[Study on energy absorption of mouthguard splints by impact test].

PURPOSE: Using impact test to study energy absorption ability of mouthguard splints of different thickness and materials. METHODS: In this experiment, group 1 was BIOPLAST 5 mm splint, group 2 was BIOPLAST 4 mm splint, group 3 was BIOPLAST 3 mm splint，group 4 was BIOPLAST 2 mm splint and group 7 was BIOPLAST 1 mm splint. Group 5 was ERKOLOC-PRO 2 mm splint, group 6 was DURAN 2 mm splint. Mouthguard splints were clashed by impact head from different heights. Digital Image Correlation System was used to record the process of the test. Images were transferred to data processing software, to analyze incident speed, incident depth and rebound height of the impact head. Absorbed energy and energy absorption ratio were calculated to analyze energy absorption ability of mouthguard splints of different thickness and materials. The data were analyzed using SPSS 22.0 software package for one-way analysis of variance and LSD. RESULTS: The higher impact head fell, the larger energy absorption ratio was. There was significant difference among group 1, 2, 3, 4, 7 in average energy absorption ratio（P<0.05）, and group 7 was the largest. There was significant difference among group 4, 5, 6 in average energy absorption ratio（P<0.05）, among which group 4 and group 5 were larger. CONCLUSIONS: 3 mm splint is good enough to be used to make mouthguard, which is also thinner and more comfortable. Splint of soft material is more suitable for mouthguard than splint of hard material.

[Study on periodontal responses on the compression side during early tooth movement into alveolar defect regenerated by a tissue engineering bone].

PURPOSE: To explore periodontal responses on the compression side during early tooth movement into alveolar defect regenerated by bone marrow mesenchymal stem cells (BMSCs) and porous granulated beta-tricalcium phosphate（ß-TCP） scaffolds. METHODS: Thirty New Zealand rabbits were used to establish bilateral mandibular defective alveolar bone model by extracting the mandibular first molars and expanding the sockets. The right mandibular alveolar defects were filled with a construct of ß-TCP scaffolds combined with BMSCs as experimental group. The left alveolar defects were repaired by ß-TCP scaffolds alone as control group. Eight weeks later, 6 rabbits were sacrificed to evaluate osteogenesis effect. The other rabbits were loaded orthodontic force to move the bilateral second molars forward for 4 weeks. Six rabbits in each group were sacrificed at 1, 2, 3, and 4 week after orthodontic tooth movement (OTM). The distance of OTM was measured, and the status of periodontal tissues was observed by H-E staining. The number of osteoclasts on the compression side of tooth was counted by tartrate-resistant acid phosphatase histochemistry. The results were compared between groups using SPSS 19.0 software package. RESULTS: After 8 weeks of bone grafting, the osteogenesis effect of the experimental group was better than the control group. The OTM distance in the experimental area was higher than that in the control area. At 2, 3 and 4 week of OTM, the number of osteoclasts in the experimental group was significantly higher than that in the control group. CONCLUSIONS: A tissue-engineered complex with ß-TCP scaffolds and BMSCs could well repair the alveolar bone defect. When the adjacent tooth moved into regenerated area, the new periodontal tissue had an active response, promoting to accelerate tooth movement.

Symmetry of root anatomy and root canal morphology in maxillary premolars analyzed using cone-beam computed tomography.

OBJECTIVE: This study aimed to use cone-beam computed tomography (CBCT) to evaluate the root anatomy and canal morphology of maxillary premolars in a Chinese population and determine their degree of bilateral symmetry. DESIGN: 774 CBCT images were retrospectively analyzed, representing 1387 maxillary first premolars and 1403 second premolars. The number of roots and canals were recorded. The morphology of root canal systems was determined according to Vertucci's classification. The symmetry of root and canal anatomies between maxillary contralateral premolars was further evaluated. RESULTS: The most common anatomy of maxillary first and second premolars was one-rooted with two canals (58.0%) and one-rooted with one canal (50.3%), respectively. The typical canal morphology was type IV (42.7%) in maxillary first premolars and type I (50.3%) in maxillary second premolars. One-rooted maxillary premolars exhibited a higher variability in the canal morphology, compared to two-rooted or three-rooted teeth. Maxillary second premolars exhibited greater anatomic symmetry than first premolars. The root and canal numbers showed bilateral symmetry between 80.2% of maxillary first premolar pairs and 81.8% of second premolar pairs. Bilateral symmetry in both number and morphology of roots and canals was observed for 72.3% of maxillary first premolar pairs and 73.2% of second premolar pairs. CONCLUSION: The root anatomy and canal morphology of maxillary premolars in a Chinese population were quite diversified. Maxillary contralateral premolars demonstrated a high degree of symmetry in root and canal anatomies, which enables practitioners to better determine the nature of the root canal system during treatment of opposite homonymous teeth.

[Analysis and prevention of dust pollution caused by 5 common prosthetic materials].

PURPOSE: To analyze and evaluate dust pollution in prosthodontic clinic and make proposal for reasonable protection. METHODS: This study analyzed the particle size, element composition and dust concentration of 5 materials which were commonly used in dental restorations (veneering ceramics, cobalt-chromium alloy, photosensitive plastic, hard base resin, advanced artificial teeth) by using scanning electron microscopy (SEM), X-ray energy dispersive spectrometer（EDS） and dust concentration laser tester, in order to assess the effects of prosthodontic dust posed on medical staff health and put forward reasonable suggestions for prevention and control of dust pollution. RESULTS: The particle size of veneering ceramics, cobalt-chromium alloy, photosensitive plastic, hard base resin and advanced artificial teeth was (2.15±3.00), (33.78±24.33), (7.78±11.86), (31.16±44.35) and (28.45±39.21)µm, respectively. The time weighted average respirable dust concentration of veneering ceramics was 0.393 mg/m2 which was beyond the scope of national security. CONCLUSIONS: Dust pollution is serious in prosthodontic clinic to which we should pay more attention and take appropriate prevention measures.

Characteristics of intrabony nerve canals in mandibular interforaminal region by using cone-beam computed tomography and a recommendation of safe zone for implant and bone harvesting.

BACKGROUND: Cone-beam computed tomography can accurately show anatomic structure of intrabony nerve canals in mandibular interforaminal region. PURPOSE: The aim was to evaluate the characteristics of intrabony nerve canals in mandibular interforaminal region by using cone-beam computed tomography (CBCT) and determine a safe zone for implant and bone harvesting. MATERIALS AND METHODS: Hemimandibles (824) CBCT images were obtained. The length of the anterior loop (AL), the length and diameter of the mandibular incisive canal (MIC) and its spatial distance in various landmarks were measured. RESULTS: The prevalence of the AL was 93.57%, and the MIC was 97.33%. The mean lengths of the anterior extension of the anterior loop (aAL), caudal extension of the anterior loop (cAL) and the MIC were 2.53 ± 1.27 mm, 6.04 ± 1.66 mm, 9.97 ± 5.15 mm, respectively. The MIC was closer to buccal border and inferior margin of mandible. The length of the AL and diameter of the MIC varied with gender. CONCLUSIONS: The safe zone recommended for implant surgery is 4 mm anterior and 8 mm inferior to the mental foramen, and 10 mm above the inferior margin of mandible. The chin bone should be harvested at least 10 mm below the tooth apices along with a limited depth of 4 mm.