CATEGORY 102 AUSTRALASIAN DENTIST CLINICAL The antagonist: a factor to consider in full-arch rehabilitation (kinetic energy/impact) By Dr. Oriol Cantó-Navés. Contracted Doctor Professor, Rehabilitation and Esthetic Dentistry Department, College of Dentistry, Universitat Internacional de Catalunya (UIC Barcelona) Corresponding author: oriolcanto@uic.es When we talk about implant rehabilitation, we must consider both aspects – surgery and prosthetics – equally, giving them the same importance. Along with this, a strict anamnesis and general evaluation of the patient are essential. It is well known how important it is to place implants in the correct position, according to the type of implant (tissue level or bone level), using bone and/or gingival grafts to ensure proper function and adequate aesthetics, following the correct surgical protocol, and maintaining good gingival health. However, when we discuss the prosthesis, we must consider the material used, especially in large rehabilitations, and specifically in so-called full-arch cases. Here, we enter a complex area where consensus is neither unanimous nor even majority. Hard materials, soft materials, ceramics, composites, metals, resins, polymers… a very wide and varied range of options, each with advantages and disadvantages. Every patient has their ideal restorative material. A brief history: The use of gold and/or gold alloys in the early days of implantology is well known, as well as the introduction of resins and composites on occlusal surfaces and aesthetic fronts in the 1980s.1 The evolution toward non-noble metals occurred due to the high cost – not expensive – of gold and/or gold alloys, along with the introduction of feldspathic ceramics to replace resins and composites that were not adequate for functional and aesthetic needs. This was several years ago.2–4 Do we remember the large metalceramic rehabilitations (noble or non-noble metal with feldspathic ceramic coverage)? If it was monomaxillary, especially in the upper arch, it was relatively straightforward. But what if it was bimaxillary? Then things got complicated. Metal-ceramic in both arches? Metalceramic upper and resin lower? Resin in both arches? Aesthetics? Function? Both? Nowadays, everything has changed significantly. With the widespread adoption of digital dentistry (digital restorative dentistry), what is being done? Large rehabilitations in monolithic zirconia or, to a lesser extent, with feldspathic ceramic layering in aesthetic areas. We can debate the aesthetic aspect, which will depend on opinion. Some may argue that good aesthetics can be achieved, while others might consider it “mediocre.” Some may prefer it to what can be achieved with high-quality ceramic or composites. However, one aspect that is rarely discussed is the importance of the impact between the upper and lower arch when the patient occludes. Do we remember when the ceramic coverage in bimaxillary metal-ceramic rehabilitations used to break? Why did it happen? Why did many professionals prefer metal-ceramic in the upper arch and a resin (classic hybrid prosthesis) rehabilitation in the lower arch? Regardless of the difficulty in achieving good ceramic coverage and the possible alteration of metal properties during ceramic firings, there was – and still is – impact between the arches that negatively affects the prosthesis and implants in the short, medium, and long term. Let’s talk a bit about physics (physics for beginners): KINETIC ENERGY. Kinetic energy can be defined as “the energy associated with objects in motion,” “the energy an object has due to its movement.” Its formula is: Where: X Ek is the kinetic energy X m is the mass (weight of the jaw, implants, and prosthesis) X V is the velocity (speed of the moving body: jaw, implants, prosthesis) Two questions we must ask: 1. The speed of mandibular closure 2. The mass (weight) of the prosthesis (antagonist) For the first question, we can refer to the literature5,6,7, which reports that mandibular closure speed ranges from 0.05 to 0.18 m/s. Each patient has their own closure speed. This speed will not change depending on the weight of the prosthesis over implants but may vary throughout the patient’s life. For the prosthesis weight, we must consider the density of the restorative material(s). Depending on whether the prosthesis is made of a single material (e.g., Figure 1: Different photos of metal-ceramic implant rehabilitations with multiple fractures
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