Flexural strength of denture base acrylic resins processed by conventional and CAD-CAM methods

Conventionally and digitally fabricated removable complete dentures: manufacturing accuracy, fracture resistance and repairability

OBJECTIVES

Conventionally and digitally manufactured removable complete dentures with different dentition forms were examined for manufacturing accuracy (trueness, precision), fracture forces under torsional loading and subsequent repairability.

METHODS

A total of 90 mandibular prostheses were manufactured. Ten were made using the injection molding technique and finished with prefabricated teeth. 40 bases each, were manufactured subtractively and additively. Digitally the prosthesis' dental arch was divided either into two quadrants or three sextants, or kept as full arch. Afterwards, ten additive and subtractive bases were finished with prefabricated teeth and ten of each with milled quadrants, sextants and full arches. After manufacturing, all specimens were rescanned for accuracy comparisons using the Root Mean Square (RMS). Lastly, all specimens were tested to failure under torsional loading.

RESULTS

Conventionally manufactured dentures showed the greatest deviation in accuracy. The type of base manufacturing did not determine the fracture resistance of the prostheses. The dentition form had a significant influence. While prefabricated teeth (86.01 ± 19.76 N) and quadrants (77.89 ± 9.58 N) showed a low fracture resistance, sextants (139.12 ± 21.41 N) and full arches (141.05 ± 17.14 N) achieved the highest fracture forces. Subtractive bases with prefabricated teeth or quadrants were assessed to be repairable, digital dentures with full arch were assessed as not repairable.

SIGNIFICANCE

The presented testing set-up is suitable to determine the fracture behavior of dentures rather than of standards. With the possibility of digital design and individual manufacturing, dentures' mechanical stability can be significantly increased, especially with suitable dentition forms.

3D-Printed Complete Dentures: A Review of Clinical and Patient-Based Outcomes

There has recently been an increasing trend to shift the fabrication of complete dentures from conventional to digital workflows to shorten the treatment time and increase patient comfort and satisfaction. Digital fabrication of complete dentures can be achieved either by a subtractive process (milling) or by an additive technique (3D printing). The milling process offers numerous advantages; however, they require large-size production machines and are associated with low production efficiency, increased cost, limited block size, and a considerable waste of material. On the other hand, 3D printing technology can potentially offer the benefits of lower manufacturing and equipment costs, good surface details, and lower material waste. Hence, 3D printing is being considered lately by some researchers as a valid choice for manufacturing digital dentures. Therefore, the aim of the current review was to identify and highlight studies on 3D-printed dentures, mainly those investigating clinical and patient-centered outcomes. A search was conducted using the databases PubMed/MEDLINE, Cochrane Library, Embase, and Google Scholar. After applying the inclusion and exclusion criteria, a total of 16 studies that investigated clinical outcomes (masticatory efficiency, biting force, retention and stability, computerized occlusal analysis, and post-insertion maintenance) as well as patient-based outcomes (patient satisfaction, oral health-related quality of life (OHRQoL), patient-related complications, patient preference, and willingness to pay) were included. After a thorough review and discussion of these articles, it could be concluded that 3D printing of complete dentures offers many advantages from both a clinical and patient-based perspective. Retention and comfort with 3D-printed dentures were found to be comparable or even superior to conventional dentures. Moreover, retention of 3D-printed dentures constructed from conventional impressions and digitized casts demonstrated improved retention when compared to a protocol adopting intraoral scanning (digital impressions). Masticatory efficiency, biting force, OHRQoL, and patient satisfaction with 3D-printed dentures varied and were inconsistent among the included studies. Most of the studies reported positive results in the different domains and assessed aspects, while others reported some concerns (especially in terms of aesthetics and phonetics). With regard to post-insertion maintenance, printed dentures showed comparable results to conventional dentures in the short term. The technique seems promising with numerous benefits; however, further clinical research with larger sample sizes and longer follow-up periods is still needed to confirm these conclusions and address the potential concerns.

Effect of thermal cycling on the flexure strength of CAD-CAM denture base materials: An in vitro study

STATEMENT OF PROBLEM

The impact of thermal cycling on the flexure strength of contemporary denture base materials remains inadequately understood despite its crucial role in determining the long-term performance of complete dentures.

PURPOSE

The purpose of this in vitro study was to evaluate the flexural strength of different CAD-CAM denture base materials and the effects of thermal cycling.

MATERIAL AND METHODS

A total of 120 rectangular specimens were fabricated from 6 denture base materials according to the International Organization for Standardization (ISO) 20795-1:2013 standard: a heat-compressed PMMA ([Lucitone 199 [C-L199]), 2 brands of milled material (Ivotion Base [M-IB] and Lucitone Digital Fit [M-LDF]), and 3 types of 3- dimensionally (3D) printed material (Lucitone Digital Print [P-LDP], Flexcera Base [P-FB], and FotoDent Dentures [P-FD]). Specimens were divided into 2 subgroups of 10; half underwent thermocycling, half did not. Thermally cycled specimens were immersed in distilled water at 37 °C for 2 days, followed by 5000 thermal cycles at 5 and 55 ºC, with a dwell time of 30 seconds. They were then subjected to a 3-point flexural strength test. Two-way ANOVA, followed by post hoc Tukey multiple comparison tests were used to assess the effect of material type and the thermal cycling process on the flexural strength of denture base materials (α=.05).

RESULTS

All materials met the ISO standard of 65 MPa flexural strength, except for thermal cycled P-FB. A significant difference (P<.05) in flexure strength value was found among various denture base materials without thermal cycling (M-LDF>M-IB≈P-FD≈P-LDP>C-L199≈ P-FB) and with thermal cycling (M-LDF> M-IB≈P-FD>P-LDP≈C-L199>P-FB). The flexural strength of tested materials was reduced significantly (P<.05) with thermal cycling.

CONCLUSIONS

Three-dimensionally printed denture base materials have a flexural strength value similar to or less than that of milled denture base materials. Thermal cycling impacts the flexural strength of denture base materials.

Mechanical properties of 3D-printed resin denture teeth: An in vitro study

PURPOSE

The purpose of this study was to compare the wear, fracture strength, and mode of failure of various brands of 3D-printed resin denture teeth with prefabricated acrylic resin. Additionally, the study aimed to analyze the different modes of failure exhibited by these teeth.

MATERIALS AND METHODS

The study utilized 90 3D-printed and 30 prefabricated, 3D-printed resin teeth from three brands: L = Optiprint Lumina, A = ASIGA DentaTooth, P = Power resins, along with prefabricated acrylic teeth from M = Major Super Lux. Each of the 30 samples per main group was divided into two subgroups: The first subgroup samples (M1, A1, L1, P1) were subjected to thermal cycling and mechanical loading; M2, A2, L2, and P2 were not aged and tested directly. A scan of a prefabricated acrylic tooth was taken using an intraoral scanner, and then the STL file was printed using an Asiga 3Dprinter. The specimens underwent aging to simulate 5 years of clinical use with 10,000 thermal cycles and 1,200,000 dynamic load cycles on a chewing simulator. Surface roughness parameters (Rz, Ra, Rq) were measured using a 3D Optical Profilometer, fracture resistance was assessed using a universal testing machine, and SEM analysis was performed to observe failure modes. Statistical analysis using T-test, one-way analysis, and two-way analysis processed by the Statistical Package for Social Sciences (SPSS) software version 23.0 (SPSS: Inc., Chicago, IL, USA) was done with a level of significance set at <0.05.

RESULTS

The results showed that the difference in surface roughness parameters (Rz, Ra, Rq) before and after aging for Group M, Group A, Group L, and Group P was statistically significant (p < 0.05). Two-way ANOVA for wear resistance between aging and groups on dependent variable Rz (p = 0.002), Ra (p = 0.001), Rq (p = 0.001) were significant. Multiple comparisons for surface roughness parameters showed Group A and Group L were lower than Group P and Group M (p < 0.05). For fracture strength, One-way ANOVA showed a significant difference between groups for fracture strength either without or after the aging procedure (p < 0.05). Multiple comparisons for fracture strength without aging showed no significant difference between Group M, Group A, and Group L (p > 0.05). After the aging procedure fracture strength for Group M was higher than Group A, Group L, and Group P (p < 0.05).

CONCLUSION

3D-printed resin teeth showed a greater and comparable wear resistance to prefabricated acrylic teeth. Fracture strength was comparable between prefabricated acrylic teeth and 3D-printed resin (Asiga and Lumina) before aging, but after aging 3D-printed resin teeth showed less fracture strength.

Mechanical Assessment of Denture Polymers Processing Technologies

BACKGROUND

Removable prostheses have seen a fundamental change recently because of advances in polymer materials, allowing improved durability and performance. Despite these advancements, notable differences still occur amongst various polymer materials and processing technologies, requiring a thorough grasp of their mechanical, physical, and therapeutic implications. The compressive strength of dentures manufactured using various technologies will be investigated.

METHODS

Traditional, injection molding, and additive and subtractive CAD/CAM processing techniques, all utilizing Polymethyl methacrylate (PMMA) as the main material, were used to construct complete dentures. The specimens underwent a compressive mechanical test, which reveals the differences in compressive strength.

RESULTS

All the specimens broke under the influence of a certain force, rather than yielding through flow, as is characteristic for plastic materials. For each specimen, the maximum force (N) was recorded, as well as the breaking energy. The mean force required to break the dentures for each processing technology is as follows: 4.54 kN for traditional packing-press technique, 17.92 kN for the injection molding technique, 1.51 kN for the additive CAD/CAM dentures, and 5.9 kN for the subtractive CAD/CAM dentures.

CONCLUSIONS

The best results were obtained in the case of the thermoplastic injection system and the worst results were recorded in the case of 3D printed samples. Another important aspect depicted is the standard deviation for each group, which reveal a relatively unstable property for the thermoplastic injected dentures. Good results here in terms of absolute property and stability of the property can be conferred to CAD/CAM milled group.

Comparison of the flexural strength of printed and milled denture base materials

BACKGROUND

To evaluate the flexural strength of digitally milled and printed denture base materials.

METHODS

The materials tested were Lucitone 199 denture base disc (Dentsply Sirona), AvaDent denture base puck (AvaDent), KeyMill denture base disc (Keystone), Lucitone digital print denture base resin (Dentsply Sirona), Formlab denture base resin (Formlabs), and Dentca base resin II (Dentca). Sixty bar-shaped specimens of each material were prepared for flexural strength testing and were divided into five groups: control, thermocycled, fatigue cycled, and repair using two different materials. The flexural strength and modulus were tested using a 3-point bend test performed on an Instron Universal Testing Machine with a 1kN load cell. The specimens were centered under a loading apparatus with a perpendicular alignment. The loading rate was a crosshead speed of 0.5 mm/min. Each specimen was loaded with a force until failure occurred. A one-way ANOVA test was used to analyze the data, followed by Tukey's HSD test (α = 0.05).

RESULTS

The milled materials exhibited higher flexural strength than the printed materials. Thermocycling and fatigue reduce the flexural strengths of printed and milled materials. The repaired groups exhibited flexural strengths of 32.80% and 30.67% of the original flexural strengths of printed and milled materials, respectively. Nevertheless, the type of repair material affected the flexural strength of the printed materials; the composite resin exhibited higher flexural strength values than the acrylic resin.

CONCLUSIONS

The milled denture base materials showed higher flexural strength than the printed ones.

Impact of adding zirconium oxide nanoparticles to the 3D printable acrylic resin base material for implant-retained overdentures: A clinical comparative parallel study

STATEMENT OF PROBLEM

Three-dimensionally (3D) printed acrylic resin base materials have been adopted in prosthetic dentistry. However, their mechanical and biological properties require improvement.

PURPOSE

The purpose of this clinical study was to evaluate the effect of adding zirconium oxide nanoparticles to a 3D printable acrylic resin base material for a 2-implant-retained complete mandibular overdenture in terms of peri-implant tissue health, surface roughness, and biofilm formation.

MATERIAL AND METHODS

Twenty edentulous patients were enrolled in this clinical parallel study. All patients received maxillary complete dentures opposing a 2-implant-retained mandibular overdenture. The participants were randomly divided into 2 equal groups according to the mandibular overdenture base material, nonmodified 3D printable acrylic resin (control group) or 3D printable acrylic resin base material modified with 3.0 wt% zirconium oxide nanoparticles (study group). Peri-implant tissue health and surface roughness were measured immediately at the insertion of the mandibular overdenture (T0), after 3 months (T1), and after 6 months (T2). Microbiological assessment of the denture base was done after 1 week, 1 month, 3 months, and 6 months of overdenture use. The data were analyzed using a statistical software program. The Wilcoxon signed-rank test, paired t test, and Fisher exact test were used to compare distributed data. The Mann Whitney U test and repeated measures ANOVA test were used to compare distributed data at different times (α=.05).

RESULTS

The gingival index (GI), plaque index (PI), probing depth (PD), and surface roughness values at the baseline, 3 months, and 6 months were statistically higher with the nonmodified compared with the modified group (P=.001). Regarding the microbiological analysis, the nonmodified group also had a statistically higher mean bacterial and Candida albicans count than the modified group (P<.05). No significant increase in the bacteria was found in the nonmodified group with time (P=.252), but, for the modified group, a statistically significant decrease in bacteria count was found with time (P<.001).

CONCLUSIONS

Adding zirconium oxide nanoparticles to a 3D printable acrylic resin base material was found to be promising. This addition improved the peri-implant tissue health and decreased surface roughness and biofilm formation.

Assessing the suitability of fused deposition modeling to produce acrylic removable denture bases

OBJECTIVE

To study the feasibility of using poly methyl methacrylate (PMMA) filament and fused deposition modeling (FDM) to manufacture denture bases via the development of a study that considers both conventional and additive-based manufacturing techniques.

MATERIALS AND METHODS

Five sample groups were compared: heat and cold cured acrylic resins, CAD/CAM milled PMMA, 3D-printed PMMA (via FDM), and 3D-printed methacrylate resin (via stereolithography, SLA). All groups were subjected to mechanical testing (flexural strength, impact strength, and hardness), water sorption and solubility tests, a tooth bonding test, microbiological assessment, and accuracy of fit measurements. The performance of sample groups was referred to ISO 20795-1 and ISO/TS 19736. The data was analyzed using one-way ANOVA.

RESULTS

Samples manufactured using FDM performed within ISO specifications for mechanical testing, water sorption, and solubility tests. However, the FDM group failed to achieve the ISO requirements for the tooth bonding test. FDM samples presented a rough surface finish which could ultimately encourage an undesirable high level of microbial adhesion. For accuracy of fit, FDM samples showed a lower degree of accuracy than existing materials.

CONCLUSIONS

Although FDM samples were a cost-effective option and were able to be quickly manufactured in a reproducible manner, the results demonstrated that current recommended testing regimes for conventionally manufactured denture-based polymers are not directly applicable to additive-manufactured denture base polymers. Therefore, new standards should be developed to ensure the correct implementation of additive manufacturing techniques within denture-based fabrication workflow.

Effects of disinfectants on physical properties of denture base resins: A systematic review and meta-analysis

STATEMENT OF PROBLEM

The disinfection of removable dental prostheses and orthodontic appliances is essential to preventing transmission of pathogens. However, whether different disinfection solutions and durations affect the physical properties of denture base resins is unclear.

PURPOSE

The purpose of this systematic review and meta-analysis was to statistically analyze the influence of disinfectants on the physical properties of denture base resins.

MATERIAL AND METHODS

A systematic search in Medline, Embase, PubMed, and Cochrane Library databases was conducted to evaluate the effects of chemical disinfection on the physical properties of denture base resins such as surface morphology, roughness, hardness, and flexural strength. Of 1909 studies, 44 studies were included in the systematic review and 41 in the meta-analysis. Heterogeneity was analyzed by using I2 statistics. The influence of different disinfection solutions and durations on the physical properties was further analyzed, and the risk of bias evaluated. Statistical analyses were performed by using the RevMan 5.4 software program with the standardized mean differences (SMDs) and 95% confidence intervals (CIs).

RESULTS

Of the 44 included studies, 40 studies were assessed as having a low risk of bias, and 4 had an unclear risk of bias. Meta-analysis results showed that compared with the control, disinfection could not significantly affect surface roughness and hardness within 60 minutes of immersion in disinfectant solutions or flexural strength within 30 minutes (roughness: P=.79, I2=0%; flexural strength: P=.08, I2=0%; hardness: P=.05, I2=19%). In addition, the physical properties were not significantly affected when glutaraldehyde, chlorhexidine, and peracetic acid were repeatedly used for more than 30 minutes.

CONCLUSIONS

Most of the disinfectants did not reduce the physical properties of denture base resin within 30 minutes of immersion. Glutaraldehyde, chlorhexidine, and peracetic acid are recommended if longer immersion or repeated disinfection is required.

Retention of titanium copings to implant-supported fixed dental prostheses

PURPOSE

The aim of this in vitro study was to assess the effects of using different cements and titanium copings designs on the retention of implant-supported fixed dental prostheses (IFDPs) using a pull-out test.

MATERIALS AND METHODS

Fifty zirconia (ZirCAD; Ivoclar Vivadent) and 20 prepolymerized denture acrylic resin (AvaDent) rectangular (36 mm × 12 mm × 8 mm) specimens were milled to mimic the lower left segmental portion of the All-on-Four IFDPs. Cylindrical titanium copings (Variobase; Straumann) (V) were used in 2 prepolymerized denture acrylic resin groups (n = 10) while conical titanium copings (Straumann) (C) were used as a control group for zirconia with 4 groups using cylindrical titanium copings. Before cementation, the outer surfaces of all titanium copings and the intaglio bonding surface of prosthetic specimens were airborne-particle abraded. All specimens were cemented following the manufacturer's recommendations and instructions according to the experimental design. After artificial aging (5000 cycles of 5°C 55°C, dwelling time 20 s; 150 N, 1.5 Hz in a 37°C water bath), all specimens were subjected to retention force testing using a pull-out test using a universal testing machine and a custom fixture with a crosshead speed 5 mm/min. Modes of failure were classified as Type 1, 2, or 3. Retention force values were analyzed by the t-test for the prepolymerized denture acrylic resin specimen groups, and 1-way ANOVA and the Tukey test for the zirconia groups at α = 0.05.

RESULTS

Mean and standard deviation retention force values varied from 101.1 ± 67.1 to 509.0 ± 65.2 N for the prepolymerized denture acrylic resin specimen groups. The zirconia groups ranged from 572.8 ± 274.7 to 1416.1 ± 258.0 N. There is no statistically significant difference in retention force values between V and C specimens cementing to zirconia with Panavia SA cement (Kuraray Noritake) (p = 0.587). The retention forces and failure modes were influenced by the cement used (p < 0.05). Modes of failure were predominantly Type 2 (mixed failure) and Type 1 (adhesive fracture from prosthetic materials) except for the quick-set resin group (Type 3, adhesive failure from coping).

CONCLUSIONS

When bonding IFDPs onto titanium copings, quick-set resin provided significantly higher retention force for prepolymerized denture acrylic resin prostheses. Conical and cylindrical titanium copings performed similarly when cemented to zirconia with Panavia SA cement under the same protocol. The stability of the bonded interface and retention forces between zirconia prostheses and titanium copings varied from the cement used.

Effect of thermal cycling on the flexural strength of 3-D printed, CAD/CAM milled and heat-polymerized denture base materials

BACKGROUND

This study compared the impact of thermal cycling on the flexural strength of denture-base materials produced through conventional and digital methods, using both subtractive and additive approaches.

METHODS

In total, 60 rectangular specimens were fabricated with specific dimensions for flexural strength tests. The dimensions were set according to the International Organization for Standardization (ISO) guideline 20795-1:2013 as 64 × 10 × 3.3 ± 0.2 mm. Specimens from each material group were divided into two subgroups (thermal cycled or nonthermal cycled, n = 10/group). We used distinct methods to produce three different denture-base materials: Ivobase (IB), which is a computer-aided-design/computer-aided-manufacturing-type milled pre-polymerized polymethyl methacrylate resin disc; Formlabs (FL), a 3D-printed denture-base resin; and Meliodent (MD), a conventional heat-polymerized acrylic. Flexural strength tests were performed on half of the samples without a thermal-cycle procedure, and the other half were tested after a thermal cycle. The data were analyzed using a two-way analysis of variance and a post hoc Tukey test (α = 0.05).

RESULTS

Based on the results of flexural-strength testing, the ranking was as follows: FL > IB > MD. The effect of thermal aging was statistically significant for the FL and IB bases, but not for the MD base.

CONCLUSIONS

Digitally produced denture bases exhibited superior flexural strength compared with conventionally manufactured bases. Although thermal cycling reduced flexural strength in all groups, the decrease was not statistically significant in the heat-polymerized acrylic group.

The Influence of Contemporary Denture Base Fabrication Methods on Residual Monomer Content, Flexural Strength and Microhardness

(1) Background: Digital technologies are available for denture base fabrication, but there is a lack of scientific data on the mechanical and chemical properties of the materials produced in this way. Therefore, the aim of this study was to investigate the residual monomer content, flexural strength and microhardness of denture base materials as well as correlations between investigated parameters. (2) Methods: Seven denture base materials were used: one conventional heat cured polymethyl methacrylate, one polyamide, three subtractive manufactured materials and two additive manufactured materials. High-performance liquid chromatography was used to determine residual monomer content and the test was carried out in accordance with the specification ISO No. 20795-1:2013. Flexural strength was also determined according to the specification ISO No. 20795-1:2013. The Vickers method was used to investigate microhardness. A one-way ANOVA with a Bonferroni post-hoc test was used for the statistical analysis. The Pearson correlation test was used for the correlation analysis. (3) Results: There was a statistically significant difference between the values of residual monomer content of the different denture base materials (p < 0.05). Anaxdent pink blank showed the highest value of 3.2% mass fraction, while Polident pink CAD-CAM showed the lowest value of 0.05% mass fraction. The difference between the flexural strength values of the different denture base materials was statistically significant (p < 0.05), with values ranging from 62.57 megapascals (MPa) to 103.33 MPa. The difference between the microhardness values for the different denture base materials was statistically significant (p < 0.05), and the values obtained ranged from 10.61 to 22.86 Vickers hardness number (VHN). A correlation was found between some results for the material properties investigated (p < 0.05). (4) Conclusions: The selection of contemporary digital denture base manufacturing techniques may affect residual monomer content, flexural strength and microhardness but is not the only criterion for achieving favourable properties.

Effect of thermocycling on surface topography and fracture toughness of milled and additively manufactured denture base materials: an in-vitro study

BACKGROUND

Studies investigating thermocycling effect on surface topography and fracture toughness of resins used in digitally manufactured denture bases are few. The study aimed to assess the impact of thermocycling on surface topography and fracture toughness of materials used for digitally manufactured denture bases.

METHODS

Water sorption, solubility, hardness, surface roughness, and fracture toughness of both three-dimensional (3D)-printed and computer-aided design, computer-aided manufacturing (CAD-CAM) milled specimens (n = 50) were assessed both prior to and following 2000 thermocycles, simulating 2 years of clinical aging. Surface hardness (n = 10) was measured using a Vickers hardness testing machine, surface roughness (n = 10) was determined by a contact profilometer, and fracture toughness (n = 20) was measured using the 3-point bend test, then studying the fractured surfaces was done via a scanning electron microscope (SEM). Prior to and following thermocycling, water sorption and solubility (n = 10) were assessed. Normally distributed data was tested using two-way repeated ANOVA and two-way ANOVA, while Mann Whitney U test and the Wilcoxon signed ranks test were used to analyze data that was not normally distributed (α < 0.05).

RESULTS

Following thermocycling, Vickers hardness and fracture toughness of both groups declined, with a significant reduction in values of the 3D-printed resin (P < .001). The 3D-printed denture base resins had a rougher surface following thermocycling with a significant difference (P < .001). The sorption and solubility of water of both materials were not affected by thermocycling.

CONCLUSIONS

Before and after thermocycling, milled specimens had lower surface roughness and a greater degree of hardness and fracture toughness than 3D-printed specimens. Thermocycling lowered hardness and fracture toughness, and increased surface roughness in both groups, but had no effect on water sorption and solubility.

Evaluation of polymethyl-methacrylate and acetal denture base resins processed by two different techniques before and after nano-chlorohexidine surface treatment

BACKGROUND

Flexible denture base polymers have gained popularity in modern dentistry however, their biofilm formation tendency, adversely affecting the oral tissue heath, remains a concern. Consequently, this study aimed to evaluate surface roughness and biofilm formation tendency of two types of denture base resins manufactured with two techniques before and after surface coating with chlorohexidine (CHX) NPs.

MATERIALS AND METHODS

Acetal (AC) and Polymethyl-methacrylate (PMMA) resins manufactured by conventional and CAD/CAM methods were shaped into disk (10 X 10 X 1 mm). They were dipped for 8 h and 24 h in colloidal suspension prepared by mixing aqueous solution of CHX digluconate and hexa-metaphosphate (0.01 M). Surface roughness, optical density (OD) of microbial growth media and biofilm formation tendency were evaluated directly after coating. Elutes concentrations of released CHX were evaluated for 19 days using spectrophotometer. Three-way ANOVA and Tukey's post-hoc statistical analysis were used to assess the outcomes.

RESULTS

AC CAD/CAM groups showed statistically significant higher roughness before and after coating (54.703 ± 4.32 and 77.58 ± 6.07 nm, respectively). All groups showed significant reduction in OD and biofilm formation tendency after surface coating even after 19 days of CHX NPs release.

CONCLUSIONS

Biofilm formation tendency was highly relevant to surface roughness of tested resins before coating. After CHX NPs coating all tested groups showed significant impact on microbial growth and reduction in biofilm formation tendency with no relation to surface roughness. Significant antimicrobial effect remained even after 19 days of NPs release and specimens storage.

Flexural strength, surface roughness, and biofilm formation of ceramic-reinforced PEEK: An in vitro comparative study

PURPOSE

This in vitro study aimed to compare flexural strength, surface roughness, and biofilm formation of ceramic-reinforced polyetheretherketone (PEEK) with conventionally heat-compressed and milled polymethylmethacrylate (PMMA) denture base materials.

MATERIALS AND METHODS

Thirty strips (6.4 mm × 10 mm × 3 mm) and 30 discs (10 mm × 1 mm) were fabricated from a heat-compressed PMMA, milled PMMA, and ceramic-reinforced PEEK, 10 each. One surface of each sample was polished to mimic the laboratory procedure for denture base materials. Strips were then subjected to a three-point bend test using a universal testing machine at a crosshead speed of 5.0 mm/min. An optical profilometer was used to assess the Ra value (mm) of the discs on polished and unpolished sides. Biofilm formation behavior was analyzed by measuring the colony-forming unit (CFU)/mL of Candida albicans on the unpolished surface of the discs. One-way ANOVA followed by Tukey multiple comparison tests were used to compare the flexural strength, Ra value, and biofilm formation of the studied materials (a = 0.05).

RESULTS

Ceramic-reinforced PEEK showed significantly higher flexural strength (178.2 ± 3.2 MPa) than milled PMMA (89.6 ± 0.8 MPa; p < 0.001) and heat-compressed PMMA (67.3 ± 5.3 MPa; p < 0.001). Ceramic-reinforced PEEK exhibited a significantly higher Ra value than the other groups on unpolished sides; however, the polishing process significantly reduced the Ra values of all studied groups (p < 0.05). There was no significant difference in C. albicans adhesion among the groups (p < 0.05).

CONCLUSION

The flexural strength of tested materials was within acceptable limits for clinical use as a denture base material. Ceramic-reinforced PEEK had the highest surface roughness; however, its similarity in biofilm formation to other groups indicates its clinical acceptability as denture base material.

Flexural Strength Analysis of Different Complete Denture Resin-Based Materials Obtained by Conventional and Digital Manufacturing

PMMA (Polymethylmethacrylate) is the material of choice to fabricate denture bases. Recently, with the introduction of CAD-CAM and 3D printers in dentistry, new materials have been proposed for complete denture manufacturing.

AIM

This study compared the flexural strength of different resins fabricated using different technologies (conventional, CAD-CAM-milled, and 3D-printed) and polymerization techniques.

METHODS

A total of 11 different resins were tested: six PMMA conventional (Acrypol R, Acrypol LL, Acrypol HI, Acrypol Fast, Acryself and Acryslef P), two milled obtained from UDMA PMMA disks (Ivotion disk and Aadva disk, control groups), two 3D-printed PMMA resins (NextDent Denture 3D+, and SprintRayEU Denture Base), and one 3D-printed composite resin (GC Temp Print). Flexural strength was measured using a universal testing machine. One-way ANOVA and Bonferroni post hoc tests were performed; the p-value was set at 0.05 to consider statistically significant differences among the groups. Spearman test was used to evaluate the correlation between polymerization technique and the flexural strength of 3D-printed resins.

RESULTS

CAD-CAM-milled specimens showed the highest flexural strength (107.87 MPa for UDMA) followed by 3D-printed composite resins (102.96 MPa). Furthermore, 3D-printed resins polymerized for 40 min with the BB cure unit showed no statistically significant differences with conventional resin groups. Moreover, in all the 3D-printed specimens, a high correlation between polymerization technique and flexural strength was found.

CONCLUSIONS

In terms of flexural strength, the polymerization technique is a determinant for both acrylic and composite resins. Temp Print can be a potential alternative to fabricating removable dentures and showed promising results when used in combination with pink color resin powder.

Evaluation of Impact Strength and Flexural Strength of Polyether Ether Ketone vs. Computer-Aided Design/Computer-Aided Manufacturing Polymethyl Methacrylate Denture Base Materials: An In-Vitro Study

OBJECTIVE

The objective is to comparatively assess the impact strength and flexural strength of polyether ether ketone (PEEK) vs. computer-aided design/computer-aided manufacturing (CAD/CAM) polymethyl methacrylate denture base material.

METHODS

A total of 90 samples were fabricated with traditional heat cure PMMA, PEEK, and CAD/CAM PMMA and divided into three groups of 30 samples each. The impact strength of all the samples was measured using an Izod impact tester with a pendulum in the air at 23±2°C. A three-point bending test was used in a Universal Testing Machine to assess the flexural strength of all the samples. The impact strength and flexural strength mean values were computed using a one-way ANOVA test.

RESULT

Impact strength and flexural strength of PEEK (IS=10.22±1.25 kJ/m2 and FS=120±8.0 MPa) is almost identical to CAD/CAM PMMA sample (IS=9.595±3.313 kJ/m2 and FS=118.11±5.00 MPa) whereas for conventional heat cure PMMA (IS=4.00±.011 kJ/m2 and FS=75.4±4.50 MPa) the values are least among the three.

CONCLUSION

 PEEK or CAD/CAM PMMA share almost identical and superior mechanical properties, and both can be used as better alternatives for complete denture fabrication rather than using conventional heat cure PMMA.

Different Polymers for the Base of Removable Dentures? Part I: A Narrative Review of Mechanical and Physical Properties

Even before considering their introduction into the mouth, the choice of materials for the optimization of the prosthesis depends on specific parameters such as their biocompatibility, solidity, resistance, and longevity. In the first part of this two-part review, we approach the various mechanical characteristics that affect this choice, which are closely related to the manufacturing process. Among the materials currently available, it is mainly polymers that are suitable for this use in this field. Historically, the most widely used polymer has been polymethyl methacrylate (PMMA), but more recently, polyamides (nylon) and polyether ether ketone (PEEK) have provided interesting advantages. The incorporation of certain molecules into these polymers will lead to modifications aimed at improving the mechanical properties of the prosthetic bases. In the second part of the review, the safety aspects of prostheses in the oral ecosystem (fragility of the undercuts of soft/hard tissues, neutral pH of saliva, and stability of the microbiota) are addressed. The microbial colonization of the prosthesis, in relation to the composition of the material used and its surface conditions (roughness, hydrophilicity), is of primary importance. Whatever the material and manufacturing process chosen, the coating or finishes dependent on the surface condition remain essential (polishing, non-stick coating) for limiting microbial colonization. The objective of this narrative review is to compile an inventory of the mechanical and physical properties as well as the clinical conditions likely to guide the choice between polymers for the base of removable prostheses.

Workflow for complete dentures fabrication in three appointments: A dental technique

This technical report describes a novel workflow for complete denture fabrication designed to abbreviate the necessary steps for dental prostheses delivery by using a 3-appointment protocol in which preliminary impressions are made in the first session together with the registration of maxillary lip support, occlusal plane, and reference lines for tooth arrangement. A trial denture is fabricated with conventional or computer-aided design and computer-aided manufacturing procedures and is evaluated in the second appointment for esthetics, the definitive impression, and the maxillomandibular relationship record to provide precise references for definitive denture fabrication.

Tensile Bond Strength between Different Denture Base Materials and Soft Denture Liners

(1) Background: Various materials are available for CAD-CAM denture base fabrication, for both additive and subtractive manufacturing. However, little has been reported on bond strength to soft denture liners. Therefore, the aim of this study was to investigate tensile bond strength, comparing between different denture base materials and soft denture liners. (2) Methods: Seven different materials were used for denture base fabrication: one heat-polymerized polymethyl methacrylate, three materials for subtractive manufacturing, two materials for additive manufacturing and one polyamide. Two materials were used for soft denture lining: one silicone-based and one acrylate-based. The study was conducted according to the specification ISO No. 10139-2:2016, and the type of failure was determined. The Kruskal-Wallis test with Dunn's post hoc test was used to analyse the values of tensile bond strength, and Fisher's exact test was used to analyse the type of failure. p Values < 0.05 were considered statistically significant. (3) Results: The tensile bond strength values were not statistically significantly different combining all the materials used for denture base fabrication with the acrylate-based soft denture liner (p > 0.05), and the average values ranged between 0.19 and 0.25 Mpa. The tensile bond strength values of the different denture base materials and silicone-based denture liner were statistically significantly different (p < 0.05), and the average values ranged between 1.49 and 3.07 Mpa. The type of failure was predominantly adhesive between polyamide and both additive-manufactured denture base materials in combination with the acrylate-based soft liner (p < 0.05). (4) Conclusions: The use of digital technologies in denture base fabrication can have an influence on different tensile bond strength values for soft denture liners, with different types of failure when compared with heat-cured PMMA. Similar tensile bond strength values were found between the acrylate-based soft denture liner and denture base materials. Significant differences in tensile bond strength values were found between the silicone-based soft denture liner and denture base materials, where the additive-manufactured and polyamide denture base materials showed lower values than heat-cured PMMA and subtractive-manufactured denture base materials.

Evaluation of physicomechanical properties of milled versus 3D-printed denture base resins: A comparative in vitro study

STATEMENT OF PROBLEM

Studies comparing the physicomechanical characteristics of denture base resins manufactured by computer-aided design and computer-aided manufacturing (CAD-CAM) milling and 3-dimensional (3D) printing are sparse, resulting in challenges when choosing a fabrication method for complete dentures.

PURPOSE

The purpose of this in vitro study was to evaluate and compare the impact strength, flexural strength, and the surface roughness of denture base resins manufactured by CAD-CAM milling and 3D printing before and after thermocycling and polishing.

MATERIAL AND METHODS

Evaluation of the physicomechanical properties (n=35) was completed before and after 500 thermocycles. Impact strength (n=14) was measured with a Charpy impact tester and flexural strength (n=14) with the 3-point bend test. Surface roughness (Ra) was evaluated (n=7) with a profilometer before and after thermocycling and polishing and by viewing the surface topography before and after polishing using a scanning electron microscope at ×2000. The Mann-Whitney U test and Wilcoxon sign rank test were used for statistical analysis (α=.05).

RESULTS

Milled specimens showed statistically significantly higher impact strength before thermocycling and statistically significantly higher flexural strength before and after thermocycling (P=.004) compared with 3D-printed specimens. The Ra values for the milled group were significantly lower than for the 3D-printed group both before and after thermocycling (P=.006) and after polishing (P=.027). Thermocycling resulted in a statistically significant difference in flexural strength (P=.018) in both groups and in surface roughness in the milled group (P=.048); but no significant effect was found on impact strength (P>.05). Ra values for the 3D-printed group decreased after polishing (P=.048).

CONCLUSIONS

Milled specimens had higher flexural and impact strength and lower surface roughness values than 3D-printed specimens. Polishing significantly reduced the surface roughness in 3D-printed specimens but had no significant effect on milled specimens.

Effect of adding a hard-reline material on the flexural strength of conventional, 3D-printed, and milled denture base materials

STATEMENT OF PROBLEM

Novel 3-dimensionally printed resin and milled polymethyl methacrylate materials have been marketed for computer-aided design and computer-aided manufacturing (CAD-CAM) denture base fabrication. However, information on the flexural strength of digitally fabricated denture base material is limited, and little is known about how they are affected by a hard-reline procedure.

PURPOSE

The purpose of this in vitro study was to assess the flexural strength of 6 digitally manufactured denture base materials and to assess the effect of a hard-reline procedure on their flexural strength.

MATERIAL AND METHODS

A total of 140 strips of denture base material were fabricated from a conventional heat-polymerized polymethyl methacrylate (L199), 3 brands of milled polymethyl methacrylate (IBC, DSL, and ADH), and 3 brands of 3D-printed resin (DFD, ADB, and DrFD) (n=20). Ten specimens in each group did not receive any treatment, and 10 were relined with a hard-reline material (ProBase Cold Trial Kit). Specimens were then subjected to a 3-point flexural strength test using a universal testing machine at a crosshead speed of 5.0 mm/min. A 1-way ANOVA test followed by the Tukey multiple comparison test was used to detect the difference in flexural strength and the strain at fracture of the different types of denture base materials (α=.05). The comparison of flexural strength between with and without hard-reline was analyzed using an unpaired t test (α=.05).

RESULTS

All materials, with or without the hard-reline, met the International Organization for Standardization (ISO) 20 795-1:2013 standard for flexural strength (65 MPa). The milled materials (DSL>IBC≈ADH) showed higher flexural strength than the 3D-printed or conventional materials (DrFD>DFD≈ADB≈L199) without a hard-reline. No statistical difference in flexural strength was found among the hard-relined denture base materials (P=.164). All 3 milled materials showed reduced flexural strength after relining, while the relined conventional (L199) and 3D-printed materials (DFD and ADB) showed notably higher flexural strength; printed DrFD showed no significant difference (P=.066). In terms of strain at fracture, the milled materials displayed higher values than those of the conventional or 3D-printed materials (P<.05).

CONCLUSIONS

All digitally fabricated denture base materials were within acceptable limits for clinical use, even after hard relining. Flexural strength was highly dependent on the type of material. Hard relining affected the flexural strength of most of the digitally fabricated denture base materials.

Effect of Denture Disinfectants on the Mechanical Performance of 3D-Printed Denture Base Materials

Denture care and maintenance are necessary for both denture longevity and underlying tissue health. However, the effects of disinfectants on the strength of 3D-printed denture base resins are unclear. Herein, distilled water (DW), effervescent tablet, and sodium hypochlorite (NaOCl) immersion solutions were used to investigate the flexural properties and hardness of two 3D-printed resins (NextDent and FormLabs) compared with a heat-polymerized resin. The flexural strength and elastic modulus were investigated using the three-point bending test and Vickers hardness test before (baseline) immersion and 180 days after immersion. The data were analyzed using ANOVA and Tukey's post hoc test (α = 0.05), and further verified by using electron microscopy and infrared spectroscopy. The flexural strength of all the materials decreased after solution immersion (p < 0.001). The effervescent tablet and NaOCl immersion reduced the flexural strength (p < 0.001), with the lowest values recorded with the NaOCl immersion. The elastic modulus did not significantly differ between the baseline and after the DW immersion (p > 0.05), but significantly decreased after the effervescent tablet and NaOCl immersion (p < 0.001). The hardness significantly decreased after immersion in all the solutions (p < 0.001). The immersion of the heat-polymerized and 3D-printed resins in the DW and disinfectant solutions decreased the flexural properties and hardness.

Effect of Fiber Reinforcement on the Flexural Strength of the Transitional Implant-Supported Fixed Dental Prosthesis

PURPOSE

The aim of this in vitro study was to assess the efficacy of fiber reinforcement to enhance flexural strength of the transitional implant-supported fixed dental prosthesis (TISFDP).

MATERIALS AND METHODS

One hundred and forty denture acrylic resin plates (64 mm × 12 mm × 5 mm) with two 7 mm diameter holes were fabricated using heat-polymerized type (Lucitone 199) and CAD-CAM prepolymerized type (AvaDent) materials to simulate a chair-side reconstruction of the TISFDP. Specimens were divided into 7 groups (n = 10) according to the airborne-particle abrasion of titanium cylinder (Straumann) surface and locations of fiber reinforcement ribbons (Ribbond-ULTRA). No cylinder surface abrasion and no fiber added acrylate specimens were used as the controls. The prosthetic screws were hand-tightened on a custom fixture with analogs. Specimen hole and cylinder were joined using a 50:50 mixture of chemically polymerized resin (QYK-SET; Holmes Dental) and repair resin (Dentsply Sirona). Ten acrylate specimens with no holes were fabricated from each tested material and assigned as positive controls. A modified four-point bending test (ASTM standard-D6272) was conducted using a universal testing machine and a custom fixture with a crosshead speed 1 mm/min. The maximum failure loads were recorded. Data were statistically analyzed using 2-way ANOVA and the Tukey tests at α = 0.05.

RESULTS

The flexural strength values ranged from 55.4 ±8.3 to 140.9 ±15.4 MPa. The flexural strength decreased significantly when fiber was attached on the titanium cylinder surface (p < 0.05). There were no statistically significant differences in flexural strength values between specimens with and without titanium cylinder surface abrasion (p > 0.05). Statistically significant improvement in flexural strength was observed in specimens with fibers attached around the specimen holes (p < 0.05) buccally and lingually. The obtained values were not statistically significantly different from the positive controls (p > 0.05). Some fixation screw fractures were observed before catastrophic failure of specimens during testing.

CONCLUSIONS

Fiber reinforcement significantly improved the flexural strength of denture acrylic resins only if placed around the specimen holes on the tension side at the site of initiation of crack propagation. Even when the specimens underwent catastrophic failure, the segments remained attached to each other with the attached fibers.

Evaluation of the mechanical properties of different materials for manufacturing occlusal splints

This study aimed to compare the mechanical properties of various occlusal plate materials by analyzing surface roughness, Knoop microhardness, flexural strength, and modulus of elasticity. Fifty samples were prepared and classified as SC (self-curing acrylic resin), WB (heat-cured acrylic resin), ME (acrylic resin polymerized by microwave energy), P (resin print), and M (polymethylmethacrylate polymer block for computer-aided design/computer-aided manufacturing). The data were analyzed using a one-way analysis of variance and Tukey's honestly significant difference test. Surface roughness was the same in all groups. The surface hardness of group M was statistically superior. The samples from groups P and M had higher flexural strength than other samples. The modulus of elasticity of group SC was statistically lower than that of other groups. The mechanical properties of the materials used to make the occlusal plates differed, and group M achieved the best results in all analyses. Therefore, clinicians must consider the material used to manufacture long-lasting and efficient occlusal splints.

Evaluation of the Effect of Different Construction Techniques of CAD-CAM Milled, 3D-Printed, and Polyamide Denture Base Resins on Flexural Strength: An In Vitro Comparative Study

PURPOSE

To compare the flexural strength of computer-aided design and computer-aided manufacturing (CAD-CAM) milled denture base resin (DBR), 3D-printed DBR, polyamide, and conventional compression-molded DBR.

MATERIALS AND METHODS

Six denture base resins were used, one conventional heat-polymerized (Vertex), two milled CAD-CAM (AvaDent and Polident), two 3D-printed (Harz and NextDent), and one flexible polyamide (Polyamide). According to ISO 20795-1:2013, 60 specimens (65×10×3 mm) were constructed and divided into six groups (n = 10), according to DBR type. The flexural strength was measured using a universal testing machine and three-point loading test. Data were collected and analyzed using one-way ANOVA and Tukey's pair-wise post hoc tests (α = 0.05).

RESULTS

One-way ANOVA results showed significant differences in flexural strengths between the tested DBRs (p˂0.001). Milled denture base resins (AvaDent and Polident) had significantly higher flexural strength values than the other groups (p˂0.001) and were followed by Vertex and NextDent, while Polyamide and Harz had the lowest values. Polyamide and Harz denture base resins had significantly lower flexural strength values than conventional denture base resin (p˂0.001).

CONCLUSION

CAD-CAM milled DBRs showed the highest flexural strength when compared with conventional compression-molded or 3D-printed DBRs, while 3D-printed DBRs and polyamide showed the lowest flexural strengths.

CAD-CAM Fabricated Denture Base Resins: In Vitro Investigation of the Minimum Acceptable Denture Base Thickness

PURPOSE

To investigate the influence of reducing material thickness on flexural properties of computer-aided design and computer-aided manufacturing (CAD-CAM) denture base resins.

MATERIALS AND METHODS

Four CAD-CAM denture base acrylic resin materials were selected; two were made via the subtractive method (AvaDent and IvoCad) and two were made with the additive method (FormLabs and NextDent). One heat-polymerized denture base material was used as a control. Specimens were fabricated with varying thicknesses (n = 10/group): 3.3 mm, 2.5 mm, 2 mm, or 1.5 mm. Flexural strength was evaluated via a three-point bending test. One- and two-way ANOVA were used for data analysis along with Tukey's post hoc comparison (α = 0.05).

RESULTS

Reducing the thickness of materials made via the subtractive method did not influence flexural strength up to 2 mm (p > 0.05). However, the difference was significant at a 1.5 mm thickness (p ˂ 0.001). For materials made via the additive method, NextDent specimens had no significant decrease in flexural strength when the thickness was reduced to 2 mm (p = 0.58). FormLabs specimens showed a significant decrease (p ˂ 0.001), although the values of flexural strength were clinically acceptable. During testing, specimens manufactured via the additive method at a 1.5 mm thickness bent without fracturing and were therefore excluded. All materials showed a reduction in elastic modulus as the thickness decreased (p ˂ 0.001).

CONCLUSION

Heat-polymerized, AvaDent, and IvoCad materials may be used for denture base fabrication at a minimum thickness of 1.5 mm. FormLabs and NextDent may be fabricated at a 2 mm minimum thickness, with clinically acceptable flexural properties.

In vitro study of surface properties and microbial adhesion of various dental polymers fabricated by different manufacturing techniques after thermocycling

OBJECTIVES

The study aims to investigate surface properties and microbial adhesion of various dental polymers fabricated by different manufacturing techniques before and after thermocycling.

MATERIALS AND METHODS

The following six materials were used to fabricate disk-shaped specimens: conventional denture polymer (Vertex Acrylic Resin, VAR), CAD/CAM denture polymer (Organic PMMA eco Pink, OP), conventional temporary polymer (Protemp™ 4, PT), CAD/CAM temporary polymer (Die Material, DM), conventional denture framework polymer (BioHPP, PB), and CAD/CAM denture framework polymer (breCAM.BioHPP, CB). The specimens were tested before and after thermocycling (5000 and 10,000 cycles, 5 °C/55 °C). Surface roughness (SR), hydrophobicity, and surface topography were determined by profilometry, water contact angle, and scanning electron microscopy (SEM). Then specimens were incubated with Staphylococcus aureus, Streptococcus mutans, and Candida albicans for 24 h, respectively. Microbial adhesion was assessed using colony-forming unit counts, XTT assay, and SEM.

RESULTS

SR and hydrophobicity of VAR group were higher than that of OP group. S. aureus and C. albicans adhesion on VAR and PT groups were higher than that on OP and DM groups, respectively. There was no difference in surface properties and microbial adhesion between PB and CB groups. After thermocycling, SR (expect OP group) of all materials increased and hydrophobicity decreased, and the amount and activity of S. aureus and C. albicans adhesion also increased. The adhesion of S. aureus and C. albicans showed a moderate positive correlation with SR, independent of hydrophobicity.

CONCLUSIONS

CAD/CAM denture polymers and temporary polymers showed less S. aureus and C. albicans adhesion when compared to conventional ones, which were mainly affected by surface roughness, independent of hydrophobicity. Thermocycling could increase surface roughness, decrease hydrophobicity, and affect microbial adhesion of the materials.

CLINICAL SIGNIFICANCE

CAD/CAM dental polymers may be a better choice for the manufacture of temporary restorations and dentures to reduce microbial adhesion.

Mechanical Properties of the Modified Denture Base Materials and Polymerization Methods: A Systematic Review

Amidst growing technological advancements, newer denture base materials and polymerization methods have been introduced. During fabrication, certain mechanical properties are vital for the clinical longevity of the denture base. This systematic review aimed to explore the effect of newer denture base materials and/or polymerization methods on the mechanical properties of the denture base. An electronic database search of English peer-reviewed published papers was conducted using related keywords from 1 January 2011, up until 31 December 2021. This systematic review was based on guidelines proposed by the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA). The search identified 579 papers. However, the inclusion criteria recognized 22 papers for eligibility. The risk of bias was moderate in all studies except in two where it was observed as low. Heat cure polymethyl methacrylate (PMMA) and compression moulding using a water bath is still a widely used base material and polymerization technique, respectively. However, chemically modified PMMA using monomers, oligomers, copolymers and cross-linking agents may have a promising result. Although chemically modified PMMA resin might enhance the mechanical properties of denture base material, no clear inferences can be drawn about the superiority of any polymerization method other than the conventional compression moulding technique.

Flexural Properties and Hardness of CAD-CAM Denture Base Materials

PURPOSE

To compare flexural strength, elastic modulus, and surface hardness of CAD-CAM milled, 3D-printed, and heat-polymerized denture base resins.

MATERIALS AND METHODS

A total of 120 specimens were fabricated from heat-polymerized acrylic resin (HP), milled resin (Avadent and IvoCad), and 3D-printed resin (ASIGA, FormLabs, and NextDent). The specimens were divided into 6 groups according to the type of denture base material n = 20/material, (10/flexural properties and 10/hardness). Flexural strength and elastic modulus of the specimens were evaluated by 3-point bending test and surface hardness by Vickers hardness test. To test flexural properties, the specimens were fabricated according to ISO 20795-1:2013 standards (64×10×3.3 ±0.2 mm). The dimensions for hardness test were 15×10×2.5 ±0.2 mm. Scanning electron microscope was used to evaluate the surface morphology of the fractured specimens. The means and standard deviations were calculated, followed by one-way ANOVA and Tukey post-hoc test (α = 0.05).

RESULTS

Milled resins showed significantly higher values for flexural strength, elastic modulus, and surface hardness, followed by HP then 3D-printed resins (P<0.001). In between milled groups, flexural strength of AvaDent was significantly higher than IvoCad (P<0.001), while elastic modulus and hardness didn't show significant difference. In between 3D-printed resins, ASIGA showed the highest flexural strength and elastic modulus, insignificantly with FormLabs (P = 0.595) and significantly with NextDent (P = 0.008). ASIGA also showed significantly the highest hardness among the 3D-printed groups. No significant difference was found between FormLabs and NextDent flexural strength (P = 0.357), elastic modulus (P = 1.00) and surface hardness (P = 0.987).

CONCLUSION

CAD-CAM milled resins had greater flexural properties and hardness compared to heat-polymerized acrylic resin and 3D-printed resins. Although 3D-printed samples showed the lowest values of tested properties, the flexural strength and modulus were above the clinically acceptable values. This article is protected by copyright. All rights reserved.

Additive Manufacturing for Complete Denture Fabrication: A Narrative Review

PURPOSE

To evaluate and compare the benefits and limitations of additive manufacturing for complete denture fabrication.

METHODS

A PubMed and Google Scholar search for topics pertaining to additive manufacturing for complete dentures was performed. The resulting articles were then divided into topics to allow a narrative review.

DISCUSSION

Determining how printing compares with conventional and milled dentures is critical for the widespread adoption of this fabrication technique. Physical properties, denture tooth bond strength, denture base adaptation and soft-liner bond strength are discussed to establish how printing compares.

CONCLUSIONS

Printing offers many advantages over milled and conventionally processed dentures; however, many questions need to be answered by research. The advantages include reduced cost of most printers compared to milling machines, less material waste, ability to print multiple dentures simultaneously, and complex designs can be fabricated that otherwise could not be milled. Current research has shown flexural strength, fracture toughness, color stability, and denture base adaptation are reduced for printed dentures when compared with milled dentures. Print orientation has been shown to influence accuracy, strength, surface roughness and C. albicans adherence which is not seen with conventional or milled denture materials. These factors do not represent a criticism of printing but rather indicate the need for more research with this new and promising denture fabrication technique. Since printing offers numerous benefits to complete denture fabrication it is likely to have a more significant role in complete denture fabrication in years to come as knowledge increases and materials/techniques continue to advance.

Comparative analysis of leaching residual monomer and biological effects of four types of conventional and CAD/CAM dental polymers: an in vitro study

OBJECTIVES

The objective of this study is to investigate leaching residual monomer and biological effects of four types of conventional and computer-aided design/computer-aided manufacturing (CAD/CAM) dental polymers on human gingival fibroblasts (HGFs).

MATERIALS AND METHODS

A total of 540 disk-shaped specimens were fabricated from four different materials (n=135 per group): compression-molding polymethylmethacrylate (PMMA) (conventional denture polymer), CAD/CAM PMMA (CAD/CAM denture polymer), bis-acrylic composite resin (conventional temporary polymer), and CAD/CAM PMMA (CAD/CAM temporary polymer). Specimens were eluted in cell culture medium for 72 h at 37°C, and the residual monomer in eluates subsequently was measured by high-performance liquid chromatography (HPLC). The biological effects of material eluates on HGFs were analyzed by CCK-8 assay, flow cytometry, real-time quantitative PCR, Western blotting, and enzyme-linked immunosorbent assay (ELISA) to identify cell death patterns and its biological mechanism.

RESULTS

Methyl methacrylate (MMA) was detected only in compression-molding PMMA, and by-products were detected in bis-acrylic composite resin. The cell proliferation of CAD/CAM denture polymer or CAD/CAM temporary polymer was greater than that of compression-molding PMMA or bis-acrylic composite resin at 72 h in culture. No apoptosis and necrosis were detected in CAD/CAM dental polymers. Apoptosis was detected only in bis-acrylic composite resin and further confirmed by the upregulation of Bax and cleaved Caspase-3, as well as the downregulation of Bcl-2 gene. And no significant variation in inflammatory cytokines secretion was observed in all materials.

CONCLUSIONS

CAD/CAM dental polymers (including temporary and denture polymers) have favorable biocompatibility due to lower residual monomer, which provides scientific evidence to the controversy of biocompatibility of conventional and CAD/CAM dental polymers.

CLINICAL RELEVANCE

The use of CAD/CAM dental polymers is recommended in the fabrication of temporary restorations and dentures due to their favorable biocompatibility.

Flexural strength of CAD/CAM denture base materials: Systematic review and meta-analysis of in-vitro studies

Introduction:

Digital complete dentures fabrication techniques are expanding. This study aimed to review flexural strength (FS) of milled and 3D-printed denture base materials to answer the study question: is FS of computer-aided designing/computer-aided manufacturing (CAD/CAM) denture base comparable to conventional heat-polymerized materials?

Materials and Methods:

Search was done within different databases for articles published between January 2010 and June 2021 using specific keywords. Articles of in-vitro studies in English language with methods following International Standards Organization standardization/ADA specifications for flexural testing of conventional and CAD/CAM (milled or printed) polymethyl methacrylate (PMMA) materials were included.

Results:

Out of the 61 studies, 9 were processed for data extraction and only 7 underwent meta-analysis. Two, six, and one study showed high, moderate, and low risk of bias, respectively. Random-effects model was used for analysis and resulted in the average FS of 120.61 MPa [95% confidence interval (CI): 109.81−131.41] and 92.16 MPa (CI: 75.12−109.19) for CAD/CAM milled and heat-polymerized PMMA, respectively.

Conclusion:

Subtractive CAD/CAM technique of denture fabrication showed satisfactory FS values, whereas additive CAD/CAM method was comparable to conventional heat-polymerized technique with lower value, requiring further investigations and improvement. The clinical use of milled denture bases is an acceptable substitution to heat-polymerized PMMA, making the denture fabrication an easier and faster process.

Effect of post-curing light exposure time on the physico-mechanical properties and cytotoxicity of 3D-printed denture base material

OBJECTIVE

This study investigated the effect of post curing light exposure time on the physico-mechanical properties and cytotoxicity of a 3D-printed PMMA-based denture material in comparison to a conventional heat-cured alternative as a control.

METHODS

3D-printed specimens were fabricated followed by post-curing for 0, 5, 10 or 20 min at 200 W and light wavelength range of 390-540 nm. Heat-cured specimens were fabricated using a standard protocol. Specimens were placed in artificial saliva at 37 ℃ for 48 h (immediate groups) and 6 months (aged group), then evaluated flexural strength/modulus, fracture toughness, microhardness, and degree of conversion. Water sorption and solubility was assessed after 28 days. Flexural strength, flexural modulus, and fracture toughness were tested through three-point bending tests, while the surface hardness was tested using Vickers's test. Fractured specimens were viewed by scanning electron microscope (SEM). Cytotoxicity in term of cell viability was evaluated using human oral fibroblasts.

RESULTS

Flexural strength/modulus, fracture toughness and surface hardness significantly improved with the increase in light curing time up to 20 min. The same pattern of improvement was found with degree of conversion, water sorption, solubility, and cell viability. There was no significant difference (p < 0.01) between heat-cured material and 3D specimens post-cured for 20 min in term of flexural strength/modulus, surface hardness, and degree of conversion at the two-storage time points.

SIGNIFICANCE

Generally, the physico-mechanical properties of the 3D-printed denture base material improve as post curing time increases up to 20 min which exhibited comparable performance as the conventional heat-cured control.

Influence of Reinforcing Agents on the Mechanical Properties of Denture Base Resin: A Systematic Review

Knowledge about the influence of fillers in denture base resin is vague. This systematic review aimed to report the reinforcing effect of fillers on the mechanical properties of denture base resin by following PRISMA guidelines. Two electronic databases (Pubmed/Medline & Web of Science) were searched for articles using the keywords: fibers in denture base, fillers in denture base, and reinforcement of denture base. Laboratory studies complying with the inclusion criteria were reviewed according to the set protocol. The established focus question was: "Do reinforcing fillers positively influence the mechanical properties of polymethyl methacrylate (PMMA) heat polymerized denture base material?" A total of twenty-nine relevant papers qualified for final inclusion. Of these, 24 were determined to have a moderate risk of bias. Micron or nano-sized metal/metal oxides particles and glass fibers were the frequently used reinforcing agents. The trend of evaluating fractural strength (FS) was common. Most of the studies limited the use of reinforcing agents up to 5 wt.%. FS, fracture toughness (FT), and impact strength (IS) tend to increase if the fillers are chemically bonded and well-dispersed in denture base resin. Though fillers with a higher elastic modulus increase the hardness of the reinforced denture base resin, they compromise other mechanical properties. Well-dispersed lower filler loading PMMA denture base resin can enhance the FS, FT, and other related mechanical properties.

Computer-assisted implant placement and full-arch immediate loading with digitally prefabricated provisional prostheses without cast: a prospective pilot cohort study

BACKGROUND

Immediate loading of implant-supported full-arch rehabilitations has become routine practice when treating edentulous patients. The combination of static computer-aided implant surgery (s-CAIS) and digital prosthetic workflow could eliminate several treatment steps and facilitate prostheses delivery. The aim of this study is to evaluate the 1-year results of digitally prefabricated polymethyl methacrylate (PMMA) provisional prostheses without a cast for full-arch computer-assisted immediate loading.

MATERIALS AND METHODS

A digital pre-operative treatment planning was realized for all patients: dental implants and screw-retained abutments were selected in the planning software and two surgical templates were fabricated for each patient. The first template was mucosa or teeth-supported to drill the holes for fixating pins, while the second template was placed after raising a full-thickness flap and was supported by pins as well as soft or hard tissue distal support. Furthermore, based on the surgical planning, interim prostheses were digitally designed and milled of PMMA resin blocks with subsequent pink resin veneering. Osteotomies and implant placement were performed through the surgical guides and all implants were immediately loaded with prefabricated full-arch interim prostheses directly connected to titanium copings with a flowable resin.

RESULTS

A total of 55 dental implants were placed in ten patients. In all cases, interim prostheses allowed the insertion of titanium copings without the need of access hole enlargement or adaptation. All the prostheses had 1 year of functional loading to simulate the long provisional phase. No screw loosening occurred at the first removal of the prostheses after implant osseointegration. No fracture occurred during the whole period. After 1 year, the mean marginal bone loss level was 0.37 ± 0.06 mm, while the implant survival rate was 98.18% (n=54/55), with just one implant failing but not affecting final prosthesis delivery to the patient.

CONCLUSIONS

Within the limitations of the present study, the authors concluded that digitally prefabricated provisional prostheses for full-arch immediate loading with s-CAIS could be a valid alternative treatment modality. Milled PMMA restorations proved to be durable enough during the long provisional phase, without prosthetic complications.

CAD-CAM complete denture resins: an evaluation of biocompatibility, mechanical properties, and surface characteristics

OBJECTIVES

This study evaluated the biocompatibility, mechanical properties, and surface roughness of CAD-CAM milled and rapidly-prototyped/3D-printed resins used for manufacturing complete dentures.

METHODS

Six groups of resin specimens were prepared, milled-base (MB), milled-tooth shade (MT), printed-tooth shade (PT), printed-base with manufacturer-recommended 3D-printer (PB1), printed-base with third-party 3D-printer (PB2), printed-base in a vertical orientation (PB2V). Human epithelial (A-431) and gingival (HGF-1) cells were cultured and tested for biocompatibility using Resazurin assays. Three-point bending and nanoindentation tests measured the mechanical properties of the resin groups. Surface roughness was evaluated using a high-resolution laser profilometer. ANOVA and post-hoc tests were used for statistical analyses (α = 0.05).

RESULTS

There were no significant differences in biocompatibility between any of the investigated groups. MB revealed a higher ultimate strength (p = 0.008), elastic modulus (p = 0.002), and toughness (p = 0.014) than PB1. MT had significantly higher elastic modulus than PT (p < 0.001). Rapidly-prototyped resin samples with a manufacturer-recommended 3D-printer (PB1) demonstrated higher ultimate strength (p = 0.008), elastic modulus (p < 0.001), hardness (p < 0.001) and a reduced surface roughness (p < 0.05) when compared with rapidly-prototyped groups using a third-party 3D-printer (PB2). Rapidly-prototyped samples manufactured with a vertical printing orientation (PB2V) revealed a significantly lower elastic modulus than samples groups manufactured using horizontal printing orientation (PB2) (p = 0.011).

CONCLUSIONS

Within the limits of this present study, CAD-CAM milled and rapidly-prototyped complete denture resins performed similarly in terms of biocompatibility and surface roughness. However, the milled denture resins were superior to the rapidly-prototyped denture resins with regard to their mechanical properties. Printing orientation and type of 3D-printer can affect the resin strength and surface roughness.

CAD-CAM removable complete dentures: A systematic review and meta-analysis of trueness of fit, biocompatibility, mechanical properties, surface characteristics, color stability, time-cost analysis, clinical and patient-reported outcomes

OBJECTIVES

This review compared Computer-aided designand Computer-aided manufactured (CAD-CAM) and conventionally constructed removable complete dentures (CDs).

DATA

Seventy-three studies reporting on CAD-CAM (milled/3D-printed) CDs were included in this review. The most recent literature search was performed on 15/03/2021.

SOURCES

Two investigators searched electronic databases [PubMed (MEDLINE), Embase, CENTRAL], online search engines (Google) and research portals. Hand searches were performed to identify literature not available online.

STUDY SELECTION

Studies on CAD-CAM CDs were included if they reported on trueness of fit, biocompatibility, mechanical, surface, chemical, color , microbiological properties, time-cost analysis, and clinical outcomes. Inter-investigator reliability was assessed using kappa scores. Meta-analyses were performed on the extracted data .

RESULTS

The kappa score ranged between 0.897-1.000. Meta-analyses revealed that 3D-printed CDs were more true than conventional CDs (p = 0.039). Milled CDs had a higher flexural-strength than conventional and 3D-printed CDs (p < 0.0001). Milled CDs had a higher flexural-modulus than 3D-printed CDs (p < 0.0001). Milled CDs had a higher yield-strength than injection-molded (p = 0.004), and 3D-printed CDs (p = 0.001). Milled CDs had superior toughness (p < 0.0001) and surface roughness characteristics (p < 0.0001) than other CDs . Rapidly-prototyped CDs displayed poor color-stability compared to other CDs (p = 0.029). CAD-CAM CDs d displayed better retention than conventional CDs (p = 0.015). Conventional CDs had a higher strain at yield point than milled CDs (p < 0.0001), and had superior esthetics than 3D-printed (p < 0.0001). Fabrication of CAD-CAM CDs required less chairside time (p = 0.037) and lower overall costs (p < 0.0001) than conventional CDs.

CONCLUSIONS

This systematic review concludes that CAD-CAM CDs offer a number of improved mechanical/surface properties and are not inferior when compared to conventional CDs.

CLINICAL SIGNIFICANCE

CAD-CAM CDs should be considered for completely edentulous patients whenever possible, since this technique offers numerous advantages including better retention, mechanical and surface properties but most importantly preserves a digital record. This can be a great advantage for older adults with limited access to dental care.

Comparison of CAD/CAM and Conventional Denture Base Resins: A Systematic Review

At present, complete dentures (CDs) remain the only treatment available for the majority of edentulous patients. CDs are primarily fabricated using a conventional method using polymethylmethacrylate (PMMA) resin. The steps involved in PMMA polymerisation directly affect the quality of the resin prosthetic base and any error reduces retention and occlusal accuracy of CDs. Furthermore, when using the conventional technique, the residual monomer alters the resin mechanical properties and may cause mucosal reactions. Recently, computer aided design and computer aided manufacture (CAD/CAM) techniques were increasingly used to fabricate CDs by machining resin discs that have been manufactured under high pressure and temperature. This systematic review compares CAD/CAM and conventional CDs according to their mechanical, physical and chemical characteristics, as well as the clinical impact of any differences between them. A review was conducted according to the preferred reporting items for systematic reviews and meta-analyses checklist on 392 publications from both PubMed and backward research. Fifteen studies have been included. Results showed that CAD/CAM resins had globally better physical and mechanical properties than conventional resins. The use of machined resin could improve the clinical performance, maintenance and longevity of CDs. Further studies in clinical use would be required to complement these results.

Properties of Acrylic Resin For CAD/CAM: A Systematic Review and Meta-Analysis of In Vitro Studies

PURPOSE

This systematic review and meta-analysis of in vitro studies compared the prepolymerized acrylic resin used for CAD/CAM complete denture manufacturing versus the heat-polymerized acrylic resin for conventional complete dentures in terms of surface roughness, wettability, hardness and flexural strength.

MATERIALS AND METHODS

An electronic search was performed in the PubMed, Embase, LILACS and Web of Science databases, without language or date restrictions. Gray literature and manual search tools were also used. The systematic review was carried out by two researchers independently, following the inclusion criteria: in vitro studies testing the CAD/CAM acrylic resin with a control group of heat-polymerized acrylic resin which compared at least one of the four material properties above. The meta-analysis was performed separately for each property, using a random effect model.

RESULTS

Of the 914 studies found by means of search strategies, 698 were selected for the systematic review. After applying the eligibility criteria, only 17 articles were selected for the qualitative analysis in the systematic review; among these, 14 were included in the quantitative meta-analysis. The CAD/CAM prepolymerized acrylic resin in blocks had similar properties when compared to heat-polymerized acrylic resin in almost all outcome measures, with the exception of a statistically significant reduction in surface roughness.

CONCLUSIONS

Based on the findings of this systematic review and meta-analysis, equally satisfactory results can be expected from dental prosthesis manufactured by the CAD/CAM system when compared to conventional ones, with the additional potential of reducing the pigmentation and attached microorganisms due to the reduced surface roughness of the prepolymerized resin.

Mechanical properties of polymethyl methacrylate as a denture base: Conventional versus CAD-CAM resin - A systematic review and meta-analysis of in vitro studies

STATEMENT OF PROBLEM

The development of polymethyl methacrylate (PMMA) computer-aided design and computer-aided manufacturing (CAD-CAM) resin blocks with reported improved mechanical properties has simplified complete denture production. However, whether the objective of improved mechanical properties has been achieved compared with conventional heat-polymerized PMMA is not yet clear.

PURPOSE

The purpose of this systematic review and meta-analysis was to evaluate the mechanical properties of denture base resins manufactured by conventional heat-polymerization and by CAD-CAM in terms of flexural strength, flexural modulus, and surface roughness.

MATERIAL AND METHODS

Electronic databases (PubMed/MEDLINE, Scopus, Web of Science) were independently searched by 2 researchers for relevant studies published up to November 2020. The population, intervention, comparison, and outcome (PICO) question was, "Does the conventionally manufactured, heat-polymerized PMMA resin, as a denture base, demonstrate the same mechanical properties as the CAD-CAM resin block?" In addition, a meta-analysis was based on the inverse variance method. Flexural strength, flexural modulus, and surface roughness were analyzed through the continuous outcome evaluated by mean difference and standard deviation, with 95% confidence intervals. To evaluated heterogeneity, the I² value (≤25%=low, ≥50%=moderate and ≥75%=high) and the P value were considered. P<.10 indicated statistical difference for heterogeneity. The effects of meta-analysis were based on the results of heterogeneity as per the studies.

RESULTS

Thirteen in vitro studies were included in the analysis. A total of 507 specimens were evaluated, 222 conventional and 285 CAD-CAM. In terms of flexural strength, the data showed no significant difference when conventional heat-polymerized PMMA was compared with CAD-CAM PMMA resins (P=.06; mean difference=18.28; 95% confidence interval:-0.42 to 36.97). In terms of flexural modulus, there was a significant difference for the CAD-CAM PMMA group (P=.01; mean difference=589.22; 95% confidence interval: 117.95 to 1060.48). In terms of surface roughness, a significant difference was observed between the groups (P=.02; mean difference=-0.53; 95% confidence interval: -0.97 to -0.09) with the conventional heat-polymerized PMMA resin having higher surface roughness values.

CONCLUSIONS

The mechanical properties of CAD-CAM PMMA resins were generally improved when compared with heat-polymerized polymethyl methacrylate resin.

A systematic review of digital removable partial dentures. Part II: CAD/CAM framework, artificial teeth, and denture base

PURPOSE

This study comprehensively reviewed the current status of the digital workflow of removable partial dentures (RPDs) and summarized information about the fabrication methods and material properties of the dental framework, artificial teeth, and denture base.

STUDY SELECTION

We performed a systematic review of the literature published in online databases from January 1980 to April 2020 regarding RPD fabrication and materials used in the related digital technology. We selected eligible articles, retrieved information regarding digital RPDs, and conducted qualitative/quantitative analyses. In this paper, the computer-aided design/computer-aided manufacturing (CAD/CAM) framework, artificial teeth, and denture base materials are reported.

RESULTS

A variety of materials, such as cobalt-chromium alloy, titanium, zirconia, and polyether ether ketone, are used for dental CAD/CAM frameworks. The mechanical strength of the metal materials used for the CAD/CAM framework was superior to that of the cast framework. However, the fitness and surface roughness of the framework and clasp fabricated using a selective laser melting (SLM) method were not superior to those obtained via cast fabrication. Most material properties and the surface roughness of poly methyl methacrylate (PMMA) discs used for digital RPDs were superior to those of heat-cured PMMA.

CONCLUSIONS

The use of a CAD/CAM framework and PMMA disc for digital RPDs offers numerous advantages over conventional RPDs. However, technical challenges regarding the accuracy and durability of adhesion between the framework and denture base remain to be solved. In digital fabrication, human technical factors influence the quality of the framework.

A Review of 3D Printing in Dentistry: Technologies, Affecting Factors, and Applications

Three-dimensional (3D) printing technologies are advanced manufacturing technologies based on computer-aided design digital models to create personalized 3D objects automatically. They have been widely used in the industry, design, engineering, and manufacturing fields for nearly 30 years. Three-dimensional printing has many advantages in process engineering, with applications in dentistry ranging from the field of prosthodontics, oral and maxillofacial surgery, and oral implantology to orthodontics, endodontics, and periodontology. This review provides a practical and scientific overview of 3D printing technologies. First, it introduces current 3D printing technologies, including powder bed fusion, photopolymerization molding, and fused deposition modeling. Additionally, it introduces various factors affecting 3D printing metrics, such as mechanical properties and accuracy. The final section presents a summary of the clinical applications of 3D printing in dentistry, including manufacturing working models and main applications in the fields of prosthodontics, oral and maxillofacial surgery, and oral implantology. The 3D printing technologies have the advantages of high material utilization and the ability to manufacture a single complex geometry; nevertheless, they have the disadvantages of high cost and time-consuming postprocessing. The development of new materials and technologies will be the future trend of 3D printing in dentistry, and there is no denying that 3D printing will have a bright future.

3D printed complete removable dental prostheses: a narrative review

Background

The purpose of this paper is to review the available literature on three-dimensionally printed complete dentures in terms of novel biomaterials, fabrication techniques and workflow, clinical performance and patient satisfaction.

Methods

The methodology included applying a search strategy, defining inclusion and exclusion criteria, selecting studies and forming tables to summarize the results. Searches of PubMed, Scopus, and Embase databases were performed independently by two reviewers to gather literature published between 2010 and 2020.

Results

A total of 126 titles were obtained from the electronic database, and the application of exclusion criteria resulted in the identification of 21 articles pertaining to printed technology for complete dentures. Current innovations and developments in digital dentistry have successfully led to the fabrication of removable dental prostheses using CAD/CAM technologies. Milled dentures have been studied more than 3D printed ones in the currently available literature. The limited number of clinical studies, mainly case reports, suggest current indications of 3D printing in denture fabrication process to be custom tray, record bases, trial, interim or immediate dentures but not definitive prostheses fabrication. Limitations include poor esthetics and retention, inability to balance occlusion and low printer resolution.

Conclusions

Initial studies on digital dentures have shown promising short-term clinical performance, positive patient-related results and reasonable cost-effectiveness. 3D printing has potential to modernize and streamline the denture fabrication techniques, materials and workflows. However, more research is required on the existing and developing materials and printers to allow for advancement and increase its application in removable prosthodontics.

Effect of toothbrush/dentifrice abrasion on weight variation, surface roughness, surface morphology and hardness of conventional and CAD/CAM denture base materials

We evaluated the effect of toothbrush/dentifrice brushing on the weight variation and surface properties of different denture bases. Four denture base materials (conventional heat cure, high impact, CAD/CAM, and polyamide resins) were subjected to toothbrushing abrasion (50,000 strokes). The weight value, surface roughness, and topography of each group were determined before and after toothbrushing. The hardness was measured by the Vickers hardness test. Data were analyzed using ANOVA and Bonferroni tests. After toothbrushing, the weight of the polyamide resin had significantly increased; significant weight losses were observed for conventional heat cure and high impact resins, but none for the CAD/CAM resin. The surface roughness of each group increased significantly owing to the wear caused by toothbrushing. The weight variation and surface roughness were not affected by the hardness. Our results suggested that denture base materials deteriorate after brushing with toothpaste, in which the polyamide resin exhibited lower levels of abrasion.

The role of polymeric nanofibers on the mechanical behavior of polymethyl methacrylate resin

This study aimed to synthesize and characterize non-woven acrylonitrile butadiene styrene (ABS), polyamide-6 (P6), and polystyrene (PS) nanofibers, and evaluate their effects on the flexural strength and fracture resistance of fiber-modified polymethyl methacrylate (PMMA) resin. ABS, P6, and PS polymer solutions were prepared and electrospun into fiber mats, which were characterized by means of morphological, chemical, physical, and mechanical analyses. The fiber mats were then used to modify a thermally-activated PMMA resin, resulting in four testing groups: one unmodified group (control) and three fiber-modified groups incorporated with ABS, P6, or PS fiber mats. Flexural strength, work of fracture, and fractographic analysis were performed for all groups. Data were analyzed using Kruskal-Wallis or ANOVA tests (α = 0.05). The fiber diameter decreased, respectively, as follows: ABS > P6 > PS. Only the P6 fiber mats demonstrated a crystalline structure. Wettability was similar among the distinct fiber mats, although tensile strength was significantly greater for P6, followed by ABS, and then PS mats. Flexural strength of the fiber-modified PMMA resins was similar to the control, except for the weaker P6-based material. The work of fracture seemed to be greater and lower when the P6 and PS fibers were used, respectively. The fiber-modified groups exhibited a rougher pattern in the fractured surfaces when compared to the control, which may suggest that the presence of fibers deviates the direction of crack propagation, making the fracture mechanism of the PMMA resin more dynamic. While the neat PMMA showed a typical brittle response, the fiber-modified PMMA resins demonstrated a ductile response, combined with voids, suggesting large shear deformation during fracture. Altogether, despite the lack of direct reinforcement in the mechanical strength of the PMMA resin, the use of electrospun fibers showed promising application for the improvement of fracture behavior of PMMA resins, turning them into more compliant materials, although this effect may depend on the fiber composition.