The mandible helps maintain facial symmetry and oral functions. Mandible defects, often a result of osteosarcoma, tobacco chewing or high-velocity impacts during human assaults and accidents, cause severe facial disfigurement, and impaired speech, mastication, swallowing and respiration (Lee et al., 2018). It is critical to expedite the mandible reconstruction to restore the oral functionality and facial form so that the remaining fragments can be retained in their original position, and the mandible can be stabilised (Schupp et al., 2007). In patients with comorbidities and/or poor socio-economic conditions, mandible defects are commonly bridged using commercially available standard implants (SI) (Koper et al., 2021; Wong et al., 2016); however, these implants lack anatomical conformity due to manual bending, accounting for micro-motion at the bone-implant interface, resulting in implant instability (Ramos et al., 2011). Moreover, repetitive preoperative or intraoperative bending of SI to match the patient's anatomy generates residual stresses in the notches/grooves (Wu et al., 2017), degrading its fatigue properties, causing implant fracture during cyclic mastication loading (Almansoori et al., 2020; Koper et al., 2021; Wong et al., 2016). In addition to bridging the gap, the implant must facilitate fixation stability during the bone-healing phase by bearing the mastication load (Wu et al., 2017). SI designs have multiple screw holes which not only make the implant more flexible, thereby inducing less strain in the bone at the anchoring sites, and ensuring a stable screw-bone interface, but also allow the surgeon to choose from multiple screw sites intraoperatively (Narra et al., 2014). However, the limited design of the SI with a predefined array of screw holes calls for unfavourable screw placement, causing uneven stress distribution in the screws resulting in bone or screw fracture (Kimura et al., 2006; Seebach et al., 2018).

In contrast, owing to the virtual reconstruction planning, custom implant (CI) offers better anatomical fit and defect-specific design (Kimura et al., 2006), making them biomechanically superior to SI (Gutwald et al., 2017; Lisiak-Myszke et al., 2020; Luo et al., 2017). However, CI often lack biomechanical analysis, resulting in overdesigned rigid implants that could cause stress-shielding or induce higher strain at the screw-bone interface, causing subsequent screw loosening (Koper et al., 2021; Narra et al., 2014). Previously, there have been instances of CI fractures wherein cracks originated from stress concentration regions while performing daily masticatory activities (Luo et al., 2017; Shi et al., 2021).

Studies reported that chances of implant fracture were higher when they were used standalone without a bone graft (Gutwald et al., 2017; Seol et al., 2014; Shibahara et al., 2002). In some cases, reconstruction without bone grafting led to bone resorption around the fixation screws, resulting in implant instability (Yi et al., 1999). Vascularised free flap technique is considered the gold standard owing to its ability to heal regardless of the condition of the recipient bed (Kumar et al., 2016; Wong et al., 2016). The fibula-free flap has traditionally been a popular choice for mandible reconstruction because of the sufficient width, thickness and volume offered by the fibular graft for the reconstructed mandible to be able to withstand mastication loads throughout a lifetime (Akashi et al., 2019). However, this technique is not suitable for patients with comorbidities, poor skin quality and previous lower limb trauma, or those who have undergone, or are scheduled for, radiation treatment (Kakarala et al., 2018; Koper et al., 2021; Zyl and Fagan, 2017).

The aim of this study was to computationally compare the importance of fibular grafts against implant customization by designing a novel implant, which combined the pros of a SI and a CI in terms of form factor and anatomical conformity, respectively, and comparing it with the SI and CI for mandibular reconstruction, in the absence and presence of a fibular graft, for implant failure during mastication tasks. It was hypothesised that reconstruction with the newly proposed implant would result in a lower probability of implant fracture and screw loosening, ensuring better implant life and stability.