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ORIGINAL ARTICLE
Year : 2014  |  Volume : 3  |  Issue : 2  |  Page : 102-106

Comparison and evaluation of tensile bond strength of two soft liners to the denture base resin with different surface textures: An in vitro study


1 Department of Prosthodontics, Meghana Institute of Dental Sciences, Nizamabad, Andhra Pradesh, India
2 Department of Prosthodontics, CKS Teja Institute of Dental Sciences, Tirupati, Andhra Pradesh, India

Date of Web Publication20-Jun-2014

Correspondence Address:
Kuncha Venu Gopal
Department of Prosthodontics, Meghana Institute of Dental Sciences, Nizamabad, Andhra Pradesh
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/2277-8632.134850

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  Abstract 

Introduction: Debonding of soft liners from the denture results in localized unhygienic conditions and often causes functional failure of the prosthesis.
Aims: The purpose of this study is to evaluate and compare of the bond strength of the two permanent soft denture liners to a denture base resin with different surface preparations.
Subjects and Methods: All the specimens were prepared by stainless steel dies which are duplicated and wax patterns were fabricated, which are then flasked and dewaxed. Heat cure denture base resin was mixed and trial packed into the mold. The specimens are recovered and divided into four sub-groups based on the surface to be prepared. The soft denture lining material, Super-soft (G.C. America Inc., USA) and Molloplast-B (Detax Gmbh and Co., KG, Germany) was packed and cured in between the two specimens. All the specimens were subjected to tension, until failure, in a Universal Testing Machine.
Statistical Analysis Used: Analysis of variance using a Fischer's F test, unpaired t-test.
Results: The tensile bond strengths of the four groups of both the soft liners were found to be very highly significant. The comparison between each group was made using a student's unpaired t-test for equality of means. It was found that when statistical analysis was made for Super-soft between group I and group II, group I and group IV the results were not significant whereas between group I and group III, group II and group III were strongly significant. The statistical analyses of the four groups of Molloplast-B soft liners were found to be very highly significant.
Conclusions: Under the conditions of this in vitro study, conclusions were, sand papering the surface of the heat polymerized denture base resin increased the bond strength of the soft liner. Preparing holes on the surface of the denture base resin increases the bond strength because increase in the surface area and mechanical inter locking. Super-soft denture liner had the highest bond strength on all the surfaces than Molloplast-B.

Keywords: Soft denture liner, surface textures, tensile bond strength


How to cite this article:
Gopal KV, Padmaja BJ, Reddy NR, Reddy BM, Babu NS, Sunil M. Comparison and evaluation of tensile bond strength of two soft liners to the denture base resin with different surface textures: An in vitro study. J NTR Univ Health Sci 2014;3:102-6

How to cite this URL:
Gopal KV, Padmaja BJ, Reddy NR, Reddy BM, Babu NS, Sunil M. Comparison and evaluation of tensile bond strength of two soft liners to the denture base resin with different surface textures: An in vitro study. J NTR Univ Health Sci [serial online] 2014 [cited 2019 Dec 9];3:102-6. Available from: http://www.jdrntruhs.org/text.asp?2014/3/2/102/134850


  Introduction Top


The major drawbacks of the permanent soft liners are the lack of a durable bond to denture base. Detachment of soft liners from the denture base is a common clinical occurrence. The bond strength of resilient liners depends upon the tensile strength of the materials. A reliable bond between denture base and soft liner is required for the denture to function properly. [1],[2]

The purpose of this study is to assess evaluation and comparison of the bond strength of the two permanent soft denture liners to a heat polymerized polymethyl methacrylate denture base resin with different surface preparations.


  Subjects and Methods Top


Permanent heat polymerized denture soft lining materials, Super-soft (G.C. America Inc., USA) and Molloplast-B (Detax Gmbh and Co., KG, Germany) [Figure 1] are used in this study. All the specimens were prepared by stainless steel dies measuring 40 mm in length, 13 mm in width and 13 mm in height (40 mm × 13 mm ×13 mm) and a cross sectional area of 13 mm × 13 mm. A 3 mm thick spacer was also prepared by stainless steel.

The dies were duplicated in a flask using reversible hydrocolloid (Wirolube, BEGO, and Germany) and a duplicating machine. The dies were removed from the flask after the reversible hydrocolloid was set. The Modeling wax No. 2 (Hindustan dental products, India) was melted and poured into the hydrocolloid mold. The wax specimens were removed from the mold and were flasked. The flask was kept in boiling water for 10 min for wax elimination.
Figure 1: (a) Molloplast-B soft denture liner used in the study (b) Super soft denture liner used in the study

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Heat polymerizing polymethyl methacrylate (Acralyn-H, Asian acrylates India) denture base resin was mixed according to the manufacturer's instructions, in a clean mixing jar and trial packed into the mold. The excess flash was removed and the trial closure was made and the flask was kept in acrylizer and slow curing cycle 165°F (74°C) for 8 h is followed in an acrylizer. After completion of curing, the flask was bench cooled slowly to room temperature. The specimens were recovered from the flask, trimmed, and polished.

The specimens were grouped into four categories as group I, group II, group III and group IV depending upon the surface to be prepared for testing. The group I specimens had a surface un-altered, which remained as a control group. The group II specimens had a surface prepared by sand paper which has grit value of 100. The specimens of group III had test surfaces drilled with holes. Six holes (0.75 mm in width and 1.00 mm in height) were drilled with a No. 14 Tungsten Carbide inverted cone bur (DIA BURS, France).

The specimens of group IV had six holes (0.75 mm in width and 1.00 mm in height) drilled on the surface to be tested with a No. 14 Tungsten Carbide inverted cone bur and the surface on the other side was prepared with sand paper which has grit value of 100.

The prepared PMMA specimens were flasked along with 3 mm stainless steel spacer invested in silicon rubber (Zeta plus; Zhermack spa) to allow for easy removal of the die and later provide space for the soft liners [Figure 2].
Figure 2: Test samples

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The soft denture lining material, Super-soft which is provided as powder and liquid, was mixed according to the manufacturer's instructions (4 ml of liquid to one measure - 5 g powder by weight) and was packed in between the two specimens. The flask was placed in the processor and the soft liner was cured for 6 h at 165°F in an acrylizer (DELTA, poly bath).

Another set of specimens were prepared in the same manner using Molloplast-B soft denture lining material (according to the manufacturer's instructions). The flask was kept in acrylizing bath and heated slowly to 100°C or 212°F. After curing, the flasks were allowed to cool to room temperature. The specimens were deflasked and the excess lining material was trimmed with a Bard Parker blade No. 15.

All the specimens were subjected to tension, until failure, in a Universal Testing Machine (Autograph, AG-IS 50 kN) using a cross head speed of 2 cm/min. The bond strength was calculated as stress at failure divided by the cross sectional area of the sample [Figure 3]. The comparative study of the adhesive bond strength was done between the two soft lining materials.
Figure 3: (a) Universal testing machine used in the study, (b) Universal testing machine with specimen

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  Results Top


The tensile bond strengths of the four groups of both the soft liners were compared by analysis of variance using a Fischer's F test and were found to be very highly significant (P < 0.000). The comparison between each group was made using a Student's unpaired t-test for equality of means. It was found that when statistical analysis was made for Super-soft between group I with group II samples, the results were not significant with a P > 0.131.

The statistical analysis between group I and group III (P < 0.000), and group II and group III (P < 0.002) were strongly significant, whereas the statistical analysis between group I and group IV is not significant with P > 0.201.

The statistical analysis of the four groups of Molloplast-B soft liners was found to be very highly significant (P < 0.000). The statistical analysis of Molloplast-B, between group I and group II samples were very highly significant with P < 0.009. The statistical analysis between group I and group III were also highly significant with P < 0.000. The statistical analysis between group I and group IV samples were strongly significant with P < 0.000.

The statistical analysis between group II and group III were significant with P < 0.037. The statistical analysis between group II and group IV samples were significant with P < 0.022. The statistical analysis between group III and group IV samples were not significant with P > 0.731.

The statistical analysis was also made between group I of Super-soft with group I of Molloplast-B, which was strongly significant with P < 0.000. The results were very highly significant with P < 0.009 when compared with group II of Super-soft and group II of Molloplast-B. The statistical analysis made between group III of Super-soft with group III of Molloplast-B was also highly significant. The statistical analysis made between group IV of Super-soft with IV of Molloplast-B was not significant [Table 1] and [Figure 4].
Table 1: Comparison of tensile strength between materials in each group

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Figure 4: Comparison of tensile bond strength between Super-soft and Molloplast-B materials

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  Discussion Top


In the present study, the highest bond strength of 26.47 kg/cm 2 was seen with group III samples of Super-soft denture liner. The lowest bond strength of 12.47 kg/cm 2 was seen with group I samples of Molloplast-B soft denture liner.

Razavi et al. have reported that soft denture lining materials that have 10 pounds/inch or 4.5 kg/cm 2 bond strength are acceptable for clinical use. [3]

The bond strength of group III samples of Super-soft ranged from 15.34 to 26.47 kg/cm 2 (mean 21.98 kg/cm 2 ) when compared to group II and group IV samples. The results showed a very highly significant variation. The bond strength of group III samples of Molloplast-B material ranged between 12.85 and 21.02 kg/cm 2 (mean 18.08 kg/cm 2 ). The results were highly significant when compared with group II and group IV samples.

When comparison was made between Molloplast-B and Super-soft, Super-soft had a better bond strength.

Craig and Gibbons advocated a roughened surface to improve the adhesive bond. Adhesive values were approximately double those of smooth surface. Store sandblasted the acrylic resin surface before placing a resilient lining material and concluded that a slightly irregular surface provided mechanical locking for the soft material, thereby increasing the strength of the bond. [7]

Kawano et al. studied the bond strength of six soft denture liners and indicated that the force for failure was 9.6 kg/cm 2 or higher for all the materials. Considering this criterion, the soft lining materials tested in this study has a satisfactory bond strength to heat polymerized denture base resin. [1],[6]

Though the test results in this study were more than the bond strength of some soft liners studied by Dootz, which were as low as 8.1 kg/cm 2 , some of the soft liners were having a bond strength of up to 88.2 kg/cm 2 . [6]

Von Fraunhofer and Sichina characterized the physical and viscoelastic properties of two resilient denture liners, the polyphosphazene based Novus and silicone based Molloplast-B. Compressibility tests indicated less force was required to compress 2 and 3 mm thickness of Novus by 0.2 and 0.4 mm than for Molloplast-B. [9]

Omer Eusay study evaluated the bond strength characteristics of resilient liners by means of 180° peeling and tensile strength testing. The tensile and peel bond strength varied significantly among resilient liners. The mode of failure of Molloplast-B and Novus liners was significantly different between the tensile bond and peel bond test methods. It was concluded that bond strength characteristics can vary according to the test method used. [9]

Garcia et al. study evaluated the effects of a denture cleanser on weight change, roughness, and tensile bond strength on two denture resilient lining materials. Within the limitations of this in vitro study, specimens immersed in polident demonstrated increased weight changes of resilient liners when compared with tap water, but surface roughness and tensile bond strength were unaffected. [12]

Minami et al., in their in vitro study evaluated the effects of surface treatments and thermocycling on the bonding of auto polymerizing silicone soft denture liner (Sofreliner) to denture base resin. The bonding surfaces of denture base cylinders were polished with 600-grit silicon carbide paper and pretreated with applications of Sofreliner Primer, Sofreliner Primer after air abrasion, Reline Primer, or Reline Primer after air abrasion. Finally they concluded that air abrasion on the denture base resin surface was not effective in enhancing failure load. Cyclic thermal stress is one factor degrading the bond between soft denture liner and acrylic resin denture base. [13]

Sarac et al. evaluated treating the denture base resin surface with chemical etchants increased the bond strength of silicone based resilient denture liner to denture base and decreased the microleakage between the two materials. Considering the results of both tests together, the use of methyl methacrylate monomer for 180 s was found to be the most effective chemical treatment. [14]

Elias and Henriques evaluated the effect of thermo cycling on tensile and shear bond strengths of three soft liner materials to denture base acrylic resin. The water stored groups had statistically significant higher bond strengths than the thermo cycled groups. After thermocycling, Mucopren-soft had the highest bond strength. The bond strength changed with their chemical composition and all of them exhibited higher bond strengths than those usually reported as clinically acceptable. [15]

Leσn et al. evaluated and compared water sorption, solubility, and tensile bond strength of two resilient liner materials polymerized by different methods after being thermal cycled. Two acrylic resin-based resilient liner materials were evaluated: 1 (Light Liner) polymerized by visible light and 1 (Ever-Soft) processed by two different methods: Hot water bath and microwave energy. They concluded that within the limitations of this study, Light Liner showed the lowest solubility values. Ever-Soft should be polymerized by microwave energy to obtain the greatest tensile bond strength values. Materials polymerized by microwave energy and visible light showed predominantly adhesive/cohesive failures. [16]


  Conclusions Top


Under the conditions of this in vitro study, the following conclusions were drawn:

  1. Sand papering the surface of the heat polymerized denture base resin increased the bond strength of the soft liner.
  2. Preparing holes on the surface of the denture base resin increases the bond strength because increase in the surface area and mechanical inter locking.
  3. Super-soft denture liner had the highest bond strength on all the surfaces than Molloplast-B.


Further study is needed on other physical properties of the soft lining materials as they also contribute for the failure of bonding between the soft liner and the denture base resin. The tensile test helped in ranking the quality of bond strength between the soft liners.

 
  References Top

1.Kawano F, Dootz ER, Koran A 3 rd , Craig RG. Comparison of bond strength of six soft denture liners to denture base resin. J Prosthet Dent 1992;68:368-71.  Back to cited text no. 1
    
2.Emmer TJ Jr, Emmer TJ Sr, Vaidynathan J, Vaidynathan TK. Bond strength of permanent soft denture liners bonded to the denture base. J Prosthet Dent 1995;74:595-601.  Back to cited text no. 2
    
3.Razavi R, Khan Z, von Fraunhofer JA. The bond strength of a visible light-cured reline resin to acrylic resin denture base material. J Prosthet Dent 1990;63:485-7.  Back to cited text no. 3
    
4.Al-Athel MS, Jagger RG, Jerolimov V. Bone strength of resilient lining materials to various denture base resins. Int J Prosthodont 1996;9:167-70.  Back to cited text no. 4
    
5.al-Athel MS, Jagger RG. Effect of test method on the bond strength of a silicone resilient denture lining material. J Prosthet Dent 1996;76:535-40.  Back to cited text no. 5
    
6.Kawano F, Dootz ER, Koran A 3 rd , Craig RG. Bond strength of six soft denture liners processed against polymerized and unpolymerized poly(methyl methacrylate). Int J Prosthodont 1997;10:178-82.  Back to cited text no. 6
    
7.Jacobsen NL, Mitchell DL, Johnson DL, Holt RA. Lased and sandblasted denture base surface preparations affecting resilient liner bonding. J Prosthet Dent 1997;78:153-8.  Back to cited text no. 7
    
8.Minami H, Suzuki S, Ohashi H, Kurashige H, Tanaka T. Effect of surface treatment on the bonding of an autopolymerizing soft denture liner to a denture base resin. Int J Prosthodont 2004;17:297-301.  Back to cited text no. 8
    
9.von Fraunhofer JA, Sichina WJ. Characterization of the physical properties of resilient denture liners. Int J Prosthodont 1994;7:120-8.  Back to cited text no. 9
    
10.Kutay O. Comparison of tensile and peel bond strengths of resilient liners. J Prosthet Dent 1994;71:525-31.  Back to cited text no. 10
[PUBMED]    
11.Kawano F, Dootz ER, Koran A 3 rd , Craig RG. Sorption and solubility of 12 soft denture liners. J Prosthet Dent 1994;72:393-8.  Back to cited text no. 11
    
12.Garcia RM, Léon BT, Oliveira VB, Del Bel Cury AA. Effect of a denture cleanser on weight, surface roughness, and tensile bond strength of two resilient denture liners. J Prosthet Dent 2003;89:489-94.  Back to cited text no. 12
    
13.Minami H, Suzuki S, Ohashi H, Kurashige H, Tanaka T. Effect of surface treatment on the bonding of an autopolymerizing soft denture liner to a denture base resin. Int J Prosthodont 2004;17:297-301.  Back to cited text no. 13
    
14.Sarac D, Sarac YS, Basoglu T, Yapici O, Yuzbasioglu E. The evaluation of microleakage and bond strength of a silicone-based resilient liner following denture base surface pretreatment. J Prosthet Dent 2006;95:143-51.  Back to cited text no. 14
    
15.Elias CN, Henriques FQ. Effect of thermocycling on the tensile and shear bond strengths of three soft liners to a denture base resin. J Appl Oral Sci 2007;15:18-23.  Back to cited text no. 15
    
16.León BL, Del Bel Cury AA, Rodrigues Garcia RC. Water sorption, solubility, and tensile bond strength of resilient denture lining materials polymerized by different methods after thermal cycling. J Prosthet Dent 2005;93:282-7.  Back to cited text no. 16
    


    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4]
 
 
    Tables

  [Table 1]



 

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Abstract
Introduction
Subjects and Methods
Results
Discussion
Conclusions
References
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