Comparison of Low and High Temperature Sintering for Processing of Bovine Bone as Block Grafts for Oral Use: A Biological and Mechanical In Vitro Study.

Large oral bone defects require grafting of bone blocks rather than granules to give physically robust, biocompatible and osteoconductive regeneration. Bovine bone is widely accepted as a source of clinically appropriate xenograft material. However, the manufacturing process often results in both reduced mechanical strength and biological compatibility. The aim of this study was to assess bovine bone blocks at different sintering temperatures and measure the effects on mechanical properties and biocompatibility. Bone blocks were divided into four groups; Group 1: Control (Untreated); Group 2: Initial boil for 6 h; Group 3: Boil 6 h followed by sintering at 550 °C for 6 h; Group 4: Boil 6 h followed by sintering at 1100 °C for 6 h. Samples were assessed for their purity, crystallinity, mechanical strength, surface morphology, chemical composition, biocompatibility and clinical handling properties. Statistical analysis was performed using one-way ANOVA and post-hoc Tukey's tests for normally distributed and Friedman test for abnormally distributed quantitative data from compression tests and PrestoBlue™ metabolic activity tests. The threshold for statistical significance was set at p < 0.05. The results showed that higher temperature sintering (Group 4) removed all organic material (0.02% organic components and 0.02% residual organic components remained) and increased crystallinity (95.33%) compared to Groups 1-3. All test groups (Group 2-4) showed decreased mechanical strength (MPa: 4.21 ± 1.97, 3.07 ± 1.21, 5.14 ± 1.86, respectively) compared with raw bone (Group 1) (MPa: 23.22 ± 5.24, p <0.05), with micro-cracks seen under SEM in Groups 3 and 4. Group 4 had the highest biocompatibility (p < 0.05) with osteoblasts as compared to Group 3 at all time points in vitro. Clinical handling tests indicated that Group 4 samples could better withstand drilling and screw placement but still demonstrated brittleness compared to Group 1. Hence, bovine bone blocks sintered at 1100 °C for 6 h resulted in highly pure bone with acceptable mechanical strength and clinical handling, suggesting it is a viable option as a block grafting material.

Different Undercut Depths Influence on Fatigue Behavior and Retentive Force of Removable Partial Denture Clasp Materials: A Systematic Review.

PURPOSE: To perform a systematic review that provides an overview of the current literature on fatigue behavior of removable partial denture (RPD) clasp materials based on different retentive areas. MATERIALS AND METHODS: The review followed the Preferred Reporting Items for Systematic Review and Meta-Analyses (PRISMA) guidelines. Electronic searches were done via PubMed, Scopus, and OVID for studies reporting on RPD clasps and the fatigue failure of clasp materials. Inclusion criteria were English language with full text and in vitro studies only. Exclusion criteria were studies that did not assess the fatigue of RPD clasp materials. A quality assessment and selection of full-text articles were performed according to Consolidated Standards of Reporting Trials criteria. RESULTS: A total of 182 articles were initially identified and screened. After applying inclusion and exclusion criteria, 15 articles were selected for the final analysis. Seven of the included studies utilized a vertical insertion/removal testing approach. Ten studies used the constant deflection test. Three studies used untapered specimens, and 12 studies used tapered specimens. Ten studies performed post-test analysis. CONCLUSIONS: Cobalt-chromium (CoCr) is the strongest material in terms of fatigue in relation to the undercut depth and the modern, digitally manufactured RPD clasp materials also exhibit comparable fatigue behavior. Recent RPD clasp materials such as polyetheretherketone (PEEK) or laser sintered CoCr, however, require further study in terms of their fatigue behavior. In order to improve the quality of future studies, a standardized and calibrated fatigue testing method is needed with standardized specimen size and shape, which will reduce the risk of bias and enable meta-analysis for bulk comparison between studies.

Effect of thermocycling on the mechanical properties, inorganic particle release and low temperature degradation of glazed high translucent monolithic 3Y-TZP dental restorations.

The influence of thermocycling on the surface deterioration of glazed monolithic high translucent 3Y-TZP dental restorations is still unclear. The purpose of this study therefore was to evaluate low temperature degradation (LTD), elemental release and surface degradation pattern after five years of simulated clinical time. A total of 123 specimens were prepared from second-generation high translucent 3Y-TZP as per ISO 6872:2015 standards (3 mm × 4 mm × 30 mm). They were classified as per glazing and thermocycling protocol; group CPT, DGT and IGT. Glaze materials were applied on one surface of the specimen and subjected to a thermocycling in artificial saliva, four-point bending test, inductively coupled plasma mass spectrometry (ICP-MS), scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDX) and x-ray diffraction (XRD). Flexural strength, characteristic strength and Weibull modulus values were derived from four-point bending test. Descriptive fractographic analysis of surfaces was conducted to observe the surface degradation characteristics and point of failure. Control/no glaze with thermocycling (CPT = 621.5, 1σ = 117.0 MPa) presented higher flexural strength values compared to glaze I with thermocycling (442.4, 1σ = 45.4 MPa) and glaze II with thermocycling (534.3, 1σ = 46.3 MPa). Characteristic strength from Weibull analysis also observed higher values (669.2 MPa) for the control specimens. XRD analysis showed that monoclinic volume fraction (Vm = 11.0, 1σ = 0.7%) was highest in control specimens. Fractographic analysis suggested that there was no correlation between the point of failure initiation and mean flexural strength values. Glazing protected the high translucent 3Y-TZP surface against LTD during thermocycling but negatively impacted on the flexural strength.

The Effect of Low-Processing Temperature on the Physicochemical and Mechanical Properties of Bovine Hydroxyapatite Bone Substitutes.

Bovine bone grafts (BBX) require protein removal as part of the manufacturing process to reduce antigenicity and, in consequence, to be safely used in humans. Deproteinisation may have direct effects on the characteristics of the bone material and on in vivo material performance. This research aimed to comprehensively study the physicochemical and mechanical properties of BBX processed at low deproteinisation processing temperatures. Cubes of bovine bone (8 mm3) were treated with temperatures between 100 °C and 220 °C at 30 °C intervals and with pressures ranging from 1.01 to 24.58 Bar. The samples were characterised topographically and mechanically using scanning electron microscopy (SEM), atomic force microscopy (AFM), and uniaxial bending tests. The organic content and the chemical composition were determined using thermogravimetric analysis (TGA) and Fourier-transform infrared spectroscopy (FTIR). X-ray diffraction (XRD) and FTIR were also used to quantitatively determine the specimen crystallinity. Increasing temperature/pressure was associated with decreasing protein levels and compressive strength and increasing surface irregularities and crystallinity. The findings suggest that low-temperature processed bone is likely to exhibit a rapid in vivo degradation rate. The deproteinisation temperature can be adjusted to tailor the graft properties for specific applications.

Evaluation of wear behaviour of various occlusal splint materials and manufacturing processes.

OBJECTIVES: To investigate the volumetric and vertical loss of occlusal splints manufactured by conventional (heat-cure), subtractive (CAD/CAM) and additive (3D-printing) methods. METHODS: Six occlusal splint materials were investigated (n = 126), using three manufacturing methods: heat-cured, CAD/CAM and 3D-printed built-in three different printing angles (0°,45°and 90°). Block-on-ring wear testing was performed with extracted human molars as the antagonist. All samples were tested with an applied force of 49N at 1 Hz and 60RPM in artificial saliva at 37 °C for six and 12 months. Scanning electron microscopy images were analysed to evaluate the wear on the tooth enamel and in the splint material. Volumetric and vertical wear loss were statistically analysed. RESULTS: The lowest volumetric and vertical loss was observed in CAD-CAM materials (6.44 ± 1.77 mm3 and 48.3 ± 7.14 µm) with no statistical significance to the heat-cured material (17.22 ± 9.23 mm3 and 148 ± 121.1 µm) after 12 months (p < 0.172). The mean volumetric loss of 3D printed materials ranged from 0.25 ± 0.15 mm3 to 0.29 ± 0.1 4mm3 with no statistical difference, whereas, the differences in vertical loss from 131.63 ± 44.1 µm to 493 ± 79.19 µm were statistically significant (p < 0.001). The highest vertical loss was observed in the KeySplint Soft 3D printed at 90° (385.35 ± 82.37 µm), whereas FreePrint Splint 2.0 with a build angle of 0° had the highest volumetric loss (204.59 ± 25.67 mm3). CONCLUSION: CAD-CAM material had the highest wear resistance followed by heat-cured material.KeySplint Soft and FreePrint Splint 2.0 3D printed materials would be preferred for patients that do not have severe bruxing episodes. No significant wear of human enamel after six and 12 months was observed under SEM for any tested materials.

Optical and mechanical properties of conventional, milled and 3D-printed denture teeth.

OBJECTIVES: Investigate the effect of various liquids on the optical properties and Vickers hardness of conventional, milled and 3D-printed denture teeth. METHODS: Six different types of denture teeth (Maxillary anteriors of three different conventional teeth, Vivodent DCL, SR Phonares II, Vita Physiodens; milled teeth, IvotionDent; and two different 3D-printed teeth, Asiga DentaTooth and NextDent C&B MFH) were investigated (total n = 336). The labial surface of each specimen was prepared to a dimension of 10 × 5 × 3mm. Specimens were immersed in artificial saliva, coffee, red wine and denture cleaner with artificial aging to simulate denture use of 12 and 24 months in vivo. Measurements of translucency parameter (TP), shade change (ΔE), surface roughness (Ra) and Vickers hardness (VHN) were conducted at baseline and after artificial aging while immersed in the liquids at each timeframe. Data were statistically analysed by ANOVA and post-hoc test (SPSS Ver 27). Surfaces of specimens were analysed under scanning electron microscopy (SEM). RESULTS: Milled teeth had the highest overall translucency parameter (5.33 ± 0.76-7.3 ± 0.99). All materials had statistically significant change in translucency parameter and shade after 24 months simulated aging (p < 0.05), especially the milled and 3D-printed teeth (p < 0.01). Surface roughness of all materials were under plaque accumulation threshold Ra = 0.2 µm. At baseline, Vita Physiodens teeth (PMMA with microfillers) demonstrated the highest hardness (33.99 kgf/mm2±3.7), whereas both 3D-printed materials exhibited the lowest hardness (13.27 kgf/mm2±0.36-18.13 kgf/mm2±0.93). Artificial saliva, red wine and denture cleaner had a statistically significant impact (p < 0.05) on hardness of all materials (12.1 kgf/mm2±1.17-30.77 kgf/mm2±2.98). CONCLUSIONS: Milled teeth exhibited the best optical properties (highest overall translucency parameter and lowest shade change). Milled teeth were also the only material that showed colour change (ΔE values) within clinically acceptable limits. Denture cleaner had the most impact on optical and mechanical properties of all materials. Surface roughness and hardness of 3D-printed teeth had the most change after artificial aging.

Optical Properties and Color Stability of Denture Teeth-A Systematic Review.

PURPOSE: To systematically review past studies to determine the effect of various solutions on the color of denture teeth, thus answering the question in regards to which type of denture teeth has the best optical properties after exposure to various solutions. The method of measuring the color of artificial teeth was also evaluated as a secondary outcome. MATERIALS AND METHODS: A search of studies that quantitatively investigated the influence of immersion solutions on the color change of denture teeth was conducted. Ovid MEDLINE, PubMed and Scopus databases were searched from 1997 to April 2021. The Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines were used during article selection. Data regarding the effect of immersion solutions, accelerated aging and surface treatments on color change were gathered. Methodologies used to assess optical properties were also summarized and compared. The modified CONSORT checklist was used to determine the risk of bias of past studied included in this review. RESULTS: One hundred thirty-three studies were identified after removing duplicates. Forty-one studies were selected for full-text analysis, and 35 remaining papers met the inclusion criteria and were therefore included in this systematic review. Thirty-two in vitro studies and 3 in vivo studies were included in the review. All studies reported that immersion in various solutions has a significant influence on the change in color and optical properties of denture teeth. However, the discoloration of denture teeth is still clinically acceptable in most studies. Exposure to various solutions also affected the translucency parameter of denture teeth. Most studies also investigated the surface roughness and hardness along with the optical properties, and reported that immersion cycles did not cause changes in surface roughness of denture teeth, while hardness was affected. The optical properties of PMMA denture teeth have been studied extensively, whereas that of CAD/CAM and 3D printed denture teeth is limited. CONCLUSIONS: Color stability of CAD/CAM milled denture teeth is comparable to conventional PMMA denture teeth. There are contradictory findings in terms of color stability of 3D printed denture teeth as compared to conventional PMMA denture teeth. Staining by coffee is worst among the common beverages and solutions investigated. Denture teeth can show color changes after immersion in staining beverages as early as one week. The degree of discoloration of denture teeth after immersion is time dependent, with the larger extent in the initial phase.

Effect of Two Brands of Glaze Material on the Flexural Strength and Probability of Failure of High Translucent Monolithic Zirconia.

(1) Background: The effect of glazing on the mechanical properties of monolithic high translucent zirconia is not well reported. Therefore, the purpose of this study was to evaluate the effect of glazing on the flexural strength of high translucent zirconia; (2) Methods: Ninety specimens were prepared from second-generation 3Y-TZP high translucent blocks and divided into three groups. Glaze materials were applied on one surface of the specimen and subjected to a four-point bending test and flexural stress and flexural displacement values were derived. Descriptive fractographic analysis of surfaces was conducted to observe the point of failure and fracture pattern.; (3) Results: Control-nonglazed (647.17, 1σ = 74.71 MPa) presented higher flexural strength values compared to glaze I (541.20, 1σ = 82.91 MPa) and glaze II (581.10, 1σ = 59.41 MPa). Characteristic strength (σƟ) from Weibull analysis also observed higher (660.67 MPa) values for the control specimens. Confocal microscopy revealed that glazed surfaces were much rougher than control surfaces. Descriptive fractographic analysis revealed that there was no correlation between the point of failure initiation and flexural strength; (4) Conclusions: The test results demonstrated that glazing significantly decreased the flexural strength and flexural displacement of the zirconia specimens.

The effect of light curing intensity on bulk-fill composite resins: heat generation and chemomechanical properties.

OBJECTIVES: The aim of this study was to assess the effect of light curing intensity and wavelength spectrum on heat generation and chemomechanical properties of bulk-fill composites. METHODS: Four bulk-fill restorative materials (Filtek bulk-fill, Tetric PowerFill bulk-fill, Beautifil Bulk restorative and Admira Fusion X-tra were used in this study. A total of 100 cylindrical specimens of each composite (n = 25/group) were prepared, then cured using monowave light curing unit (LCU) with a single light intensity of 1470 mW/cm2, and polywave LCU with three different light intensities (1200,2100, 3050mW/cm2). The temperature change during polymerisation was measured by five K-type thermocouples placed in each 1 mm layer from top to bottom. Hardness and degree of conversion of composites at each level were evaluated. Results were statistically analysed. RESULTS: The use of polywave LCU resulted in statistically higher peak temperatures ranging between 31.4-63.5 °C compared to the temperature generated by monowave LCU ranging between 29.5-60 °C (p < .05). Curing using polywave LCU with the highest light intensity of 3050 mW/cm2 caused the highest peak temperature irrespective of the composite types. There was no significant difference in hardness with different light curing intensities and curing times, regardless of the bulk-fill resin materials (p > .05). A positive correlation was also found between the hardness and the DoC of the four bulk-fill composites. CONCLUSION: The change in temperature during polymerisation of bulk-fill composites were found to be proportional to the increase in light curing intensity. Mechanical properties of the bulk-fill composites were dependent on the composition and the type of photoinitiators.

Fibre-reinforced and repaired PMMA denture base resin: Effect of placement on the flexural strength and load-bearing capacity.

OBJECTIVES: To measure the effect of placement of glass fibre mesh on the flexural strength and load bearing capacity of repaired polymethylmethacrylate (PMMA) denture base resin. MATERIALS AND METHODS: A total of 150 heat-polymerised acrylic resin specimens were fabricated with dimensions of 5 × 30 × 50 mm for flexural strength testing. Specimens were divided into 5 groups according to repair width and placement of the fibre mesh. Three groups (n = 90) had a repair width of 20 mm (including the control group), and two groups (n = 60) had a narrower repair width of 16 mm. Fibre mesh was either embedded at the neutral (bottom of the repair area) or tension (top of the repair area) zone of the specimen when subjected to flexural strength testing. Half of the specimens from each group were subjected to artificial ageing by thermocycling (5 °C and 55 °C, 30s dwell time) for 10,000 cycles to stimulate 12 months in vivo. All the specimens were stored in distilled water at 37 °C for 24 h prior to testing. The flexural strength of the specimen was obtained by three-point bend testing, and data were statistically analysed using ANOVA and post-hoc analysis (SPSS; significance level p < 0.05). Probability of failure was calculated using Weibull analysis. Scanning electron microscopy analysis was used to identify the mode of failure. RESULTS: Specimens repaired with the 20 mm fibre mesh placed in the tension zone showed the highest mean flexural strength (101.33 ± 12.66 MPa) with statistical significance (p = 0.05) to the other groups except for the specimens repaired with the 16 mm fibre mesh placed in the tension zone (p = 0.072). The highest Weibull modulus was found in the thermal cycling group of the specimens with 20 mm repair width repaired with the fibre mesh embedded at the neutral zone (10.01). The lowest Weibull modulus was found in the non-thermal cycling group of the control group (3.15). CONCLUSION: Placing fibre mesh in the tension zone of a PMMA specimen significantly improved the flexural strength of the repair. Placing the fibre mesh in the neutral zone or the fibre mesh width was short of the lower support rollers resulted in no significant increase in flexural strength compared to the non-reinforced control group. Ageing via thermal cycling resulted in a decrease in flexural strength across all sample groups. This study highlights the importance of recognising the valid repair region and to have the mesh embedded in certain dimensions, otherwise it will have no significant contribution towards the repair and increase of flexural strength of the denture.

Real-time in vitro measurement of denture-mucosa pressure distribution in a typical edentulous patient with and without implants: Development of a methodology.

PURPOSE: To measure the pressure distribution on the oral mucosa in vitro by comparing the pressure distributions under a complete denture and that of an implant overdenture. MATERIALS AND METHOD: Anatomically accurate models and conventional Class I complete denture (CD) were produced and subjected to cyclic loading using a 100 N vertical centric and unilateral masticatory load with the universal testing machine (Instron 3369). Four miniature pressure sensors were positioned at four different locations in the intaglio surface of the denture and recorded pressure at 100 Hz frequency measured during a 10-cycle load at 1 Hz. Testing was repeated in different clinical combinations; CD vs. single implant overdentures (1-IOD), CD vs. two, three and four implant overdentures (2-IOD, 3-IOD vs. 4-IOD). The pressure profile (kPa) of complete dentures were measured and compared to the implant overdenture combinations. Collected data was statically analysed using SPSS and one-way analysis of variance. RESULTS: The highest mean pressure was observed in CD group, with the mean mandible buccal ridge pressure value of 212.82 kPa ± 136.9 due to its surface area. There were no statistically significant differences between the group combinations (p = 0.146) but between various locations in the mean pressure recorded across the five denture/overdenture combinations. CONCLUSION: CD experienced large pressure values on mandibular denture. 1-IOD demonstrated the most pressure in comparison to CD where with an increase in the number of implants used, it transformed the denture from being pure-borne mucosa to an implant overdenture, providing support and distributing the pressure amongst the implants.

Topographical mapping of the mechanical characteristics of the human neurocranium considering the role of individual layers.

The site-dependent load-deformation behavior of the human neurocranium and the load dissipation within the three-layered composite is not well understood. This study mechanically investigated 257 human frontal, temporal, parietal and occipital neurocranial bone samples at an age range of 2 to 94 years, using three-point bending tests. Samples were tested as full-thickness three-layered composites, as well as separated with both diploë attached and removed. Right temporal samples were the thinnest samples of all tested regions (median < 5 mm; p < 0.001) and withstood lowest failure loads (median < 762 N; p < 0.001). Outer tables were thicker and showed higher failure loads (median 2.4 mm; median 264 N) than inner tables (median 1.7 mm, p < 0.001; median 132 N, p = 0.003). The presence of diploë attached to outer and inner tables led to a significant reduction in bending strength (with diploë: median < 60 MPa; without diploë: median > 90 MPa, p < 0.001). Composites (r = 0.243, p = 0.011) and inner tables with attached diploë (r = 0.214, p = 0.032) revealed positive correlations between sample thickness and age. The three-layered composite is four times more load-resistant compared to the outer table and eight times more compared to the inner table.

Investigation of dental elastomers as oral mucosa simulant materials.

OBJECTIVE: To measure mechanical properties of dental soft liners in tensional stress to identify their suitability as human oral mucosa simulant materials. METHODS: Eleven different dental elastomers were subjected to tensile testing to obtain their tensile strength and elastic moduli (n = 15/group) according to the ISO-527 method. Fractured surfaces of one specimen per sample group were examined under the light microscope and scanning electron microscope (SEM). Energy-dispersive X-ray spectroscopy (EDS) was performed for the elemental analysis or chemical characterization of each sample group. The obtained data were quantitatively and qualitatively analysed. They were also statistically analysed using SPSS version 25. RESULTS: The tensile strength of dental elastomers ranged from 0.43 MPa (±0.09) to 7.41 MPa (±1.11) and had statistically significant differences between tested groups (p = 0.001). Vertex soft heat-cure soft liner, GC impression silicones and Silagum soft liners were found to have tensile strengths close to that of the oral mucosa reported by previous studies. SEM analysis revealed that the elastomers with higher filler contents showed rough fractured surface with plucking of particles after tensile fracture. CONCLUSION: This is the first study assessing the suitability of dental elastomers as human oral mucosa simulant materials which can be used for in vitro, mathematical modeling and finite element analysis (FEA) to study masticatory force distribution in oral mucosa. Out of 11 studied, six (Vertex Soft, GC heavy and Light body, Molloplast B, Algin X Ultra and Exaclear) dental elastomers showed similar mechanical properties to the Theil embalmed gingival tissues. Vertex Soft, GC Light body, and Molloplast B may be used for the majority of oral mucosal model when considering tensile strength as the primary factor for mechanical stimulation.

Comparison of hardness and polishability of various occlusal splint materials.

OBJECTIVES: To measure polishability of occlusal splint materials manufactured by various methods. METHODS: Seven occlusal splint materials manufactured by four different methods - Heat cured (Vertex Rapid simplified Clear), CAD-milled (Ceramill a-splint), Vacuum-formed (Proform splint) and 3D-printed (Freeprint Ortho, KeySplint Soft, DentaClear and FreePrint Splint 2.0) were tested for gloss, roughness, and surface hardness and elastic modulus. For all groups, the tests were repeated with the materials polished with three different polishing burs, pumice and high shine. All polishing procedures were standardised by applying the force of 1 N for 1 min at the set speed. 3D printed materials were further tested with additional specimens manufactured at different printing angles of 0°, 45° and 90°. Data was statistically analysed using ANOVA (SPSS Version 26) and MatLab (R2020a). Polished surfaces of each specimen were analysed under scanning electron microscope. RESULTS: Vacuum-formed materials showed the highest polishability (80.61 ± 0.98 GU) with no statistical significance to heat-cured or CAD-milled (p = 1.00). Pumice and high shine polish significantly improved the gloss for all groups. The mean gloss and surface roughness for all 3D-printed materials ranged from 75.24 ± 25.05 GU to 0.18 ± 0.21 GU and 2.73 ± 3.18 µm to 0.06 ± 0.01 µm, which was significantly lower (p < 0.001) than heat-cured, CAD-milled and vacuum-formed materials. The highest hardness (0.40 ± 0.009 GPa), elastic modulus (6.06 ± 1.49 GPa) and gloss were found when materials were 3D-printed at 45°, with the lowest surface roughness. CONCLUSION: Statistically significant differences in polishability were found among the different occlusal splint materials. The polishability and surface hardness of 3D-printed occlusal splint materials was influenced by the print angle. The 0° 3D-printed occlusal splint materials produced the highest gloss and the lowest surface roughness pre-polished, indicating that no polishing is required. While the 3D-printed occlusal splint materials at 45oand 90° required polishing with burs, pumice and high shine to reduce the surface roughness, there were layering structures created during printing.

Adhesion of Denture Characterizing Composites to Heat-Cured, CAD/CAM and 3D Printed Denture Base Resins.

PURPOSE: To measure the adhesion of the denture characterizing composite to heat-cured, CAD/CAM and 3D printed denture base resins. METHODS AND MATERIALS: Two different denture characterizing composites with different viscosities (SR Nexco; high viscosity (SR) and Kulzer Cre-active; low viscosity (K)) and three denture base resins (Heat cure, CAD-milled and 3D printed) were investigated. 60 beams (25 × 4 × 3 mm) were fabricated for each denture base resin; 30 were bonded to SR and 30 to K to form a beam 50 × 4 × 3 mm. These were further divided (n = 10/group) to simulate the effects of 0, 6, and 12 months intraorally via thermocycling. The beams were subjected to a 4-point bend test using the chevron-notched beam method. Fracture toughness K1C (MPa ·m1/2 ) and flexural bond strength (MPa) were calculated. All specimens were analyzed for the mode of failure under the light microscope and selected specimens under scanning electron microscope. Results were statistically analyzed using ANOVA (SPSS Ver 25). RESULTS: The mean K1C was highest for the SR composite bonded to the heat-cured denture resin group (0.28 ± 0.11), followed by CAD/CAM (0.18 ± 0.04) and 3D printed groups (0.23 ± 0.16). Differences were not statistically significant (p = 0.268). Within each group, aging showed no statistical significance between the mean K1C and flexural bond strength (p = 0.209). The mean K1C for the K composites bonded to the three different denture bases were significantly lower compared to the SR group (p < 0.001). The mean K1C for the heat-cured denture resin group was (0.21 ± 0.1), followed by CAD/CAM (0.13 ± 0.04) and 3D printed groups (0.03 ± 0.02). Within each of the K group, aging showed a statistical significance for both the mean K1C and flexural bond strength (p = 0.002). CONCLUSION: The high viscosity SR showed significantly higher K1C and flexural bond strength to the lower viscosity K when bonded to heat-cured, CAD-milled and 3D printed denture base resins. Heat-cured denture base resins produced the highest K1C and flexural bond strength when bonded to two different types of characterizing composites.

Mechanical properties of human oral mucosa tissues are site dependent: A combined biomechanical, histological and ultrastructural approach.

AIM: To investigate load-deformation properties of Thiel-embalmed human oral mucosa tissues and to compare three different anatomical regions in terms of mechanical, histological and ultrastructural characteristic with focus on the extracellular matrix. MATERIALS AND METHODS: Thirty specimens from three different regions of the oral cavity: attached gingiva, buccal mucosa and the hard palate were harvested from two Thiel-embalmed cadavers. Mechanical properties were obtained, combining strain evaluation and digital image correlation in a standardised approach. Elastic modulus, tensile strength, strain at maximum load and strain to failure were computed and analysed statistically. Subsamples were also analysed using scanning electron microscopy (SEM) and histological analysis. RESULTS: The highest elastic modulus of 37.36 ± 17.4 MPa was found in the attached gingiva group, followed by the hard palate and buccal mucosa. The elastic moduli of attached gingiva differed significantly to the buccal mucosa (p = .01) and hard palate (p = .021). However, there was no difference in the elastic moduli between the buccal mucosa and hard palate (p > .22). The tensile strength of the tissue samples ranged from 1.54 ± 0.5MPa to 3.81 ± 0.9 MPa, with a significant difference between gingiva group and buccal mucosa or hard palate (p = .001). No difference was found in the mean tensile strength between the buccal mucosa and hard palate (p = .92). Ultrastructural imaging yielded a morphological basis for the various mechanical properties found intraorally; the attached gingiva showed unidirectional collagen fibre network whereas the buccal mucosa and hard palate showed multi-directional network, which was more prone to tension failure and less elasticity. CONCLUSION: This is the first study assessing the various morphological-mechanical relationships of intraoral soft tissues, utilising Thiel-embalmed tissues. The findings of this study suggest that the tissues from different intraoral regions showed various morphological-mechanical behaviour which was also confirmed under the SEM and in the histological analysis.

Evaluation of surface roughness, hardness and elastic modulus of nanoparticle containing light-polymerized denture glaze materials.

STATEMENT OF PROBLEM: The surface hardness and roughness of different glaze materials for denture base acrylic resins have not been well reported. PURPOSE: The purpose of the study was to measure the surfaces hardness, elastic modulus and surface roughness of 5 different light-polymerized glaze materials for poly methyl methacrylate (PMMA) denture base materials. MATERIAL AND METHODS: A total of 210 PMMA resin specimens (10 × 5 × 2 mm) were prepared (30 per group); control group was untreated, group 1 was surface treated with conventional pumice and high shine paste; group 2 to 6 specimens were glaze coated with different commercially available denture glaze materials. 20 specimens out of 30 underwent thermocycling to simulate 6 months and 12 months in vivo. Nanoindentation was performed to measure the surface hardness and elastic modulus. Surface roughness was quantitatively analysed using surface metrology software and qualitatively analysed under scanning electron microscope (SEM). Collected data was statistically analysed using SPSS version 24. RESULTS: The mean surface hardness of tested specimens ranged from 0.33 ±0.09 GPa to 0.68 ±0.10 GPa. Specimens coated with Optiglaze produced statistically higher surface hardness compared to other groups (P< 0.01). Aging of 6 months and 12 months was found to have no statistical significance for all groups' surface hardness values. For elastic modulus, specimens coated with Nanovarnish produced statistically higher values compared to other groups (P= 0.03). Thermocycling showed no influence on the elastic modulus of specimens. The mean surface roughness of all groups ranged from 0.16 ±0.01 to 0.30 ±0.02 µm with no statistical significance between groups (P= 0.67). However, under SEM analysis, surfaces showed increased roughness over time. CONCLUSIONS: Statistically significant differences in surface hardness and elastic modulus were found among the different types of surface coated denture acrylic resins. Silica-nanoparticle containing surface coatings produced the highest surface hardness and elastic modulus, however there was no statistical significance found in aging for 6 and 12 months. Contrary to expectations, the surface roughness did not have a significant increase in all groups over time, despite changes observed under SEM. CLINICAL IMPLICATIONS: This study will contribute to our understanding of surface glazed PMMA acrylic resin denture materials and how it improves the surface strength. This research can help dental clinicians and technicians select the most effective polishing and coating material for the dentures.

The influence of undercut depths on the accuracy of casts poured from irreversible hydrocolloid impression materials.

OBJECTIVES: To evaluate the elastic recovery of a typical irreversible hydrocolloid impression material in terms of the amount of undercut identified and additional thickness of spacer provided before custom tray fabrication. METHODS: This study surveyed the undercut depths of the teeth surfaces and lingual sulci of one hundred partially dentate mandibular dental casts which were subsequently scanned and the data exported as STL files. A typical cast from each undercut category (0.5mm, 1mm, 1.5mm, 2mm, 2.5mm, 3mm, 4mm, 5mm) was 3D printed. Three custom trays were constructed with spacer thicknesses representing 20%, 30% and 50% compression against the wall of the custom trays on removal, impressions recorded, and casts fabricated in dental stone. Measurements for elastic recovery of irreversible hydrocolloid were done using an internal caliper and a digital caliper. All measurements were done by the principal investigator. Non-parametric analyses were used for comparisons of the undercut values between the 3D printed and poured casts to determine the amount of elastic recovery of the irreversible hydrocolloid impression material. RESULTS: There was no statistically significant difference in measurements between the original 3D printed casts and the poured casts, irrespective of percentage compression (p > 0.05). CONCLUSIONS: In removable partial denture construction, casts should be blocked out parallel to the path of insertion and then an additional 3mm of spacer applied as a standard technique before custom tray fabrication to ensure elastic recovery of the irreversible hydrocolloid impression. CLINICAL IMPLICATIONS: In severe undercut situations, accurate impressions can be taken using irreversible hydrocolloid by blocking out all undercut surfaces on the teeth and lingual sulci before adapting additional three-millimetre wax spacer on casts when constructing custom trays thereby ensuring accurate and reliable impressions for removable prosthesis construction.

Bond Strength of Denture Teeth to Heat-Cured, CAD/CAM and 3D Printed Denture Acrylics.

PURPOSE: To establish the fracture toughness (K1C ) and flexural bond strength of commercially available denture teeth to heat cured, CAD/CAM and 3D printed denture-based resins (DBRs). MATERIALS AND METHODS: Three types of DBRs (Heat cure, CAD-milled and 3D printed) and four different types of commercial denture teeth (Unfilled PMMA, double cross-linked PMMA, PMMA with nanofillers and 3D printed resin teeth) were investigated. DBR and epoxy embedded denture teeth (n = 30 per group) specimen beams (25 × 4 × 3 mm) were fabricated. The testing ends of all the specimens were surface treated, bonded and processed according to manufacturer's instructions. Twenty specimens were thermal cycled to simulate the effects of 6 and 12 months intraorally. A 4-point bend test, using the chevron-notched beam method was done and K1C (MPa ·m1/2 ) and flexure bond strength (MPa) were calculated. All specimens were analysed for the mode of failure under the light microscope and selected specimens under scanning electron microscope. Results were statistically analysed using ANOVA (SPSS Ver 24). RESULTS: The mean K1C was the highest for the teeth bonded to the heat-cured DBR group (1.09 ± 0.24), followed by CAD/CAM (0.43 ± 0.05) and 3D printed groups (0.17 ± 0.01). Differences were statistically significant (p < 0.01). Within each group, aging showed statistically significantly lower values but no statistical significance between the mean K1C and flexural bond strength (p = 0.36). The dominant mode of failure was cohesive in the CAD/CAM groups and adhesive in the heat-cured and 3D printed groups. CONCLUSION: Teeth bonded to heat-cured DBRs produced the highest K1C .The bond strength decreased significantly with aging. Teeth bonded to CAD/CAM and 3D printed DBRs showed significantly lower bond strength, with no significant influence of aging.

Real-time pulp temperature change at different tooth sites during fabrication of temporary resin crowns.

AIM: To record the pulp temperature at different tooth sites during fabrication of two different temporary crown systems. METHODOLOGY: Two temporary crown systems were investigated; a conventional direct fabricated and a preformed thermoplastic resin system. Extracted caries-free human teeth (incisor, premolar and molar) were prepared for full coverage ceramic restoration with roots sectioned below the cemento-enamel junction. Thermocouple wires were secured at the surface of crown material, the cut dentine and inside the pulp cavity. Provisional crowns (n = 10/group) from each system were formed prior to placement in a water bath of 37 °C to simulate pulpal temperature. Temperatures were recorded using a K-type thermocouple data logger to collect the mean and peak temperature during crown fabrication. Statistical analysis was carried out on all tested groups and heat flow was calculated. RESULTS: For direct fabricated crowns, the mean rise in pulpal temperature recorded was 0.1 °C with the mean temperature range of 37.3 °C-37.8 °C. For the preformed thermoplastic crowns, the mean rise in pulpal temperature recorded was 37.3 °C-45.1 °C. The increase in temperature was significantly higher (6.5 °C for the incisor group, 7.5 °C for the premolar group, and 6.7 °C for the molar group). For both crown systems, the temperature difference between the three different sites; pulp, crown and tooth surface showed a statistical difference (P < 0.01). CONCLUSIONS: The direct fabrication system showed minimal temperature changes within the teeth, while the preformed thermoplastic fabrication system showed larger temperature change in the teeth.