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Objective@#To investigate the stress corrosion and electrochemical corrosion resistance of titanium produced through laser rapid forming (LRF), and to provide a basis for their clinical application.@*Methods@#Forged commercial pure titanium (CP-Ti) was used as control group and LRF pure titanium was used as LRF group. All samples were placed in acidic artificial saliva containing fluorine (pH=7), and loaded with a stress of 1.2 × σ0.2 Pa (σ0.2 represents the yield strength of material). Stress corrosion resistance of specimens that have been soaked for 30 days was analyzed by naked eye observation, X-ray diffraction analysis and scanning electron microscopy. For samples placed in artificial saliva, neutral fluoride solution (pH=7) and acidic fluoride solution (pH=3) (4 test pieces in each corrosive medium), and their electrochemical corrosion resistance was evaluated by free corrosion potential (Ecorr) measurements, corrosion current (Icorr), electrochemical impedance spectroscopy (EIS), and anodic polarization curves.@*Results@#With the prolongation of immersion time, the corrosion products gradually increased. The stress corrosion of CP-Ti group was significantly more than that of LRF-Ti group, and the pit diameter was significantly larger than that of LRF-Ti group. The electrochemical corrosion results showed that the Ecorr (-469 mV) of LRF-Ti in artificial saliva was higher than that of CP-Ti (-555 mV), and the Ecorr (-925 mV) of LRF-Ti was higher than that of CP-Ti (-943 mV) in neutral fluoride solution. In acid fluoride solution, the Ecorr (-943 mV) of LRF-Ti was higher than that of CP-Ti (-956 mV). The Ecorr of the same metal was the highest in artificial saliva and the lowest in acid fluoride solution; the Icorr of the same metal was the lowest in artificial saliva and the highest in acid fluoride solution.@*Conclusions@#Under the same corrosion conditions, LRF Ti demonstrated better stress and electrochemical corrosion resistance than CP-Ti.
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Objective@#To evaluate the antiseptic effect of combined using of 5% sodium hypochlorite and calcium silicate-based root canal sealer against Enterococcus faecalis (Ef) biofilms in infected dentinal tubules in vitro.@*Methods@#Cells of Ef were inoculated into the dentinal tubules of single-rooted teeth (without caries, periapical lesions and malformations extracted due to periodontal disease or orthodontic reasons; collected from Department of Maxillofacial Surgery, The First Affiliated Hospital of Zhengzhou University) with centrifugation and incubated in brain-heart infusion (BHI) to form 3-week-old biofilms. The infected samples were subjected to sodium hypochlorite or sterile water bathing for 10 minutes followed by calcium silicate-based root canal sealer (iRoot SP) (calcium silicate-based group), Gutta-percha group and sterile water group placed on the root canal wall for 1, 4 and 12 weeks. There were two samples in each treatment at each point. The antiseptic effectiveness of combined use of sodium hypochlorite and calcium silicate-based root canal sealer was analyzed by laser scanning confocal microscope (LSCM), ANOVA and LSD-t test.@*Results@#After treatment with 5% sodium hypochlorite, in calcium silicate-based group for 4 and 12 weeks more Ef biofilm cells [(75.3±3.5)% and (74.8±3.8)%] were killed than in Gutta-percha group [(65.9±4.1)% and (63.0±3.7)%] and sterile water group [(63.9±4.0)% and (64.2±3.5)%] (P<0.05). After being treated with sterile water, the proportion of dead bacterial cells in calcium silicate-based group for 1, 4 and 12 weeks [(27.5±4.6)%, (43.0±4.4)% and (40.3±6.1)%] were more than those in Gutta-percha group and sterile water group (P<0.05). After being treated with 5% sodium hypochlorite or sterile water, more biofilm bacteria were killed in calcium silicate-based group for 4 and 12 weeks than in calcium silicate-based group for 1 week (P<0.05).@*Conclusions@#The combined use of sodium hypochlorite and calcium silicate-based root canal sealer kills more biofilm cells in infected dentinal tubules.
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Objective@#To evaluate the antimicrobial activity of nonequilibrium plasma against Enterococcus faecalis (Ef) biofilms in vitro and to obtain novel evidence of root canal disinfection with nonequilibrium plasma.@*Methods@#Sterile cover slips and single-rooted canals were filled with Ef and incubated to form 1-week-old and 3-week-old biofilms, respectively. The infected samples were subjected to nonequilibrium plasma, 2% chlorhexidine digluconate (CHX) and saline for 3, 10 and 30 minutes, respectively. After treatment, the killing effectiveness of nonequilibrium plasma was analyzed by using laser scanning confocal microscopy (LSCM) and colony forming unit (CFU) counting.@*Results@#The 3-dimentional reconstruction LSCM images showed that about 48.3%-79.8% of 1-week-old Ef biofilm cells and 40.0%-67.4% of 3-week-old biofilm cells were killed by nonequilibrium plasma and 2% CHX compared to saline (P<0.05). The proportion of killing activity was lower after 3 minutes (40.0%-50.9% killing) than after 10 minutes (65.3%-77.8% killing) and 30 minutes (66.4%-79.8% killing) (P<0.05). And the killing of biofilm bacteria was fastest during the first 3 minutes (13.3%-17.0% killing per minute) and slow down greatly after 10 minutes. Remarkably more bacteria were killed in 1-week-old Ef biofilms (48.3%-79.8% killing) than in 3-week-old biofilms (P<0.05).@*Conclusions@#The nonequilibrium plasma killed more Ef biofilm cells in infected root canals showed promotional as an additional approach against bacterial biofilms during root canal disinfection.
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Objective To investigate labial and lingual alveolar bone plate thickness of the mandibular anterior teeth by using cone-beam computed tomography (CBCT),in order to provide a reference for immediate implantation.Methods 132 individuals with normal occlusion were examined with CBCT,and their mandibular anterior teeth were analyzed.The labial and lingual alveolar bone plate thickness at the level of the apical,1/4 of the apical,1/2 of the middle and 1/4 of the cervical were measured.The differences of the thickness were compared among the side and gender.Results There were no significant differences between the left and right sides. Except on the 1/4 of the cervical,the thickness of lingual bone plate was thicker than that of labial bone plate.The frequency of the thickness of the labial bone larger than 2 mm on the 1/4 of the cervical of the center incisor,lateral incisor,and canine were 0,0 and 1.5 1%,respectively,and on 1/4 of the middle were 0.76%,1.44% and 3.79%,respectively.The lingual bone plate thickness showed significant difference between genders.Conclusion Reference values of alveolar bone plate thickness in anterior teeth of normal occlusion were established by using CBCT,which can provide clinical instruction for immediate implant.
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Previously, the choice of prosthetic implant-retained overdentures has depended on data from previous studies about the retention-fatigue strength of the attachment system selected. Little or no data have been available on the correlation between the attachment system selected and the overdenture support configuration. The purpose of the present study was to evaluate the retention force and fatigue resistance of three attachment systems and four support designs of overdenture prosthesis. Four lower edentulous acrylic models were prepared and eight combinations of attachments groups were investigated in the study. These included: O-Rings with mini-dental implants (MDIs), Dalbo elliptic with Dalbo Rotex and fabricated flexible acrylic attachments with both MDI and Dalbo Rotex. The study was divided into four test groups: groups A and B, controls, and groups C and D, experimental groups. Control group A contained three overdenture supports: two free standing MDIs in the canine region and at the midline, and one simulated tooth root with Dalbo Rotex screwed in. Control group B contained four overdenture support foundations: two free standing MDIs in the right canine region and the first premolar region, and two simulated tooth roots with Dalbo Rotex screwed in at the same MDI position, but on the left side of the model. Experimental group C contained three overdenture support foundations: two free standing MDIs in the canine region and at the midline, and one simulated tooth root with MDI screwed in. Experimental group D contained four overdenture support foundations: two free standing MDIs in the right canine region and the first premolar region, and two simulated tooth roots with MDIs screwed in at the same MDI position, but on the left side of the model. Each group was further divided into two subgroups according to attachment type used. Five samples were prepared for each group. Retention force (N) values were recorded initially (0 cycles) and after 360, 720, 1440 and 2880 insertion and removal cycles. During the tensile test a cross-head speed of 10 mm/min was applied. Values of absolute force (AF) and relative force (RF) were statistically analyzed by two-way ANOVA and multiple comparison Tukey's tests between groups and cycles periods. The results of fatigue tests showed a 50% reduction in retention force in the subgroups with flexible attachments. A triangular design of overdenture support foundations with O-Ring attachments revealed the lowest value of AF and a relatively high reduction in RF. The four overdenture support designs with flexible acrylic attachments improved the retention force and reduced the fatigue retention. Furthermore, the results of the investigation demonstrate that flexible acrylic attachments for both teeth and implant-supported overdentures offer a wide range of retention forces.
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Recently, plasma sterilization has attracted increasing attention in dental community for the atmospheric pressure non-equilibrium plasma jet (APNPs), which is driven by a kilohertz pulsed DC power, may be applied to the dental and oral diseases. However, it is still in doubt whether APNPs can effectively kill pathogenic bacteria in the oral cavity and produce no harmful effects on normal oral tissues, especially on normal mucosa. The aim of this study was to evaluate the bacterial-killing effect of APNPs in the biofilms containing a single breed of bacteria (Porphyromonas gingivalis, P.g.), and the pathological changes of the oral mucosa after treatment by APNPs. P.g. was incubated to form the biofilms in vitro, and the samples were divided into three groups randomly: group A (blank control); group B in which the biofilms were treated by APNPs (the setting of the equipment: 10 kHz, 1600 ns and 8 kV); group C in which the biofilms were exposed only to a gas jet without ignition of the plasma. Each group had three samples and each sample was processed for up to 5 min. The biofilms were then fluorescently stained, observed and photographed under a laser scanning confocal microscope. In the animal experiment, six male Japanese white rabbits were divided into two groups randomly (n=3 in each group) in terms of the different post-treatment time (1-day group and 5-day group). The buccal mucosa of the left side and the mucosa of the ventral surface of the tongue were treated by APNPs for 10 min in the same way as the bacterial biofilm experiment in each rabbit, and the corresponding mucosa of the other sides served as normal control. The clinical manifestations of the oral mucosa were observed and recorded every day. The rabbits were sacrificed one or five day(s) after APNPs treatment. The oral mucosa were harvested and prepared to haematoxylin and eosin-stained sections. Clinical observation and histopathological scores were used to assess mucosal changes. The results showed the obvious P.g. biofilms were formed at 10 days, and most of the bacteria in groups A and C were alive under a laser scanning confocal microscope, but the bacteria in the group B were almost all dead. In animal experiment, no ulcers, anabrosis and oral mucositis were found in both the 1-day and 5-day groups. The average mucous membrane irritation index was -0.83 and -0.67 in the 1-day and 5-day groups, respectively, suggesting that no intense mucosal membrane irritation responses occurred. It was concluded that APNPs could effectively kill P.g. in the biofilms and did not cause any pathological changes in the normal mucosa, suggesting that the plasma jet (APNPs) may be applied to oral diseases as a novel sterilization device in the future.