News Feature

Optimizing intraoral and extraoral substrates for maximal adhesive potential

Article by Dr. Clarence Tam HBSc, DDS, FIADFE, AAACD

A NOVEL MDP-BASED SURFACTANT SOLUTION

The everyday practice of adhesive restorative dentistry, whether utilizing direct or indirect restorations, is fraught with the need for ideal environmental conditions to generate an optimal prognosis. The bonding of composite resin is the foundation of direct and indirect restoratives, as it provides the link between restoration and tooth. As dentistry strives to be minimally invasive, the treatment of the bonding interface is reflected in this philosophy by the use of self-etching multi-substrate acidic monomers such as 10-methacryloyloxyldecyl dihydrogen phosphate (10-MDP). There are myriad opportunities for both intaglio and fitting surfaces to be contaminated with varying agents to the detriment of restoration prognosis.

Some of the contaminants to be considered are of course, moisture from exhalation, ambient humidity in the oral cavity, blood, saliva and artificial sources such as provisional cement during a two-stage indirect delivery technique. Moisture is an agent which is only welcomed via a controlled approach during the dentin penetration phase of priming the substrate for adhesion, however if excessive in quantity will compromise the hybridization of the interface. Blood and saliva are ubiquitous in restorative dentistry, and best controlled via the application of rubber dam as part of an absolute isolation philosophy. Contamination of the prepared surface can also occur through artificial cements or lubrication agents. Hemostatic agents such as ferric sulfate and aluminum chloride have the ability to deposit insoluble precipitates on the surface of the tooth in a manner that 33% orthophosphoric acid can only partially remove. Also considered is the particulate deposition of dentin and enamel as part of standard tooth preparation. This smear layer is residual on the dentin surface, often occludes dentinal tubules, and is an obstacle that must be overcome in order to bond to the hydroxyapatite and collagen fibrils of the surface.

Overall, the risks to adhesive compromise and at worst, adhesive failure are high. This report details the use of a novel solution for debriding both indirect restorative and tooth intaglio with a 10-MDP salt-based solution that has the flexibility to be used both extraorally and intraorally.

ENDEMIC CONTAMINANTS: MOISTURE, BLOOD AND SALIVA

Moisture is a critical component to maximize the adhesive bond strength of certain modern universal adhesives. The presence of moisture allows for increased penetration of bonding solutions into dentinal tubules and between collagen fibrils, ultimately bolstering the resilience of the hybrid layer¹. During the cementation of an indirect restoration, both salivary and blood contamination of the mating surfaces have been shown to have a deleterious effect on bond strengths, with blood contamination faring the worst in all conditions². Van Meerbeck et al reported on technique sensitivity with one-step contemporary universal adhesives³. The basis of his findings note that these adhesives require water as an ionization medium for the self-etching reaction, with the need to evaporate water from the interfacial surfaces in order to maximize bond strengths. Despite this, these interfaces are considered semi-permeable which predisposes the hybrid layer to an increased risk of hydrolytic degradation in adhesive solutions that are not 2-hydroxyethyl methacrylate-free (HEMA-free), which has a greater affinity for water.

Periera et al tested varying degrees of wetness of dentin substrate controlled with variables such as short vs. long air blasts, wet vs. dry cotton pellets, microbrush use and an intentionally over-wet surface. In all groups, the “wettest” dentin intaglio surface resulted in the lowest shear bond strength⁴.

The influence of saliva and blood contamination is clearly negative in situations where the bonding interface was contaminated before or after adhesive application. For saliva, this reduction is due to the deposition of salivary glycoprotein on the surface, and relative to blood, macromolecules such as fibrinogen and platelets block access to the tubules for effective bonding. Blood contamination was found consistently to be more profoundly deleterious on bond strength relative to saliva².

In general, on smear layer-affected dentin, chlorhexidine was consistently superior to other agents such as ethanol, EDTA, aloe vera in establishing the highest shear bond strength to dentin. On dentin that had previously been etched and contaminated with blood and saliva, the agent subsequently applied that showed the highest recovery of shear bond strength was 37.5% phosphoric acid⁵. A study on the nanomechanical and nanoroughness of etched dentin and self-etching adhesive treated dentin both contaminated with saliva revealed that KATANA™ Cleaner was capable of restoring control values of complex modulus and nanoroughness relative to control⁶.

SYNTHETIC WORKFLOW CONTAMINANTS: DENTAL STONE, HEMOSTATIC AGENTS, ROOT CANAL SEALERS AND PROVISIONAL CEMENTS

A 2020 study by Marfenko et al demonstrated that salivary contamination showed significantly lower bond strengths relative to intaglio contamination by dental stone from laboratory processes. The application of a silane coupling agent to the intaglio surface has a protective effect on the bond strength⁷. The caveat is that lithium disilicate-based restorations are often requested pre-etched with hydrofluoric acid from the laboratory. Often, the case is returned to the clinician on the secondary or primary model. If already treated with hydrofluoric acid, the surface can now be considered recontaminated with the stone or resin model or simply skin oils from handling. The unprotected surface needs to be decontaminated in any case following the try-in procedure, which now may feature elements of dental stone, blood and saliva, not to mention hemostatic agents such as aluminum chloride and ferric sulphate. If silane coupling agents are applied prior to try-in, the question of whether the intaglio surface was truly contaminant-free after removal from the model.

Aluminum chloride is a hemostatic agent that leaves an insoluble precipitate on the surface of the dentin, that is only partially removed when treated with phosphoric acid, resulting only in a partial recovery of shear bond strength relative to control. The application of ethylene diacetyl tetrasodium acetate (EDTA) returned the bond strengths to the level of normal dentin⁸. The bonding of polycrystalline ceramic restorations and metal alloys is contaminated with saliva upon try-in. This can be removed via steam cleaning and air particle abrasion set at 2.5 bar for 15 seconds⁹. Phosphoric acid is often mistakenly applied as a cleaning agent to the intaglio surface. In polycrystalline ceramics such as tetragonal zirconia polycrystal, this is disastrous, as phosphates will bond firmly to the free sites that the 10-MDP monomer normally bonds to as part of the APC protocol of zirconia bonding, significantly compromising bond strength (Blatz, 2016)¹⁰. A study of modern surface cleaners demonstrated successful debridement of the surface using KATANA™ Cleaner for both blood and saliva-contaminated substrates^{11, 12}.

Provisional cements are thought to have a deleterious effect on the shear bond strength of adhesively-bonded indirect ceramic restorations. Ding et al (2022) uncovered that resin-based and non-eugenol cement use in the provisional phase decreased the bond strength relative to control, whilst the use of calcium hydroxide and polycarboxylate cements exhibited acceptable metrics. Debridement of the prepared surface with air particle abrasion (APA) resulted in recovery of decreased bond values to that of control¹³. Equally useful was the application of Immediate Dentin Sealing (IDS)¹⁴, a technique characterized ideally by APA before adhesive bonding and the application of a resin coat, occluding both the dentin tubules as well as the oxygen inhibition layer, allowing the resin-dentin bond to mature and strengthen in the absence of stresses. This approach is effective in minimizing post-operative hypersensitivity and bacterial ingress, as well as optimizing the shear bond strength particularly when indirect ceramics are concerned¹⁵. Hardan et al found that the shear bond strength was highest when IDS was completed using a three-step etch and rinse adhesive protocol¹⁴.

Hemostatic agents used in clinical dentistry exhibit a pH of 1.1 to 3.0 and are as acidic as self-etching primers¹⁶. Chaibutyr and Kois found that dentin when contaminated with 25% aluminum chloride or 13% ferric sulphate demonstrated a significantly lower shear bond strength to dentin, which was significantly recovered using the etch-and-rinse approach¹⁷. This approach albeit successful was only able to achieve partial reversal of shear bond strength deficits relative to control, with a pre-etching application of EDTA required in order for full recovery⁸. KATANA™ Cleaner was found to have a positive effect on the cleaning of dentin contaminated with both aluminum chloride and ferric sulphate.

The bonding of dentin substrate contaminated with root canal sealers is a concern for the integrity of core buildups post-endodontic treatment. The use of KATANA™ Cleaner was found to be generally superior to the ethanol test subgroup in the removal of zinc-oxide eugenol-based sealer with equal performance to 70% ethanol for the epoxy resin-based sealer¹⁸.

CLINICAL CASE DEMONSTRATION

A 35 year old ASA 1 female patient presented to the practice with multiple failing composite restorations in the second quadrant that were planned for replacement. Prior to the delivery of topical and local anaesthesia, it is common procedure in the practice to ascertain shade specifics of planned restoratives before potential dehydration can affect the optical properties of the natural tooth. Smart monochromatic composites (Fig. 1) are a class of direct restoratives that leverages the ability of its nanofiller composition and refractive index to mimic the structural color of the surrounding enamel and dentin¹⁹. This typically enables a clinician to have a simplified selection of shades on hand.

Two carpules of 2% Lignocaine with 1:100,000 epinephrine were delivered via buccal infiltration before absolute isolation was achieved using a non-latex rubber dam (Isodam HD Heavy, 4D Rubber, UK) (Fig. 2). The old restorations were excavated along with caries (Fig. 3), and the dentin structure assessed for residual decay with a detector dye (Caries Detector, Kuraray Noritake Dental Inc.). The preparation cavosurface margins were gently bevelled before surface treatment with air particle abrasion (30psi, 29 micron aluminum oxide in a 17.5% ethanol carrier, Aquacare UK) (Fig. 4). The enamel margins were etched with 33% orthophosphoric acid and rinsed (Fig. 5). The preparation surfaces were decontaminated further of any residual smear or powder residue using a MDP-based surfactant (KATANA™ Cleaner, Kuraray Noritake Dental Inc.) (Fig. 6). A single step self-etching universal adhesive was applied to the preparation as per manufacturer instructions and air thinned before light curing (Fig. 7).

Fig. 1

Fig. 2

Fig. 3

Fig. 4

Fig. 5

Fig. 6

Fig. 7

A matrix-in-matrix approach was utilized for the second bicuspid as the first step to allow for simultaneous anatomic construction of the mesial and distal marginal ridges. This technique does not require the use of a wedge as the outer circumferential Tofflemire matrix (Omnimatrix, Ultradent Products) tightens cervically around the inner anatomically-curved sectional matrix (Garrison Firm Band, Garrison Dental Solutions) allowing for a hermetic gingival seal (Fig. 8). If required, the setup may be further modified by the use of Teflon inserted between the two matrices to provide better proximofaciolingual adaptation. As a result, finishing and contour creation post-band removal is kept to a minimum. Following this, a traditional sectional matrix system may be employed to close contacts and build marginal ridges in the conventional manner (Fig. 9).

Following marginal ridge construction, the matrix assembly was removed and with the Class II lesions converted into a Class I situation, microlayering proceeded with a high flexural strength flowable liner (CLEARFIL MAJESTY™ Flow, Kuraray Noritake Dental Inc.) prior to the application of a monochromatic composite resin (CLEARFIL MAJESTY™ ES-2 Universal U shade, Kuraray Noritake Dental Inc.). The buccal cusps were constructed first as the author considers this essential to establishing restoration lobe proportions (Fig. 10). Subsequent layers were completed in a lobe-by-lobe approach to finish the occlusal anatomy (Fig. 11 and 12). The restoration was checked for occlusal functional conformativity, finished and polished to high shine (Fig. 13).

Fig. 8

Fig. 9

Fig. 10

Fig. 11

Fig. 12

Fig. 13

DISCUSSION

Dental substrates are often contaminated in both direct and indirect restorative processes. Historically, etch-and-rinse approaches have been successful for at least the partial recovery of bond strength however it is not practical in situations where selective or self-etching is the adhesive strategy. The restorative dentist in these cases can use the 10-MDP monomer in self-etching systems to target non-demineralized dentin such as CLEARFIL™ Universal Bond Quick to establish an acid base resistance zone (ABRZ) otherwise known as Super Dentin²⁰. The presence of the operative smear layer impedes full access of the self-etching primer to the dentin substrate in some cases. In such cases, without KATANA™ Cleaner, APA is required to transform the substrate back to control bonding potential. APA as a modality is only utilized by a subset of dental practitioners often due to financial constraints or lack of technique experience. KATANA™ Cleaner thus represents a versatile tool for the decontamination and optimization of substrate surfaces for adhesive bonding both in intraoral and extraoral applications. Its ability to re-establish ideal bonding values in areas that are not effectively reached by APA such as endodontic canal anatomy in a non-invasive manner literally cements it as a truly indispensable tool for the modern restorative dentist.

Disclaimer: Some indications are not described in the product’s Instructions for Use and are based on published research and/or the author’s experience. Before using each product, read carefully the Instructions for Use supplied with the product for full details and workflows.

Dentist:

CLARENCE TAM

References

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