Three-dimensional finite element analysis of effect of root canal taper and post on tooth stress distribution / 中华口腔医学杂志

<p><b>OBJECTIVE</b>To evaluate the effect of root canal taper and post on tooth stress distribution.</p><p><b>METHODS</b>Three-dimensional finite element models of human mandibular first molar with root canals prepared with 35# K file, ProTaper and Profile were established. The tooth were restored with fiber-resin, stainless steel and silver amalgam posts respectively. A vertical load on tooth occlusal surface was simulated. Marc software was used to analyze and calculate the stress distributions in the tooth restored with three kinds of different root canal posts, especially the in the cervical part and root.</p><p><b>RESULTS</b>Different tapered root canals had no obvious influence on stress distribution in all three different posts. Stress distribution of stainless steel post located at the cervical and middle part of distal root, the highest Von-Mises stress was about 45 MPa. Stress distribution of silver amalgam post located at the orifice of root canal and pulp fundus, the highest Von-Mises stress was about 16 MPa. Stress distribution of fiber-resin post had no obvious stress concentration.</p><p><b>CONCLUSIONS</b>Fiber-resin post is the most ideal root canal post. Stainless steel post causes remarkable stress concentration in the root, which may raise the possibility of root fracture.</p>

Survey of root canal curvature of anterior teeth from Chuang population / 华西口腔医学杂志

<p><b>OBJECTIVE</b>To investigate the root canal curvature of permanent anterior teeth from Chuang population.</p><p><b>METHODS</b>245 anterior teeth from Chuang population were collected and examined by X-ray radiography both from labiolingual and mesiodistal directions. For 218 type I anterior teeth, degree of root canal curvature, radius of curvature and length of the curved part of root canal were measured by a special electronic vernier caliper according to Schneider's and Schäfer's method and the data obtained were analyzed.</p><p><b>RESULTS</b>Root canals of anterior teeth from Chuang population were mainly of type I. The number of type II, III, IV were about 13 in mandibular central and 12 in mandibular lateral incisors. The incidence of curvature in maxillary central incisors, lateral incisors, canines and mandibular central incisors, lateral incisors, canines were 40%, 80%, 77%, 65%, 66%, 73% in mesiodistal directions, 62%, 69%, 70%, 62%, 41%, 61% in labiolingual directions respectively. The most curvature was moderate and happened in apical third. The heaviest curvature occurred in maxillary canines in mesiodistal direction and mandibular canines in labiolingual direction. The shortest radius and length of curvature occurred in maxillary lateral incisors.</p><p><b>CONCLUSION</b>Root canal curvature of anterior tooth in Guangxi Chuang population is complex. The incidence of type II, III, IV is high in mandibular incisors.</p>

Root canal treatment of mandibular first premolar with 3 root canals: a case / 华西口腔医学杂志

The occurrence of three canals in mandibular premolars is very rare. This article reported and discussed the treatment of a mandibular first premolar with 3 root canals, specially in aspect of root-detecting and root-shaping.

Effect of composite restoration on the reinforcement of teeth / 中华口腔医学杂志

<p><b>OBJECTIVE</b>To determine the effect of composite restoration on reinforcement of weakened tooth structure and the possible mechanism.</p><p><b>METHODS</b>Sixty freshly extracted non-carious maxillary premolars were collected and divided into 6 groups with 10 specimen in each group. MOD cavities (buccolingual width: 2.8 to 3.2 mm; palatal cusp width: 2.0 mm; cusp height: 5.0 mm) were prepared individually. Group 1 was prepared and not restored (control). The other 5 groups were restored with silver amalgam alloy (group 2), Z250 without bonding (group 3), F2000 (group 4), Z250 (group 5) and Z350 nanocomposite (group 6) (3M ESPE) respectively. The fracture resistance of the tested teeth was determined by applying a vertical splitting load through a specially shaped steel rod at a crosshead speed of 1 mm/min. The data were analyzed by ANOVA.</p><p><b>RESULTS</b>The average fracture resistance of the 6 groups was: (245.29 +/- 39.49) N (group 1), (255.09 +/- 42.14) N (group 2), (267.34 +/- 31.56) N (group 3), (293.90 +/- 33.42) N (group 4), (337.81 +/- 32.63) N (group 5) and (349.08 +/- 32.93) N (group 6). There was no significant difference between the group 1, group 2 and group 3. The fracture resistance of group 4, group 5 and group 6 was higher than that of group 1 and group 2 (P < 0.05). Significant difference was noted between group 5 and group 3 (P < 0.01). The fracture resistance of group 4 was much lower than that of group 5 and group 6 (P < 0.01). No significant difference was found between group 5 and group 6.</p><p><b>CONCLUSIONS</b>The use of composite increased the fracture resistance of the tooth with an MOD restoration. This effect was related to the adhesive force, polymerization shrinkage stress and the elastic modulus of the composite.</p>

Influence of soft-start irradiation on polymerization shrinkage stress of universal hybrid composite resins / 中华口腔医学杂志

<p><b>OBJECTIVE</b>To compare the difference between soft-start curing mode and standard curing mode in polymerization shrinkage stress of universal hybrid composite resins and to study effect of the soft-start curing mode on the decrease of shrinkage stress.</p><p><b>METHODS</b>Three universal hybrid resins (A: Charisma, B: TPH Spectrum, and C: Esthet-X) were respectively filled in cavities (4 mm in diameter) of epoxide resin disks, 16 specimens of each. Off them, eight of the specimens for each composite resin were exposed using soft-start mode and the other eight using standard mode. Polymerization contraction stress was calculated during 48 h after curing with photo-elastic stress analysis.</p><p><b>RESULTS</b>Three composite resins cured with soft-start mode showed the same trend of shrinkage stress changing as that with standard curing mode and values of polymerization shrinkage stress at 24 h after curing were (3.80 +/- 0.31) MPa, (3.21 +/- 0.40) MPa, and (2.84 +/- 0.22) MPa respectively for A, B and C composite resins. The corresponding figures for the composites with standard curing mode were (4.19 +/- 0.24) MPa, (3.69 +/- 0.33) MPa, and (3.14 +/- 0.28) MPa. Three composite resins cured with soft-start mode had significantly lower polymerization shrinkage stress compared with standard curing mode at 24 h after curing (P < 0.05).</p><p><b>CONCLUSIONS</b>Using soft-start curing mold can reduce, to some extent, the polymerization shrinkage stress of universal hybrid composite resins.</p>

Transcriptional regulation of dentin sialophosphoprotein by c-Jun/c-Fos / 华西口腔医学杂志

<p><b>OBJECTIVE</b>To investigate the role of c-Jun and c-Fos as transcriptional factors in regulation of dentin sialophosphoprotein (DSPP) gene by a promoter-luciferase reporter gene construct in odontoblast cell line MDPC-23.</p><p><b>METHODS</b>Endogenous c-Jun or c-Fos protein was determined by immunocytochemistry. The role of c-Jun or c-Fos in transcription of DSPP was investigated in co-transfection experiments using promoter-luciferase reporter gene construct containing the sequence between -791 bp and +54 bp of mouse DSPP gene.</p><p><b>RESULTS</b>c-Jun and c-Fos was expressed by MDPC-23 cells, and located in the nucleus of MDPC-23 cells. Overexpression of c-Jun or c-Fos significantly inhibited luciferase activity of DSPP promoter.</p><p><b>CONCLUSION</b>These findings suggest c-Jun and c-Fos down-regulated the transcription of DSPP gene as a transcriptional factor in odontoblast.</p>

Immortalized human odontoblast-like cell line expressed dentin extracellular matrix in vitro / 华西口腔医学杂志

<p><b>OBJECTIVE</b>To determine whether dentin matrix proteins were expressed by the human odontoblast-like cell line hTERT-hOd-1 in vitro.</p><p><b>METHODS</b>Collagen type I, bone sialoprotein (BSP), dentin matrix protein 1 (DMP1) and the marker for odontoblast, dentin sialophosphoprotein (DSPP) and dentin sialoprotein (DSP) were detected in these cells by immunohistochemistry, RT-PCR and in situ hybridization. During being cultured in mineralizing medium for 5 weeks, the secretion of OC and activity of ALP were measured once a week.</p><p><b>RESULTS</b>DSPP, DMP1, BSP and collagen type I were expressed in hTERT-hOd-1 either at mRNA or protein level. Under the induction of mineralizing medium, the cells showed higher activity of ALP and increased secretion of OC.</p><p><b>CONCLUSION</b>hTERT-hOd-1 expressed dentin extracellular matrix in vitro, which means the cell line has the potential of mineralization.</p>

Cloning and sequencing of the upstream of mouse dentin sialophosphoprotein promoter / 华西口腔医学杂志

<p><b>OBJECTIVE</b>To clone and sequence the upstream of mouse dentin sialophosphoprotein promoter.</p><p><b>METHODS</b>Genomic DNA was obtained from Balb/c mouse blood. The upstream of mouse dentin sialophosphoprotein promoter segments was obtained by PCR. Then the segments were inserted into T-vector. The plasmids were identified by digestion with the restriction enzyme analysis. The positive clone was sequenced and compared with Genebank.</p><p><b>RESULTS</b>The upstream of mouse dentin sialophosphoprotein promoter was divided into three sequences and three different target segments with 997 bp, 1004 bp and 674 bp in length were obtained. After identified, sequenced and compared with Genebank, the sequences of the segments were consistent with those displayed on Genebank by 99%.</p><p><b>CONCLUSION</b>The clone of the upstream of mouse dentin sialophosphoprotein promoter was successful. This work will help to study the regulation of DSPP expression.</p>

Bone morphogenetic protein-2-induced alpha 2 (I) collagen expression in odontoblastic MDPC-23 cells mediated by Smad proteins / 中华口腔医学杂志

<p><b>OBJECTIVE</b>To characterize the role of Smads proteins in alpha 2 (I) collagen (COL1A2) gene expression induced by bone morphogenetic protein-2 (BMP-2) in odontoblast cell line MDPC-23.</p><p><b>METHODS</b>Endogenous Smad protein expression was determined by immunocytochemistry. Smads function and their role in COL1A2 gene expression were investigated in cotransfection experiments using promoter-luciferase reporter gene construct.</p><p><b>RESULTS</b>MDPC-23 cells expressed Smad1, Smad5 and Smad6. BMP-2 promoted the activation of COL1A2 promoter reporter construct. Transient overexpression of Smad1 or Smad5 was enhanced, while overexpression of Smad6 inhibited BMP-2-induced COL1A2 promoter activity. BMP-2 inducibility could be blocked by overexpression of Smad1 or Smad5 dominant negative mutant.</p><p><b>CONCLUSIONS</b>Smad signaling is functioning and appears to be involved in BMP-2-induced COL1A2 collagen transcription in MDPC-23. Smad signaling may play an important role in odontoblast differentiation and dentin extracellular matrix formation mediated by BMP-2.</p>