[Research and application of three-dimensional printed template in endodontics].

With the progress of technology, three-dimensional (3D) printing technology has become more and more widely used in stomatology. 3D printed template has played an irreplaceable role in oral implantation; at the same time, 3D printed template, which has been successfully applied to the calcified root canal negotiation, endodontic treatment of dental invaginatus, apical surgery and autotransplantation, has also provided a new concept and treatment mode for the diagnosis and therapy of endodontic diseases. This review, summarized the research and application of 3D printed template from the perspective of the treatment of endodontic deseases.

[Biomechanical behaviors of cervical spinal cord injury related to various bone fragment impact velocities: a finite element study].

Objective: To establish a three-dimensional (3D) finite element (FE) model of the whole cervical spinal cord (WSCS) and explore the biomechanical behaviors of cervical spinal cord injury related to different bone fragment impact velocities by FE analysis. Methods: A 3D FE model of WCSC was established based on the morphologic data of each segment of the human cervical cord. The reconstruction structures, which included the dura mater, the cerebrospinal fluid, the gray and white matter in the C(2) to C(7) cervical vertebrae, were validated.On the validated WCSC model, three kinds of pellets with same mass (7 g) but different impact areas (314, 157 and 78.5 mm(2)) were created to represent the bone fragments.These were positioned in the middle of the spinal cord to impact at various initial velocities.The maximum of von Mises stress and the reduction of the cross-sectional area (CSA) of the spinal cord were measured from each impact. Results: The compression of WCSC (percentage) and the time to reach maximum compression were similar with the results reported in literatures, indicating the validity of the model.Regardless of the impact areas of the pellet, the maximum of von Mises stress and the reduction of CSA of the spinal cord increased with the increased velocity.The maximum of von Mises stress was 5.0-7.0 kPa at a pellet velocity of 1.5 m/s, and the reduction of CSA was 9.3%-12.3%.At a velocity of 3.5 m/s, the maximum of von Mises stress was 42-54 kPa and the reduction of CSA was over 30%.The stress of the spinal cord significantly increased when pellet velocity exceeded 3.5 m/s, and the fastest increase was recorded at 4.5 m/s.The von Mises stress of the spinal cord ranged between 240 and 320 kPa at a velocity of 6.0 m/s, and CSA decreased by more than 50%. Conclusion: The 3D FE model of WSCS could provide more insights on the biomechanical mechanisms of spinal cord injury through various bone fragment impacts in burst fracture.When the impact velocity of the bone fragment exceeds 3.5 m/s, the maximum stress significantly increases and the reduction of CSA of the spinal cord is over 30%, and this could possibly lead to the contusion injury of the spinal cord.

[Radiological analysis of coronal and sagittal spinopelvic parameters in patients with degenerative lumbar kyphoscoliosis].

Objective: To review and compare radiological parameters between degenerative lumbar kyphoscoliosis (DLKS) and degenerative lumbar kyphosis (DLK), and analyze the relationships between coronal and sagittal deformities and compensatory mechanisms of sagittal balance. Methods: A total of 82 patients with lumbar degenerative deformities were enrolled for our radiographic study at Department of Spinal Surgery, Peking University People's Hospital from January 2016 to May 2017. These patients were divided into two groups: DLKS group (39 patients) with lumbar coronal and sagittal deformities, and DLK group (43 patients) just with lumbar sagittal deformity. Complete spinopelvic radiographic parameters were compared. Results: The Cobb angle and lumbar lordosis of DLKS group were (23.0±11.8)° and (18.2±12.1)°, while the lumbar lordosis of DLK group was (20.4±10.2)°. In DLKS group, Cobb angle had correlations with lumbar lordosis(r=-0.338, P=0.035), and central sacral vertical line distance had significant correlations with thoracolumbar junctional angle (r=0.488, P=0.002) . Moreover, no significant differences of all sagittal spinopelvic parameters were found between two groups (P>0.05). In DLKS group, significant correlations between lumbar lordosis and sacral slope (r=0.617, P=0.000), and correlations between lumbar lordosis and thoracic kyphosis(r=-0.363, P=0.023) were observed. In DLK group, lumbar lordosis showed significant correlations with thoracic kyphosis(r=-0.341, P=0.025) and sacral slope (r=0.772, P=0.000). According to Nash-Moe grading scale of apical vertebral rotation, 10 patients were with Ⅰ-Ⅱ grade while 29 patients with Ⅲ-Ⅴ grade in DLKS group. Conclusions: Both as typical lumbar degenerative deformities, there are some correlations between scoliosis and kyphosis. However, coronal scoliosis may not influent sagittal morphological parameters for DLKS patients. Thoracic curve changes and pelvic backtilt are both important for maintaining the sagittal balance in patients with degenerative lumbar kyphoscoliosis.

Effect of high-fructose corn syrup on the acidogenicity, adherence and biofilm formation of Streptococcus mutans.

BACKGROUND: Although high-fructose corn syrup (HFCS) as a kind of sugar has been widely used in manufactured foods recently, there is little information available regarding its cariogenicity. The aim of this study was to evaluate the cariogenic potential of HFCS. METHODS: Streptococcus mutans UA159 was inoculated into HFCS media and cultivated. The pH of each culture was measured to assess acidogenicity. Spectrophotometric turbidity was measured to determine the percentage of adherence. Confocal laser scanning microscopy and SYTO-9 staining were employed to observe biofilm formation. Sucrose media was used as a positive control. RESULTS: The ΔpH in HFCS media was significantly larger than that in sucrose media and the pH in HFCS media decreased faster (p < 0.05). The percentage of adherence of S. mutans in HFCS media was significantly lower than that in sucrose media (p < 0.05). The biofilm formed in sucrose media was significantly thicker than that in HFCS media (p < 0.05). CONCLUSIONS: The results of this study suggest that the cariogenicity of S. mutans in the presence of HFCS may differ compared to its cariogenicity in the presence of sucrose. Further in vivo studies need to be undertaken to resolve this uncertainty.

Preliminary study of the presence and association of bacteria and archaea in teeth with apical periodontitis.

AIM: To investigate, by reverse transcription polymerase chain reaction (RT-PCR), the presence and association of bacteria and archaea in primary and secondary root canal infections. METHODOLOGY: A total of 77 root canal samples from 77 Chinese patients, 42 with necrotic pulp tissues (primary infection) and 35 with failed prior conventional root canal treatment (secondary infection), aseptically exposed at the first patient visit, were studied. Total RNA was isolated directly from each sample, and 16S rRNA gene-based RT-PCR assays were used to determine the presence of bacteria and archaea, respectively. RESULTS: Bacteria were detected in 39/42 (93%) of root canal samples from teeth with primary infections, and archaea in 16/42 (38%). In the cases diagnosed as secondary root-infected canals, bacteria were detected in 30/35 (86%), whilst archaea were detected in 6/35 (17%) of cases. Amongst the canals, which were positive for bacteria, archaea were always found in combination with bacteria. The incidence of symptomatic cases positive for both bacteria and archaea (16/22, 73%) were significantly higher than those positive for bacteria alone (21/47, 45%) (P < 0.05). CONCLUSIONS: This study confirms the presence of archaea in root canal infections and further implicates them in an association with clinical symptoms. The nature of this association requires further study.

[Establishing a FEM of mandibular first molar and stress analysis].

OBJECTIVE: Establishing a finite element model of mandibular first molar with analysis of the stress distribution to each of the tooth parts on the model. METHODS: The right mandibular first molar in vitro was scanned and the image was processed. The three dimensional finite-element model was established by the special software and loaded on it. RESULTS: Stress distribution on each part of the tooth was obtained. The maximum values of compressive stress, tensile stress and mises stress were calculated. CONCLUSION: In the research and analysis of the tooth stress, the finite element method is simple, effective, safe and reliable.

[Assessment accuracy of electronic root canal length measurement]

OBJECTIVE: To see the accuracy of "ROOT ZX" electronic root canal measurement in clinical endodontic practice. METHODS: Root canal length of 176 anterior teeth were measured by "ROOT ZX",after radiographs were taken,the distance between reamer tip and toot apex was measured,and then compared it with the distance between apical foramen and root apex of extracted teeth. RESULTS: Statistical analysis indicated no significant difference between two groups. CONCLUSION: It shows: that the electronic device can measure the root canal length accurately.It is believed that it has a higher value in clinical endodontic practice.

[Effect on preparing curved artificial root canal with five handle endodontic instruments II comparision of shaping ability]

OBJECTIVE:To compared the shaping ability of five handle endodontic instruments. METHODS: The canal shape of prepared artificial root canals with five handle endodontic instruments were observed by light-microscope. RESULTS: Apical zips,elbows and perforations were not found. Ledges occurred in speciments of K-Flex group and they were relating to resinous plugs.The apical transportatins were relating to resinous plugs.The apical transportations of K-Flex group and H file group are much greater than other groups. CONCLUSION: Unifile or K file is first choice to prepare curved artificial root canals with routine preparation technique by comprehensive evaluaion of the cutting ability and shaping ability of five handle endodontic instruments.

[A comparative study on preparation techniques for fine curved canal of posterior teeth]

A comparison of canal shape produced by routine preparation technique,ultrasonic technique and step-back technique for fine curved canal of posterior teeth was done in this article.The result showed that the canal shape prepared with step-back technique was better,for its postoperative angle change and apical transportation were less than the other two groups.On the contrary,the canal shape prepared with routine technique was worst.Therefore it was concluded that the step-back technique was the first choice for preparing the fine curved canal of posterior teeth.Routine technique was not suitable to prepare the fine curved canal of posterior teeth.

[A comparative study of apical sealing ability on filling techniques for curved canal of posterior teeth]

A comparison of apical leakage produced by three preparation technique and two obrutation methods was done in this article.The fine curved canals were prepared with routine prepartion technique,ultrasonic technique,step-back technique and filled with traditional lateral condensation,warm gutta-percha lateral condensation separately.The result showed that the apical sealing ability of warm gutta-percha lateral condensation was superior to traditional lateral condensation.It could remedy the defect of irregular canal shape of fine curved canal preapred with routine technique and ultrasonic technique in some degree by the improvement of apical sealing ability.