Adhesive systems

Adhesive systems are used to attach composite filling material to hard tooth tissues and to close dentin tubules (dentine wound treatment "ad integrum").

Adhesion to enamel
Enamel has more mineral components than organic, its etching creates interprismatic spaces into which bond can flow better and thus hold microretention. It does not have to be hydrophilic. The bond strength is 30–40 MPa. A composite without a bond does not leak into interprismatic spaces and therefore does not hold itself, as it is too viscous.

Binding quality Enamel depends on:

Avoiding contamination – never let the patient rinse after we have etched the enamel. After etching, the enamel must not be contaminated. That's why we prefer to work with kofferdam. In case of accidental contamination, etch again (2-3 s), then rinse.

Etching time – 20–30 s (orthophosphoric acid), a little longer for temporary teeth. If we etch too long (60 s), the result is worse. The top layer of enamel prisms breaks off and the interprismatic spaces prepared for bond leakage are clogged.

Type of etch, consistency – it must not be too viscous, it must be a solution or a thin gel. If the etching agent was too viscous (thick gel), it would not flow into the whole cavity, into the subsecurvature. We choose the type of etching according to the character of the cavity. For class I, we can choose a solution. On vertical surfaces, we will rather use gel. The gel etching (contains silica particles) must be rinsed longer.

Skew – the enamel must be slanted to ensure better cavity closure. Composite materials adhere better to enamel than to dentin. Temporary teeth are harder to etch than permanent ones (thanks to aprimatic enamel).

The state of enamel before etching (machining) – whether we etch aprimatic enamel (aprismatic enamel is located on the necks), milk teeth, fluorine-impregnated enamel. We must achieve the so-called appearance of shiny ice.

Composition of enamel – presence of aprismic enamel, too fluoridated, demineralized, etc.

Adhesion to dentin
The bond to dentin is threefold: chemical, micromechanical (today the most common) and mixed. Dentin etching is performed 5–10 s.

Chemical bond

In 1956 a weak chemical bond to dentin (2–3 MPa) – 1st generation bonds. She could not maintain the contraction forces of the composite and the teeth died.

Micromechanical coupling

A hybrid layer is formed, which is made up of:
 * collagen fibers (living matter);
 * HEMou.

We penetrate the surface part of the dentin with an adhesive, after solidification we form a hybrid layer that holds it (about 2 μm ~ 20 MPa thick). This micromechanical bond was not possible until hydrophilic materials, i.e. HEMA (does not shy away from dentin), were formed. HEMA is the basis of the primer. It penetrates into the surface part of the dentin and allows the penetration of the binding resin. Hydrophobic resin does not leak into the tubules.


 * Mixed binding After the dentin is etched, a primer and adhesive are applied to penetrate the surface part of the dentin to form a hybrid layer (1–2 μm thick) behind which it is held with a force of 15–20 MPa.

Create a Hybrid tier
Remove the smear-layer (grit after preparation), rinse the dentin and etch briefly. Then we impregnate the surface parts of the collagen fibers with a primer, which are erect, fluffed and remain erect even after the composite is applied. Let the primer act for 20-30 s and then blow lightly. It should shine. Next, dry the layer, apply bond resin, spread it and remove the excess. We enlighten and this leads to polymerization. Finally, we apply the composite resin.

The hybrid layer consists of:
 * demineralized dentin (i.e. actually collagen – dentin is "collagen coated with a mineral"),
 * the latter is impregnated with resin,
 * resin bundles in tubules,
 * microsheaves penetrating into lateral connectors between tubules

Primer
Most primers include:
 * binding resin (HEMA)
 * Solvent: water, or acetone, or alcohol

Primer with acetone
It is very volatile (must not be left open) and has a short expiration date. It is also sensitive to processing – acetone does not penetrate into dry dentin, is hydrophilic → needs wet bonding, penetrates well and dissolves regularly.

Wet bonding = application of the bond to wet (primerated) dentin

Water primer
It is easy to process - not so sensitive to overdrying or wet. Even if the dentin is overdried, the primer rehydrates it and penetrates it. The disadvantage is that it dissolves the resin poorly.

Primer with alcohol and water
It has properties between water and acetone, it is a reasonable compromise.

Note: before applying the primer with acetone solvent, we can leave the cavite wet until it shines in places. After primer primer, dry.

Classification of adhesive systems

 * by generation – from the third generation onwards, these are already modern systems;
 * According to the method of dentin treatment – division into "total etch" and "self etch" systems. Within these two groups, adhesive systems can be further divided according to the number of steps (1, 2 and three-step).

Related Articles

 * Composite materials
 * Making a composite filling