OBJECTIVEThis study aimed to evaluate the effect of resin infiltration and fluoride solution on masking different demineralized white spot lesions by assessing color change.

METHODSArtificial white spot lesions were produced on 60 human molars. Each sample had at least two enamel surfaces opened (named A and B). The samples were randomly divided into groups 1, 2, and 3 according to their time of demineralization (24, 48, and 72 h). After demineralization, the A spot of each sample was treated by resin infiltration. The B spot was treated with 0.1% fluoride solution daily for 30 days. After the remineralization of the B spot, resin infiltration was used again on the B spot of each sample. Color assessment was performed by a spectrophotometer in five distinct stages: baseline, after the production of artificial caries, after resin infiltration of A spots, after 30 days of fluoride solution treatment of B spots, and after resin infiltration of remineralized B spots.

RESULTSBefore demineralization, the L* values of spots A and B in all groups were not significantly different (P > 0.05), whereas the L* values of spots A and B were significantly increased after demineralization. The L* values of A spots recovered significantly after treatment by resin infiltration (P<0.05), but only groups 1 and 2 reached the baseline. The L* values of B spots had no significant differences (P > 0.05) after fluoride treatment compared with that after demineralization. After resin infiltration on B spots, the L* values recovered but could not reach the baseline nor the level of A spots treated by resin infiltration only.

CONCLUSIONResin infiltration is a more effective treatment for masking white spot lesions than traditional fluoride treatment. The effect of masking white spot lesions has certain relationships with the degree of demineralization and activity of the lesion.

Enamel hypoplasia is a surface defect of the tooth crown caused by a disturbance of enamel matrix secretion.Enamel hypoplasia may be inherited,or result from illness,malnutrition,trauma,or high concentrations of fluorides or strontium in the drinking water or food.Different types of enamel hypoplasia have been distinguished,such as pit-type,plane-type,and linear enamel hypoplasia.Hypoplasia has been related to the intensity and duration of stress events,the number of affected ameloblasts,and their position along the forming tooth crown.Amelogenesis imperfecta(AI) is a heterogeneous group of inherited defects in dental enamel formation,most teeth are affected in both the primary and permanent dentition.The malformed enamel can be unusually thin,soft,rough and stained.The strict definition of AI includes only those cases where enamel defects occur in the absence of other symptoms.Currently,there are seven candidate genes for AI: amelogenin,enamelin,ameloblastin,tuftelin,distal-less homeobox 3,enamelysin,and kallikrein 4.Since the enamel is formed according to a strict chronological sequence,and once formed,undergoes no repair or regeneration.Then the analysis the phenotype of enamel hypoplasia can provide insights of the severity of inherited or environmental stress and the molecular mechanism during the period of enamel formation.

Objective: To evaluate shaping ability of nickel-titanium rotary instruments (Hero 642) in curved root canals. Methods:The computer assistant measure system of simulated root canal was used for quantitative analysis of root shape in eight simulated root canals during nickel-titanium rotary instruments (Hero 642) shaping process. Results:Nickel-titanium rotary instruments (Hero 642) could keep the curved angles in simulated canals very well. The cutting of Hero 642 in curved root canals was balanced and there was almost no transportation of canals central lines when the simulated canals were prepared to 0.02 taper 25~# and 30~# files. Conclusion:Nickel-titanium rotary instruments (Hero 642) has good shaping ability. In preparation of highly curved canals, the master apical file (MAF) may be Hero 642 0.02 taper 30# files.

Objective:To study the biological characteristics of new retrograde filling materials iRoot BP plus and iRoot FS.Methods:(1 )The roots were cut into 3 mm in length,and the root canals were pre-pared to 1 mm in diameter,followed by being filled with iRoot BP plus,iRoot FS,or mineral trioxide ag-gregate (MTA).The specimens were immersed in simulated body fluid (SBF).The ability of minerali-zation in vitro was detected through three studies.First,the mineralization of specimens was analyzed through scanning electron microscope observations and energy dispersive X-ray spectrometer.Then,the pH of SBF was monitored using pH meter.(2)The extracts were gained by immersing blocks of iRoot BP plus,iRoot FS,and MTA (8 mm diameter and 2 mm height)into dulbecco’s modified eagle medium (DMEM).The effects of the extracts on proliferation of MG63 cells were detected through MTT assay. The gene expression level of alkaline phosphatase (ALP)was analyzed by quantitative real-time PCR, and the expression of ALP activity was observed by ALP activity staining.Results:(1 )The formation of minerals could be observed on the surfaces of iRoot BP plus,iRoot FS,and MTA at the end of 24 h,and there were more amounts of apatite aggregated after 14 days.The values of Ca/P ratios of apatites were 1.43,1.39,and 1.51,respectively.(2)The pH of SBF could be raised to 8.09 ±0.07,7.91 ± 0.06,and 8.1 1 ±0.06,respectively,significantly higher than the blank.(3)The extracts of iRoot BP plus,iRoot FS,and MTA of dilutions of 1∶5 and 1∶10 presented no effect of proliferation of MG63 cells. (4)iRoot BP plus and iRoot FS could significantly up-regulated the levels of ALP messenger RNA ex-pression,while there was no obvious difference in ALP staining among the iRoot BP plus,iRoot FS, MTA,and the blank.Conclusion:The present study shows that iRoot has displayed good mineralization capability in vitro and capability to promote differentiation and mineralization of MG63 cells,inferring that iRoot may have good bioactivity.

Objective: To evaluate the adaptation of different materials for gingival layer in Class Ⅱrestorations using Micro-CT.Methods:Eighteen extracted human premolars were selected, and ClassⅡcavities were prepared.The teeth were randomly divided into six groups and restored using layering tech-nique.Six materials were used for gingival layer, including four injectable materials:Beautifil Flow Plus F00 (F00), Beautifil Flow F10 (F10), Filtek Z350 Flowable (Z350F), FujiⅡLC CAPSULE (Fuji), and two packable materials: BeautifilⅡ (BF), Filtek Z350 (Z350).The restored teeth were scanned with micro-CT and the images were 3D reconstructed to evaluate the volumes and the distribution of the voids on the restoration-tooth interface of the gingival layer.The volume of the voids were statistically analyzed using nonparametric Jonckheere-Terpstra tests.Results: The volumes ( mm3 ) of the voids on the restoration-tooth interface were: Z350F (0.000 15), F10 (0.000 39), F00 (0.012), Fuji (0.070), Z350 (0.16) and BF (0.20).There were significant differences between Z350F/F10 and Fuji/Z350/BF (P<0.05).Most of the voids were found on the point-line angles of the cavities.Con-clusion:The voids on the restoration-tooth interface were mainly on the point-line angles of the cavities. Injectable materials with high flowablility could reduce the restoration-tooth interface voids significantly when used for the gingival layer in ClassⅡrestorations.

Objective:To evaluate the synergistic antibacterial effects of lysozyme with ethylenediami-netetraacetic acid disodium salt (EDTA-2Na) on Enterococcus faecalis (E.faecalis) and Porphyromonas endodontalis ( P.endodontalis) .Methods:E.faecalis and P.endodontalis were cultured and adjusted to 108 CFU/mL.Then 0.3, 0.5, 1, 2, 5, 10, 50, 100, 150 and 300 g/L of lysozyme were prepared with deionized water;and the lysozyme solutions were mixed with 0.5, 1.0, 2.0 g/L of EDTA-2Na, re-spectively.The bacteria and lysosome with/without EDTA-2Na interacted for 15 min, then water-soluble tetrazolium (WST) working solution was added and the activity of the bacteria was calculated by mea-suring optical densities at 450 nm and 630 nm with microplate spectrophotometer .Results:Regarding the pure lysozyme from 0.5 g/L to 150 g/L, more E.faecalis and P.endodontalis were inhibited when the concentration of lysozyme was higher , especially for E.faecalis.There was synergistic effect of lysozyme with EDTA-2Na on antibacterial activity , which was related to the concentration of lysozyme .On E.fae-calis, the antibacterial activity of lysozyme with EDTA-2Na was 1.2-3.7 folds than the pure lysozyme when the concentration of lysozyme was 0.5-50 g/L (P<0.05), and on P.endodontalis, the antibac-terial activity of lysozyme with EDTA-2Na was 1.3 -3.5 folds than the pure lysozyme when the concentration of lysozyme was 0.5-10 g/L (P<0.05).When the concentration of lysozyme was higher than 100 g/L, EDTA-2Na did not show synergistic effect on the antibacterial activity (P>0.05). Conclusion: For E.faecalis and P.endodontalis, a low concentration of lysozyme with EDTA-2Na showed significant synergistic antibacterial activity , while a high concentration of lysozyme with EDTA-2 Na did not .

Objective: To compare the incidences of root cracks after canal instrumentation with HyFlex CM system and the ProTaper Universal system .Methods:Sixty mandibular incisors were mounted in resin blocks with simulated periodontal ligaments , and the apex was exposed .The control group of 20 teeth was not prepared , and the other 40 teeth were divided into 2 experimental groups ( n=20 ) .The 40 root canals of the experimental groups were instrumented using HyFlex CM and ProTaper Universal to the major apical foramen ( AF).The horizontal sections 1 mm, 2 mm, and 3 mm from the apex were observed under an optical stereomicroscope at 25 ×magnification .The presence of cracks was noted . Results:No cracks were found in the control teeth .Cracks were found in 1 of 20 ( 5%) teeth in HyFlex CM group , and 17 of 20 ( 85%) teeth in ProTaper Universal group .The difference between the two experimental groups was statistically significant (P<0.01).Conclusion: The HyFlex CM files caused fewer root cracks than the ProTaper Universal files during the root canal instrumentation .

Objective To investigate the short-term improvement of life quality in patients with obstructive sleep apnea hypopnea syndrome(OSAHS)after temperature-controlled radiofrequency ablation(TCFR).Methods Totally 70 patients with OSAHS were diagnosed by polysomnography(PSG)and received TCRF in our department.The Epworth Sleepiness Scale(ESS)and Calgary Sleep Apnea Quality of Life Index(SAQLI)were surveyed before and after the therapy.The results were followed up for six months after the operation.Results The pre-operative scores of ESS was correlated with body mass index(BMI),apnea hypopnea index(AHI),lowest saturation(LSaO2)and the scores of SAQLI(correlation coefficient:0.410,0.371,-0.441,and-0.411 respectively;all P

Objective:To compare the assessments of the presence or absence and the changes of post-treatment periapical lesions using periapical radiographs versus cone-beam computed tomography (CBCT).Methods:Imaging records were selected from a sample of 233 radiographic examinations (in-cluding periapical radiographs and CBCT)of patients with chronic apical periododontitis who received treatment and review in Department of Cariology and Endodontology of Peking University School of Stoma-tology.After testing the inter-observer and intra-observer agreement,two observers determined the pre-sence or absence of a periapical lesion and classified the changes of lesions in 4 categories:absence,re-duction or enlargement of lesion,or uncertain.The differences between CBCT and periapical radiographs in detecting the presence or absence and the changes of periapical lesions were compared using McNemar test and Fisher’s exact test respectively.Results:In the study,233 teeth were assessed with both periapi-cal radiographs and CBCT images.Periapical lesions were detected in 178 teeth on CBCT scans and in 146 teeth on periapical radiographs.CBCT images revealed a significantly larger number of lesions than were revealed by periapical radiographs (P <0.01 ).There was disagreement on the changes of lesions between the two radiological technologies in 25% teeth,and the difference was statistically significant (P <0.01 ). Conclusion:Significant differences were observed between periapical radiographs and CBCT in detection of post-treatment periapical lesions and assessment of the changes of periapical lesions.

Objective:To develop a new type of microelectrode used to measure free fluoride in minim solution. Methods:F--ion sensitive field transistor( F--ISFET) microelectrode was developed based on H+-ISFET combined with an Ag/AgCl referential electrode of microtube. The F--ISFET was used to determine the free fluoride ions in saliva and dental plaque fluid in microliter. And its property was investigated. Results:The test limit of F--ISFET was 10 -6 mol/L-10 -1mol/L, the linear test limit was 10 -6mol/L-10 -4mol/L, the sensitivity was 30-55 mV/pF, the responding time was less than 30 seconds, r2 was 0.97, the reclamation was 94%-104%. Conclusion:F--ISFET can be used to measure free fluoride ions in dental plaque.