Could Botox side effect be creating forehead dent and creases? (Photos)

I can't imagine any reason for a dent to be created in the middle of your forehad. I don't see muscle hypertrophy as a cause because when people have overcompensating from lateral forehead creating a Mr. Spock raised eyebrow we don't see muscle hypertrophy there.See your doctor to have an in person evaluation to ensure there is nothing else contributing to this.The information provided in Dr. Shelton's answer is for educational purposes only and is not intended to constitute medical advice.  The information provided should not be relied upon as a substitute for consultations with a qualified health professional who may be familiar with your individual medical needs. 

It’s very hard to see the dent you speak of, although there is a trace of some indentation which should not have anything to do with Botox injections.

Thank you for your question and for sharing your photographs plasticsurgery88. I understand your concern. Botox is a purified protein used to address wrinkles associated with facial expression. When injected into the skin Botox will relax the muscles and smoothen out the overlying wrinkles. The most common areas of treatment are in the upper face. These include the horizontal lines seen on the upper forehead when one raises the brows, the vertical lines seen between the brows when one frowns (frown lines), and the crow's feet seen around the eyes when one smiles.
It is difficult to make an assessment without a formal exam in the office where I can view the skin in multiple angles and observe wrinkles formed with facial expression. However, I hope the information provided here is useful.The appearance of frown lines is variable from person to person. Usually they are in a vertical orientation but sometimes they can be oblique and sometimes a horizontal line is seen across the upper portion of the nasal bridge. The most common variation is to have two parallel lines, hence the common term "11's" to describe them. But some people have one, three, or more lines. Some people also will see a bulge in the area when contracting the muscle. This bulge is smoothened out after a Botox treatment.
The pivotal studies used 20 units of Botox in the glabella area between the brow to address the frown lines. These studies demonstrated that the peak results are seen 14 days after the treatment and most people enjoy their results for 3-4 months. At that point, a maintenance treatment is recommended. While some people start to see results as early as the next day, it can take two weeks for full results so patience is important. We have our patients return two weeks after their treatment to assess their results via photographs. At that time additional units may be added if necessary. 
When patients present with concerns about specific wrinkles in the upper face such as the frown lines, I always assess and usually treat the other wrinkles in the upper face including the horizontal forehead wrinkles and crow’s feet. The reason is to maintain a harmonious and natural balance to the appearance of the upper face. The muscles in the glabella which are responsible for the formation of the frown lines serve to pull down on the inner brows when a person frowns. Similarly, the muscles around the eyes which are responsible for the formation of the crow’s feet seen when smiling (orbicularis oculi) are also responsible for pulling down on the brows, but in this case the outer brows. On the other hand, the muscle in the upper forehead which is responsible for the formation of the horizontal forehead wrinkles when a person raises the brows (frontalis) serves to pull the brows upward. If one of these muscles is relaxed with Botox and the others are not, the other muscles will still be active. This will lead to an unbalanced and unnatural appearance of the upper face where the brow can be elevated, depressed, or uneven in shape or position. Therefore, I recommend that my patients take a global approach to the upper face when receiving Botox treatments and treat all three of these areas. Sometimes bunny lines on the bridge of the nose are also treated.
If I had a patient with the concern described here I would say that it is difficult to see the dent in the photograph and that it does not have any relationship to the Botox. There are bony changes that occur over time and the dent seen may be secondary to that.With any injection, there are risks such as pain, bleeding, bruising, redness, swelling, tenderness, and infection. We take special precautions to minimize these risks such as using a painless technique. We also treat bruises with a laser as early as the next day. Bruises usually resolve within two weeks if untreated. After a laser treatment bruises usually resolve in 1-3 days, but may still take two weeks for full resolution. In addition to these risks, with Botox there is also a risk that the product spreads or diffuses to nearby structures. Spread to nearby muscles can lead to side effects such as the temporary appearance of droopy eyelids or a temporary asymmetric smile.

After a Botox treatment, I recommend that my patients avoid heat exposure, alcohol consumption, and strenuous exercise for 24 hours and not lie down flat for four hours. This is because all of these activities may possibly lead to the movement of the product and consequent side effects such as droopy eyelids. Although there have been no definitive studies shown that these actually occur and some physicians do not provide such aftercare instructions, in the absence of data I err on the side of caution and recommend that my patients avoid such activities.

Please consult with a doctor for specific recommendations. Good luck!