There are some guidelines regarding the preparation dimensions for onlay or overlay that a dentist should follow for an optimal final result. First, the axial walls should have a divergence angle of 15 degrees. The internal angles should be rounded. The proximal step width should be at least 1 mm and the width of the occlusal isthmus should be at least 2mm. Sufficient clearance between the proximal step edge and the adjacent tooth should be ensured – at least 0,5mm. Furthermore, the dimensional demands of the restorative material should be respected. Both Initial LiSi Block and CERASMART270 are designed to push the boundaries of minimal thickness of the restoration. For initial LiSi Block restorations the recommended minimal thickness for an onlay or overlay is 1 mm throughout the entire restoration. For CERASMART270 restorations the recommended minimal thickness is at least 1,5mm occlusally and in the equator area and 1mm at the proximal step. These recommendations should be taken into account when preparing a tooth to provide sufficient space for the chosen material.

When the proximal margin of the preparation is subgingivally, the clinician might stumble upon some difficulties – it is difficult to take an exact analog or digital impression, it is difficult to place a rubber dam, the visibility is compromised and therefore the successful sealing of the margins is questionable. In cases where it is possible deep margin elevation is recommended. By performing this procedure, the proximal margin will be elevated slightly supragingivally and therefore impression taking, isolation and visibility will be improved.

In order to ensure longevity of the tooth a short-fiber reinforced flowable composite ever X Flow is an ideal choice. Thanks to the short fibers everX Flow is efficiently replaces the missing dentin and reinforces the tooth. Not only will it provide exceptionally high fracture toughness but will also allow for easy manipulation and placement due to its thixotropic viscosity.

Immediate dentin sealing (IDS) is a dental technique of applying a bonding agent to the freshly cut dentin surface of a tooth immediately after preparing it. The bonding agent seals the exposed dentinal tubules, preventing fluid exchange between the tooth and the oral environment.

IDS has been shown to have several benefits, including reducing postoperative sensitivity, preserving the pulp vitality, improving the bond strength of the final restoration, and improving the longevity of restorations.

Enamel surface can be exposed after immediate dentin sealing by carefully using a fine grit diamond bur.

When performing DME, it is important to use a matrix band that can adapt closely to the tooth surface and create a tight seal around the preparation margin. There are several matrix systems available, and the choice of matrix band will depend on the specific needs of the case.

Commonly used matrix systems for DME are sectional matrix system or circumferential matrix system. In cases where it is difficult to achieve a perfect seal there are some additional recommendations. One example is the use of matrix in matrix technique, where usually a sectional matrix is placed inside of a circumferential matrix. Another useful tip is to pack Teflon tape into the are between the matrix and the adjacent tooth to achieve a tight seal.

Placement of the rubber dam is always recommended. It is better to isolate the whole working quadrant or at least the two adjacent teeth to the tooth being restored. To achieve a perfect isolation dental floss and teflon tape can be used. To ensure the stability of the clamp, it is important that the clamp is in contact with the tooth in 4 contact points.

Additionally, the correct size of the perforation of the rubber dam is essential to prevent leakage. Make sure to choose the appropriate size on the perforating tool. Once the rubber dam is in position, inverting it at the gingival margins of isolated teeth is another beneficial step for tighter seal and improved visibility.

In some cases, the margin of the defect is so subgingival that adequate isolation is impossible. In this case deep margin elevation is not recommended as the lack of the isolation could lead to compromised bonding of the composite material. Therefore, other options like surgical gingivectomy or crown lengthening procedures should be considered.