food.
In extensive bilateral midfacial defects and total or partial maxillectomy cases prosthetic rehabilitation is achieved using two-part prosthesis i.e. antral and oral part. Retention of the antral part is achieved by engaging soft and hard tissue undercuts or with the help of resilient liners and the oral part is attached to the antral part by different types of attachments.
Cast partial prosthesis:
In hemi-maxillectomy cases or in cases with firm, retained teeth prosthesis with metal framework or cast partial prosthesis serve as the best treatment modality. Cast framework partial dentures are more comfortable, durable, and biocompatible and have enhanced longevity, stability and esthetics as compared to resin-based prosthesis.
CAD-CAM and SLS technology:
The computer-aided design and computer aided manufacturing (CAD-CAM) technology and selective laser sintering (SLS) technology are also used in the fabrication of prosthesis for maxillofacial defects. SLS technique has advantages of improved mechanical properties, higher patient satisfaction in terms of prosthesis cleaning, speaking, mastication and comfort, reduced laboratory time, and availability of saved data for future prosthesis reproduction.
In bilateral hemi-maxillectomy cases zygomatic implants can be a solution to the lack of maxillary bony support for prosthetic rehabilitation. Zygoma implant reconstruction of acquired maxillary defects is a safe, predictable, and cost-effective treatment modality. Disadvantages associated with prosthodontic rehabilitation include the need for periodic recalls and replacement, problems with prosthesis retention, and the sense that the prosthesis is not a “natural” part of one’s body.
Mucormycosis management by mid face reconstruction:
Midface reconstruction after resection due to mucormycosis extends to the regions from the orbit to the alveolar bone, involves the nasal bone medially and may be unilateral and bilateral. Smaller defects involve only the alveolar ridge and can be corrected using ridge form plates and bone grafting. Massive defects require a combination of procedures such as osteocutaneous flaps and patient specific implants.
Computer-assisted 3D modelling and virtual surgical planning helps to understand the anatomy, osteotomy of the donor and recipient sites, and planning of patient-specific implants, all of which aid in the precise placement of the bone graft in the best position for dental rehabilitation.
The orbital wall reconstruction is made by mirroring data from the normal side. 3D printed models are used as a template to pre-surgically adapt a titanium mesh or plate to fit exactly into the orbital wall defects, reducing surgical time. Stereolithographic models created from CT scans of patients are used to reshape a sheet of titanium in order to create patient-specific implants for reconstruction of the orbital floor.
The CT scan data is used to generate a CAD design for the implant, and orbital implants are machined in bio ceramic material. An extensive maxillary resection extending from the orbital floor to the alveolus is treated using a combination of CT scan data, virtual surgical planning, patient specific titanium implants, and flap reconstruction.
The virtual surgical planning also determines the placement of Dental implants. For defect correction, the defective region is imaged and data from the opposite side is mirrored with reference to the mid sagittal plane. The scapula is used as the donor site, and virtual surgical planning is used to determine an optimal location for the graft that would fit the design of the alveolar reconstruction.
The titanium implant that supports the midfacial region is then created. Traditional plates and screws are used to secure the titanium implant and flap to the basal bone. The scapula flap is then positioned in the optimal location for dental implant placement. Later, as a secondary procedure, the dental implants are placed.
The process of making the implants and designing the scapula flap is an important part of the procedure, and the final success is dependent on placing the implant and graft in the predetermined 3dimensional location. Intraoperative navigation systems allow for precise placement.
Maxillomandibular impressions are taken with trial dentures and articulated to achieve precise dental implant implant placement to achieve exact occlusion, as well as guides for resection of fibula and dental implant placement. The guides are used for fibula resection and dental implant placement. Stable occlusion and good aesthetics are achieved postoperatively.