Objective To verify the feasibility and accuracy of the microsphere diffusion method by the method of electron microscopy; meanwhile, to measure and compare the four different micro-gaps of the four different implant-abutments stressed by different horizontal loads. Method Four kinds of implant based micro-gap models were constructed in vitro (Group A: Anatomic all ceramic abutment; Group B: SynOcta octagonal titanium base; Group C: Procera titanium base all ceramic abutment; Group D: Procera all ceramic abutment, Polystyrene microspheres were added into the implants (0.2-5 μm). At the same time, the different horizontal loads (0, 50, 100, 150 N) were given. The maximum particle size of micro diffusion was measured by laser particle size analyzer. At the same time, the time required to measure the maximum width was recorded. On the other hand, scanning electron microscopy was used to measure the width of the slit of the 8 observation points of each slit model, and the maximum value was obtained. The differences between the two methods were analyzed by t test. Results ①There was no significant difference in the accuracy of the micro slit width between the microspheres diffusion method and the electron microscope (P<0.05). ②Micro diffusion method to detect micro slit width took up to 15 minutes. ③When there was no external load, the micor-gaps of A and D groups were significantly larger than B, C groups (P<0.05). ④In B, C groups, 100N and 150 N load micro-gaps were significantly greater than 0 N (P<0.05); 150 N load of micro-gap was significantly greater than 50 N (P<0.05). Conclusion Microsphere diffusion method is simple, efficient and accurate to measure the maximum width of micro-gap between implant and abutment. The result of the experiment shows that the micro-gap of the implant-procelain interface is significantly larger than that of the implant-titanium interface, meanwhile, the micro-gap of the implant-titanium interface will increase significantly when stressed by the larger horizontal loads.

Objective　Toexplore the effectof fiber-reinforced composites on the fracture load and fracture mode of resin veneer cemented with different types of fiber-reinforced composite(FRC). Methods　30 maxillary incisors were randomly divided into 3 groups. Group1 was restored with composite veneers. Group 2 was restored with composite veneer reinforced with FRC in one direction. Group 3 was restored with composite veneer reinforced with FRC in two directions. All specimens were thermocycled. Initial fracture loads and final fracture loads were tested with a universal testing machine. Fracture modes of different groups were observedand studied.Results　For the initial fracture load, there was no statistically significant difference(P>0.05)among the test groups. According to the statistical results, the final fracture loads had no significant difference (P>0.05) between Group 2 and Group 3. The final fracture load of Group 1 was significantly lower than Group 2 and Group 3(P<0.05). In Group 2 and Group 3, the final fracture loads were significantly higher than the initial fracture loads (P<0.05). Repairable small fractures were observed in most specimens of Group 3, and irreparable fractures were observed in specimens of Group 1 and Group 3. Conclusions　FRC is helpful to increase final fracture load of composite resin veneer. And the fractured resin veneer is more convenient to be repaired by the reinforcement of bidirectional FRC.

Objective To compare the accuracy of two methods of flap and flaplss in the posterior region when using the CAD/CAM template. Methods Cone Beam CT data and plaster models were selected from 20 patients with posterior teeth implantation. The flap and flapless resin models were fabricated by 3D printing technique. The surgical guides were used to simulate dental implant placement on the two kinds of models, respectively. The preoperative and postoperative implant position deviations were calculated and then accuracies of the two surgical procedures were compared. Results The top deviations of the flap and the flapless way were（0.95±0.36）mm，（1.33±0.43）mm, respectively. The bottom deviations were（1.53±0.56）mm,（1.94±0.30）mm, respectively. The angle deviations were（3.45±1.10）°，（3.31±1.55）°, respectively. The depth deviations were（0.75±0.47）mm，（1.43±0.41）mm, respectively. Conclusion There is a statistically significant difference in the deviation of the implant between flap and flapless methods, while there is no statistical difference in angle deviation. CAD/CAM guided implant flap approach is more accurate than the flapless procedure in distance deviation.

Objective To evaluate the changes of alveolar bone and soft tissue after 6 months of the front tooth extraction site preservation by cone beam computed tomography (CBCT) and model measurement. Method A total of 32 teeth from 29 patients with indications for the front tooth extraction were enrolled. Deproteinized boving bone mineral (DBBM, Bio-Oss) and absorbable biofilm (Hao) were used in experimental group, when the extraction site was performed, and the control group received no special treatment after routine extraction. The gypsum model was employed before the operation (baseline) and after six months, while the CBCT was taken immediately after the operation (baseline) and six months later as well. The changes of alveolar bone and soft tissue were analyzed by CBCT and model measurement. Results The data obtained by CBCT were statistically significant in height of labial and temporal alveolar bone(P<0.05). After 6 months, the labial and temporal alveolar bone height of the experimental group was significantly higher than that of the control group (P<0.05), which were 16.31± 0.94m and 18.61 ± 1.10mm respectively. The alveolar bone width, measured at 20% and 70% of the root length, were also significantly higher than the control group (P<0.05), which were 4.43 ± 0.32mm and 4.79 ± 0.37mm respectively, but there was no significant difference between two groups at 50% of the root length (P>0.05). The soft tissue was significantly higher in the control group (9.26 ± 0.40 mm) than the treatment group (P < 0.05) at the highest point of the maxillary gingival margin and the lowest point of the mandibular gingival margin, but in soft tissue between mesial papilla and distal nipple, there was no statistically significant difference (P>0.05). Conclusions The simultaneous preservation of extraction sites of the front teeth have positive significance for the preservation of height, width and alveolar soft tissue after tooth extraction, which is worthy of promotion in clinical practice.

Abstract：　Objective　 To compare the inhibitory effect of three endodontic irrigating reagents (NaOCl, H2O2, PVP-I) on four kinds of bacteria (E.f, F.n, P.g, P.e) in human root canals after chemo-mechanical preparation. Methods　60 single root teeth with chronic apical periodontitis were randomly divided into three groups. The first group (n=20) was irrigated with 2.5% NaOCl. The second group (n=20) was irrigated with 3% H2O2. The third group (n=20) was irrigated with 1% PVP-I. Clinical periapical indexes was presented by the diameter of image shadows. The symptoms of pain and swelling were documented and measured before and after the root canal treatment. Real-time quantitative-polymerase chain reaction (qRT-PCR) was used to compare the positive rates and quantities of four bacteria (E.f, F.n, P.g and P.e) in different groups. Statistical analysis was performed using the Mann–Whitney test. Results The symptom of pain and swelling was significantly decreased and relieved in all three groups after root canal treatment. The bacteria load was reduced significantly after treatment in three gourps. There was no significant inhibitory effect on P.e in three groups（P >0.05）,whereas the numbers of E.f, F.n and P.g were reduced significantly (P<0.05). The numbers of E.f, F.n and P.g were reduced significantly in both NaClO-group and the (PVP-I)-group comparing to the H2O2-group (P<0.05). The detection rate of P.e in the (PVP-I)-group was lower than the H2O2-group (P<0.05). Conclusions 2.5% NaClO, 1% PVP-I and 3% H2O2 can effectively inhibit the growth of E.f, F.n, P.g and P.e in infectious root canals. There was no significant inhibitory effect on these four bateria between 2.5%NaClO and 1% PVP-I, but both showed inhibitory effect on E.f, F.n and P.g comparing to 3% H2O2. 1% PVP-I showed better inbitory effect on P.e than 3% H2O2.

Objective: To investigate the crown-root length of upper central incisors in early youth and explore the related hard tissue measurement items. Methods: The cone-beam CT (CBCT) of 100 patients with malformed malocclusion was selected. The crown-root length of the upper central incisors and the related hard tissue 3D measurement indexes were measured by MIMICS17.0 software. The Spearman correlation analysis was carried out on the crown-root length of the upper central incisors and the related hard tissue 3D measurement indexes using the SPSS21.0 software. Results：①The root length was positively correlated with the lip inclination and the thickness of the alveolar bone in the apical labial side.②The crown root ratio of the upper central incisors was negatively correlated with the lip inclination and the thickness of the alveolar bone in the apical labial side.③The thickness of the alveolar bone in the apical labial side was positively related to the lip inclination, and was negatively correlated with the crown root ratio. Conclusion: There is a correlation between the length of the root, the crown root ratio, the lip inclination, the thickness of the alveolar bone in the apical labial side of the upper central incisors. It has a guiding significance for the clinical work.

Abstract: Objective: To observe the thickness of maxillary sinus mucosa and analyze the influence of sex, age and loss of posterior teeth, and to evaluate the relationship between periapical disease of maxillary posterior teeth and the maxillary sinus mucosa thickening. Methods: CBCT images were collected from 334 Chinese patients（including 636 sinus）. In NNT, the thickness of maxillary sinus mucosa(Type A:≤2mm；Type B：＞2mm) was recorded in the sagittal and coronal planes. Sex, age, side and loss of adjacent posterior teeth were also recorded. In patients without tooth loss, the affected relationship was recorded, including Type os(the lesion had a certain distance to the MSF), Type co(the lesion contacted the MSF) and Type is(the lesion intruded into the MSF). All patients were divided into three age groups:18-40 years，41-60 years and ＞60 years. Results: The proportion of pathological maxillary sinus mucosal thickening was 40.4%. There was a significant increase in the proportion of pathological mucosal thickening when periapical disease existed(P < 0.05) and the thickness of sinus mucosa had no significant difference with three different affected relationship(P＞0.05). The proportion of mucosal thickening in the male(45.6%) was significantly greater than that of women (36.3%) (P < 0.05).The pathological thickening ratio of maxillary sinus mucosa in people over 40 years old was significantly greater than those under 40 (P < 0.05).The proportion (58.9%) of the pathological mucosal thickening with posterior tooth loss was significantly higher than that tooth loss (35.7%) (P < 0.05). Conclusions: There was a high proportion of patients with pathological mucosal thickening in male, middle-aged and elderly patients and people with tooth loss. Periapical lesion is the main factor leading to the thickening of the maxillary sinus mucosa, and the incidence of mucosal thickening is significantly increased with the gradual invasion of periapical lesion. The possibility of maxillary sinusitis could not be ruled out even if the lesion was not reached in the MSF.

Objective: To compare the efficiency of root canal removal with three simulated treatments of D-RaCe, ProTaper, and Mtwo via simulated root canal. Methods:There are 30 transparent resin root canals were randomly selected and divided into 3 groups. D-RaCe, ProTaper, and Mtwo were used to remove the root fillings. The operation time was recorded, and the images after removal of the root fillings were collected. Image analysis software was used to calculate the residuals. Area, compare the overall clearance rate of the three species. The apical part was divided into three sections from 0-2mm, 2-4mm, and 4-6mm from the apical foramen. The residual area was calculated and the best clearance rate among the three retreatment groups was compared. Result: The shortest operating time for D-RaCe. All samples had residual fillings in the root canal, and there was no significant difference in overall clearance between ProTaper and Mtwo (p>0.05), and all were superior to those in D-RaCe group (p<0.05). In the 0-2mm and 2-4mm sections of the apical foramen, the clearance rate in the D-RaCe group was the lowest, and there was no statistical difference in the 4-6mm sections (p>0.05). Conclusion: The D-RaCeTM has a short operating time, higher fatigue resistance and anti-break ability. ProTaper and Mtwo re-treatments were able to remove most of the root fillings. The clearance rate in the 0-2mm and 2-4mm sections from the apical foramina was better than that in the D-RaCe group.

Objective: To discuss the application of three-dimensional digital technology in diagnostic set-up of orthodontic cases by comparing results’ consistency of tooth extraction or not based on two different therapeutic regimens with or without the three-dimensional digital technology.Methods: 40 orthodontic first-visit cases with complete history information in recent 5 years were selected as the research samples after the preliminary screening by an orthodontist with intermediate certificate in our hospital. All the samples were divided into two groups, and the therapeutic regimens were designed by 6 orthodontists with secondary senior position according to the impression models, X ray examinations, facial & oral pictures and analysis of traditional routine data measurement. Additionally, the three-dimensional digital technology, as an aiding method, was applied in the second group. Results of the therapeutic regimens were divided into tooth extraction, non-extraction and boardline cases. Statistical analysis was applied to compare the results consistency of tooth extraction situation between the two groups. Results: With a standard of completely consistent results of 6 orthodontists，consistency rate of tooth extraction, non-extraction and boardline cases of the first group were 7.50%, 2.50% and 12.93%, respectively with the 22.50% general coincidence rate, and the second group were 42.50%，20.00% and 2.50%, respectively with the 65.00% general coincidence rate. Set value of the extraction case as 1, and boardline case as 0, and non-extraction case as -1.Six doctors separately value the 40 cases ,and then summit every single case with the absolute value of what the doctor evaluates. We performed paired design and analyze the data with Wilcoxon rank test. The coincidence rates of extraction and non-extraction of the second group were higher than the first one, the coincidence rate of boardline cases of the second group was lower than the first one, and the differences were significant based on the statistics analysis.Conclusions: It can offer beneficial reference for tooth extraction or not by aiding three-dimensional digital technology into the design of orthodontic therapeutic regimens.

Objective　To study the effects of the thermal conductivity of gold-alloy, gold-alloy-porcelain, zirconia all-ceramic on the health of the tooth pulp. Methods The coefficients of thermal conductivity of gold-alloy, gold-alloy-porcelain, zirconia all-ceramic, autogenous teeth, composite resin cement were measured in the laboratory. 158 vital pulp abutment teeth repaired by gold alloy casted full crowns, gold-alloy-porcelain crowns and zirconia all-ceramic crowns were followed up for 2 years. Compared with 158 autogenous adjacent teeth, the numbers of cases of pulpitis and apicitis were counted, and then compared with the coefficients of thermal conductivity of the materials. Results After resin bonding, the thermal conductivity coefficient of 86% gold-alloy was 37.89W/(m?K), 3 cases of pulpitis occurred in 21 vital pulp abutment teeth. The thermal conductivity coefficient of 86% gold-alloy-porcelain was 0.85W/(m?K), 1 case of pulpitis occurred in 58 vital pulp abutment teeth. The thermal conductivity coefficient of zirconia all-ceramic was 0.82W/(m?K), no case of pulpitis and apicitis occurred in 79 vital pulp abutment teeth. The thermal conductivity coefficient of healthy teeth was 0.66W/(m?K), no case of pulpitis and apicitis occurred in 158 vital pulp abutment teeth. The positive rates of pulpitis and apicitis of abutment teeth restored by 86% gold-alloy-porcelain crowns were significantly higher than those of abutment teeth restored by other crow restoration materials with low thermal conductivity coefficient (P<0.01). Conclusions Abutment teeth pulp health can be influenced by the thermal conductivity of crowns, for example, too high crown thermal conductivity has a negative effect on the health of the tooth pulp. It is recommended that the combination of zirconia ceramic + resin adhesive with the closest thermal conductivity to natural teeth be the first choice for crown restoration materials.

Objective　To compare the clinical effects of fiber post, fiber-post zirconia + all-ceramic crown and direct resin filling restoration on endodontically treated premolars with severe wedge-shaped defects. Methods　Ninety-seven patients with 135 endodontically treated premolars with severe wedge-shaped defects were randomly divided into three groups. After repairing them with the three methods, the success rate and the performance satisfaction of the different groups were observed in 24 months. Results　At the final follow-up, the success rate of the group which was restored by fiber posts was 95.6%, the success rate and performance satisfaction of the group by fiber-post zirconia + all-ceramic crown was 93.3% and the success rate and performance satisfaction of the third group by composite resin was 82.2%. There was no statistically significant difference in the success rate between the fiber post group and the fiber-post zirconia + all-ceramic crown group (P>0.05), while the statistical difference of the success rate between the fiber post group and the composite resin group was significant (P<0.05). The satisfaction rate of fiber-post zirconia + all-ceramic crown group was the highest. Conclusions　As far as the observation is concerned, the clinical effects of the fiber post and the fiber-post zirconia + all-ceramic crown group are basically the same, and fiber post is a relatively reliable method to restore endodontically treated premolars with severe wedge-shaped defects.

Objective To assess the effect of topical fluoride varnish in prevention of first permanent molar caries of school-age children and provide evidence for formulating caries prevention strategies. Methods Using cluster random sampling method, in November 2014, 666 children of 6-7 years old in the first grade of primary school in Dahua County, Guangxi province were randomly selected and divided into two groups. From November 2014 to May 2017, the children in the test group were treated with fluoride varnish every six months, along with oral health education; whereas children in the control group were only given oral health education. In November of 2014, 2016, and 2017, oral examinations were performed on all subjects to collect data on the first permanent molars and conduct statistical analysis. Results After 2 years of intervention, the incidence of dental caries in the first permanent molar in the test group was lower than that in the control group, and the difference was statistically significant (P<0.05). After 3 years of intervention, there was a significant difference between two groups on the prevalence and incidence of caries, mean DMFT and mean DMFS (P<0.05). The incidence of maxillary and mandibular first molar, fissure and proximal surface caries of first permanent molars in the test group were lower than that of control group, but there was no significant difference in the incidence of proximal surface caries (P>0.05). Conclusion The topical application of fluoride varnish is effective in prevention of caries of first permanent molars, and longer the exposure time of fluoride varnish, better the effect of prevention.

Insufficient alveolar bone volume caused by bone resorption has become a common problem for implant placement. Autogenous bone grafting and guided bone regeneration technique have shown good effects on the bone augmentation. These techniques have been widely used for overcoming hard-tissue defects in preprosthetic surgeries. However, the bone remodeling and the augmented bone stability are both considered to be the important factors of the success of the dental implant treatment. The volumetric extents of these two methods are clear, but their long-term stability of the bone blocks gradually attracts more attention. This review aims at demonstrating the advantages of guided bone regeneration compared with autogenous bone grafting in terms of long-term stability.

Guided bone regeneration (GBR) has some application disadvantages, including poor resistance to resorption and collapse of absorbable barrier membranes, suboptimal bone regeneration due to a second surgical procedure to remove the non-resorbable membrane and the frequent occurrence of membrane exposure to the oral cavity, and the displacement of bone substitute particles and loss of the contour in the augmented site during the placement of membrane. Especially in non-space-maintaining defects, GBR always shows the unpredictability of regenerative capacity because conventional bone substitute materials are only osteoconductive and not osteoinductive scaffolds, and the barrier membrane can’t maintain a stable space for bone regeneration due to unfavorable defect morphologies. Autogenous block grafting may exhibit significant advantages over GBR using particulate substitutes with regard to bone regenerative capacity and biomechanical properties. Even in non-space-maintaining defects, it can provide the osteogenic cells that are necessary for the remodelling and formation of new bone, ideal contour reconstruction and optimal resistance to micromovement and resorption. The conclusion of our standpoint is that GBR is not superior to autogenous grafting in long-term stability of grafted bone.

The alveolar bone defect in oral and maxillofacial surgery is the main cause of oral dysfunction, how to repair bone defect and restore its function is the focus in recent years. The current clinical technology based on the use of bone reconstruction have certain limitations, then tissue engineering and bone mesenchymal regenerative medicine came into being. Because of the proliferation and differentiation of mesenchymal stem cells ，MSCs can replace the damaged tissue, it is expected to become an effective alternative for the treatment of bone defect. Recent studies have shown that mesenchymal stem cells can secrete growth factors, these growth factors play an important role in the process of repair and regeneration of tissues. This indicates that the mode based on the proliferation and differentiation of mesenchymal stem cells to repair bone defect have turn to another direction, namely the mesenchymal stem cell paracrine growth factor induced bone repair. This paper summarizes the recent basic research of bone defect repair and clinical experimental results, focus on the new direction of mesenchymal stem cells paracrine effects of bone repair treatment and related growth factors.

Platelet-rich fibrin (PRF), as a platelet concentrated product, can store rich growth factors in its three-dimensional fibrous tissue structure, which can significantly promote the healing of oral and maxillofacial soft and hard tissue defects. PRF contains a large number of platelets, in which a variety of cytokines can regulate the normal growth metabolism, most of them binding to specific high affinity membrane receptors to play its regulatory role. PRF is playing an increasingly important role in the field of dental implants today. This review will outline the latest advances of PRF in the field of dental implants.

　Periodontitis is a chronic inflammatory disease characterized by periodontal tissue inflammation and alveolar bone destruction. Researches have detected Th17 cells at different stages of periodontitis, suggesting that Th17 cells participate in the progress of periodontitis. This article reviews the role of Th17 cells in the development of periodontitis.

Nowadays, in the context of the wave of precision medicine research, sleep medicine is also deep involved in it. However, compared with other diseases, diseases like obstructive sleep apnea (OSA) seem to have an urgent need of the research idea of precision medicine. This paper first sketches the research development of OSA, then further explores why OSA urgently needs the research approach of precision medicine and how precision medicine can be applied into clinical research of OSA.

Bulk-fill resin-based composite (bulk-fill RBCs) materials are increasingly being used for the clinical restoration nowadays. The outstanding advantages of bulk-fill RBCs is the capability to be placed and cured in 4-6mm increments one time ,which is easy to operate. Resin polymerization shrinkage,marginal microleakage and stability in the long term of properties are highly correlated with clinical effects. It is hot pot in bulk-fill RBCs study to insure higher depth of cure,lower polymerization shrinkage and clinical evaluation. The paper mainly reviews the advances on the above-mentioned aspects .

Abstract: With the discovery of dental restorative bonding technology,the adhesive properties of adhesives have become a hot research topic.Clinically, all kinds of bonding systems were used to repair residual roots and crowns with fiber post bonding. However, the lack of bond strength and microleakage will lead to failure of clinical repair. In this paper ,the adhesive strength and microleakage of adhesive are reviewed, in order to provide evidence based medicine for clinical selection of fiber post bonding system.