Matrix systems in dentistry

Instruments and devices for matrix fixation

For successful work with carious cavities involving contact surfaces (predominantly class II), specialized instruments are used:

• Strip matrix — placed directly on the prepared cavity, simulating the missing wall.
• Wooden wedge — inserted into the interproximal space to create a tight fit of the matrix to the cervical area and to separate the adjacent teeth.
• Universal matrix retainer — a mechanism for secure fixation and tensioning of the matrix band.
• Wedge holder — an instrument for precise and safe positioning of the interproximal wedge.
• Special tweezers — an instrument with a special inner surface relief of the jaws, ensuring a firm grip and retention of wooden wedges without the risk of slipping.

In modern practice, sectional matrix systems are also actively used. They consist of the matrix itself (which is fixed with a wedge) and a special retaining ring. If an extensive mesio-occluso-distal (MOD) cavity is being restored, two matrices must be placed simultaneously, each fixed with a separate retaining ring.

Three main rules for filling class II cavities

When restoring contact surfaces, the dentist must strictly control three key aspects of restoration:

1. Control of the base liner. The cement base on the occlusal surface and especially in the cervical area must under no circumstances protrude from under the main restorative material. Otherwise, the cement will undergo rapid dissolution under the influence of oral fluid.
2. Prevention of an overhanging margin. The matrix must fit as tightly as possible to the tooth tissues. Any gap will lead to material leakage and the formation of an overhanging filling margin. Such a defect causes constant pressure irritation, which inevitably leads to inflammation of the gingival papilla and the marginal gingiva.
3. Restoration of the contact point. A correct anatomical contact must be created between the restoration and the adjacent intact tooth.

Pathogenesis in the absence of a contact point

Ignoring or incorrectly contouring the interproximal contact triggers a clear pathological cascade leading to periodontal disease:

• During chewing, food debris easily penetrates the interproximal space.
• Constant mechanical trauma and irritation of the interproximal gingival papilla occur.
• Experiencing discomfort, the patient attempts to remove the trapped food with toothpicks and other objects, causing additional trauma to the gingiva.
• Clinical outcome: persistent inflammation develops (gingivitis or papillitis), which subsequently leads to bone resorption and periodontal pocket formation.

Features of working with various materials

The tactics of using matrices vary depending on the chosen filling material:

When working with cements (silicin) in class III and IV cavities: The material is placed in a single portion using a flat plastic instrument. For contouring the lateral surfaces, a celluloid strip pre-lubricated with petroleum jelly is used. It is inserted into the interproximal space and pressed tightly against the tooth, controlled with a flat plastic instrument so that the cement does not extrude beyond the cavity. The contact point is created by lightly pressing with a condenser on the middle of the not-yet-hardened filling.

When working with amalgam (class II cavities):

• Traditional technique: the matrix system with wedges and rings is installed, the base is placed (on the floor, walls, and gingival area), after which amalgam condensation is performed.
• Technique for restricted access (cavity on the distal contact surface): the base and the initial portions of amalgam are placed first, and only then is the matrix installed for the final filling.
• Matrix removal: after contouring, the matrix is removed extremely carefully, pressing it against the adjacent tooth so as not to accidentally dislodge the fresh restoration. Then, a condenser or a dense cotton pellet is used to press on the center of the filling until contact with the adjacent tooth is achieved.

Tactics for filling adjacent cavities

If carious lesions are located on the contacting surfaces of adjacent teeth, the treatment approach depends on the material:

• General rule: cavities are filled in a single visit, but strictly sequentially. First, one tooth is completely restored, the filling is allowed to harden, and only then is the second one started.
• Rule for amalgam: restoration is performed on separate visits. During the first visit, one cavity is filled, and the second (prepared) one is sealed with a temporary filling made of artificial dentin. Permanent filling of the second tooth is performed at the next visit. This guarantees correct anatomical contouring and reliable creation of the contact point.

Briefly: answers to topical questions

Class and exam questions

What else to study on this topic

• Stages of preparation and conditioning of class I and II carious cavities for amalgam
• Justification for the thick consistency and thickness of the base liner under amalgam
• Rules for placement, condensation, and removal of excess mercury when working with amalgam
• Algorithm for finishing and polishing amalgam restorations (after 24 hours)
• Use of parapulpal pins in the restoration of Class IV cavities

Other topics in "Chapter 9. Restoration of anatomical form and function of the tooth"

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.