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Introduction:
- Bonding has gradually become established in dentistry as an effective way to ensure the retention of our restorations, while remaining conservative and aesthetic. However, to address the complexity of bonding to dental tissue, the materials at our disposal are constantly evolving.
- In order to bond effectively, it is necessary to know the advantages and disadvantages of each glue; it is also necessary to understand how adhesion to tooth tissue occurs in order to be able to choose the best compromise in any situation.
- It is by taking into account the condition of the dental tissues and the nature of the prosthetic piece that bonding can be effective.
I. Definition:
According to LAROUSSE:
- To fix, to adhere something to something else, by means of a suitable glue or adhesive.
In prosthesis : is an assembly process in which the parts to be joined are joined together thanks to the good hold of a surface layer, by its adhesion and cohesion, without significantly modifying the structure of the glued parts. “A. Rochette and BL Mena”
II. The different glues:
II.1: Required qualities:
- Biocompatibility; non-cytotoxic to the pulp-dentin organ and to the material of the prosthetic part.
- Durability: preservation of the adhesive bond over time
- The adhesive character: immediately ensures an adherent seal
- Waterproofing: prevents the penetration of bacteria and fluids that cause sensitivity and cavities.
- Ease of handling.
II.2: The different types of glues :
II.2.1: Resins: Resins, which result from the polymerization of methacrylic molecules. They are found in glues and in composite materials. We distinguish:
- The adhesive : it is a very fluid resin which infiltrates the roughness of the treated dental surfaces and thus forms a mechanical keying.
- Glues : are loaded with particles and create the mechanical bond between the adhesive layer and the prosthesis.
II.2.1.1: Classification:
A/ Depending on the need for etching:
- Resin requiring etching: Those products which require etching followed by rinsing, prior to use.
- Self-etching systems: These are products that are applied directly to tooth surfaces without any preliminary treatment. This class includes all self-etching systems.
B / According to the type of polymerization:
- Self-polymerizing resins : the setting reaction is chemical (base – catalyst).
Features :
• Interest in very deep cavities
• Complete polymerization
• Implementation time counted
• Fairly long and delicate finish.
- Light-curing resins : require a light source to trigger the setting reaction.
Features :
• Longer implementation time.
• Removal of excess before polymerization.
• Faster finishing.
• Risk of incomplete polymerization in the case of thick and opaque restorations.
Mixed polymerization (dual): polymerization by light to initiate the setting reaction of the most superficial composite completed by a chemical phenomenon of self-polymerization for the deepest composite.
II.2.2 “4 META” resins: This is an acrylic resin containing two new compounds:
•4-META (4-methacryloyloxyethyl trimellitate anhydride)
• tri-n-butyl borane (TBB).
Features :
- A product of choice for bonding metal alloys
- Adhesion to dental tissues, and in particular dentin, is effective, thanks to the creation of a quality hybrid layer.
- A particularity of 4-META resins is that they retain a certain plasticity after polymerization, and thus partially absorb mechanical stresses and therefore limit the risk of detachment.
- The trade name for this type of resin is Super Bond .
II.2.3. MDP “methyl diphosphate” resins: In 1981, Kuraray developed a phosphate-containing monomer that improved adhesion to dentin.
- “MDP” resin improves adhesion to enamel and dentin
- Provides very effective bonding to metal alloys.
- The setting of the material is anaerobic and therefore allows for a long working time
- Polymerization is triggered after the application of an insulating gel
- PANAVIA is the trade name for this MDP resin.
II.2.4. Resin-modified glass ionomer cements (hybrids), CVIH:
- They possess true chemical adhesion to the mineralized tissues of the tooth, as well as with certain alloys. However, the inherent strength of the material is lower than the adhesion strength achieved.
- CVIs are therefore most often reinforced with a resin (hybrid glass ionomer cements) .
- The adhesion of modified CVIs could be improved by applying an adhesive system before the placement of the CVIH
- This adhesion is achieved without the need for surface treatment.
- The mechanical behavior of CVI is very close to that of dentin (rigidity, thermal expansion). But their abrasion resistance is low and their aesthetic rendering is inferior to composite resins.
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III. Membership mechanism:
How ?
The mechanism keeping the adhesive in intimate contact and permanently connected to the solid surface can be:
- Chemical: the adhesive maintains primary chemical bonds with the solid surface, particularly with the calcium in hydroxyapatite.
- Mechanical: or micromechanical, or even nanomechanical due to the penetration of the liquid adhesive into the irregularities of the solid surface.
- Or a combination of both.
III.1. 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, whereas dentin is softer and more flexible.
- This tissue duality gives the tooth very significant mechanical resistance, however it complicates the adhesion processes.
III.1.1. Bonding to enamel :
- III.1.1.1. Specificity of the enamel:
The mineral matter is organized in the form of hydroxyapatite crystals.
- These crystals are grouped into bundles of hexagonal prisms.
It was Dr. Michael Buonocore who first demonstrated that an acid could alter the surface of dental enamel and allow it to be bonded with a resin.
The dissolution of prisms creates a microrelief on the surface of the enamel
The resin seeps into these crevices, adhering by mechanical keying.
- III.1.2. Bonding to dentin : Dentin bonding remains a challenge today because many elements prevent effective adhesion.
III. 1.2.1 membership mechanism:
- The key to dentin adhesion lies in the ability of the adhesive to penetrate the dentin tubulins. These intratubular extensions 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; what is called the hybrid layer is created .
NB:
The hybrid layer: The hybrid layer is an interweaving of two types of polymers: the collagen fibers of the dentin matrix (polymer of natural origin) on the one hand, and the macromolecules of the adhesive (synthetic polymer) on the other hand.
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- Etching/rinsing: at the level of the dentin surfaces by acid attack allows:
-to eliminate most of the sludge
-to open the tubular orifices,
-to superficially demineralize the peri- and inter-tubular areas (a few μm)
- But the presence of rinse water hinders the infiltration of the treated surface by the hydrophobic adhesive resin.
- So what can be done to remove the water and allow the resin to penetrate?
- This problem can be solved by using an agent called a primer.
The primer: or (the primer) is a liquid which keeps the collagen network sufficiently porous.
Therefore, the application of a primer appears to be essential to allow permeability of the demineralized dentin after evaporation of the water it contains.
Once the water is removed, the surface has a hydrophobic character conducive to the penetration of the resin.
Why is the adhesion mode of dentin different from that of enamel?
- Dentin is much less mineralized than enamel.
- it is organized differently.
- dentin does not allow a relief to be created on its surface by acid attack.
- In addition, the presence of water, particularly in the cellular extensions, is not favorable.
III.2. Bonding to reconstruction materials:
- Bonding ceramics
- Resin bonding
- Metal bonding
III.2.1/ Bonding the ceramic:
Bonding is an effective way to overcome the fragility of ceramics; we distinguish:
- Etchable ceramics: feldspathic or pressed Empress type
- Non-etching reinforced ceramics: Alumina or zirconia reinforced ceramics (Inceram®, Procera®)
- a/Etchantable ceramics: feldspathic or pressed Empress type
- – Etched with a strong hydrofluoric acid, creating reliefs suitable for bonding (it must be rinsed thoroughly).
- – In a second step, a silane is deposited on the surface of the ceramic, which creates a chemical bond with the bonding resin.
- Since this type of ceramic is sufficiently translucent, a photopolymerizing adhesive system can be used.
- NB/
- silane: generic name for hydrogen compounds of silicon. Silane derivatives are the most commonly used today.
- – These are bodies => double function or bipolar creating a chemical union between calcium in the enamel and acrylic.
- – The formula is schematized by: R-Si-(OR*)3
- In addition, the silane would have the advantage of increasing the wettability of the resin at the level of the interprismatic grooves created by the acid treatment.
- b/ Non-etching reinforced ceramics: Ceramics reinforced with alumina or zirconia (Inceram®, Procera®)
- The treatment is done by:
- – Sandblasting the intrados of the prosthesis with alumina
- – An artificial deposit of silica the adhesion values obtained immediately are very important.
- – The use of 4-META or MDP type glue allows for high adhesion values to be obtained
- – Since these ceramics are more or less opaque, it is important to use an adhesive system that is partly or completely chemopolymerizing, and not just photopolymerizing.
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III.2.2/ Resin bonding:
- Treatment of the intrados of the prosthetic part: to improve bonding by systematically carrying out sandblasting with alumina.
- – etching with hydrofluoric acid
- – secondly, application of a silane .
- -If the prosthetic part is not too thick (< 2-3 mm), a light-curing adhesive can be used. Beyond this thickness, a chemo-curing adhesive must be used.
III.2.3/ Bonding the metal:
- Bonding to metal alloys was first achieved by mechanical retention :
• first in the form of macro-retention (perforated fins of Rochette bridges);
• then micro-retention by alumina sandblasting.
- Thanks to 4-META (Superbond®) type adhesives, the adhesion values obtained on alloys are of the same order of magnitude as the adhesion to dental tissues.
- In order to increase this adhesion, surface treatments have been proposed, which consist of depositing silica on the surface of the metal.
- This silica is then coupled to the bonding resin by the application of a silane.
- The recommended protocol is therefore to sandblast the prosthetic part with 50 μm alumina, then to use a 4-META or Panavia® type resin.
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IV/ Bonding protocol:
- First of all, the surfaces to be bonded should be cleaned ( descaling
Ultrasonic and the use of a fluoride-free abrasive paste allow for effective cleaning of dental surfaces).
- Fluoride applications should be deferred until dental treatment sessions.
bonding, because fluorides decrease adhesion values.
- Using a rubber dam is the best way to achieve a clean, dry surgical field.
- Membership is obtained in two stages:
- The first application is that of the etching agent (37% orthophosphoric acid for 15 seconds).
- The etching gel is rinsed thoroughly, for a time at least equal to that of its application
- The tooth surfaces are then gently dried (intensive drying prevents the formation of the hybrid layer and increases the risk of postoperative pain).
- The product containing the primer and the adhesive is then applied.
Membership is obtained in 1 step.
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Deep cavities may require root canal treatment.
Interdental brushes effectively clean between teeth.
Misaligned teeth can cause chewing problems.
Untreated dental infections can spread to other parts of the body.
Whitening trays are used for gradual results.
Cracked teeth can be repaired with composite resins.
Proper hydration helps maintain a healthy mouth.