Is a receding lower jaw by 3 cm or more considered a defect that permits the use of fillers for its correction Islamically?

It is not possible to definitively affirm or deny the presence of disfigurement in the case of the questioner, as the ruling on disfigurement has two extremes and a middle ground. The protrusion of the jaw may reach the extent of disfigurement or it may not. The common perception among people is the reference point for this; if it deviates from what most observers consider unsightly, then it is so, and if it does not deviate from what most of them consider as such, then it is not. If the ruling is unclear, then the extent of the individual's own distress is considered.