Modern dentistry offers various ways to repair damaged or decayed teeth. One of the most common approaches is the placement of a crown. However, an increasing number of practitioners are opting for partial restorations such as inlays, onlays, and veneers to provide their patients with a durable solution that can last for up to 15 to 20 years. Later on, there is often still the option to fit a crown if needed. In this blog post, we explain why partial restorations sometimes present the better choice and what advantages they can offer over crowns.

Patients today face different challenges than they did a few years ago. Despite advances in preventive oral care, cavities still occur, causing irreversible loss of tooth structure. Additionally, we are increasingly observing stress fractures and erosion due to chemical influences, such as the consumption of acidic foods and beverages or the use of certain medications. We also see tooth wear, or attrition, orginiating from mechanical forces such as bruxism. Foreign objects can also cause damage.

When providing dental treatment, we should consider: How can we best restore lost tooth structure? How long should restorations last? What can patients afford given their current situation? How many additional procedures can they undergo?  Life expectancy increases, so does the number of natural teeth retained into old age. People's dentitions need to function effectively for a longer time, even at age 80 or 90.

Any dental intervention should generally be as minimally invasive as possible and as invasive as necessary to prevent the recurrence of cavities and abrasion. In each case, we need to determine whether partial restorations such as inlays and onlays are suitable or if a crown is absolutely necessary. Partial restorations as inlays and onlays offer excellent esthetic outcomes. They can be designed to match the shade and shape of natural teeth with precision. Modern materials meet these requirements with ease. Is there still a need for full-coverage crowns? Yes, definitely. However, by considering the occlusion and utilising advanced techniques, we can create partial restorations that last for a long time. What is important is that the restorations remain fracture-free, bacterial adherence is minimised, recurrent caries is prevented and the occlusal scheme is retained.

Onlays are a valuable option in restorative dentistry because they help preserve the remaining healthy tooth structure. While crowns, which cover the entire tooth, are excellent solutions, they are not very conservative. The amount of tooth structure that needs to be removed for a crown is significant – ranging from approx. 67.5 to 75.6% - compared to only 5.5 to 27.2% for inlays and onlays^[1]. The goal should always be to preserve as much of the healthy tooth as possible.

Occlusal onlays made of lithium disilicate often present an effective treatment option in patients with severe wear. A small study from 2019 found a 100% success rate over 11 years in this context^[2]. A more recent study supports these findings, showing a survival rate of 98.4% in patients with severe wear, with a 100% survival rate for inlays and a 85.7% survival rate for onlays^[3]. These results suggests that IPS e.max lithium disilicate is suitable not only for anterior but also for posterior teeth. Although onlays may entail a higher risk of fracture in those cases, a survival rate of 85.7% after twelve years is clinically acceptable, as most of the tooth structure is preserved. Additionally, recent publications indicate that onlays generally require fewer post-prosthetic endodontic interventions compared to posterior crowns. If an onlay does fracture beyond repair, a crown can still be placed afterwards.

Why should we rush the process? Why are we in such a hurry? Our goal should be to delay more invasive treatment, if possible. An onlay restoration can easily last for 10 or 20 years. If the onlay is no longer adequate after 20 years, it was still a worthwhile alternative up to that point. The patients have been well served, and other treatment options are still available. We should not jump to definitive, final treatments right from the beginning. Instead, why not provide patients with a solution that can last for 20 years and then another one for another 20 years?  

Our IPS e.max lithium disilicate glass-ceramic combines  high strength and durability^[4,5] with translucency and excellent esthetic properties. It is available both as conventional press ceramic, known as IPS e.max Press, and as CAD/CAM blocks, known as IPS e.max CAD. IPS e.max provides a hight stability of 470 MPa (IPS e.max Press) and  520 MPa (IPS e.max CAD) respectively^[6,7], while long-term studies confirm its outstanding material properties. The fact that lithium disilicate glass-ceramic can be etched ensures that a strong micromechanical bond to the tooth structure will form during adhesive cementation. In addition, the material exhibits an enamel-like wear rate, contributing to lasting occlusal schemes. Alongside the survival rate, research from Dr Malament's team shows that occlusal adjustments to ceramic restorations, followed by polishing of the adjusted area, do not impact the clinical longevity and durability of the restorations^[4].

Partial restorations are a practical and often preferable alternative to crowns, and in many cases, they are the better choice. They are less invasive, preserve natural tooth structure, and can maintain the function and aesthetics of teeth for many years, as demonstrated, for instance, in long-term studies conducted by Dr Malament and his team (published in the Journal of Prosthetic Dentistry, JPS, USA). By using clinically proven materials such as the IPS e.max Press lithium disilicate glass-ceramic and state-of-the-art techniques, you can offer your patients a conservative and lasting treatment that ensures long-term dental health and improves their quality of life in the long term.

^[1] Edelhoff D und Sorensen J. Tooth structure removal associated with various preparation designs for posterior teeth. Int. J. Periodontics Rest. Dentistry Jun 2002
^[2] Edelhoff D, Gueth JF, Erdelt K, Brix O, Liebermann A. Clinical performance of occlusal onlays made of lithium disilicate ceramic in patients with severe tooth wear up to 11 years. Dental Materials, 2019, Sep;35(9):1319-1330.
^[3] Margvelashvili-Malament M, Thompson V, Polyakow V, Malament KA. Over 14-year survival of pressed e.max lithium disilicate glass-ceramic complete and partial coverage restorations in patients with severe wear: A prospective clinical study. Submitted for publication in JPD 2024
^[4] Malament KA, Margvelashvili-Malament M, Natto Z, Thompson V, Rekow D, Att W. Comparison of 16.9-year survival of pressed acid etched e. max lithium disilicate glass-ceramic complete and partial coverage restorations in posterior teeth: Performance and outcomes as a function of tooth position, age, sex, and thickness of ceramic material. JPD 2020 Sept 20.
^[5] Schweiger M., Biaxial flexural strength of IPS e.max lithium disilicate products, Test Report, Ivoclar Vivadent, 2016.
^[6] Mean biaxial flexural strength IPS e.max Press, R&D Ivoclar, Schaan.
^[7] Mean biaxial flexural strength IPS e.max CAD, R&D Ivoclar, Schaan