Effect of Beverage Solutions on Flexural Strength of PEEK CAD –CAM, 3D Printing Denture Base and Heat Cure Acrylic Resin Denture Base Materials

This research was to evaluate the effect of distilled water (D


Introduction :
Denture base material must come into touch with a variety of foods and beverages, making them susceptible to changes in physical structure and appearance as a result of the absorption process (1) .Poly methyl methacrylate (PMMA) resin material has been the "gold standard" for manufacturing traditional complete dentures because of its low cost, ease of handling and manipulation, good physical and mechanical properties and appropriate esthetic appearance (2) .With the advancement of digital technology, novel CAD-CAM-based procedures for material processing in dentistry, such as subtractive milling (SM) and additive manufacturing (AM), have emerged (3) .One advantage of fabricating denture bases digitally is the ability to create dentures in less time and with fewer processing steps, digital methods were also developed to address possible processing issues that may arise when the standard conventional procedure is used (4)   .Additive 3D printing has several benefits over subtractive milling, including the ability to create intricate forms, being less expensive due to less material waste, and not exhibiting rotary burr wear (5) .PMMA is known to have several limitations when used as the main material for dentures, most notably in terms of mechanical properties.PEEK was developed to overcome the constraints of PMM (6) .PEEK has good mechanical properties as well as biocompatibility (7) .But, PEEK is expensive material.Flexural strength (FS) is an important factor in determining a material's mechanical stiffness and strength (8) .(FS) is required for the rehabilitation of patients with longterm edentulous conditions, lengthy treatment times, or para -functional habits (9)   .
PEEK Samples Processing: Samples of PEEK had been digitally designed using CAD software ( halot sky, korea), then kept in (STL) file, and then transferred to exocad dental CAD/CAM (MAXX milling machine, dry-milling , 5 axes, korea), for milling PEEK blank (Dental Direk, Germany) according to the manufacturer's instructions.

3D Printing Samples Processing:
The same STL file format of PEEK CAD-CAM utilized for 3D printing sample.The (STL) file was sent to 3D printing machine (3D printing Asiga Max Machine, Australia), the 3D printing (Mack 4D Denture, Germany ) had been utilized for fabricated samples printed in 385 nm wavelength according to manufacturer's instructions, with direct light processing (DLP).A50-micrometer layer thickness was chosen for printing the samples, at 0 angle orientation with supporting structures (2) .Then the printed samples were cleaned 2x 3 min in with isopropyl alcohol (99.9%) (essentq, spain) in ultrasonic Bath (acuretta, Taiwan), to remove the excess resin.After complete drying, the specimens were polymerized in post polymerized unite (UV pre pro post curing machine ,Taiwan) for 18 min at 405 wave length.
Heat Cure Acrylic Resin samples processing: Specimens prepared using a compression mold method that mimicked laboratory procedures for denture base fabrication.Wax specimens were prepared with specified dimensions, then wax specimens were embedded in type IV dental stone (Elite®, Italy) in metallic flasks (Ash, England).The de-waxing procedure is then performed (10) .Acrylic (Veracril®/Opti-Cryl®, New Stetic S.A.) that had been heat polymerized was used.It was combined in a volumetric ratio of 3:1 with methyl methacrylate (MMA) monomer.According to the product's instructions, the mixture should be allowed to stand for 10 minutes before passing the plastic stage.It was then deposited in mechanical pressing molds to make test examples.The molds were pressed to 2000 Psi pressure in a laboratory hydraulic press for 5 minutes before being transferred to a thermal reservoir and subjected to a 90-minute heating curve at 73°C, after that a curve of 95°C was used for thirty minutes.Finally, the molds were removed from the reservoir and left outdoors for cooling (11) .All examples had one surface that was finished and polished to appered like a polishing surface and the other like a tissue surfaces (12) .The specimens had been fined by employing silicon carbide polishing (paper water proof, Greece) with a universal polishing equipment (universal polisher, Spectrographic Ltd.Metaserv, England)with running water.Polishing was accomplished with a muslin linen brush accompanied with polishing paste (Universal polishing paste, Ivoclar vivadent, Germany), and polishing machine (13,14) , and all samples were then had been kept in distilled water at 37 degrees Celsius for 24 hours in accordance with ISO 20795-1:2013.
Flexural Strength Tester:The three-point loading with Universal testing Machine (Gester Total Test Solution Machine, china), was used for this test.Test machine setup was according to the ISO (20795-1:2013) specifications, where the machine has a center loading plunger and two supports with 3.2mm diameter polish cylindrical surfaces and a 50mm gap area between them.The support is perpendicular to the center line and parallel to each other.The loading plunger is located in the center of the two supports.The impact speed used was 5mm/min.The measurement was performed at a constant speed of 5 millimeters per minute (15) .The specimen was displaced as the force on the loading plunger was gradually increased from zero until fracture occurred, and the fracture load was recorded in Neutin Unite.The following equation was used to determine the flexural strength in Mega Pascal (16) .σ = 3FL/2bh 2 F: Maximum load before fracture (neutin ).L: Distance between the supports (mm).b: Width of the specimen (mm).h: Height of the specimen (mm).

Beverage media preparations:
Cola ready-made (Coke®, Iraq), D.W. readymade (Iraq), 2 g of coffee (Mahmood® CoffeeClassic Brazilian, Turkey) and tea (Cihan Tea, Sirilanka) dissolved in 200 milliliter of distilled boiling water for 2 min (12) .The coffee and tea solutions were then stirred for 10 minutes until the temperature approached 37°C, and then filtered to eliminate any particulate residues (17) .The pH of the solutions was calculated using a pH meter (eco test PH2, China) to assess the PH value of solutions media ( Distilled Water 7, Tea 4.8, Coffee 4.2, Cola 2.3).
Immersion Periods Protocol: According to (Guler et al ,. 2005) (18) , the average time spent consuming one cup of a drink is 15 minutes, while the average coffee consumption among coffee drinkers is 3.2 cups per day.As a consequence, keeping the drink for 24 hours was equivalent to drinking it over the course of a month.Six days simulate the beverage's use over a six-month span (12) .12 days of liquid consumption over the course of a year (19) .Drinking beverages for 24 days encourages over two years (20) .Each experimental specimen was suspended and immersed in the solutions by threads, ensuring that it did not come into contact with the container or other specimens, and at the end, a label indicating that the specimen's codes were present.All containers were labeled with the type of solution and kept in (37°C) incubator (INB EN, JRAD, Syria), to simulate the oral environment, which was refreshed daily (12)   .

Results:
PEEK Denture Base: The results for the effect of beverage media on the flexural strength of PEEK denture base, mean and standard deviation Table (1) explained that the flexural strength was impacted by all beverage solutions when compared to the control group, the most decreasing in flexural strength of PEEK denture base was there in 24 immersion days in cola (252.0960MPa ± 5.19825) followed by coffee (253.4360MPa ± 6.60975) followed by tea (253.7780MPa ± 6.44697) followed by distilled water (254.1420MPa ± 7.41318) as comparing with control(260.2420MPa± 5.08412).
One-way analysis of variance (ANOVA) Table (2) revealed that there is no statistically significant difference in the impact of all beverage solutions on the flexural strength of PEEK denture base (at p ≤ 0.05).

Flexural Strength of 3D Printing
Denture Base: The resulting for the effect of beverage media on the flexural strength of 3D Printing Denture Base, mean and standard deviation Table (3) interpreted that flexural strength declined in all beverage solutions, the most decreasing in flexural strength of 3D printing denture base was gained in 24 immersion days in cola (103.1680MPa ±12.26532) followed by coffee (105.4360MPa ±12.36951) followed by tea (107.4530MPa±11.47399) followed by distilled water (109.1320MPa±11.66156) as comparing with control(119.7140MPa ± 12.25421).One-way analysis of variance (ANOVA) Table ( 4) displayed there was no significant difference in the impact of beverage solutions on flexural strength of 3D Printing denture base (at p ≤ 0.05).

Flexural Strength of Heat Cure Acrylic
Denture Base: The research resulting for the effect of beverage solutions on flexural strength of heat cure acrylic denture base, mean and standard deviation Table (5)  expressed that the flexural strength was decreased by all of beverage solutions the most decreasing in flexural strength of heat cure acrylic resin denture base was obtained in 24 immersion days in cola (118.5640MPa±13.06764) followed by coffee (122.3640MPa± 9.78213) followed by tea(123.5600MPa±14.05144) followed by distilled water (126.3620MPa ± 11.35254) as comparing with control (134.6420MPa ± 9.79330).One-way analysis of variance (ANOVA) Table (6) presented that there was no significant difference for the effect of beverage solutions on the flexural strength of heat cure acrylic denture base (at p ≤ 0.05).

Discussion:
High level of flexural strength is very important due to the uneven force distribution the base will withstand as the alveolar ridge irregularly resorbs.Therefore, it should be capable to challenge plastic deformation and fatigue resistance under repeated loads (21) .PEEK Denture Base: Findings supported by the fact that Polymer networks absorb water, which could result in mechanical weakness due to microstructural changes that affect the mechanical characteristics of the polymer polymers (22) .The effect of beverage solutions on PEEK flexural strength could be described as PEEK having pH-sensitive chemical linkages that degrade when pH changes (23) .The slight decrease in PEEK flexural strength in distal water compared to other beverages media could be ascribed to the fact that water containing weak electrolytes (24) .The research results in agreement with Fathy et al .(2021) (23) who noticed that the flexural strength of the PEEK polymer was impacted by aging it in various pH aqueous media.
Non-significant difference effect of all beverage media on flexural strength of PEEK denture base, the results showed that PEEK samples had no significant fluid sorption or solubility in storage conditions, which has little impact on its mechanical properties (25,26) .

3D Printing Denture Base:
The results interpreted that flexural strength was affected in all beverage media in comparing with control group, the lesser value scored in cola.The research results are in agreement with Alzaid et al .(2022) (10) ; Gad MM et al .(2022) (27) .Water aging of polymer materials can cause plasticization and deterioration of mechanical properties owing to polymer chain damage.(e.g., cleavage of ester bonds) (28) .Moreover, the results could be explaining by the rising water sorption may be ascribed to the printed layering technology used to create 3D-printed resins.The absorbed water enters between the layers and is diffused into the polymer of the resin, filling inter polymeric gaps with water and driving the polymer chain away from adjacent chains.This phenomenon may have a negative effect on the layering interface, causing resin swelling and separation of the printed layers, negatively affecting mechanical properties (29) .In addition might be due to residual monomer release could be higher under conditions linked with acidic media as opposed to neutral media, leading to reducing the flexural strength of acrylic resin (30) .The little reducing in 3D printing flexural strength in distilled water compared to other beverages media could be attributed to the fact that water lacks active ingredients capable of dissolving the polymer (24) .PH influenced the water sorption and solubility behavior of dental resin materials, resulting in a decrease in flexural strength (31) .Non-significant difference for effect of beverage media on the flexural strength of 3D Printing denture base, the results could be linked to reason that Polymer chemistry, PH, and polarity of the liquid media in which the polymers are soaked, as well as immersion duration, are all variables that can affect polymer solubility and induce embrittlement (32) .
Heat Cure Acrylic Denture Base: The research interpreted that the flexural strength was impacted by all of beverage media in comparing with control group, agreed with Jagini et al .(2019) (33) ; Gad MM et al .(2022) (27) .This is prone to water sorption effects because water can function as a plasticizer, compromising mechanical and flexural strength (3) .Furthermore different PH level aging medium ended in negatively affect the resin material mechanical properties because of absorption of media active particles that could result in plasticization of the resin and embrittlement of the macromolecular skeleton through hydrolysis and osmotic cracking (23,34) .In addition the DW is devoid of active particles leading to lesser decreasing in heat cure acrylic flexural strength (24) .The results in agreement with Fathy et al. (2021) (23) who obesrved that aging the heat cure acrylic resins in different levels of pH aqueous media had been deteriorated the flexural strength of heat cure acrylic resin.Non-significant difference for effect of beverage media on flexural strength of heat cure acrylic denture base, the result could be related to fact that polymeric materials which had been immersed in the strength of liquid media decreased over time, and the time required by different polymers to achieve their "equilibrium strength" varied.The balance strength may be greater or less than the as-fabricated strength.This was followed by an explanation of the impact of short and long term, as well as their environment, on the properties of dental polymer (35) .

Conclusion:
All beverage solutions non significantly affected the flexural strength of all tested materials.The highest reduction was in cola then coffee then tea then the least reduction was in distilled water and the reduction increased as immersion time increased.The high flexural strength was there in PEEK but, highly cost then heat cure acrylic resin then3Dprinting.

Table ( 1
): Mean and standard for the effect of beverage media on the flexural strength of the PEEK denture base

Table ( 5
): Mean and standard deviation for the effect of beverage media on the flexural strength of heat cure acrylic denture base

Table ( 6
): One-way analysis of variance (ANOVA) for the effect of beverage media on the flexural strength of heat cure acrylic denture base