Abstract
The present study assessed the retention forces corresponding to different telescopic systems used in removable prosthetic dentures. The telescopic systems were represented by Co–Cr alloy or zirconia-based primary crowns and Co–Cr secondary crowns. All crowns were manufactured using computer-aided design/computer-aided manufacturing technology (CAD/CAM). Two types of reference abutment teeth (upper canine and first upper molar) were selected in order to obtain the telescopic crowns and two taper angles—of 0° and 2°—were used for the design of the crowns. A number of 120 samples of telescopic crowns were obtained and subjected to mechanical tests, following a specific protocol, on a mechanical testing equipment. The retention of the telescopic systems was evaluated for different sets of cycles (up to 360), represented by movements that simulate the intraoral insertion and disinsertion of the telescopic systems. The present study highlights that the telescopic systems in which the primary crown is made of zirconia ceramics presents more advantages than those made of Co–Cr. All telescopic systems studied, highlighted that by modifying the taper angle from 0° to 2°, the retention forces have decreased, irrespective of the materials used for the fabrication of the primary crown, suggesting that by using a taper angle of 0°, which is known to be ideal, more efficient, and reliable prosthesis can be developed. Thus, even though the ceramic–metallic telescopic system exhibited the highest retention, all telescopic crowns evaluated registered values between 2–7 N, indicating that they are suitable for clinical use.
Highlights
Telescopic systems are used to retain removable dentures that are usually recommended for patients with few residual teeth—or who have lost their teeth due to periodontal disease, to patientsMaterials 2020, 13, 4814; doi:10.3390/ma13214814 www.mdpi.com/journal/materialsMaterials 2020, 13, 4814 who have undergone surgical treatment, or in cases of occlusal vertical dimension reduction caused by the pathological wear of the teeth [1,2,3]
The classic telescopic system is made of two separate elements, consisting of the primary crown—permanently cemented on the prepared abutment tooth—and the secondary crown—that is placed on the mucosal aspect of a removable prosthetic denture [6,7,8,9,10,11,12]
It can be said that zirconia primary crown telescopes presented more advantages, compared to Co–Cr alloyin primary crowns, especially terms of the retention forcestoevolution, but
Summary
Telescopic systems are used to retain removable dentures that are usually recommended for patients with few residual teeth—or who have lost their teeth due to periodontal disease, to patientsMaterials 2020, 13, 4814; doi:10.3390/ma13214814 www.mdpi.com/journal/materialsMaterials 2020, 13, 4814 who have undergone surgical treatment (i.e., for craniofacial malignant tumors), or in cases of occlusal vertical dimension reduction caused by the pathological wear of the teeth [1,2,3]. The materials used for crowns manufacturing are gold, titanium, titanium alloys, cobalt–chromium alloys, zirconium-based ceramics, and polymers (especially in the case of three-element systems [14,15,16,17,18,19,20,21,22,23,24,25]). These are materials with different friction coefficients and hardness [26,27,28]. The components of a telescopic crown can be made of the same material or of different ones, which leads to the formation of friction nodes with different tribological features [29]
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