The Effect of Zirconium Oxide Nanoparticle on the Tear Strength of Maxillofacial Silicone

فادهلأا : دهت ةساردلا ف  ( ةفلتخملا زيكارتلا ريثأت نم ققحتلا ىلإ ٠.٥  ، ٪ ١  ، ٪ ١.٥  ، ٪ ٢  ةةيونانلا موينوكرزلا ديسكأ تائيزج نم )نزولاب ٪ ةفرغلا ةرارح ةجردب نكربملا نيكفلاو هجولل نوكيليسلا ةدام قزمت ةمواقم ىلع . لمعلا قرطو داوملا ( هعومجم ام ريضحت مت : ٥٠ )  عابتاب ةنيع صتلا تاميلعت ن( تاةعومجم مةمم ىةلإ تمسقو عين ١٠ تاةعومجملا اةما ، ةةيونانلا تاميةسجلا نودةب )ة باةضلا ةةعومجملا( أ ةةعومجملا .) ( ةةعومجملا مةم ةةيونانلا موةينوكرزلا ديةسكا عةم ةةيبيرجتلا ٠.٥  ( ةةعومجملا ,)٪ ١  ملا ,)٪ ( د ةةعومج ١.٥  ( ةةم ةةعومجملا و )٪ ٢  )٪ انيع. رابتما ةلآ ة ساوب اهسايق مت زمتلا ةمواقم ت  ةلماش .  جئاتنلا ةةعومجملا ترةهلأ .تاةعومجملل ة ةسوتملا ميةقلا نيةب رةيبك قرةف كانم ناك : ( ة باضلا ٢١.٩١  ةعومجم نم لك عم يونعم ريغ اًقرف )مم / نتوين ٠.٥  ( ٪ ٢٢ .٤٦  ومجم و )مم / نتوين ةع ٢  ( ٪ ٢٣.٢٢ نكلو ،)مم / نتوين امًهم اًقرف  تاعومجملا عم ةياغلل ١  ( ٪ ٢٥.٣٧ )مم / نتوين  و ١.٥  ( ٪ ٢٧.٤٤ ةعومجم ترهلأ امنيب . )مم / نتوين ٠.٥  ٪ ZrO2 ًاةيونعم ًاةقرف نيتعومجملا اتلك عم ( ١  ، ٪ ١.٥  ٪ ZrO2) عةم يوةنعم قرةف كانم نكي مل نكلو ٢ ٪ ZrO2. ةةعومجم ترةهلأ ١ ٪ ZrO2 عةم ًاةيونعم ًاةقرف ةعومجم ١.٥ ٪ ZrO2 م قرفو ع يونع ةعومجم عم ملا ٢  ٪ ZrO2. ةعومجملا نكل ١.٥ ٪ ZrO2 ةعومجملا عم ريبك قرف اهل ٢ ٪ ZrO2.  تئجئتنتسلاا  ةيونانلا تاميسجلا جمد : ZrO2 تازيكرتب ١  ، ٪ ١.٥  ةةجرد مةف نكربملا نوكيليسلا ةدامل قزمتلا ةوق نيسحت ىلإ ىدأ نزولاب ٪ ةفرغلا ةرارح .  ABSTRACT Aims: The study aimed to investigate the outcome of different concentrations (0.5%, 1%, 1.5%, 2% by weight ) of zirconium oxide (ZrO2) nanoparticle on tear strength of room temperature vulcanized maxillofacial silicone material. Materials and methods: A total of (50) samples were prepared following the manufacture instruction and divided into five groups (n=10). The group A (control group) without nanoparticle, group B (0.5% ZrO2), group C (1% ZrO2), group D (1.5% ZrO2), group E (2% ZrO2). The tear strength samples were measured by a universal testing machine. Result: there was a highly significant difference between the groups' mean values. The control group (21.91 N/mm) showed non-significant difference with both 0.5% ZrO2 group (22.46 N/mm) and 2% ZrO2 (23.22 N/mm), but a highly significant difference with groups 1% ZrO2 (25.37 N/mm) and 1.5% ZrO2 (27.44 N/mm). Whereas the 0.5% ZrO2 group showed a highly significant difference with both groups (1% and 1.5% ZrO2),but no significant difference with 2% ZrO2 group. 1% ZrO2 group showed a significant difference with 1.5% ZrO2 group and a highly significant difference with 2% ZrO2 group. But group 1.5 % ZrO2 has a highly significant difference with group 2% ZrO2. Conclusion: Incorporation of ZrO2 nanoparticle at 1% and 1.5% by weight enhanced the tear strength of the VST 50F RTV maxillofacial silicone material.


INTRODUCTION
The maxillofacial prosthesis is utilized for replacing the lost facial parts that have been missing since inherent anomalies, trauma, and tumors. Such a prosthesis's chief objective is the similar creation of lost details, thereby having patients with an ordinary appearance, psychological wellbeing, and social acceptance (1) .
Materials used to construct maxillofacial prosthesis must have particular ideal properties, such as good tensile strength, tear strength, flexibility, low water sorption, good color stability. Finally, it should be biocompatible (2) .
Several materials as wood, wax, metal, ivory, and polymers such as acrylic resins, polyurethane elastomers, and silicone elastomers have been used to construct facial prostheses (3).
Silicone is presented in 1960 till now; it's the most widely used materials in constructing facial prosthesis because of their easiness of handling, flexibility, texture similar to the skin, and biocompatibility (4) (5) . Nevertheless, the silicone material has some disadvantages due to its short lifetime, color instability, and silicone deterioration; for instance, it shows altered surface, ill-fitting boundaries due to insuffi- Incorporating nanoparticles into the material has become one of the main ways to improve material properties (7) . Nano-sized particles incorporated into the maxillofacial silicone elastomer to enhance its mechanical properties and viscosities as these particles achieve the mission of supporting the cross-linked polymer by dispersing into the matrix (8) Many types of nanoparticles have been added to silicone material and tested.
Such research has confirmed nanosized particle's usefulness in enhancing silicone elastomer's mechanical properties, especially the tear strength (5,8) .
The present study aims to assess the Then the Computer-controlled Laser cutting machine (Boye Laser Application Technology Co., Ltd, China) was used to cut spaces in the plastic mold into which the material will pour (10) .  (11) .
However, for the experimental groups (B, C, D, E), the nanoparticle was placed into a clean mixing bowl with a clean spatula and weighted by digital electrical balance, then mixed with preweighed base manually for 1min. Followed by mechanical mixing for 10 minutes, the first 3 minutes, the vacuum turned off to prevent nanopowder suction. Then for the remaining 7 minutes, the vacuum turned on to avoid bubbles of air (12) . before adding the (part B), the mixture was left to stand for approximately two minutes since the mechanical mixer's revolving movement produced heat, which may decrease the working time for the material (13) .
According to manufacturer instruction, the modified base was mixed with the cross-linker. The mixture returned to the multi vac 4; vacuum mixer to be mixed mechanically for 5 minutes with the vacuum turned on. To have an accurate result, the mixing of silicone material should be at a controlled temperature of (23±2°C) and relative humidity (RH) of (50±10%) (14) .
The silicone mixture was poured slowly inside the plastic molds' shaped spaces, and the holes should be overfilled with the mix (15) ; a few minutes were needed before placing the cover to allow entrapped air bubbles to reach the surface. Now the plastic mold cover gradually and slowly applied to stare from one end to the other one. Once the cover ultimately settled a moderate hand pressure was applied by one hand until the molds' parts were tightened by a screw and nuts in four corners, and the pressure was involved in four sides of the mold using the G clamps (china).
According to product information, silicone material was vulcanized at 2-3 hours at 23 ± 1 °C. in demolding, the sample should be carefully removed from the mold without any strain (16) then scalpel and blade 10# (Dr. Quillel Surgicals, Pakistan) were used for removing flashes surrounding the sample (17) .
A custom-made lightproof box was used for storing the samples in an airconditioned room until testing. The temperature was (10-30 °C), and RH did not exceed 80% (18) . Before testing, the samples were conditioned in controlled temperature and humidity, as mentioned above for 16 h at a minimum (18) . Tear strength   The data were statistically analyzed using a one-way ANOVA test and post hoc (Tukey HSD). A probability (P) value > 0.05 was considered statistically non-significant, while P ≤ 0.05 was considered statistically significant, and P ≤ 0.01 was considered highly significant.  .

DISCUSSION
Despite their extensive use, they are far away from ideal. Silicone maxillofacial prostheses need replacement due to deterioration in physical and mechanical properties; such problems take many researchers' interest to investigate maxillofacial silicone elastomers (19).
A tear-strength test indicates an elastomeric material's resistance to rupture when exposed to a tensile force acting upright to a surface flaw (20) . the most important property for maxillofacial prostheses is the tear strength, from a clinical point of view (2) .
A proliferation in the tear strength of silicone can encourage the high esthetic value of the facial prosthesis. It allows thinner boundaries, especially in the eye and nose prosthesis, are liable to tearing as the prosthesis is detached from the close facial tissue (21) .
To reach the amount of reinforcement necessary for good mechanical properties, nanoparticle addition is highly essential. The amount of improvement depends mostly on the quantity of filler loaded, filler characteristics (a specific surface area or particle size, surface activity, and structure), polymer properties, and processing conditions (22) .
The statistical results showed a highly significant increase (p < 0.01) in the mean val-  (23) .
Tear strength increase can also be clarified by the polymer's capability to disperse strain energy adjacent to the rising cracks' tip. As tearing extents, nanoparticles will distribute the energy inside the silicone matrix, creating it more unaffected by tearing. A more significant load will be required to entirely breakdown the polymer matrix (24) .
Tear strength test results in this study agree with Shakir and Abdul-Ameer (12)  with group E, this explained why the quantity of nano-oxide measured for addition in the silicone elastomer should be at a correct level, (8) since too little amount may not be enough for cause changes as for group (B) or in contrast even if the nano-oxide particles might support the silicone matrix but the addition in higher concentration as for group E result in agglomeration of nanoparticles within silicone matrix due to increased surface energy and chemical reactivity of these small-sized nanoparticles (25) resulting in the formation of agglomeration of nano oxides that would result in the tear strength reduction, by performing as stress concentration sites inside the silicone matrix (26).
while in contrast to others studies that did not agree with the finding for the present study, which verified that the addition of nanoparticle into RTV silicone elastomers results in a reduction in the tear strength such as wang et al. (27) who added TiO2 nanoparticle at a concentration of 6% to MDX4-4210 RTV maxillofacial silicone, They reported the reduction in the tear strength of silicone elastomers