Restorative adhesive therapies: principles and techniques

Adhesive restorative therapies: principles and techniques

Introduction: The considerable contributions of adhesive dentistry, in terms of tissue economy, biocompatibility and aesthetics are part of the clinical evidence.

1. Definitions:
   1. Adhesive dentistry:

(or micro-dentistry, minimal dentistry): Specificity of dentistry based on the bonding capabilities of composite resins in such a way as to only remove infected dentin and thus replace destroyed dental tissues, even at an advanced stage, while preserving as much healthy tissue as possible. From the moment a restorative material is bonded to dental structures, one can be conservative and must be as conservative as possible.

2. Adhesive restoration:

A prosthetic part or conservative plastic filling that restores the form, function and aesthetics of the tooth by using coupling agents that chemically and mechanically bond the material to the dental tissues.

1. Tissue economy principle:

The maximum conservation of healthy parts of the tooth has allowed the evolution of current interventions because they are the very substrate of bonding and adhesion techniques. The approach then becomes more biological and less mechanistic and thus ensures the longevity of the restored tooth.

• Maintaining pulp vitality :

is ensured by the preservation of a parapulp cavity guaranteeing pulp protection against surgical attacks while allowing normal function of the tooth ;

• Access to the carious lesion must allow tissue savings both quantitatively and qualitatively in the beam structures of the tooth while sparing the enamel.

peripheral; Current techniques therefore target the preparation of cavities on the respect of dental tissues and no longer on the filling material

2. Membership:

Bonding protocols now allow for sufficiently strong adhesions to enamel and dentin to be achieved so that they are durable in the oral environment. Advances in adhesion seek to reduce infiltration at the interfaces.

2. Bonding to dental tissues:

The two tissues that make up the tooth, enamel and dentin, are quite different in their chemical composition and physical properties. Enamel is a hard and brittle tissue, while dentin is softer and more flexible.

1. Specificity of enamel
   1. Constitution:

• Enamel is the most mineralized tissue in the human body. It is made up of 96% mineral matter, 4% water and some organic matter.

• The mineral matter is organized into long hydroxyapatite crystals. These crystals are grouped into bundles of prisms. Within the prisms, the hydroxyapatite crystals are oriented parallel to the long axis of the bundle, and in a different orientation within the inter-prismatic substance. This inter-prismatic substance allows the cohesion of the prisms between them. The prisms originate at the enamel-dentin junction and join the surface of the crown.
• The organic matrix consists of glycoproteins and polysaccharides.

2. Membership method:

• It was Dr. Michael Buonocore who first demonstrated that an acid could alter the surface of dental enamel and allow it to be bonded by a resin.
• The greater dissolution of the core of the prisms will in fact create a microrelief on the surface of the enamel. A resin can then infiltrate these created crevices and ensure adhesion by mechanical keying.

2. Specificity of dentin:
   1. Constitution:

Dentin is an extracellular matrix secreted by odontoblasts that calcifies through the accumulation of hydroxyapatite. It is ultimately less mineralized than enamel. It is traversed by fine tubules (50,000/mm2). These tubules are perpendicular to the pulp-dentin junction and contain fine cytoplasmic extensions of the odontoblasts. These cellular extensions are at the origin of the sensitivity of dentin to stimuli (hot, cold, contact).

2. Membership method:

• Much less mineralized than enamel and differently organized, dentin does not allow a relief to be created on its surface by an acid attack ( Figure 1 ). In addition, the presence of water, particularly in the cellular extensions, is not favorable to good contact between the resin and the dentin.
• The key to dentin adhesion lies in the ability to penetrate the dentin tubules

by the adhesive. These intratubular extensions (Figure 2) (tags ) will mechanically anchor the resin to the dentin.

• Another important part of the retention is achieved by infiltration of the collagen fibers of the prepared dentin surface by the adhesive. This creates what is called the hybrid layer . When the tubules are scarce, adhesion is mainly ensured by the hybrid layer.

Figure 1: Observation in electron microscopy

scanning (x 300) of a dentin section. Figure 2: Resin Tags

The upper, unetched part is covered with dentin smear. The lower, etched part reveals the dentin tubules.

3. Implementation:

• While adhesion to enamel has been a phenomenon that has been controlled for a long time, the same cannot be said for the adhesive treatment of dentin. It is tempting to make the most of the natural presence of a network of tubules in order to anchor the resin in the dentin. This mechanical anchoring is, however, made uncertain by two factors:
  • The first is the exudation of plasma fluid through the tubules as a result of tissue preparation. It is practically impossible to dry the dentin surface.
  • The second element is that these canaliculi will be partly blocked by the accumulation of preparation residue: the “dentin smear”.
• The smear layer is a film consisting of a matrix, formed from a mixture of denatured collagen and water of dentin origin, in which hydroxyapatite crystals removed during milling are incorporated. Other elements of exogenous origin are also present, such as saliva, blood, and microorganisms. The thickness of this layer varies from 0.5 to 1.5 μm. This coating covers the dentin and seals the dentin tubules. It penetrates more or less deeply into them and creates canalicular plugs.
• It was long thought that this smear layer should be preserved, which, by sealing the tubules, allowed bonding to a dry surface. However, the smear layer is only weakly adherent to dentin (5 MPa) and limits anchoring to this value. In addition, the preservation of the smear layer limits the depth of infiltration of the resin into the dentin tubules. The presence of bacteria is inevitable in this smear layer, and can be the cause of pulp aggression.
• At the dentin level, the etching acid has a dual role of surface demineralization and elimination by dissolution of the dentin smear obstructing the tubules

allowing deep anchoring (resin flanges) of the adhesive at the level of the canaliculi.

• The surface of the dentin must then be treated with a conditioning liquid called a “primer” to ensure resin penetration into the tubules. The composition of the primer is generally as follows:
  • a weak acid (citric, maleic, phosphoric, nitric, succinic, or ethylenediaminetetraacetate [EDTA]), which dissolves the smear layer so as to expose the underlying dentin.
  • Hydroxyethyl methacrylate (HEMA) or hydrophilic dimethacrylate: HEMA has a hydrophilic hydroxyl function, capable of binding to collagen, and a methacrylate end that can polymerize with the hydrophobic monomers contained in the adhesive Figure 3

Figure 3: Chemical configuration of the Primer

• It is a crosslinking agent that penetrates with the dentin sludge dissolved by the acid into the tubules. Its hardening after polymerization causes mechanical anchoring;
• a solvent that increases surface wettability.
• The primer is an adhesion promoting agent, whose role is to allow good penetration of the adhesive monomers into the collagen matrix and tubules by replacing the hydrophilic aqueous medium with a hydrophobic medium conducive to the diffusion of the resin. Its small size and its partially hydrophilic character allow it to diffuse well into the tubules.
• It is then necessary to treat the dentin with an adhesive that will then induce a structural change in it. The coupling agent or ” bonding ” is used. This is an organic or organo-mineral molecule with two active sites:

• a site that can react with the dentin surface
• and another to interact with the bonding composite.
• In this way, we obtain an intimate adhesion between the different materials present.

4. Classification of adhesives:

The concept of adhesive generation no longer makes sense today and the classification that referred to it has been abandoned because it did not take into account the mode of action or the effectiveness of its products.

There are two main classes of adhesives:

• those which are applied after etching with orthophosphoric acid then rinsing the dental surfaces are called M&R.
• Those that do not require etching have an intrinsic acidic character that allows them to simultaneously attack and penetrate dental tissue. These are self-etching systems or SAM for short.

In each class, we can distinguish 2 types of adhesives depending on the number of implementation sequences

• 3 or 2 for M&R systems.:
  • We will have M&R3 (etching-rinsing, then application of “primer” then adhesive resin “bonding”. M&R2 groups together the “Primer” packaging and the adhesive

simplifying the procedure

• 2 or 1 for SAMS. SAM2 involves the first deposition of a “Primer” which contains acid monomers and water which will condition the dental surfaces, this first layer is simply dried without rinsing, followed by the application of “Bonding”.

SAM1 contain mixtures of acid primer and bonding, they do not require

only one application sequence

a) Respective advantages and disadvantages of M&R and SAM:

• M&R systems

• Implementation is quite lengthy, with the preliminary sequences of etching with orthophosphoric acid and rinsing. The multiplicity of steps is a potential source of error.
• Rinsing can cause unexpected bleeding of an inflamed gum near a preparation that is not always well isolated, hence contamination of the prepared surfaces.
• They can cause post-operative sensitivity. Their application must be done on slightly damp dentin but not too much, which is not easy to control.
• On the other hand, the prior use of orthophosphoric acid gives them good potential for adhesion to enamel.
• The SAMs:

• Simpler and often faster to implement thanks to the elimination of the rinsing sequence.
• The absence of rinsing has two other favorable consequences:
  • It reduces the probability of blood contamination of the preparations and, above all, it considerably reduces the risk of post-operative sensitivities, since the dentin smear is not eliminated but on the contrary consolidated and sealed. The plugs that it forms at the level of the tubular orifices are sufficiently hermetic to prevent the movements of dentin fluids which generate sensitivity.
• SAMs necessarily contain water necessary for the ionization of its acid components. The presence of water in their composition can present 2 disadvantages:
  • The first is a degradation of some of its constituents by hydrolysis, resulting in a loss of effectiveness.
• the second is the possibility of residual water remaining after drying in the adhesive joint, which harms the quality of its polymerization and therefore its resistance.

• SAMs have a less acidic character than phosphoric acid. Their etching capacity on enamel is weaker than that of M&R, therefore their adhesion too. It is however possible to optimize their adhesion to enamel by carrying out a preliminary etching with phosphoric acid of the enamel margins, but just and only the enamel margins. This additional operation of course complicates the procedure
• Overall, we see that M&R and SAM are quite complementary since the disadvantages of one correspond to the advantages of the other; Also, the practitioner should have an adhesive system of each class to be able to respond to the particularities of each clinical situation.
• Over the years, manufacturers have sought to make adhesive systems simpler and

more reliable, while maintaining the same properties. Universal adhesives have therefore been proposed and show real interest in their versatility to be used as MR, SAM or in a combined way

• These adhesives are presented as being effective with or without prior etching of dental structures (use with etching like an MR system, or without etching like a SAM system): this is the first definition of universal adhesive systems.
• These universal adhesives are applicable on dental structures but

also on prosthetic intrados: this is the second definition of universal adhesive systems

• In indirect techniques, they do not all have the same scope of application, some being suitable for a wider range of materials (composite, ceramic, alloy, precious and non-precious metals), others being suitable for repairing prostheses fixed in the mouth.
• For a universal adhesive, manufacturers indicate that we can work with selective, total or no etching (self-etching), and that we can treat different substrates, dental or prosthetic. Therefore, the universal system is presented as little sensitive to operator manipulation.
• The difference between SAM1 and universal is that it contains MDP (methacryloyloxydecyl dihydrogen phosphate) and not MHP (phosphoric acid ester monomer manufacturer’s secret), and that it also contains silane. The rest of the composition is generally the same as that of MR2.

1. Operating protocol
2. Select a product appropriate to the clinical situation:

For adhesive restorations of anterior teeth using direct or indirect techniques, the choice will generally fall on an M&R system . Good isolation by an operating field is easy, so the risks of contamination are low. The effectiveness of phosphoric pre-etching of the chamfered enamel makes it possible to limit the degradation of the margins, especially their dyschromia, and therefore to maintain aesthetics in the medium and long term.

Conversely, in all situations where the establishment of the surgical field remains difficult to control, the use of SAMs is preferable; this is particularly the case for cervical lesions close to the epithelial attachment and deep cavities of the posterior sector.

2. Store your product in a cool place.

3. Shake the bottle before use or choose single-dose bottles: refrigerate every evening to avoid hydrolysis accelerated by temperature.
4. Read the instructions and follow the procedures carefully, particularly the application times.
5. For M&R , first etch the enamel for 15 to 30 seconds, then the dentin but no more than 15 seconds: the application range of an orthophosphoric acid gel on the enamel is quite wide for effective etching. It extends from 15 seconds to one minute. On the other hand, the contact of this acid with the dentin must be limited to 15 seconds maximum to allow complete infiltration of the resin over the entire demineralized area.

It is now well established that it is not the thickness of the hybrid layer which determines the quality of adhesion and sealing, but the quality of its impregnation by the monomers. A demineralized zone incompletely infiltrated with resin is a source of post-operative sensitivities.

6. For M&R2 , the dentin must be a little moist before application: dry without drying out to avoid evaporation of the water which keeps the collagen network open to allow infiltration of the resin

Use a damp, pre-wrung cotton ball or mini brushes for small cavities

Some authors recommend not drying the surface with compressed air after rinsing but prefer to use the tip of a saliva suction device to evaporate the residual water. That said, no trace of water should be visible after this operation.

7. Apply the adhesive by firmly rubbing the cavity walls:

Apply with pressure to promote infiltration of the adhesive (use of mini brushes is more effective than paintbrushes, the minimum application time must be respected).

8. Pay attention to the drying of the adhesive, this is the most critical sequence:

drying of the deposited adhesive layer is necessary before polymerization to evaporate the solvents contained in the products and ensure good sealing of the joint, this step is especially crucial for SAMs given the water in their composition

9. Check the appearance of the adhesive layer: just before proceeding with the polymerization, the practitioner must check the appearance of the adhesive layer that he has applied. This layer must be uniformly shiny.
10. Ensure good polymerization of the adhesive: this is the setting of the adhesive by photopolymerization. The quality of this operation will give the glued joint most of its immediate and long-term performance.
11. Preparation principles for bonded materials:

• In all cases where bonding is possible, retention, stability and support are ensured by this bonding . Bonding obturation techniques are therefore the techniques of choice which best meet the criteria for tissue conservation.
• The preparation will be limited to the curettage of all pathological dentin tissue.
• Enamel preparation is limited to the removal of cracked enamel. The enamel edges will be finished to ensure the best possible adhesion and seal to the enamel. It can take different forms; it is important to choose the one that provides the best compromise between aesthetics, seal and material strength.
• The straight bevel presents the best aesthetics. Generally, the length of the bevel is limited to about 1 mm (which corresponds to an angulation of about 45°), so as not to have a limit too thin thickness of the composite.

• The concave fillet or bevel would allow, due to its greater thickness, better resistance to abrasion, however to the detriment of aesthetics: even if the color of the composite is the same as that of the tooth, the anisotropy of the two media is perceived in the light exactly like two fragments of a broken and re-coapted mirror.
• The concave bevel is therefore reserved for the palatal surfaces of the anterior sector and the molar occlusal surfaces due to its better occlusal resistance. A straight bevel can be combined with a fillet to improve aesthetics.
• If until recent years the creation of a bevel seemed essential to ensure the watertightness and stability of the filling, the appearance of enamel-dentin adhesives since the 4th ^generation calls this notion into question. Indeed, with adhesion over the entire dentin surface, the bevel is not necessary to ensure stability, and the watertightness is greatly improved. In addition, it is known that the degradation of composites – under the effect of shear forces combined with the progressive hydrolysis of the silane bonds and the matrix – begins in the areas of low thickness, that is to say at the level of the bevel. Thus, in the absence of aesthetic necessity, a bevel is no longer created in the areas supporting occlusal contacts. More specifically, an occlusal path must not pass over a bevel.
• Obviously, Black’s classification can no longer be adapted to cavity shapes so different from those of amalgam preparations. Mount and Hume in 1997 proposed a classification that is – in a very slightly modified form – used today for cavity preparations for composites.
• This classification describes three sites (Si) of caries appearance:

• site 1: pit, groove and coronal defect lesions;
• site 2: lesions of contact areas;
• site 3: coronary and/or radicular cervical lesions.
  • Five stages (Sta) of development are distinguished for each carious site, starting from stage 1 representing a loss of substance of 1/5 of the coronal part, stage 2 representing a loss of 2/5 of the coronal part, etc. up to stage 5 representing the loss of the entire dental crown. Stage 5 obviously involves prosthetic restoration after endodontic treatment.

We then obtain a classification by site and stage or Si-Sta classification.

• Stage 1 preparations : are very small volume decays, they are particularly suitable for the conservation of important anatomical elements, in particular the marginal ridges.

Cavities via vestibular or lingual access can be achieved under several conditions:

• sufficient strength of the cavity ceiling
• perfect accessibility to preparation instruments, adhesives and composite materials

• Care must be taken not to perform subgingival preparation.
• Cavity preparation under a dam is then an important factor in the success of the preparation, the dam allowing compression and gingival repression.
• Tunnel-type cavities can be achieved under the same conditions; they are preferred in cases of low coronal height, or very large contact surface or in cases of gingival coverage.
• If the implementation of the adhesive is delicate, the use of a glass ionomer in a sandwich technique can be judicious. The sandwich technique consists of filling the cavity in two parts; a deep filling reconstituting the dentin is carried out with a conventional glass ionomer cement (CVI) or hybrid which allows a relatively weak but reliable spontaneous adhesion to the dentin; the surface filling replaces the enamel with

composite that is well resistant to occlusal wear. In the case of tunnel cavities, the CVI is injected into the deep (proximal) part of the tunnel, and the proximal enamel is not then replaced with composite. We speak of an open tunnel when the proximal enamel is removed, but whenever possible it is preserved and it is then a closed tunnel.

• Stage 2 preparations : are more mutilating and result in irreversible loss or weakening of the marginal ridge, allowing more conventional access to the caries.
• Stage 3 preparations : present a significant loss of tooth volume, they lead to a clear weakening of at least one cusp of the tooth. Fragile or unsupported dental or enamel sections remain. We then seek to improve the biomechanical cohesion of the reconstituted tooth: to minimize the risk of fracture, no sharp angles are made, the residual sections that are too weak or protruding are also reduced. A peripheral bevel encompasses the enamel sections in the mass of the restoration. Often these cavities are filled using the direct technique although the large volume of composite compared to the residual tissues is an unfavorable factor. It is therefore more appropriate to fill these cavities using indirect or semi-direct techniques .
• Stage 4 preparations: present an even greater loss of volume, they cause cusp loss. These preparations are not compatible with the in situ implementation of restorative materials and their treatment requires indirect or semi-direct techniques, except for site 3 caries. The adhesion surface on the enamel and dentin is low compared to the decay and the “occlusive” surface. We then seek to ensure a cavity shape improving stabilization and tooth-material resistance: the residual sides that are too weak or protruding are reduced. The unsupported enamel sides are eliminated, the edge finish will be close to 90°. The bottom of the cavity is, if necessary, slightly flattened, in stages so as to preserve a maximum of healthy tissue. A perfect undercut is not necessarily sought, two possibilities will present themselves: either the undercut is slight and then it is filled with the bonding composite. Either the undercut is clear, and it is entirely possible to carry out a partial filling of the cavity, either with a bonded composite or with a CVI in order to fill this undercut. The impression and the bonding of the indirect reconstruction are then carried out on this partially filled cavity.
• Si-Sta 3.4: generally concern four cervical surfaces of the tooth and therefore do not allow the insertion of a filling performed using the indirect technique. They are therefore filled using the direct technique. However, it should be noted that before the appearance of fourth-generation dentin adhesives, these Si-Sta 3.4 were very rarely subject to conservative treatment and directed our therapeutic choices towards prosthetics.

6. Composites used for adhesive restorations:

• Composites are the standard materials for direct restorations. Using an adhesive, they are bonded to the tooth, allowing for the preservation of dental structures. Their optical and mechanical properties also make them essential for a wide variety of therapeutic indications.
• Three categories of composites can be used:
  • hybrid composite resins,
  • condensable composites
  • fluid composites.

1. Summary table of clinical indications for composites:

Composite type	Properties	Clinical indications
Hybrid composites (Hybrids, Microhybrids, Nanofilled Microhybrids)	Their main characteristics are: A wide choice of color, degree of opacity, translucency and fluorescence. A high capacity to mimic dental structures and excellent polishing ability. Abrasion and wear similar to that of dental structures. Mechanical resistance still perfectible. A relatively controlled but still existing setting shrinkage rate and water absorption.	Undifferentiated use between the anterior and posterior sectors
Condensable composites	Condensable composites They have been proposed to replace amalgam without changing the handling habits of practitioners. However, given their lack of mechanical superiority (compared to hybrids) and their disappointing aesthetic rendering on the one hand, and on the other hand the appearance of small, easy-to-use consumables allowing a good point of contact to be ensured even with hybrids, they seem to be gradually disappearing from the market.	they are reserved for the posterior sector

Fluid composites

They have the advantage of having: A high wettability of dental surfaces regardless of their irregularities, promoting tissue preservation and avoiding the inclusion of air bubbles at the interface. High flexibility (lower modulus of elasticity) allowing it to absorb stresses. However, their main disadvantages are having: High polymerization shrinkage. Low wear resistance and hardness.

used either in a thin layer as a viscoelastic seal (cavity floor or sealing of cervical margins) under a more loaded composite (preferably compactable composites), or for restorations subject to low constraints (small losses of substances or cervical lesions, for example). The recent development of so-called “Bulk Fill” composites promises a significant time saving on the production of posterior composites. These particular composites require special instrumentation. These composites have the capacity to be photopolymerized in mass (up to a height of 4 mm in a single time) with a degree of conversion which would be adequate even in depth

Conclusion : Modern dentistry aims at maximum conservation of residual structures in order to optimize the longevity of the tooth on the arch thanks to the evolution of the principles in adhesive dentistry .

Adhesive restorative therapies: principles and techniques

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Adhesive restorative therapies: principles and techniques