Wear of various restorative materials against 5Y-ZP zirconia.

STATEMENT OF PROBLEM: The ceramic 5-mol% yttria-stabilized zirconia (5Y-ZP) has been developed for dental use in the esthetic zone with greater translucency than 3-mol% yttria-stabilized zirconia (3Y-ZP). However, studies on the wear behavior of 5Y-ZP zirconia against clinically relevant antagonist materials are lacking. PURPOSE: The purpose of this in vitro study was to investigate the wear behavior of 5Y-ZP zirconia against the antagonists 5Y-ZP zirconia, lithium disilicate, palladium alloy, and human enamel. MATERIALS AND METHODS: Flat specimens (n=8) were fabricated from 5Y-ZP zirconia, lithium disilicate, palladium alloy, and human central incisor enamel. A custom wear-simulating device with a sliding pin-on-plate configuration was used for a total of 120 000 wear cycles at 1.6-Hz frequency under a 49-N vertical load while submerged in distilled water at room temperature. The wear volume and maximum wear depth of flat specimens were evaluated with a 3D profilometer. Scanning electron microscopy was used to analyze the characteristics of the worn surfaces. RESULTS: After wear simulation, the 5Y-ZP zirconia and palladium-silver alloy specimens exhibited the least amount of material loss, both in terms of maximum wear depth and wear volume (0.079 ±0.042 µm, 0.001 ±0.001 mm3 and 0.637 ±0.307 µm, 0.001 ±0.000 mm3, respectively). This was followed by human enamel (6.034 ±1.086 µm, 0.009 ±0.001 mm3) and by lithium disilicate, which showed excessive material loss (38.342 ±2.569 µm, 0.213 ±0.024 mm3). Scanning electron microscopy revealed variations in wear mechanisms among the materials. CONCLUSIONS: The 5Y-ZP zirconia and palladium-silver alloy exhibited the lowest wear, followed by human enamel and lithium disilicate. Slight grain dislodgement was displayed on worn 5Y-ZP surfaces, while more apparent grain dislodgement and wear grooves were found on lithium disilicate. Plastic deformation of worn palladium-silver alloy accumulated at the end of wear track. Cracks were detected in the human enamel specimens.

Effect of Number and Location on Stress Distribution of Mini Dental Implant-Assisted Mandibular Kennedy Class I Removable Partial Denture: Three-Dimensional Finite Element Analysis.

Purpose: To investigate effects of number and location on patterns of von Mises stress distribution and volume average stress on abutment tooth, edentulous ridge, mini dental implant, and surrounding bone of mini dental implant-assisted mandibular Kennedy class I removable partial denture. Materials and Methods: Eight three-dimensional finite element models of mandibular Kennedy class I with different numbers and locations of mini dental implants were constructed. Mini dental implants were generated in the area of second premolar, first molar, and second molar, respectively. A static load of 400 N was applied on all models. The von Mises stress and volumetric average stress were calculated by three-dimensional finite element analysis. Result: The minimum volumetric average stress of abutment tooth was found in the model, where there was one mini dental implant at the second molar position and 2 mini dental implants at first molar and second molar positions. The model with three mini dental implants had reduced volumetric average stress of abutment tooth, which was not different from the model with two mini dental implants. However, the minimum volumetric average stress of mini dental implant and surrounding bone were found when three mini dental implants were applied, followed by two and one mini dental implants, respectively. Conclusion: Placing at least one mini dental implant at a second molar position can help reduce stress transferred to the abutment tooth. Stresses around each implant and surrounding bone reduced with increased numbers of mini dental implants.

Wear Behavior of Different Generations of Zirconia: Present Literature.

Objective: The wear behavior of the novel zirconia generation is less well understood and may be affected by compositional modifications compared to the conventional zirconia. Materials and Methods: Combinations of keywords such as "zirconia," "high translucent," and "wear" were searched in PubMed and Google Scholar databases up to May 2021. The total of 23 relevant articles was selected according to inclusion criteria. Results: Reports show comparable wear resistance of translucent zirconia to the conventional zirconia despite an increased cubic phase content and lower mean flexural strength. A meticulously polished surface creates the lowest surface roughness, producing favorable zirconia wear resistance and antagonist wear compared to a glazed surface. In comparison to other ceramic materials, zirconia produces the least wear on an enamel antagonist and almost undetectable wear when opposed by zirconia. Wear when paired against resin materials yields a favorable outcome, whereas wear behavior against a metal antagonist varies with the surface hardness of the metal. Conclusions: All zirconia generations are considered wear-friendly to all types of antagonists. Nonetheless, comparative studies on antagonist wear opposing zirconia of different compositions are still limited and further investigation is required.