When upper teeth are removed, the maxillary sinus enlarges to push down into the space where the tooth was inside the bone [which is called pnuematization of the maxillary sinus]. As the bone heals, it leaves an atrophied maxillary bone ridge which is too small to support an implant [the artificial tooth root replacement]. If you want a dental implant in this area, we will need to regrow the bone where the sinus intruded into the maxillary ridge–which is called a sinus lift. The video shows the process–we are simply re-making the foundation of the dental implant. In summery of the sinus lift process: bolts under stress need firm material for support, dental implants need bone for the same reason.