A periodontal probe and recording apparatus for measuring the depth of a pocket formed by the gum (gingival tissue) surrounding a tooth. The periodontal probe and recording apparatus are comprised of a probe tip with a simplified spring tension device electrically connected via a transducer to the recording...http://www.google.com.tw/patents/US4791940?utm_source=gb-gplus-share專利 US4791940 - Electronic periodontal probe with a constant force applier
