Shear bond strength of denture teeth to two chemically different denture base resins after various surface treatments

Bonding Efficiency between Artificial Teeth and Denture Base in CAD/CAM and Conventional Complete Removable Dentures

A common challenge encountered with both traditional and digitally produced dentures involves the extraction of artificial teeth from the denture base. This narrative review seeks to present an updated perspective on the adherence of synthetic teeth for denture base materials, employing diverse methods. Dental technicians often employ chemical approaches and mechanical techniques (including abrasion, laser treatment, and abrasive blasting) to augment the retention of denture teeth. However, the efficacy of these treatments remains uncertain. In certain instances, specific combinations of Denture Base Resin (DBR) materials and artificial teeth exhibit improved performance in conventional heat-cured dentures following these treatments. The primary reasons for failure are attributed to material incompatibility and inadequate copolymerization. As new denture fabrication techniques and materials continue to emerge, further research is imperative to identify optimal tooth-DBR combinations. Notably, 3D-printed tooth-DBR combinations have demonstrated reduced bond strength and less favorable failure patterns, while utilizing milled and traditional combinations appears to be a more prudent choice until advancements in additive manufacturing enhance the reliability of 3D-printing methods.

Application of Laser Treatment in Adhesive Bonding of Liners to Polymethyl Methacrylate Denture Resins: A Systematic Review and Meta-Analysis

Objective: This systematic review and meta-analysis aimed to assess the influence of laser treatment on adhesive bonding of liners to polymethyl methacrylate (PMMA) denture base resins. Methods: The focused question was: "Does the application of laser treatment (Intervention) influence the adhesive bonding strength (Outcome) of liners to PMMA denture base resins (Population) as compared with untreated or unconditioned surfaces (Control)?" In vitro and clinical reports as well as reports on influence of laser treatments on bonding strength of liners to PMMA denture resins in comparison with untreated surfaces were included. Reports without any control group[s], without any application of laser[s] for PMMA denture bases that did not utilize PMMA denture bases, and not evaluate bond strength of PMMA denture base resins were excluded. An electronic search was conducted on PubMed, Scopus, and Web of Science. Meta-analyses were performed for calculating the standard mean difference (SMD) with a 95% confidence interval (95% CI). Results: Nine of the 12 included studies found that laser irradiation treatment produced significant surface texture alterations of the PMMA denture base and improved the adhesion between the PMMA denture base and soft lining. According to the meta-analysis, tensile bond strength showed an SMD of -2.49% (95% CI: -3.89 to -1.08; p = 0.0005), suggesting a statistically significant difference between the control and test groups (i.e., favoring laser-treated samples than untreated samples). Regarding shear bond strength scores, the outcomes showed an SMD of -2.24% (95% CI: -3.79 to -0.69; p = 0.005), suggesting a statistically significant difference between the control and test groups (i.e., favoring laser-treated samples than untreated samples). Conclusions: Despite the high heterogeneity among the included studies, it can be concluded that laser treatment might improve the bonding strengths of liners to PMMA denture base resins as compared with untreated surfaces. To validate the aforementioned conclusions, further verification is required through the implementation of well-designed randomized controlled trials with large sample sizes.

Adhesion of Conventional, 3D-Printed and Milled Artificial Teeth to Resin Substrates for Complete Dentures: A Narrative Review

BACKGROUND

One type of failure in complete or partial dentures is the detachment of resin teeth from denture base resin (DBR). This common complication is also observed in the new generation of digitally fabricated dentures. The purpose of this review was to provide an update on the adhesion of artificial teeth to denture resin substrates fabricated by conventional and digital methods.

METHODS

A search strategy was applied to retrieve relevant studies in PubMed and Scopus.

RESULTS

Chemical (monomers, ethyl acetone, conditioning liquids, adhesive agents, etc.) and mechanical (grinding, laser, sandblasting, etc.) treatments are commonly used by technicians to improve denture teeth retention with controversial benefits. Better performance in conventional dentures is realized for certain combinations of DBR materials and denture teeth after mechanical or chemical treatment.

CONCLUSIONS

The incompatibility of certain materials and lack of copolymerization are the main reasons for failure. Due to the emerging field of new techniques for denture fabrication, different materials have been developed, and further research is needed to elaborate the best combination of teeth and DBRs. Lower bond strength and suboptimal failure modes have been related to 3D-printed combinations of teeth and DBRs, while milled and conventional combinations seem to be a safer choice until further improvements in printing technologies are developed.

The Shear Bond Strength between Milled Denture Base Materials and Artificial Teeth: A Systematic Review

The data about bond strength between digitally produced denture base resins and artificial teeth are scarce. Several studies investigated shear bond strength values of milled denture base resins and different types of artificial teeth. The purpose of the present study was to compare and evaluate the available evidence through a systematic review. A bibliographic search was conducted in PubMed, Scopus, and Web of Science to assess adequate studies published up to 1 June 2022. This review followed the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines. The appropriate studies that determined the shear bond strength values between milled denture base resins and artificial teeth were selected. The initial search identified 103 studies, which were included in the PRISMA 2020 flow diagram for new systematic reviews. Three studies met the inclusion criteria, and all of them present a moderate risk of bias (score 6). Two studies found no statistical differences between heat-polymerized and CAD/CAM (milled) denture base materials when attached with different types of artificial teeth, while one study showed higher values of CAD/CAM (milled) denture base materials. Bonding agents ensure bonding strength at least similar to the conventional methods. In order to improve the quality of future studies, it would be advantageous to use a larger number of specimens with standardized dimensions and a blinded testing machine operator to decrease the risk of bias.

The Effect of Acrylic Surface Preparation on Bonding Denture Teeth to Cellulose Fiber-Reinforced Denture Base Acrylic

Patients who require dental prosthetic restoration using frame dentures in the front part of the mouth very frequently report that teeth fall out of their dentures. However, the available scientific papers are insufficient to compare the various methods of improving the connection between the denture base and the artificial tooth and choosing the best solution. This paper focuses on providing all parameters, enabling the reproduction of tests, and accounting for all variables. The paper uses an original method of creating grooves, sandpaper, sandblasting, and cutting the acrylate layer with a burr in one and two directions. Developed surfaces were additionally subjected to detailed examination. This study used 180 specimens divided into three groups and subjected to various environments (dry, artificial saliva, and thermocycles). Shearing and tensile strength tests were performed. The best results were obtained with a carbide burr. The increase in connection durability was as follows in the case of the shear test: 116.47% in dry samples, 155.38% in samples soaked in artificial saliva, and 46.59% in samples after thermocycles. The increase in tensile resistance was: 198.96% in a dry environment, 88.10% before being soaked in artificial saliva, and 94.04% after thermocycles.

Effect of repair methods and materials on the flexural strength of 3D-printed denture base resin

PURPOSE

The aim of this study was to evaluate the flexural strength of a 3D-printed denture base resin (Cosmos Denture), after different immediate repair techniques with surface treatments and thermocycling.

MATERIALS AND METHODS

Rectangular 3D-printed denture base resin (Cosmos Denture) specimens (N = 130) were thermocycled (5,000 cycles, 5℃ and 55℃) before and after the different repair techniques (n = 10 per group) using an autopolymerized acrylic resin (Jet, J) or a hard relining resin (Soft Confort, SC), and different surface treatments: Jet resin monomer for 180 s (MMA), blasting with aluminum oxide (JAT) or erbium: yttrium-aluminum-garnet laser (L). The control group were intact specimens. A three-point flexural strength test was performed, and data (MPa) were analyzed by ANOVA and Games-Howell post hoc test (α = 0.05). Each failure was observed and classified through stereomicroscope images and the surface treatments were viewed by scanning electron microscope (SEM).

RESULTS

Control group showed the highest mean of flexural strength, statistically different from the other groups (P < .001), followed by MMA+J group. The groups with L treatment were statistically similar to the MMA groups (P > .05). The JAT+J group was better than the SC and JAT+SC groups (P < .05), but similar to the other groups (P > .05). Adhesive failures were most observed in JAT groups, especially when repaired with SC. The SEM images showed surface changes for all treatments, except JAT alone.

CONCLUSION

Denture bases fabricated with 3D-printed resin should be preferably repaired with MMA+J. SC and JAT+SC showed the worst results. Blasting impaired the adhesion of the SC resin.

Evaluation of Shear Bond Strength Between Denture Teeth and 3D-Printed Denture Base Resin

PURPOSE

The aim of this study was to evaluate the bond strength between two types of artificial teeth with a 3D-printed denture base resin using different bonding agents.

MATERIALS & METHODS

Two types of artificial teeth were evaluated: 3D-printed (Cosmos TEMP) and prefabricated polymethylmethacrylate (Biotone) bonded to cylinders (2.5 mm in height and 5 mm in diameter) of 3D-printed denture bases (Cosmos Denture designing by Meshmixer and printed by Flashforge Hunter DLP Resin 3D Printer). Two combinations between denture base and artificial teeth were eveluated: Cosmos Denture - Biotone, n = 30, and Cosmos Denture - Cosmos TEMP, n = 30. For each combination, the specimens were randomly distributed according to the bonding agent: 1. autopolymerized acrylic resin-Duralay, n = 10; 2. 3D-printed resin Cosmos TEMP, n = 10; and 3. methylmethacrylate monomer (MMA) + 3D-printed resin Cosmos TEMP, n = 10, totaling 60 specimens. The application of MMA was done conditioning the tooth surface for 180 seconds; the other agents were applied on the same surface. The virtual design of the 3D-printed resin teeth was obtained by scanning the first maxillary molar of the prefabricated teeth as the same protocol of cylinders. The control group (n = 10) was a conventional heat-polymerized denture base resin (Lucitone 550) bonded to the prefabricated resin teeth (Biotone). The shear bond tests were performed by applying a perpendicular force to the artificial tooth - denture base resin, through a chisel at 1mm / min until failure. Two-way ANOVA and Bonferroni post hoc tests (α = 0.05) were used for multiple comparisons.

RESULTS

For the Biotone tooth, the bond strength was significantly higher using MMA + Cosmos TEMP (10.04 MPa), and similar to the control (11.84 MPa, p = 0.484). For the 3D-printed tooth (Cosmos TEMP), the bond strength using the agents Cosmos TEMP (9.57 MPa) and MMA + Cosmos TEMP (12.72 MPa) were similar to the control (11.84 MPa, p = 0.169 and p = 1, respectively), but different from each other (p = 0.016).

CONCLUSIONS

From the results, it is recommended to use: MMA + Cosmos TEMP bonding agent for the Biotone tooth; and Cosmos TEMP or MMA + Cosmos TEMP bonding agents for the Cosmos TEMP tooth, both attached to the 3D-printed denture resin Cosmos Denture. This article is protected by copyright. All rights reserved.

The Effect of Salinized Nano ZrO2 Particles on the Microstructure, Hardness, and Wear Behavior of Acrylic Denture Tooth Nanocomposite

The wear of acrylic denture teeth is a serious problem that can change the vertical dimensions of dentures. This study evaluates the effect of adding salinized nano ZrO₂ particles on the microstructure, hardness, and wear resistance of acrylic denture teeth. Heat polymerizing polymethyl methacrylate resin was mixed with salinized ZrO₂ at concentrations of 5 wt.% and 10 wt.%. Acrylic resin specimens without filler addition were used as a control group. SEM/EDS analyses were performed and the Vickers’ hardness was evaluated. Two-body wear testing was performed using a chewing simulator with a human enamel antagonist. After subjecting the samples to 37,500 cycles, both height loss and weight loss were used to evaluate the wear behavior. The microstructural investigation of the reinforced-denture teeth indicates sound nanocomposite preparation using the applied regime without porosity or macro defects. The addition of zirconium oxide nanofillers to PMMA at both 5% and 10% increased the microhardness, with values of up to 49.7 HV. The wear mechanism in the acrylic base material without nanoparticle addition was found to be fatigue wear; a high density of microcracks were found. The addition of 5 wt.% ZrO₂ improved the wear resistance. Increasing the nanoparticles to 10 wt.% ZrO₂ further improved the wear resistance, with no microcracks found.

Comparative Effect of Different Surface Treatments on the Shear Bond Strength of Two Types of Artificial Teeth Bonded To Two Types of Denture Base Resins

PURPOSE

This in vitro study aims to assess the impact of various surface treatments on the shear bond strength (SBS) of two types of artificial teeth and denture base resins (DBRs).

MATERIALS AND METHODS

Two types of DBRs (CAD/CAM-milled and heat-polymerized) and two types of denture teeth (acrylic and composite) were investigated. Teeth were cut into slices (5 × 5 × 2 mm) and divided according to surface treatment into four subgroups (n = 10): no treatment (control), air abrasion (Alumina-blasting; AB), bur roughening, and dichloromethane (DCM) subgroups. According to manufacturer recommendations, the treated tooth slices were bonded to the acrylic disk of DBRs. The SBS test was performed using a universal testing machine. ANOVA was used for results analysis followed by Tukey's post hoc tests (α = 0.05).

RESULTS

DCM and AB increased the SBS of acrylic teeth to heat-polymerized DBR compared with other groups (p < 0.001). All surface treatments showed no significant difference in CAD/CAM DBR with acrylic teeth (p = 0.059; AB, p = 0.319; bur roughening, p = 0.895; DCM), while there was a significant decrease in SBS with composite teeth (p ˂ 0.001). Between teeth, acrylic teeth showed a statistically significant increase in SBS compared to composite teeth (p < 0.001).

CONCLUSION

AB and DCM application improved the SBS for acrylic teeth with the heat-polymerized DBR when compared with the untreated group, but none of the surface treatment agents showed significant improvement with CAD/CAM DBR. All surface treatment agents reduced the SBS for composite teeth with CAD/CAM DBR while AB only increased the SBS with heat-polymerized DBR.

Numerical Analysis of the Bond Strength between Two Methacrylic Polymers by Surface Modification

The creation of acrylic dentures involves many stages. One of them is to prepare the surfaces of artificial teeth for connection with the denture plates. The teeth could be rubbed with a chemical reagent, the surface could be developed, or retention hooks could be created. Preparation of the surface is used to improve the bond between the teeth and the plate. Choosing the right combination affects the length of denture use. This work focuses on a numerical analysis of grooving. The purpose of this article is to select the shape and size of the grooves that would most affect the quality of the bond strength. Two types of grooves in different dimensional configurations were analyzed. The variables were groove depth and width, and the distance between the grooves. Finally, 24 configurations were obtained. Models were analyzed in terms of their angular position to the loading force. Finite element method (FEM) analysis was performed on the 3D geometry created, which consisted of two polymer bodies under the shear process. The smallest values of the stresses and strains were characterized by a sample with parallel grooves with the grooving dimensions width 0.20 mm, thickness 0.10 mm, and distance between the grooves 5.00 mm, placed at an angle of 90°. The best dimensions from the parallel (III) and cross (#) grooves were compared experimentally. Specimens with grooving III were not damaged in the shear test. The research shows that the shape of the groove affects the distribution of stresses and strains. Combining the selected method with an adequately selected chemical reagent can significantly increase the strength of the connection.

Bonding Behavior of Conventional PMMA towards Industrial CAD/CAM PMMA and Artificial Resin Teeth for Complete Denture Manufacturing in a Digital Workflow

When applying a digital workflow, custom artificial resin teeth have to be integrated into a milled complete denture base, using polymethylmethacrylate (PMMA) applied with a powder–liquid technique. Debonding of denture teeth from dentures is reported to be a frequent complication. No evidence is provided as to which method of surface treatment may enhance the bonding strength. The bonding strength between artificial teeth and PMMA (Group A, n = 60), as well as between the PMMA and industrial PMMA (Group B, n = 60), was investigated following no treatment, monomer application, sandblasting, oxygen plasma, and nitrogen plasma treatment. Surface-roughness values and SEM images were obtained for each group. Shear bond strength (SBS) and fracture mode were analyzed after thermocycling. Within Group A, statistically significant higher SBS was found for all surface treatments, except for nitrogen plasma. In Group B, only nitrogen plasma showed a statistically lower SBS compared to the reference group which was equivalent to all surface treatments. Conclusions: Within the limitations of the present study, the monomer application can be proposed as the most effective surface-treatment method to bond custom artificial teeth into a milled PMMA denture base, whereas nitrogen plasma impairs the bonding strength.

Comparison of shear bond strengths of different types of denture teeth to different denture base resins

PURPOSE

To determine the shear bond strengths of different denture base resins to different types of prefabricated teeth (acrylic, nanohybrid composite, and cross-linked) and denture teeth produced by computer-aided design/computer-aided manufacturing (CAD/CAM) technology.

MATERIALS AND METHODS

Prefabricated teeth and CAD/CAM (milled) denture teeth were divided into 10 groups and bonded to different denture base materials. Groups 1-3 comprised of different types of prefabricated teeth and cold-polymerized denture base resin; groups 4-6 comprised of different types of prefabricated teeth and heat-polymerized denture base resin; groups 7-9 comprised of different types of prefabricated teeth and CAD/CAM (milled) denture base resin; and group 10 comprised of milled denture teeth produced by CAD/CAM technology and CAD/CAM (milled) denture base resin. A universal testing machine was used to evaluate the shear bond strength for all specimens. One-way ANOVA and Tukey post-hoc test were used for analyzing the data (α=.05).

RESULTS

The shear bond strengths of different groups ranged from 3.37 ± 2.14 MPa to 18.10 ± 2.68 MPa. Statistical analysis showed significant differences among the tested groups (P<.0001). Among different polymerization methods, the lowest values were determined in cold-polymerized resin.There was no significant difference between the shear bond strength values of heat-polymerized and CAD/CAM (milled) denture base resins.

CONCLUSION

Different combinations of materials for removable denture base and denture teeth can affect their bond strength. Cold-polymerized resin should be avoided for attaching prefabricated teeth to a denture base. CAD/CAM (milled) and heat-polymerized denture base resins bonded to different types of prefabricated teeth show similar shear bond strength values.

Investigation of Impact Strength, Water Sorption and Cytotoxicity of Denture Base Resin Reinforced with Polypropylene Fiber: In Vitro Study

Aim:

Polymethyl methacrylate is the common material used as a denture base. Ease of application, stability in the oral environment are its advantages; however, its mechanical properties should be enhanced. This study aimed to evaluate the effect of different ratios of polypropylene fiber (PPF) in addition to denture base materials on impact strength, water sorption, and cytotoxicity.

Materials and Methods:

Heat-cure acrylic resin specimens were prepared according to the manufacturer’s instruction by adding PPFs of 6 mm length in different ratios (1, 3, 5, 10, and 20 wt%). In order to determine the impact strength, specimens were subjected to a Charpy impact test machine after being kept in distilled water at 37°C for 48 h. A span of 40 mm was adjusted and a 0.5 J pendulum was used. The fractured surface of specimens was also analyzed using a scanning electron microscope. In addition, mouse fibroblast cells and agar diffusion tests were used for cytotoxicity determination. The results were analyzed using the Kruskal–Wallis and the Mann–Whitney U tests for determining impact strength, and Kruskal–Wallis and Tukey’s range tests were performed for determining water sorption values ( P = 0.05).

Results:

5 wt% PPF group exhibited the highest water sorption and impact strength values, and the difference was statistically significant ( P < .05). On the other hand, no cytotoxic effects were determined in PPF added groups. Furthermore, increased fiber concentration caused less water sorption.

Conclusion:

Addition of PPFs in acrylic resin increased the impact strength and decreased water sorption without any cytotoxic effects.

Influence of silanized silica and silanized feldspar addition on the mechanical behavior of polymethyl methacrylate resin denture teeth

STATEMENT OF PROBLEM

Artificial denture teeth made of polymethyl methacrylate (PMMA) resin have good adhesion to the denture base but are relatively soft and have limited wear resistance during function.

PURPOSE

The purpose of this in vitro study was to evaluate the influence of the addition of 2 inorganic nanofillers on the flexural strength, maximal displacement, elastic modulus, Isolde impact resistance, and Brinell hardness of acrylic resin denture teeth.

MATERIAL AND METHODS

Heat polymerizing polymethyl methacrylate resin was mixed with silanized silica or silanized feldspar in concentrations of 5 wt%, 10 wt%, and 15 wt%. The first test was conducted after 24 hours of storage in laboratory conditions, and the second assessment was conducted after 3 months of storage in distilled water at 37 °C. The Brinell hardness was evaluated, and the elastic modulus and maximal displacement at fracture were calculated. The flexural strength and Isolde impact resistance were measured with a 3-point flexural test. Acrylic resin specimens without filler addition were used as a control group. Statistical analysis included 2-way ANOVA for independent variables (α=.05) and the Student t test for time-dependent changes (α=.05). These were performed with Statistica 12 software.

RESULTS

The acrylic resin specimens modified with the addition of silanized feldspar had significantly higher Brinell hardness, elastic modulus, maximal displacement, and flexural strength and also had no adverse effect on Isolde impact resistance compared with the conventional acrylic resin. Silica filler increased the Brinell hardness and elastic modulus of acrylic resins but significantly reduced the flexural strength and Isolde impact resistance.

Comparative Analysis of the Water Sorption and Cytotoxicity of Two different Denture Base Systems: An in vitro Study

AIM

Different biomaterials and techniques have been introduced in the field of prosthetic dentistry with the purpose of replacement and rehabilitation of the edentulous areas. Due to their shorter setting time, the light-activated restorative and prosthetic materials have the capability of releasing few amount of cytotoxic materials in the oral cavity. Polymer materials [urethane dimethacrylate (UDMA) and bis-acryl] are assumed to have high mechanical properties. Polymethyl methacrylate (PMMA) offers numerous advantages of being highly esthetic in nature and at the same time being cost-effective. Hence, this study aimed to assess and compare the water sorption and cytotoxicity of light-activated UDMA denture base resin and conventional heat-activated PMMA resin.

MATERIALS AND METHODS

This study included assessment and comparison of water sorption and cytotoxicity of heat-activated PMMA resin and light-activated UDMA denture base system. Fabrication of heat-activated PMMA resin and UDMA specimens was done by investing the wax patterns in stone molds using manufacturer's instructions. Contraction of the specimens was done for assessment of cytotoxicity and water resorption of the UDMA and PMMA resin samples. All the results were analyzed by Statistical Package for the Social Sciences software version 18.0. Chi-square test and one-way analysis of variance tests were used for the assessment of the level of significance; p < 0.05 was taken as significant.

RESULTS

Mean lysis score observed in the PMMA and UDMA groups was 0.4 and 0.3 respectively. While observing at the 3 months time, the mean water resorption in the PMMA and UDMA groups was found to be 37.9 and 40.2 respectively. Significant difference in relation to water resorption was observed between the two study groups only at 3 months time.

CONCLUSION

Both materials used in this study are nontoxic. Furthermore, UDMA resin materials exhibited lower water resorption after more than 1 month of time of storage.

CLINICAL SIGNIFICANCE

Water resorption is similar for different denture base resin systems till 1 months time.

Effect of potentially chromogenic beverages on shear bond strength of acrylic denture teeth to heat-polymerized denture base resins

Background:

Detachment of denture acrylic resin artificial teeth from denture base resin is one of the most common problems presented by denture wearers. Purpose: This study investigated the shear bond strength (SBS) and fracture type of bonding interface of two commercial acrylic teeth (Vipi Dent Plus e Biolux) to two denture base resins (Vipi Cril e Lucitone 550) after immersion in potentially chromogenic beverages (coffee, cola soft drink, and red wine) or control solution (distilled water).

Materials and Methods:

Maxillary central incisor acrylic teeth were placed at 45° to denture base resin and submitted to short polymerization cycle according to manufacturers. Specimens were divided according to the combination tooth/resin/solution (n = 8) and submitted to bond strength tests in a universal testing machine MTS-810 (0.5 mm/min). Subsequently, fracture area was analyzed by stereomicroscope at a magnification of ×10 and categorized into adhesive, cohesive, or mixed failure.

Results:

The bond strength of teeth/denture base resins interface was not significantly affected by tested solutions (P > 0.087), except for Biolux teeth immersed in coffee (P < 0.01). In all conditions, the Vipi Dent Plus teeth showed higher bond strength to Lucitone and Vipi Cril resins when compared to Biolux teeth (P < 0.003). All specimens’ failure modes were cohesive.

Conclusions:

The SBS of acrylic teeth to denture base resins was not generally influenced by immersion in the tested staining beverages.

Comparative failure load values of acrylic resin denture teeth bonded to three different heat cure denture base resins: An in vitro study

Aim and Objectives:

Acrylic teeth are used for fabrication of dentures. Debonding of tooth – denture base bond is routine problem in dental practice. The aim of this study was to comparatively evaluate failure load of acrylic resin denture teeth bonded to three different heat resin.

Materials and Methods:

Four groups were created out of test samples central incisors (11). Group I: Control, whereas Group II, Group III and Group IV were experimental groups modified with diatoric hole, cingulum ledge lock and Teeth modified with both diatoric hole and cingulum ledge lock, respectively. These test specimens with 3 teeth (2 central [11, 21] and 1, lateral [12] incisors) positioned imitating arrangement of teeth in the conventional denture, prepared by three different heat cure materials (DPI, Trevalon, Acralyn-H). A shear load was applied at cingulum of central incisor (11) at 130° to its long axis using universal tester at a cross head speed of 5 mm/min until failure occurred. Failure load test was conducted and statistical analysis was performed using SPSS 16 software package (IBM Company, New York, U.S).

Results:

Highest failure load was seen in Group IV specimens, prepared by Trevalon but did not significantly differ from that of DPI.

Conclusion:

The failure load of bonding denture teeth to three different heat cure materials was notably affected by modifications of ridge lap before processing. The specimens with a combination of diatoric hole and cingulum ledge lock, prepared by Trevalon showed highest failure load but did not significantly vary from that of DPI. The control group prepared by Acralyn-H showed lowest failure load but did not significantly differ from that of DPI.

Influence of Surface Modifications of Acrylic Resin Teeth on Shear Bond Strength with Denture Base Resin-An Invitro Study

BACKGROUND

Debonding of artificial teeth from the denture base is an important issue for edentulous patients rehabilitated with conventional or implant supported complete dentures.

AIM

The purpose of this study was to evaluate shear bond strength between denture base resin and acrylic resin denture teeth subjected to three different surface modifications on the ridge lap area as compared to unmodified denture teeth.

MATERIALS AND METHODS

Forty acrylic resin central incisor denture teeth were selected and randomly divided into four test groups. The teeth in each group were subjected to one of the three different surface modifications, namely, chemical treatment, sandblasting and placement of retentive grooves on the ridge lap area respectively, prior to packing of the denture base resin. The group with unmodified teeth served as control. Forty acrylic resin test blocks thus obtained were tested for shear bond strength between acrylic resin teeth and denture base resin in Universal Testing Machine. Data obtained was statistically analysed using one-way ANOVA and Student- Newman- Keul's test (p< 0.05).

RESULTS

Analysis of shear bond strength revealed that retentive grooves on the ridge lap area showed highest bond strength values followed by sandblasting and both were statistically significant compared to the control and chemically treated groups. Unmodified surface of the resin teeth showed the least bond strength.

CONCLUSION

Within the limitations of this invitro study the placement of retentive grooves or sandblasting of the ridge lap area showed highly significant improvement in shear bond strength compared to the unmodified surface. Chemical treatment did not result in any significant improvement in the shear bond strength compared to the unmodified surface.

Effect of different temporary crown materials and surface roughening methods on the shear bond strengths of orthodontic brackets

OBJECTIVE

The aim of this study was to evaluate the effect of different temporary crown materials (TCMs) and surface roughening methods on the shear bond strength (SBS) of orthodontic brackets.

BACKGROUND DATA

TCMs are widely used during orthodontic treatment in teeth in need of prosthetic treatment, to prevent damage to the final restoration. However, there is no consensus considering the best method for roughening of the surface of TCMs.

METHODS

Five different TCMs [Dentalon Plus-(D), Basworth Trim II-(B), Voco Structure Premium-(V), 3M ESPE Protempt 4-(P), and Revotek LC-(R)] were used in this study. Different surface roughening methods (37% phosphoric acid, sandblasting, and Er:YAG laser) were employed in three subgroups (n=20). The SBS test was used to assess the durability of all groups. Scanning electron microscopy (SEM) analysis was performed on a representative specimen in each group.

RESULTS

The highest mean SBS value was observed in group V, followed by groups D and P, regardless of the surface treatment. The lowest SBS values were observed in group B. The laser-irradiated groups had higher SBS values than the sandblasted and acid-etched groups. Furthermore, a significant difference in SBS values was observed between the laser-irradiated group V and all other groups (p<0.005).

CONCLUSIONS

The effects of the chemical nature of TCMs on the SBS values appeared to be clinically negligible, whereas the type of surface treatments had a significant influence on bond strengths. Er:YAG laser irradiation caused a significant increase in bond strength between the TCMs and orthodontic brackets.

A comparison of shear bond strength of ceramic and resin denture teeth on different acrylic resin bases

The purpose of this study is to compare the shear bond strength of different resin bases and artificial teeth made of ceramic or acrylic resin materials and whether tooth-base interface may be treated with aluminium oxide sandblasting. Experimental measurements were carried on 80 specimens consisting of a cylinder of acrylic resin into which a single tooth is inserted. An ad hoc metallic frame was realized to measure the shear bond strength at the tooth-base interface. A complete factorial plan was designed and a three-way ANalysis Of VAriance (ANOVA) was carried out to investigate if shear bond strength is affected by the following factors: (i) tooth material (ceramic or resin); (ii) base material (self-curing or thermal-curing resin); (iii) presence or absence of aluminium oxide sandblasting treatment at the tooth-base interface. Tukey post hoc test was also conducted to evaluate any statistically significant difference between shear strength values measured for the dif-ferently prepared samples. It was found from ANOVA that the above mentioned factors all affect shear strength. Furthermore, post hoc analysis indi-cated that there are statistically significant differences (p-value=0.000) between measured shear strength values for: (i) teeth made of ceramic material vs. teeth made of acrylic resin material; (ii) bases made of self-curing resin vs. thermal-curing resin; (iii) specimens treated with aluminium oxide sandblasting vs. untreated specimens. Shear strength values measured for acryl-ic resin teeth were on average 70% higher than those measured for ceramic teeth. The shear bond strength was maximized by preparing samples with thermal-curing resin bases and resin teeth submitted to aluminium oxide sandblasting.

In vitro comparison of the cytotoxicity and water sorption of two different denture base systems

PURPOSE

Denture base resins have the potential to cause cytotoxicity in vivo, and the mechanical properties of resins are affected by water sorption. There is a correlation between residual monomer and water sorption. Thus, the purpose of this study was to evaluate water sorption and cytotoxicity of light-activated urethane dimethacrylate (UDMA) denture base resin compared to a conventional heat-activated polymethyl methacrylate (PMMA) resin.

MATERIALS AND METHODS

Two denture base resins, heat-activated PMMA (Meliodent) and light-activated UDMA (Eclipse), were used in this study. Cytotoxicity (5 × 1 mm(2) ) and water sorption (1 × 1 mm(2) ) specimens were made following the manufacturers' instructions (n = 10). Cytotoxicity tests of denture base resins were performed according to ISO10993-5:1999, and water sorption was evaluated according to ISO 1567:1997. ANOVA tests were employed for evaluating data (α = 0.05).

RESULTS

There was no cytotoxic effect in either the PMMA or UDMA group. In addition, contrary to short-term water storage, a significantly lower water sorption value was shown for UDMA resins compared to PMMA resins in both 3- and 6-month storage periods (p = 0.043 and p = 0.002, respectively).

CONCLUSION

The tested denture base materials adhered to the ISO standards for both cytotoxicity and water sorption. The cytotoxicity of the light-activated UDMA resin tested was statistically similar to that of the heat-activated PMMA resin; however, the UDMA resin exhibited decreased water sorption in long-term water storage.