1

Introduction

In adhesive dentistry bonding to the tooth tissues is usually based on the replacement of tooth minerals, removed by acid etching, by low viscous resin monomers. After curing of the resins, a strong micro-mechanical bond is created by interlocking of the monomers in the tooth surface creating a hybrid layer. Adhesive techniques have been improved substantially during the last decades and are now involved in most of the clinical procedures. Enamel–resin bonds, produced after acid etching with phosphoric acid have shown to be satisfactory and stable over time . Adhesion to dentin on the other hand has been difficult to achieve and less durable . The introduction of primers containing amphiphilic monomers, dissolved in solvents like water, acetone or alcohol to promote wetting of the dentin and replace water, changed dentin bonding to a more reliable clinical procedure. Two alternative strategies are used to obtain the bond. Etch-and-rinse adhesives, which pretreat the smear layer and the underlying tooth tissues with phosphoric acid followed by the application of a primer and an adhesive in two steps or one step. In the second approach, the self-etching adhesives (SEA) or etch-and-non-rinse systems are the acid and the primer combined into one step. This is followed by the application of the adhesive in the two-step SEA, while in the one-step SEA, all components are included in one step, as two-bottles or one-bottle systems. The SEA simultaneously self-etch and infiltrate the dental tissues. They are supposed to make the bonding procedure more user-friendly, eliminating the risk of over-etching and over-drying. In two-step self-etching adhesives there is a separate priming step with more hydrophilic monomers and a more hydrophobic bonding step. SEA are either mild or strong. A strong self-etch approach is more favorable for the bond to enamel. Mild etching systems give better bonding to the dentin, but demineralize enamel less effectively than traditional phosphoric acid (that needs to be rinsed of). The hybrid layer of the SEA is much thinner compared to the traditional etch-and-rinse systems. The immediate bonding effectiveness of many simplified systems has been quite favorable both in the laboratory and in short-time evaluations . Due to their high content of hydrolytical components and increased permeability of the hybrid layer, the bonds with SEA appear more vulnerable to degradation in the mouth . Among the self-etch adhesives, the two-step adhesive Clearfil SE Bond has been associated with favorable laboratory and short-time clinical results . Clinical evaluations investigating the long-time effectiveness of self-etch systems are sparse . Studies have shown that filled adhesives could act as stress buffers, relieving polymerization stresses that occur at the interface between tooth substance and resin composite, thus improving interfacial adaptation.

The aim of this study was to investigate the clinical dentin bonding effectiveness of a mild two-step self-etching system and a heavily filled two-step etch-and-rinse adhesive including a natural resin. The hypothesis tested was that there was no difference in clinical long-term retention to dentin between the self-etching system and the etch-and-rinse adhesive.

2

Materials and methods

A total of 119 class V restorations were placed in 72 patients (30 men and 42 women) with a mean age of 60.1 years (range 42–84), for whom treatment of non-carious cervical lesions was indicated. One experienced operator, familiar with adhesive dentistry placed the restorations in dentin lesions without any intentional involvement of the enamel incisal of the lesion. This in order not to enlarge the retention area. Seventy restorations were placed in premolars, nine in molars and 40 in incisors/cuspidates. Sixty-five lesions were placed in the maxilla and the others in the mandibula.

Pre-operatively, the lesions were categorized by the operator compared to lesion models in terms of depth (shallow, moderate, deep) and size (small, moderate, deep) of the lesion, the area of the dentin surface estimated as sclerotic tissue (none, <50%, >50%), and after randomization of the lesions these were roughened or not by diamond bur before application of the adhesive system ( Table 1 ) . The lesions were filled in randomly order by two adhesive systems. The two-step etch-and-rinse adhesive PQ1, which is heavily filled with fluoride-releasing radiopaque filler (40%) (Ultradent, USA) was applied with the hybrid resin composite Tetric Ceram (Ivoclar/Vivadent, Schaan, Liechtenstein). The mild two-step SEA (Clearfil SE Bond, Kurary, Tokyo, Japan; Lot 51137) was used in combination with the nano-filled hybrid resin composite Point 4 (Kerr Corp., Orange, USA). The operative field was isolated with cotton rolls and a saliva suction device. Before conditioning, the lesions were cleaned pre-operatively from plaque and/or saliva if necessary. The adjacent gingiva was retracted by gingival retraction instruments when necessary to secure unrestricted contamination free access to the field . No enamel bevel was placed nor other ways were used to get extra mechanical retention. The materials were applicated on the dentin lesions according to the manufacturers instructions ( Table 2 ). The lesions were mostly filled with an oblique incremental layering technique there the first oblique layer was placed in the incisal/occlusal part of the lesion. Each layer was cured for 20–40 s using a well controlled light-curing device (Astralis 7, Vivadent, Schaan, Liechtenstein, Demetron light meter, Kerr, Orange, CA, USA). After polymerization, the restorations were finished with fine diamond burs (DZ, Berlin, Germany) and polishing stones under water spray (Shofu Dental Co., Ratingen, Germany).

Participant information about the follow-up evaluations were performed according to the rules in the Biomaterial group Umeå at the Dental School. Concomitant treatment was given to the patients in conformity with normal clinical routines at the Dental School. The study was approved by the local ethical committee of the University of Umeå, Sweden.

2

Materials and methods

A total of 119 class V restorations were placed in 72 patients (30 men and 42 women) with a mean age of 60.1 years (range 42–84), for whom treatment of non-carious cervical lesions was indicated. One experienced operator, familiar with adhesive dentistry placed the restorations in dentin lesions without any intentional involvement of the enamel incisal of the lesion. This in order not to enlarge the retention area. Seventy restorations were placed in premolars, nine in molars and 40 in incisors/cuspidates. Sixty-five lesions were placed in the maxilla and the others in the mandibula.

Pre-operatively, the lesions were categorized by the operator compared to lesion models in terms of depth (shallow, moderate, deep) and size (small, moderate, deep) of the lesion, the area of the dentin surface estimated as sclerotic tissue (none, <50%, >50%), and after randomization of the lesions these were roughened or not by diamond bur before application of the adhesive system ( Table 1 ) . The lesions were filled in randomly order by two adhesive systems. The two-step etch-and-rinse adhesive PQ1, which is heavily filled with fluoride-releasing radiopaque filler (40%) (Ultradent, USA) was applied with the hybrid resin composite Tetric Ceram (Ivoclar/Vivadent, Schaan, Liechtenstein). The mild two-step SEA (Clearfil SE Bond, Kurary, Tokyo, Japan; Lot 51137) was used in combination with the nano-filled hybrid resin composite Point 4 (Kerr Corp., Orange, USA). The operative field was isolated with cotton rolls and a saliva suction device. Before conditioning, the lesions were cleaned pre-operatively from plaque and/or saliva if necessary. The adjacent gingiva was retracted by gingival retraction instruments when necessary to secure unrestricted contamination free access to the field . No enamel bevel was placed nor other ways were used to get extra mechanical retention. The materials were applicated on the dentin lesions according to the manufacturers instructions ( Table 2 ). The lesions were mostly filled with an oblique incremental layering technique there the first oblique layer was placed in the incisal/occlusal part of the lesion. Each layer was cured for 20–40 s using a well controlled light-curing device (Astralis 7, Vivadent, Schaan, Liechtenstein, Demetron light meter, Kerr, Orange, CA, USA). After polymerization, the restorations were finished with fine diamond burs (DZ, Berlin, Germany) and polishing stones under water spray (Shofu Dental Co., Ratingen, Germany).

Table 1

The relative frequencies of Class V non-carious lesions investigated, degree of sclerotic dentin, depth and size of lesions and number of roughened lesions before conditioning.

Class V lesion	Clearfil SE	PQ 1
No.	55	64
Non-sclerotic lesions	22.0	15.7
<50% sclerotic tissue	14.6	25.5
>50% sclerotic tissue	63.4	58.8
Shallow	61.0	58.8
Moderate depth	12.2	13.7
Deep	26.8	27.5
Small sized	24.3	31.4
Moderate	36.6	27.5
Large	39.0	41.2
Roughened lesions	63.4	51.0

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