Correlation between microtensile bond strength data and clinical outcome of Class V restorations

d e n t a l m a t e r i a l s 2 7 ( 2 0 1 1 ) 114–125

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Correlation between microtensile bond strength data and clinical outcome of Class V restorations Siegward D. Heintze a,∗ , Chaiyasri Thunpithayakul b , Steven R. Armstrong c , V. Rousson d a

R&D, Ivoclar Vivadent, 9494 Schaan, Liechtenstein Department of Operative Dentistry, Faculty of Dentistry, Chulalongkorn University, Bangkok, Thailand c Department of Operative Dentistry, College of Dentistry, The University of Iowa, Iowa City, IA, USA d Biostatistics Unit, Institute for Social and Preventive Medicine, University of Lausanne, Switzerland b

a r t i c l e

i n f o

a b s t r a c t

Article history:

Objective. To determine if the results of resin–dentin microtensile bond strength (␮TBS) is

Received 26 October 2009

correlated with the outcome parameters of clinical studies on non-retentive Class V restora-

Received in revised form

tions.

30 March 2010

Methods. Resin–dentin ␮TBS data were obtained from one test center; the in vitro tests were

Accepted 6 September 2010

all performed by the same operator. The ␮TBS testing was performed 8 h after bonding and after 6 months of storing the specimens in water. Pre-test failures (PTFs) of specimens were included in the analysis, attributing them a value of 1 MPa. Prospective clinical stud-

Keywords:

ies on cervical restorations (Class V) with an observation period of at least 18 months were

Bond strength

searched in the literature. The clinical outcome variables were retention loss, marginal dis-

Microtensile

coloration and marginal integrity. Furthermore, an index was formulated to be better able to

Clinical

compare the laboratory and clinical results. Estimates of adhesive effects in a linear mixed

Class V

model were used to summarize the clinical performance of each adhesive between 12 and 36

Correlation

months. Spearman correlations between these clinical performances and the ␮TBS values were calculated subsequently. Results. Thirty-six clinical studies with 15 adhesive/restorative systems for which ␮TBS data were also available were included in the statistical analysis. In general 3-step and 2-step etch-and-rinse systems showed higher bond strength values than the 2-step/3-step selfetching systems, which, however, produced higher values than the 1-step self-etching and the resin modified glass ionomer systems. Prolonged water storage of specimens resulted in a significant decrease of the mean bond strength values in 5 adhesive systems (Wilcoxon, p < 0.05). There was a significant correlation between ␮TBS values both after 8 h and 6 months of storage and marginal discoloration (r = 0.54 and r = 0.67, respectively). However, the same correlation was not found between ␮TBS values and the retention rate, clinical index or marginal integrity. Significance. As ␮TBS data of adhesive systems, especially after water storage for 6 months, showed a good correlation with marginal discoloration in short-term clinical Class V restorations, longitudinal clinical trials should explore whether early marginal staining is predictive for future retention loss in non-carious cervical restorations. © 2010 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

∗

Corresponding author. Tel.: +423 2353570; fax: +423 2331279. E-mail address: [email protected] (S.D. Heintze). 0109-5641/$ – see front matter © 2010 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.dental.2010.09.005

d e n t a l m a t e r i a l s 2 7 ( 2 0 1 1 ) 114–125

1.

Introduction

Dental adhesive systems are evaluated in the laboratory using various methods: bond strength tests, penetration of tracers along the restorative material/tooth substance interface, morphological characteristics of the interface, and marginal adaptation of restorations [1]. Bond strength tests are the most widely used laboratory method for assessing the ability of a dental bonding system to establish a bond between the restorative material and the biologic substrate, i.e. dentin and/or enamel. There are a variety of different approaches to test for the bonding capabilities. To date, there is no international consensus on which is the most appropriate approach and what should be the adequate parameters to evaluate the bond strength. The ISO Technical Specification on “Testing the adhesion to tooth structure” (No. 11405, first edition 1994, second edition 2003) [2] describes the methodology for shear and tensile bond strength tests, which are also the most popular tests [1]. Application of the ␮TBS test has substantially increased over the last 3–5 years. Many studies publish tests after only 24 h of water storage. However, it has been proven that prolonged water storage is a challenge for the interface between restorative material and tooth substance and may degrade this bond over time [3]. The different dental adhesive system formulations and the components of the resin–dentin bond react differently to this challenge. The clinical significance of bond strength tests has been discussed in many papers [4–9]; however, many researchers doubt the importance of these laboratory tests. The failure to correlate bond strength results on a product level with clinical outcomes, even with early adhesive systems that showed low bond strength, supports this skepticism [8,10]. Bond strength may be correlated to the ability of a restorative material to be held in place when mechanical retention is weak or missing. This is notably the case with cervical non-retentive lesions (Class V), also called non-carious cervical lesions (NCCL) that are restored with resin-based composites (RBC), mostly without further cavity preparation or roughening of dentin. The American Dental Association (ADA) previously defined an adhesive system to be adequate and acceptable for clinical use (“full acceptance”) if the retention rate of restorations placed in non-carious lesions is higher than 90% after an observation period of 1.5 years [11]. Many of the newer adhesive systems, especially the one-step selfetching systems, would not have received ADA acceptance. The ADA acceptance program was abandoned by the end of 2008 [12]. The question is whether the high frequency of clinical failures of a specific product is predictable by bond strength tests. If there were an acceptable correlation between bond strength test results and the clinical performance of an adhesive system in cervical restorations, one would be able to improve the adhesive prior to the time-consuming and expensive clinical trial phase. Both dentists and patients would benefit from such an approach. The objective of the present study was to determine whether results from ␮TBS 8 h post-bonding or 6 months of water storage of the specimens of a variety of different adhe-

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sive/restorative systems correlate with the clinical outcome of non-retentive cervical restorations, notably with retention loss, marginal discoloration and marginal integrity. The null hypothesis was that there was no significant correlation between the 8 h or 6-month ␮TBS on dentin and the outcome of the clinical trials.

2.

Materials and methods

2.1.

Microtensile bond strength

The ␮TBS testing procedure for all adhesive/restorative materials was performed by the same operator (TC) in the same laboratory with the same methodology. Sixty-four caries- and defect-free extracted human molar teeth, obtained according to institutional review board requirements, were stored in 0.5% chloramine T at 4 ◦ C and used within 6 months after extraction. The teeth were cleaned and mounted in dental stone (Die-Keen® Green, Heraeus Kulzer, Inc., Armunk, NY). Occlusal enamel was partially removed using a 600grit wheel model trimmer (3/4HP Wet Model Trimmer, Whip Mix Corporation, Louisville, KY, USA). The remaining occlusal enamel was removed with a water-cooled carbide bur (#55, Brasseler, Savannah, Georgia) in an electric handpiece rotating at 200,000 rpm (KaVo Electromatic and Intramatic 25LHA: KaVo America Corporation, Lake Zurich, IL) mounted in a CNC Specimen Former (University of Iowa, Iowa City, IA) to expose superficial to middle dentin. After rinsing for 5 s with 35% phosphoric acid to confirm that all central enamel had been removed, an additional 0.1 mm of occlusal dentin was removed to expose unaltered dentin substrate for bonding. The teeth were randomly distributed across 16 adhesive/restorative systems (four teeth per adhesive). Manufacturer’s instructions were followed for adhesive application as closely as possible with the following exceptions: (1) drying distance, pressure, and angulations were modified to ensure that excess moisture/solvent was completely removed from the flat occlusal surface, and (2) based on pilot study results, priming and priming/adhesive application times and the number of coats were increased for Syntac, Futurabond NR, and Xeno III to reduce the frequency of pre-test failures. See Table 1 for adhesive system composition, batch number and mode of application. Light curing was performed with an Optilux 500 curing unit (Demetron/Kerr, Danbury, CT, USA) using a radiant emittance of no less than 550 mW/cm2 as measured with a radiometer in the wavelength range of 400–500 nm (Curing Radiometer model 100, Demetron Research Corp., Danbury, CT, USA). Immediately after the application of the adhesive, the resinbased composite Z100 (shade A1, 3 M ESPE, St Paul, MN, USA) was used to incrementally build a composite “crown” that was 4–5 mm in height with peripheral borders maintained entirely in dentin. The initial increment was limited to approximately 0.5 mm thickness. The composite was heated up to 54 ◦ C (Calset Model 201 120 V, AdDent Inc., Danbury, CT, USA) to increase flow and adaptability [13]. Each increment was light cured for 40 s from a distance of 1 mm using the same light curing unit and radiant emittance. After completion of the buildup, all restored teeth were left on the bench for 15 min

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Table 1 – Composition, batch number and mode of application of adhesive. Materials Three-step etch-and-rinse systems Adper Scotchbond Multi-purpose

All-Bond 2

PermaQuick

Two-step etch-and-rinse systems One-Step

Prime&Bond NT Dual Cure

Batch no.

Manu-facturer

Etchant: 35% phosphoric acid Primer: HEMA, polyalkenoic acid copolymer, water Adhesive: bis-GMA, HEMA, photoinitiator Etchant: 32% phosphoric acid with benzalkonium chloride Primer A: NTG-GMA, acetone, ethanol, water Primer B: BPDM, acetone, ethanol, photoinitiator Adhesive: bis-GMA, HEMA, camphorquinone, amine activator Etchant: 37.5% phosphoric acid Primer: HEMA, GPDM, PAMM, ethyl alcohol, camphorquinone, water Adhesive: bis-GMA, HEMA, barium aluminum borosilicate glass, fumed silica, disodiumhexafluorosilicate, glycerol dimethacrylate, camphorquinone Etchant: 35% phosphoric acid Primer: Canadian balsam, HEMA, methacrylic acid, camphorquinone, phosphate monomer in ethanol Adhesive: bis-GMA, TEGDMA, HEMA, diluent monomer, tertiary amine, camphorquinone, proprietary glass silicate filler

6GK 6BB

3M ESPE

Etchant: 32% phosphoric acid with benzalkonium chloride Adhesive: bis-GMA, HEMA, BPDM, acetone, photoinitiator Etchant: 34% phosphoric acid, water, silicon dioxide, surfactants, blue colorant Adhesive: di- and trimethacrylate resins, dipentaerythritol penta acrylate monophosphate, nanofillers, amorphous silicon dioxide, photoinitiators, stabilizers, cetylamine hydrofluoride, acetone

0500011271

6PK 0600001909 0600001616

Bisco

Procedure Etch 15 s, Rinse 15 s, Dry 5 s from 0.5 cm, Prime 30 sA , Dry 5 s from 0.5 cm, Adhesive 2 coatsA , LC 10 s Etch 15 s, Rinse 15 s, Dry 2 s from 0.5 cm, Prime 5 coatsA , Dry 5 s from 0.5 cm, Adhesive 2 coatsA , LC 20 s

0600001614 0600001539 444288 423881

Kerr

440996

B0FTQ B1Z74

Ultradent

Etch 15 s, Rinse 20 s, Dry 5 s from 0.5 cm, Prime 30 s with light scrubbingB , Dry 5 s from 0.5 cm, Adhesive 2 coatsA , LC 30 s

Etch 15 s, Rinse 15 s, Dry with Kimwipes, Prime 30 sA , Dry 12 s from 1 cm, LC 20 s, Adhesive 2 coatsA , Dry 5 s from 2 cm, LC 20 s

B1YFR

Bisco

0500020767 051282 051211

Dentsply

Etch 15 s, Rinse 15 s, Dry with Kimwipes, Adhesive 2 coatsA with agitation, Dry 10 s from 2 cm, LC 10 s Etch 15 s, Rinse 10 s, Dry with Kimwipes, Adhesive 2 coatsA 30 s, Dry 5 s from 2 cm, LC 10 s

d e n t a l m a t e r i a l s 2 7 ( 2 0 1 1 ) 114–125

OptiBond FL

Components

Table 1 – (Continued) Materials Two-step self-etch systems Clearfil SE Bond

Syntac

Futurabond NR

iBond Xeno III

Glass-ionomer systems Fuji BOND LC

Fuji II LC

Batch no.

Manu-facturer

Primer: 10-MDP, HEMA, hydrophilic dimethacrylate, dl-camphorquinone, N,N-diethanol-p-toluidine, water Adhesive: 10-MDP, bis-GMA, HEMA, hydrophobic dimethacrylate, dl-camphorquinone, N,N-diethanol-p-toluidine, silanated, colloidal silica Primer: polyethylene glycol dimethacrylate, maleic acid, ketone Adhesive: polyethylene glycol dimethacrylate, glutaraldehyde Heliobond: bis-GMA, triethylene glycoldimethacrylate, photoinitiator

00599B

Kuraray

Prime 20 sA , Dry from 0.5 cm, Adhesive 2 coatsA , Dry from 2 cm, LC 10 s

Ivoclar-Vivadent

Prime 30 sA , Dry from 0.5 cm, Adhesive 2 coatsA 10 s, Dry from 0.5 cm, Heliobond 2 coatsA , Dry 5 s from 2 cm, LC 20 s

Compartment #1: methacrylate phosphates, photoinitiator, stabilizer Compartment #2: water, complexed fluorides, stabilizer Adhesive: bis-GMA, hydroxyethylmethacrylate, BHT, ethanol, organic acids, fluoride, initiator Adhesive: acetone, 4-META, glutaraldehyde, initiator Liquid A: HEMA, purified water, ethanol, BHT, highly dispersed silicon dioxide Liquid B: phosphoric acid modified polymethacrylate resin, mono fluorophosphazene modified methacrylate resin, UDMA

240465

3M ESPE

Mix Unidose 5 s, Adhesive 15 sB did not replenish, Dry from 1 cm until no fluid movement then from 0.5–1 cm, Second coat of adhesive, Dry 1 cm until no fluid movement, LC 10 s

610064

VOCO

Mix 5 sA , Adhesive 1 coat 20 sA , Dry 5 s from 2 cm, LC 10 s

010074

Heraeus-Kulzer

0508001872

Dentsply

Adhesive 3 coats 30 sA , Dry from 5 cm until no fluid movement then additional drying from 1 cm until dry, LC 20 s Mix 5 s, Adhesive 45 sA , Dry 5 s from 2 cm until no fluid movement, LC 10 s

Cavity conditioner: 20% polyalkenoic acid, 3% aluminum chloride Powder: fluoroaluminosilicate glass Liquid: polyalkenoic acid, HEMA, dimethacrylate, camphorquinone, water Cavity conditioner: 20% polyacrylic acid, 3% aluminum chloride Capsule: fluoroaluminum silicate glass, polyacrylic acid, HEMA

Procedure

00844A

G04550 G08116 G04743

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One-step self-etch systems Adper Prompt L-Pop

Components

0509000753

0503021

GC

0503031 0503021 0503021 0510241

GC

Condition 10 sB , Rinse 10 s, Dry with Kimwipes, Mix powder/liquid 10 sB , Adhesive 2 coats, LC 20 s, Apply vaseline after RBC placement then left in humidity 1 wk Condition 10 sB , Rinse 10 s, Dry with Kimwipes, Mix capsule 10 s with 4,000 RPM, LC 20 s

117

118

BHT: butylated hydroxytoluene; bis-GMA: bisphenol A diglycidylmethacrylate; BPDM: biphenyl dimethacrylate; GPDM: glycerophosphoric acid dimethacrylate; HEMA: 2-hydroxyethyl methacrylate; 4-META: 4-methacryloxyethyl trimellitic anhydride; MDP: 10-methacryloyloxydecyl dihydrogen phosphate; NTG-GMA: N-tolylglycine glycidyl methacrylate; PAMM: mono (2-methacryloxyethyl) phthalate; PENTA: phosphonated penta-acrylate ester; TEGDMA: triethyleneglycol dimethacrylate; UDMA: urethane dimethacrylate; A = with supplied brush; B = with microbrush; LC = light-cure.

6ET

6EE

131595

6BF Vitremer

Ketac-Fil Plus

Powder: calcium aluminofluorosilicate glass Liquid: polyethylene polycarbonic acid, tartaric acid, water Primer: Vitrebond copolymer, HEMA, ethanol, photoinitiators Powder: fluoroaluminosilicate glass, microencapsulated potassium persulfate, ascorbic acid, pigments Liquid: polycarboxylic acid modified with pendant methacrylate groups, Vitrebond copolymer, water, HEMA, photoinitiators

240436

3M ESPE

3M ESPE

Condition 10 sB , Rinse 15 s, Dry with Kimwipes Mix capsule 10 s with 4,200 RPM, Apply Vaseline, then leave in humidity 1 wk Prime 30 s from 2 cmB , Dry until no fluid movement, LC 20 s, Mix powder/liquid 45 s, LC 40 s

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before storing them in 100% humidity. After 1 h of storage, the restored teeth (except for Fuji BOND LC and Ketac-Fil Plus, which were stored for 1 week) were sectioned perpendicular to the adhesive-tooth interface with three water-cooled lowspeed diamond saw blades (IsoMet 1000, Buehler Ltd., Lake Bluff, IL, USA) separated by 2 mm spacers using a cutting speed of 125 rpm and the application of a 150-g weight. Two sections were accomplished at right angles to yield four rectangular 2 mm × 2 mm sticks that were sectioned free from the dental stone mounting using a 1 in. diamond disk mounted in a dental lab motor (Kavo EWL Typ 950, Kavo Dental Corporation, Lake Zurich, IL, USA). Using a CNC Specimen Former, the sticks (n = 256) were trimmed with a 0.8-␮m, ultrafine cylindrical diamond bur (#012, Brasseler, Savannah, Georgia, USA) into dumbbell-shaped tensile test specimens with a round crosssectional area of 0.5 mm2 , a gage length of 1 mm, and a radius of curvature or ‘neck’ of 0.6 mm. They were examined under a stereomicroscope at 50× magnification (Stemi 2000, Zeiss, NY, USA) to verify proper fabrication. The diameter of each specimen was measured with a digital caliper (Digimatic caliper, Mitutoyo Corporation, Kawasaki, Japan). Equal numbers of the specimens from each tooth were randomly allocated to two groups: (1) 8 h post-bonding (which corresponds to immediate testing), and (2) 6-month storage at 37 ◦ C in artificial saliva [14], which contained 0.1% sodium azide to inhibit microbial growth [15]. Microtensile testing was performed at a crosshead speed of 1 mm/min with a calibrated Zwick material testing machine (Zwick Materials Testing Machine Z2.5/TN1S, Zwick/Roell, Ulm, Germany) and testXpert software after the defined storage times. The specimen was gripped centrally with respect to the test axis with a non-gluing passive gripping device (Dircks Device, The University of Iowa, Iowa City, IA, USA). No specimens fractured outside of the test region (gage area) and the mean ␮TBS per tooth was used as the statistical unit.

2.2. Collection of clinical trial data and adhesive-related parameters in non-carious Class V restorations Prospective clinical studies on Class V restorations were searched in MEDLINE (search period 12/2008) and IADR abstracts (1994–2008). The search words were “Class V” or “cervical” or “abfraction lesion” and “clinical”. The inclusion criteria were as follows: 1. Prospective clinical trial involving at least 1 adhesive/restorative (ARS) system in Class V cavities. 2. Minimum duration of 18 months. 3. The study had to report the following outcome variables: retention, marginal discoloration, marginal integrity, secondary caries.

2.3.

Statistical analysis

To test whether the ␮TBS results after 8 h of water storage differ from those after 6 months, the non-parametric Wilcoxon test was applied (p < 0.05). The following clinical outcomes were retrieved from the studies: R = 100 − (% of retention loss), MD = 100 − (% of marginal discoloration) and MI = 100 − (% of

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Table 2 – Pre-test failures and mean microtensile bond strength data on prepared dentin 8 h post-bondinga and after 6-months of water storage (n = 4 teeth per adhesive; n = 16 specimens per adhesive system). No.

Adhesive/restorative system

Three-step etch-and-rinse 1 Adper Scotchbond Multi-Purpose 2 All-Bond 2 3 OptiBond FL 4 PermaQuick Mean of group Two-step etch-and-rinse 5 One-Step 6 Prime&Bond NT Dual Cure Mean of group Two-/three step self-etch 7 Clearfil SE Bond 8 Syntac Mean of group One step self-etch 9 Adper Prompt L-Pop 10 Futurabond NR 11 iBond 12 Xeno III Mean of group Glass ionomer 13 Fuji BOND LCa 14 Fuji II LC 15 Vitremer Mean of group Total a

Pre-test failures (preparation)

8-h ␮TBS (SD)

6-month ␮TBS (SD)

Mean difference within storage interval (%)

52.9(18.1) 39.8(7.9) 56.7(3.5) 60.9(8.7) 52.6(10.9)

54.5(10.5) 37.0(10.0) 45.1(8.6) 45.3(13.1) 45.5(10.7)

3.0 −7.0 −20.4 −25.6 −13.5

2

1

49.6(14.0) 52.8(5.6) 51.2(10.5)

26.8(18.5) 48.9(2.8) 37.8(13.2)

−46.0 −7.4 −26.2

2

1 1

51.7(6.0) 18.8(13.1) 35.2(10.2)

48.5(2.9) 27.3(17.6) 37.9(12.6)

−6.2 45.2 19.5

2.7(3.4) 16.4(7.3) 25.1(6.1) 13.1(11.1) 14.1(7.5)

3.2(4.4) 15.6(18.6) 22.0(14.5) 7.7(4.6) 12.1(12.2)

17.6 −5.3 −12.3 −41.6 −15.3

12.0(7.0) 23.1(3.3) 15.6(5.1) 17.2(5.1)

7.2(4.3) 18.6(8.9) 18.4(1.7) 14.7(5.8)

−40.3 −19.4 17.9 −14.5

13 8 1 9

4 2

2 2

40

8

Fuji Bond LC was stored 1 week in 100% humidity before trimming for ␮TBS testing.

detectable margins). Since most experiments had 0% of secondary caries, this outcome variable was not considered. Following a comparative study of marginal adaptation and the outcome of Class V clinical studies [16], the clinical performance was summarized by combining three clinical outcomes into one clinical index: CI = (4R + 2MD + 1MI)/7. A first look at the data roughly revealed that linear deterioration occurred over time. However, a simple regression model Y = 100−ˇt + error (equivalent to (100 − Y)/t = ˇ + error, where Y = dependent variable (retention, marginal discoloration), ˇ = coefficient based on study characteristics (type of adhesive, dentin preparation, random effect) and t = time) was not adequate, as the error was not normally distributed (data not shown). Thus, we applied a square root transformation and opted for the model



Lost or damage due to human error

100 − Y = ˇ + error t

for which normality could be assumed. Since this model implies Y = 100−(ˇ + error)2 t, the slope −(ˇ + error)2 characterizing deterioration was, logically, forced to be negative and the quantity −ˇ2 was interpreted as median slope of deterioration. Using a linear mixed model, we allowed the above coefficient beta to depend on the fixed effects of preparation, beveling, type of isolation and the adhesive and the random effect of the experiment to account for the fact that measurements within the same experiment were correlated. We did not include a study effect, since it would have been too much confounded with the adhesive effect. Estimates of the

adhesive effects in this model were used to summarize the clinical performance of each adhesive between 12 and 36 months. They were inverted and centered in such a manner that a positive value corresponds to a performance above average, and a negative value to a performance below average (a zero value represents average performance). Spearman correlations between these clinical performances and the ␮TBS values were calculated.

3.

Results

3.1.

Microtensile dentin bond strength

Four specimens were produced from each of the sixty teeth, resulting in 240 specimens. Eight specimens were accidentally broken (human error – data excluded) leaving a total of 232 specimens for analysis. A total of 192 specimens survived the preparation procedure (8-h: 97 specimens; 6-month: 95 specimens) for mechanical testing, while 12 PTFs occurred during diamond saw sectioning and 28 during dumbbell trimming. Data were analyzed including PTFs (Table 2) with an arbitrarily assigned bond strength of 1 MPa; which is half way between zero and the 1 N pre-load value, given a cross-sectional area of 0.5 mm2 [17]. When classified by adhesive system, PTFs did not occur in 3-step etch-and-rinse adhesives, while 2 specimens of the 2-step etch-and-rinse and 2 of the 2-step self-etch adhesives failed during dumbbell trimming. In the 1-step self-etch group,

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d e n t a l m a t e r i a l s 2 7 ( 2 0 1 1 ) 114–125

Fig. 1 – Scatterplots of clinical outcome variables (R = retention, MD = marginal discoloration, MI = marginal integrity, CL = clinical index) versus mirotensile data for 15 adhesive systems, together with Spearman correlations and associated p-Values. The numbers of the adhesive systems are plotted (see Table 2). A: microtensile 8 h, B: microtensile 6 months of water storage of specimens.

d e n t a l m a t e r i a l s 2 7 ( 2 0 1 1 ) 114–125

Table 3 – References for clinical studies included in the comparative analysis. 1 Abdalla AI, Alhadainy HA, Garcia-Godoy F. Clinical evaluation of glass ionomers and compomers in Class V carious lesions. Am J Dent 1997;10:18–20. (Fuji II LC + Vitremer) 2 Abdalla AI, Garcia-Godoy F. Clinical evaluation of self-etch adhesives in Class V non-carious lesions. Am J Dent 2006;19(5):289–92. (Clearfil SE) 3 Abdalla AI, Garcia-Godoy F. Clinical performance of a self-etch adhesive in Class V restorations made with and without acid etching. J Dent 2007;35:558–63. (Futurabond NR) 4 Alhadainy HA, Abdalla AI. 2-year clinical evaluation of dentin bonding systems. Am J Dent 1996;9(2):77–9. (Scotchbond Multipurpose, Syntac) 5 Aw TC, Lepe X, Johnson GH, Mancl LA. A three-year clinical evaluation of two-bottle versus one-bottle dentin adhesives. J Am Dent Assoc 2005;136(3):311–22. (Scotchbond Multipurpose) 6 Baratieri LN, Canabarro S, Lopes GC, Ritter AV. Effect of resin viscosity and enamel beveling on the clinical performance of Class V composite restorations: three-year results. Oper Dent 2003;28(5):482–7. (One-Step) 7 Belluz M, Pedrocca M, Gagliani M. Restorative treatment of cervical lesions with resin composites: 4-year results. Am J Dent 2005;18:307–10. (One-Step) 8 Brackett WW, Browning WD, Ross JA, Brackett MG. Two-year clinical performance of a polyacid-modified resin composite and a resin-modified glass-ionomer restorative material. Oper Dent 2001;26(1):12–6. (Fuji II LC) 9 Brackett WW, Dib A, Brackett MG, Reyes AA, Estrada BE. Two-year clinical performance of Class V resin-modified glass-ionomer and resin composite restorations. Oper Dent 2003;28(5):477–81. (Fuji II LC) 10 Brackett WW, Brackett MG, Dib A, Franco G, Estudillo H. Eighteen-month clinical performance of a self-etching primer in unprepared class V resin restorations. Oper Dent 2005;30(4):424–9. (One-Step) 11 Browning WD, Brackett WW, Gilpatrick RO. Two-year clinical comparison of a microfilled and a hybrid resin-based composite in non-carious Class V lesions. Oper Dent 2000;25(1):46–50. (Scotchbond Multipurpose) 12 Burgess JO, Gallo JR, Ripps AH, Walker RS, Ireland EJ. Clinical evaluation of four Class 5 restorative materials: 3-year recall. Am J Dent 2004;17:147–50. (Fuij II LC) 13 Dalton Bittencourt D, Ezecelevski IG, Reis A, Van Dijken JW, Loguercio AD. An 18-months’ evaluation of self-etch and etch & rinse adhesive in non-carious cervical lesions. Acta Odontol Scand 2005;63(3):173–8. (Adper Prompt-L-Pop) 14 Ermis RB. Two-year clinical evaluation of four polyacid-modified resin composites and a resin-modified glass-ionomer cement in Class V lesions. Quintessence Int 2002;33(7):542–8. (Prime & Bond NT) 15 Ermis RB, Van Landuyt K, Cardoso MV, Peuman M, Van Meerbeek B. Eighteen-month clinical effectiveness of a one-step self-etch adhesive. J Dent Res 2008:573 [PEF:Abstract Nr.]. (OptiBond FL) 16 Folwaczny M, Loher C, Mehl A, Kunzelmann KH, Hickel R. Tooth-colored filling materials for the restoration of cervical lesions: a 24-month follow-up study. Oper Dent 2000;25(4):251–8. (Syntac) 17 Franco EB, Benetti AR, Ishikiriama SK, Santiago SL, Lauris JR, Jorge MF, Navarro MF. 5-Year clinical performance of resin composite versus resin modified glass ionomer restorative system in non-carious cervical lesions. Oper Dent 2006;31:403–8. (Vitremer) 18 Gladys S, Van Meerbeek B, Lambrechts P, Vanherle G. Marginal adaptation and retention of a glass-ionomer, resin-modified glass-ionomers and a polyacid-modified resin composite in cervical Class-V lesions. Dent Mater 1998;14:294–306. (Fuji II LC, Vitremer) 19 Loguercio AD, Reis A, Barbosa AN, Roulet JF. Five-year double-blind randomized clinical evaluation of a resin-modified glass ionomer and a polyacid-modified resin in noncarious cervical lesions. J Adhes Dent 2003;5:323–32. (Vitremer) 20 Matis BA, Cochran MJ, Carlson TJ, Guba C, Eckert GJ. A three-year clinical evaluation of two dentin bonding agents. J Am Dent Assoc 2004;135(4):451–7. (Scotchbond Multipurpose) 21 Önal B, Pamir T. The two-year clinical performance of esthetic restorative materials in non-carious cervical lesions. J Am Dent Assoc 2005;136:1547–55. (Scotchbond Multipurpose, Vitremer) 22 Özgünaltay G, Önen A. Three-year clinical evaluation of a resin modified glass-ionomer cement and a composite resin in non-carious class V lesions. J Oral Rehabil 2002;29(11):1037–41. (Scotchbond Multipurpose) 23 Perdigão J, Carmo AR, Anauate-Netto C, Amore R, Lewgoy HR, Cordeiro HJ, Dutra-Correa M, Castilhos N. Clinical performance of a self-etching adhesive at 18 months. Am J Dent 2005;18:135–40. (Clearfil SE Bond) 24 Perdigão J, Carmo AR, Geraldeli S. Eighteen-month clinical evaluation of two dentin adhesives applied on dry vs moist dentin. J Adhes Dent 2005;7(3):253–8. (Prime & Bond NT) 25 Peumans M, Munck J, Van Landuyt K, Lambrechts P, Van Meerbeek B. Three-year clinical effectiveness of a two-step self-etch adhesive in cervical lesions. Eur J Oral Sci 2005;113(6):512–8. (Clearfil SE Bond) 26 Peumans M, Van Meerbeek B, Lambrechts P, Vanherle G. Two-year clinical effectiveness of a resin-modified glass-ionomer adhesive. Am J Dent 2003;16(6):363–8. (Fuji Bond LC) 27 Ritter AV, Heymann HO, Swift Jr EJ., Sturdevant JR, Wilder AD, Jr. Clinical evaluation of an all-in-one adhesive in non-carious cervical lesions with different degrees of dentin sclerosis. Oper Dent 2008;33:370–8. (iBond) 28 Schattenberg A, Werling U, Willershausen B, Ernst CP. Two-year clinical performance of two one-step self-etching adhesives in the restoration of cervical lesions. Clin Oral Investig 2008;12:225–32. (Xeno III). 29 Schwartz RS, Haveman CW, Conn LJ, Summitt JB, Robbins JW. Clinical evaluation of a one-bottle adhesive: 18-month results. J Dent Res 2000;75(Spec Issue A) [Abstract No 1534]. (One-Step) 30 Smith CD, Dickinson GL, Morris CF, Cliett BA. Two-year clinical evaluation of non-retentive Class V restorations. J Dent Res 2000;75(Spec Issue A):396 [Abstract No. 3031]. (All Bond 2) 31 Türkün LS. Clinical Performance of a New Antibacterial Adhesive System at 18-months. J Dent Res 2004;86(Spec Issue A) [Abstract No 0226]. (Xeno III) 32 Türkün SL. Clinical evaluation of a self-etching and a one-bottle adhesive system at two years. J Dent 2003;31(8):527–34. (Prime & Bond NT, Clearfil SE Bond) 33 Tyas MJ. Clinical performance of two dentine adhesives: 2-year results. Aust Dent J 1996;41(5):324–7. (Scotchbond Multipurpose)

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Table 3 – (Continued) 34 Van Dijken JW. Clinical evaluation of three adhesive systems in class V non-carious lesions. Dent Mater 2000;16(4):285–91. (Fuji II LC, One-Step) 35 Van Meerbeek B, Kanumilli PV, De Munck J, Van Landuyt K, Lambrechts P, Peumans M. A randomized, controlled trial evaluating the three-year clinical effectiveness of two etch & rinse adhesives in cervical lesions. Oper Dent 2004;29(4):376–85. (OptiBond FL, Permaquick) 36 Van Meerbeek B, Peumans M, Gladys S, Braem M, Lambrechts P, Vanherle G. Three-year clinical effectiveness of four total-etch dentinal adhesive systems in cervical lesions. Quintessence Int 1996;27(11):775–84. (Scotchbond Multipurpose) References of excluded clinical studies on Ketac-Fil 1 Brackett WW, Gilpatrick RO, Browning WD, Gregory PN. Two-year clinical performance of a resin-modified glass-ionomer restorative material. Oper Dent 1999;24:9–13. 2 Powell LV, Gordon GE, Johnson GH. Clinical comparison of Class V resin composite and glass ionomer restorations. Am J Dent 1992;5:249–52.

11 specimens failed during sectioning, mostly from the Adper Prompt L-Pop subgroup, and 19 specimens failed while trimming (see Table 2). Four specimens of the RMGIC Fuji BOND LC subgroup debonded during the trimming step. All Ketac-Fil Plus specimens failed during the preparation and trimming phase and were therefore excluded from further analysis. The ␮TBS results for each adhesive system after 8 h and 6 months of storage as well as the result for each adhesive class, once the different systems had been grouped, are presented in Table 2. Generally at 8 h, the 3-step and 2-step etch-andrinse systems showed higher bond strength values than the 2-step/3-step self-etching systems, which had higher values than the 1-step self-etching and the glass ionomer and resin modified glass ionomer systems. One exception is the 2-step self-etching adhesive system Clearfil SE. After 6 months water storage the same rank order existed except that the 2-step etch-and-rinse was then equivalent to the 2-step/3-step selfetching systems. Prolonged water storage of ␮TBS specimens resulted in a decrease of the mean bond strength values compared to the values obtained 8 h after bonding in 11 ARS. In 5 ARS, there was, surprisingly, an increase of bond strength after storage. However, the decrease was only statistically significant for 5 of the ARS and the increase was statistically significant for only 1 (Syntac) (Wilcoxon test, p < 0.05).

3.2. data

Correlation between laboratory data and clinical

As all Ketac-Fil specimens suffered PTFs in the laboratory, the results of the clinical studies were excluded from the analysis (n = 2, see Table 3). Thirty-six clinical studies with 15 adhesive systems/restorative materials, for which also microtensile data were available, were included in the statistical analysis (Table 2). The clinical studies reported on the outcome of 41 different experiments. Of the 36 clinical studies, the dentin was prepared in 14 clinical experiments and no preparation was performed in 22 experiments. In 18 of the 36 studies, the enamel was beveled. As far as the type of isolation is concerned, in 16 studies absolute isolation with rubberdam was reported, and in 16 studies relative isolation with cotton rolls; in 4 studies no information was given. Scatterplots on the correlation between microtensile strength and clinical data are shown in Fig. 1 after 8 h and 6 months of water storage. Statistically significant positive correlations were only found for both the 8-h and 6-month data

and marginal discoloration (MD), but not for retention, clinical index, and marginal integrity.

4.

Discussion

The ␮TBS test is claimed to have several advantages [3,18–20]: (1) multiple specimens can be prepared from a single tooth; (2) stress distribution may be applied more uniformly during loading as compared to conventional tensile testing and shear bond strength measurements; (3) fewer dentin cohesive failures occur; (4) bond strength values are higher than those measured with conventional tensile and shear bond strength tests due to the decreased number of defects in the substrate or bond interface; (5) additional research designs can be performed to eliminate tooth dependency, for example, multiple surfaces within the same cavity, various substrates within a tooth can be evaluated; (6) accelerated environmental aging is feasible by aqueous storage due to short diffusional distances; (7) very small surface areas can be examined; and (8) SEM fractography can be readily performed to determine the mode of failure. As the ␮TBS test is very laborious and techniquesensitive some of these advantages cited in the literature have to be critically examined. The main advantage is perhaps that – in contrast to shear bond tests – the main failure mode is adhesive and not cohesive and one can better differentiate between adhesive systems. The PTFs were included into the statistical analysis with the value of 1 MPa as suggested previously [17]. To ignore these PTFs would bias the results [21,22]. There are many factors that have an influence on the result of bond strength tests. According to an extensive metaanalysis [23], the main influencing factors on adhesion tests to dentin were – in descending order according to the statistically proven importance – dentin depth, crosshead speed, specimen storage time and tooth storage maximum time, bonding area, tooth storage temperature, sample storage temperature and composite stiffness. Already in this meta-analysis – although only limited data were available – storage time of specimens of more than 24 h was inversely correlated with bond strength. Most of the adhesive systems that were developed in the 1990s showed mean ␮TBS values above 35 MPa in tests after 24 h [24]. The single-bottle self-etching systems that were brought on the market more recently, however, show a greater variability of bond strength values on dentin and may reach

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only 15 MPa in ␮TBS tests [25]. In the present study, prolonged water storage of ␮TBS specimens resulted in a statistically significant decrease of the mean bond strength values compared to those of 8-h post-bonding in 5 out of 16 ARS, while in 1 ARS (Syntac) a statistically significant increase was observed. The product-related decrease of bond strength is in line with other laboratory studies [26]. The increase of Syntac cannot be explained. The high PTF rate of the glass ionomer cement (Ketac-Fil) can be explained by the low mechanical properties of the material, which lead to early failures in bond strength testing and different mechanical test methods may be required for glass ionomer systems. The resin modified glass ionomer cements like Fuji II LC have better mechanical properties, which also lead to higher bond strength results. Some confounding factors have to be discussed. Firstly, in some adhesive systems the application protocol deviated from the instructions of use of the manufacturer, which, however, were followed in the clinical studies. The rationale for doing so were the results of pilot studies that decreased the number of PTFs [27–29]. Other studies have already proven that increasing the number of coatings leads to increased ␮TBS values, especially with 1-step self-etching adhesive systems [27,30]. Secondly, the clinical studies differ with regard to the preparation of the cavities, as in about 40% of the clinical experiments dentin was prepared, while in about 60% no preparation was performed. However, the dentin preparation did not affect the correlation rate. A similar result was obtained when the marginal adaptation of cervical restorations was compared with the clinical outcome of Class V restorations [16]. The adhesive system Syntac is somehow unique as it does not require an dentin etching with phosphoric acid. This adhesive consists of a 3-step system with a primer that contains weak maleic acid, which sufficiently decalcifies the dentin so that the bonding material can penetrate into the tubules; the enamel, however, is insufficiently etched by maleic acid. The special composition explains why the bond strength values of Syntac are lower compared to Clearfil SE, which has the specific acidic monomer 10-MDP that decalcifies dentin better than maleic acid. As for the laboratory study, acid-etching of the dentin with phosphoric acid was neither performed in the clinical studies on Syntac (study nos 5 and 16; see Table 3). The bond strength results of the present study partly reflect the results reported in clinical studies on the retention loss of non-retentive non-carious cervical restorations, when looking at the adhesive systems on a group level. A review of 2005 regarding the effectiveness of adhesive systems in non-retentive cervical lesions concluded that 3-step etch-and-rinse adhesive systems and 2-step self-etch adhesive systems showed a clinically reliable and predictably good clinical performance, whereas 2-step etch-and-rinse adhesive systems performed less favorably and the 1-step self-etching adhesives showed the highest retention loss of them all [31]. A recent update to this data set has shown that the newer onestep self-etching adhesives have improved retention rates and bond strength studies that include a durability challenge to the adhesive system show a modest, but statistically significant, correlation with NCCL RBC retention rate data [9]. Interest-

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ingly, restorations made with glass ionomer cements showed the highest retention rate. The variability of the clinical results was pronounced for each adhesive class; the lowest variability occurred in the 3-step etch-and-rinse adhesives (0–16% retention loss), while the highest variability was found in the 1-step self-adhesive systems (0–48% retention loss), which is partly in line with the results of the present laboratory study. If Syntac is removed from the group of self-etching adhesive systems, the clinical results on a group level match, to a certain degree, the bond strength results of the laboratory test, whereas the low bond strength values for the glass ionomer cements are in contrast to the high clinical retention. The reason for that has been discussed above. Not only do the clinical results vary considerably between the different adhesive systems of the same class of adhesives, but there is also a great variability of results for the same product when evaluated in different studies. For instance, the adhesive system Prompt L-Pop, an earlier version of Adper Prompt L-Pop, showed a retention loss of restorations in noncarious cervical lesions of 35% [32], 13.5% [33], and 4% [34] within 1 year. Whether this large variation is due to the influence of the operator, patient-related factors or whether it may express some sort of technique-sensitivity of the product remains unclear. When trying to correlate bond strength values to the clinical retention rates of cervical restorations on a product level, a clear correlation could not be established [24,25,35]. The present study came to the same result. Even the ␮TBS data after prolonged water storage of the specimens did not match with the retention rates of Class V restorations. However, there was a significant correlation between the ␮TBS data and marginal discoloration. Marginal discoloration is indicative for gap formation and macroleakage [36,37]. Subsequently, the bond between the restorative material and the tooth substrate may be disintegrated and the result is loss of retention. However, whether marginal discoloration is an early sign for subsequent loss of retention is speculative, as longitudinal systematic clinical trials to investigate this issue have not been conducted to date. Furthermore, the evaluation of marginal stain is subjected to a greater inter-examiner variability than the evaluation of retention loss. The complex relationship between marginal quality and restoration failure deserves greater investigation. The presence of discoloration and defects at the resin-based composite margins may be due to material performance and/or operator error and is assumed to be an indicator of progressive marginal deterioration leading to loss of restoration retention or recurrent caries. Recurrent caries is not commonly observed in the clinical trial observation periods routinely reported; however, retention loss is increasingly observed over these study periods [38]. Restorations placed in primary and permanent teeth have shown recurrent caries to occur more frequently in RBCs as compared to amalgams [39,40]. Additionally, stained dentin margins have been demonstrated to have more wall lesions [41] and plaque [37,42] than unstained dentin margins. Clinical trials have reported that the presence of marginal discoloration is dependent, to a certain extent, on the marginal adaptation of the restoration, stating that marginal staining occurs due to small fractures of the material at the margins or an increased microleakage [43–45]. A 2 year clinical trial

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with 100% retention rate demonstrated significant deterioration in marginal adaptation after 6 months with an increasing marginal discoloration over the remaining study period [46]. This same research group also observed that incisal marginal discoloration was always noticed in combination with a small marginal defect and that this correlation was also noticed in other Class V clinical studies [47–49]. A trial evaluating the restoration of NCCLs with and without occlusal and gingival retentive grooves found a significantly higher retention with retention grooves and less marginal staining [50]. Clinical trials of appropriate design are necessary to evaluate potential clinical parameters for failures of restorations that occur at a later stage. An analysis of 5 year failure rates from a multi-center trial revealed that posterior composite restorations with marginal deterioration at 3 years were 5.3 times more likely to have failed by 5 years than restorations with alpha-rated marginal adaptation at 3 years [51]. Similarly restorations with marginal discoloration at 3 years were found to be 3.8 times more likely to have failed at 5 years than restorations with no marginal discoloration at 3 years. Notably, restorations with both marginal deterioration and marginal discoloration at 3 years failed 8.7 times more frequently than restorations with sound margin at 3 years. These authors concluded that clinical investigations of present-day posterior composite materials should seek to determine if marginal deterioration and cavomarginal discoloration constitute important predictors of the failure of posterior composites, especially when marginal deterioration and cavomarginal discoloration occur simultaneously. Most of the clinical studies on Class V restorations have an observation period of only 2–3 years, which can be explained by the fact that ADA acceptance for an adhesives system used to require a period of only 1.5 years [11] thus limiting the broader examination of the complex relationship between common clinical evaluation parameters. In 2006, a study which showed the retention loss of 7 adhesive systems over a period of 13 years was published [38]. This study showed that Class V restorations which are placed with adhesive systems that demonstrate a retention loss of around 10–20% within the first 5 years of service may exhibit a sharp increase in retention loss in the years thereafter (up to 50–60%). Furthermore, adhesive systems that showed a retention loss of 80% or more after 10 years already exhibited high failure rates 1–2 years after insertion. In contrast, 2 of the 4 adhesive systems that demonstrated low failure rates within the first 4 years showed a significant increase at the 6-year recall. The correlation between bond strength results and retention loss as observed in clinical results might have been different if the observation period of the selected clinical trials had been longer.

5.

Conclusions

As there was a significant correlation between ␮TBS values and an outcome parameter (marginal discoloration) of clinical studies on Class V non-retentive restorations, the null-hypothesis had to be partly rejected. However, there was no significant correlation with the clinical index, retention rate or marginal integrity. As ␮TBS data of adhesive systems,

especially after water storage for 6 months, showed a good correlation with marginal discoloration in short-term clinical Class V restorations, further investigations and longitudinal clinical trials should explore the clinical relevance of laboratory studies and whether early clinical marginal staining is predictive of future retention loss in non-carious cervical restorations.

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