Indirect/Lab-Based
While ceramic materials still rule when it comes to extracoronal restorations, indirect resin restorations are favored by 60% of our Editorial Team for inlays. However, with the success of direct resins, which allow maximum conservation of healthy tooth structure, inlays are slowly but surely becoming extinct. Nevertheless, indirect resins still offer benefits over ceramics.
One of the main reasons for changing from a ceramic material to resin is the hardness of the former. Since all ceramic materials are harder than tooth structure, they have the potential to abrade opposing natural teeth at an accelerated rate. This problem is compounded by the fact that partial coverage, bonded ceramic restorations have their occlusion adjusted after they are seated. This means that the ceramic material is being polished in the mouth, which is much more difficult than extraoral polishing. Even though this subject has not been thoroughly researched, we know the intraoral adjustment of ceramic materials may result in a surface that has the potential to be very abrasive to opposing teeth.
While it is possible to polish a ceramic material in the mouth back to its original smooth and glossy surface, this is a time-consuming, tedious, and very difficult task. Since this repolishing is usually less than perfect, the roughened ceramic material not only creates a potential problem with wear, but it also affects the esthetics. There are instances when it may be necessary to reshape a porcelain veneer intraorally, but the difficulty to easily recreate the smooth, glossy surface makes us hesitant to alter its surface.
In addition, the margins on bonded, partial coverage ceramic restorations can still leave a lot to be desired. Recall examinations may reveal margins that are no longer smooth due to the washout of the resin cement. In addition, if an overhang is discovered after the restoration is bonded, it is not an easy procedure to remove it.
Resins, on the other hand, are soft enough to prevent wear of opposing teeth. If they must be adjusted for occlusion or contours, they can be repolished simply and effectively. And their esthetics can be excellent, certainly the equal of ceramics when it comes to inlays and onlays.
Despite the emergence of resins for posterior, partial coverage restorations, ceramic materials still reign supreme when it comes to veneers and crowns. This is due to the much more sophisticated shading systems with ceramics, as well as their ability to hold its surface gloss and texture for many years.
ADVANTAGES OF INDIRECT RESINS
- Inlays tend to fit better
- Easier to adjust and polish
- Not as hard or abrasive to opposing teeth
- Can be repaired with similar material in the mouth
DISADVANTAGES OF INDIRECT RESINS
- Long-term wear resistance and strength still a question
- Polish and surface texture tend to fade
- Labs not as familiar compared to ceramics
Composition Most are hybrids, but one product in this group layers a microfill over a hybrid base and another is a nanohybrid.
Fiber Reinforcement Typically used for some posterior crowns and all bridges. As a rule, anterior crowns and partial coverage restorations do not require fiber reinforcement and may actually be a detriment since more tooth structure needs to be removed to provide space for the fiber.
Curing Unit The main idea is to enhance the physical properties of the resin. It is felt that by increasing the material's physical properties, it will provide increased clinical performance including better wear resistance. This is accomplished by a combination of factors. Some systems use heat, which has been shown in studies to enhance physical properties. Heat plus light has been shown to be even more effective than merely heat. And still others use very high intensity light, vacuum, and/or pressure.
Suggested Restorations All of these materials can be used for virtually any type of restoration.
Bond Strength Tests Our tests were done to discover the best way to bond to indirect resin. For all the materials, it was found sandblasting with CoJet produced the highest bond strengths for all the materials.
Fluorescence Many venues use black light for its special effects. If a restorative material does not exhibit fluorescence similar to tooth structure, it could create an embarrassing situation for a patient. This test shows how the material appears in vivo under black light. Materials exhibiting fluorescence that do not match that of natural teeth would not be a good choice in the mouth of patients with high esthetic needs.
