Polymerization Efficiency of Glass-Ionomer and Resin Adhesives under Molar Bands

Objective: To determine the degree of cure of a light-cured resin-modified glass ionomer (RMGI) under molar bands compared with a light-cured resin and a dual-cured resin. Materials and Methods: The 3 cements used were Fuji Ortho LC, Eagle Spectrum resin, and Variolink II dual-cure. Each sample was indirectly light cured for 20 seconds (10 seconds occlusally, 10 seconds cervically) under sections of molar bands, and the degree of cure was evaluated with micro-MIR FTIR spectroscopy. Results: The RMGI exhibited a significantly higher mean degree of cure (55.31%) than both of the resins (Eagle 19.23%; Variolink II, 25.42%), which did not differ significantly at α = .05 level of significance. Conclusion: Higher degree of conversion can be obtained from RMGIs under molar bands compared with composite resin adhesives provided the proper curing technique is used

Torsional instability of hinged flanges stiffened by lips and bulbs

Based on torsional instability theory, buckling charts are presented for determining the critical strain of hinged flanges stiffened by idealized lip and bulb elements

Handbook of structural stability part V : compressive strength of flat stiffened panels

A generalized crippling analysis for short monolithic panels with formed or extruded stiffeners is presented. Methods are presented for determining if riveted panels act in a monolithic manner and for determining the strength of those which do not. The failure modes of intermediate-length and long stiffened panels are discussed and methods given for estimating column strength. Theory and test data on optimum stiffened panels are presented and the various factors of importance in box types of construction are considered

Handbook of structural stability part IV : failure of plates and composite elements

Available theories on failure of flat plates are reviewed, and test data on the postbuckling behavior, effective width, and failure of flat curved plates are correlated. Test data on the crippling strength of various formed and extruded shapes are reviewed, from which a generalized method of crippling analysis is formulated. This analysis is then applied to a variety of sections and materials in common use

Do the Mechanical and Chemical Properties of Invisalign\u3csup\u3eTM\u3c/sup\u3e Appliances Change After Use? A Retrieval Analysis

Aim: To investigate the mechanical and chemical alterations of Invisalign appliances after intraoral aging. Materials and methods: Samples of Invisalign appliances (Align Technology, San Jose, California, USA) were collected following routine treatment for a mean period of 44±15 days (group INV), whereas unused aligners of the same brand were used as reference (group REF). A small sample from the central incisors region was cut from each appliance and the buccal surface was analysed by attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy (n = 5). Then the appliances were cut (n = 25) and embedded in acrylic resin, ground/polished in a grinding polishing machine, and the prepared surfaces were subjected to Instrumented Indentation Testing under 4.9 N load. Force-indentation depth curves were recorded for each group and the following parameters were calculated according to ISO 14577-1; 2002 specification: indentation modulus (E IT), elastic to total work ratio also known as elastic index (ηIT), Martens Hardness (HM), and indentation creep (C IT) The mean values of the mechanical properties were statistically analysed by unpaired t-test (a = 0.05). Results: ATR-FTIR analysis confirmed the urethane based structure of the appliances, without important chemical differences attributed to the aging process. INV group showed significantly lower E IT (REF: 2466±20, INV: 2216±168MPa), HM (REF: 119±1, INV: 110±6 N mm−2) and higher ηIT (REF: 40.0±0.3, INV: 41.5±1.2%), and C IT (REF: 3.7±0.2 INV: 4.0±0.1%). The increase in ηIT indicates that INV is a more brittle than REF, whereas the increase in C IT, a decrease in creep resistance. Conclusion: Despite the lack of detectable chemical changes, intraoral aging adversely affected the mechanical properties of the Invisalign appliance