The Filtek Matrix: Finishing and Polishing Technique
As with any direct composite procedure, it is very important to contour and polish well to achieve natural results. The Filtek Matrix will take you through composite build-up and provide a better shape while minimizing voids compared to freehanding because you are filling rather than layering. Still, it’s up to you to successfully finish the restoration.
When contouring a restoration, created with the Filtek Matrix or otherwise, I utilize a “divide and conquer” approach. If you focus on each anatomical component of the restoration one by one, the sum of the parts will be an anatomical tooth. During each step, it’s important to only focus on the feature at hand and not be distracted by other features. The “divide and conquer” principle covers ten anatomical features, which you can explore in more detail in the article, “A systematic approach to contouring and polishing anterior resin composite restorations: A checklist manifesto.”1 While each area is important, the Filtek Matrix takes you further than traditional direct composite restorations anatomically, so you can save time on build-up before the final finish:
The length of the teeth:
Traditionally, you would determine length based on adjacent teeth along with the esthetic and functional parameters of the restoration and use abrasive discs, such as 3M™ Sof-Lex™ Contouring and Polishing Discs, to reach the proper length. However, with the Filtek Matrix, you don’t even have to think about this step – length is already incorporated into the design of the matrix – it may just need smoothing (fig 6).
Figure 6: Smoothing the incisal edge with a 3M™ Sof-Lex™ Finishing and Polishing Disc.
Incisal-facial line angle:
This anatomical feature is also provided by the matrix. The incisal-facial line angle should follow a natural arch form.
Facial profile/crest of contour:
A normal incisor contour has three planes: cervical, middle and incisal. Usually, the crest of contour (the greatest bulge of the tooth), is naturally positioned between the middle and gingival third of the teeth, and can be evaluated from an occlusal view. If necessary, it should be refined with a fine diamond bur or disc (fig 7).
This can be a challenging feature to obtain with the Filtek Matrix, due to excess material, but can be achieved with careful attention and practice – make sure to take advantage of 3M’s training kits with practice models to refine your technique.
Figure 7: a. A line is traced between the middle and gingival thirds of the restorations. b. A fine diamond bur is used to define and align the facial contours.
Line angles:
Line angles represent the transition between the buccal and lingual with the proximal surfaces; these lines can affect the visual perception of a tooth and should be carefully placed to ensure a natural appearance (fig 8). These angles are vital because they can optically change the appearance of a tooth. If the line angles are too far apart, the tooth will look wider; if they are too close together, the tooth will look narrower.2 The facial angle, in particular, can be challenging with the Filtek Matrix due to material excess – which is why it’s so important to remove as much excess as possible before removing the matrix.
Figure 8: a. The desired line angles are traced onto the restorations. b. The lines are refined with 3M™ Sof-Lex™ Finishing and Polishing Disc at speeds below 8000 RPM.
Embrasures:
Each embrasure – incisal, facial, gingival, and lingual – should be contoured with a disc to achieve the proper shape and size. Gingival embrasures are the hardest for practitioners to control and prevent excess, but the Filtek Matrix features a fin that helps prevent excess material in this area.
However, while embrasures are built into the Filtek Matrix, they may need an adjustment here and there to make sure they are smooth and excess-free. After using the Filtek Matrix, the embrasures may be joined, but it’s a smaller area to break through, and it’s much easier to separate the teeth. To break the contact, I like to use a serrated blade. It will cut the composite, separate it, but not remove it – then I can smooth the edges (fig 9).
Figure 9: a. A curved surgical blade (#12) is used to remove excess material in a shaving motion, not to cut the composite. b. A serrated blade is used to separate the teeth if there is bonding matrial between adjacent teeth. A diamond strip can be used to further smooth the interproximal areas if necessary.
Point angles:
Also built-up in the Filtek Matrix, point angles, or the junction of the line angle, embrasure, and incisal edge, should be a single point. Refinements can be made if necessary.
Axial inclination:
Every tooth is mesially inclined at varying degrees, which is particularly important when restoring multiple teeth. When working with the Filtek Matrix, this may need a bit of extra work, because of excess in the facial area. Look from the facial and make sure every tooth is mesially inclined, and the contralateral teeth match.
Depressions and elevation:
Adding depressions and elevations ensure a natural appearance that blends into the patients smile. Most anterior teeth have three elevations, corrresponding to the enamel mamelons, and two depressions, which I obtain by penciling over the facial surface, then using a fine-grit flame finishing diamond bur at about 10,000 RPM (fig 10).
Figure 10: A fine diamond bur is used to create depressions.
Surface texture:
While patients may want a smooth feel to their teeth, teeth themselves aren’t completely flat. Natural teeth feature perikymata and imbrication lines that cross the enamel surface and break light reflection. These textures can be achieved by using a fine grit diamond bur in a single direction, from mesial to distal.
Gloss:
A high final luster and gloss are critical to an esthetic restoration and can be achieved with wheels, discs, or abrasive cups in progressively decreasing grits. I like to start with a coarse grit cup and obtain my final polish with a very fine grit diamond-impregnated polisher. I think it gives you a surface indistinguishable from glazed ceramic (fig 11, 12)
Figure 11: a. A polishing cup is used to finish the restoration. b. Final results.