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    How to use cavity liners to provide better care

    Why one practitioner says that TheraCal LC® from Bisco is the closest thing to an ideal material.

    As dental students, most of us were indoctrinated with the calcium hydroxide philosophy. That is, we placed calcium hydroxide under all restorations. Brands such as Dycal® (Dentsply Sirona) and Life™ (Kerr) were to dentists as ubiquitous as Kleenex is to our patients. The philosophy served the profession well, until the concept was challenged.1,2

    The renegades who challenged the calcium hydroxide cult met stiff resistance and, in my humble opinion, were treated as heretics.3, 4 A slew of scientific articles debated the issue of pulpal protection, some with dramatic titles (“The disastrous effects of the ‘total etch technique’ in vital pulp capping in primates”) while other studies had totally differing results.5,6 Now after almost two decades of clinical practice, literally tens of millions of human teeth in this country have had dentin etched (76 million composite restorations in one year alone, 2004), and the pulps have survived.7

    Etching preperationThere is good reason for the survival of the vast majority of dental pulps. Dentin has significant buffering capacity, as would logically be expected due to evolutionary development.8 In addition, the dentino-pulpal complex utilizes a dentino-pulpal fluid flow that helps protect the pulp and remineralizes the dentin.9 In the diseased state, the dentin caries progresses due to the extreme acidity of lactic, acetic and, interestingly, propionic acids produced by cariogenic bacteria.10

    The acidic environment demineralizes the dentin but — equally importantly — stimulates the matrix metalloproteinases (MMPs 1, 2, 8 and 9) to break down the collagen matrix.11 Humans and our microbiome have co-evolved so that we have developed symbiotic relationships, including within the oral cavity. Indeed, the host and the symbiont microbiome form a holobiont virtually sharing the hologenome.12 It has been recently stated that the microbiome is even the driving force of evolution.13 As such, the dental caries process has developed a complex microbiome, not only of cariogenic bacteria but also of commensal competitive bacteria that help to control the carious progression.14 A process that is just now being appreciated.

    One curious concept is that somehow a few seconds exposure of dentin to acid etch would severely injure pulpal tissue while the carious process has often exposed the very same dentin to a harsh acidic environment over a period of months (and during that same time the pulp was also challenged by bacterial toxins)15, 16 — especially as the overriding constant factor effecting pulpal vitality is now considered to be the presence of bacteria.17, 18 As in all surgical procedures, control of pathogenic bacteria is of primary importance.19

    This is where both of the opposing camps were actually correct. The alkalinity of the calcium hydroxide products provided protection against pathogenic bacteria.20, 21 In addition, the presence of the calcium ions may strongly induce dentin bridge formation.22 A restoration that does not leak is always essential to survival of the pulp.23 The only issue with etching the dentin was the removal of the smear layer that would subsequently increase dentin permeability with hydrophilic adhesives.24 The increase in permeability would allow for not only bacterial invasion but also the penetration of cytotoxic resin components.25

    Up next: Using an etching technique

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