Chengfei Zhang

In vivo study of the healing processes that occur in the jaws of rabbits following perforation by an Er,Cr:YSGG laser

This study investigates the healing process that takes place in the bone and soft tissue of the maxilla and the mandible after perforation by an Er,Cr:YSGG laser device. The jaws of New Zealand white rabbits were irradiated with an Er,Cr:YSGG laser, forming wounds 0.4xa0mm in diameter. Irradiation parameters were as follows: repetition rate was 20xa0pulse/s, pulse duration was 140–200xa0μs, power was 2xa0W, exposure time was 10xa0s, energy density was 80xa0J/cm2. After sacrifice at 0–56xa0days post-surgery, gross observations and histological examinations were performed. Effective hemostasis was achieved after Er,Cr:YSGG laser surgery. There was a minimal delay before the healing began. After 56xa0days all of the bone defects had been completely replaced by new bone. In conclusion, the Er,Cr:YSGG laser allows precise surgical ablation with minimal thermal damage to adjacent tissues in vivo. The overall subsequent healing was favorable. This laser may potentially be used in minor oral surgery.

Effects of CO2 Laser in Treatment of Cervical Dentinal Hypersensitivity

The effectiveness of CO2 laser therapy in the reduction and elimination of dentinal hypersensitivity in vivo and its thermal effects on tooth surfaces in vitro were investigated. Twenty-three patients with 91 sensitive teeth participated in this study and were followed for 3 months. The parameters used with CO2 laser were 1 W in a continuous wave mode and irradiation time ranging from 5 to 10 s. Hypersensitivity was assessed by thermal stimulus (a blast of air from a dental syringe). Thermal effects were measured by thermography using 10 extracted human teeth. After laser treatment, all patients were immediately free from sensitive pain. Over 3 months, the CO2 laser treatment reduced dentinal hypersensitivity to air stimulus by 50%. All teeth remained vital with no adverse effects. Thermography revealed no temperature increase on irradiated tooth surfaces subjected to water coolant. These results show that the CO2 laser is useful in the treatment of cervical dentinal hypersensitivity without thermal damage to pulp.

Prevalence, phenotype, and genotype of enterococcus faecalis isolated from saliva and root canals in patients with persistent apical periodontitis

INTRODUCTIONnThe aim of this study was to investigate the prevalence, phenotype, and genotype of Enterococcus faecalis isolated from saliva and root canals in patients with endodontic treatment failure.nnnMETHODSnSamples were collected from 32 adults undergoing retreatment for periapical lesions after endodontic treatment performed at least 2 years previously. Isolates that were presumed to be E. faecalis were identified by both API20 Strep kits and 16S rRNA sequencing. Phenotypic tests for hemolysin and gelatinase production and antibiotic susceptibility were performed. Genotype analysis comprised virulence gene detection and pulsed field gel electrophoresis (PFGE).nnnRESULTSnThe prevalence of E. faecalis was 18.8% in saliva and 40.6% in root canals (P = .666, Fisher exact test). Of the 19 isolates of E. faecalis, 6 were from saliva and 13 were from root canals. In 3 patients, E. faecalis isolates from saliva were more resistant to gentamicin than those from root canals. The genes ace, asa, gelE, cylA, and efaA were detected from all isolates. PFGE after SmaI digestion showed a genetic correlation among all isolates of 62%-100%.nnnCONCLUSIONSnPhenotype and genotype evidence of potential virulence factors was identified in E. faecalis from both saliva and root canals. A single patient might carryxa0different E. faecalis strains in saliva and root canals.

Micro-computed Tomographic Comparison of Nickel-Titanium Rotary versus Traditional Instruments in C-Shaped Root Canal System

INTRODUCTIONnThe purpose of this study was to assess the efficacy of instrumentation of C-shaped canals with ProTaper rotary system and traditional instruments by using micro-computed tomography (micro-CT).nnnMETHODSnTwenty-four mandibular molars with C-shaped canals were selected in pairs and sorted equally into 2 groups, which were assigned for instrumentation by ProTaper rotary system (ProTaper group) or by K-files and Gates-Glidden burs (Hand Instrument group). Three-dimensional images were constructed by micro-CT. The volume of dentin removed, uninstrumented canal area, time taken for instrumentation, and iatrogenic error of instrumentation were investigated.nnnRESULTSnHand Instrument group showed greater amount of volumetric dentin removal and left less uninstrumented canal area than ProTaper group (P < .01). The time needed for instrumentation was shorter for ProTaper group than for Hand Instrument group (P < .05). No instrument breakage occurred in both groups, but more conspicuous procedural errors were detected in Hand Instrument group than for ProTaper group.nnnCONCLUSIONSnIt was concluded that ProTaper rotary system maintained the canal curvature with speediness and few procedural errors, whereas traditional instrumentation can clean more canal surface.

Effects of pulsed Nd:YAG laser irradiation on root canal wall dentin with different laser initiators

The effects of pulsed Nd:YAG laser irradiation with different laser initiators on the permeability and ultrastructure of the root canal wall dentin were investigated in vitro. Forty extracted human single-rooted teeth were randomly assigned to four groups. Group 1 teeth were not lased as a control. Group 2 specimens received four 10-s duration laser exposures for a total exposure of 40 s/canal. In group 3 specimens, the root canals were painted with black ink and then lased by the same method as group 2 teeth. In group 4 specimens, root canals were treated with 38% Ag(NH3)2F and then lased by the same method as group 2 teeth. Laser parameters were set at 2 W, 20 pps. After being placed in 0.6% rhodamine B solution for 48 h, the teeth were sectioned for study by stereoscope and scanning electron microscopy. Statistical analysis showed there were significant differences (p < 0.05) in dentin permeability in the apical areas between groups 3 and 1, 4 and 1, and 4 and 2. Scanning electron microscopic examination showed that laser treatment alone had no obvious effects on the root canal wall. The root canal surfaces prepared for by laser irradiation with black ink or 38% Ag(NH3)2F revealed melting, smear layer evaporation, and open dentinal tubules. Black ink was more effective than 38% Ag(NH3)2F as a Nd:YAG laser initiator.

Comparison of the antibacterial effect and smear layer removal using photon-initiated photoacoustic streaming aided irrigation versus a conventional irrigation in single-rooted canals: an in vitro study.

OBJECTIVEnThe Er:YAG laser with photon-induced photoacoustic streaming (PIPS) technique was reported to be effective in root canal disinfection. This study attempted to further investigate the antibacterial efficacy and smear layer removal ability of PIPS in comparison with conventional syringe irrigation in vitro.nnnMETHODSnFor antibacterial analysis, 48 single-rooted human teeth were prepared and inoculated with Enterococcus faecalis, and then divided into six groups of eight roots each. The colony-forming units (CFUs) per milliliter were determined after infection as the baseline. Then, the teeth were subjected to either PIPS plus 3% sodium hypochlorite (PIPS+NaOCl) or conventional syringe irrigation with 0.9% saline, 3% NaOCl, 17% ethylenediaminetetraacetic acid (EDTA), 0.2% chlorhexidine gluconate (CHX), or 3% NaOCl alternating with 17% EDTA. The reduction of CFUs in the individual group was determined. Additionally, scanning electron microscopy (SEM) examination of the canal walls for E. faecalis colonization was performed. For comparing the smear removal efficacy, another 48 single-rooted teeth, assigned to different groups as mentioned, were irrigated after mechanical instrumentation. The presence of a smear layer at different levels of the root canal was scored by SEM examination.nnnRESULTSnNo significant differences were found in CFU reduction. No bacteria could be observed by SEM in the NaOCl, NaOCl+EDTA, and PIPS+NaOCl groups. The scores of smear layer of the NaOCl+EDTA and PIPS+NaOCl groups were significantly lower than those of the other groups in the coronal and middle third of the root canal. None of the methods can effectively remove smear layer in the apical third.nnnCONCLUSIONSnPIPS system supplied with NaOCl and conventional syringe irrigation with NaOCl+EDTA are comparable in their ability to remove E. faecalis and smear layer in single-rooted canals.

The Effect of Cultured Autologous Periodontal Ligament Cells on the Healing of Delayed Autotransplanted Dog's Teeth

INTRODUCTIONnThe regeneration of the periodontal structure for avulsed teeth extended dry times has been a goal of dentists. The aim of this study was to investigate a new strategy of delayed replantation for avulsed teeth that were not suitable for immediate replantation.nnnMETHODSnExtracted dogs premolar teeth were maintained in a dry environment for a month after isolation and proliferation of the periodontal ligament (PDL) cells. Then, tooth roots coated with 1 x 10(6) cultured autologous PDL cells were autotransplanted in artificial sockets created in the mandible. The dogs were sacrificed 60 days after transplantation. Histologic analyses showed that a root-PDL-bone complex was found in all cases of the PDL cell-loaded samples.nnnRESULTSnThe new PDL-like connective tissue was located between the alveolar bone and the transplanted roots, with fibers inserting into the newborn cementum on one end and alveolar bone on the other. For the control samples, no PDL-like tissue was found, and ankylosis was commonly observed.nnnCONCLUSIONSnThe results indicated that cultured autologous PDL cells assist in the re-establishment of periodontal architecture of autotransplanted teeth that is devoid of viable periodontal cells.

Role of polymorphonuclear neutrophils in the clearance of enterococcus faecalis derived from saliva and infected root canals

OBJECTIVESnThe goal of this study was to measure (1) the ability of polymorphonuclear neutrophil leukocytes (PMNs) to kill oral Enterococcus faecalis strains, (2) up-regulation of inflammatory mediators by PMNs in interaction with E. faecalis, and (3) the ability of E. faecalis to cause inflammation in mouse muscle tissue.nnnMETHODSnFifteen endodontic and nine saliva strains of E. faecalis were isolated and identified by specific 16S ribosomal RNA (16S rRNA) primers. The bacteria were grown in BHI broth and incubated with mouse PMN in appropriate media to determine the ability of the PMNs to kill the bacteria. In other experiments up-regulation of interleukin (IL)-1α, tumor necrosis factor α (TNF-α), matrix metalloproteinase-8 (MMP-8), and cyclooxygenase (COX)-2 messenger RNA in the PMNs was measured after exposure of the leukocytes to the bacteria using real-time polymerase chain reaction. Finally, the inflammatory potential of and PMN response to E. faecalis suspension in mouse muscle tissue was examined from histological sections using hematoxylin-eosin staining and immunostaining.nnnRESULTSnMurine PMNs killed about 80% of the E. faecalis cells in 1 hour, irrespective of the source of isolation of the strains. Quantitative PCR results showed that IL-1α, TNF-α, MMP-8, and COX-2 messenger RNA were markedly up-regulated in E. faecalis-stimulated PMNs or in E. faecalis-invaded muscular tissues. MMP-8 messenger RNA level was positively related to COX-2 messenger RNA level. Histological evaluation and immunostaining disclosed that all E. faecalis strains could recruit PMNs to the local infectious sites and cause abscess formation.nnnCONCLUSIONnE. faecalis strains from saliva and infected root canals have the potential to recruit PMNs in the infectious sites leading to inflammation via up-regulation of PMN IL-1α, TNF-α, MMP-8, and COX-2. PMNs can play an important role in killing of E. faecalis.