One of the most frequent pathology in our daily restorative practice is represented by the proximal caries. Restoring the class II cavities in a proper way is very important in order to obtain a functional contact surface between the teeth. The aim of this article is to show some steps of choosing a proper matrix and to illustrate how to use this matrix to achieve a functional contact surface.
Over time, two types of matrix system have been proposed: circumferential matrix and sectional matrix. Some studies conclude that the use of the sectional matrix system in two-surface Class II cavities results in statistically significantly tighter proximal contacts than the use of the circumferential matrix system (1).
If we compare the marginal ridge fracture strength of Class II composite resin restorations placed with a straight or contoured matrix band using composite resins, the use of a contoured matrix results in a stronger marginal ridge of a Class II composite resin restoration (2).
Starting from these studies we conclude that the sectional contoured matrix is one of the best choices to restore class II cavities.
There are different matrix dimensions. Some of the matrix systems have a convexity intended to reproduce the marginal ridge. That is why it is important to choose the right width of the matrix, in order to use this benefit.
To use this matrix in a proper way and to obtain a good result, it is important to have a good preparation of the tooth. In most cases, it is necessary to put the margin of the preparation outside the contact point, as shown in picture 4, in a safer and easy to clean zone, because the matrix must be placed passively.
Otherwise, there will always be the risk to deform the matrix.
If the matrix is placed passively we can obtain a very nice contour.
Another condition to obtain a good contact surface is to have a separation between the teeth to compensate the thickness of the matrix and the contraction of composite polymerization. The separation rings are the most useful tools for this purpose (3).
If the gingival margin of the preparation is not very sub gingival, the separation between the teeth can be obtained by using strong rigid wedges.
One of the most important steps to obtain a good proximal morphology is to have a very good adaptation of the matrix to the preparation margins (gingival and proximal walls).
In most of the cases using different types of wedges can lead to a very good adaptation of the matrix to the gingival margin of the preparation.
If we cannot obtain a good adaptation using only a wedge we can improve the situation by using teflon tape.
This teflon tape can be compressed between the matrix and the adjacent tooth, between the matrix and the ring or even under the ring. His role is to push the matrix to the preparation walls.
If the cervical margin is placed very sub gingivally, the wedge will bend the matrix.
In these cases it is necessary to use another material (such as teflon tape) to obtain a good adaptation of the matrix to the gingival wall and not to use wooden wedge.
Regarding the adaptation of the matrix to the proximal walls, the separation ring can be very helpful.
It is necessary to apply the ring to the prepared tooth in order to push the matrix to the preparation walls, otherwise, the ring itself can bend the matrix.
Sometimes it is necessary to improve the quality of the adaptation by using other materials (teflon tape, liquid dam, flowable composite, etc).
Before placing any composite material, it is necessary to customize the contact point, to transform it into a contact surface and to place it more vestibular or oral, more gingival or occlusal, depending on what we need.
In conclusion, a functional contact surface is achieved by using a good matrix system, a good separation between the teeth and by having a very nice adaptation of the matrix to the preparation walls. It is necessary not to put any composite material in a class II cavities before having these 3 parameters completed. In this way, we can obtain a nice proximal design and we can save a lot of time in the finishing steps.
1. Wirsching E., Loomans BA, Klaiber B, Dorfer Ce: Influence of matrix systems on proximal contact tightness of 2- and 3-surface posterior composite restorations in vivo. J.Dent 2011 May;39(5):386-90.
2. Loomans BA, Roeters FJ, Opdam NJ, Kuijs RH; J Dent 2008; 36: 828-832
3. Loomans BA, Opdam NJ, Bronkhorst EM, Roeters FJ, Dörfer CE. Oper Dent. A clinical study on interdental separation techniques. 2007 May-Jun;32(3):207-11.