Dent in my forehead, would it's appearance be improved by a filler or Botox? (photo)

From your photos the dent appears to be an anatomical concern and not to do with your glabellar muscles. Botox can actually make indentations and contours more prominent, so I would advise against the use of Botox. Filler would be your best option. Ensure you visit a highly skilled and board certified practitioner who has extensive experience in this technique. I believe you could also benefit from a combination of chemical peels and laser to improve the texture of the skin and encourage collagen production to fill out indentations.

From your picture, it looks like the "dent" is in the middle of your forehead and does not extend into your glabellar area(area between your brows). I think a filler would be best to be used in this area. Botox is injected into muscles and used to temporarily improve lines in your forehead (and other places on your face) so I would not suggest using Botox for your contour defect. The price of fillers varies depending on how much one uses and which type of filler is used. You should definitely see a Plastic Surgeon for an evaluation of what filler is best for you. 
Best wishes, 
Dr. Suzette Miranda 

This can be improved with a combination of well-placed fillers, lasers and microneedling/prp. I recommend getting a consultation with a facial sculpting expert. Best, Dr. Emer

Thank you for your question ReeSherlock. Botox is a purified protein used to address wrinkles associated with
facial expression. It is difficult to make an assessment with only a still photograph. I observe my patients making facial expressions such as frowning and raising the brows to make an assessment. If the wrinkles change with expression then they are secondary to muscle contraction. These muscles can be relaxes with Botox. If there is no change with facial expression then Botox will not address the concern. Pricing varies from office to office. Please consult with a doctor for specific recommendations. Good luck!

Botox is typically used to smooth out wrinkles or relax the muscles. It may not be the best option for you. I've seen satisfactory results when fillers are used for cases like yours. Having dermal fillers injected in the dent will help smooth the area.

Filler is going to be the best product for filling in a dent. Figuring out which one would be best for your anatomy will require an in person assessment. Schedule a consultation with a board certified plastic surgeon to discuss. Cost will depend on the type of filler as well as the amount needed. 

The filler would need to be applied by a skilled injector who would do submission while injecting the product. I would think that sculptra could be used .The cost varies in different parts of  the country.Hope this helps,Dr Beverly Johnson