A female patient who smokes 2 packs per year AND takes estradiol experiences implant failure. What is the PRIMARY cause?

Smoking is the most significant modifiable risk factor for implant failure. Nicotine and carbon monoxide impair microvascular circulation, reduce oxygen delivery, inhibit osteoblast activity, and impair immune function — all of which compromise osseointegration. Smoking increases implant failure rates by 2–3× compared to non-smokers. Estradiol (estrogen) generally has a positive effect on bone density — it is used in postmenopausal women to prevent osteoporosis and is not a primary cause of implant failure.