How to use cavity liners to provide better care

April 20, 2018

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

There 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

 

Fortunately, we now have better adhesive agents that not only penetrate the etched dentin replacing the smear layer (which ironically contains bacteria, yet it has been advocated to leave this contaminated debris) - the adhesives provide a better layer of protection from pathogenic bacteria as the smear layer produces voids in the hybrid layer.26 Smear layers, left intact, reduce the bond strength of the dentin adhesives.27 Unfortunately, some dental products still contain cytotoxic components capable of pulpal insult.28-30 Also, hydrophilic dental adhesives degrade over time and stimulate MMP activity, leaving voids in the hybrid layer and allowing for decreased bond strength and increasing microleakage.31

Resin-modified glass ionomers play an extremely important role in clinical dentistry. The fluoride release is quite beneficial in re-mineralizing enamel and inhibiting cariogenic biofilms.32 However, they are quite acidic with a setting pH below 3 and the polyacrylic acid component actually inhibits apatite formation, a key precursor of dentin bridge formation.33-35 However, the release of fluoride from RMGIs helps enamel by creating fluorapatite, thereby reducing solubility36 - which is not, however, as much benefit for dentin that contains over 33 percent organic matter with only 45 percent calcium hydroxyapatite, making fluorapatite formation less significant.37

The above notwithstanding, the overall clinical benefits of glass ionomer products cannot be discounted - especially in the caries-prone individual, and as polymerization contraction stress relief under restorations is quite significant.38 Unfortunately, cytotoxic constituents of glass ionomer products may again be detrimental to pulp vitality.39,40 Of interest is that clinical manifestations of pulpal irritation are not always indicative of histological findings, further confusing the situation.41

The ideal pulp capping or deep cavity material would be light-cured for easy placement and time control. The material would be alkaline and calcium-releasing to encourage dentin bridge formation. In addition, the material would have sufficient mechanical properties. The dental material closest to having all these properties is TheraCal LC® (BISCO), a light-cured, resin-based dicalcium and tricalcium silicate.42,43

Clinical case

A 7-year-old male patient presented with a history (maternal report) of severe dental apprehension and extensive recurrent caries. Upon examination the patient was noted to have a strong but manageable gag reflex, some airway concerns and slight “long face syndrome.” The dentition was mixed with permanent first molars and incisors. Patient reported sensitivity with eating on the upper-right quadrant and the primary molars restorations in that quadrant presented with severe micro-leakage (Fig. 1). The patient was appointed for restorative care as soon as possible.

 

Fig. 2                                                                      Fig. 3

Upon the operative visit he remained very cooperative. Single Tooth Anesthesia® (Milestone Scientific) was utilized for local anesthesia and a rubber dam placed (Fig. 2). Removal of the previous restorations was quick, as they demonstrated no evidence of bond with tooth structure. Gross caries was present under the restorations along with obvious micro-leakage staining (Fig. 3).

Following gross carious dentin removal, the pulps were not exposed but a pinking blush was noticeable. Following debris removal by copious rinsing, the enamel margins were etched with UNI-ETCH® w/ BAC (BISCO). The dentin was etched to remove the smear layer but not widen the dentinal tubules (Figs. 4-5). 

Fig. 4                                                                                    Fig. 5      

Leaving dentin moist (dentin should never be dried anyway) TheraCal LC is applied and light-cured. Because TheraCal LC incorporates hydrophilic monomers, it spreads better on moist dentin and adheres after light curing (Fig. 6). The alkaline pH and calcium release, very similar to ProRoot MTA (Dentsply), stimulates dentin formation and inhibits bacterial growth.44,45

The etched dentin was hybridized with ALL-BOND UNIVERSAL® adhesive (BISCO), a seventh-generation adhesive, and was restored with a resin-based dual cure (bulk fill) composite (Fig. 6). After removal of the rubber dam, the patient thanked me for making him “numb.” He claimed it was the first time he had been anesthetized for dental care. His mother was unaware that he had never received anesthesia for treatment, and had thought that he was just being “too sensitive.” The patient has returned for recare appointments and the teeth have remained asymptomatic (Fig. 7).

Fig. 6                                                                                       Fig. 7

Proper restorative care should include local anesthesia when appropriate, proper isolation and the correct choice of dental materials. TheraCal LC is the modern replacement for older cavity liners such as Dycal and Life, which are not indicated for placement under newer restorative materials (resin-based composites) used in the contemporary dental practice.

 

References:

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