Obiective:This study aimed to explore the effects of different types of palatal lateral excisions on the growth and deveiopment of the maxilla and dental arch.and to investigate the underlying mechanisms.Methods:A total of 1123-week-old Sprague-Dawley(SD)male rats were randomly divided into a control and 3 experimental groups:the mucoperiosteal denudation group,the mucosal flap excision group,and the periosteum excision group.In the experimental groups,bilateral mucoperiosteal,mucosal flap and periosteum were excised respectively in the lateral one half of the palate.Four rats in each group were randomly chosen for sacrifice every two weeks.The maxilla was dissected following the excision.The widths of the maxilla and dental arch were measured and the histological phenomena were investigated at different phases.At the same time.12 animals in each group were sequentially injected with calcein every two weeks.Three animals in each group,whose fluorescent labeling was used,were sacrificed for investigating bone formation at Week 8 following injection.Results:(1)Each experimental group presented the constriction of the maxilla and dental arch.The upper first molars in the experimental groups inclined medially.The mucoperiosteal denudation group showed the largest degree of effect followed by the periosteum excision group.The indices of the mucosal flap excision group,which retained the structures of the periosteum layer,had the most approximate values to the control group;(2)Different histological changes among the experimental groups were detected.The fibers penetrated into the palatal bone asSharpeys fibers in the mucoperiosteal denudation group.The pattern of bone deposition was the bundle type.Sharpeys fiberswerenotfoundinthemucosaI flapandperiosteum excisiongroups andthedepositions ofpalatalbonewerethelamellartypeasthose in the control group;(3)The rates ofbone deposition in the experimental groups decreased compared with the control group.The rates in different phases were the most approximate values to those of the control group in the mucosal flap excision group,which has the same structure of periosteum as the control group.Conclusion:There were different effects on the growth and development of the maxilla and dental arch in different typos of palatal lateral excisions.Periosteum is important for bone formation and deposition pattem.The prevention of Sharpeys fibers forming and attaching to the palatine can effectively avert the following malformation.