Brain activation patterns during unilateral premolar occlusion.

OBJECTIVE: To observe the characteristics of brain activation during unilateral premolar occlusion. METHODS: Functional magnetic resonance imaging was collected from 10 healthy volunteers during occlusion of the left first premolar (L1), left second premolar (L2), and right first premolar (R1). The brain activation patterns were analyzed, and the primary sensorimotor cortex, supplementary motor area, insula, thalamus, and prefrontal cortex were chosen as regions of interest. RESULTS: Single premolar occlusion activated the precentral gyrus, postcentral gyrus, cerebellum, thalamus, frontal lobe, hippocampus, cingulate gyrus, and parietal lobe. The brain areas showing activation during single premolar occlusion were similar to those activated by chewing. The activation pattern of L1 was more similar to that of L2 than R1. No significant left and right hemisphere differences in signal intensity were detected within the regions of interest. CONCLUSION: Brain activation patterns from two ipsilateral premolars were more similar than the pattern from a contralateral premolar.

[Three-dimensional finite element analysis of effect of root canal taper and post on tooth stress distribution].

OBJECTIVE: To evaluate the effect of root canal taper and post on tooth stress distribution. METHODS: 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. RESULTS: 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. CONCLUSIONS: 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.

[Correlation of ornidazole concentration in saliva and serum of healthy volunteers].

OBJECTIVE: To investigate the distribution of ornidazole in the salivary and serum of healthy adults and explore the feasibility of monitoring serum drug concentration with salivary. METHODS: Six volunteers received a single dose of 0.6 g ornidazole via intravenous infusion. The concentrations of ornidazole in the saliva and serum were assayed by high-performance liquid chomatography, and the correlation of the drug concentrations in saliva to that in serum was analyzed. RESULTS: The concentration of ornidazole in the saliva was strongly associated with that in the serum (r = 0.825-0.969), and the ratio of saliva-to-serum concentration (S/P) of ornidazole was 0.99 ± 0.13. CONCLUSION: Detection of saliva ornidazole concentration is feasible for monitoring the therapeutic concentration of ornidazole.

[Influence of soft-start irradiation on polymerization shrinkage stress of universal hybrid composite resins].

OBJECTIVE: 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. METHODS: 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. RESULTS: 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). CONCLUSIONS: Using soft-start curing mold can reduce, to some extent, the polymerization shrinkage stress of universal hybrid composite resins.