[An analysis of the wall width before and after root canal therapy in mandibular second molars with C-shaped canals].

PURPOSE: To measure the wall width in mandibular second molars with C-shaped canals before and after root canal therapy using cone-beam CT(CBCT). METHODS: A total of 55 mandibular second molars from 38 patients which met the criteria for inclusion at Nanjing Stomatological Hospital, Affiliated Stomatological Hospital of Medical School of Nanjing University from January 2020 to July 2021 were analyzed．From this sample, ten teeth had been treated, while another 45 of them not. CT images of the teeth were reestablished by Mimics software 20.0. Then we made a section every 1mm perpendicular to the long axis of the teeth from apex to pulp floor. The first slice from apex to pulp chamber was named the slice 1. Along the slice 1 to crown 1 mm was called slice 1, and so forth. The wall thickness at different locations of all the slices was measured. The data was entered into SPSS 20.0 software package for analysis. RESULTS: Regardless of whether the teeth were treated or not, both the mesial and distal canal walls' average width were thicker than 1mm in all slices. At the same time, the mesial and distal canal walls' width were thicker than the width of buccal and lingual canal walls in all the slices from C-shaped root canal, except slices which were near pulp chamber(P＜0.05). As for the C-shaped root canals without root canal therapy, the width of lingual wall in the slice 1 to 4, as well as apex third root, was thinner than 1 mm. The width of buccal canal wall was thicker than the width of lingual canal wall in all slices except slice 11 and 12. As for the C-shaped root canals with root canal therapy, the width of buccal canal wall in slice 1 to 5, equivalent of apex half root, and the width of lingual wall in the slice 1 to 7, amount to apex two-thirds of root, was thinner than 1 mm. The width of buccal canal wall was thicker than the width of lingual wall in all slices except slice 1 and 9. There was no significant difference between the distal canal walls' width of C-shaped canals with and without root canal therapy(P＞0.05) . There was significant difference between the buccal canal walls' width of C-shaped canals with and without root canal therapy, as same as the mesial canal walls' width and the width of lingual canal wall (P＜0.05). CONCLUSIONS: The lingual canal walls' width in apex third root of C-shaped root canal were thin before canal preparation. The buccal walls' width in apex half root and the lingual canal walls' in apex two-thirds of root of C-shaped root canal were thin after canal preparation.

[Guided endodontic access of calcified root canal by laser melting templates].

OBJECTIVE: The aim of this study is to treat calcified root canal and assess the accuracy of guided endodontics using laser melting templates. METHODS: Two cases with calcified anterior teeth were treated with laser melting templates. Cone beam computed tomography (CBCT) was used to scan the maxillary teeth of patients before surgery to establish the root canal system model. The maxillary impression of the patient was made and it was scanned by a 3D scanner. The CBCT scans were matched with surface scans of plaster model. Mimics 19.0 and 3-matic 11.0 software were used to design the virtual planning to access cavities. The templates were produced by laser melting 3D printing. Access cavity was prepared under the guidance of laser melting template. Then the deviations of planned and prepared cavities in three dimensions and angle were measured. RESULTS: The two teeth obtained satisfactory results. The first case had a angle deviation of 1.77°, a drilling base deviation of 0.403-0.497 mm, and a tip of 0.433-0.537 mm. The second case had a angle deviation of 3.26°, a drill base deviation of 0.18-0.347 mm, and a tip of 0.310-0.463 mm. CONCLUSIONS: Laser melting template-guided endodontics is an effective technique for the treatment of calcified root canal and can be used as a new strategy for the treatment of calcified canal.

[An exploration on computerized examination system of dental objective structured clinical examination].

PURPOSE：In view of the present problems of clinical skill examination, in order to evaluate the candidate's clinical ability comprehensively and objectively, we constructed and implemented dental objective structured clinical examination system mainly based on computer. METHODS：This system was a multi-station examination which had 3 parts and 8 sites. The stations were composed of a variety of testing methods, including choice questions, auxiliary examinations, case analysis and basic operation skill. RESULTS: By using the computerized dental objective structured clinical examination system, we could smoothly test the ability of stomatological students in a relatively short time. The clinical ability, learning ability and professional quality could be evaluated more objectively in many ways. CONCLUSIONS：This system help students adapt to early examination of medical practitioners, improve students' clinical skills, and is worthy of wide application.

Analysis of Mtwo rotary instrument separation during endodontic therapy: a retrospective clinical study.

To analyze the incidence of instrument separation (IS) and the factors influencing it, when associated with Mtwo rotary system (VDW, Munich, Germany) during endodontic therapy. A retrospective study involving a total of 24,108 root canals (11,036 endodontic treated teeth) was conducted at Nanjing Stomatology Hospital between January 2011 and March 2013. The information included were tooth type, root canal curvature, number of fractured instruments, length of the separated fragments, and the distance from broken tip to apex. The incidence of IS was observed to be 2.2 % according to the number of teeth and 1.0 % according to the number of root canals. Many of the separated fragments were 2-4 mm in length and the mean length was 3.07 ± 1.46 mm, and 78.4 % of fractures occurred in the apex. The mean length of separated fragments in severely curved canals was maximum, while ultra-severe curved canals was observed to be minimum. Mtwo instruments demonstrated an extremely low fracture rate during endodontic therapy. Molar teeth (especially lower molars) and the degree of canal curvature had a significant effect on the incidence of IS.

[The influence of age upon circadian rhythm of human pulp sensibility].

OBJECTIVE: To explore the influence of age on the circadian rhythm of pulp sensibility, guide the diagnosis and treatment of dental and endodontic diseases. METHODS: The first lower molars of young, middle-aged, and aged volunteers were inspected for the threshold of pulp sensitivity. Each inspection was implemented every 4 hours earlier, totally 7 times during 24 hours. All values of pulp sensibility threshold from each volunteer were analyzed by Halberg methods for cosinor-rhythmometry. The chronobiology characteristics of pulp sensibility were compared among young, middle-aged, and aged. RESULTS: The pulp sensibility threshold values of the young, middle-aged, and aged indicated to have the circadian rhythm alternation in period of 24 hours, with fitting well to a cosine curve. The trend of rhythm curve was similar to all three age groups. The acrophase and bathyphase appeared at 0:00 and 12:00 separately. The values and amplitudes of pulp threshold sensibility showed to be: young>aged> middle-aged. CONCLUSION: The circadian rhythm of pulp sensibility changes according with age. The pulp sensibility threshold value is lower in aged people than in the young, and the lowest sensibility threshold is in middle-aged people. Besides, the extent of rhythm fluctuation is the least in middle-aged people.

[Effect of light-emitting diode curing light and halogen light on microleakage of extracted teeth].

OBJECTIVE: To evaluate the effect of light-emitting diode (LED) curing light and Halogen dental curing light on the microleakage of Clearfil AP-X composite restorations and to provide evidence for clinical use of LED curing light. METHODS: Class V cavities were prepared in 73 freshly extracted teeth. The teeth were randomly divided into two groups being exposed to light-emitting diode curing light MORITA PENCURE and halogen light 3M ESPE Elipar 2500 respectively, and then treated with thermocycling (500 cycles, 5-55 degrees C), section and dyeing. The amounts of dye infiltration and marginal seal were examined by stereomicroscope and scanning electron microscope (SEM) respectively. RESULTS: No significant differences were found in the amount of dye infiltration shown in the stereo-photomicrograph between the two groups. However, the SEM revealed better marginal seals of those teeth exposed to LED curing light. CONCLUSION: The LED curing light may be able to achieve the same or better effect on reducing microleakage compared with the Halogen dental curing light. Further studies are needed.

[Chronobiology of pulp sensibility in young people].

OBJECTIVE: To explore the biological clock of pulp sensibility in young people so as to enrich the theory of pulp-chronobiology and conduce to clinical diagnosis and the treatment of pulposis. METHODS: 40 healthy young volunteers (20 males and 20 females) were examined. Pulp sensibility test was performed using the pulp sensibility tester produced in France. Pulp sensibility reading was obtained at each 4 hours from 8:00 a.m. till next 8:00 a.m., thus there were totally seven time-pints in 24 hours. And the readings were averaged. RESULTS: The pulp sensibility data of every volunteer were analyzed by methods for cosinor-rhythmometry, and significant difference (P<0.05) was found. The acrophase and bathyphase appeared at 0:00 and 12:00 separately. We did not find significant difference of the mesor, amplitude and phase between young males and females (P> 0.05). CONCLUSION: Circadian rhythm is demonstrated in thepulp sensibility data of young people; the highest pulp sensibility is at 12:00 while the lowest is at 0:00.