Hard Reline Materials Research Articles

Effect of adhesives and mechanical surface treatments on the hard relining of CAD-CAM denture bases.

The aim of this study was to evaluate the impact of mechanical roughening, adhesive applications, and aging on the bonding between CAD-CAM denture base materials with distinct chemical contents and hard relining material. A total of 300 denture base specimens were produced by additive, subtractive, and conventional heat-polymerization techniques (N=100). The specimens have been classified into five subgroups based on the particular surface treatments administered (n=20): (1) Hard relining material's adhesive application (control); (2) Tungsten carbide bur application for 1min, and hard reline material's adhesive application; (3) Airborne-particle abrasion (APA) with 110 μm Al2O3, and hard reline material's adhesive application; (4) Scotchbond Universal application; and (5) Visio.link application. Representative specimens from each subgroup were examined under a Scanning Electron Microscope (SEM). Subsequently, self-cure hard relining material was condensed in the center of the specimens. Half of the specimens were thermally aged with 5000 cycles at 5°C-55°C. The shear bond strength (SBS) test was performed, and failure loads were recorded. The data was evaluated by Robust ANOVA and Bonferroni test (p<0.05). No statistically significant difference was obtained between the production techniques (p = 0.051). The lowest SBS was observed in the control group among surface treatments, while mechanical surface treatments and universal adhesive showed the highest SBS for both aged and non-aged groups. Aging caused a significant decrease for all test groups (p=0.001). Mechanical surface treatments and universal adhesive applications are more effective for maintaining adhesion across all production techniques.

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

Statement of problemNovel 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. PurposeThe 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 methodsA 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). ResultsAll 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). ConclusionsAll 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.

Tensile bond strength of soft and hard relining materials to conventional and additively manufactured denture-base materials.

Studies comparing tensile bond strength of various soft and hard denture liner materials to conventionally and additively manufactured denture base resins are lacking. The purpose of this study was to investigate the tensile bond strength between chair- and laboratory-side soft and hard relining materials and denture-base materials produced by additive manufacturing and conventional methods. A total of 120 dimethacrylate-based additively manufactured and polymethylmethacrylate (PMMA)-based conventionally fabricated dumbbell-shaped denture-base resins were produced. Heat-cured laboratory-side soft reline material, self-cured chair-side soft reline material, and self-cured chair-side hard reline material were attached to the denture bases. The tensile force was applied to the specimens with a universal testing machine at a crosshead speed of 5mm/min. The obtained data were analyzed with two-way ANOVA and post hoc Tukey tests. The significance level was set at α= 0.05. The highest tensile bond strength values were obtained in the specimens from the conventionally manufactured base and self-cured chair-side hard reline material group, and the lowest was seen in the additively fabricated base and self-cured chair-side soft reline material group (p<0.001). Conventionally manufactured base material's tensile bond strength was higher than that of additively fabricated resin, and self-cured chair-side hard reline material's strength was higher than that of laboratory-side and chair-side soft reline materials (p<0.001). However, no significant difference emerged between laboratory-side and chair-side soft reline materials (p= 0.405). All the specimens used in the present study had tensile bonding stress values for clinical use. Both denture base resins provided an increased bond to the chair-side hard relining material, although an improved bond did not emerge for the chair-side and laboratory-side soft denture reline materials.

Comparison of the Water Sorption and Solubility of Four Reline Acrylic Resins after Immersion in Food-Simulating Agents.

Objectives:Water sorption and water solubility adversely affect the mechanical properties and biocompatibility of the denture material. This study aimed to evaluate the water sorption and solubility of three direct hard reline acrylic resins and a heat-curing one after immersion in food-simulating agents.Materials and Methods:This study was performed on four groups of samples (n = 10 per group). The samples were made of three direct hard reline acrylic resins (TDV Cold Liner Rebase, Tokuyama Rebase II Fast, GC Reline Hard) and a heat-curing one (Meliodent). Each group was divided into four subgroups (n = 10) to undergo 7-day immersion in distilled water, 75% ethanol/water, 0.02 N citric acid, and heptane. Water sorption and solubility were calculated according to Oysaed and Ruyter formula. The statistical analyses were done by using SPSS software (version 22). Kruskal–Wallis H Test and Dunn's test were used to detect any significant difference among the groups (P < 0.05).Results:The median range of water solubility and water sorption values were −0.87–4.92 and 3.75–27.25 μg/mm3, respectively. The median solubility and sorption values of different resins differed significantly in the same solution (P < 0.05). Besides, immersion in different solutions caused significant differences in the median solubility and sorption values of each reline material (P < 0.05), except for Meliodent whose solubility was not significantly affected by different solutions (P = 0.16).Conclusions:Water sorption and solubility values of the tested hard reline resins were within the range of International Standards Organization 1567:1999. Given the low sorption and solubility values, these hard reline materials can be safely used in clinical situations.

Bond strength of hard direct reline materials to heat-cured acrylic denture base after immersion in denture cleansers.

Immersion-type denture cleansers are commonly used for denture hygiene maintenance. Hence, it is crucial to investigate the effect of denture cleansing solutions on bond strength between direct reline materials and denture base resin. This in vitro study aimed to determine the effect of denture cleansers on bond strength between direct hard reline materials and denture base resin. Cylindrical columns of hard-liners (Hard GC Reline, TDV Cold Liner Rebase, Tokuyama Rebase II Fast) were bonded to heat-polymerized denture base resin. A total of fifty specimens were fabricated for each reline material and divided into five groups (n = 10): Group I (control): No solution was used; Group II: Specimens were stored in distilled water for 60 days; Groups III, IV, and V: Specimens were stored in distilled water for 60 days with daily immersion in either sodium hypochlorite, calgon + sodium hypochlorite, or dentipur tablet for 5 min. The shear bond strength was examined at a cross-head speed of 1 mm/min. Failure mode was evaluated by stereomicroscope. Data were analyzed by two-way ANOVA and Chi-square test (α=0.05). The results showed no significant interaction between the direct hard-liners and denture cleansers (P = 0.119). Hard GC Reline had the highest bond strength, followed by Tokuyama Rebase II Fast, and then, TDV Cold Liner Rebase. No significant difference existed in bond strength between samples immersed in water and cleansers or between the cleansers themselves. Hard GC Reline had more mixed failure mode compared to TDV Cold Liner Rebase and Tokuyama Rebase II Fast. There was a significant correlation between mixed mode of failure and higher values of bond strength (P = 0.008). Within the limitations of the present study, denture cleansing solutions could not significantly influence the bond strength between hard direct liners and denture base resin.

The Effect of Food‐Simulating Agents on the Bond Strength of Hard Chairside Reline Materials to Denture Base Resin

To investigate the influence of food-simulating agents on the shear bond strength between direct hard liners and denture base acrylic resin. In addition, mode of failure was evaluated. One hundred fifty cylindrical columns of denture base resin were fabricated and bonded to three types of hard reline materials (Hard GC Reline, Tokuyama Rebase II Fast, TDV Cold Liner Rebase). Specimens of each reline material were divided into five groups (n = 10) to undergo 12-day immersion in distilled water, 0.02 N citric acid aqueous solution, heptane, and 40% ethanol/water solution at 37°C. The control group was not immersed in any solution. The shear bond strength test was performed, and the failure mode was determined. Statistics were analyzed with two-way ANOVA and chi-square test (α = 0.05). Significant interaction was found between the hard liners and food simulating agents (p < 0.001). The shear bond strength of Tokuyama in 40% ethanol and TDV in heptane decreased significantly (p = 0.001, p < 0.001 respectively); however, none of the solutions could significantly affect the shear bond strength of Hard GC Reline (p = 0.208). The mixed failure mode occurred more frequently in Hard GC Reline compared with the other liners (p < 0.001) and was predominant in specimens with higher bond strength values (p = 0.012). Food simulating agents did not adversely affect the shear bond strength of Hard GC Reline; however, ethanol and heptane decreased the bond strength of Tokuyama and TDV, respectively. These findings may provide support to dentists to recommend restricted consumption of some foods and beverages for patients who have to use dentures relined with certain hard liners.

Effect of different housing retaining materials on the flexural strength of an acrylic resin overdenture base

Statement of problemAn attachment housing inside an overdenture may weaken the acrylic resin base. The type of housing retaining material may affect the strength of the housing retaining material-acrylic resin base assembly. The effect of different housing retaining materials on the strength of acrylic resin base is unknown. PurposeThe purpose of this in vitro study was to evaluate the effects of different materials used to retain the housing on the flexural strength of a poly(methyl methacrylate) (PMMA) resin base. Material and methodsSixty PMMA specimens (64×10×4 mm) were prepared with a clearance inside to allow the insertion of overdenture housings. Five different materials were used for housing orientation: an autopolymerizing composite resin, an acrylic resin reline material, a heat-polymerized PMMA, an autopolymerizing PMMA (n=10), and a control group (n=10) were prepared without any preparation or housing. The specimens were thermocycled 5000 times between 5°C and 55°C. The flexural strength data were analyzed by an analysis of variance using the maximum likelihood estimation method to eliminate the needs for normality within the groups and for equality of variances between the groups. If statistically significant, resolution of the significance factor was obtained by pairwise comparisons using the Tukey adjustment (α=.05). ResultsThe fracture values were statistically significantly higher (P<.05) for the control group (90.22 ±12.46 MPa) than the test groups (heat-polymerized, 27.36 ±4.86 MPa), the autopolymerizing material (26.78 ±6.72 MPa), the acrylic resin reline material (16.94 ±4.38 MPa), the Ufigel (16.07 ±3.40 MPa), and the autopolymerizing composite resin (19.37 ±3.13 MPa). Heat- and autopolymerizing PMMA groups were significantly different from acrylic resin-based hard reline materials (P<.05). However, the remaining groups were not significantly different from each other. All fractures included both the PMMA and retaining material except for one of the hard reline groups, which separated from the PMMA. ConclusionsThe tested retaining materials significantly reduced the flexural strength of PMMA denture base. The flexural strength of the resin base with housing was significantly higher when PMMA-based retaining materials were used than when acrylic resin-based hard reline materials were used.

The effect of denture cleansers on surface roughness and bond strength of a denture base resin‏

Purpose: The purpose of this study was to evaluate the effect of different denture cleaning regimens on surface roughness of denture base material and bond strength to hard reline material.Materials and methods: 100 disk-shaped specimens were prepared from a denture base resin and immersed into the following five groups (n = 20): Group C: Corega Tabs, Group P: Protefix Tabs, Group CU: ultrasonic device with Corega Tabs and Group PU: ultrasonic device with Corega Tabs, and Control: distilled water. All cleaning protocols were applied for 90 times to each specimen according to the instructions of the manufacturers. Surface roughness values were measured using a profilometer and surface evaluations were performed with scanning electron microscope (SEM). Reline materials were applied on the specimens and shear tests were performed using a Universal Testing Machine. Data were analyzed using One-way ANOVA and Tukey’s post hoc tests were used for comparison among groups with a significance level of 0.05.Results: Group PU and group CU showed significant increase in surface roughness values compared to group P, C, and Control (p < 0.05). Control group showed significantly lower shear bond strength values compared to the other groups (p < 0.01). Group P exhibited higher shear bond strength values compared to group C (p = 0.003). No significant differences were found between group P and PU (p = 0.945), same results were found between group C and CU (p = 0.283).Conclusion: Using denture cleansers with ultrasonic devices significantly affected the surface topography of denture bases. All tested cleaning regimens increased the bond strength of hard reline material to the denture base.

Usefulness of a rotation–revolution mixer for mixing powder–liquid reline material

PurposeThe purpose of this study was to evaluate the distribution of bubbles, degree of mixing, flowability and mechanical strength of powder–liquid reline material by manually and with a rotation–revolution (planetary) mixer, and to determine the usefulness of a rotation–revolution mixer for this application. MethodsPowder–liquid reline material (Mild Rebaron, GC, Tokyo, Japan) was mixed with a powder to liquid ratio of 1:0.62 according to the manufacturer's instruction. Two methods were used to mix it: mixed by manually (“manual-mixing”) and automatically with a rotation–revolution mixer (Super Rakuneru Fine, GC, Tokyo, Japan; “automatic-mixing”). Disc-shaped specimens, 30mm in diameter and 1.0mm in thickness, were used to observe the distribution of bubbles in at 10× magnifications. Flowability tests were carried out according to the JIS T6521 for denture base hard reline materials. A three point bending test was carried out by a universal testing machine. Elastic modulus and flexural stress at the proportional limit were calculated. ResultsA median of 4 bubbles and inhomogeneous were observed in manual-mixed specimens. However, no bubbles and homogeneous were observed in automatic-mixed specimens. Flowability was within the JIS range in all mixing conditions and did not differ significantly across conditions. The elastic modulus was the same for manual-mixed and automatic-mixed specimens. On the other hand, the flexural stress at the proportional limit differed significantly between manual-mixed and automatic-mixed specimens. ConclusionThe results confirm that rotation–revolution mixer is useful for mixing powder–liquid reline material. Automatic-mixing may be recommended for clinical practice.

Influence of surface characteristics on the adhesion of Candida albicans to various denture lining materials

Objective. This study evaluated the influence of surface characteristics of various denture lining materials on the adherence of Candida albicans. Materials and methods. Four different types of materials (tissue conditioners, acrylic and silicone soft liners and hard reline materials) were selected. Disk-shaped material specimens were prepared and their surface roughness values (Ra) measured using a profilometer. The contact angles of four reference liquids were measured on the material surfaces and surface energy parameters (total surface energy, acid and base components, degree of hydrophobicity/hydrophilicity) of the materials were calculated in accordance with acid-base theory. Specimens were incubated with C. albicans and adhering fungi quantified using the colony counting method. Data were statistically analyzed using a one-way ANOVA with Games–Howell post-hoc test (α = 0.05). Pearson correlation analysis was applied to detect correlations between surface characteristics and Candida adhesion. Results. Significant differences in the surface roughness of the materials were found (p < 0.001). The acrylic soft liners were more hydrophilic than the other materials. Overall, the acrylic soft liners and tissue conditioners showed significantly greater Candida adhesion than silicone soft liners and hard reline materials (p < 0.05). The Pearson correlation analysis indicated that the base component and degree of hydrophobicity/hydrophilicity of the materials (p = 0.005/0.008), rather than the total surface energy and the surface roughness (p = 0.093/0.057), affected C. albicans adherence in a statistically significant way. Conclusions. The adhesion of C. albicans to denture lining materials can be accounted for in terms of interfacial acid-base interactions.

Changes in roughness of denture base and reline materials by chemical disinfection or microwave irradiation: Surface roughness of denture base and reline materials

ObjectiveThe effect of disinfection by immersion in sodium perborate solution and microwave irradiation on surface roughness of one denture base resin (Lucitone 550 -L), 3 hard chairside reline resins (Tokuyama Rebase II-TR, New Truliner-NT, Ufi Gel hard-UH) and 3 resilient reline materials (Trusoft-T; Sofreliner-S, Dentusil-D) was evaluated. Material and methodsThirty specimens of each material were made and divided into 3 groups: Control - not disinfected; P - daily disinfection by immersing in sodium perborate solution (3.8%); MW - microwave disinfection (6 min/650 W). Roughness measurements were made after polymerization (baseline) and after 1, 3 and 28 days. Roughness differences relative to the baseline readings were analyzed by Student's t-test (P=0.05). ResultsAt baseline, Trusoft showed the highest (P<0.001) mean surface roughness (3.54 µm), and its surface roughness was significantly reduced after 28 days of disinfection by immersion in sodium perborate (P=0.013). Roughness measurements of material Trusoft were not performed after microwave disinfection due to the severe alterations on the surface. In the 3 groups evaluated, changes in roughness were significant for materials Ufi Gel hard (from 0.11 to 0.26 µm; P≤0.041) and New Truliner (0.19 to 0.76 µm; P≤0.019). The roughness of materials Lucitone 550 (0.37 µm), Tokuyama Rebase II (0.37 µm), Sofreliner (0.49 µm) and Dentusil (0.38 µm) remained unaffected (P>0.05). ConclusionsThe roughness of the hard reline materials Ufi Gel hard and New Truliner was adversely affected by microwave disinfection, immersion in water or in sodium perborate. Microwave disinfection caused severe alterations on the surface of the resilient liner Trusoft.

Denture-related stomatitis managed with tissue conditioner and hard autopolymerising reline material

To compare the response of denture-related stomatitis (DS) under management with a tissue conditioner (TC) and autopolymerising hard reline material (AHRM). Denture-related stomatitis affects up to 75% of denture wearers; not wearing the denture at night, using TC or prescribing topical or systemic antifungal agents could reduce its incidence. This was a double-blind study consisting of 44 participants with DS who wear denture; they were randomly divided into two unmatched groups according to the material used for the management of DS. The TC was replaced weekly, and the AHRM was placed at the beginning of the study and was not changed for 4 weeks. A dentist performed an initial and a weekly clinical diagnosis for DS; the clinical situation was recorded by means of photographs for each week. Both TC and AHRM were effective in the management of DS. Significant differences were found in the DS resolution time (p < 0.001), taking longer for the TC. Both the tissue conditioner and AHRM are effective for the management of DS, but AHRM requires less time for recovery and as a result fewer appointments are required for the patient.

A comparison of bond strengths among chairside hard reline materials

Several chairside hard resin reline materials have been introduced to improve the fit and function of existing denture bases. However, it is not known whether the bond strengths among the various chairside reline and denture base materials are significantly affected by their differences in chemical composition. This study evaluated the bond strengths of five chairside hard reline materials (Extoral VLC, Flexacryl Hard, Kooliner, Light Liner, and Triad Hi-Flow VLC reline material) to two different denture base resins (Lucitone 199 and Triad VLC) by use of a three-point transverse flexural test. The reline resins are representative of autopolymerizing, light- and dual-cured materials. The results indicate that Triad VLC reline resin with bonding agent gave the highest bond strengths to Triad VLC denture base resin. Light Liner reline resin gave the highest repair bond strengths to Lucitone 199 denture base resin.