PROgress in Science and Education with Ceramics is the interdisciplinary specialist network for metal-free restorations and will focus entirely on minimal invasiveness in 2024. This is because new technologies and materials now allow completely new scope and much gentler forms of preparation, from which all patients should benefit. The PROSEC workshop Minimally Invasive Indirect Restorations at the Polyclinic for Dental Prosthetics at Düsseldorf University Hospital for dental technicians and dentists with speakers Prof. Dr. Petra Gierthmühlen (Clinic Director) and Dr. Frank Spitznagel kicked off the event at the end of November.

Minimally invasive pioneering work
When Prof. Dr. Petra Gierthmühlen started researching minimally invasive treatment options, she was met with a lot of scepticism: “I had to do an incredible amount of research to prove that minimally invasive works and started implementing it clinically very early on. Today it is on everyone’s lips,” the speaker recalled her way back. According to Gierthmühlen, minimally invasive dentistry has clear advantages: “If you prepare an anterior tooth for a conventional crown, you remove almost 70% of it. In my opinion, that is far too much! The removal of tooth structure can be significantly minimized with veneers. It is only a quarter or at least only half that of a conventional crown. This is absolutely desirable, especially for young patients. We always want to stay in the enamel during preparation. Most treatments are therefore possible without anesthesia.” Only 10 % of total veneer cases can be solved without preparation. In the rest of the cases, the preparation has to be minimally invasive.

Advantages of digital treatment concepts
“What is possible digitally in terms of morphology and how precisely this can be implemented during milling is truly fascinating today,” said Gierthmühlen, impressed by the new technological and material developments. The correct anatomical position of the upper jaw can now be transferred three-dimensionally to a Facescan so that restorations can be designed in the correct vertical dimension when the bite is raised. The mock-up try-in can also take place virtually and then be produced economically with CAD/CAM support in order to check the function and esthetics on the patient. “The precision with which mock-ups can be made today thanks to the digital world naturally makes major work extremely predictable,” said Gierthmühlen, particularly with regard to complex complete restorations, and backed this up with numerous clinical case studies and an overview of the current study situation.

Minimally invasive “material jungle”
Dr. Frank Spitznagel gave an overview of the materials that are now available for the digital workflow. “You can’t say one fits all. Every material has its justification. For example, it’s about financial possibilities, the shade of the stump, the defect and the minimally invasive form of preparation,” said Spitznagel, describing the decision-making process. It is a balancing act between strength and aesthetics as well as the question of whether this is used chairside or in the laboratory. Spitznagel described the different classes of material in the form of a profile, went into their microstructure and properties and assessed their suitability for minimally invasive forms of restoration. He expanded on this with the current material science and clinical study situation as well as various clinical cases. Interestingly, according to current data, monolithic single-tooth restorations made of high-strength zirconium dioxide did not perform better clinically than those made of glass or hybrid ceramics.

New forms of preparation
“Thanks to advances in adhesive technology, ceramic partial restorations no longer require retentive preparation. The classic isthmus is no longer necessary. The occlusal margins should be shortened anatoform,” said Spitznagel, describing the new preparation method. Restoration margins should also lie in the enamel so that restorations can withstand the highest possible fracture load. Feather margins and uneven layer thicknesses in the marginal area should be avoided. Otherwise, according to Spitznagel: “Ceramics like rounded inner edges and no sharp points. We actually always perform a chamfer preparation at the preparation margins. For minimally invasive preparations, we stay supragingival if possible, epigingival in the esthetic zone and sometimes slightly subgingival with 0.5 millimetres if there are defects.” Spitznagel then demonstrated the preparation of a full veneer and onlays, which the participants then carried out themselves on the phantom head.

Minimally invasive paradigm shift
The speaker duo Gierthmühlen-Spitznagel offered a complete theoretical and practical package that clearly demonstrated that minimally invasive dentistry works and that the new digital technologies and materials available offer completely new possibilities. Gierthmühlen therefore expressed a wish at the end of her lecture: “My field of activity with tabletops, veneers, inlays, onlays, partial crowns and adhesive bridges is still a niche compared to conventional crowns and bridges. I hope that after this course you will move more into this minimally invasive field of activity and start doing more of these restorations next week.”

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