In our own experience, lyophilized cartilage's biocompatibility is a foremost attribute, facilitating integration with the host tissue without eliciting notable adverse immunological responses. The preservation technique, which involves freezing and dehydration, retains the native extracellular matrix structure of the cartilage. This ensures that the graft, once rehydrated and implanted, can readily assimilate with surrounding tissues, paving the way for optimal healing and integration.

A notable characteristic of lyophilized cartilage is its surgical adaptability. The material can be sculpted intraoperatively, allowing for tailored grafting solutions specific to the patient's anatomical requirements, thus optimizing both aesthetic and functional outcomes. Therefore, it is our surgeons experience, that this material is for example a very beneficial material for zygomatic bone augmentation for patients with central and lateral midface hypoplasia (i.e., after large advancements of the upper jaw in the LeFort-I level or of the midface in the LeFort-II level).

Furthermore, the use of lyophilized cartilage diminishes donor site morbidity concerns, as it obviates the need for autologous cartilage harvest, a procedure which can introduce additional complications and patient discomfort.

In the realm of tissue preservation, the lyophilization process effectively reduces the graft's antigenicity while preserving its biomechanical and biochemical properties. This ensures that the grafted material incites minimal inflammatory or foreign body reactions in the recipient site.

Generally, we use lyophilized cartilage for zygomatic bone augmentation, especially if the forward displacement of the upper jaw is greater and harmonization of the midface is necessary as a result. In this case, we can cut lyophilized cartilage to size intraoperatively and insert it into a tissue cavity prepared to accommodate the desired volume.

The procedure begins with infiltration of the oral vestibulum using 1% lidocaine with epinephrine. An incision is made in the vestibular mucosa (bilaterally in isolated augmentation cases) and dissection is carried down to the zygomaticoalveolar crest. A subperiosteal dissection is performed, creating a pocket that accommodates the desired cartilage volume and patient-specific augmentation needs. It is important to not overdissect the pocket. Based on preoperative planning and discussion with the patient, the lyocartilage is cut into the desired shape intraoperatively, and consecutively introduced into the subperiosteal pocket. After confirming the desired effect on the facial contour, the cartilage is fixed to the overlying soft tissues using absorbable sutures (3–0 vicryl). A layered closure is then performed.

Silicone implants are ubiquitously used with good biocompatibility and are one of the most commonly used material for facial implantology (36). Silicone polymers can behave differently based on their degree of total number of chains and complexity of crosslinkage (degree of polymerization and cross-linkage). Vulcanization is the methods that allows creation of longer-chain highly crosslinked silicone polymers that increases the viscosity. Silicone can thus be prepared as a solid, gel or be used in liquid formulation depending on the chemical properties. The material is typically incapsulated by a fibrous membrane over time and is not incorporated into the host. This makes removal simple, however can lead to seroma formation, unwanted shift of the implant, extrusion, poor aesthetic results and thus may require removal (36). These features, however, make silicone implants ideal for breast reconstruction.

Common complications related to the use of silicone for facial augmentation is the possibility of migration, bony resorption, visibility of soft tissue capsule. In a review, silicone for augmentation of malar, chin and mandible contour was associated with a 5% complication rate (2.2% infection) and bone resorption occurred in 55% of patients (2). Reoperation with removal was necessary in about 4.1% of patients. In a larger meta-analysis including 443 patients (all facial areas), infection rate was low at 1.6% with overall low complication rates. Poor cosmetic outcome was the lowest (compared to other commonly used materials such as Medpor) at 2.7% (34). Rubin and Yaremchuk reported that silicone implants had one of the highest rates of removal due to implant related complications (11.7% compared to 0.5% of porous polyethylene and 1.3% of hydroxyapatite) (4).

Polyethylene is another common polymer used in facial implantology. Based on composition, polyethylene polymers can have a wide range of consistencies and mechanical durability.

In contrast to silicone implants, polyethylene implants such as MedPor are porous implants (100–150 µm pore size) that support ingrowth of tissue by the host and thus less likely to be incapsulated but rather incorporated (40). Porous polyethylene implants can be modified intraoperatively to achieve the desired results for a patient and are typically screw fixated. Removal of porous implants such as MedPor is much more difficult compared to silicone implants due to the ingrowth of the hosts connective tissue. In case of MedPor for microtia repair this is a desired feature (41). Medpor complications for similar location as silicone implants (malar, chin, mandible) was only 0.7% infections, 5% need for removal or reoperation and a rate of 3.9% for undesired prominence (vs. only 1.4% for silicone implants). In a larger meta-analysis including all areas of the face, infection rate was found to be about 1.2%. Poor cosmetic outcome was noted in about 5% (34).

Polyether-ether-ketone (PEEK) is another polymer that is commonly employed for cranial vault reconstruction, spine surgery and facial augmentation due to its inherent high mechanical strength, low interference with CT/MRI imaging modalities (radiographically translucent) and excellent biocompatibility. Custom made PEEK implants have been used with high success rates in cranial vault reconstruction, with overall low complication rates (42). In small sample cohort study, it was shown that custom made PEEK onlay implants can become osseointegrated over time (bone formation around the implant) (24). Studies indicate that titanium covered PEEK implants have even better osseointegrative properties in preclinical studies (43). In another study, custom made PEEK implants were used for augmentation of various defects. The reported infection rate was 8% which is slightly higher compared to other materials as described above (44). This is likely related to the tendency of PEEK implants to favor biofilm formation/bacterial adhesion compared to other implant materials (38). In a recent study, Sarfraz et al. compared the behavior of different bacterial strains (S. mutans, aureus, E. faecalis, E. coli) on Titanium and PEEK implants with either saliva contamination or without (38). The authors showed that (a) saliva coating of the implant material led to improved attachment of most bacteria to the material and (b) that PEEK allowed for better adhesion than titanium (38).

In our practice, PEEK implants coated with hydroxyapatite (intended to improve osseointegration and thus positional stability of the implant) are used with good success. Hydroxyapatite coating of PEEK implants was shown to have improved osseointegration and fixation of the implants (45). Other coating strategies include bioglass (calcium sodium phosphosilicate) and β-tricalcium phosphate (46).

PEEK's radiolucency stands out as a distinct advantage, ensuring transparency in radiological images. This permits a clear postoperative assessment, unmarred by the artifacts commonly associated with metallic implants. In the realm of biomechanics, PEEK's modulus of elasticity mirrors that of cortical bone. This similarity minimizes stress shielding between the implant and surrounding bone tissue, potentially fostering improved osseointegration and long-term stability.

A salient benefit of PEEK is its adaptability during surgery. Unlike many implant materials that are rigid in their form, PEEK allows for intraoperative modifications. This malleability ensures a precise fit tailored to the patient's specific anatomical nuances, paving the way for enhanced aesthetic and functional outcomes. From a tissue compatibility standpoint, PEEK implants have shown commendable biocompatibility in my practice, manifesting minimal inflammatory or foreign body reactions in surrounding tissue.

In conclusion, PEEK, with its unique properties and bolstered by clinical evidence, emerges as an excellent choice for craniofacial surgical applications. Its advantages in imaging, biomechanical compatibility, intraoperative adaptability, and tissue tolerance underscore its prominence as a preferred material in this domain.

An example of an acrylic material is poly-methylmethacrylate (PMMA) and it has been used in the setting of many craniofacial defect repairs including orbit, malar eminence and skull defects (4, 36). PMMA is radiolucent and does not interfere with standard imaging modalities. Similar to silicone, PPMA is non-absorbable and gets encapsulated and not incorporated by the host. The material is characterized by initially easy pliability after mixing the monomeric powder and liquid polymer. Over time the material hardens in an exothermic reaction into the desired shape and becomes a material with high mechanical resilience (40). PMMA has extensively been used for cranioplasty.

In a meta-analysis of facial implant materials, PMMA was found to have the highest relative rate of hematoma formation after implantation (6%). Infection was noted in approximately 3% of cases (34). However, due to difficulties re-shaping this material, the risk of plate fractures and infections as well as the lack of osseointegration, this material is not typically used for midfacial augmentation or reconstruction, especially in load bearing areas. Of note, for soft tissue augmentation substances such as Artecoll (PMMA-Microspheres) exist and can be used for correction of for example facial folds, augmentation of lip, chin and malar eminence (47).