Development of poly(methyl methacrylate)/poly(lactic acid) blend as sustainable biomaterial for dental applications.

Poly(lactic acid) (PLA) is gaining popularity in manufacturing due to environmental concerns. When comparing to poly(methyl methacrylate) (PMMA), PLA exhibits low melting and glass transition temperature (Tg). To enhance the properties of these polymers, a PMMA/PLA blend has been introduced. This study aimed to investigate the optimal ratio of PMMA/PLA blends for potential dental applications based on their mechanical properties, physical properties, and biocompatibility. The PMMA/PLA blends were manufactured by melting and mixing using twin screw extruder and prepared into thermoplastic polymer beads. The specimens of neat PMMA (M100), three different ratios of PMMA/PLA blends (M75, M50, and M25), and neat PLA (M0) were fabricated with injection molding technique. The neat polymers and polymer blends were investigated in terms of flexural properties, Tg, miscibility, residual monomer, water sorption, water solubility, degradation, and biocompatibility. The data was statistically analyzed. The results indicated that Tg of PMMA/PLA blends was increased with increasing PMMA content. PMMA/PLA blends were miscible in all composition ratios. The flexural properties of polymer blends were superior to those of neat PMMA and neat PLA. The biocompatibility was not different among different composition ratios. Additionally, the other parameters of PMMA/PLA blends were improved as the PMMA ratio decreased. Thus, the optimum ratio of PMMA/PLA blends have the potential to serve as novel sustainable biomaterial for extensive dental applications.

Thermal Change Affects Flexural and Thermal Properties of Fused Deposition Modeling Poly(Lactic Acid) and Compression Molding Poly(Methyl Methacrylate).

OBJECTIVE: Polylactic acid (PLA) is one of the most widely used materials in three-dimensional (3D) printing technology due to its multiple advantages such as biocompatibility and biodegradable. However, there is still a lack of study on 3D printing PLA for use as a denture base material. The goal of this study was to compare 3D printing PLA to traditional poly(methyl methacrylate) (PMMA) as a denture basis. MATERIALS AND METHODS: The PMMA (M) and PLA (L) specimens were fabricated by compression molding, and fuse deposition modeling technique, respectively. Each specimen group was divided into three different temperature groups of 25°C (25), 37°C (37), and 55°C (55). The glass transition temperature (Tg) of raw materials and specimen was investigated using differential scanning calorimetry. The heat deflection temperature (HDT) of each material was also observed. STATISTICAL ANALYSIS: The data of flexural strength and flexural modulus were analyzed with two-way analysis of variance, and Tukey honestly significant difference. The Tg and HDT data, on the other hand, were descriptively analyzed. RESULTS: The results showed that PLA had lower flexural strength than PMMA in all temperature conditions, while the PMMA 25°C (M25) and PMMA 37°C (M37) obtained the highest mean values. PLA 25°C (L25) and PLA 37°C (L37) had significant higher flexural modulus than the other groups. However, the flexural properties of L55 could not be observed, which may be explained by Tg and HDT of PLA. CONCLUSION: PLA only meets the flexural modulus requirement, although it was greater than flexural modulus of PMMA. On the other hand, PMMA can meet both good flexural strength and modulus requirement. However, increase in temperature could reduce flexural strength and flexural modulus of PMMA and PLA.

The Influence of Different Surface Cleansing Agents on Shear Bond Strength of Contaminated Lithium Disilicate Ceramic: An In Vitro Study.

MATERIALS AND METHODS: Seventy LDS specimens were randomly divided into seven groups. The first group was noncontaminated surface (PC). The six other groups were contaminated with the saliva and silicone disclosing medium and treated with no surface cleansing agent (NC); phosphoric acid (PO); Ivoclean (IV); sodium hydroxide solution (NA); Restorative Cleansing Agent (RC); and hydrofluoric acid (HF). Then, LDS specimens were cementated with Panavia V5 to resin composite rod. Each specimen was subjected to an SBS test. The modes of failure was inspected under light microscope. The surface element of each group was examined by SEM-EDS. RESULTS: The results were analyzed with one-way ANOVA and Tamhane's T2. The mean SBS value of NC was significantly lower than others (p < 0.05), and HF was significantly higher than others (p < 0.05). However, PC, PO, IV, NA, and RC were not significantly different from each other (p > 0.05). The mode of failure was mostly adhesive failure in every group. The surface showed similar amount of elements in every group. CONCLUSIONS: The SBS of LDS was reduced by saliva and silicone disclosing medium contamination which can be restored using acid- and alkaline-based surface cleansing agents before the cementation procedure.

Effect of different cleansing agents and adhesive resins on bond strength of contaminated zirconia.

PURPOSE: This study was observed the effect of cleansing agents and adhesive resins on shear bond strength (SBS), surface morphology and phase transformation of saliva and silicone disclosing medium contaminated zirconia. METHODS: The 110 zirconia specimens size 5×5×1mm were fabricated and randomly divided into 5 surface treated groups: Non-contaminated (PC) Saliva and silicone disclosing medium contaminated without cleansing (NC) Surface contaminated and cleansing with Phosphoric acid (PO) Ivoclean (IC) or Hydrofluoric acid (HF). The twenty of each surface treated specimens were selected and bonded with Panavia F2.0 (P) and Superbond C&B (S) for SBS test (n=10). The data was analyzed by Kruskal-Wallis H and Mann-Whitney U test. The remaining specimens of each surface treated groups were examined by SEM and XRD. RESULTS: The saliva and silicone disclosing medium contaminated zirconia without cleansing group (PNC) had the lowest SBS when Panavia F2.0 was used for cementation (p<0.05). The SBS of surface cleansing groups (PPO, PIC and PHF) were not different from the non-contaminated group (PPC) (p>0.05). However, there were no difference in SBS among groups when cementation with Superbond C&B (SPC, SNC, SPO, SIC and SHF) (p>0.05). There was no morphologic changing that could be observed by SEM. The XRD showed little phase transformation when surfaces were contaminated and cleaned. CONCLUSIONS: The saliva and silicone disclosing medium contaminated zirconia should be cleaned with Phosphoric acid, Ivoclean or Hydrofluoric acid for 20s prior to cementation with Panavia F2.0. However, the surface cleansing was not necessary when cementation with Superbond C&B.

Ultrasonic cleaning reduces the residual monomer in acrylic resins.

BACKGROUND/PURPOSE: The residual monomer remaining in acrylic resin can cause an allergic reaction and is toxic to oral soft tissue. This study determined the effect of the duration of ultrasonic cleaning on the amount of residual methyl methacrylate monomer in one heat-polymerized acrylic resin, Meliodent, and three autopolymerized acrylic resins, Unifast Trad Ivory, Unifast Trad Pink, and Unifast III. MATERIALS AND METHODS: Thirty-six disc-shaped specimens of each brand were prepared and randomly divided into six groups: control (no treatment), positive control, and ultrasonic treatment in 50°C water for 3 minutes, 5 minutes, 10 minutes, or 15 minutes. The residual monomer was extracted and analyzed using high performance liquid chromatography. RESULTS: There were no significant differences in the residual monomer amount in the Meliodent groups. The amounts of residual monomer in the autopolymerized acrylic resin positive control group and ultrasonic treatment groups were significantly lower than those of the control group for the Unifast Trad Ivory, Unifast Trad Pink, and Unifast III groups (P < 0.05). The amount of residual monomer was not significantly different between the ultrasonic treatment in 50°C water (3 minutes for Unifast Trad Pink and 5 minutes for Unifast Trad Ivory and Unifast III) groups and the positive control group (P > 0.05). CONCLUSION: Ultrasonic treatment with 50°C water for 3-5 minutes for autopolymerized resin and 3 minutes for heat-polymerized acrylic resin reduced the amount of residual monomer similarly to previously recommended methods, using shorter treatment times.

The effect of various frequencies of ultrasonic cleaner in reducing residual monomer in acrylic resin.

Monomer remaining in denture base acrylic can be a major problem because it may cause adverse effects on oral tissue and on the properties of the material. The purpose of this study was to compare the effect of various ultrasonic cleaner frequencies on the amount of residual monomer in acrylic resin after curing. Forty-two specimens each of Meliodent heat-polymerized acrylic resin (M) and Unifast Trad Ivory auto-polymerized acrylic resin (U) were prepared according to their manufacturer's instructions and randomly divided into seven groups: Negative control (NC); Positive control (PC); and five ultrasonic treatment groups: 28 kHz (F1), 40 kHz (F2), 60 kHz (F3) (M=10 min, U=5 min), and 28 kHz followed by 60 kHz (F4: M=5 min per frequency, U=2.5 min per frequency, and F5: M=10 min followed by 5 min per frequency, U=5 min followed by 2.5 min per frequency). Residual monomer was determined by HPLC following ISO 20795-1. The data were analyzed by One-way ANOVA and Tukey HSD. There was significantly less residual monomer in the auto-polymerized acrylic resin in all ultrasonic treatment groups and the PC group than that of the NC group (p<0.05). However, the amount of residual monomer in group F3 was significantly higher than that of the F1, F4, and PC groups (p<0.05). In contrast, ultrasonic treatment did not reduce the amount of residual monomer in heat-polymerized acrylic resin (p>0.05). The amount of residual monomer in heat-polymerized acrylic resin was significantly lower than that of auto-polymerized acrylic resin. In conclusion, ultrasonic treatment at low frequencies is recommended to reduce the residual monomer in auto-polymerized acrylic resin and this method is more practical in a clinical situation than previously recommended methods because of reduced chairside time.