| OBJECTIVETo examine the relationship between the root resorption of maxillary central incisors and dubious risk factors by t - test, correlation and regression. The further aim was to determine which factors were clinically relevant in predicting the extent of EARR.METHOD1. Sample selection64 cases, which had already been finished correction, were selected from the files of Orthodontic Department, China Medical University. The cases were selected if the following criteria were fulfilled:(1)ach case had available pretreatment and posttreatment lateral cephalo-grams, panoramic radiograghs, study casts, and complete records, moreover the posttreatment panoramic radiographs were taken before removal of the fixed appliance.(2)he orthodontists participating this study had already been in practice for at least 5years.(3)ll subjects were more than 12years of age at the time of initial records.(4)ll subjects had no history of trauma, or endodontically treatment to the permanent maxillary central incisors either before or during treatment, and hadn' t previous orthodontic treatment. The subjects with impacted or supernumerary incisors were excluded.(5)11 subjects were treated with the edgewise 0.022 * 0.028 inch brackets.(6)11 subjects had good compliance.(7)he subjects with bruxism were excluded.2. Methods2.1 EARR measurementMeasurements were made on the pretreatment and posttreatment panoramic radiographs. The radiographs were coded at random and were scanned at * 10 magnification into a computer by someone, and were measured with photoshop 7.0 software by another one (accuracy to 0. 1mm). A long axis was drawn through the center of the incisal edge and root apex. A cementoenamel junction (CEJ) plane was drawn through the mesial and distal CEJs. Crown and root lengths were measured along the long axis as the distance from the incisal edge to the CEJ plane intersection and the CEJ plane intersection to the apex respectively. The occlusogingival distances of the bases (BL) of the bonded brackets in the maxillary central incisors were measured on the posttreatment panoramic radiographs, while the true distance of the base ( BL' ) was measured by vernier caliper ( accuracy to 0. 02mm). If it was assumed that the true dimension of the crown remains constant through time, the values of root resortion ( AR)were calculated by the foUowing formula: R = BL' * (C2 * TL1 - Cl * TL2)/BL * Cl. The root resorption values of the left and right central incisors in each arch were combined and averaged for statistical analysis.2. 2 case recordsThe characteristics recorded in the case for each patient included :(1)sex; (2) initial age; (3)treatment time; (4)whether the case was treated by the extraction of permanent teeth; (5)Angle' s class of malocclusion; (6)number of months with rectangular wires; (7)number of months with Class I elastics and all kinds of elastics between upper and lower arches.2.3 Examination of cephalogramsEach pretreatment lateral cephalogram was scanned into a computer at the true size, and was measured with the software of Cephalometric Master, which was designed by FYI company ( USA), and cooperated by Blue Pacific Ocean Company (Beijing). The following measurements of facial structure were taken: SNA (degrees) , APDI (degrees) , ODI (degrees) , Ul - SN (degrees) , OP -SN (degrees) , overbite (millimeters) and overjet (millimeters).To determine the horizontal ( Dx' ) and vertical ( Dy' ) movements of theapex of the maxillary central incisors from pretreatment to posttreatment, a method described by A. David Mirabella and Jon'Artun was used. The outline and trabecular pattern of the maxilla and the outlines of the pterygomaxillaru fissure and the key ridges were traced on the lateral cephalograms before treatment. The incisal edge ( UI1) and the long axis ( Ulaxisl) of the maxillary incisor also traced. The cephalometric tracing at the pretreament was superimposed on the corresponding cephalogram after treatment according to the "best anatomic fit... |
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