[Application of Low Dose Spiral CT in Diagnosing Impacted Teeth in Children and Adolescents].

UNLABELLED: [ABSTRACT] OBJECTIVE: To determine the value of low dose spiral CT scanning in diagnosing impacted teeth of children and adolescents. METHODS: A total of 153 children and adolescents with confirmed impacted teeth in West China Second University Hospital, Sichuan University were enrolled in this study. They were divided into 5 groups according to the different spiral CT scan parameters (tube current time product, scanning thickness and collimation value): Group A (n=30, 330 mAs, 6 X 0. 75 mm and 3. 0 mm), Group B (n=30, 140 mAs, 6 X 0. 75 mm and 3. 0 mm), Group C (n=30, 80 mAs, 6 X 0. 75 mm and 3. 0 mm), Group D (n=31, 80 mAs, 6 X 1. 50 mm and 5. 0 mm), and Group E (n=32, 50 mAs, 6 X 1. 50 mm and 5. 0 mm). There were no significant differences in general clinical features (P>0. 05) among the participants of the five groups. The phantoms were used to measure spatial resolution and contrast resolution of the scan images. Dose length product (DLP) was recorded during CT scanning for calculating effective dose (ED) of exposure. The quality of images was evaluated using a list of quality scoring criteria. RESULTS: (1) Under 330, 140, 80, 80 and 50 mAs, the images had a spatial resolution of 1.0 mm, with contrast resolution of 2. 0, 3. 0, 4. 5, 4. 5 and 6. 0 mm, respectively. (2) Significant differences in ED values were found among the five groups (F=1 064. 119, P=0. 000) and between every two of those groups (P<0. 05). Group E had the lowest ED (0. 19 mSv), 86. 52%, 67. 24%, 45. 71%, and 38. 71% lower than that in Group A, B, C and D, respectively (P<0. 05). (3) All of the five groups obtained an image quality score above 3, and no statistical differences appeared among the 5 groupl (F=1. 978, P>0. 05). The diagnostic results of the spiral CT were consistent with those of orthodontic surgery. CONCLUSION: Low dose spiral CT scanning can meet the image quality requirements for diagnosing impacted teeth, minimizing radiation exposure effectively.

[Influence of different designs of marginal preparation on stress distribution in the mandibular premolar restored with endocrown].

OBJECTIVE: To evaluate the effect of different designs of marginal preparation on stress distribution in the mandibular premolar restored with endocrown using three-dimensional finite element method. METHODS: Four models with different designs of marginal preparation, including the flat margin, 90° shoulder, 135° shoulder and chamfer shoulder, were established to imitate mandibular first premolar restored with endocrown. A load of 100 N was applied to the intersection of the long axis and the occlusal surface, either parallel or with an angle of 45° to the long axis of the tooth. The maximum values of Von Mises stress and the stress distribution around the cervical region of the abutment and the endocrown with different designs of marginal preparation were analyzed. RESULTS: The load parallel to the long axis of the tooth caused obvious stress concentration in the lingual portions of both the cervical region of the tooth tissue and the restoration. The stress distribution characteristics on the cervical region of the models with a flat margin and a 90° shoulder were more uniform than those in the models with a 135° shoulder and chamfer shoulder. Loading at 45° to the long axis caused stress concentration mainly on the buccal portion of the cervical region, and the model with a flat margin showed the most favorable stress distribution patterns with a greater maximum Von Mises stress under this circumstance than that with a parallel loading. Irrespective of the loading direction, the stress value was the lowest in the flat margin model, where the stress value in the cervical region of the endocrown was greater than that in the counterpart of the tooth tissue. The stress level on the enamel was higher than that on the dentin nearby in the flat margin model. CONCLUSIONS: From the stress distribution point of view, endocrowns with flat margin followed by a 90° shoulder are recommended.

[Tissue engineered tympanic membrane repairment materials with adipose-derived stem cells].

OBJECTIVE: To explore the morphology, proliferative activity and adhesion of adipose-derived stem cells (ASC) seeded in the polylactic-co-glycolic acid (PLGA) scaffold, and to provide experimental data for fabricating tissue engineered tympanic membrane repairment materials. METHODS: Wistar rats were selected, and the ASC were isolated and co-cultured with the PLGA scaffold. The morphology and proliferative activity of ASC in the scaffold were examined by immunofluorescence of Vimentin and Ki67 respectively. All the immunofluorescence signals were analyzed by a confocal laser scan microscopy system FLUOVIEW FV1000. The adhesion of ASC to the PLGA scalfold was determined by scanning electron microscopy. RESULTS: Immunofluorescence of vimentin showed rats ASC displayed normal morphology and grew orderly in the PLGA scalfold. Immunofluorescence of Ki67 showed the normal active proliferation of ASC in the scaffolds. The Ki67 mean positive index (x(-) ± s) of the ASC in the scalfold was (8.21 ± 1.76)%, while in control group (cultured without PLGA scalfold) was (9.06 ± 1.95)%. There was no statistic significance between the two groups (t = 1.03, P = 0.30). Scanning electron microscopy demonstrated ASC adhered well to the PLGA scalfold, the pseudopodia of ASC could also be observed and the proliferative cell conjunction was tight. CONCLUSION: ASC has good biocompatible to the PLGA scaffold and could normally adhere and proliferate in PLGA scaffold.