Light-cured lining materials: A laboratory study

doi:10.1016/0109-5641(94)90032-9

Dental Materials

Volume 10, Issue 3, May 1994, Pages 196-202

https://doi.org/10.1016/0109-5641(94)90032-9 Get rights and content

Abstract

Objectives. The purpose of this study was to compare seven light-cured lining materials (four glass ionomer and three non-glass ionomer), with a chemical-cured glass ionomer lining material.

Methods. Specimens were prepared and tested according to the methods prescribed in Australian/International Standards for compressive strength, diametral tensile strength, depth of cure, radiopacity, and acid erosion. Other tests were adhesion to dentin and adhesion to resin composite.

Results. Compressive strengths ranged from 48.6 MPa to 307.1 MPa, and diametral tensile strengths from 5.8 MPa to 34.8 MPa. Most of the light-cured materials were stronger than the chemical-cured glass ionomer. Depth of cure increased with increased irradiation times, with values of 0.63 mm to 6.43 mm for 60 s irradiation. Radiopacity was in the range of 0.91 mm Al to 1.07 mm Al. All materials were unaffected or only slightly affected by acid erosion. Adhesion to dentin was effectively zero for the non-glass-ionomer products. Adhesion to composite was from 6.23 MPa to 25.1 MPa, and thermocycling affected only three light-cured and the one chemical-cured glass ionomer.

Significance. All products complied with the requirements of standards, where available. Incremental placement and curing is necessary for some products. Adhesion to dentin is better with glass ionomers, whereas their adhesion to composite may be unreliable.

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To formulate and evaluate new dual cured resin composite based on the inclusion of eugenyl methacrylate monomer (EgMA) with Bis-GMA/TEGDMA resin systems for intracanal post cementation and core build-up restoration of endodontically treated teeth.
EgMA was synthesized and incorporated at 5% (BTEg5) or 10% (BTEg10) into dual-cure formulations. Curing properties, viscosity, T_g, radiopacity, static and dynamic mechanical properties of the composites were determined and compared with Clearfil™DC Core-Plus, a commercial dual-cure, two-component composite. Statistical analysis of the data was performed with ANOVA and the Tukey's post-hoc test.
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Methods: Methacrylate functionalized Ta₂O₅ nanoparticles (<50 nm) in methanol-dissolved or powder forms were mixed into either glycerol dimethacrylate (GDMA) or a bisGMA, TEGDMA, bisEMA mixture (GTE). Specimens were made in a split brass mold (2×2×15 mm) and compared with an aluminum stepwedge (99.5% pure Al) and a dentin slice of the same thickness. Kodak Ultraspeed periapical X-ray film on a lead plate at a target distance of 45 cm was exposed at 70 kVp and 10 mA, for 0.5 s and processed automatically. Optical density was measured (n=3) with an RMI Processor Control Densitometer. Radiopacity was calculated as percent relative linear attenuation coefficient (Alpha). ANOVA and Student–Newman–Keuls comparisons were used to determine significance at the 95% confidence level.
Results: Radiopacity increased significantly with Ta₂O₅ loading (p=0.001). Ta₂O₅ nanoparticle filled resins enter the optimal range of diagnostic detectability (α=150–250) at 50 wt.% and approach equivalence with enamel at approximately 70 wt.%.
Significance: The introduction of tantalum oxide nanoparticle filler has potential as a miscible component of a resin composite to provide radiopacity for microfiller-type restorative materials and to circumvent the need for hydrolysis-prone glass reinforcing fillers.
Aluminium radiopacity standards for dentistry: An international survey
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Objective: the aims of this study were to determine the appropriate composition and purity limits of aluminium alloy radiopacity standards for dental biomaterials, taking into account the current status in representative laboratories worldwide, and to formalise the calculation procedure for processing radiopacity data.
Methods: a series of aluminium step-wedges were obtained from academic and industrial research laboratories. These were analysed by energy dispersive X-ray procedures. The set of step-wedges were independently characterised for radiopacity at two University dental schools.
Results: the percentage of aluminium together with the percentages of minor alloying elements (magnesium, manganese, iron and silicon) have been determined as mass percentages. For each centre, the optical density versus step-height for all wedges was judged to fall on a common curve, with the main exception of one step-wedge that was found to contain 4% copper, by mass. A suitable calculation procedure was described explicitly.
Conclusion: of the examined representative step-wedges, all but the aluminium–4% copper material were satisfactory and gave results comparable with wedges of high purity. Limits should therefore be revised for composition of aluminium radiopacity step-wedges or test blocks to a more realistic level of purity. Alloys with more than 0.05% copper or 1.0% iron should be excluded and the aluminium content should be at least 98% by mass. In the calculations deployed for deriving radiopacity as `equivalent aluminium thicknesses', an appropriate linear regression procedure should be employed and considerable care taken in the evaluation of materials of low or borderline radiopacity, relative to specification limits. The method described is principally suitable for materials with radiopacity greater than 1 mm. For materials with radiopacity less than 1 mm aluminium, thicker specimens (2 mm) should be used.
Resin-modified glass-ionomers
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This paper reviews the current status of resin-modified glass-ionomers and presents the results of recent findings of research in some key areas. The debate on nomenclature pertaining to these products is perceived as being pointless and the need for application-based ISO standards is raised. Setting characteristics are similar in many respects to those of light-activated composites, although some products have limited working time due to the influence of the acid–base setting reaction and sensitivity to ambient light. Water absorption and swelling are generally very high. The clinical significance of swelling after water exposure is unknown. Mechanical properties of most materials lie between those of the composites and conventional glass-ionomers depending upon the resin content of the matrix phase of the set material. Some products demonstrate an inherent adhesion to enamel, although etching may be required in order to make the bond clinically effective. Bonding to dentine is probably through a more complex mechanism than that involved with conventional glass-ionomers. Conditioning and priming of dentine is often advocated. Fluoride release rates and their clinical significance is an area which requires clarification and standardization. The key factor appears to be the frequency with which the storage water is changed. Equilibration is reached within minutes for some materials and their true fluoride-releasing potential can only be judged under dynamic test conditions.
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Methods. Four groups (A-D) of three specimens (5 × 4 × 1 mm) were prepared from each material and subjected to the following treatments: A: mixing; B,C: mixing, 60 s irradiation, 20 min dark/dry storage; and D: mixing, 20 min dark/dry storage and then 60 s irradiation. Micro-multiple internal reflectance FTIR spectroscopy was used to determine: 1) the curing efficiency of the products immediately after irradiation; 2) the effect of irradiation 20 min after dark/dry storage on the curing efficiency; and 3) the extent of the acid-base reaction on irradiated and non-irradiated specimens after 20 min dark/dry storage.
Results. The curing efficiency immediately after irradiation was determined from the percentage of residual double bonds which ranged from 33–50% for these materials. Irradiation after 20 min dark/dry storage significantly reduced curing efficiency in all the products, except Variglass. The latter showed no acid-base reaction under the conditions of this study. Non-irradiated specimens after the dark storage period demonstrated higher car☐ylate yields compared to their irradiated analogues. Non-irradiated specimens from Vitremer had the highest car☐ylate yield and a curing efficiency of ∼50% residual double bonds.
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Light-cured lining materials: A laboratory study

Abstract

J Am Dent Assoc

Am Dent Assoc

J Can Dent Assoc

Br Dent J

Dental water-based cements

Effects of 15 vs. 60 second enamel acid conditioning on adhesion and morphology

Oper Dent

A new laboratory method for evaluating the relative solubility and erosion of dental cements

J Oral Rehab

Communication between the oral cavity and the dental pulp associated with restorative treatment

Oper Dent

Thermal fatigue in teeth

J Dent Res

Bacterial microleakage and pulpal inflammation in experimental cavities

Int Endod J

Depth of cure of light-cured glass-ionomer cements

Quint Int

Dentinal shear bond strength, mikroleakage, and contraction gap of visible light-polymerized linear/bases

Quintessence Int

Restorative dental materials

Restorative dental materials

Relaxation of polymerization contraction stresses by flow in dental composites

J Dent Res

A comparison of four modes of evaluating depth of cure of light-activated composites

J Dent Res

Adhesion test methods