Regarding Botox or neurotoxin treatment to the chin area, treating the mentalis muscle is best for softening chin dimpling in animation. An overactive mentalis or mentalis strain is usually associated with oral incompetence or inability to close the mouth but can lead to deepening of chin crease. Filler can also be used to soften a prominent crease or provide more projection to the chin (without surgery) to improve facial aesthetics, but one of the more common problems I encounter after jawline or chin filler injection is poor placement or over treatment which can often result in a more masculine squared off shape to chin. Often the best solution for this is to dissolve the filler you have and then re-inject with more centralized/targeted filler injection to address your concerns.
My suggestion would be to reach out to the surgeon who performed the original procedure. There are many variations in the technique utilized for forehead reduction surgery. Based on photos it is difficult to postulate exactly what is causing your "depressions," but the surgeon who performed the initial surgery would be the best person to address this issue. They know exactly what hardware was used and how the bone was cut in your case therefore would be the best person to offer an appropriate treatment.
"Botox resistance" is a term used to describe a situation in which a person appears to have reduced responsiveness to the effects of Botox (Botulinum toxin) injections over time. This phenomenon can occur in some individuals but sometimes can be just a result of natural age-related changes such as loss of skin turgor and increased elasticity. Filler works via adding volume so there is no increased risk of "rejecting" filler if you have developed botox resistance, but overall there may be better solutions to address your concerns such as Laser or even surgery. I recommend you schedule a consultation with a board-certified plastic surgeon. Often injectors who are not appropriately trained do not have the appropriate knowledge base, training, or privileges to recommend or administer more advanced treatments for facial aging.
While it is unusual to have nerve damage after Botox or any neurotoxin injection, it is a very rare complication from injection. It is much more likely that the Botox has migrated to your Risorius or Zygomaticus major, as this is a more common cause of asymmetric smile after neurotoxin injection. There is a "zone of safety" well-described in the literature when injecting the masseter muscle but the product can migrate. Botox can take over 3 months to wear off, so I expect that any asymmetry to your smile will improve.
