## 1 Introduction  
Histological studies of hard-tissue specimens, such as bone and teeth, are mainly performed by embedding the samples in different media--paraffin or various resin-based materials [1; 2; 3; 4]. Traditional paraffin embedding requires the decalcification of the samples before their processing. This can be achieved using different acids (inorganic and organic) or chelating agents. Some researchers have suggested that strong inorganic acids provide rapid decalcification but could cause serious tissue damage and/or impair the staining results [5; 6; 7; 8]. Conversely, weak organic acids and chelating agents, such as ethylenediaminetetraacetic acid (EDTA), are not that aggressive to tissues and preserve their integrity. Their utilization, however, takes considerable time; e.g., EDTA decalcification could take weeks or months, even for small sample sizes [7; 8]. Recently, some combined solutions (mixtures of weak and strong acids) have been used to overcome difficulties with decalcifying hard tissues. They provide rapid decalcification (for about 6 h) without causing damage to the tissue microarchitecture [9; 10; 11]. A major limitation of paraffin embedding compared to plastic embedding is that it requires the decalcification of the specimens. Furthermore, paraffin-based media are not appropriate for embedding specimens that contain implants made of very hard materials, such as metals, ceramics, and polymers [12]. On the other hand, plastic embedding preserves the bone integrity necessary for static and dynamic histomorphometry. The method allows for the evaluation of samples that contain implants, as well as for immunohistochemical and biomechanical analyses, which are essential for some diagnostic purposes [13]. As an alternative to paraffin histology, plastic embedding has been successfully applied to the evaluation of hard tissues. It provides structural integrity and stabilization, which are necessary to perform static and dynamic histomorphometry, and also allows for immunohistochemistry [8; 12; 13; 14; 15]. The observation of both mineralized bone and unmineralized osteoid, along with their well-preserved cellular components, provides essential information about bone formation and resorption [16]. A major advantage of resin-based embedding is that it allows for the evaluation of the bone-implant interface in undecalcified sections [17; 18; 19]. Although plastic embedding does not require decalcification, it has some other disadvantages. The embedding process is multi-stage and time-consuming and involves working with dangerous and expensive reagents. In addition, the method is laborious and poses an increased risk of errors. In some cases, the complete removal of the resin is difficult, which further hinders the staining process [20; 21; 22]. Moreover, plastic embedding is incompatible with some staining techniques and can be more challenging and demanding. Paraffin and plastic embedding have different processing and sectioning protocols. Plastic embedding does not require decalcification, and clearing is not always necessary. In addition, there are different sectioning techniques for plastic-embedded samples. The most common resin-embedding media are the following: glycol methacrylate, methyl methacrylate (MMA), and epoxy resins. When selecting an embedding medium, the hardness of the tissues must be considered. If there is a mismatch between them, this could lead to a separation between soft- and hard-tissue structures and fractures [1; 2]. Plastic-based embedding medium is harder and more elastic than paraffin medium, which facilitates the sectioning of hard slices. The sectioning of plastic-embedded samples can be performed using microtones with special knives or via the sawing-grinding technique. The first method allows us to obtain slices with a thickness of 10 \(\upmu\)m. When sawing and grinding, the samples are cut into thicker slices with precise saw blades and then ground and polished [23; 24; 25]. Rabbit models have been commonly used for in vivo studies of the musculoskeletal system.