Lithium Disilicate
Translucency matters for posterior restorations
Dhaval Patel, DDS
The advent of CAD/CAM technology has enabled clinicians to perform dentistry more predictably. Rapid improvements in the technology have spawned several computerized devices that can fabricate ceramic restorations within a matter of minutes. For example, the CEREC® CAD/CAM system (Dentsply Sirona) is designed to be used chairside, eliminating the need for conventional impression taking, temporary restorations, and multiple appointments. The host of available CAD/CAM systems in the dental world has encouraged several manufacturers to introduce a variety of materials in chairside blocks. The IPS e.max® CAD (Ivoclar Vivadent) lithium disilicate glass ceramic block is one that is extremely popular among CAD/CAM dentists. This article discusses factors to consider when choosing the correct translucency (ie, high translucency [HT], medium translucency [MT], or low translucency [LT]) for posterior restorations.
IPS e.max CAD
IPS e.max CAD is a lithium disilicate glass ceramic that has enhanced translucency, durability, and strength for full anatomical restorations. Due to the use of new technologies and optimized processing parameters, IPS e.max lithium disilicate has evolved beyond previously available lithium disilicate ceramics.
IPS e.max lithium disilicate restorations exhibit superior durability, featuring an average biaxial flexural strength of 500 MPa. When fabricated to full contour, the monolithic structure is the most robust ceramic system tested to date. The opalescence, translucency, and light diffusing properties of IPS e.max lithium disilicate were all designed to replicate natural tooth structure for beautiful esthetics and undetectable restorations.
IPS e.max CAD HT and MT
HT and MT work extremely well when using them for partial coverage restorations such as inlays, onlays, and crownlays. When doing partial coverage preparations, the clinician is primarily replacing the enamel, and HT and MT blend well with the cavosurface margins that are within enamel. The translucency of these blocks makes them virtually invisible once incorporated into the surrounding dentition. The following two clinical cases of partial coverage restorations performed with with HT and MT illustrate how well these translucencies blend with the surrounding tooth structure.
Case 1: Two-Surface Mesio-Occlusal Inlay on Tooth No. 3
A patient presented with the chief complaint of sensitivity to sweets on tooth No. 3 (Figure 1). During diagnosis, a radiograph revealed decay on the mesial surface along with a mesial marginal groove. The tooth was prepped for a two-surface mesio-occlusal inlay, and IPS e.max CAD HT was selected as the material of choice (Figure 2). After the restoration was designed with the CEREC® Omnicam intraoral scanner, it was milled using the inLab MC XL milling machine. It was then stained and glazed with IPS e.max CAD Crystall Stains and Glaze materials (Ivoclar Vivadent) per the manufacturer’s instructions (Figure 3). Finally, the restorations were adhesively cemented into the patient’s mouth. The final postoperative image shows how well the material blends in with the surrounding tooth structure (Figure 4).
Case 2: Four-Surface Onlay on Tooth No. 30
A patient presented for an initial exam, and during evaluation of the radiographs, a large recurrent decay was found on the distal surface of tooth No. 30 (Figure 5). The old restoration was removed, and the decay was cleaned. Following this, a mesio-occlusal-distal-lingual onlay was milled with IPS e.max CAD MT (Figure 6). The restoration was stained and glazed to match the other teeth, then bonded into place (Figure 7). It’s ability to match the natural dentition is readily apparent in the final postoperative image (Figure 8).
IPS e.max CAD LT
Because the preparation is within the dentin, IPS e.max CAD LT works really well on complete coverage restorations. Using the HT translucency in these cases would allow the dentin to shine through, resulting in restorations that end up looking gray. When compared with HT and MT, the LT translucency performs really well in blocking the dentin because of its higher opacity. Other situations in which the LT translucency is preferred include those involving preparations with moderately dark stumps and the need to match an adjacent porcelain-fused-to-metal or porcelain-fused-to-zirconia restoration.
Case 3: Full-Coverage Crown on Tooth No. 4
A patient presented to the office dissatisfied with the appearance of the crown on tooth No. 4 (Figure 9). The radiograph did not reveal any decay or open margins, and the current porcelain-fused-to-metal restoration was clinically acceptable. However, a visual exam revealed a supragingival margin exposing a dark stump, which resulted from root canal treatment completed several years prior. In addition, the shade was poorly matched. The old crown was removed, and IPS e.max CAD LT was selected as the restorative material of choice. After staining and glazing, the restoration was bonded in place. The final postoperative image demonstrates that IPS e.max CAD LT worked well in blocking the dark stump, and with the help of staining and glazing, it is virtually undetectable within the surrounding unrestored teeth (Figure 10).
Conclusion
IPS e.max CAD is an extremely versatile material that can be used for many different indications. The HT and MT translucencies work well when restoring partial coverage preparations with margins that are high and dry and primarily in the enamel, whereas the LT translucency works well when restoring complete coverage preparations that are within the dentin or have a dark stump. These are general recommendations based on the author’s experience. Dentists should always use their clinical judgement when selecting from these blocks or other materials.
For more information, contact:
Pacific Dental Services
714-845-8500
pacificdentalservices.com
About the Author
Dhavel Patel, DDS
Private Practice
Roseville, California
