Abstract
Background:
Clinically, adhesion failure is the most critical problem because of the failure of the optimal bond between denture base and the soft liner.
Objectives:
This study was performed to assess the tensile bond strength of two temporary soft liners to different denture base resins.
Materials and Methods:
Forty-eight blocks with 16 samples each of heat-cured denture base resin of three different types were fabricated from custom-made stainless steel die after de-waxing mold space. Surface roughening of each acrylic resin specimens which bonds with soft liners was done by abrading the surface and to this temporary soft liners (Perma soft denture liner and Pro soft denture liner) were bonded. The universal testing machine was used to test the tensile strength of bonded space. The results were statistically analyzed using the Statistical Software IBM SPSS Statistics for Windows, version 20.0. (Armonk, NY, USA: IBM Corp.) using the Chi-square test, Post hoc Tukey's HSD, and two way ANOVA tests.
Results:
It was observed that Perma soft was prevalent over Pro-soft denture liner on the basis of tensile bond strength with all three different types of denture base resins. Trevalon HI and acrylic composite exhibited better bond strength results with both Perma soft and GC Pro-soft denture liner as compared to other types of denture base resins.
Conclusion:
Perma soft had a better bond strength compared to Pro-soft denture liner in bonding modified denture base and conventional resins.
Keywords: Denture base resins, soft liners, tensile bond strength, les résines de base de Râtelier, les paquebots mous, la force d’obligation extensible
Résumé
Fond:
Cliniquement, l’échec d’adhésion est le problème le plus critique à cause de l’échec de l’obligation optimale entre la base de râtelier et le paquebot mou.
Objectifs:
Cette étude a été exécutée pour évaluer la force d’obligation extensible de deux paquebots mous temporaires à de différentes résines de base de râtelier.
Matériel et Méthodes:
les blocs de Forty-eight avec 16 échantillons chacune de résine de base de râtelier heat-cured de trois différents types ont été fabriqués de l’acier inoxydable custom-made meurent après que de-waxing moisissent l’espace. Le fait de rendre rude de surface de chaques exemplaires de résine en acrylique que les obligations avec moules paquebots ont été faits en abrasant la surface et à ce temporaire les paquebots mous (Perma le paquebot de râtelier mol et le paquebot de râtelier mol Avantageux) étaient bonded. La machine de mise à l’essai universelle a été utilisée pour évaluer la limite élastique à traction d’espace bonded. Les résultats ont été statistiquement analysés en utilisant le Statistique Le logiciel IBM la Statistique de SPSS pour Windows, la version 20.0. (Armonk, NEW YORK, Etats-Unis: Société d’IBM.) l’utilisation de l’épreuve de Chi-square, Postez le HSD de Tukey hoc, et deux voie.
Résultats:
Il a été remarqué que Perma mol était qui prévaut sur le paquebot de râtelier Pro-soft sur la base de l’obligation extensible la force avec tous les trois différents types de râtelier base des résines. Trevalon SALUT et le composite en acrylique a exposé de meilleurs résultats de force d’obligation avec tant Perma mous que GC Pro-soft le paquebot de râtelier en comparaison d’autres types de râtelier basent des résines.
Conclusion:
Perma mol avait une meilleure obligation la force comparée au paquebot de râtelier Pro-soft dans bonding a modifié la base de râtelier et les résines conventionnelles.
INTRODUCTION
Removable dental prosthesis used to replace missing teeth relies on residual alveolar bone and the overlying mucoperiosteum. Removable denture bases are made of conventional heat-cured poly methyl methacrylate (PMMA) resins as they have fracture toughness and rigidity.[1] These prosthesis adversely affected by high-stress concentrations during function which can be a source of significant harm to the supporting tissues ensuing in accelerated ridge resorption and soft-tissue damage to the denture-bearing areas. Relining of such denture base can reduces the damage to the supporting structures and improves stability, retention of denture. Relining can be done at chair side or in the laboratory because of simplicity in technique. They operate as a cushion for the denture bearing mucosa through absorption, dampening, and reorganization of forces conveyed to the stress-bearing areas of edentulous ridges. One of the most serious problems with these materials is leaching out of plasticizers and other soluble ingredients, and absorption of water and saliva, bond failure between the resilient denture liner and denture base, which in turn results into ingress of oral fluids and microorganisms at their interface, plaque formation and separation of the reline material from the denture base.[2,3]
Various soft liners are used in the form of plasticized polyvinyl resin and silicone elastomers. Permanent soft liners are classified as heat-polymerized silicone, autopolymerized silicone, autopolymerized acrylic resin, and heat-polymerized acrylic resin. Silicone-based denture liners have a diverse molecular structure in contrast to PMMA denture base resin and cannot be chemically bonded with PMMA. Bonding between them entirely depends on an interfacial adhesion. Dissimilar types of chemical etchants (such as dichloromethane, MMA monomer, chloroform, acetone, and methylene chloride) can be applied for the surface treatment of the denture base resin earlier to the application of silicone-based denture liner to develop the bond strength of the liner with the denture base resin. It is suggested that the bond strength between the dentures reline and denture base resins could affect the mechanical strength of the reline denture base.[3,4]
Relining and rebasing of denture base are frequently done procedure in dentistry. A soft-tissue liner is inserted at under surface of denture so that here is no trauma to underlying soft tissue of ridges. In dentistry, apart from soft-tissue liners, hard-tissues liners are also used. However, in patients who cannot bear hard-tissue liner, a permanent soft cushion is placed on the undersurface of denture.[5]
Recent studies have demonstrated that, silicone-based liners are more resilient and resistant to aged deformation than acrylic-based denture liners, long-term dentures are lined with silicone based liners. However, it has found that acrylic-based soft denture liners reveal better visco-elastic properties and has better improvement to masticatory function.[6]
al-Athel and Jagger studied the different bond strength assessment methods such as peel test, tensile bond strength, and shear bond strength between the soft liner and denture base interface. They suggested that sufficient bond strength is of paramount importance between the soft liner material and denture base to overcome the interfacial separation at the denture borders.[7]
Roughening the fitting surface of the denture base to which the resilient lining materials are to be applied has a weakening effect on the bond between the lining and the denture base. Long-term exposure of the liners to water has a destructive effect.[8]
An important factor for studying failure strength is bonding compatibility of denture base material with soft-liner material. There is similar chemical structure of PMMA temporary soft liners and PMMA denture base materials. For acrylic-based liners, it is unnecessary to apply bonding agent before the use of a liner, hence bonding agents were not advised.[9] It has been advised to improve bond strength by mechanical roughening using sandblasting or lasers and treatment with denture base monomers.[10]
There are very few reported studies on comparison of auto- and heat-polymerizing denture liners after surface treatment with various chemicals and thermo cycling. Available studies on perma soft and pro soft liner comparison are very limited. Hence, the present study was conducted to assess the tensile bond strength of two soft liners (Perma soft denture liner [Dentsply GmbH, Germany], and Pro soft denture liner [Perma Laboratory, USA]) with three types denture base resins (conventional denture base resins and glass-reinforced denture base resins [Acrylic composite] and high impact denture-based resin [Trevalon HI]).
MATERIALS AND METHODS
The present in vitro study was conducted on 2018 in the department of prosthodontics, Institute of Dental Sciences, Siksha O’ Anusandhan, after obtaining ethical approval from the Institutional Ethics Committee, IRB Ref. No. IDS# Res. 002/2018.
This study was conducted on the hypothesis that, bond strength between the denture reliner and denture base resins could affect the mechanical strength of the reline denture base interface. Use of Perma soft and prosoft could increase the bond strength between denture base and soft liners. The present in vitro study evaluate and compares the tensile bond strength of three different denture base resins bonded to two different soft liners.
Table 1 shows the composition of commercially available soft liners; Perma soft denture liner (Group A) and Pro soft denture liner (Group B). Table 2 indicates the different denture base resins: (1) Conventional denture base resins, (2) glass-reinforced denture base resins (acrylic composite), and (3) high-impact denture-based resin (Trevalon HI) used in the study.
Table 1.
Temporary soft liners used in the study
| Temporary soft liner | Company | Composition | Percentage |
|---|---|---|---|
| Perma soft denture line (Group A) | DENTSPLY GmbH, Germany | PEMABPBG | 84.2 |
| PMMADBP | 12.4 | ||
| Et OH | 3.6 | ||
| Pro soft denture liner (Group B) | Perma Laboratory, USA | PEMABPBG | 100 |
| DBP | 5.3 | ||
| EtOH | 15.8 |
PEMA=Polyethyl methacrylate, PMMA=Polymethyl methacrylate, BPBG=Butyl pthalyl butyl glycolate, DBP=Dibutylpthalate, EtOH=Ethyl alcohol
Table 2.
Commercially available denture base resins used in the study
| Company | Denture base product |
|---|---|
| Dental Products of India, Mumbai | Conventional denture base resins |
| Dentsply India Pvt. Ltd., Gurgaon | Glass reinforced denture base resins (Acrylic composite) |
| Dentsply India Pvt. Ltd., Gurgaon | High impact denture based resin (Trevalon HI) |
HI=High impact
A total of 48 heat-processed acrylic resin blocks made up of PMMA were divided into three groups, with 16 each type of three different denture base materials ((1) conventional denture base resins, (2) glass reinforced denture base resins [Acrylic composite], and (3) high impact denture-based resin [Trevalon HI]). The sample size was calculated by the following formula: 
, assuming (p) = 90 as the bond strength with 9% margin of error, formula used was n = where P is bond strength, q = 1 − p, d is the margin of error, Zα/2 is the ordinate of standard normal allocation at α% level of implication.
Resin blocks of dimension 1.4 cm × 1.4 cm × 0.25 cm were obtained by processing wax blocks of similar size poured out of a custom-made stainless steel die. These acrylic blocks were smoothened and were stored in distilled water at 37°C ± 1°C for 50 ± 2 h for the denture base polymer to reach water saturation. The control group was not used in this study.
Surface roughening of each acrylic resin specimens which bonds with soft liners were done by abrading the surface with 1000 grit silicon carbide abrasive paper then bonded to either of two soft liners: Perma soft denture liner and Pro soft denture liner. Each soft liner were mixed according to the manufacturer instructions and bonded to create denture base space. All the specimens were thermo cycled in a distilled water bath between 5°C and 55°C for 250 cycles with a dwell period of 60 s in each bath to simulate the oral conditions.[2]
The tensile strength is a measure of the ability of a material to withstand a longitudinal stress, expressed as the greatest stress that the material can stand without breaking. A shear load is a force that tends to produce a sliding failure on a material along a plane that is parallel to the direction of the force. Bond strength (Mpa) was deliberated as stress at failure divided by the cross sectional area of the sample.
All the samples were tested for tensile bond strength in a universal testing machine (Electro Universal testing machine, Ji’nan Xinluchang Testing Machine Co., LTD., China). Stereomicroscope used for the visual inspection of the deboned surface to confirm the mode of failure. The bond testing was done at a cross speed of 20 mm/min.
The results were statistically evaluated using the statistical software IBM SPSS Statistics for Windows, version 21.0. Armonk, NY, USA: IBM Corp. Bond strength in Group A and Group B was expressed as mean.
Descriptive analysis was done using the Chi-square test, post hoc Tukey's HSD, and two-way ANOVA test. To cheek the hypothesis, post hoc honestly significance test was used for comparing the mean of bond strength in Group A and Group B and 95% Confidence interval showed upper and lower values. P value was considered statistically significant at <0.05.
RESULTS
It was found that Perma soft denture liner had the highest tensile bond strength with all three different types of denture base resins, with a mean of 0.45 ± 0.06 MPa while Pro soft denture liner gave a mean of 0.38 ± 0.12 MPa [Table 3]. The result was significant statistically.
Table 3.
Bond strength in Group A and B
| Temporary soft liners | Denture base resins | Bond strength, mean±SD (MPa) | 95% CI | |
|---|---|---|---|---|
|
| ||||
| Lower bound | Upper bound | |||
| Perma soft denture liner (Group A) | Conventional denture base resins | 0.44±0.03 | 0.32 | 0.56 |
| Acrylic composite | 0.49±0.16 | 0.40 | 0.58 | |
| Trevalon HI | 0.43±0.05 | 0.38 | 0.48 | |
| Pro soft denture liner (Group B) | Conventional denture base resins | 0.31±0.05 | 0.24 | 0.38 |
| Acrylic composite | 0.42±0.16 | 0.28 | 0.56 | |
| Trevalon HI | 0.42±0.04 | 0.26 | 0.58 | |
Significance P<0.05, test used: Post hoc Tukey’s HSD. CI=Confidence interval, SD=Standard deviation, HSD=Honestly significant difference, HI=High impact
Perma soft denture liner in Group A showed bond strength of 0.44 ± 0.03 MPa with conventional denture base resins, 0.49 ± 0.16 MPa with Acrylic composite, and 0.43 ± 0.05 MPa with Trevalon HI. There was significance difference in obtained results.
Pro soft denture liner in Group B showed tensile bond strength of 0.31 ± 0.05 with conventional denture base resins, 0.42 ± 0.16 MPa with acrylic composite, and 0.42 ± 0.04 MPa with Trevalon HI. There was non-significant difference.
In this study, we found that permasoft denture liner-acrylic composite combination had the highest 24-h bond strength of 0.49 ± 0.16 MPA, whereas pro soft denture liner-Conventional denture base resins had lowest 24-h bond strength values of 0.31 ± 0.05 [Table 3, Graph 1]. It has suggested that 4.5 kg/cm2 or 0.44 MPa is the preferred adhesive value for soft-lining materials. Graph 1 shows mean bond strengths of Group A and B with resin 1 (Conventional denture base resins), 2 (Acrylic composite), and 3 (Trevalon HI). There was highest mean tensile bond strength with Perma soft denture liner compared to Pro soft denture liner.[11,12]
Graph 1.
Mean bond strengths of Group A and B with resin 1 (Conventional denture base resins), 2 (Acrylic composite) and 3 (Trevalon HI)
The tensile bond strength observed among the different soft liners with various denture bases was statistically nonsignificant (P = 0.151) [Table 4].
Table 4.
Tensile bond strength of soft liners with denture base resins
| Source | F statistic | Significant (P) |
|---|---|---|
| Temporary soft liners | 6.213 | 0.014** |
| Denture base resins | 3.921 | 0.024** |
| Temporary soft liners × Denture base resins | 1.926 | 0.151 |
**Denotes a significant difference P<0.05, Test used: two way ANOVA
Table 5 shows that multiple comparisons among the denture base resins showed significant difference (P < 0.05).
Table 5.
Multiple comparisons among the denture base resins
| Resin (I) | Resin (J) | Mean difference (I−J) | P | 95% CI | |
|---|---|---|---|---|---|
|
| |||||
| Lower bound | Upper bound | ||||
| Conventional denture base resins | Acrylic composite | 0.0683 | 0.021** | −0.008781 | 0.148321 |
| Acrylic composite | Trevalon HI | 0.0152 | 0.812 | −0.062435 | 0.094241 |
| Trevalon HI | Conventional denture base resin | 0.08 | 0.071 | 0.007281 | 0.164125 |
**Denotes a significant difference P<0.05, Test used: Post hoc test. CI=Confidence interval, HI=High impact
DISCUSSION
With all three different types of denture base resins, we observed significantly (P - 0.014) higher tensile bond strength found in Group A as compared to Group B.
In this study, it was found that acrylic composite denture base resin (0.49 Mpa and 0.42) showed highest bond strength values as compared to other two types of resins with both Permasoft soft denture liner and Pro soft denture liner groups. Similar results were seen in studies by Kim et al.[13] and Khanna et al.[14] for PMMA versus UDMA specimens, GC Reline Ultrasoft versus GC Reline, and Super-Soft liners versus Luci-Sof liner, respectively.
Chauhan et observed from the study that Viscogel, a temporary soft liner, had better bond strength over GC soft liner in bonding conventional and modified denture base resins.[15] These results are in accordance to our results. Safari et al. evaluated the effect of beverages on the hardness of two temporary acrylic-based soft-lining materials and their bond strength to the denture base resin. They found that drinking Coca-Cola and alcoholic beverages did not cause any problems for the temporary acrylic soft liners.[16] Lassila et al. in their study found that both bond strength and hardness of soft liners to fiber-reinforced and unreinforced PMMA denture-base resin were not affected in the presence of beverages.[17]
Rajaganesh et al. found that the silicone-based soft liner showed higher shear bond strength to heat polymerized acrylic resin than acrylic-based soft liner both before and after thermal cycling.[2] Naik and Jabade found that the tensile bond strength of SuperSoft (acrylic-based liner) was better compared to Molloplast B.[18]
In the present study, we observed that only perma soft denture liner – acrylic composite combination was found to be acceptable. Further, its clinical use should be evaluated. The adhesion was found to be lower than the recommended value in all other temporary soft liner-resin group specimens.
Denture soft liners are used to assist in providing a distribution of a functional load on the denture-bearing area, by reducing local stress concentrations and improving the retention of the dentures. This study suggested that Perma soft denture liners are better than Pro soft denture liner. Further studies are required with larger sample size with different materials.
CONCLUSION
We found that Perma soft denture liner exhibited higher tensile bond strength compared to Pro soft denture liner when used bonded to, conventional and modified denture base resins. Both Trevalon HI and acrylic composite showed higher bond strength with Perma soft denture liner and Pro soft denture liner.
Limitation
In the present study, we check only tensile strength between the soft liner and denture base using only two types on soft liners. Visco elastic properties and shear bond strength of soft liners were not checked.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
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