Sandwich technique methods
The sandwich technique implies the combined use of a base lining material and a composite. There are two main approaches:
- Closed method: the base material is completely hidden under the layer of restorative composite and does not come into contact with oral fluid.
- Open method: the liner (compomer or glass ionomer cement) is partially covered by the composite, maintaining contact with the oral cavity. It is most often used for Class II cavities, especially when it is difficult to place the composite on the gingival wall.
The protocol depends on the base material. Traditional chemically cured glass ionomer cements (GICs) require two visits because they harden over 24 days hours. If the composite is applied immediately, its polymerization shrinkage will tear the immature GIC away from the floor. When using packable light-cured GICs, the restoration can be completed in one visit.
Layered restoration method
Used for extensive Class I and II cavities. The essence lies in combining different types of composites to minimize polymerization stress and utilize the best properties of each material.
Order of layer placement:
- Adhesive system (applied to the walls and floor).
- Flowable composite (Flowable) — lines the floor and adapts to the complex shape of the cavity.
- Packable composite (Packable) — restores the main volume of the destroyed dentin.
- Microhybrid composite — forms the superficial (enamel) layer 1–1.5 mm thick to restore occlusion.
Restoration using posts
If the crown walls are thinner than 1 mm or destroyed down to the gingiva, post systems are used. The post is fixed in the root canal and serves as a framework for the restoration.
Mandatory conditions for post placement:
- Preservation of the cementoenamel junction.
- High-quality endodontic treatment.
- Root wall thickness of at least 1 mm (cervical and middle thirds).
- Post length should be 2/3 of the root length and not less than the length of the future crown.
- 3–5 mm of the root filling must remain in the apical part.
According to the fixation method, metal posts are divided into active (threaded, create tension) and passive (held only by cement). The cylindrical shape provides better retention than the conical one.
Fiberglass and carbon fiber posts
In modern dentistry, this is the most optimal option. They consist of an epoxy matrix (about 37%) and directed fibers (about 63%).
Advantages of such posts:
- Their modulus of elasticity is close to that of dentin, which prevents root fractures.
- The fibers are located along the main axis, ensuring uniform distribution of chewing load (unlike conical posts).
- They are corrosion-resistant and biocompatible.
- Due to the non-smooth surface and chemical affinity, they form a single monoblock with the adhesive and composite, reducing the load on the remaining tooth tissues.
Briefly: answers to topical questions
What matrix systems are used for the correct formation of the contact point during the restoration of Class II cavities?
For the correct formation of the contact point during the restoration of Class II cavities, sectional and strip matrix systems are used.
- Sectional matrix system — includes a metal sectional matrix, a wedge, and a retaining ring (ring spring retainer). The ring ensures tight adaptation of the matrix margins and physiological separation of adjacent teeth. In extensive MOD cavities, two matrices with two rings are installed.
- Strip matrix system — includes a strip matrix, a wooden wedge, and a universal matrix retainer for fixation.
What functions does flowable composite perform in layered restoration?
In layered restoration, flowable composite acts as the first adaptive (super-adaptive) layer.
It lines the floor of a carious cavity of complex configuration. Due to thixotropy, the material spreads to form a thin film and easily penetrates hard-to-reach areas of the cavity without flowing off the back surface. After this, the packable composite is placed, restoring the lost dentin volume.
What functions do interdental wedges perform when restoring the contact point?
When restoring the contact point, interdental wedges act as a fixative and ensure proper adaptation of the matrix system.
Main functions of interdental wedges:
- Separation (wedging) of adjacent teeth.
- Reliable retention of the matrix in the specified position.
- Tight adaptation of the matrix in the gingival part of the tooth.
- Prevention of filling material overflow (overhanging margins) into the interproximal space.
The wedge is inserted into the interdental space strictly after placing the matrix.
What are the full indications for the open sandwich technique?
The open sandwich technique is used in situations where it is technically difficult to apply the composite material to the gingival wall of the cavity.
Most often, this technique is used for the restoration of Class II carious cavities. The feature of the method is that the base material (glass ionomer cement or compomer) is only partially covered by the composite, maintaining open contact with the surrounding tissues of the tooth and oral cavity.
Class and exam questions
Why is restoration performed in two visits when using chemically cured glass ionomer cement?
Glass ionomer cement hardens in 24 hours. Composite shrinkage upon immediate placement would cause the unpolymerized base to detach from the cavity floor.
What is the difference between open and closed sandwich techniques?
In the closed method, the base layer is completely covered by the composite. In the open method, the base material (usually on the gingival wall) is in contact with the oral cavity.
What are the parameters of a properly prepared post space?
Length — 2/3 of the root, root wall thickness — at least 1 mm on each side, preservation of 3–5 mm of the apical filling, support on dentin (shoulder) of 0.3 mm.
Why are fiber-resin posts better than metal posts?
They have the elasticity of dentin, do not cause corrosion, and together with the composite cement form a single monoblock preventing root fracture.
What else to study on this topic
- Mechanism of GIC detachment from the cavity floor when exposed to a curing light
- Hydrodynamic effect and causes of postoperative sensitivity
- Criteria for a properly performed restoration
- Classification of posts by design and manufacturing method
- Requirements for periodontal and periapical tissue health prior to restoration
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