**5. Implant selection**

The surgeon must be able to make a decision regarding the selection of an implant based on chemical composition, physical structure, and planned site for application. Characteristics of an ideal implant include biocompatibility, chemical inertness, lack of elicitation of foreign body or hypersensitivity reaction, non-carcinogenicity, and ease of shaping and carving [42].

Common implant materials include expanded PTFE, methyl methacrylate, porous polyethy‐ lene, and silicone rubber. Porous polyethylene and silicone rubber implants are the most commonly used. Silicone rubber implants can be easily trimmed, being flexible, conform well to underlying anatomy and become well encapsulated. They can be easily be removed or replaced if necessary.

The structure of porous polyethylene implants allows better tissue integration, but this can also be extremely problematic when attempting to remove or replace an implant. Significant tissue injury, defects or implant fragmentation can occur with removal.

Most patients, as they age, lose volume in the submalar region. The submalar area includes the hollow area of the infraorbital, anterolateral maxillary region, and canine fossa regions. Most of these patients have a hollow submalar region. They usually have adequate and welldefined zygomatico-malar esthetics and adequately projected cheekbones. These patients are best treated with only submalar augmentation, as their problem is loss of submalar volume.

The second type of common facial esthetic deficiency found is in patients who have adequate submalar and anterior maxillary projection but deficient cheekbones and hypoplasia of the zygomatico-malar regions. These patients are best treated with a malar implant.

The third type of common midfacial aging change is seen in a patient who has submalar deficiency in addition to need of more zygomatico-malar augmentation. These patients need both submalar and malar augmentation. These patients are well treated with the combined submalar shell implant. This implant is designed to augment the submalar region as well as a portion of the zygomatico-malar region.

Careful examination and thorough analysis aid in coming to a decision about what size of implant to use to achieve the desired effect [43]. Clinical photography serves as a powerful tool. A similar approach is applied to the chin and prejowl complex. This approach helps determine what type of implant to use.

Fewer surface imperfections allow greater resilience against degradation by mechanical forces [44]. This advantage must be balanced with the increased possibility of migration as compared with porous implants. The implant should not create a severe immune response, one that may harm the host or damage the implant. Synthetic implants stimulate inflammatory response with acute and chronic phases [45]. Significant immunogenicity can result in degradation or rejection of the implant. Bacteria are capable of implant invasion when pore size decreases. Implants with pore sizes between 1 and 50 microns may be more susceptible to infection than materials with larger pores, because they do not permit tissue granulation and delivery of host inflammatory cells to mount an adequate immune response.
