Operative II: Matrix Application (Reading)

Q: What is one of the most important steps in restoring Class II preparations with direct composites?

A: Proper matrix selection and setup.

Q: What are the two main purposes of using a matrix in restorative procedures involving a proximal surface?

A: (1) Confine the restorative material excess and (2) assist in the development of the appropriate axial tooth contours.

Q: How do Class II composites differ from amalgam in establishing proximal contacts?

A: Class II composites are almost totally dependent on the contour and position of the matrix, unlike amalgam which can be condensed against the matrix.

Q: What helps achieve sufficient separation of teeth to compensate for the thickness of the matrix material?

A: Early wedging and retightening of the wedge during tooth preparation.

Q: Before placing the composite material, what must the matrix material do?

A: Be in absolute contact with (i.e., touching) the adjacent contact area.

Q: When is the matrix generally applied in relation to adhesive placement?

A: Before adhesive placement.

Q: Why is an ultrathin metal matrix band generally preferred for Class II composite restorations?

A: Because it is thinner than a typical metal band and can be contoured better than a clear polyester matrix.

Q: What technique allows for successful placement and light curing of composite with a metal matrix?

A: Using an incremental technique.

Q: Why are precontoured sectional metallic matrices preferable over a Tofflemire-type band for two-surface restorations?

A: Because only one thickness of metal matrix material is encountered instead of two, making contact generation easier. (Look up "matrix-in-matrix" or "back-to-back" techniques to better visualize two metal matrix stacking)

Q: What are some features of precontoured sectional matrices?

A: They are easy to use, very thin, and come in different sizes to accommodate varied occlusogingival heights of the proximal box.

Q: What determines the selection of a sectional matrix system?

A: Operator preference.

Q: What two roles can a bitine ring play in sectional matrix systems?

A: (1) Aid in stabilizing the sectional matrix and (2) provide additional tooth separation while the composite is inserted.

Q: What is the primary benefit of sectional matrix systems?

A: A simpler method for establishing an appropriate composite proximal contour and contact.

Q: What may happen if bitine ring prongs are misapplied in wide faciolingual proximal preparations?

A: Deformation of the matrix band, resulting in poor restoration contour.

Q: What matrix system is used when both proximal surfaces are involved?

A: A Tofflemire retainer with an ultrathin (0.025 mm or 0.001 inch) and burnishable matrix band.

Q: How is the matrix band managed for proper proximal contacts and embrasures?

A: The band is contoured, positioned, wedged, and shaped as needed.

Q: What should be done to a metal matrix band before placement in posterior composites?

A: It should be burnished on a paper pad to impart proper proximal contour.

Q: What is an alternative to burnishing a regular matrix band in a Tofflemire retainer?

A: Using an ultrathin precontoured metal matrix band.

Q: How far should matrix material extend in relation to gingival and occlusal margins?

A: At least 1 mm beyond the gingival margin and the area corresponding to the marginal ridge.

Q: Why shouldn't the matrix extend further subgingivally or occlusally?

A: So as not to interfere with the restorative procedure.

Q: What is done if a wedge was used during tooth preparation before matrix installation?

A: It is removed so the matrix band can be installed and immediately reinserted.

Q: What are the three purposes of a wedge at the gingival margin?

A: (1) Hold the matrix in position, (2) provide slight separation of the teeth, and (3) prevent a gingival overhang of the composite material.

Q: Why must a wedge be used to separate teeth?

A: To compensate for the thickness of the matrix if the restoration is to have appropriate proximal contacts.

Q: What types of wedges are available for use?

A: Several types of commercial wedges in assorted sizes.

Q: What type of wedge is indicated for most preparations?

A: An anatomical (triangle-shaped) wedge of compatible size.

Q: How should the wedge be sized and positioned for optimal access?

A: It should be kept as short as possible and should not push the matrix onto the preparation space.

Q: From which direction is the wedge placed in posterior restorations?

A: From the larger to the smaller interproximal gingival embrasure, typically from a lingual approach, just apical to the gingival margin.

Q: What should the wedge do once placed?

A: Engage (stabilize) the matrix band.

Q: What can help wedge placement when using a rubber dam?

A: A small amount of water-soluble lubricant on the tip of the wedge.

Q: What is the rubber dam technique for wedge placement?

A: The rubber dam is first stretched gingivally (on the side from which the wedge is inserted), then released gradually during wedge insertion.