Surface Roughness, Hardness and FTIR of the Modified Soft Liner with Different Metal Oxide Nanoparticles

Aims: To study the effect of metal oxide nanoparticles (MgO, ZrO2, ZnO) on acrylic based soft liner surface properties and FTIR. Materials and Methods: Acrylic-based soft-liner specimens were prepared by adding three different concentrations (0.5, 1


INTRODUCTION
Tissue side alteration was carried out to ensure the fitness of denture after a period of service due to changing in ridge form can be obtained by replacing an existent inner surface of the denture by relining (1) .
The soft liner was used for relining to improve the denture wearers' comfort and improve prosthodontic treatment. The acrylic-based soft liner is a mixture of methyl methacrylate and 30% to 60% plasticizer that mainly responsible for softness and corrupted liner properties (2) .
Long term uses of soft liners may lead to fungal colonization by Candida albicans that enhanced by the presence of saliva and serum pellicles (3) .
Drawbacks of the relining materials are mainly the lack of a durable bond to the denture base. The liners detachment from the denture base is a common clinical occurrence (4) .
The acrylic-based soft lining seems to be more prone to degradation, where plasticizer loss appears to be due to osmotic gradients, oil solubility (5) .
Discolouration of denture base relining materials is observed after longterm use by accumulation of stain, absorption of water, dissolution of ingredients, microorganism and intrinsic pigments degradation (6) The addition of silver NPs with different concentration to soft-liner increases the shore A hardness value as the nanoparticles increased, (7) while, the addition of TiO2 nanoparticles to liner displayed hardness values lower than the acceptable range (8) .
Soft liner with silver nanoparticle shows high water absorption and solubility in contrast to low-level concentration of silver. (9) The addition of silver NPs (0.5, 1, 2, and 3 wt %) and thermocycling of siliconbased soft liner reduces the tensile strength to denture acrylic resin (10) .

The addition of silver NPs and ZrO 2
NPs to the soft liner with different concentration shows a significant increase in light absorption and decreased translucency (11,12) .
Fungal colonization on soft liner surface (initial adherence) is influenced by surface roughness, in which rough surface more prone to microorganisms' colonization (13) . The surface roughness was measured by a profilometer (14) .

The interest in Magnesium oxide
NPs was increased for biomedical applications (such as implants, bone surgery, antimicrobial agents, etc.) due to their biodegradable, nontoxic (15) Zinc oxide (ZnO) is listed as safe by the U.S. Food and Drug Administration that used for a long time as cosmetic or pharmaceutical ointments (16) .
ZrO2 nanomaterials are non-toxic, biocompatible and bioinert so is widely used in medical and orthopaedic applications, mainly replacement of damaged parts of the human skeleton, bones, and teeth (17) .  (18,19) .
Soft liner dough was packed and cured in prepared stone mold (with specific dimension for each test) in the water bath for 90 min at 70Cº and 30 min at 100 Cº (according to manufacturer instruction).  (20) .
Prepared specimens were stored in distilled water at 37ºC for 24 hours before the testing procedure performed (21) .  (22) .

Surface roughness:
Soft liner with nanoparticles samples were prepared by investing elastic foil with 10 mm × 10 mm × 2 mm dimension in dental stone (23) . Then the samples were removed from the mold after water bath polymerization. Samples were left intact without smoothing and polishing to represent the surface texture of the denture tissue site, the samples were stored in distilled water for 24 hours at 37Cº (24) .
A profilometer (Talysurf , Taylor Hobson, UK) was used to measure the surface roughness with 0.25µm Dimond stylus head at 0.5mm/s speed and cut off length 2.5 mm.. The stylus of the device that travels over the whole surface of the measurement of the specimen was recorded (25) .

FTIR analysis:
The

RESULTS AND DISCUSION
Surface hardness: