Light-polymerized Acrylic Resin Research Articles

Influence of Various Chemical Surface Treatments, Repair Materials, and Techniques on Transverse Strength of Thermoplastic Nylon Denture Base.

The process of repairing the fractured nylon denture bases and addition of acrylic teeth to the previously worn nylon denture bases has not been widely studied. This study aims to assess the transverse strength of nylon denture bases repaired by various resin materials, different curing techniques, and types of surface treatments. Materials and Methods. One hundred fifty thermoplastic nylon denture base samples were fabricated using plastic patterns measuring 65 × 10 × 2.5 mm (length, width, and thickness, respectively). These samples were then divided into three equal groups. Fifty samples were repaired by microwave heat-polymerization, fifty samples were repaired using the Ivomate autopolymerization, and the other fifty were repaired using light-polymerized acrylic resin. Each of these three groups was further divided into five subgroups of ten samples based on the type of surface treatment. The samples in the control group did not undergo any surface treatment, and the other four groups were chemically surface treated with monomer, acetone, ethyl acetate, and isopropanol, respectively. A three-point bending test was used to calculate the transverse strength values of the samples. Fourier transform infrared (FTIR) analysis was conducted to determine the component of functional groups between the polyamide nylon base and poly(methyl-methacrylate) PMMA repair materials. A polarizing microscope was utilized to investigate the mode of failure at the fracture surfaces. Results. The collected data were analyzed with one-way ANOVA and Sidak's multiple comparison test to show the differences among different groups. For surface treatments, the highest transverse strength values were obtained by monomer-treated samples (18.29 N/mm2); however, the lowest values were obtained in non-surface treated samples (5.58 N/mm2). While for repair techniques, the highest transverse strength values were obtained by microwave processing, followed by Ivomate and then the light-cured polymerization. The means were found to be significant (p < 0.001). FTIR analysis shows the presence of hydrogen bonding which is due to the ester and amid groups which enhance the bond strength of the surface-treated samples. The interface of the polarizing microscope images revealed a cohesive fracture within repair materials rather than the adhesive nature. Conclusion. The microwave-polymerized resin was considered as the most effective repair technique along with monomer chemical etchant which creates a tight adhesion between PMMA and nylon denture base in comparison to other groups.

Influence of Different Repair Acrylic Resin and Thermocycling on the Flexural Strength of Denture Base Resin.

Background and Objectives: Fractured acrylic denture base is a common occurrence in clinical practice. The effective denture repair procedure is cost-effective, time conserving, and results in lesser time without denture for the patient. Along with various reinforcements and surface modifications; different acrylic resins are investigated in improving the flexural strength of the fractured site. The aim of this study was to evaluate the flexural strength of a polymethyl methacrylate (PMMA) denture base repaired with heat-polymerized (HPA), auto-polymerized (APA) and light-polymerized acrylic (LPA) resins after thermocycling. Materials and Methods: Forty rectangular shaped (50 mm × 25 mm × 3 mm) PMMA specimens were fabricated. Group 1 specimens (n = 10) were kept as controls and the remaining 30 samples were sectioned at the center with a repair site dimension of 3 mm. The samples from three groups (n = 10) were repaired with HPA, APA, and LPA resins, respectively. The specimens were thermocycled for 5000 cycles and subjected to a three-point flexural test. The maximum load required to fracture the specimens was recorded, and further analyzed with ANOVA and the Games-Howell Post hoc test at the significance level p = 0.05. Results: The average maximum load and flexural strength of the control group was 173.60 N and 13.02 Mpa and corresponding values for denture repaired with HPA was 87.36 N and 6.55 Mpa. The corresponding values for APA resin and LPA resins were 62.94 N, 57.51 N, and 4.72 Mpa, 4.06 Mpa, respectively. Conclusions: The PMMA specimens repaired with HPA resins resulted in a significantly higher load to fracture compared to APA resin and LPA resin.

A comparative evaluation of flexural strengths of two different chairside repair materials with and without modification of implant attachment housings: An in vitro study

Statement of Problem: Implant overdentures become thinner and weaker after direct transfer of implant attachment housings. The introduction of a metal housing changes the character of the repair as denture has to be relieved to provide space for the housings; therefore, a strong method of repair is desirable to avoid prosthesis fracture. Purpose: The purpose of this study was to compare flexural strength of two different chairside repair materials with and without modification of implant attachment housings. Materials and Methods: Eighty 13 mm × 10 mm × 41 mm heat-polymerized acrylic resin blocks were processed, assessed for porosities, and polished. An 8.5-mm diameter hole was created to a depth of 5 mm in the center of each block. Two different attachment housings sandblasted and nonsandblasted were placed into the blocks with two different repair materials: autopolymerized acrylic resin (APAR) and light-polymerized acrylic resin. Later blocks were immersed in water for 7 days in an incubator. A three-point bend test was done in a universal testing machine, and load to fracture was recorded (MPa). Results were compared with one-way analysis of variance (α = 0.05). Results: The mean maximum strength of APAR groups was significantly higher than light-polymerized acrylic resin groups. Groups with sandblasted attachment housings showed significantly higher strength compared to nonsandblasted groups. Conclusions: The flexural strength of self-cured acrylic resin with and without sandblasting of attachment was significantly higher than light-cured acrylic resin with and without sandblasting of attachment housings. Sandblasting produced higher flexural strength in denture blocks repaired with self-cured acrylic.

Fully digital fabrication of an occlusal device using an intraoral scanner and 3D printing: A dental technique

This dental technique describes a fully digital method for fabricating occlusal devices using a complete-arch intraoral scan and 3D printing. The maxillary and mandibular arches of a healthy, fully dentate volunteer were digitized using an intraoral scanner. A second scan and modified recording of the centric relation enabled a virtual arrangement of the maxillary and mandibular arches, both in centric relation and in the desired vertical dimension of occlusion. An occlusal device was subsequently designed virtually and fabricated from a light-polymerizing acrylic resin using a 3D printer. The occlusal device was tested for fit, occlusion, and patient-friendly handling. As only minor occlusal corrections were required, the fully digital procedure described is suitable for the fabrication of occlusal devices.

A technique to splint and verify the accuracy of implant impression copings with light-polymerizing acrylic resin

Transferring the implant position from the mouth to the definitive cast is one of the most critical steps in implant prosthodontics. To achieve a passive fit of the prosthesis, an accurate implant impression is crucial because discrepancies can induce both biologic and technical complications. Analysis of available research data suggests that a direct (pick-up) impression technique with splinted copings is the technique of choice, particularly for multiple implants. However, the traditional method of splinting the copings with autopolymerizing acrylic resin is a technique-sensitive and time- consuming procedure. This report describes a straightforward method of splinting impression copings with light-polymerizing acrylicresin, with minimal amount of autopolymerizing acrylic resin. The method also can be used to verify splinting accuracy.

A simple technique to control the heat generated during light polymerization of custom impression trays

Custom traysare commonly made with a light-poly-merizing acrylic resin material (TriadTruTray; Dentsply Intl) over a waxspacer. The material is polymerizedin a light unit (Triad 2000; DentsplyIntl). The manufacturer recommendsa polymerization time of 2 minutes,followed by removal of the softenedwax. This frequently results in thewax melting, which produces a residuefilm on the custom tray surface. Aprocedure for preventing the wax spacerfrom melting during the polymerizationof light-polymerized acrylic resin isdescribed.

Effect of repair resin type and surface treatment on the repair strength of heat-polymerized denture base resin

Acrylic resin denture fracture is common in prosthodontic practice. When fractured denture bases are repaired, recurrent fractures frequently occur at the repair surface interface or adjacent areas. The purpose of this study was to evaluate the effect of different surface treatments on the flexural strength of the acrylic resin denture base repaired with heat-polymerized acrylic resin, autopolymerizing resin, and light-polymerized acrylic resin. Ninety-six specimens of heat-polymerized acrylic resin were prepared according to the American Dental Association Specification No. 12 (65.0 × 10.0 × 2.5 mm) and sectioned into halves to create a repair gap (3.0 × 10 × 2.5 mm). The sectioned specimens were divided into 3 groups according to their repair materials. The specimens from each group were divided into 4 subgroups according to their surface treatments: a control group without any surface treatment; an experimental group treated with methyl methacrylate monomer (MMA group); an experimental group treated with airborne-particle abrasion with aluminum oxide particles of 250-μm particle size (abrasion group); and an experimental group treated with erbium:yttrium-aluminum-garnet laser (laser group). After the surface treatments, the 3 materials were placed into the repair gaps and then polymerized. After all of the specimens had been ground and polished, they were stored in distilled water at 37°C for 1 week and subjected to a 3-point bend test. Data were analyzed with a 2-way analysis of variance, and the Tukey honestly significant difference test was performed to identify significant differences (α=.05). The effects of the surface treatments and repair resins on the surface of the denture base resin were examined with scanning electron microscopy. Significant differences were found among the groups in terms of repair resin type (P<.001). All surface-treated specimens had higher flexural strength than controls, except the surface treated with the methyl methacrylate in the heat-polymerized group. A significant difference between the control and abrasion groups (P=.013) was found. The scanning electron microscopy observations showed that the application of surface treatments modified the surface of the denture base resin. The repair procedure with heat-polymerized resin exhibited significantly higher flexural strength than that of the autopolymerized and light-polymerized resins. In addition, the airborne-particle abrasion with aluminum oxide particles of 250-μm particle size improved the flexural strength of the specimens tested.

Strength comparison of four techniques to secure implant attachment housings to complete dentures

Implant overdentures become thinner and weaker after direct transfer of implant attachment housings. While much has been published on denture repair, these data do not directly apply to implant overdentures because the introduction of a metal housing changes the character of the repair. It is desirable to make a strong repair to avoid prosthesis fracture. The purpose of this study was to compare the flexural strengths of 4 different methods for chairside direct transfer of implant attachment housings. Eighty 11.5 × 9.1 × 39 mm heat-polymerized acrylic resin blocks were processed, assessed for porosities, and polished. An 8.5 mm diameter hole was drilled to a depth of 5 mm in the center of each block. Attachment housings were set into the bases with 4 different repair materials: autopolymerized acrylic resin (APAR), light-polymerized acrylic resin (LPAR), autopolymerized acrylic resin with silanated attachment housings (APSAH), and light-polymerized acrylic resin with silanated attachment housings (LPSAH). Blocks were immersed in water for 30 days in an incubator. A 3-point bend test was done in a universal testing machine, and load to fracture was recorded (MPa). Results were compared with 2-way ANOVA (α=.05). APSAH had the highest mean flexural strength at fracture (863.1 ±87 MPa) as compared to APAR (678.4 ±72.4 MPa), LPAR (550.9 ±119.3 MPa), and LPSAH (543.2 ±100.8 MPa). A comparison among the 4 groups showed that there were significant differences in maximum flexural strength (P<.001). The mean maximum strength of autopolymerized acrylic resin groups was significantly higher than light-polymerized acrylic resin groups. Silanation increased strength significantly compared to nonsilanated groups. The flexural strength of autopolymerized acrylic resin with silanated attachment housings was significantly higher than autopolymerized acrylic resin alone, light-polymerized acrylic resin alone, or light-polymerized acrylic resin with silanated attachment housings. Autopolymerized acrylic resin produced stronger constructs than light-polymerized materials.

Fabrication of a cast-based implant surgical guide using guide sleeves

A unique method for fabricating cast-based surgical guides is presented. A proposed position and mesiodistal angulation of the implant are verified with periapical radiography and registered with a commercially available guide sleeve. The sleeve is attached to a surgical guide made of light-polymerized acrylic resin. The surgical guide can be used in a broad range of situations and allows for accurate implant placement in a prosthetically driven position with surgical access and visibility, simplicity, and cost efficiency.

Influence of a cobalt-chromium metal framework on surface roughness and Knoop hardness of visible light-polymerized acrylic resins

Although visible light-polymerized acrylic resins have been used in removable partial dentures, it is not clear whether the presence of a metal framework could interfere with their polymerization, by possibly reflecting the light and affecting important properties, such as roughness and hardness, which would consequently increase biofilm accumulation. The aim of this study was to compare the roughness and Knoop hardness of a visible light-polymerized acrylic resin and to compare these values to those of water-bath- and microwave-polymerized resins, in the presence of a metal framework. Thirty-six specimens measuring 30.0 × 4.0 ± 0.5 mm of a microwave- (Onda Cryl), a visible light- (Triad) and a water-bath- polymerized (Clássico) (control) acrylic resins containing a cobalt-chromium metal bar were prepared. After processing, specimens were ground with 360 to 1000-grit abrasive papers in a polishing machine, followed by polishing with cloths and 1μm diamond particle suspension. Roughness was evaluated using a profilometer (Surfcorder SE 1700) and Knoop hardness (Kg/mm2) was assayed using a microhardness tester (Shimadzu HMV 2000) at distances of 50, 100, 200, 400 and 800 μm from the metal bar. Roughness and Knoop hardness means were submitted to two-way ANOVA and compared by Tukey and Kruskal Wallis tests at a 5% significance level Statistically significant differences were found (p<0.05) for roughness and Knoop hardness, with light-polymerized resin presenting the highest values (Ra = 0.11 μm and hardness between 20.2 and 21.4 Kg/mm2). Knoop values at different distances from the metal bar did not differ statistically (p>0.05). Within the limitations of this in vitro study, it was concluded that the presence of metal did not influence roughness and hardness values of any of the tested acrylic resins.

Do Patients Have a Preference for Major Connector Designs?

The aim of this research was to evaluate patients' preferences for resin analogs of four major connector designs formulated to have equal rigidity once fabricated in the same alloy. Nineteen Kennedy Class I or II partially edentulous patients participated at two centers. The four major connector analogs (MCAs) were fabricated for each subject using light-polymerizing acrylic resin. The subjects were asked to wear each of them in the mouth for 30 seconds in six pairs in random order, and to report their preference for each pair. Based on these data, the four analogs were ranked in a descending preference order for each patient. Within-subject comparisons preferences were performed with the Friedman test, and the multiple comparisons were performed with the Wilcoxon Signed Ranks test for data of each sample independently. Statistically significant and consistent preference orders were revealed for both samples, and the thin and wide design was significantly preferred to the thick and narrow design. However, a higher variation was observed for the first preference of each subject. Subjects demonstrated a tendency to prefer thinner MCAs. However, the individual predilections of patients may not be an appropriate basis for an attempt to find a 'best design' applicable to all patients.

Patients' preference for acrylic resin major connector analogues formulated for titanium alloy removable partial dentures

Aim of this study was to determine patients' preference to acrylic resin major connector analogues (MCA) that simulated strengthened major connector designs formulated for Ti-6Al-7Nb alloy. Four MCA namely wide design (Wide), design with 2 strengthening ridges (2SR), design with 1 strengthening ridge (1SR), and thick design (Thick) were fabricated using light-polymerizing acrylic resin for 10 patients with Kennedy Class I or II partially edentulous maxillary arches. They were asked to wear each MCA in the mouth for 30 seconds in 6 pairs, and to report their preference for each pair. Using these data the 4 MCA were ranked in a descending preference order for each patient. A within-subject comparison of preferences was performed with the Friedman test and multiple comparisons with Wilcoxon Signed Ranks test. A statistically significant preference order was revealed: Wide, 1SR, 2SR, and Thick (P < 0.008). The wide design (P < 0.004) and the 1SR (P < 0.01) were significantly preferred to the thick design. However, individual data showed that the first preference varied depending upon the subject. Thinner designs tended to be preferred to the thicker design by the subjects, while none of the designs tested were consistently selected as the best design.

A denture tooth position index fabricated with light-polymerized acrylic resin

A denture tooth position index transfers the position of the denture teeth to the master cast during metal framework and bar-substructure fabrication stage. This article describes the use of light-polymerizing acrylic resin to fabricate a tooth position index.

Factors that affect the adhesion of two irreversible hydrocolloid materials to two custom tray materials

Statement of Problem. Little evidence is available on the length of time that adhesive should be allowed to dry before irreversible hydrocolloid impression making. Purpose. This study investigated the effect of adhesive drying times on the bond strengths of 2 irreversible hydrocolloid impression materials to 2 “custom” tray materials. Material and Methods. A total of 1632 specimens were tested: 816 in tensile tests and 816 in tests of the shear bond strength (megapascals) of 2 irreversible hydrocolloid impression materials to an autopolymerizing and a visible light-polymerizing acrylic resin tray material. In the first part of the investigation, a single coat of adhesive was applied to specimen plates that simulated the custom impression tray surface; in the second part, a second coat of adhesive was applied after the irreversible hydrocolloid was removed, and the effect of this second coating on bond strength was examined. In both parts, the adhesive was allowed to dry for a range of times (0 to 8 minutes at 30-second intervals, for a total of 17 time periods) before the addition of the impression material. The specimen plates were placed in a humidor and separated in a universal testing machine operated at a crosshead speed of 100 mm/min with 0- to 5-kN load cell. Data from each of the 1632 specimens were collected and evaluated with analysis of variance, regression analysis, and t tests (P<.05). Results. Significant differences in mean bond strengths were found between specimens with a 4-minute adhesive drying time (0.179 MPa tensile, 0.068 MPa shear) and specimens with a 0-minute drying time (0.065 MPa tensile, 0.015 MPa shear). Any period over 4 minutes produced no significant difference. The mean bond strengths of the single-coated specimens were 0.179 MPa (tensile) and 0.076 MPa (shear). These values were significantly greater than those for specimens with a second adhesive layer (0.136 MPa tensile, 0.035 MPa shear) over all time periods. Mean tensile bond strengths (0.158 MPa) were consistently higher than shear bond strengths (0.056 MPa) for all combinations of tray material, adhesive application, and time. Conclusion. Within the limitations of this study, the results suggest that adhesive applied to the autopolymerized and light-polymerized custom tray materials tested should be allowed to dry for at least 4 minutes before irreversible hydrocolloid is applied. Better results were obtained when the adhesive layer from a failed irreversible hydrocolloid impression was removed and replaced rather than overlaid with an additional adhesive coating. (J Prosthet Dent 2002;88:423-30.)

Dimensional accuracy of dental casts: Influence of tray material, impression material, and time

This study evaluated the influence on dimensional accuracy of dental casts made with different types of trays and impression materials and poured at different and multiple times. Two types of stock trays (plastic stock tray, perforated metal stock tray) and 4 types of custom tray materials (autopolymerizing acrylic resin, thermoplastic resin, and 2 types of light-polymerized acrylic resins) were used with 2 types of impression materials (addition polymerizing silicone and polyether), to make impressions of a metal master model. Each tray and impression material was used to make 5 impressions. Casts were made by multiple pourings at 30 minutes, 6 hours, 24 hours, and 30 days after impression making. Using a measuring microscope, 12 distances were calculated based on measurements of 8 reference points. The absolute value of the difference of each measurement was calculated, as was the corresponding measurement on the master model. A Bayesian model using a simple noninformative prior was used to analyze these data. Statistical differences within 6 microm were found only with thermoplastic resin tray material for addition silicone, and for thermoplastic resin tray material and 1 type of light-polymerized acrylic resin for polyether. Neither stock trays nor custom trays contributed to the differences in accuracy of the casts. All deviations in casts made with silicone impression material were within a clinically acceptable range. For the polyether, distortions occurred that were clinically unacceptable. Impressions made from polyether distorted over time. Silicone impression material has dimensional stability up to 30 days. Accurate casts can be made with either stock trays or custom trays. An impression made from polyether should be poured only once and within 24 hours after impression making, because of the distortion of the material over time. Silicone impression material has better dimensional stability than polyether. .