Introduction to Matrix in Dentistry

Introduction to Matrix and Wedging

• Matrix is a properly contoured piece of metal or other material used to support and shape a dental restoration during placement and hardening.
• The function of matrix is crucial in controlling the placement and contour of restorations.
• Without a matrix wall, there's no method to control the placement and contour of the restoration.

Function of Matrix

• Matrix establishes proper contour and contact.
• It prevents marginal overhangs.
• It increases density and adaptation of the restoration.
• It provides a smooth surface for biocompatibility with surrounding soft tissues.

Requirements of an Ideal Matrix

• Easy adaptation to teeth.
• Easy contouring.
• Easy introduction and removal.
• Sufficient rigidity.
• Thin enough to avoid interfering with contact tightness.
• Smooth and highly polished surface.
• Compatible with restorative material.

Classification of Matrix

• Based on material (metal or plastic).
• Based on thickness (thick, thin, ultra-thin).
• Based on rigidity (rigid or flexible).
• Based on circumference (circumferential or sectional).

Circumferential Matrix

• A type of matrix that encircles the tooth.
• Examples include the Tofflemire matrix, a universal system commonly used in the United States.

Tofflemire Matrix (Universal Matrix)

• Consists of matrix bands and a retainer.
• Matrix bands: flat bands; available in 3 thicknesses: 0.0010, 0.0015, and 0.0020 inches. Wider bands are stiffer against deformation during filling condensation; thinner are often used for class 2 fillings
• Matrix retainer: used to hold the matrix band in place. The open side (slot) of the retainer should face gingivally when the band is placed around the tooth.

Flat Bands

• Bands that are flat and should be contoured before or after placement.
• Available in three sizes: Universal (#1), Broad (#2), Narrow (#3). The #2 band has additional extensions for deeper gingival margins, while the #3 is narrower with projections for even deeper gingival margins.

Precontoured Bands

• Manufactured with a predetermined shape for ease of use.
• Removal from interproximal contacts while maintaining shape of marginal ridge.

Retainer

• Used to hold the matrix band in place.
• Two types of retainers: straight or contra-angled.
• Contrangled used when a buccal wall is missing or a buccal cavity present.
• The open side (slot) of the head (retainer) should face gingivally when the band is placed.

Assembly and Placement

• The occlusal portion of the band extends 1.5–2.0 mm above the marginal ridge.
• The gingival portion is seated 0.5 mm below the gingival margin.

Indication for Matrix Use

• Class I composite restorations with buccal or lingual extensions.
• Restoring Class II cavities on one or both proximal surfaces of posterior teeth.

Ultradent Omni Matrix

• Disposable Tofflemire retainer and band system.
• Adjustable circumference.
• Easy release after restoration.
• Superior visibility and ease of use.
• Available in stainless steel and mylar.

B-Automatrix

• Retainerless matrix system.
• Designed for various tooth shapes and sizes.
• Components include the automatrix band, tightening device, and shielded nippers.

Advantages of Automatrix System

• Convenience.
• Improved visibility.
• Ability to position auto-lock loop on facial or lingual surfaces.

Disadvantages of Automatrix System

• The band is flat, difficult to burnish; sometimes unstable.
• Developing proximal contours and contact may be challenging.

C-T-Band Matrix

• Pre-made T-shaped brass or stainless steel matrix band (long arm wraps around the tooth, over short arm and bent back on long arm).

II - Sectional Matrix

• Relatively easy to use, very thin, and available in various sizes.
• Studies show their use results in tighter anatomical and consistent contact formation.
• Useful for composite restorations.

Systems with Bitine Rings

• Aid in stabilizing the matrix band and providing additional tooth separation during composite insertion.
• Improve the method for establishing composite proximal contour and contact.

B-Anterior Matrix

• Clear polyester matrix (Myla/Celluloid).
• Available for Class III and IV preparations (pre-contoured or flat).

Cervical Clear Matrix

• Used for Class V light-cured tooth restorations.
• Handle assists in positioning the matrix. Curing tip aids placement maintenance and curing.

C-Walser Matrix

• Available in various shapes (X-, O-, ON-, XF-shapes).
• Used for biplane fillings, MOD fillings, single/free-standing teeth, and terminal teeth.

Wedges

• Used for pre-wedging; promoting conservative preparation; protecting adjacent teeth.
• Prevents marginal overhangs.
• Maintains proper temporary tooth separation.
• Ensures close adaptability of the matrix.
• Aids in retraction of the rubber dam and gingiva.

Types of Wedges

• Classified according to material: Wooden (triangular, round, anatomical), and Plastic/light reflecting.

Wooden Wedges

• Available in various sizes, and color-coded.
• Straight or anatomically shaped.
• Absorb water, expand, and thus improve separation. Ideal for deep/wide proximal preparations due to base-heavy design

Plastic/Light Reflecting Wedges

• Transparent plastic with light-reflecting property.
• Aids in assessing light direction for composite curing and assessment for initial curing of class II composites. Anatomical shape, curved tip, and soft mouldable base.

Wedge Placement

• Insert from widest embrasure.
• Base should lie gingival to gingival margin.
• Wedge should be tight enough against tooth & matrix band (explorer use).

Wedge Placement Notes

• Use care when placing wedges if a rubber dam isn't used.
• Avoid placement in inflamed gingiva; this can cause bleeding. Improper wedge position at occlusal or apical of gingival margin will result in incorrect restoration contour and concavity/overhang.

Wedging Techniques

• Single wedge technique.
• Piggy-back wedging technique; used for gingival recession, with smaller wedges placed below main wedge to fill space, and press against margin.
• Double-wedge technique; used in cases of wider faciolingual proximal box by placing 2 wedges from facial and lingual embrasure; ensures proper filling and marginal support.
• Wedge wedging technique; used for mesial surface first premolars which may have concavity; wedge placed between existing matrix and tooth to prevent overhang and create proper tooth support.