Acceleration and deceleration of bone like crystal and bone formation of electrically polarized hydroxyapatite (HA) ceramics were demonstrated by in vitro and in vivo evaluations. The electrical polarizability and large induced surface charge of HA were proved by ther-mally stimulated current measurements (TSDC) . Cultured osteoblastic cells were found to be activated on the overgrown bone-like HA layers on the negatively charged surfaces while the cells directly placed on the positively charged surfaces were lower proliferated. The negatively charged HA surface exhibited the enhanced osteogenesis with direct bone contacting in early stage of rabbit tibial and femoral implantations. The positively charged surface resulted in a small amount of bone formation on the ceramic surface. On the contrary in the zone isolated by a fibrous layer, a large volume of bones newly formed. In orthopedic and dental fields, it is useful that the outstanding bone-formability in early stage on the negatively charged surface conducts more rigid initial fixation. The positive surface charges show the new bone conducting property affecting over a long distance and have the possibility of controlling osteogesis.

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A 7-month-old female miniature dachshund was referred for acute and progressive hindlimbs paresis. Survey radiographs of the thoracic vertebrae revealed a circumscribed calcified mass around the spinous processes at T2-T4. MR images of the lesion delineated severe spinal cord compression by the mass at T3. After the MRI examination, laryngeal paresis appeared and respiratory distress was progressed. As the cause of these clinical signs was suspected to be cord compression by this mass lesion, the mass was surgically removed. After the surgery, hindlimbs paresis and respiratory distress disappeared in several days. The excised mass was histologically diagnosed as osteochondroma.
At seven months after the surgery, the dog was normal on physical and neurological examinations.

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A 7-year-old spayed female cat was admitted because of persistent vomiting. The patient had a palpable mass in the abdominal cavity, and showed incomplete ileus in the jejunnum, Exploratory laparotomy was performed. The mass lesion was resected and end-to-end anastomosis was conducted. The resected mass was histologically diagnosed as adenocarcinoma. Five months after surgery, the cat was re-examined becaese of vomiting, anorexia and a palpable mass. Lung metastasis was observed on thoracic radiographs. On laparotomy, tumor recurrence at the anastomosis area in addition to peritonitis, ascites and metastatic lesions in the liver, spleen, urinary bladder and intestinal tract was observed. The patient survived for 169 days after the first surgery.

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