Marginal Leakage

Lack of adhesion of a dental restoration to tooth structure results in microleakage at tooth-restoration interface. This occurrence can result in discoloration at the margin of the restoration, or in the formation of caries. Occlusal forces on the restoration and differences between the coeffidents of thermal expansion of the cement and tooth material can lead to leakage. In addition, oral fluids and moisture may affect the adhesion. Microleakage of composite resin restorations has been reviewed by Ben-Amar [233]. Microleakage is not as serious a problem with glass-ionomer cements as it is with resin-based restorative materials, due to reduced polymerization shrinkage [234]. 

The excellent performance of GICs as dental materials has lead to their evaluation as biocompatible bone reconstruction materials. Initial results from in vivo and in vitro studies appear very promising [253-257]. 

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Andrews, J. T. Hembree, J. H. (1976). In vivo evaluation of the marginal leakage of four inlay cements. Journal of Prosthetic Dentistry, 35, 532-7. 

X. Chen, V. Cuipers, M. Fan, J.E. Frencken, Marginal leakage of two newer glass ionomer-based sealant materials assessed using micro-CT, J. Dent. 38 (2010) 731-738. 

Therefore even marginal leakage would increase the self-discharge of that cell. Those cells in series of batteries would be deep discharged during the subsequent discharge operation of the battery with the consequence of premature depletion. 

Operating Pressure - The operating pressure is the gauge pressure to which the equipment is normally subjected in service. A process vessel is usually designed for a pressure which will provide a suitable margin above the operating pressure, in order to prevent leakage of the relief device. 

Hydrolytic decomposition brings disadvantages. There is continued leakage at the margins where complete dissolution can occur (Gourley Rose, 1972) and, indeed, these bases have been observed to disappear entirely (Akester, 1979 Barnes Kidd, 1979). 

Thermal expansion differences exist between the tooth and the polymer as well as between the polymer and the filler. The tooth has a thermal expansion coefficient of 11 x 10-6/°C while conventional filled composites are 2-4 times greater [63, 252], Stresses arise as a result of these differences, and a breakdown between the junction of the restoration and the cavity margin may result. The breakdown leads to subsequent leakage of oral fluids down the resulting marginal gap and the potential for further decay. Ideal materials would have nearly identical thermal expansion of resin, filler, and tooth structure. Presently, the coefficients of thermal expansion in dental restorative resins are controlled and reduced by the amount and size of the ceramic filler particles in the resin. The microfilled composites with the lower filler loading have greater coefficient of thermal expansions that can be 5-7 times that of tooth structure. Acrylic resin systems without ceramic filler have coefficients of thermal expansion that are 9 times that of tooth structure [202-204, 253],... 

The other way is to approach as closely as possible the point above which problems with gas leakage begin to occur while still leaving a reasonable safety margin. 

Zero leakage Requires high margin between operating and opening pressures... 

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