To observe the buccal bone plate height and socket alteration with a buccal partial root in a tooth socket.

Four adult male Beagle dogs were used. Bilateral mandible the 2ⁿd to 4^th premolar distal roots were randomly divided into three groups, i.e., the group of blood filling (the root was extracted and the wound was sutured after blood filling) , the group of Bio-Oss Collagen (the root was extracted and the wound was filled with Bio-Oss Collagen and covered with Bio-Gide before suturing) and the group of buccal partial root combined with blood filling (the lingual partial root was removed while the buccal partial root was kept; the wound was sutured after blood filling) . CBCT analysis was carried out on the first day and 12^th week post operation. Vertical buccal bone plate alteration and osteogenesis effect in sockets were observed with the 12^th week CBCT images. Statistical analysis was carried out with SPSS 21.0 and the significance level was 0.05.

The buccal bone plate height in the group of blood filling reduced (1.63 ± 0.67) mm, while that of the group of Bio-Oss Collagen and the group of buccal partial root combined with blood filling was (0.77 ± 0.58) mm and (0.06 ± 0.10) mm, respectively. The vertical height alteration of buccal bone plate was much less in the group of Bio-Oss Collagen than the group of blood filling (Z=-2.205, P= 0.027) . So was the group of buccal partial root combined with blood filling compared with the group of blood filling (Z=-3.361, P= 0.001) and the group of buccal partial root combined with blood filling compared with the group of Bio-Oss Collagen (Z=-2.260, P= 0.024) . The sockets were comparatively empty in the group of blood filling. High density bone graft substitute was observed in the group of Bio-Oss Collagen. Cancellous bone was observed in the group of buccal partial root combined with blood filling.

A buccal partial root resided in the tooth socket seems have a better ability to maintain the height of the buccal bone plate than Bio-Oss Collagen. A buccal partial root may accelerate new bone formation and be in favor of tooth socket healing.