Surface preparation for adhesive systems
To allow adhesive system components and acid etchant to penetrate the tooth tissue structure unhindered, an impeccably clean surface is required.
Professional hygiene procedures must be performed without fail before starting treatment. This includes removing the pellicle, dental plaque, as well as supragingival and subgingival calculus. Cleaning is carried out using special brushes and rubber polishing cups.
Important limitation: it is strictly prohibited to use pastes containing glycerin, fluorides, or flavorings during hygienic processing. Residues of these substances on the enamel block the acid-etching process and impair adhesive penetration, nullifying the quality of the entire subsequent restoration. Furthermore, plaque removal significantly improves accuracy when selecting the color of the composite material.
Preparation guidelines for adhesive restorations
The modern approach to caries treatment using light-cured composites dictates moving away from classical, rigid Black's rules. The priority is maximum preservation of healthy tissues (conservative preparation). However, the cavity shape must take into account the physical and chemical properties of composites and adhesives.
- Smoothing angles: All sharp edges inside the cavity must be rounded. The presence of sharp angles creates internal stress zones. During polymerization (especially if the adhesive system used has insufficient elasticity), this can provoke material detachment from the tooth walls.
- Creating a bevel (chamfer): In Class III, IV, and V cavities, a 45-degree bevel is formed along the enamel margin. The depth of the bevel should be approximately half the thickness of the enamel layer. This significantly increases the contact area between the tooth surface and the adhesive/composite, improves marginal adaptation, and makes the restoration margin visually undetectable. On the vestibular surface, the prismless enamel layer may also be removed.
- Class I and II cavities: Creating a bevel is contraindicated on the occlusal surfaces of posterior teeth. Composite material wears down faster than natural enamel, so the restoration margin must not fall into areas of occlusal contacts with antagonists.
Operating field isolation
Working with adhesive systems tolerates no moisture. Saliva, blood, or gingival fluid getting onto the prepared tissues destroys the adhesive layer.
Two types of isolation are used in clinical practice:
- Relative: Use of a saliva ejector, high-volume evacuator, and cotton rolls. To protect cervical cavities from exudate, a retraction cord is placed into the gingival sulcus.
- Absolute (rubber dam, cofferdam): Performed using latex or non-latex sheets secured to the teeth with special clamps. There are also anatomical systems that fixate without clamps (e.g., OptraDam), and systems with pre-formed projections (OptiDam).
Absolute isolation guarantees the complete absence of operating field contamination, which is a prerequisite for high-quality adhesion. In addition, it protects the patient from aggressive solutions and small instruments, improves visibility for the clinician, and eliminates the need to constantly replace soaked cotton rolls.
Indications and limitations for direct restoration
Direct restoration involves working with composite materials directly in the patient's oral cavity. It is indicated for the treatment of caries, its complications, dental trauma, non-carious lesions, and for aesthetic correction at the patient's request.
However, there are factors that make the use of composites and adhesive systems impossible:
- Inability to adequately isolate the tooth from moisture (absolute contraindication).
- Presence of allergy to material components.
- Incompatibility with eugenol, phenol, or iodoform (these preparations inhibit polymerization).
- Deliberate non-compliance with hygiene by the patient (relative contraindication, sharply reducing the lifespan of the restoration).
- Bruxism, combination of tooth wear with a direct bite (in such cases, adhesive restorations fracture; prosthetic structures are preferred).
Briefly: answers to topical questions
Which generations of adhesive systems require mandatory total-etching of enamel and dentin?
Mandatory total-etching of enamel and dentin is required by 4th-generation adhesive systems. This technique provides tissue hybridization and is characterized by low postoperative hypersensitivity. The bond strength to dentin for such systems is 17–25 MPa. Systems of this generation contain from two to five components. Typical representatives are All Bond It, Pro Bond, Scotchbond MP, Tenure, Bond It, and Syntac.
What are the main components of a classical three-step adhesive system?
A classical adhesive system consists of three sequentially applied components.
- Conditioner — demineralizes enamel and dentin, most commonly 37% phosphoric acid.
- Primer — forms the hybrid layer, contains a mixture of hydrophilic compounds, alcohol, or acetone.
- Adhesive — provides the bond between the composite and the hybrid layer and enamel, consists of unfilled resins.
What solvents are used in the primers of adhesive systems?
Alcohol or acetone is used as solvents in the primers of adhesive systems. They are included in the mixture along with hydrophilic compounds.
What is the mechanism of hybrid layer formation?
The mechanism of hybrid layer formation consists of impregnating demineralized dentin with polymer resin. The process includes the following stages:
- Demineralization of the underlying dentin and partial impregnation or dissolution of the smear layer (smear layer).
- Penetration of hydrophilic primer monomers into dentinal tubules.
- Formation of a homogeneous zone where demineralized dentin bonds with polymer resin.
As a result, infiltrated tubules with polymer tags are formed, which ensures strong bonding of the composite to dental tissues and creates a protective barrier for the pulp.
What instruments and materials are needed for classical rubber dam placement?
The following are needed for classical rubber dam placement:
- Sheet — a latex or non-latex dam.
- Clamps — for securing the sheet on the tooth.
- Frame — for stretching the sheet.
- Forceps for placing clamps.
- Punch — for creating holes in the sheet for the teeth.
- Stamping template — for marking the location of the target tooth on the elastic sheet.
Class and exam questions
Why is it forbidden to use fluoride-containing pastes before applying an adhesive system?
Pastes containing fluorides, glycerin, or flavorings leave a residue on the enamel that prevents normal acid etching. This blocks the penetration of the adhesive into the dental tissues.
Why smooth out sharp angles of the carious cavity?
Sharp edges create stress during composite shrinkage. If the adhesive system is insufficiently elastic, the filling material will detach from the tooth in these areas.
What role does the bevel (chamfer) play in the restoration of anterior teeth?
A 45-degree bevel increases the contact area of the enamel with the adhesive system, improves marginal seal integrity, and makes the filling margin visually undetectable.
What else to study on this topic
- Tooth color topography and optical properties of composites
- Shade matching techniques using the Vita Shade guide
- Application of matrix systems and wedges in restoration
- Specifics of cavity filling with amalgam
- Vertical gutta-percha condensation method
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