Research progress on the low-temperature degradation of zirconia in prosthetic dentistry / 中华口腔医学杂志

Zirconia is widely used in the field of dentistry because of its superior mechanical and esthetic characteristics. However, the tetragonal zirconia polycrystal restorations commonly used in clinics will degrade at low temperatures in the oral environment, resulting in increased surface roughness, microcracks, and decreased mechanical properties. Low-temperature degradation of zirconia can be affected by grain size, stress, stabilizer content and type, surface treatment, sintering conditions, and other factors. Through a literature review and analysis, this review summarizes the research progress on the low-temperature degradation of zirconia in prosthetic dentistry to provide references for the improvement of zirconia in clinical and research applications.

Esthetic evaluation of conventional and socket shield technique immediate implant restoration / 中华口腔医学杂志

Objective: To evaluate the pink and white esthetics of conventional and socket shield technique (SST) immediate implant restoration. Methods: Thirty volunteers were recruited according to preset criteria, and were assigned to 3 groups. Natural teeth group (ten undergraduates or postgraduates from Peking University School and Hospital of Stomatology in January 2020, n=10): all volunteers' maxillary anterior teeth were natural teeth with healthy gingiva, and none of the teeth were restored by crowns or composite. Conventional group and SST group (patients had a maxillary central incisor immediate implant placed in Department of Prosthodontics, Peking University School and Hospital of Stomatology during October 2016 to January 2021, n=10 for each group): the volunteer had an unrestored natural maxillary central incisor, and the contralateral maxillary central incisor was restored by conventional or SST immediate implant placement, temporization and all ceramic final restoration, photos were taken 12 months post-surgery. Three groups of evaluators namely layperson (staff from Second Clinical Division of Peking University School and Hospital of Stomatology and 2 family members, n=10), dental students (class 2015 undergraduates from Peking University School and Hospital of Stomatology, n=10) and prosthodontists (from Department of Prosthodontics, Peking University School and Hospital of Stomatology, n=10) were invited to assess the esthetics using pink esthetic score (PES) and white esthetic score (WES). The results were statistically analyzed. Results: PES and WES of natural teeth group [9(8, 10) and 8(7, 10)] were significantly higher than conventional group [7(6,8) and 7(6,9)] (H=287.08, 132.79,P<0.01) and SST group [7(6, 9) and 8(7, 9)] (H=216.01, 101.21, P<0.01). SST group yielded higher PES than the conventional group (H=-71.06, P<0.01), yet had similar WES (H=-31.57, P>0.05). Dental students had significant lower PES and WES than prosthodontists (H=-120.90, -218.86, P<0.01) and layperson (H=-109.55, 134.97, P<0.01). Prosthodontists and layperson got similar PES (H=-11.36, P>0.05), however yielded different WES (H=-83.89, P<0.01). Conclusions: SST immediate implant placement obtained better pink esthetics than conventional protocol 12-month after implant surgery, profession may have significant impact on evaluators during pink and white esthetic evaluation.

Marginal features of CAD/CAM laminate veneers with different materials and thicknesses / 北京大学学报(医学版)

OBJECTIVE@#To analyze the marginal roughness and marginal fitness of chairside computer-aided design and computer-aided manufacturing (CAD/CAM) laminate veneers with different materials and thicknesses, and to provide a reference for the clinical application of laminate veneers.@*METHODS@#The butt-to-butt type laminate veneers were prepared on resin typodonts, the preparations were scanned, and the laminate veneers were manufactured by chairside CAD/CAM equipment. The laminate veneers were divided into four groups (n=9) according to the materials (glass-matrix ceramics and resin-matrix ceramics) and thickness (0.3 mm and 0.5 mm) of the veneers, with a total of 36. The marginal topo-graphies of each laminate veneer were digitally recorded by stereomicroscope, and the marginal rough-nesses of the laminate veneers were determined by ImageJ software. The marginal fitness of the laminate veneers was measured by a fit checker and digital scanning and measuring method. At the same time, the mechanical properties of glass-matrix ceramic and resin-matrix ceramic bars (n=20) were tested by a universal testing device.@*RESULTS@#The marginal roughness of 0.3 mm and 0.5 mm glass-matrix ceramic laminate veneers was (24.48±5.55) μm and (19.06±5.75) μm, respectively, with a statistically significant difference (P < 0.001). The marginal roughness of 0.3 mm and 0.5 mm resin-matrix ceramic laminate veneers was (6.13±1.27) μm and (6.84±2.19) μm, respectively, without a statistically significant difference (P>0.05). The marginal roughness of the glass-matrix ceramic laminate veneers was higher than that of the resin-matrix ceramic laminate veneers with a statistically significant difference (P < 0.001). The marginal fitness of 0.3 mm and 0.5 mm glass-matrix ceramic laminate veneers were (66.30±26.71) μm and (85.48±30.44) μm, respectively. The marginal fitness of 0.3 mm and 0.5 mm resin-matrix ceramic laminate veneers were (56.42±19.27) μm and (58.36±8.33) μm, respectively. There was no statistically significant difference among the 4 groups (P>0.05). For glass-matrix ceramics, the flexural strength was (327.40±54.25) MPa, the flexural modulus was (44.40±4.39) GPa, and the modulus of resilience was (1.24±0.37) MPa. For resin-matrix ceramics, the flexural strength was (173.71±16.61) MPa, the flexural modulus was (11.88±0.51) GPa, and the modulus of resilience was (1.29±0.27) MPa. The flexural strength and modulus of glass-matrix ceramics were significantly higher than those of resin-matrix ceramics (P < 0.001), but there was no statistically significant difference in the modulus of resilience between the two materials (P>0.05).@*CONCLUSION@#The marginal roughness of CAD/CAM glass-matrix ceramic laminate veneers is greater than that of resin-matrix ceramic laminate veneers, but there was no statistically significant difference in marginal fitness among them. Increasing the thickness can reduce the marginal roughness of glass-matrix ceramic laminate veneers, but has no effect on the marginal roughness of resin-matrix ceramic laminate veneers.

Effect of a novel radio-frequency atmospheric-pressure glow discharge plasma jet treatment on crosslinking of dentin collagen / 北京大学学报(医学版)

OBJECTIVE@#To investigate the effect of a noval radio-frequency atmospheric-pressure glow discharge (RF-APGD) plasma jet on crosslinking of dentin collagen.@*METHODS@#(1) Twenty intact third molars were collected. The middle dentin discs were prepared for each tooth by low-speed water-cooled Isomet saw, and then immersed in 10% (mass fraction) H3PO4 solution for 16 h to obtain fully demine-ralized dentin collagen. The twenty dentin discs were then randomly divided into five groups. The control group was untreated while the four experimental groups were treated by plasma jet with gas temperature of 4 ℃ for different times (20 s, 30 s, 40 s, and 50 s). The structure and crosslinking degree of dentin collagen were characterized by attenuated total reflection-Fourier transform infrared spectroscopy. The surface morphology of demineralized dentin was observed by scanning electron microscope, and the microstructure was observed by transmission electron microscope. (2) Fourty non-caries third molars were collected to prepare 5 g fine dentin powder, then completely demineralized with 10% H3PO4 solution. The control group was untreated, while the four experimental groups were treated by plasma jet for 20 s, 30 s, 40 s and 50 s. The crosslinking degree of each group was determined by ninhydrin colorimetric method. (3) Forty intact third molars were collected to obtain dentin strips. Only two central symmetrical dentin strips (nasty 80) were taken from each tooth and immersed in 10% H3PO4 solution for 16 h to obtain fully demineralized dentin collagen. Eighty dentine collagen fiber strips were randomly divided into five groups. The control group was untreated and the axial surfaces of dentin collagen fiber strips in the expe-rimental groups were treated with the plasma jet for 20 s, 30 s, 40 s and 50 s. The ultimate tensile strength of dentin was measured by universal mechanical machine.@*RESULTS@#(1) The surface morphology of demineralized dentin observed by scanning electron microscope showed that the network structure of collagen fibers on the surface of demineralized dentin treated with the plasma jet for 20 s, 30 s and 40 s could maintain the uncollapsed three-dimensional structure, and part of the microstructure was destroyed after plasma jet treated for 50 s. After being treated by plasma jet for 20 s, 30 s and 40 s, the three-dimensional structure was uncollapsed, and the typical periodic transverse pattern of natural type Ⅰ collagen fiber could be seen. The results of infrared spectra showed that the secondary conformation of dentin collagen fibers was the same as that of the control group after being treated with the plasma jet, and the intensity of amide band was significantly increased after being treated for 30 s and 40 s. (2) The results of ninhydrin crosslinking test showed that the crosslinking ratio of dentin collagen treated by plasma jet for 30 s and 40 s was the highest, and the difference was statistically significant (P < 0.05). (3) The results of dentin ultimate tensile strength showed that the control group was (1.67±0.24) MPa, and the plasma jet treated 20 s, 30 s, 40 s and 50 s groups were (4.21±0.15) MPa, (7.06±0.30) MPa, (7.32±0.27) MPa, and (6.87±0.17) MPa, which were significantly different from that of the control group (P < 0.05).@*CONCLUSION@#The novel RF-APGD plasma jet treatment can promote the crosslinking degree of demineralized dentin collagen and improve their ultimate tensile strength.

Morphology accuracy evaluation of direct composite occlusal veneer using two types of modified stamp-technique / 北京大学学报(医学版)

OBJECTIVE@#To evaluate the morphology accuracy of direct occlusal veneer using two types of modified stamp-technique, comparing the Results of two types of stamp and different composite resin.@*METHODS@#Model scanner was used to get the original data from the standard resin teeth in plastic model. Two types of stamps were made: solid silicon stamp and transparent silicon stamp. In the study, 54 resin tooth were randomly divided into 9 groups: Groups 1-8 were restored by direct composite resin, using general and bulk-filled composite resin in occlusal veneer (1 mm or 2 mm) with two types of stamp-technique (the solid silicon, and the transparent silicon), and the control group was restored by indirect way using CAD/CAM composite resin restoration by biocopy technique to mimic the original shape of the teeth. After the resin teeth were prepared for occlusal veneer, the direct and indirect composite resins were restored. After the restoration was finished, the data were obtained again by the same model scanner in the plastic model. 3D comparisons were made using the original and restoration data, the average difference and the root mean square of difference (RMS) were recoded from the software. The RMS of all the groups were analyzed using one way ANOVA (α=0.05).@*RESULTS@#The RMS of occlusal surface in solid silicon stamp group was (0.136±0.031) mm, in transparent silicon group was (0.130±0.024) mm, and in control group was (0.130±0.009) mm. There were no significant difference. While the RMS of buccal/lingual surface in solid silicon stamp group was the smallest [(0.135±0.020) mm, P < 0.05], and in transparent silicon group it was (0.147±0.021) mm, and control group (0.153±0.014) mm. The general composite resin using the two types of stamp had the largest occlusal RMS in 2 mm occlusal veneer, which were significantly larger than control group (P < 0.05).@*CONCLUSION@#The direct occlusal veneer using two types of modified "stamp-technique" had relatively good morphology accuracy. Direct occlusal veneer using bulk-filled composite resin made with two types of stamp technique had even more accurate morphology than using general composite resin. The solid silicon stamp had a better morphology accuracy in buccal/lingual surface than the transparent silicon stamp.

Three-dimensional movement of posterior teeth after losing the interproximal and occlusal contacts in adults / 北京大学学报(医学版)

OBJECTIVE@#To observe the movement of posterior teeth after losing the interproximal and occlusal contacts in adults from the amount and speed of mesial-distal, buccal-lingual, occlusal-gingival and three-dimensional movements.@*METHODS@#Twenty cases of metal post-core restoration from the Department of Prosthodontics, Peking University School and Hospital of Stomatology were recruited into this study, which was an observational study. The restored teeth had complete mesial, distal, and occlusal contacts before treatment. All the interproximal and occlusal contacts were removed during the preparation for the post-core. The three-dimensional positions of the post-core preparation were obtained by the intraoral scanner at the day of tooth preparation and that of post-core placement. The amounts of mesial-distal, buccal-lingual and occlusal-gingival tooth movement were measured in the software. On this basis, the amount of three-dimensional tooth movement was calculated. The speed of tooth movement was calculated based on the elapsed time between the two scans.@*RESULTS@#Ten females and ten males with an average age of (29.5±4.9) years were recruited. The average elapsed time was (10.9±2.7) days. The amount of the mesial-distal tooth movement was (134.8±61.2) μm, of the buccal-lingual tooth movement was (110.3±39.5) μm, of the occlusal-gingival tooth movement was (104.8±57.5) μm, and of the three-dimensional tooth movement was (211.4±71.0) μm, respectively. The amounts of mesial-distal, buccal-lingual and three-dimensional tooth movements were larger in female than in male (P < 0.05). The speed of the mesial-distal tooth movement was (13.1±7.8) μm/d, of the buccal-lingual tooth movement was (10.6±4.5) μm/d, of the occlusal-gingival tooth movement was (10.1±6.8) μm/d, and of the three-dimensional tooth movement was (20.5±9.7) μm/d, respectively. The speed of mesial-distal and buccal-lingual tooth movements were larger in female than in male (P < 0.05). The speed of three-dimensional tooth movement was slightly larger in female than in male, while there was no significant difference between different genders (P>0.05).@*CONCLUSION@#The three-dimensional position of posterior teeth changed after losing the interproximal and occlusal contacts in adults. The female had more significant and faster tooth movement than the male.

Study on the correlation between the mandibular masticatory muscle movement and sleep tooth wear / 华西口腔医学杂志

OBJECTIVE@#To investigate the correlation between the clinical diagnostic criteria of sleep bruxism and the frequency of mandibular movements during sleep.@*METHODS@#Video polysomnography was used to record 20 healthy adults with at least one of the following clinical symptoms and signs: 1) report of frequent tooth grinding; 2) tooth wear and dentin exposure with at least three occlusal surfaces; 3) masticatory muscle symptoms in the morning; 4) masseter muscle hypertrophy. The rhythmic masticatory muscle activity (RMMA) and isolated tonic activity were scored to compare the correlations with clinical symptoms and signs. Finally, the incidence of temporomandibular disorders (TMD) was investigated in patients with isolated tonic and RMMA subjects.@*RESULTS@#Among the 20 subjects, RMMA events were observed (5.8±3.1) times·h⁻¹ and isolated tonic episodes were observed (2.1±0.9) times·h⁻¹. The frequency of RMMA events was significantly greater in the patients with acoustic molars than in those without (P<0.05). Similarly, the frequency of RMMA events was significantly greater in the patients with tooth attrition than in those without (P<0.05). However, no difference was observed between the occurrence of RMMA and the symptoms of masticatory muscles or masseter hypertrophy in the morning. The incidence of TMD was significantly higher in the patients with RMMA than in the isolated tonic patients.@*CONCLUSIONS@#The clinical symptoms and signs often used to diagnose sleep bruxism are different clinical and physiological mandibular movements during sleep. RMMA during sleep can reflect the occurrence of tooth attrition and the high risk of TMD.

Blood pressure and heart rate changes of 640 single dental implant surgeries / 北京大学学报(医学版)

OBJECTIVE@#To investigate the blood pressure and heart rate changes and influencing factors during single dental implant surgery.@*METHODS@#A retrospective cohort study was conducted. Six hundred and forty cases underwent single dental implant placement in Department of Prosthodontics, Peking University School and Hospital of Stomatology from January 2016 to December 2016 were recruited in this study according to the inclusion and exclusion criteria. They were divided into different groups according to the exposure factors which were patient characteristics (gender, age) and surgical procedures (immediate placement, flap elevation, bone grafting). The correlation between blood pressure and heart rate variability during single dental implant surgery and the patient characteristics and surgical procedures were analyzed.@*RESULTS@#The average systolic blood pressure variability was 9.47%±6.45% (maximum 46.04%), the average diastolic blood pressure variability was 12.18%±9.39% (maximum 88.00%), and the average heart rate variability was 10.59%±7.68% (maximum 49.12%). The effects of age and bone grafting on blood pressure variability, and of gender and immediate placement on heart rate variability, were statistically significant (P < 0.05), respectively. The incidence of abnormal intraoperative blood pressure rise was 4.69%, of which there were 4 cases (0.63%) of systolic blood pressure ≥180 mmHg and/or diastolic blood pressure ≥110 mmHg. The incidence of abnormal intraoperative heart rate rise was 6.72%. Hierarchical analysis showed a higher risk of abnormal intraoperative blood pressure rise in the elderly (≥60 years) male patients [P < 0.05, RR=3.409 (95%CI: 1.155-10.062) ] and flap elevation with bone grafting cases [P < 0.05, RR=2.382 (95%CI: 1.126-5.040)], respectively. There was no statistically significant association between abnormal heart rate rise and patient characteristics or surgical procedures (P>0.05).@*CONCLUSION@#There was a certain risk of blood pressure and heart rate variability during dental implant surgery. Elderly male patients and flap elevation with bone grafting were risk factors of abnormal intraoperative blood pressure rise.

Esthetic proportions of maxillary anterior teeth of 120 Chinese adults / 北京大学学报(医学版)

OBJECTIVE@#To analyze the esthetic proportions of maxillary anterior teeth in term of the apparent widths proportion of the adjacent teeth and width/height ratio of the clinical crown in 120 Chinese adults.@*METHODS@#Maxillary gypsum casts were obtained from the dental laboratories of stomatological hospitals in North China, Southeast China, and Southwest China, according to the inclusion criteria and exclusion criteria. Standardized digital photographs of each cast were recorded. The apparent widths and actual widths and heights of the central incisors, lateral incisors and canines were determined by ImageJ software for the calculation of apparent widths proportion of the adjacent teeth and width/height ratio of the clinical crown. The ideal apparent widths proportion (Golden proportion and Preston proportion) and width/height ratio (0.80) were tested. The gender, arch side, and regional differences were investigated.@*RESULTS@#The apparent widths proportion of the lateral/central incisor was 0.724±0.047, of the canine/lateral incisor was 0.814±0.092. The width/height ratio of the central incisor was 0.848±0.072, of the lateral incisor was 0.834±0.094, of the canine was 0.883±0.098. The esthetic proportions were different from the predicted ideal ratio (P < 0.001). The apparent widths proportion of lateral/central incisor was significantly larger in the right side than that in the left side (0.730± 0.044 vs. 0.718±0.050), and was significantly smaller in North China than that in Southwest China (0.711±0.051 vs. 0.731±0.044). The width/height ratio of the central incisor was significantly larger in the female than that in the male (0.855±0.074 vs. 0.835±0.068), and in the right side than that in the left side (0.855±0.073 vs. 0.842±0.072). The width/height ratio of the lateral incisor was significantly larger in the female than that in the male (0.843±0.097 vs. 0.817±0.084).@*CONCLUSION@#The apparent widths proportion of adjacent teeth and the width/height ratio of the clinical crown in Chinese adults are different from the foreigner's. The esthetic proportion parameters have significant population specificity, and the measurements cannot be generalized as well as it should be applied with caution.

Effects of loupes and microscope on the prosthodontist's posture from ergonomic aspects / 北京大学学报(医学版)

OBJECTIVE@#To assess the effects of loupes and microscope on the posture of prosthodontists when preparing the laminate veneer, and to assess the clinical value of loupes and microscope from the ergonomic aspects.@*METHODS@#Twenty young prosthodontists from Department of Prosthodontics, Peking University School and Hospital of Stomatology were recruited into this study, which was a prospective, single blind, self-control trials. The research hypothesis was concealed and the participants were deceived about the precise purpose of the study to counterbalance the lack of direct blinding. The prosthodontists prepared laminate veneers of open window type in the artificial dental model, under routine visual field (control group), 2.5× headwear loupes (loupes group), and 8× operating microscope (microscopic group) by turning. The participants were photographed from profile view and front view. Thereafter, the subjective assessment was performed by themselves using the visual analogue score (VAS). The expert assessment was performed by two professors using modified-dental operator posture assessment instrument on the basis of photographs of the profile view and front view.@*RESULTS@#The subjective assessment scores for the control group, loupes group and microscopic group were 4.55±1.96, 7.90±1.12, and 9.00±0.92, respectively. There was significant difference between the three groups' subjective scores (P < 0.05). The expert assessment scores for the control group, loupes group and microscopic group were 16.38±1.52, 15.15±1.30, and 13.60±0.88, respectively. There was significant difference between the three groups' expert assessment scores (P < 0.05). Specifically, the three groups' expert assessment scores were significantly different (P < 0.05) in trunk position (front to back) (1.33±0.41, 1.03±0.11, 1.00±0.00), head and neck position (front to back) (2.75±0.38, 2.13±0.36, 1.23±0.38), elbows level (1.38±0.43, 1.40±0.45, 1.13±0.22), and shoulders level (1.43±0.41, 1.23±0.34, 1.13±0.28). Thereinto, the microscopic group was better than loupes group in head and neck position (front to back) and elbows level (P < 0.05).@*CONCLUSION@#Loupes and microscope improve the posture of the prosthodontist when preparing the laminate veneer, in which the microscope is better than loupes. Therefore, the magnification devices have clinical value from the ergonomic aspects.

Effect of different plasma treated zirconia on the adhensive behaviour of human gingival fibroblasts / 北京大学学报(医学版)

OBJECTIVE@#To evaluate the effect of different cold atmospheric plasma (CAP) treatment on the surface chemical and physical properties of zirconia and adhensive behaviour of human gingival fibroblasts (HGFs) cultured on zirconia disks.@*METHODS@#The zirconia disks were divided into four groups and treated using helium, argon and mixture of argon and oxygen cold atmospheric plasma for 90 s or left untreated. The surface morphology, wettability and chemical elements were analyzed right after treatment. Human gingival fibroblasts were grown from biopsies obtained from a periodontally healthy human subject during periodontal surgery. HGFs were seeded on zirconia disk, and cells density was measured at the time point of 3 hours. Indirect immunofluorescence (IIF) was performed for morphometric examination at the time point of 3 hours.@*RESULTS@#The crystallographic structure of zirconia was analyzed previously and the results suggested that it fitted the properties of zirconium yttrium oxide. After helium, argon and mixture of argon and oxygen cold atmospheric plasma treatment, the surface morphology and roughness of zirconia disks remained the same. The contact angle of zirconia decreased significantly(P<0.05)after CAP treatment: from 68.38° to 17.90°. After different CAP plasmas treatment, the atomic percentage of carbon on the outermost surface of the three groups decreased, as did the surface C/O ratio. The surface C/O ratio of zirconia decreased from 1.07 to 0.33. Fibroblasts density increased on CAP treated disks, especially the ones treated by mixture of argon and oxygen CAP(P<0.05). Cells of the three CAP plasma treatment groups spread better and had more protrusions, as well as larger surficial areas.@*CONCLUSION@#Based on the results of this study after being treated by different kinds of CAP plasmas for 90 s, the surface wettability increased and the elements changed significantly with no changes in the tomography and roughness of the materials. The CAP treatment enhances the adhensive behavior of fibroblasts on zirconia by increasing the oxygen functional groups and promoting the cell density. Wettability of zirconia, an important physicochemical property, has a vital influence on the cell behaviors.

Effect of a novel cold atmospheric plasma jet treatment with different temperatures on resin-dentin bonding / 北京大学学报(医学版)

OBJECTIVE@#To investigate the effect of different treatment temperatures of a novel cold atmospheric plasma jet treatment on the resin-dentin bonding.@*METHODS@#(1) Fifty-two freshly extracted, non-carious and intact third molars were collected. The occlusal one-third of the crown was removed by means of a water-cooled low-speed Isomet saw. One dentin disc [(900 ±100) μm] was prepared for each tooth. The fifty-two dentin discs were randomly divided into control group and experimental groups, of which four were in control group, and forty-eight were divided into four experimental groups according to the different treatment temperatures (4 °C, 10 °C, 20 °C and 30 °C) of the novel radio-frequency atmospheric-pressure glow discharge (RF-APGD) plasma jet, twelve in each group. Each experimental group was divided into three subgroups according to different treatment time (10 s, 20 s and 30 s), with four in each subgroup. The occlusal one-third of the crown was removed by means of a water-cooled low-speed Isomet saw. The morphology of demineralized dentin surfaces was analyzed using field emission scanning electron microscopy. (2) Twenty unerupted, non-carious and intact third molars were randomly divided into five groups, four in each group: control group, untreated; 4 °C, 10 °C, 20 °C and 30 °C experimental groups, each group was treated with the RF-APGD plasma jet for 20 s. The micro-tensile resin dentin bond strength was tested after 20 s RF-APGD plasma jet treatment with different temperatures, using a universal mechanical machine.@*RESULTS@#(1) The field emission scanning electron microscopy results indicated that when compared with the control group, a 10 s RF-APGD plasma jet treatment with 30 °C and 20 °C collapsed the collagen scaffold. Collagen fibrils maintained an uncollapsed three-dimensional structure after the 4 °C RF-APGD plasma jet treatment for even 30 s treatment. (2) The microtensile resin dentin bond strength results of the 4 °C RF-APGD plasma jet treatment group (57.8±0.7) MPa were significantly higher than that of the control group [(47.4±0.5) MPa] and 10 s, 20 s and 30 s RF-APGD plasma treatment group [(51.9±0.7) MPa,(29.7±1.0) MPa and (22.2±1.5) MPa] with statistically significant difference (P<0.05). Compared with the control group, the micro-tensile bond strength increased about 21.9% and 9.5% after 4 °C and 10 °C RF-APGD plasma jet treatment, respectively.@*CONCLUSION@#Compared with other treatment temperatures, this novel RF-APGD plasma jet treatment with the temperature of 4 °C can preserve the three-dimensional morphology of demineralized dentin better, and can improve the resin-dentin bonding.

Effects of different surface treatments on the zirconia-resin cement bond strength / 北京大学学报(医学版)

OBJECTIVE@#To evaluate the effects of different surface treatments on the shear bond strength between zirconia and resin cement.@*METHODS@#Forty zirconia discs were randomly divided into four groups (10 discs in each group) for different surface treatments: control, no surface treatment; sandblast, applied air abrasion with aluminum oxide particles; ultraviolet (UV), the zirconia sample was placed in the UV sterilizer at the bottom of the UV lamp at 10 mm, and irradiated for 48 h; cold plasma, the discs were put in the cold plasma cabinet with the cold plasma generated from the gas of He for 30 s. Specimens of all the groups were surface treated prior to cementation with Panavia F 2.0 cement. The surface morphology and contact angle of water were measured. The shear bond strengths were tested and the failure modes were examined with a stereomicroscope.@*RESULTS@#Surface morphology showed no difference between the UV/cold plasma group and the control group. Sandblasted zirconia displayed an overall heterogeneous distribution of micropores. The contact angle of the control group was 64.1°±2.0°. After sandblasting, UV irradiation and cold plasma exposure, the values significantly decreased to 48.8°±2.6°, 27.1°±3.6° and 32.0°±3.3°. The values of shear bond strength of the specimens with sandblasted (14.82±2.01) MPa were higher than those with no treatment (9.41±1.07) MPa with statistically significant difference (P<0.05). The values of shear bond strength of the specimens with UV irradiation (10.02±0.64) MPa were higher than those with no treatment (9.41±1.07) MPa, but without statistically significant difference (P>0.05). The values of cold plasma group (18.34±3.05) MPa were significantly higher than those of control group (9.41±1.07) MPa, even more than those with sandblast(14.82±2.01) MPa (P<0.05). X-ray photoelectron spectroscopy (XPS) showed increase in oxygen (O) and decrease in carbon (C) elements after UV and cold plasma treatment. The surface C/O ratio also decreased after UV and cold plasma treatment.@*CONCLUSION@#Zirconia specimens treated with UV and cold plasma could significantly improve the hydrophilicity. The surface morphology was unaffected by the UV irradiation and cold plasma treatments. The improvements of ziconia shear bond strength were slight in UV group without statistically significant difference. Cold plasma treatment significantly improved the shear bond strength between zirconia and resin cement.

Stability of phonetics to determine the horizontal jaw relation in healthy adults / 华西口腔医学杂志

<p><b>OBJECTIVE</b>The aim of this study was to compare the mandibular position when speaking with the intercuspal position and to check the stability of phonetics when determining the horizontal jaw relation in healthy adults.</p><p><b>METHODS</b>A total of 19 healthy volunteers were recruited. Seven Chinese letters, namely, /xi/, /er/, /yi/, /ci/, /mi/, /ni/, and /ri/, were chosen in the test. O-bite was used to record the mandibular position when speaking these letters. A full-adjusted articulator was used to find the mandibular position during speech, and the mandibular position was measured using a vernier caliper. The mandibular position during speech with intercuspal position was compared in both anterior-posterior and left-right directions of the horizontal plane. Multi-factor analysis of variance was conducted for the statistical analysis of the effect of objects and letters on the mandibular position.</p><p><b>RESULTS</b>1) The mandibular position was in front of the intercuspal occlusion position when speaking all seven letters, and almost no deviation was observed in the left and right directions (the mandibular position value of 82% was in the range of 0.5 mm). 2) Different objects had different mandibular positions during speech, whereas different letters did not. The distance between the centric relation position and the intercuspal position had a positive correlation with the range of the mandibular position during speech.</p><p><b>CONCLUSION</b>The mandibular position was in front of the intercuspal position when speaking all seven words in the test. In the same object, the mandibular position was stable during speech.</p>

Impact of temperature on mortality in three major Chinese cities / 生物医学与环境科学（英文）

<p><b>OBJECTIVE</b>To study the relation between temperature and mortality by estimating the temperature-related mortality in Beijing, Shanghai, and Guangzhou.</p><p><b>METHODS</b>Data of daily mortality, weather and air pollution in the three cities were collected. A distributed lag nonlinear model was established and used in analyzing the effects of temperature on mortality. Current and future net temperature-related mortality was estimated.</p><p><b>RESULTS</b>The association between temperature and mortality was J-shaped, with an increased death risk of both hot and cold temperature in these cities. The effects of cold temperature on health lasted longer than those of hot temperature. The projected temperature-related mortality increased with the decreased cold-related mortality. The mortality was higher in Guangzhou than in Beijing and Shanghai.</p><p><b>CONCLUSION</b>The impact of temperature on health varies in the 3 cities of China, which may have implications for climate policy making in China.</p>

Coverage errors of five shade guide systems to vital natural teeth / 中华口腔医学杂志

<p><b>OBJECTIVE</b>To compare the coverage errors (CE) of five different shade guides in anterio vital natural teeth of selected people.</p><p><b>METHODS</b>Anterior vital natural teeth were measured with Crystaleye spectrophotometer, color coordinates of the teeth and five shade guides A (VITA Classical), B (VITA 3D-Master), C (Chromascop), D (Shofu Vintage Halo NCC) and E (Noritake)were analyzed with the supporting software. The CE of the five shade guide systems to natural teeth were evaluated in cervical, body and incisal regions, and difference in CE among shade guides was determined.</p><p><b>RESULTS</b>In the cervical region, shade guide A had the maximal CE value (3.09 ± 0.97) and shade guide D had the minimal CE value (1.62 ± 0.75).In the body region, CE of shade guide B (1.65 ± 0.64) and shade guide D (1.52 ± 0.74) were lower than those of shade guides A (2.04 ± 0.80), C (2.04 ± 0.90) and E (2.02 ± 0.84) (P < 0.05).In the incisal part, all CE were below 2.00, and again shade guide A had the maximal CE value (1.81 ± 0.86) and shade guide D had the minimal CE value (1.28 ± 0.55).</p><p><b>CONCLUSIONS</b>Within the limitation of the study, shade guide D had better color coverage of natural teeth in cervical, body and incisal regions.</p>

Effect of multiple coatings of one-step self-etching adhesive on microtensile bond strength to primary dentin / 中国医学科学杂志(英文版)

<p><b>OBJECTIVE</b>To investigate the effect of multiple coatings of the one-step self-etching adhesive on immediate microtensile bond strength to primary dentin.</p><p><b>METHODS</b>Twelve caries-free human primary molars were randomly divided into 2 groups with 6 teeth each. In group 1, each tooth was hemisected into two halves. One half was assigned to control subgroup 1, which was bonded with a single-step self-etching adhesive according to the manufacturer's instructions; the other half was assigned to experimental subgroup 1 in which the adhesive was applied three times before light curing. In group 2, the teeth were also hemisected into two halves. One half was assigned to control subgroup 2, which was bonded with the single-step self-etching adhesive according to the manufacturer's instructions; the other half was assigned to experimental subgroup 2 in which three layers of adhesive were applied with light curing each successive layer. Microtensile bond strength was immediately tested after specimen preparation.</p><p><b>RESULTS</b>When the adhesive was applied three times before light curing, the bond strength of the experimental subgroup 1 (n=33, 57.49 +/-11.61 MPa) was higher than that of the control subgroup 1 (n=31, 49.71 +/-11.43 MPa, P<0.05). When using the technique of applying multiple layers of adhesive with light curing each successive layer, no difference of immediate bond strength was observed between the control subgroup 2 and the experimental subgroup 2 (P>0.05).</p><p><b>CONCLUSION</b>strength to primary dentin when using the technique of light-curing after applying three layers of adhesive.</p>

Ultrastructural study of sclerotic dentin surface following the application of the Er, Cr: YSGG laser / 中华口腔医学杂志

<p><b>OBJECTIVE</b>To investigate the ultrastructure character of sclerotic dentin surface conditioned by the Er, Cr: YSGG laser and acid etching.</p><p><b>METHODS</b>Sixteen human teeth with sclerotic dentin were randomly assigned to 4 groups, and conditioned with acid etching (Group A), laser irradiation (Group B), laser irradiation after acid etching (Group C), or acid etching after laser irradiation (Group D) respectively. The characters of surface ultrastructure were observed using scanning electron microscope (SEM).</p><p><b>RESULTS</b>In Group A, the majority of dentin tubules were blocked by sclerotic rods. In Group B, the honeycomb-like change was found on the sclerotic dentin surface. The surface structure of Group C was similar to that of Group B. In group D etching wiped off the honeycomb-like structure.</p><p><b>CONCLUSIONS</b>The sclerotic dentin surface treated with laser irradiation turns into uniform honeycomb-like structure. The rough surface may be beneficial to bonding strength on sclerotic dentin after laser irradiation.</p>

Computerized image processing in esthetic rehabilitation of anterior teeth / 中华口腔医学杂志

<p><b>OBJECTIVE</b>To investigate the application of computerized image processing in esthetic rehabilitation of anterior teeth.</p><p><b>METHODS</b>Thirteen patients with esthetic problems in anterior teeth were included in this study. Oral digital images were obtained before and during treatment with a digital camera. All the oral esthetic data of the patients, including tooth shape, tooth shade, tooth characteristic color, incisal transparency, incisal curve, smile line, and gingival curve et al, were collected and analyzed. Diagnostic images of the anticipated esthetic outcome were created by computerized image processing software and transferred to the technician. Restorations were made according to the images by the technician.</p><p><b>RESULTS</b>All anterior teeth of 13 patients were restored with this method and good esthetic results were achieved.</p><p><b>CONCLUSIONS</b>Computerized image processing is a useful method in the esthetic rehabilitation of anterior teeth.</p>

Micro-tensile bond strength to sclerotic dentin in non-carious cervical lesions / 中华口腔医学杂志

<p><b>OBJECTIVE</b>This in vitro study was to evaluate the micro-tensile bond strength (microTBS) of three adhesives to sclerotic dentin in non-carious cervical lesions.</p><p><b>METHODS</b>The maxillary premolars extracted due to periodontitis and with non-carious cervical lesions were collected. The non-carious, natural cervical sclerotic lesions were bonded with a total-etching adhesive Scotchbond Multi-Purpose, a two-step self-etching adhesive Contax, and an all-in-one self-etching adhesive Adper Prompt L-Pop. Artificially prepared wedge-shaped lesions were also made in sound premolars and bonded with the same adhesives as the controls. MicroTBS of these three adhesives was measured.</p><p><b>RESULTS</b>MicroTBS of Scotchbond and Contax to sclerotic dentin was significantly lower than to normal dentin. But microTBS of Adper Prompt L-Pop to normal dentin was significantly lower than to sclerotic dentin. MicroTBS to sclerotic dentin was Scotchbond 46.805 MPa, Adper Prompt L-Pop 39.045 MPa, and Contax 29.852 MPa.</p><p><b>CONCLUSIONS</b>In sclerotic dentin the microTBS was decreased because of the inferior micro-morphology of resin tags. Adhesives with low pH value might bond to sclerotic dentin effectively.</p>