[Detection and analysis of dental dust concentration in the department of prosthodontics].

PURPOSE: To detect and analyze dental dust pollution in the department of prosthodontics and propose reasonable protective measures. METHODS: Individual dust sampling pumps were used to detect the concentration of respirable dust produced by five common dental materials (hard resin base, advanced artificial teeth, photosensitive plastic, cobalt-chromium alloy, veneering ceramics) in the department of prosthodontics. X-ray diffraction (XRD) was used to detect the concentration of free silica respirable dust in veneer porcelain dust. Inductively coupled atomic emission spectrometry (ICP-AES) was used to detect the thoracic dust of cobalt element and the inhalable dust concentration of chromium element in cobalt-chromium alloy dust. The results were compared with the occupational exposure limits set by China and the United States. RESULTS: The respiratory dust concentration of the five common dusts in the department of prosthodontics was far lower than occupational exposure limits set by China and the United States. The concentration of free silica in veneer porcelain, cobalt and its compounds in cobalt-chromium alloys were below the lower detection limit. Chromium and its compounds can be detected, and its concentration was also far below the occupational exposure limit. CONCLUSIONS: Problem of dust pollution in the department of prosthodontics exists, which is mainly caused by heavy metal pollution (such as chromium). Protective measures such as ventilation and wearing professional mask should be taken to protect the health of dental practitioners.

[Effect of strontium ranelate on chondrogenic differentiation of rat bone mesenchymal stem cells].

PURPOSE: The aim of present study was to explore the effect of strontium ranelate (SrR) on the proliferation and chondrogenic differentiation of rat bone mesenchymal stem cells (BMSCs). METHODS: Rat BMSCs were isolated and cultured in chondrogenic differentiation medium containing 0.25-2.0 mmol/L strontium ranelate. CCK-8 assay was used to study the influence of cell proliferation. Toluidine blue staining and alizarin blue staining were used to observe chondrogenic differentiation. Quantitative hydroxyproline (Hyp) activity assay was conducted. PCR and Western blots were used to detect the expression of related genes and proteins. Statistical analysis was performed using SPSS 22.0 software package. RESULTS: 0.25 mmol/L strontium ranelate did not inhibit the proliferation of BMSCs and promote the expression of chondroitin sulfate and proteoglycan. Hyp assay showed a higher content of collagen fibers in extracellular matrix in 0.25 mmol/L SrR treatment group. PCR and WB also showed up-regulated expression of Sox-9, Col-Ⅱ gene and protein, Aggrecan protein, and suppressed expression of MMP-9 gene. CONCLUSIONS: 0.25 mmol/L SrR could significantly promote chondrogenic differentiation of BMSCs.

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.

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.

[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.

Analysis of the Root and Canal Morphologies in Maxillary First and Second Molars in a Chinese Population Using Cone-beam Computed Tomography.

INTRODUCTION: We analyzed and characterized the root and canal morphologies in maxillary first and second molars in a large sample of Chinese patients using reconstructed cone-beam computed tomographic (CBCT) imaging. METHODS: Maxillary first (n = 1558) and second (n = 1539) molars were collected from Chinese patients (N = 844) who had undergone in vivo CBCT imaging. The root canal number and morphology were determined according to Vertucci's classification. RESULTS: A single root was found in 0.06% of first molars, which showed type I canal systems. However, second molars with a single root (4.2%) showed widely varied canal systems. The buccal roots of first molars with 2 separate roots showed type I, II, or III canal systems, whereas those of 2-rooted second molars showed widely varied canal systems. The incidence of fused roots was 1.38% for first molars and 23.9% for second molars, whereas canal fusion within fused roots was observed in 4.5% of first molars and 10.6% of second molars. Additional canals were observed in 67.8% and 29.7% of mesiobuccal roots, 1.8% and 0.7% of distobuccal roots, and 0.7% and 0.3% of palatal roots in 1523 and 1017 first and second molars with 3 separate roots, respectively. The mesiobuccal root canal number showed bilateral symmetry between 79% of first molars and 82.3% of second molars, with a concurrence rate of 59.8% between adjacent molars. CONCLUSIONS: We reported the root and canal morphologic variations in maxillary first and second molars, which have not been reported for Chinese populations. Further studies should focus on canals in fused roots and mesiobuccal roots.