Bone loss is quite common, frequent and is usually a result of either missing teeth or Peri-implantitis or advanced periodontitis.
Right in the first 12 months after a tooth loss, 25% of the bone loss has been reported and it continues to wear away with passage of time. In Normal situation, your jawbone is supported, strengthened and preserved due to presense of tooth. When the tooth s extracted, the pressure and biting forces are no longer transmitted to the bone around the tooth, as a result the bone resorbs.
In the case of periodontitis or peri-implantitis, the bacteria colonizing in your gums and mouth will gradually eat away your underlying jawbone that connects the tooth (or implant) to the bone.