Efficacy of flowable composite resin as stress-absorbing liners in Class I cavity restorations / 中华口腔医学杂志

<p><b>OBJECTIVE</b>To evaluate the efficacy of flowable composite resin(FCR) as stress-absorbing liners in Class I cavity restorations in vitro.</p><p><b>METHODS</b>Thirty Class I cavities of 4 mm in diameter and 2 mm in depth were prepared in polycarbonate (PC) plates and divided into three groups, ten each. After application of an adhesive, cavities in each group were restored using one of the following methods: A: restored with Charisma without any lining of FCR; B: lined with Revolution Formula 2 twice before restoration with Charisma; C: lined with Teric Flow twice before restoration with Charisma. All cavities were observed under a photoelastic microscope and photoelastic images were recorded at 3 min and 24 h after curing and the shrinkage stresses on the cavity wall were calculated. The polymerization shrinkage(v%) of the three composite resins was measured using bonded discs method and their elastic moduli were measured according to ISO standard.</p><p><b>RESULTS</b>The shrinkage stresses at 3 min and 24 h of the three methods were as follows,A: (4.93 ± 0.28), (5.87 ± 0.40) MPa, B: (4.90 ± 0.30), (5.84 ± 0.33) MPa, and C: (4.76 ± 0.28),(5.83 ± 0.37) MPa.No significant difference was found in results among different groups. The polymerization shrinkage(v%) in group A,B, and C were (2.63 ± 0.04)%, (4.56 ± 0.06)%, and (3.98 ± 0.02)%. The elastic modulus in group A, B, and C were (9.59 ± 0.65), (4.25 ± 0.51), and (5.41 ± 0.79) GPa.</p><p><b>CONCLUSIONS</b>Under present study condition, using a FCR as stress-absorbing liner under composite resin restoration does not significantly decrease the polymerization shrinkage stresses at the cavity wall.</p>

Detection of marginal leakage of Class V restorations in vitro by micro-CT / 中华口腔医学杂志

<p><b>OBJECTIVE</b>To evaluate the reliability and superiority of micro-CT in marginal leakage assessment of Class V restorations.</p><p><b>METHODS</b>Class V preparations with gingival margins in dentin and occlusal in enamel were made in sixteen extracted non-carious human molars and restored with dental bonding agents and composite resin. All teeth were then immersed in 50% ammonia-silver nitrate solution for 12 hours, followed by developing solution for 8 hours. Each restoration was scanned by a micro-CT and silver leakage was measured and three-dimensional image of the silver leakage alone cavity wall were reconstructed. Afterward, all restorations were sectioned and examined for leakage depth using a microscope. The silver leakage depth of each restoration obtained by micro-CT and microscope were compared for equivalency.</p><p><b>RESULTS</b>The silver leakage depths in gingival wall obtained with micro-CT (0.78 mm) and microscope (0.74 mm) showed no significant difference (P > 0.05), while the judgment of leakage depths in occlusal wall in micro-CT image (0.40 mm) was affected by adjacent enamel structure, giving less leakage depths compared to microscope (0.72 mm)(P < 0.01). The three-dimensional shapes of the microleakages displayed clearly by micro-CT alone wall of Class V restorations were multiform and some leakages showed channels on their way to spreading.</p><p><b>CONCLUSIONS</b>Micro-CT can detect precisely the silver leakage in the dentin wall of a restoration and display its three-dimensional shape fully. Enamel structure affects the detection of the silver leakage next to it.</p>

The study on fabrication of dental restoration using PMMA-ZrO2 composites via CAD/CAM / 中华口腔医学杂志

<p><b>OBJECTIVE</b>To obtain dental restorations by machining PMMA-ZrO2 organic-inorganic composites with the dental CAD/CAM system.</p><p><b>METHODS</b>Partially sintered Zirconia compacts (PSZC) were prepared via isostatic pressing and partially sintering, with Zirconia nanopowder as raw materials. PMMA-Zirconia organic-inorganic composites were prepared by vacuum infiltrating the prepolymerized MMA into the PSZC, followed by in-situ polymerization. The mechanical properties and machinability of composites were studied. The composites were machined on the dental CAD/CAM system to obtain dental restoration.</p><p><b>RESULTS</b>At 71.44% TD of PSZC, the composite had a 3-point bending strength of (202.56 +/- 3.09) MPa, fracture toughness of (4.30 +/- 0.16) MPa.m(1/2), elasticity modulus of (58.71 +/- 1.98) GPa, and Vickers hardness of (3.82 +/- 0.34) GPa, respectively. A premolar crown was fabricated by CAD/CAM system in 16 mins, and was verisimilitude, without any cracks.</p><p><b>CONCLUSIONS</b>The composite at 71.44% TD of PSZC has good mechanical properties and dental restorations can be manufactured by PMMA-Zirconia composites via dental CAD/CAM system.</p>