Biomedical subjects

Dong-xu Liu

Publications and source records attributed to Dong-xu Liu.

5 recordsLinked to original sources

PubMed2004

[FEM study on displacement, position of rotation center and stress distribution of PDL under various loading force systems].

OBJECTIVE: To investigate the displacement, the position of rotation center and the stress distribution of PDL under different loading force system (Moment/Force, M/F) by simulating clinical loading force system. METHODS: A three-dimensional finite element model of upper central incisor, which consists of 945 isoparametric elements and 1,245 nodes was developed. The displacement, the position of the rotation center and the stress distribution of PDL were analyzed under 13 types of loading force system. RESULTS: 1. Different force system led to different types of tooth movement. When M/F= -9.15:1, -10.30 - -10.50:1 and -10.90:1, it brought the result of controlled tipping movement, the bodily movement and the root movement; 2. The graph of the center rotation was a hyperbolic asymptotic line: Mx/Fy = -10.50 (horizontal axis) and L = 6.75 (vertical axis). Moreover, a little change of M/F between -9.15 and -10.90 led to apparent change of the position of rotation center. 3. The maximum strain and stress during the tipping movement were 1.47 x 10(-2) MPa and -2.81 x 10(-2) MPa, and during the bodily movement the results were 1.10 x 10(-2) MPa and -1.86 x 10(-2) MPa, while during the root movement were 0.96 x 10(-2) MPa and -2.58 x 10(-2) MPa. CONCLUSION: 1 . Different force system (M/F) leads to different types of tooth movement. 2. It is necessary to adjust the force system accurately to obtain prescient tooth movement, especially when M/F changes between -9.15:1 and -10.90:1. 3. This study suggested that the tooth movement style and the force system (M/F) should be controlled to protect the periodontal tissue.

Dental Stress Analysis↗

PubMed2003

[Developing a straight wire bracket placement gauge].

OBJECTIVE: To develop a new straight wire bracket placement gauge, providing measurement instrument for it's accurate position. Methods The gauge was made of 3.0 mm x 6.0 mm stainless steel, after being curved in certain form, made by machine process and cleaned through removing tough and polishing. The bracket placement gauge is divided into three parts: the middle straight stem, the curve head and the measurement head. It was 146 mm long, the angle between straight stem and curve was 145 degrees,the angle between the curve and measurement head was 105 degrees.The measurement head was made of occlusion placement item and slot placement item. The occlusion placement item was 10 mm long and 2 mm thick. The slot placement item was 2 mm long and 0.4 mm thick. This suit of gauge had 7 pieces, the measurement scope was 2.5 mm-5.5 mm which reflected the different vertical distances from occlusion edge to the middle point of slot. RESULTS: This gauge can determine the vertical position of bracket. CONCLUSION: The gauge improve the accuracy with individual straight wire bracket position table.

Humans↗

PubMed2002

[Clinical results of skeletal class III malocclusion in 11 children aged from 10 to 14 years].

OBJECTIVE: The aim of this study is to investigate the clinical effects of combined protraction facemask and rapid maxillary expansion in the treatment of Class III malocclusion in 11 children aged from 10 to 14 years. METHODS: The observation group included 11 subjects in late mixed dentition or early permanent dentition, and the control group included 32 subjects in early mixed dentition. Protraction facemask and rapid maxillary expansion device was used and the mean treatment time was 6 months. Cephalometric radiographs were taken at the initiation of treatment (T1) and after 6 months of treatment (T2). In this way,(T2-T1) represented cephalometric changes after the treatment and cephalometric analysis based on a new basecranical reference system was used to compare the changes. RESULTS: All the subjects had the following changes: the maxilla moved forward,the mandible exhibited a downward and backward rotation and the forward growth was restricted. The overjet correction of the observation group was 5.3mm, 51% of the overjet correction was due to skeletal changes and 49% due to dental changes.9 cases obtained normal overjet and overbite and molar relationship. CONCLUSION: The combination of protraction facemask and rapid maxillary expansion is helpful to the correction of Class III malocclusion in children aged from 10 to 14 years. It can alleviate the degree of deformation,avoid surgery, and improve the relationship between hard and soft tissue.

English Abstract↗

PubMed2002

[Study of tooth movement under different loading force system by FEM].

OBJECTIVES: To investigate different type of tooth movement under different force systems by simulating clinical loading force systems. METHODS: Develop a three-dimensional finite element model of upper central incisor, which consists of 945 isoparametric elements, 1245 nodes. Analyse the types of tooth movement under different force system with a horizontal force of 1 N being applied at the upper central incisor. RESULTS: Different force systems(M/F) lead to different types of tooth movement. This study showed the relation between them. When M/F =-9.15:1,it bringed the result of the controlled tipping movement, When M/F=-10.30 -10.50:1, it bringed the bodily movement; While M/F=-10.90:1, it lead to the root movement. CONCLUSION: This study suggested that it is necessary to adopt different loading force systems in order ot obtain determined tooth movement.

English Abstract↗

PubMed2002

[Periodontal status of mandibular incisors after pronounced orthodontic advancement during adolescence].

OBJECTIVE: To analyze whether pronounced orthodontic advancement of the mandibular incisors during Class II correction in the mixed dentition results in gingival recession. METHODS: Through mandibular superimposition of the pretreatment and posttreatment cephalograms of 67 Class II patients who were treated, 45 patients with a minimum of a 1-mm advancement of the CEJ and a minimum of a 2-mm advancement of the IE were identified.Using the same protocol in Class II patients,30 individuals who finished treatment at a similar time and age,but with no advancement of the CEJ and a maximum of 1-mm advancement of the IE were identified. A total of 30 patients with pronounced advancement and 21 patients with no advancement could meet for a follow-up examination with a mean period of 7.83 years and 9.38 years after treatment, respectively. Through measuring cephalograms,study models,as well as clinical examinations to analyze the periodontal status of mandibular incisors. RESULTS: Clinical examinations at the time of follow-up revealed no differences in the amount of recession,the width of attached gingiva,the length of supracrestal connective tissue attachment,the probing pocket depth, gingival bleeding index or visible plaque index of the mandibular incisors between the patients in the 2 groups. No differences in the number of mandibular incisors that developed recession from T1 to T2 and from T2 to T3.The increase of mandibular incisor crown height demonstrated no difference from T2 to T3 between the patients in the 2 groups. CONCLUSION: Pronounced advancement of the mandibular incisors may be performed in adolescent patients with dentoalveolar retrusion without increasing the risk of recession.

English Abstract↗