Influence of incorporation of ZrO2nanoparticles on the repair strength of polymethyl methacrylate denture bases.
BACKGROUND
Repeated fracture of the denture base is a common problem in prosthodontics, and it represents a nuisance and a time sink for the clinician. Therefore, the possibility of increasing repair strength using new reinforcement materials is of great interest to prosthodontists.


OBJECTIVE
This study aimed to evaluate the effects of incorporation of zirconia nanoparticles (nano-ZrO2) on the flexural strength and impact strength of repaired polymethyl methacrylate (PMMA) denture bases.


METHODS
One hundred eighty specimens of heat-polymerized acrylic resin were fabricated (90 for each test) and divided into three main groups: one control group (intact specimens) and two groups divided according to surface design (45° bevels and butt joints), in which specimens were prepared in pairs to create 2.5 mm gaps. Nano-ZrO2was added to repair resin in 2.5 wt%, 5 wt%, and 7.5 wt% concentrations of acrylic powder. A three-point bending test was used to measure flexural strength, and a Charpy-type test was used to measure impact strength. Scanning electron microscopy was used to analyze the fracture surfaces and nano-ZrO2distribution. The results were analyzed with a paired samplet-test and an unpairedt-test, with aP-value of ≤0.05 being significant.


RESULTS
Incorporation of nano-ZrO2into the repair resin significantly increased flexural strength (P<0.05). The highest value was found in the bevel group reinforced with 7.5% nano-ZrO2, whereas the lowest value was found in the butt group reinforced with 2.5% nano-ZrO2. The impact strength values of all repaired groups were significantly lower than those of the control group (P<0.05). Among repaired groups, the higher impact strength value was seen in the butt group reinforced with 2.5% nano-ZrO2. The bevel joint demonstrated mainly cohesive failure, whereas the butt joint demonstrated mainly adhesive failure.


CONCLUSIONS
Incorporation of nano-ZrO2into the repair resin improved the flexural strength of repaired denture bases, whereas it decreased impact strength, especially with high nano-ZrO2concentrations.
Department of Substitutive Dental Sciences.
Mohammed M
MM
Gad
Department of Restorative Dental Sciences, College of Dentistry, University of Dammam, Dammam, Saudi Arabia; Department of Dental Materials, College of Dentistry, Al-Azhar University, Assiut, Egypt.
Ahmed
A
Rahoma
Department of Substitutive Dental Sciences.
Ahmad M
AM
Al-Thobity
Department of Prosthetic Dental Sciences, College of Dentistry, King Saud University, Riyadh, Saudi Arabia.
Aws S
AS
ArRejaie
D000180:Acrylic Resins / Q000737:chemistry; D003764:Dental Materials / Q000737:chemistry*; D003819:Denture Bases; D003780:Denture Repair; D006801:Humans; D008422:Materials Testing; D053758:Nanoparticles / Q000008:administration & dosage* / Q000737:chemistry; D058105:Polymerization; D019904:Polymethyl Methacrylate / Q000737:chemistry*; D013314:Stress, Mechanical; D013499:Surface Properties; D015040:Zirconium / Q000008:administration & dosage / Q000737:chemistry*
D000180:Acrylic Resins; D003764:Dental Materials; D019904:Polymethyl Methacrylate; D015040:Zirconium; C028541:zirconium oxide
PMMA; ZrO2 nanoparticles; denture repair; flexural strength; impact strength