Finite element analysis of stress relaxation in soft denture liner

Development of an optimal relief method for the palatal plate by stress analysis

BACKGROUND

Plate dentures cannot be easily modified after fabrication; therefore, the sites and magnitude of relief must be effectively assessed at the time of fabrication. However, a considerable variation exists in the magnitude of optimal relief and relief range, and there are no guidelines that present these clearly, leading the dentists to decide subjectively. Thus, this study aims to develop an optimal relief method to improve the stress bearing capacity of the palatal mucosa.

METHODS

The objective of this study, namely, the borderline, was set in steps. A three-dimensional finite element model for the pseudopalatal plate was created and used to evaluate the changes in stress distribution in the palatal mucosa due to the selective relief of stresses above the borderline. The resulting data were used to develop the optimal relief method.

RESULTS

In the relief model with a borderline of 0.04 MPa or higher, the distribution volume at which a high stress of 0.20 MPa or higher is generated was approximately 800% of that with the no-relief model, and in the relief model with a borderline of 0.06 MPa or higher, the respective ratio was approximately 280%. On the other hand, the relief models with a borderline of 0.14 MPa or higher were approximately 60%. In the mid-palatal relief model, the distribution volume at which a stress of 0.20 MPa or higher was generated was 180% of that in the relief model.

CONCLUSIONS

The supportive strength of plates can be increased by selectively applying optimal relief rather than standard relief, allowing for easier and more effective plate-denture treatment.

Stress distribution analysis of oral mucosa under soft denture liners using smoothed particle hydrodynamics method

This study aims to simulate the stress distributions of oral mucosa under different soft denture liners using the smoothed particle hydrodynamics (SPH) method. The Young's modulus and viscosity of denture liners composed of silicone (Sofreliner Super Soft and Sofreliner Tough Medium, Tokuyama Dental), acrylic (Vertex Soft, Vertex Dental), and a tissue conditioner (Visco-gel, Dentsply Sirona) were measured using a creep meter. A numerical simulation model that represents the stress distribution of oral mucosa under soft denture liners was also developed using the SPH method. The oral mucosa was divided into four regions: A) buccal border, B) buccal shelf, C) crest of residual ridge, and D) lingual border. For each region, the von Mises stress (hereafter, referred to as "Mises stress") of the oral mucosa was calculated. Based on a creep test, Sofreliner Super Soft and Sofreliner Tough Medium silicone liners showed an elastic behavior, whereas Vertex Soft acrylic liner and Visco-gel tissue conditioner showed a viscoelastic behavior. In addition, Sofreliner Super Soft and Visco-gel exhibited a large strain. The numerical simulation revealed that the mean Mises stress was the highest in region A and lowest in region D. Vertex Soft acrylic liners resulted in a statistically lower Mises stress on the oral mucosa compared to the other three soft denture liners. Different soft denture liner materials lead to different stress distributions on the oral mucosa. The acrylic soft denture liners cause a lower Mises stress on the oral mucosa than the silicon soft denture liners. This suggests that acrylic soft denture liners would be more effective for manufacturing painless dentures than silicone soft denture liners.

Root canal reconstruction using biological dentin posts: A 3D finite element analysis

Background. Several types of post have been developed for clinical use. A biological dentin post obtained from an extracted tooth eliminates the problems arising from material differences and reduces the fracture rate in teeth undergoing root canal treatment. This study used finite element analysis to compare a biological dentin post with posts made of two different materials. Methods. Three 3D models of the upper central incisor were created, and stainless-steel, glass fiber and biological dentin posts were applied to these models. The restoration of the models was completed by applying a composite as the core structure and a ceramic crown as the superstructure. Using finite element stress analysis in the restoration models, a 100-N force was applied in the vertical and horizontal directions and at a 45º angle, and the suitability of the biological dentin post was evaluated by comparing the data. Results. Under the applied forces, the greatest stress accumulation was seen in the models with the stainless steel post. Because the stainless steel post was more rigid, stress forces accumulated on the surface instead of being transmitted to the tooth tissue. In the models with the glass fiber and biological dentin posts, the post material responded to the stratification in tandem with the dental tissue and did not cause excessive stress accumulation on the tooth or post surfaces. Conclusion. The results showed that biological dentin posts prevent the accumulation of stresses that might cause fractures in teeth undergoing root canal treatment. In addition, the physical compatibility and biocompatibility of a biological dentin post with the tooth imply that it is a good alternative to the types of post currently used.

Changes in hardness of addition-polymerizing silicone-resilient denture liners after storage in artificial saliva

STATEMENT OF PROBLEM

The hardness of silicone resilient denture liners was reported to be more stable than that of acrylic resin resilient denture liners. However, the changes in hardness of these materials in artificial saliva are unclear.

PURPOSE

The purpose of this in vitro study was to evaluate changes in the hardness of addition-polymerizing silicone-resilient denture liners for long-term use after storage in artificial saliva.

MATERIAL AND METHODS

Four addition-polymerizing silicone resilient denture liners were tested: GC Reline Soft, Elite Soft Relining, Megabase, and Mucopren Soft. All were long-term relining materials of the soft type. Fifteen disk-shaped specimens were prepared for each of the tested materials (40 mm in base diameter, 8 mm in thickness). Their initial hardness was assessed with a Shore A durometer, after which they were stored in artificial saliva at a temperature of 37°C. Hardness was examined after 7, 30, and 90 days. Statistical analysis was performed using parametric ANOVA for dependent and independent variables and Tukey honest significant difference (HSD) post hoc tests (α=.05).

RESULTS

All resilient denture liners increased in hardness during the experiment. The change was least for Elite Soft Relining, and GC Reline Soft was the hardest material. Initially, Megabase and Mucopren Soft were significantly softer than the other 2 materials, but their hardness increased rapidly after the first 7 days of specimen conditioning, achieving values close to Elite Soft Relining.

CONCLUSIONS

Within the limitations of the study, room temperature vulcanizing addition-polymerizing polyvinyl siloxanes of the soft type have different initial hardness, and this changes with storage time in artificial saliva at the temperature of the oral cavity.

Stress Distribution under Commercial Denture Liners- A Finite Element and Clinical Analysis

INTRODUCTION

Previous studies have shown that 20-30% of denture users have been dissatisfied with their dentures.

AIM

To evaluate the stress pattern under elastic and viscoelastic denture liners using 3-Dimensional Finite Element Analysis (FEA) and its clinical correlation using a questionnaire.

MATERIALS AND METHODS

The study had both in-vitro and in-vivo phases. In in-vitro phase fabrication of a virtual parametric model of edentulous maxilla and dentures with overlying mucosa was made. A virtual load of 166N was analyzed at three points (Point A=anterior ridge, Point B=right posterior ridge and Point C=left posterior ridge). For the in-vivo phase, 20 edentulous patients were provided conventional complete dentures (Group-I). The dentures were lined with silicone (elastic) liners (Group-II) and acrylic resins (viscoelastic) liners (Group-III) at regular (2 months) intervals. After each reline, the patients were evaluated using food eating ability and denture assessment questionnaires. The results were statistically analyzed. The statistical analysis was done using SPSS (Statistical Package for Social Sciences) version 15.0 statistical analysis software. Other than standard statistical test Analysis of Variance (ANOVA) and Post-Hoc tests (Tukey-HSD) were used.

RESULTS

At loading, the in-vitro result for Groups-II and III revealed pressures of 0.074231N and 0.0678364N at Point A, 0.098764N and 0.093642N at Point B, and 0.099876N and 0.093746N at Point C respectively. The in-vivo study revealed that the mean quality of life score for different groups ranged from 23.65±4.00 (Group I) to 33.10±6.15 (Group III). The mean quality of life score for Group II was 29.50±5.08.

CONCLUSION

The viscoelastic liner provided the most uniform stress distribution and performed better than an elastic liner with hard, firm and soft foods.

Biomechanics of oral mucosa

The prevalence of prosthodontic treatment has been well recognized, and the need is continuously increasing with the ageing population. While the oral mucosa plays a critical role in the treatment outcome, the associated biomechanics is not yet fully understood. Using the literature available, this paper provides a critical review on four aspects of mucosal biomechanics, including static, dynamic, volumetric and interactive responses, which are interpreted by its elasticity, viscosity/permeability, apparent Poisson's ratio and friction coefficient, respectively. Both empirical studies and numerical models are analysed and compared to gain anatomical and physiological insights. Furthermore, the clinical applications of such biomechanical knowledge on the mucosa are explored to address some critical concerns, including stimuli for tissue remodelling (interstitial hydrostatic pressure), pressure–pain thresholds, tissue displaceability and residual bone resorption. Through this review, the state of the art in mucosal biomechanics and their clinical implications are discussed for future research interests, including clinical applications, computational modelling, design optimization and prosthetic fabrication.

Shape Optimization for Additive Manufacturing of Removable Partial Dentures--A New Paradigm for Prosthetic CAD/CAM

With ever-growing aging population and demand for denture treatments, pressure-induced mucosa lesion and residual ridge resorption remain main sources of clinical complications. Conventional denture design and fabrication are challenged for its labor and experience intensity, urgently necessitating an automatic procedure. This study aims to develop a fully automatic procedure enabling shape optimization and additive manufacturing of removable partial dentures (RPD), to maximize the uniformity of contact pressure distribution on the mucosa, thereby reducing associated clinical complications. A 3D heterogeneous finite element (FE) model was constructed from CT scan, and the critical tissue of mucosa was modeled as a hyperelastic material from in vivo clinical data. A contact shape optimization algorithm was developed based on the bi-directional evolutionary structural optimization (BESO) technique. Both initial and optimized dentures were prototyped by 3D printing technology and evaluated with in vitro tests. Through the optimization, the peak contact pressure was reduced by 70%, and the uniformity was improved by 63%. In vitro tests verified the effectiveness of this procedure, and the hydrostatic pressure induced in the mucosa is well below clinical pressure-pain thresholds (PPT), potentially lessening risk of residual ridge resorption. This proposed computational optimization and additive fabrication procedure provides a novel method for fast denture design and adjustment at low cost, with quantitative guidelines and computer aided design and manufacturing (CAD/CAM) for a specific patient. The integration of digitalized modeling, computational optimization, and free-form fabrication enables more efficient clinical adaptation. The customized optimal denture design is expected to minimize pain/discomfort and potentially reduce long-term residual ridge resorption.

Effect of Food Simulating Agents on the Hardness and Bond Strength of a Silicone Soft Liner to a Denture Base Acrylic Resin

STATEMENT OF THE PROBLEM

Bonding failure between acrylic resin and soft liner material and also gradual loss of soft liner resiliency over time are two impending challenges frequently recognized with a denture base embraced with a resilient liner. Since patients drink various beverages, it is crucial to assess the influences of these beverages on physical characteristics of soft liners.

PURPOSE

This in vitro study envisioned to assess the influence of food simulating agents (FSA) on the hardness of a silicone soft liner by employing a Shore A durometer test and also evaluate its bond strength to a denture base resin by using tensile bond strength test.

MATERIALS AND METHODS

To test the hardness of samples, 50 rectangular samples (40 mm × 10 mm × 3 mm) were prepared from a heat-polymerized polymethyl methacrylate (Meliodent). Mollosil, a commercially available silicone resilient liner, was provided and applied on the specimens following the manufacturer's directions. In order to test tensile bond strength, 100 cylindrical specimens (30 mm × 10 mm) were fabricated. The liners were added between specimens with the thicknesses of 3 mm. The specimens were divided into 5 groups (n=10) and immersed in distilled water, heptane, citric acid, and 50% ethanol. For each test, we used 10 specimens as a baseline measurement; control group. All specimens were kept in dispersed containers at 37ºC for 12 days and all solutions were changed every day. The hardness was verified using a Shore A durometer and the tensile bond strength was examined by an Instron testing machine at a cross-head speed of 5 mm/min. The records were analyzed employing one-way ANOVA, Tukey's HSD, and LSD tests.

RESULTS

The mean tensile bond strength ± standard deviation (SD) for Mollosil was as follows for each group: 3.1 ± 0.4 (water), 1.8 ± 0.4 (citric acid), 3.0 ± 0.4 (heptane), 1.2 ± 0.3 (50% ethanol), and 3.8 ± 0.4 (control). The hardness values for each group were: 28.7 ± 2.11 (water), 33.2 ± 2.82 (citric acid), 39.2 ± 4.8 (heptane), 32.3 ± 3.56 (50% ethanol) and 22.2 ± 2.08 (control). Mean values for hardness indicated that all of the food simulating agents significantly increased hardness of the Mollosil soft liner compared to the control group (p<0.05). The results of tensile bond strength depicted that water and FSA decreased the bond strength of the soft liner -denture base resin compared to the control group and it was statistically significant (p<0.05).

CONCLUSION

The food simulating agents could influence the mechanical properties of silicone soft liners; hence, clinicians should inform their patients concerning their possible adverse effects and complications.

Biomechanical factors related to occlusal load transfer in removable complete dentures

Owing to economic conditions, removable dentures remain popular despite the discomfort and reduced chewing efficiency experienced by most denture wearers. However, there is little evidence to confirm that the level of mucosal load exceeds the pressure pain threshold. This discrepancy stimulated us to review the current state of knowledge on the biomechanics of mastication with complete removable dentures. The loading beneath dentures was analyzed in the context of denture foundation characteristics, salivary lubrication, occlusal forces, and the biomechanics of mastication. The analysis revealed that the interpretation of data collected in vivo is hindered due to the simultaneous overlapping effects of many variables. In turn, problems with determining the pressure beneath a denture and analyzing frictional processes constitute principal limitations of in vitro model studies. Predefined conditions of finite element method simulations should include the effects of oblique mastication forces, simultaneous detachment and sliding of the denture on its foundation, and the stabilizing role of balancing contacts. This review establishes that previous investigations may have failed because of their unsubstantiated assumption that, in a well-working balanced occlusion, force is only exerted perpendicular to the occlusal plane, allowing the denture to sit firmly on its foundation. Recent improvements in the simulation of realistic biomechanical denture behavior raise the possibility of assessing the effects of denture design on the pressures and slides beneath the denture.

Influence of Different Soft Liners on Stress Distribution in Peri-Implant Bone Tissue During Healing Period. A 3D Finite Element Analysis

The aim of this study was to evaluate the stress distribution in the bone adjacent to submerged implants during masticatory function in conventional complete dentures with different soft liners through finite element analysis. Three-dimensional models of a severely resorbed mandible with 2 and 4 submerged implants in the anterior region were created and divided into the following situations: (1) conventional complete dentures (control group); and conventional complete dentures with different soft liner materials, (2) Coe-Comfort, (3) Softliner, and (4) Molteno Hard. The models were exported to mechanical simulation software and 2 simulations were done with the load in the inferior right canine (35 N) and the inferior right first molar (50 N). The data were qualitatively evaluated using the maximum principal stress and microstrain values given by the software. The use of soft liners provides decreased levels of stress and microstrains in peri-implant bone when the load was applied to canine teeth. Considering all of the values obtained in this study, the use of softer materials is the most suitable for use during the period of osseointegration.

Analysis of stress on mucosa and basal bone underlying complete dentures with different reliner material thicknesses: a three-dimensional finite element study

The aim of this study was to determine the optimal thickness of reliner material that provides the least amount of stress on thin mucosa and supporting bone in patients with complete removable dentures using a three-dimensional finite element analyses. The model was obtained from two CT scans of edentulous mandibles with dentures supported by the alveolar ridge. After virtual reconstruction, the three-dimensional models were exported to the solidworks cad software and divided into six groups based on the thickness of the reliner material as follows: (i) without material, (ii) 0·5 mm, (iii) 1 mm, (iv) 1·5 mm, (v) 2 mm and (vi) 2·5 mm. The applied load was 60 N and perpendicular to the long axis of the alveolar ridge of all the prosthetic teeth, and the mucosal thickness used was 1 mm. The analyses were based on the maximum principal stress in the fibromucosa and the minimum principal stress in the basal bone. Stress concentration was observed in the anterior zone of the mandible in the mucosa and in the bone. The maximum and minimum principal stress in the mucosa and bone, respectively, decreased, whereas the thickness of the reliner material increased until 2 mm, which transmitted the lowest stress, compared with the control. Reliner materials with a thickness of 2·5 mm showed higher stress values than those with a thickness of 2 mm. In conclusion, reliner material with a thickness of 2 mm transmitted the lowest amount of stress to the mucosa and bone in 1 mm of mucosa thickness.

Finite Element Analysis of Soft-lined Mandibular Complete Denture and its Supporting Structures

Background and aims

There are many edentulous people with severely resorbed residual ridges and non-resilient lin-ing mucosa that are unable to tolerate occlusal forces during functional and parafunctional movements. Lining the tissue surface of dentures with a flexible material can theoretically distribute and absorb forces with cushioning effect. The aim of this study was to evaluate the effect of a soft liner on stress levels in mandibular complete denture and its supporting struc-tures by finite element analysis.

Materials and methods

A simplified 3-dimensional finite element model of relatively resorbed mandible, mucosa, denture and a soft liner was prepared. Then the model, with and without soft liner, underwent normal vertical and lateral occlusal forces. The stresses were analyzed using the ANSYS 12 software.

Results

Using the soft liner increased stress levels up to 18.5% and 30% in the cortical bone and mucosa, respectively, after vertical load was applied in the incisor region. Application of bilateral vertical load on the molar area increased stress in cortical bone u to 44% and in the mucosa up to 29%. Unilateral loading in the canine area increased stress level in the mucosa up to 63.5%. The highest stress was seen at denture base followed by the cortical bone.

Conclusion

Use of soft liners increased stress in denture supporting structures. Higher level of stress concentration was observed primarily in the denture base followed by the cortical bone.

Strain analysis of maxillary complete denture with three-dimensional finite element method

STATEMENT OF PROBLEM

The fracture of maxillary complete dentures has been reported as the most common prosthesis failure.

PURPOSE

The purpose of this study was to evaluate strain distribution in dentures during application of occlusal load with 3-dimensional (3-D) finite element analysis (FEA).

MATERIAL AND METHODS

A maxillary complete denture was converted into a 3-D numerical model by an advanced topometric sensor digitizer (ATOS). The denture surfaces were scanned with fringes. Ten measurements were made for each scan of the denture in top, left, right, back, and front orientations by tilting the scanning table. The individual scans were merged by the digitizing software into a single image. A haptic device with a freeform system (PHANTOM) was used to create the mucosa in contact with the intaglio surface of the denture model. Supporting bone was then constructed from the mucosa model. The posterior teeth were loaded with an occlusal force of 230 N, and the basal bone was constrained for performing FEA.

RESULTS

The highest tensile and compressive strains were found at the incisal and labial frenal notches, respectively. Strains on the intaglio surface of the denture were primarily compressive. The buccal flange exhibited tensile strains in the horizontal direction but compressive strains in the vertical direction. The labial flange showed compressive strains in both directions. The posterior border of the denture flexed away from the mucosa during occlusal loading.

CONCLUSIONS

Three-dimensional FEA provided different views of strain distribution in the denture and indicated that denture failure was unlikely to occur at the shallow labial frenal notch because the strain is compressive. The high tensile strain concentration at the incisal notch is likely to be the cause of denture fracture during clinical service.

Development of an RPD CAD system with finite element stress analysis

The structural design of removable partial dentures (RPDs) is critical for preventing distortion of the prosthesis, protecting abutment teeth and residual ridges as well as for high masticatory performance. The aim of this study was to clarify the feasibility and utility of a computer-aided designing (CAD) system with finite element analysis (FEA) for molar teeth arrangement in unilateral distal extension base RPDs. The shapes of artificial teeth and residual ridge were measured and converted into point group data. Solid models were created from surface-modelled point group data in a 3D surface CAD format. An occlusal rim was created on the residual ridge mucosa and the occlusal rim - residual ridge mucosa model with FEA function was created. Stress distribution on the residual ridge mucosa was compared by changing the loading point. The artificial teeth were then arranged in locations with the lowest amount of stress. After building an artificial teeth - saddle - residual ridge mucosa model, stress distribution in the residual ridge mucosa was re-evaluated by simulating occlusal force. On the occlusal rim - residual ridge mucosa model, stress was reduced when the loading point was located around the buccal shelf where functional cusps of artificial teeth were charted. It was confirmed that stress distribution in the residual ridge mucosa was equalized on the artificial teeth - saddle - residual ridge mucosa model. This system might be clinically useful tool for designing RPDs if FEA-guided designing of retainers and connectors can be added.

Effect of oxygen plasma treatment on the bonding of a soft liner to an acrylic resin denture material

Mechanical roughening reportedly had a weakening effect on bond strength. Therefore, the purpose of this study was to evaluate the effect of an alternative surface roughening method, namely oxygen plasma treatment, on the tensile bond strength between denture base resin and soft liner. The soft liner used in this study was Soft Reverse, whilst the denture base material was Zi Ran. Three groups of specimens were prepared, comprising untreated specimens and oxygen plasma-treated specimens with exposure to air for 1 day and 2 days. All specimens were subjected to surface composition analysis and tensile bond strength testing. All data were analyzed using one-way ANOVA, and their mean values were compared using Tukey's HSD test (p<0.01). Highest tensile bond strength was observed in the 1-day exposure group (5.2 MPa), whilst the lowest in the control group of untreated specimens (2.8 MPa). Hence, results of this study clearly indicated that oxygen plasma treatment was effective in enhancing tensile bond strength.

Effect of thermocycling on tensile strength and tear resistance of four soft denture liners

This study evaluated the effect of thermocycling on the tensile strength and tear resistance of four long-term soft denture liners. One light-activated (Astron Light, AL), two chemically activated (GC Reline Soft, GC; Silagum Comfort, SC), and one heat-cured (Molloplast-B, MLP) soft liner materials were tested. Dumbbell and trouser-leg specimen geometries were used for tensile strength and tear resistance tests, respectively. A total of 120 specimens were prepared. Test specimens for each material (n=5) were subjected to thermal cycling for 1000 and 3000 cycles between 5 degrees C and 55 degrees C in a thermocycler. Before thermocycling, AL gave the lowest tensile strength, while SC exhibited the highest tear resistance value among the materials tested (p < 0.05). Thermal cycling significantly affected the tensile strength of AL as well as the tear resistance values of AL, MLP, and GC materials. This in vitro study revealed that the tensile strength and tear resistance values of the soft liner materials tested varied according to their chemical compositions.

The effect of occlusal contact localization on the stress distribution in complete maxillary denture

The fracture of acrylic resin dentures is an unresolved problem in removable prosthodontics despite many efforts to determine its cause. Unfavourable occlusion could be playing an important role in the fracture of the denture. The aim of this study was to investigate the effect of occlusal contact localization on the stress distribution in complete maxillary denture bases utilizing two-dimensional finite element analysis. The results of this study have shown that maximum compressive stresses in a complete maxillary denture under functional masticatory forces concentrates always on the artificial tooth/denture base junction irrespective to the occlusal contact localization. Tensile stresses were observed in areas toward the midline, although the midline itself usually had lower stresses. Shifting the occlusal contacts to a more buccal localization resulted in an increase of the calculated stresses. As a conclusion, it can be speculated that the buccal placement of the occlusal contacts may play a role in the fatigue fracture of the complete maxillary denture.

Clinical evaluation of a new resilient denture liner. Part 1: Compliance and color evaluation

PURPOSE

A new experimental resilient denture liner (MPDS-SL; Lai Laboratories, Burnsville, MN) and Molloplast-B (Buffalo Dental Manufacturing, Syosset, NY) were clinically evaluated for compliance and color change over a 1-year period.

MATERIALS AND METHODS

In this crossover study, each of 20 patients had 2 dentures fabricated with long-term, silicone-based resilient liners, 1 denture with Molloplast-B and the other with MPDS-SL. Each denture was used for 6 months, during which time each patient kept a journal detailing his or her use and cleaning regimen. The 2 materials were assessed for compliance and color at the beginning of the study and again after 3 months and 6 months of use. Compliance was determined by applying a 3-lb force to the surface of the material following a square-wave pattern, using a closed-loop servohydraulic testing system. The force and position values were recorded using a storage oscilloscope. Compliance was measured at 3 locations on each denture and analyzed using data-acquisition software. Images of the dentures were captured using a zoom stereomicroscope with a charge-coupled video camera and image analysis software. The color was measured at 3 locations on each denture; RGB and L* a* b* were calculated.

RESULTS

Compliance increased from baseline to 3 months and from 3 months to 6 months for almost all locations on both materials. Molloplast-B and MPDS-SL differed in average change in compliance at 6 months; the average change in compliance from baseline to 6 months was 453 (standard error, 46) for Molloplast-B and 284 (standard error, 46) for MPDS-SL (p = 0.019). For both materials, color changed significantly from baseline to 3 months and from baseline to 6 months (p < 0.01). MPDS-SL changed significantly less than Molloplast-B from baseline to 6 months for R (p = 0.039), G (p = 0.037), B (p = 0.005), and L* (p = 0.042).

CONCLUSION

For both materials, compliance increased over 6 months of wear. The color change for MPDS-SL was considerably less significant than that for Molloplast-B.

In vitro hardness, water sorption, and resin solubility of laboratory-processed and autopolymerized long-term resilient denture liners over one year of water storage

STATEMENT OF PROBLEM

The clinical properties of resilient denture liners may be influenced by the method by which they are polymerized.

PURPOSE

This in vitro study investigated material property changes of 2 new resilient denture lining materials that represent 2 different curing modes: autopolymerization and conventional laboratory processing.

MATERIAL AND METHODS

Two silicone-based liner products were tested; one was allowed to autopolymerize (Tokuyama Soft Relining Paste), and the other was laboratory processed (Luci-Sof). Ninety-six disk-shaped specimens (31 x 10 mm) were fabricated in aluminum ring molds for hardness testing. Sixty bar-shaped specimens (44 x 8.5 x 1.2 mm) were fabricated in aluminum molds for water sorption and resin solubility testing. Shore A hardness was determined directly after specimen fabrication and after 1 day, 1 week, 1 month, 6 months, and 1 year of water storage at 37 degrees C. Water sorption and resin solubility were determined at the same time intervals. Analysis of variance and appropriate t tests were used to determine the effect of immersion duration both within and between the products tested. All statistical testing was performed at alpha=.05.

RESULTS

The hardness values of the laboratory-processed material were consistently greater than those of the autopolymerized material. After 1 week of water storage, the hardness of the autopolymerized specimens stabilized, whereas the hardness of the laboratory-processed specimens increased with immersion duration. Water sorption values for the 2 test products were similar after 6 months and after 1 year of water storage. At 1 month, 6 months, and 1 year, significantly lower resin solubility (P<.05) was recorded for the autopolymerized specimens compared with their laboratory-processed counterparts.

CONCLUSION

Within the limitations of this study, the laboratory-processed material was harder than the autopolymerized product and demonstrated greater resin solubility over time. The latter result was not expected.