Bond strength of soft liners to denture base resins and the influence of different surface treatments and thermocycling: A systematic review

SYSTEMATIC REVIEW

Bond strength of soft liners to denture base resins and the influence of different surface treatments and thermocycling: A systematic review Byrasandra Channappa Muddugangadhar, MDS,a Dipal P. Mawani, MDS,b Arindam Das, BDS,c and Arindam Mukhopadhyay, BDSd Studies to develop comfortable ABSTRACT acrylic resin dentures have been Statement of problem. Occasional debonding between soft liners and denture base resin is a focus of prosthodontic studies common and limits the longevity of a relined prosthesis. 1 and practice. Conventional Purpose. The purpose of this systematic review was to compare the bond strength of commercially complete dentures fail to satisfy available soft liners with that of polymethyl methacrylate (PMMA) and urethane dimethacrylate patients with traumatized mu(UDMA) denture base resins after different surface treatments and thermocycling. cosa, undercuts in the underMaterial and methods. Searches were performed by 2 independent reviewers in the MEDLINE/ lying bone, ridge atrophy, or PubMed and Cochrane Library databases from January 1990 to December 2018 to identify bruxism.2-4 With the advent of published journal articles related to this subject. Subsequently, a hand search was also carried soft liners, management of such out for all the articles mentioned in the references of the identified full articles. situations has become relatively Results. A total of 61 articles were initially identified through database searches by the 2 reviewers. satisfactory. When convenTwenty-four of the 61 articles met the inclusion criteria for qualitative analysis. Four of 6 articles tional complete dentures are showed that laser pretreatment of denture base resins increased their bonding to soft liners. relined with soft liners, they Seven of 8 articles concluded that airborne-particle abrasion caused deterioration of the bonding become more comfortable as between the liner and denture base resin. Four of 6 studies showed that acid etching, silica they reduce local stress concoating, primer or monomer application, and immersion in acetone or isobutyl methacrylate centrations, promoting a heal(iBMA) resulted in improved bond strengths between the liner and resin. One study reported that oxygen plasma treatment also resulted in improved bond strengths. Seven of 8 articles ing effect on mucosa,5-7 and concluded that thermocycling resulted in decreased bond strengths. provide an equalized functional load on the entire dentureConclusions. Laser treatment, oxygen plasma pretreatment, primer or monomer application, and immersion in acetone or iBMA resulted in improved bonding of the denture base resin to soft bearing area.8-10 liners. However, airborne-particle abrasion and thermocycling resulted in deterioration of the Soft liners can be divided bond. (J Prosthet Dent 2019;-:---) into 4 groups according to their chemical structure: plasticized polymethyl methacrylate denture base resin, special adacrylic resins (autopolymerized or heat-polymerized), hesives are applied on the intaglio surface of the dentures vinyl resins, polyurethane, and silicone rubbers.11 A to improve the bond strength between the denture base hydroxy- or vinyl-terminated polydimethylsiloxane and the liner.12,13 The adhesives contain a polymeric (PDMS)12,13 is the chief component of silicone-based substance (organosilanes or molecules of PMMA) liners. Owing to their structural differences with

a

Professor, Department of Prosthodontics, M R Ambedkar Dental College and Hospital, Bengaluru, Karnataka, India. Private practice, Mawani Orthodontic Multispecialty Dental Clinic, Surat, Gujarat, India. c Postgraduate student, Department of Prosthodontics, M R Ambedkar Dental College and Hospital, Bengaluru, Karnataka, India. d Postgraduate student, Department of Prosthodontics, M R Ambedkar Dental College and Hospital, Bengaluru, Karnataka, India. b

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Clinical Implications No current consensus suggests the use of specific soft lining materials in various clinical situations. Measuring the bond strength of soft liners to pretreated and untreated denture base resins gives an overview of the approximate service period of the resilient liners and techniques of how to prolong their longevity.

dissolved in a solvent. However, they are not adequate to prevent debonding between the denture base resin material and the soft liner after a certain period of usage of the relined prosthesis.5-7,14-16 Other drawbacks of soft liners include loss of softness over time, plaque formation, bacterial growth, and fungal colonization by Candida albicans.5-7,14-16 A clinically acceptable bond strength of resilient soft liners to denture bases is reported to be 0.44 MPa, and a minimum thickness of 2 to 3 mm of soft liner is necessary to serve its purpose.17-19 Among the various methods of testing the mechanical properties of soft liners, tensile, shear, and peel bond strength testing are widely accepted.6,20-22 Al-Athel and Jagger22 reported that shear stress best simulated the situation in which a liner functions in the oral conditions. Despite chemical similarities to conventional acrylic resin denture base material, acrylic resinebased liners show lower bond strength because of incomplete penetration of monomer into the high-density cross-linked denture polymer.23,24 However, silicone-based liners have an improved adhesive bonding system that can better penetrate the acrylic resin.25 The adhesive system contains a silicone polymer in volatile solvents, which results in better bond strength of silicone-based liners.25 The purpose of this systematic review was to compare the bond strength of commercially available soft liners with that of polymethylmethacrylate (PMMA) and urethane dimethacrylate (UDMA) denture base resins after different surface treatments such as laser treatment;20,26-30 airborne-particle abrasion;1,20,23,26,27,31-34 chemical surface pretreatments such as acid etching and monomer wetting;1,27,28,32-34 oxygen plasma treatment;35 and thermocycling.12,15,26,29,34,36-38 MATERIAL AND METHODS This systematic review was conducted in accordance with the Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) guidelines.39 To identify the studies eligible for this review, a detailed search strategy was developed and applied in the MEDLINE/PubMed and Cochrane Library databases. The keywords used were “soft liner” and “bond strength.” The query THE JOURNAL OF PROSTHETIC DENTISTRY

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translation generated was (soft[All Fields] AND ("dental cavity lining"[MeSH Terms] OR ("dental"[All Fields] AND "cavity"[All Fields] AND "lining"[All Fields]) OR "dental cavity lining"[All Fields] OR "liner"[All Fields])) AND (bond[All Fields] AND strength[All Fields]). In addition, manual searches were conducted in review studies relevant to the subject. A hand search of the references of full articles that comprised journal articles published from January 1990 to December 2018 was made. (No studies related to this topic were available before 1990.) Two independent reviewers (D.P.M., A.D.) reviewed all the articles published in English. Initially, titles and abstracts of all available articles were read. The studies were then included or excluded from the total sample by following the inclusion and exclusion criteria (Table 1). Disagreements between the 2 reviewers regarding including studies were resolved by discussion between them. If the title and abstracts of articles failed to provide sufficient information, full reports were obtained. The full-text reading of such publications was performed by both the reviewers and then resolved with discussion. The data obtained were pooled into tables followed by descriptive summarization and determination of the characteristics from the included studies. RESULTS The search using the keyword phrases “soft liner” and “bond strength” yielded 61 articles in the PubMed/ Medline database. After removal of duplicated articles, the 24 articles which met the inclusion criteria were included for qualitative analysis (Fig. 1). Supplemental Table 1 (available online) shows studies comparing bond strength between laser-pretreated denture base resins and soft liners. Supplemental Table 2 (available online) shows studies that compared the bond strength between airborne-particleeabraded denture bases and soft relining materials. Supplemental Table 3 (available online) lists the studies that showed the results of acid etching, silica coating, and primer or monomer application on the bond strength between denture base resins and soft liners. Supplemental Table 4 (available online) shows the results of studies that compared the bond strength between oxygen plasmae treated denture base resins and soft liners. Supplemental Table 5 (available online) lists the studies that demonstrated the results of thermocycling on the bond strength between denture base resins and soft liners. In the 25 included studies, 11 denture base resins (9 heat-polymerizing resins, 1 autopolymerizing resin, and 1 light-polymerizing resin) and 20 soft relining materials (15 silicone-based liners and 5 acrylic resinebased liners) were compared (Tables 2 and 3). Most studies concluded that laser treatment, oxygen plasma pretreatment, acid Muddugangadhar et al

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Table 1. Inclusion and exclusion criteria Inclusion Criteria

Exclusion Criteria

Studies published only in English language

Case reports

Studies measuring the tensile, shear, or peel bond strength of different types of commercially available silicone-based and acrylic resinebased soft liners to heat-, auto-, or light-polymerizing denture base resins after different surface pretreatments and thermocycling

Studies measuring water resorption, effect of beverages, effect of antimicrobial agents, or denture cleansers on soft liner materials

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Identification Screening

Lawrence and Li40 reported that Nd:YAG laser irradiation increases the surface roughness of PMMA from 1.95 to 2.22 mm. When high-energy laser beams strike the acrylic resin denture base, they cause instant evaporation of water along with volumetric expansion of the acrylic resin. This leads to ablation of the surrounding materials and increase in its surface area.28 Scanning electron photomicrographs have confirmed that the liner penetrates into these created irregularities or spaces, thus increasing the bond strength.28 Nakhaei et al26 concluded that Er:YAG laser irradiation increased the tensile bond strength of liners to PMMA resin, and Akin et al20 reported that Er:YAG laser treatment at 200 mJ, 10 Hz, and 2 W for 20 seconds increased the bond strength between the PMMA denture base and liner. In another study, Akin et al28 reported that Er:YAG laser treatment at 300 mJ, 3 W, and pulse duration of 700 mm increased the bond strength of silicone-based liner to UDMA resin. However, Gundogdu et al27 reported that Er:YAG laser treatment at 150 mJ and 100 mm did not increase the bond strength of PMMA resin to heat-polymerizing and autopolymerizing silicone-based soft liners. Usumez et al30 also concluded that the surface roughness of denture base resin increased with Nd:YAG laser treatment. Scanning electron micrographs showed that the surface roughness after Nd:YAG laser treatment increased because of redeposition of induced debris on the surface, porosities, and heat-induced fractures.30 However, despite an increase in surface roughness, the increase in tensile bond strength over control specimens was not statistically significant. This can be attributed to the varied size of irregularities created by the sweeping

Studies screened based on title and abstract (n=61)

Eligibility

DISCUSSION

[Soft liner] [bond strength] (MEDLINE/PubMed and Cochrane Library) January 1990 to December 2018 (n=61)

Full text articles assessed for eligibility (n=24)

Included

etching, iBMA, primer, and monomer application increased the bond strength between denture base resins and soft liners.18-26 Airborne-particle abrasion caused deterioration in the bond strength between denture bases and soft liners.1,20,23,25-28 Thermocycling also resulted in decreased bond strength between denture bases and soft relining materials.7,12,14,18,21,25,29 The results of this review also suggest that silicone-based liners showed better bond strength to denture base resins than the acrylic resinebased liners. Urethane dimethacrylate (UDMA) and polymethyl methacrylate (PMMA) resins showed similar bond strengths to resilient liners.

Studies in which silver incorporated or fiber-reinforced soft liners were used

Studies included in the review (n=24)

Excluded: Did not meet inclusion criteria (n=37)

Figure 1. Selection process flowchart.

motion of the hand during conditioning with the laser beam which did not adequately facilitate the flow of liner material.30 Tugut et al29 reported that Er:YAG laser beam at 3 W, 10 Hz, and 300 mJ was enough to create pits of small sizes on the surface of acrylic resin to which liner can penetrate, thus increasing the bond strength. However, Er:YAG laser at 400 mJ and 4 W created cavities instead of pits, thus decreasing the bond strength.29 Gundogdu et al27 and Akin et al20 concluded that airborne-particle abrasion of the acrylic resin denture base with 50-mm alumina decreased the bond strength between the denture base and liner material. Atsu and Keskın1 concluded that pretreatment of denture bases with 50-mm alumina and 30-mm silica-coated alumina resulted in the decrease of bond strength between acrylic resin denture bases and liners. Surapaneni et al,32 Minami et al,34 and Kulkarni and Parkhedkar23 reported similar results. Such findings can be explained by stresses produced at the interface between the acrylic resin denture base and the resilient liner.41 The size of the irregularities produced by airborne-particle abrasion may not be adequate to allow liner material to penetrate.26,42 However, Khanna et al31 concluded that abrading the surface of acrylic resin denture with 250-mm alumina

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Table 2. List of denture base resins included S No.

Name of Denture Base Resin

1

Triplex

Ivoclar Vivadent AG

Manufacturer

Chemical Structure

Mode of Polymerization

PMMA

Heat-polymerizing

2

QC-20

Dentsply Sirona

PMMA

Heat-polymerizing

3

Meliodent

Bayer Dental

PMMA

Heat-polymerizing

4

Paladent

Kulzer GmbH

PMMA

Heat-polymerizing

5

Trevalon

Dentsply Sirona

PMMA

Heat-polymerizing

6

DPI Heat Cure

Dental Products of India

PMMA

Heat-polymerizing

7

Zi Ran

Nissin

PMMA

Heat-polymerizing

8

Classico

Artigos Odontologicos Classico LTDA

PMMA

Heat-polymerizing

9

Lucitone 199

Dentsply Sirona

PMMA

Heat-polymerizing

10

Shofu Pour resin

Shofu

PMMA

Autopolymerizing

11

Eclipse

Dentsply Sirona

UDMA

Light-polymerizing

PMMA, poly(methyl) methacrylate; UDMA, urethane dimethacrylate.

Table 3. List of soft liners included S No.

Name of Soft Liner

Chemical Structure

Mode of Polymerization

1

Ufi Gel C

VOCO

Manufacturer

Silicone-based

Autopolymerizing Autopolymerizing

2

Ufi Gel P

VOCO

Silicone-based

3

Mollosil

Detax GmbH & Co.

Silicone-based

Autopolymerizing

4

Permafix

Kohler

Silicone-based

Autopolymerizing

5

Sofreliner

Tokuyama

Silicone-based

Autopolymerizing

6

GC Reline Soft

GC America

Silicone-based

Autopolymerizing

7

Mollosil Plus

Detax GmbH & Co.

Silicone-based

Autopolymerizing

8

Mucopren Soft

Kettenbach GmbH & Co.

Silicone-based

Autopolymerizing

9

DentuSil

Bosworth Company

Silicone-based

Autopolymerizing

10

Molloplast B

Detax GmbH & Co KG.

Silicone-based

Heat-polymerizing

11

Luci-Sof

Dentsply Sirona

Silicone-based

Heat-polymerizing

12

Permaflex

Kohler

Silicone-based

Heat-polymerizing

13

Flexor

Schutz-Dental GmbH

Silicone-based

Heat-polymerizing

14

COE-SOFT

GC America

Acrylic resinebased

Autopolymerizing

15

Soft Reverse

Nissin

Acrylic resinebased

Autopolymerizing

16

Pro Tech

Professional Products Inc

Acrylic resinebased

Heat-polymerizing

17

Super-Soft

GC America Inc

Acrylic resinebased

Heat-polymerizing

18

PermaSoft

Austenal Inc

Acrylic resinebased

Heat-polymerizing

increased the bonding of acrylic resin and silicone-based resilient liners to denture bases. The stronger bond of acrylic resinebased liners can be attributed to the similar chemistry of acrylic resinebased soft liners and PMMA denture bases. Nakhaei et al26 stated that airborne-particle abrasion of acrylic resin denture bases with 110-mm alumina improves their bonding with resilient liners by producing irregularities that help in mechanical interlocking between the acrylic resin and the liner. Surapaneni et al32 reported that monomer increased the bond strength of denture bases to resilient liners, and Minami et al34 reported a similar effect with primer application. Monomer wetting and acetone application may lead to superficial crack propagation and formation of several 2-mm-diameter pits.43 The acrylic resin denture base swells up on monomer application, thus facilitating the infiltration of the liner adhesive primer into the pits and cracks, resulting in lower microleakage

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and increased bond strength.44 Methyl methacrylate monomer has the ability to reach deep into the polymer chains and facilitate the penetration of adhesive primer.32 Akin et al33 reported that when soft liners were immersed in isobutyl methacrylate (iBMA), their tensile bond strength increased and all the specimens showed adhesive failure, which is unlikely for materials showing adequate tensile strength. Such findings can be explained by elongation of the resilient liners upon immersion in iBMA and 2-hydroxyethyl methacrylate (HEMA) groups, thus making them more resistant to tears and ruptures under tensile stress.33 When PMMA and these chemicals interact with each other, the alkyl groups of the methacrylate may form hydrogen bonds with the C-H groups. Furthermore, these chemicals have solvent effects on the surface of the denture base resins leading to surface roughening and increasing the bond strength.33

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Gundogdu et al27 concluded that acid etching of denture bases with 36% phosphoric acid was optimal in increasing bond strength. However, Atsu and Keskın1 reported that silica coating, adhesive, and silane application resulted in deterioration of bond strength. Such findings can be explained by irregularities of the 30-mm size created by silica coating systems, which were insufficient for the soft lining material to flow into the denture base acrylic resin.42 Akin et al28 concluded that bonding agent application on urethane dimethacrylate (UDMA)based resins did not increase the bond strength between the resin and soft liner. Such findings can be explained by failure of formation of a chemical bond between the liner and UDMA resin.28 Furthermore, the surface layer was not dissolved by the bonding agent, and thus, the surface area for bonding was not enlarged.28 Zhang et al35 reported that oxygen plasma treatment increased the tensile bond strength between acrylic resine based soft liner and acrylic denture base. Oxygen plasma treatment introduced CeO and C=O groups onto the polymer surface, which increased the surface hydrophilicity and thus facilitated the penetration of soft liner into irregularities of the surface of the denture base.45-47 Reactive groups open the bonds on the surface, increasing the surface energy and, consequently, the wettability. The authors also reported that these surface-modified polymers showed a time-dependent aging process and that the hydrophobic nature of the surface is restored over time.47,48 Such findings can be explained by reorientation of hydrophilic groups underneath the surface and continuous diffusion of residual monomers from the polymers.47,48 Thus, further laboratory and clinical studies are needed to investigate how this aging process affects the bond strength between denture base resins and liners. Soft denture liners are subjected to changing temperatures in the oral environment.36 This tends to have a deleterious effect on the mechanical and physical properties of the liner materials, thus limiting their clinical use.36 Thermocycling causes repeated expansion and contraction between the soft liner and denture base material, resulting in stress buildup at the bonded interface and thermal volumetric changes.34 Subjecting the soft lining materials to thermocycling to simulate the oral environment has been included in many studies. Nakhaei et al26 reported that the tensile bond strength of silicone-based liners to acrylic resin denture base material decreased after 5000 thermocycles, and Elias and Henriques,37 after 3000 cycles. Similarly, Minami et al34 reported reduction in the tensile bond strength values of silicone-based liners after thermocycling. Tugut et al29 concluded that thermocycling resulted in decreased bond strength of silicone-based liners to both PMMAbased and UDMA-based denture base resins. However, they concluded that UDMA resin showed comparatively

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better bonding to silicone-based liners and that Molloplast B showed better bonding to both the resins when compared with Permaflex. Kulak-Ozkan et al38 concluded that thermocycling caused a reduction in tensile bond strength of both autopolymerizing and heatpolymerizing silicone-based liners to acrylic resin denture bases. Before thermocycling, heat-polymerizing siliconebased liner (Molloplast B) demonstrated the best tensile bond strength, but after thermocycling, autopolymerizing silicone-based liner (Mollosil) showed better results than other heat-activated silicone-based liners. This can be attributed to the higher water uptake of Molloplast B due to its filler content.38 Demir et al12 concluded that Permaflex showed decreased peel bond strength to acrylic resin denture base material after thermocycling. However, Molloplast B was relatively stable in terms of peel bond strength, before and after thermocycling. Rajaganesh et al36 reported that thermocycling increased the shear bond strength of silicone-based liners but decreased the shear bond strength of acrylic resinebased soft liners to denture base acrylic resins. Such findings can be explained by hydration and stress concentration at the bonding interface in the presence of the residual monomer.34,36 Hydrolytic degradation of the bond occurs on diffusion of water into the bonding interface.34 Continued polymerization and minimal water absorption of siliconebased liners are the main reasons for its better shear stresseresisting properties.36,38 Filler particles present in silicone-based liners are responsible for its reduced water absorption.49,50 However, acryloxy silane improves the bonding of fillers to resin, leading to better cross-linkage and complete polymerization.23 This results in a denser and less viscoelastic material with negligible amounts of residual monomer.36,38 Pinto et al7 reported that thermocycling decreased the tensile bond strength of Molloplast B and Pro Tech liners but had no significant effect on Flexor and PermaSoft liners. Such findings can be explained by less absorption of water by Flexor than Molloplast B.7 Flexor is marketed with a sealer which increases the resiliency period of the liner by reducing water absorption and plasticizer loss.16,51 However, Molloplast B showed the best bond strength of all silicone and acrylic resinebased liners, regardless of thermocycling.7 Thermocyclic stress on acrylic resinebased soft liners results in leaching out of plasticizers, leading to rapid hardening of the material.52,53 Thus, they cannot be used as long-term denture relining material. The authors are unaware of any article providing clinical data about the bonding between liners and denture base resins. Thus, the lack of clinical data is a limitation of this systematic review, and clinical studies should be carried out to support the data provided by the in vitro studies.

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CONCLUSIONS Based on the findings of this systematic review, the following conclusions were drawn: 1. Laser pretreatment, oxygen plasma treatment, acid etching, silica coating, primer or monomer application, and immersion of denture bases in acetone or isobutyl methacrylate are effective ways of increasing the bond strength between denture base resins and resilient soft liners. 2. Airborne-particle abrasion reduced the bond strength between denture base resins and soft liners. 3. Silicone-based liners generally demonstrated higher bond strength to denture base acrylic resins than acrylic resinebased soft liners because of their better adhesive systems. REFERENCES 1. Atsu S, Keskın Y. Effect of silica coating and silane surface treatment on the bond strength of soft denture liner to denture base material. J Appl Oral Sci 2013;21:300-6. 2. Crum RJ, Loiselle RJ, Rooney GE. Clinical use of a resilient mandibular denture. J Am Dent Assoc 1971;83:1093-6. 3. Heartwell C, Rahn AO. Syllabus of compete dentures. 4th ed. Philadelphia: Lea & Febiger; 1986. p. 423-56. 4. Wendt DC. The degenerative denture ridgedcare and treatment. J Prosthet Dent 1974;32:477-92. 5. Kawano F, Dootz ER, Koran A, Craig RG. Comparison of bond strength of six soft denture liners to denture base resin. J Prosthet Dent 1992;68:368-71. 6. Mutluay MM, Ruyter IE. Evaluation of bond strength of soft relining materials to denture base polymers. Dent Mater 2007;23:1373-81. 7. Pinto JR, Mesquita MF, Henriques GE, de Arruda Nóbilo MA. Effect of thermocycling on bond strength and elasticity of 4 long-term soft denture liners. J Prosthet Dent 2002;88:516-21. 8. Wright PS. A three-year longitudinal study of denture soft lining materials in clinical use. Clin Mater 1986;1:281-9. 9. Braden M, Wright PS, Parker S. Soft lining materials: a review. Eur J Prosthodont Restor Dent 1995;3:101-13. 10. Baysan A, Parker S, Wright PS. Adhesion and tear energy of a long-term soft lining material activated by rapid microwave energy. J Prosthet Dent 1998;79: 182-7. 11. O’Brien WJ. Dental materials and their selection. 4th ed. Chicago: Quintessence Pub Co; 2009. p. 750-1. 12. Demir H, Dogan A, Dogan OM, Keskin S, Bolayir G, Soygun K. Peel bond strength of two silicone soft liners to a heat-cured denture base resin. J Adhes Dent 2011;13:579-84. 13. Dogan OM, Keskin S, Dogan A, Ataman H, Usanmaz A. Structure-property relation of a soft liner material used in denture applications. Dent Mater 2007;26:329-34. 14. Bates JF, Smith DC. Evaluation of indirect resilient liners for dentures: laboratory and clinical tests. J Am Dent Assoc 1965;70:344-53. 15. Pinto JR, Mesquita MF, de Arruda Nóbilo MA, Henriques GE. Evaluation of varying amounts of thermal cycling on bond strength and permanent deformation of two resilient denture liners. J Prosthet Dent 2004;92:288-93. 16. Polyzois GL, Frangou MJ. Influence of curing method, sealer, and water storage on the hardness of a soft lining material over time. J Prosthodont 2001;10:42-5. 17. Khan Z, Martin J, Collard S. Adhesion characteristics of visible light-cured denture base material bonded to resilient lining materials. J Prosthet Dent 1989;62:196-200. 18. Craig RG, Gibbons P. Properties of resilient denture liners. J Am Dent Assoc 1961;63:382-90. 19. Wright PS. Soft lining materials: their status and prospects. J Dent 1976;4: 247-56. 20. Akin H, Tugut F, Mutaf B, Akin G, Ozdemir AK. Effect of different surface treatments on tensile bond strength of silicone-based soft denture liner. Lasers Med Sci 2011;26:783-8.

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21. Aydın AK, Terzio g lu H, Akınay AE, Ulubayram K, Hasırcı N. Bond strength and failure analysis of lining materials to denture resin. Dent Mater 1999;15:211-8. 22. 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. 23. Kulkarni RS, Parkhedkar R. The effect of denture base surface pretreatments on bond strengths of two long term resilient liners. J Adv Prosthodont 2011;3:16-9. 24. Emmer TJ, Vaidynathan J, Vaidynathan TK. Bond strength of permanent soft denture liners bonded to the denture base. J Prosthet Dent 1995;74:595-601. 25. Madan N, Datta K. Evaluation of tensile bond strength of heat cure and autopolymerizing silicone-based resilient denture liners before and after thermocycling. Indian J Dent Res 2012;23:64-8. 26. Nakhaei M, Dashti H, Ahrari F, Vasigh S, Mushtaq S, Shetty RM. Effect of different surface treatments and thermocycling on bond strength of a silicone-based denture liner to a denture base resin. J Contemp Dent Pract 2016;17:154-9. 27. Gundogdu M, Yesil Duymus Z, Alkurt M. Effect of surface treatments on the bond strength of soft denture lining materials to an acrylic resin denture base. J Prosthet Dent 2014;112:964-71. 28. Akin H, Tugut F, Guney U, Kirmali O, Akar T. Tensile bond strength of silicone-based soft denture liner to two chemically different denture base resins after various surface treatments. Lasers Med Sci 2013;28:119-23. 29. Tugut F, Akin H, Mutaf B, Akin GE, Ozdemir AK. Strength of the bond between a silicone lining material and denture resin after Er: YAG laser treatments with different pulse durations and levels of energy. Lasers Med Sci 2012;27:281-5. 30. Usumez A, Inan O, Aykent F. Bond strength of a silicone lining material to alumina-abraded and lased denture resin. J Biomed Mater Res B Appl Biomater 2004;71:196-200. 31. 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Zhang H, Fang J, Hu Z, Han Y, Bian J. Effect of oxygen plasma treatment on the bonding of a soft liner to an acrylic resin denture material. Dent Mater 2010;29:398-402. 36. Rajaganesh N, Sabarinathan S, Azhagarasan NS, Shankar C, Krishnakumar J, Swathi S. Comparative evaluation of shear bond strength of two different chairside soft liners to heat processed acrylic denture base resin: an in vitro study. J Pharm Bioall Sci 2016;8:154-9. 37. 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. 38. Kulak-Ozkan Y, Sertgoz A, Gedik H. Effect of thermocycling on tensile bond strength of six silicone-based, resilient denture liners. J Prosthet Dent 2003;89:303-10. 39. Moher D, Liberati A, Tetzlaff J, Altman DG. Preferred reporting items for systematic reviews and meta-analyses: the PRISMA statement. Int J Surg 2010;8:336-41. 40. Lawrence J, Li L. Modification of the wettability characteristics of polymethyl methacrylate (PMMA) by means of CO2, Nd: YAG, excimer and high power diode laser radiation. Mater Sci Eng A 2001;303:142-9. 41. Amin WM, Fletcher AM, Ritchie GM. The nature of the interface between polymethyl methacrylate denture base materials and soft lining materials. J Dent 1981;9:336-46. 42. 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. 43. Sarac YS, Sarac D, Kulunk T, Kulunk S. The effect of chemical surface treatments of different denture base resins on the shear bond strength of denture repair. J Prosthet Dent 2005;94:259-66. 44. Saraç YS¸, Bas¸o g lu T, Ceylan GK, Saraç D, Yapici O. Effect of denture base surface pretreatment on microleakage of a silicone-based resilient liner. J Prosthet Dent 2004;92:283-7. 45. Chen M, Zamora PO, Som P, Peña LA, Osaki S. Cell attachment and biocompatibility of polytetrafluoroethylene (PTFE) treated with glowdischarge plasma of mixed ammonia and oxygen. J Biomater Sci Polym Ed 2003;14:917-35. 46. Chan CM, Ko TM, Hiraoka H. Polymer surface modification by plasmas and photons. Surf Sci Rep 1996;24:1-54.

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47. Lim H, Lee Y, Han S, Kim Y, Song JM, Kim JS. Wettability of poly (styrene-co-acrylate) ionomers improved by oxygenplasma source ion implantation. J Polym Sci B Polym Phys 2003;41: 1791-7. 48. Xu H, Hu Z, Wu S, Chen Y. Surface modification of polytetrafluoroethylene by microwave plasma treatment of H2O/Ar mixture at low pressure. Mater Chem Phys 2003;80:278-82. 49. Arvind S, Chandrashekharan N. Phillips’ science of dental materials. 1st South Asian ed. India: Elsevier Saunders; 2014. p. 550-2. 50. Braden M, Wright PS. Water absorption and water solubility of soft lining materials for acrylic dentures. J Dent Res 1983;62:764-8. 51. Gronet PM, Driscoll CF, Hondrum SO. Resiliency of surface-sealed temporary soft denture liners. J Prosthet Dent 1997;77:370-4. 52. Murata H, Kawamura M, Hamada T, Saleh S, Kresnoadi U, Toki K. Dimensional stability and weight changes of tissue conditioners. J Oral Rehabil 2001;28:918-23.

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53. Murata H, Hamada T, Toki K, Nikawa H. Effect of addition of ethyl alcohol on gelation and viscoelasticity of tissue conditioners. J Oral Rehabil 2001;28: 48-54. Corresponding author: Dr Byrasandra Channappa Muddugangadhar Department of Prosthodontics and Crown and Bridge Including Implantology M R Ambedkar Dental College and Hospital 1/36, Cline Road, Cooke Town Bengaluru, Karnataka INDIA. Pin-711202 Email: [email protected] Copyright © 2019 by the Editorial Council for The Journal of Prosthetic Dentistry. https://doi.org/10.1016/j.prosdent.2019.06.013

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Supplemental Table 1. Included studies comparing bond strength of laser-pretreated denture bases to soft liners Materials Used Acrylic Resin

Author

Year

Mohammadreza et al

2016

Triplex

Molloplast B

Group 1: no surface pretreatment Group 2: airborne particle abrasion (aluminum oxide particles) Group 3: laser pretreatment (Er:YAG) Group 4: airborne particle abrasion + laser pretreatment (Er:YAG)

Thermocycled and subjected to tensile stress using a universal testing machine

Groups 2, 3, 4: significant increase in tensile bond strength than group 1. No significant difference was found in between groups 2, 3, 4. Thermocycling resulted in decrease in tensile bond strength in all the groups.

Gundogdu et al

2014

QC-20

Molloplast B and Ufi Gel P

Group 1: no surface pretreatment Group 2: acid etching (36% H3PO4) Group 3: laser pretreatment (Er:YAG) Group 4: airborne particle abrasion (aluminum oxide particles) Group 5: acid etching + laser pretreatment (Er:YAG) Group 6: airborne particle abrasion + laser pretreatment (Er:YAG) All groups were divided into 2 subgroups. Each subgroup was treated with one of the liners.

Subjected to tensile stress using a universal testing machine

Molloplast B group showed significantly higher tensile bond strength than the Ufi Gel P group. Highest bond strength was seen in group 2 and lowest in group 4. Groups 3, 5, 6 did not increase tensile bond strength over group 1.

Hakan et al

2013

Meliodent Molloplast B and Eclipse

Group 1: PMMA without surface pretreatment Group 2: Eclipse without surface pretreatment Group 3: Eclipse with surface pretreatment by Eclipse bonding agent Group 4: Eclipse with laser pretreatment (Er:YAG)

Subjected to tensile stress using a universal testing machine

Group 1 and 2 showed similar bond strength. Group 4 showed significant increase in bond strength. Group 3 showed the lowest bond strength.

Tugut et al

2010

Paladent

Permaflex

Group 1: No surface pretreatment Group 2: 100 mJ, 10 Hz, 1 W, long pulse duration for 20 s. Group 3: 200 mJ, 10 Hz, 2 W, long pulse duration for 20 s. Group 4: 200 mJ, 10 Hz, 2 W, very short pulse duration for 20 s. Group 5: 300 mJ, 10 Hz, 3 W, long pulse duration for 20 s. Group 6: 400 mJ, 10 Hz, 4 W, long pulse duration for 20 s.

Subjected to Tensile stress using a Universal testing machine

Groups 2, 3, 4, 5, 6 showed higher tensile bond strengths than Group 1. Group 5 showed the best tensile bond strength among all the groups.

Hakan et al

2011

Paladent

Permaflex

Group 1: no surface pretreatment Group 2: airborne particle abrasion (aluminum oxide particles) Group 3: laser pretreatment (Er:YAG) Group 4: airborne particle abrasion + laser pretreatment (Er:YAG) Group 5: laser pretreatment (Nd:YAG) Group 6: airborne particle abrasion + laser pretreatment (Nd:YAG) Group 7: laser pretreatment (KTP) Group 8: airborne particle abrasion + laser pretreatment (KTP)

Subjected to tensile stress using a universal testing machine

Group 3 showed the best tensile bond strength among all groups. Airborne particle abrasion had a weakening effect on the bond. Nd:YAG and KTP lasers did not increase the bond strength.

Usumez et al

2004

Paladent

Molloplast B

Group 1: airborne particle abrasion (aluminum oxide particles) Group 2: laser pretreatment (Nd:YAG) Group 3: no surface pretreatment

Subjected to tensile stress using a universal testing machine

Group 1 showed the highest tensile bond strength. Group 2 did not show any significant increase in tensile bond strength over group 3.

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Liner

Study Groups

Analysis Methods

Outcome

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Supplemental Table 2. Included studies comparing bond strength of airborne particleeabraded denture bases to soft liners Materials Used Acrylic Resin

Author

Year

Mohammadreza et al

2016

Triplex

Molloplast B

Liner

Group 1: no surface pretreatment Group 2: airborne particle abrasion (aluminum oxide particles) Group 3: laser pretreatment (Er:YAG) Group 4: airborne particle abrasion + laser pretreatment (Er:YAG)

Study Groups

Thermocycled and subjected to tensile stress using a universal testing machine

Analysis Methods

Groups 2, 3, 4 significant increase in tensile bond strength than group 1. No significant difference was found in between groups 2, 3, 4. Thermocycling resulted in a decrease in tensile bond strength in all the groups.

Outcome

Khanna et al

2015

Trevalon

Luci-Sof and Super-Soft

Group 1: no surface pretreatment Group 2: airborne particle abrasion (aluminum oxide particles) Group 3: pretreatment with monomer Group 4: lining material processed with acrylic resin dough. Both the liners were applied to all these group of samples.

Thermocycled and subjected to tensile stress using a universal testing machine

For silicone liner: Group 3 showed best bond strength followed by group 2. Group 4 showed decrease in bond strength than control. For acrylic liner: Groups 2, 3, 4 showed a significant increase in bond strength over control.

Gundogdu et al

2014

QC-20

Molloplast B and Ufi Gel P

Group 1: no surface Subjected to tensile pretreatment stress using a universal Group 2: acid etching (36% testing machine H3PO4) Group 3: laser pretreatment (Er:YAG) Group 4: airborne particle abrasion (aluminum oxide particles) Group 5: acid etching + laser pretreatment (Er:YAG) Group 6: airborne particle abrasion + laser pretreatment (Er:YAG) All groups were divided into 2 subgroups. Each subgroup was treated with one of the liners.

Molloplast B group showed significantly higher tensile bond strength than the Ufi Gel P group. The highest bond strength was seen in group 2 and lowest in group 4. Groups 3, 5, 6 did not increase tensile bond strength over group 1.

Saadet et al

2013

QC-20

Ufi Gel P

Group 1: application of adhesive (Ufi Gel P) (control) Group 2: airborne particle abrasion (aluminum oxide particles) Group 3: silica coated and silanized with a silane coupling agent (CoJet system) Group 4: silica coated and adhesive application Group 5: silica coated, silane application, and adhesive treatment.

Surapaneni et al

2013

DPI Heat Cure

Subjected to tensile Ufi Gel P and Group 1: no surface stress using a universal GC Reline Soft pretreatment. testing machine Group 2: airborne particle abrasion (aluminum oxide particles) Group 3: pretreatment with methyl methacrylate monomer Group 4: pretreatment with acetone. Both the liners were applied to all the aforementioned group of samples.

Thermocycled and subjected to tensile stress using a universal testing machine

Groups 2, 3, 4, 5 showed deterioration in bond strength compared with group 1.

Group 3 showed the best bond strength followed by group 4 and control. Group 2 showed deterioration in bond strength over control. GC Reline Soft showed better performance than Ufi Gel P

(continued on next page)

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Supplemental Table 2. (Continued) Included studies comparing bond strength of airborne particleeabraded denture bases to soft liners Materials Used Acrylic Resin

Author

Year

Kulkarni et al

2011

Trevalon

Subjected to tensile Super-Soft and Group 1: no surface stress using a universal Molloplast B pretreatment testing machine Group 2: airborne particle abrasion (aluminum oxide particles) Group 3: pretreatment with monomer Both the liners were applied to all the aforementioned groups of samples.

Mean tensile bond strength of Super-Soft was significantly higher than that of Molloplast B for all the groups of surface treatment. Group 3 showed significantly increased bond strength for both the liners. Group 2 showed lower bond strength for both the liners than control.

Hakan et al

2011

Paladent

Permaflex

Group 1: no surface Subjected to tensile pretreatment stress using a universal Group 2: airborne particle testing machine abrasion (aluminum oxide particles) Group 3: laser pretreatment (Er:YAG) Group 4: airborne particle abrasion + laser pretreatment (Er:YAG) Group 5: laser pretreatment (Nd:YAG) Group 6: airborne particle abrasion + laser pretreatment (Nd:YAG) Group 7: laser pretreatment (KTP) Group 8: airborne particle abrasion + laser pretreatment (KTP)

Group 3 showed increased tensile bond among all groups. Airborne particle abrasion had a weakening effect on the bond. Nd:YAG and KTP lasers did not increase bond strength.

Minami et al

2004

Shofu Pour Resin

Sofreliner

Group 1: application of Sofreliner Primer. Group 2: airborne particle abrasion, followed by application of Sofreliner Primer Group 3: application of Reline Primer Group 4: airborne particle abrasion, followed by application of Reline Primer

Air abrasion showed a decrease in the mean bond strength. Thermocycling also lead to a reduction in bond strength. Group 1 showed the best tensile bond strength, followed by group 3.

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Liner

Study Groups

Analysis Methods

Half of the samples from each group were stored in distilled water (control), and the rest were thermocycled. Following which they were subjected to tensile stress using a universal testing machine

Outcome

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Supplemental Table 3. Included studies comparing bond strength of acid-etched, monomer-/primer-wetted, and silica-coated denture bases to soft liners Materials Used Acrylic Resin

Author

Year

Gundogdu et al

2014

QC-20

Molloplast B and Ufi Gel P

Subjected to tensile stress Group 1: no surface pretreatment using Group 2: acid etching (36% H3PO4) a universal testing machine Group 3: laser pretreatment (Er:YAG) Group 4: airborne particle abrasion (aluminum oxide particles) Group 5: acid etching + laser pretreatment (Er:YAG) Group 6: airborne particle abrasion + laser pretreatment (Er:YAG) All groups were divided into 2 subgroups. Each subgroup was treated with one of the liners.

Molloplast B group showed significantly higher tensile bond strength than Ufi Gel P group. The highest bond strength was seen in group 2 and lowest in group 4. Groups 3, 5, 6 did not increase tensile bond strength over group 1.

Akin et al

2014

Paladent

Permaflex

Group 1: No pretreatment of Subjected to tensile stress resilient liners. using Group 2: resilient liners were immersed a universal testing machine into isobutyl methacrylate (iBMA) for 1 min. Group 3: resilient liners were immersed into isobutyl methacrylate (iBMA) for 3 min. Group 4: resilient liners were immersed into 2-hydroxyethyl methacrylate (HEMA) for 1 min. Group 5: resilient liners were immersed into 2-hydroxyethyl methacrylate (HEMA) for 3 min

Group 3 showed the most tensile strength. Immersion in iBMA showed higher trensile bond strength than HEMA.

Saadet et al

2013

QC-20

Ufi Gel P

Thermocycled and subjected Groups 2, 3, 4, 5 showed Group 1: application of adhesive deterioration in bond strength to tensile stress using a (Ufi Gel P) (control) when compared with group 1. universal testing machine Group 2: airborne particle abrasion (aluminum oxide particles) Group 3: silica-coated and silanized with a silane coupling agent (CoJet system) Group 4: silica-coated and adhesive application Group 5: silica coated, silane application, and adhesive treatment.

Surapaneni et al

2013

DPI Heat Cure

Ufi Gel P and GC Reline Soft

Group 1: no surface pretreatment. Group 2: airborne particle abrasion (aluminum oxide particles) Group 3: pretreatment with methyl methacrylate monomer Group 4: pretreatment with acetone. Both the liners were applied to all the aforementioned group of samples.

Hakan et al

2013

Meliodent and Eclipse

Molloplast B

Subjected to tensile stress Group 1: PMMA without surface using pretreatment a universal testing machine Group 2: Eclipse without surface pretreatment Group 3: Eclipse with surface pretreatment by Eclipse bonding agent Group 4: Eclipse with laser pretreatment (Er:YAG)

Minami et al

2004

Shofu Pour Resin

Sofreliner

Group 1: application of Sofreliner Primer. Group 2: airborne particle abrasion, followed by application of Sofreliner Primer Group 3: application of Reline Primer Group 4: airborne particle abrasion, followed by application of Reline Primer

Muddugangadhar et al

Liner

Study Groups

Analysis Methods

Subjected to tensile stress using a universal testing machine

Half of the samples from each group was stored in distilled water (control), and the rest were thermocycled. Following which, they were subjected to tensile stress using a universal testing machine

Outcome

Group 3 showed the best bond strength, followed by group 4 and control. Group 2 showed deterioration in bond strength over control. GC Reline Soft showed better performance than Ufi Gel P Group 1 and 2 showed similar bond strength. Group 4 showed a significant increase in bond strength, whereas group 3 showed the lowest bond strength.

Airborne particle abrasion showed a decrease in the mean bond strength. Thermocycling also lead to a reduction in bond strength. Group 1 showed the best tensile bond strength, followed by group 3.

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Supplemental Table 4. Included studies comparing bond strength of oxygen plasmaetreated denture bases to soft liners Materials Used Author

Year

Acrylic Resin

Huaiqin et al

2010

Zi Ran

Liner

Study Groups

Analysis Methods

Outcome

Soft Reverse

Group 1: no surface pretreatment Group 2: oxygen plasma treatment done

Subjected to tensile stress using a universal testing machine

Group 2 showed increased tensile bond strength compared with group 1.

Supplemental Table 5. Included studies comparing the effect of thermocycling on bond strength of surface-pretreated denture bases to soft liners Materials Used Author

Year

Acrylic Resin

Mohammadreza et al

2016 Triplex

Molloplast B

Liner

Group 1: no surface pretreatment Group 2: airborne particle abrasion (aluminum oxide particles) Group 3: laser pretreatment (Er:YAG) Group 4: airborne particle abrasion + laser pretreatment (Er:YAG)

Study Groups

Thermocycled and subjected to tensile stress using a universal testing machine

Analysis Methods

Groups 2, 3, 4 show significant increase in tensile bond strength than group 1. No significant difference was found in between groups 2, 3, 4. Thermocycling resulted in a decrease in tensile bond strength in all the groups.

Rajaganesh et al

2016 DPI Heat Cure

COE-SOFT and GC Reline Soft

Group 1: application of soft Subjected to shear stress using liner. No thermocycling a universal testing machine Group 2: application of soft liner followed by thermocycling. Both the liners were applied to equal number of samples in both the groups.

Silicone-based soft liner showed higher shear bond strength than the acrylic soft liner both before and after thermocycling. Thermocycling increased shear bond strength for the silicone liner but decreased it for the acrylic liner.

Tugut et al

2015 Meliodent and Eclipse

Molloplast B and Permaflex

Group 1: PMMA denture base resin Group 2: UDMA denture base resin Both the liners were applied to equal number of samples in both the groups.

Demir et al

2011 Meliodent

Molloplast B and Permaflex

Group 1: Molloplast B packed Peel bond strength testing was against polymerized, smooth, performed on a universal testing denture base resin material. machine. Group 2: Permaflex packed against polymerized, smooth, denture base resin material. Group 3: Molloplast B packed against unpolymerized PMMA dough Group 4: Permaflex packed against unpolymerized PMMA dough

Elias et al

2007 QC-20

Mucopren Soft, Mollosil Plus, and DentuSil

The 3 liners were applied to equal number of specimens of acrylic resin. For each specimen/liner combination: Group 1: water stored, no thermocycling (control) Group 2: thermocycled.

Half the samples of each group were subjected to tensile stress using a universal testing machine, and the other half of the samples were thermocycled and then subjected to tensile stress using a universal testing machine.

Subjected to shear and tensile stress using a universal testing machine

Outcome

Thermocycling resulted in decreased tensile bond strength for both the groups. UDMA resin showed better bonding to both the liners. Molloplast B showed better bonding to both the denture base resins than Permaflex. The packing of both the siliconebased liners with unpolymerized PMMA dough showed better peel bond strength than when packed with polymerized PMMA. Thermocycling showed decreased peel bond strength for Permaflex material to PMMA denture base resin. Molloplast B did not show any significant decrease in peel bond strength after thermocycling. Thermocycling resulted in a significant reduction in tensile and shear bond strength of all the silicone-based liners to acrylic resin. Mucoprene Soft showed the best tensile and shear strength under both the tested conditions. (continued on next page)

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Supplemental Table 5. (Continued) Included studies comparing the effect of thermocycling on bond strength of surface-pretreated denture bases to soft liners Materials Used Author

Year

Minami et al

2004 Shofu Pour Resin

Sofreliner

Group 1: application of Following which they were Sofreliner Primer. subjected to tensile stress using Group 2: airborne particle a universal testing machine abrasion, followed by application of Sofreliner Primer Group 3: application of Reline Primer Group 4: airborne particle abrasion, followed by application of Reline Primer

Airborne particle abrasion showed a decrease in the mean bond strength. Thermocycling also led to a reduction in bond strength. Group 1 showed the best tensile bond strength, followed by group 3

Pinto et al

2004 Classico and Lucitone 199

Permasoft, Pro Tech, Flexor, and Molloplast B

All the liners were applied to equal number of specimens of acrylic resin. For each specimen/liner combination: Group 1: thermocycled. Group 2: water stored, no thermocycling (control)

Subjected to tensile stress using a universal testing machine.

Thermocycling decreased the tensile bond strength of Molloplast B and Pro Tech liners but did not have any significant effect on Flexor and Permasoft liners. Molloplast B showed the best tensile bond strength among all the liners regardless of thermocycling.

Muddugangadhar et al

Acrylic Resin

Liner

Study Groups

Analysis Methods

Outcome

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