Prevalence of dental erosion and associated drinks in 12-year-old population of Beijing / 中华口腔医学杂志

<p><b>OBJECTIVE</b>To investigate the prevalence of dental erosion and associated drinks in 12-year-old adolescence of Beijing.</p><p><b>METHODS</b>A random sample of 12-year-old adolescence of Beijing (n=844) was examined for dental erosion and required to fill a questionnaire of acidic drink intake. The grade criteria suitable for the survey of the dental erosion was used in the study.</p><p><b>RESULTS</b>The prevalence of dental erosion was 61.8%, of which mild enamel was 74.1%, severe enamel erosion 24.9% and dentine erosion 1.0%. Statistic analysis showed that a large amount of intake of carbonated drink or juice were risk factors.</p><p><b>CONCLUSIONS</b>Attention should be paid to the prevalence of dental erosion among Chinese adolescence.</p>

A three-dimensional finite element analysis of 0.02 taper 20# stainless steel K files during root canal instrumentation / 中华口腔医学杂志

<p><b>OBJECTIVE</b>To investigate the stress distribution of stainless steel K (SSK)files during root canal instrumentation.</p><p><b>METHODS</b>A three-dimensional finite element model was established and analyzed under curved and torsional conditions by ANSYS 9.0.</p><p><b>RESULTS</b>A finite element model of a 0.02 taper SSK 20# file was established. Under curved conditions, the stress was focused on the cutting edge when point contact occurred or the file was turned counterclockwise. The stress was focused between the cutting edges when line contact occurred or the files turned clockwise. The stress was much greater when the file contacted with the inner surface of the canal model by one point than by a line or when the file was engaged closer to the tip.</p><p><b>CONCLUSIONS</b>The max pulling stress was focused on the surface of the file which indicated the starting point of the fracture.</p>

Clinical effects of calcium hydroxide-based sealer on chronic apical periodontitis / 中华口腔医学杂志

<p><b>OBJECTIVE</b>To evaluate the results of calcium hydroxide-based sealer Sealapex in the treatment of chronic apical periodontitis.</p><p><b>METHODS</b>A total of 100 cases with chronic apical periodontitis were included and divided into two groups, calcium hydroxide sealer (Sealapex) group and ZOE sealer group, and Sealapex and ZOE sealer were respectively used. All cases were followed up for two years after treatment and the clinical results compared between the two groups. The evaluation was based on clinical examination and radiographic assessment using periapical index (PAI) and digital subtraction radiography (DSR) technique.</p><p><b>RESULTS</b>There was no significant difference between the ZOE group and Sealapex group in overall healing rates and mean quantitative analysis at 3 months and 2 years after treatment (P = 0.206, 0.776). A correlation was found between PAI and DSR (P < 0.01, gamma = 0.58).</p><p><b>CONCLUSIONS</b>Sealapex sealer could obtain satisfactory effects for the treatment of chronic apical periodontitis. The combination of DSR and PAI methods was able to monitor the radiographic bone changes of periapical disease.</p>

The correlation between the enlargement of root canal diameter and the fracture strength and the stress distribution of root / 中华口腔医学杂志

<p><b>OBJECTIVE</b>To investigate the correlation between the extent of cutting of the root canal wall and the root fracture strength and the stress distribution.</p><p><b>METHODS</b>Fifteen pairs of root sections were into 3 groups with canal wall thickness of 1.00 mm, 0.75 mm and 0.50 mm respectively. The maximum load was tested required for fracture for each group through fracture test in a universal testing machine, and compared with that for the original canal. The stress and its distribution of the root with normal wall thickness (1.2 mm) and roots with 75%, 50% and 25% respectively of the normal wall thickness were examined by three-dimensional finite analysis. The maximum Von Mises stress of the root of each model was calculated.</p><p><b>RESULTS</b>The mean fracture strengths of the groups with canal wall thickness of 1.00 mm, 0.75 mm and 0.50 mm were (4 432.41 +/- 563.59) N, (4 137.43 +/- 680.29) N and (3 749.87 +/- 554.17) N respectively. The maximum load of fracture resistance is a linear function of the root canal wall thickness (r = 0.972, P < 0.001). The three-dimensional finite analysis revealed that the enlargement of root canal diameter brought on increase of stress of root canal wall, and the stress and its distribution altered with further decrease of the wall thickness. The stress of lateral loading was greater than that of vertical loading.</p><p><b>CONCLUSIONS</b>The results suggests that clinical root canal treatment should be designated to remove just the infected tissue and avoid over-cutting of the hard tissue.</p>

Clinical effect of the restoration for pathological tooth wear / 中华口腔医学杂志

<p><b>OBJECTIVE</b>To investigate the effect of the restoration for pathological tooth wear.</p><p><b>METHODS</b>A total of 48 pathological weared premolars and molars with restorable space in occlusal surface in 10 patients were restored by composite resins. The patients' masticatory function (biting force, masticatory efficiency, the surface electromyographic (EMG) activity of masseter muscles and anterior temporalis) were compared before and after the treatment. At the same time, the restorations were evaluated according to the modified the United States Public Health Service (USPHS) criterion.</p><p><b>RESULTS</b>After the treatment, patients' clinical syndrome disappeared, the biting force was improved (P < 0.05) and the masticatory efficiency was increased significantly (P < 0.01). EMG activity, the asymmetry index and the action index of the tested muscles during different status had no significant change (P > 0.05). The composite resin restorations of the 48 teeth were all evaluated as A after three month and one year.</p><p><b>CONCLUSIONS</b>Restoring the pathological weared posterior teeth with composite resins is an effective treatment to relieve the patients' syndrome, improve their masticatory efficiency and biting force.</p>

Establishment of the three-dimensional finite element model of the first permanent mandibular molar and its stress analysis / 中华口腔医学杂志

<p><b>OBJECTIVE</b>To establish more rational three dimensional finite element model (FEM) of the first permanent mandibular molar and to study the internal stress distribution.</p><p><b>METHODS</b>The FEM was applied to analyze the stress distribution of the first permanent mandibular molar under various loading conditions.</p><p><b>RESULTS</b>Under all five loading conditions, the maximum von-Mises stress and compressive stress in enamel were larger than that in dentin, and the tensile stress in enamel was smaller than that in dentin. When vertical force and buccal-lingual oblique force were loaded, the stresses in the enamel and dentin were minimum; when lingual-buccal oblique force was loaded, the stresses were maximum; the stresses were mainly distributed at cervical region, furcation and apical area of the mesial-lingual root canal wall.</p><p><b>CONCLUSIONS</b>The stress value changes and stress distribution in the enamel and dentin were closely related with the direction of the occlusion force.</p>

Enamelin transcriptional expression in developing postnatal rat tooth germ / 中华口腔医学杂志

<p><b>OBJECTIVE</b>To observe the transcriptional expression of enamelin in developing postnatal rat first mandibular molar germs, for further studies of functions of enamelin in enamel development and mineralization.</p><p><b>METHODS</b>Tissue slices of first mandibular molar germ of rat 1, 3, 7, 10, 14 days after birth were prepared. The enamelin mRNA expression was identified by in situ hybridization.</p><p><b>RESULTS</b>Enamelin mRNA was observed in both ameloblast and odontoblast in 1-10 day old rat postnatal first mandibular molar germs. Enamelin mRNA appeared very weakly at 1st day, and increased through 3rd day, reached the maximum at 7th day, and reduced at 10th day and became negative at 14th day postnatally; while the expression of enamelin mRNA in odontoblast maintained lower from 1st to 10th day and negative at 14th day postnatally.</p><p><b>CONCLUSION</b>Enamelin gene transcriptional expression lasts from preameloblast to maturation ameloblast, which suggests that enamelin may participate in the development of enamel and mantle dentin.</p>

Preliminary study of tooth measured by a noncontact 3D image survey system / 中华口腔医学杂志

<p><b>OBJECTIVE</b>To perform the quantitative study of tooth occlusal surface wear by a noncontact 3D image survey system.</p><p><b>METHODS</b>Thirty-two old people's complete dental casts in five years which had normal occlusion were studied. The same way was used to determine the individual reference surface, and the range of the maxillary first molar occlusal surface was delimited by the unite regulation. Then the quantity of wear in five years and wear rate of maxillary first molar occlusal surface were measured by the noncontact 3D image survey system.</p><p><b>RESULTS</b>Wear of maxillary first molar occlusal surfaces was as follows: the mean height loss was 0.293 mm in five years and the mean wear rate was 0.059 mm/year; the mean volume loss was 97.881 mm(3) in five years and the mean wear rate was 19.576 mm(3)/year.</p><p><b>CONCLUSIONS</b>Under the necessary conditions, the noncontact 3D image survey system is an effective method to measure the wear of dental occlusal surface, but some set-up conditions need to be improved further.</p>

Two-dimensional finite element stress analysis of simulating restored teeth with wedge-shaped defects under loads / 中华口腔医学杂志

<p><b>OBJECTIVE</b>To study the concentration of stresses at the cervix with simulating restoration of tooth defects.</p><p><b>METHODS</b>A two-dimensional finite element model of a mandible first premolar with defect from longitudinal section was developed. The model was simulatedly restored, respectively by composite resin and glass ionomer cement, and then investigated stress variation in the cervical area.</p><p><b>RESULTS</b>In the restored models, both of materials improved the concentration of stresses at the cervical area. The composite resin and the glass ionomer cement restorations made the maximum principal stresses declined respectively to 36.2 MPa and 42.5 MPa, which were close to the value of normal tooth in the deepest area of defects.</p><p><b>CONCLUSION</b>The concentration of stresses are improved in the cervical area with teeth defects restored.</p>