1

Introduction

Although the longevity of direct composite restorations was considered as too short (3–5 years) in the previous decade , recently published randomized controlled clinical trials show a favorable clinical performance of these restorations after long-term clinical functioning . An important factor contributing to increased longevity is improved bonding efficiency of the contemporary adhesives. Adhesives used in combination with a direct composite material can be divided into 3-step and 2-step etch-and-rinse adhesives (3E&Ra, 2E&Ra), and 2-step and 1-step self-etch adhesives (2SEa, 1SEa) . The group of self-etch adhesives can be further subdivided depending on the pH of the self-etching primer. Mild/intermediate SEa (SEa_m/i) contain a self-etching primer with pH ≥ 1.5, by which the hybrid layer is not completely demineralized. In addition, they contain a functional monomer that can chemically bond to the hydroxyapatite (Hap) left in the hybrid layer. Strong SEa (SEa_s) have a self-etching primer with pH < 1.5. These adhesives do not have a chemical bonding potential .

The best lesions to test the clinical effectiveness of adhesives are non-carious cervical lesions (NCCLs). In these lesions the restoration will be bonded to both enamel and dentin. The largest part of the tooth surface to bond to consists of dentin, while at the incisal side the restoration margin ends in enamel. In addition, these restorations do not provide any or only minimal macroretention to test adhesive bonding effectiveness . A recently published systematic literature review of NCCL clinical trials evaluating the clinical effectiveness of contemporary adhesives reports that the lowest annual failure rate (AFR, expressed as loss of retention in function of time) for adhesives combined with a restorative material was recorded in the 2SEa_m/i (2.5 ± 1.5) subcategory . The most frequently tested (12 times) adhesive in this subcategory, Clearfil SE Bond (Kuraray Noritake, Tokyo, Japan), showed the lowest AFR (2.2 ± 1.2). Its high quality bonding performance in vivo can be explained by the presence of the functional monomer 10-MDP, which creates a very stable chemical bond with the Hap left in the hybrid layer . In addition, it forms a regular nano-layered structure at the Hap surface . The strong hydrophobicity of the nano-layered structure helps to protect the hybrid layer against hydrolytic bond degradation processes . This results in the well-documented favorable in-vitro durability of dentin bonds produced by 10-MDP based adhesives .

The NCCL clinical trials evaluating Clearfil SE Bond in the systematic review of Peumans et al. only included 2 long-term clinical trials (evaluation period longer than 5 years): (1) an 8-year evaluation of van Dijken , (2) another 8-year clinical trial was carried out by our research group recording a 97% retention and success rate. Given that adhesive systems show such a high success rate after 8 years, a longer-term evaluation is interesting to gather more precise information regarding bond longevity in these NCCLs.

Therefore, the aim of this clinical trial was to evaluate the 13-year clinical performance of the mild 2SEa, Clearfil SE Bond in NCCLs. As with the 8-year recall, the influence of prior selective enamel etching of cavity margins on the restorations’ clinical performance was assessed.

2

Materials and methods

The clinical effectiveness of Clearfil SE (Kuraray Noritake), was evaluated when applied strictly following a self-etch approach on both enamel and dentin (according to manufacturer’s instructions; abbreviated as ‘CSE-NE’) and compared to the application of the same adhesive following the same application protocol, but after the enamel cavity margins were selectively acid-etched with 40% phosphoric acid (abbreviated as ‘CSE-E’). Clearfil AP-X (Kuraray Noritake) was used as restorative composite ( Table 1 ).

Twenty-nine non-hospitalized patients were enrolled in the study (mean age at baseline: 58 years, 11 male and 18 female patients). They were recruited from the University Hospital Leuven, and were in need of cervical restorations. Patients with compromised medical history, severe or chronic periodontitis, extreme caries sensitivity and heavy bruxism were excluded from the study. Prior to participating in the study all patients signed a written consent. The clinical trial protocol was approved by the Commission for Medical Ethics of the Catholic University of Leuven. Essentially, the teeth were randomly assigned for restoration either following the CSE-NE or CSE-E application procedure using randomization tables. 50 restorations per group were placed in cervical non-carious erosion/abrasion/abfraction lesions of incisives, canines and premolars. Only maximum two restorations per group were placed in one patient so that per patient restorations prepared following the two different protocols were mutually compared.

The restorations were placed from September 2000 to January 2001 by two specially instructed and experienced dentists from the university dental school. All restorative procedures were done under rubberdam isolation. Regarding tooth preparation, the dentin walls of the lesions were superficially roughened with a coarse diamond and a short enamel bevel (1–2 mm) was made. The restorative procedure is described in detail in the 2-year report .

After 13 years, the clinical performance of the restorations was recorded in terms of (1) restoration retention, (2) enamel and dentin marginal integrity, (3) marginal discoloration, (4) caries occurrence, (5) post-operative sensitivity and (6) preservation of tooth vitality following a modified USPHS index system . The first four parameters were considered the key parameters for overall clinical success. Retention loss, severe marginal defects and/or discoloration that needed intervention (repair or replacement) and occurrence of caries along the restoration margins were considered as clinical failures.

Marginal integrity was evaluated using a sharp probe and mirror. Post-operative sensitivity was measured by blowing a stream of compressed air at a distance of 2–3 cm from the cervical restoration for 3 s while shielding the adjacent teeth with fingers and by moving the probe over the restored tooth surface. A persistent reaction after air-blowing or probing the restored tooth surface was recorded as post-operative sensitivity. Clinical photographs were taken at this recall. Statistical analysis compared the ratings of retention, marginal integrity, marginal discoloration and overall clinical success on a pair-wise basis between the experimental and the control group using the McNemar test ( p < 0.05).

2

Materials and methods

The clinical effectiveness of Clearfil SE (Kuraray Noritake), was evaluated when applied strictly following a self-etch approach on both enamel and dentin (according to manufacturer’s instructions; abbreviated as ‘CSE-NE’) and compared to the application of the same adhesive following the same application protocol, but after the enamel cavity margins were selectively acid-etched with 40% phosphoric acid (abbreviated as ‘CSE-E’). Clearfil AP-X (Kuraray Noritake) was used as restorative composite ( Table 1 ).

Twenty-nine non-hospitalized patients were enrolled in the study (mean age at baseline: 58 years, 11 male and 18 female patients). They were recruited from the University Hospital Leuven, and were in need of cervical restorations. Patients with compromised medical history, severe or chronic periodontitis, extreme caries sensitivity and heavy bruxism were excluded from the study. Prior to participating in the study all patients signed a written consent. The clinical trial protocol was approved by the Commission for Medical Ethics of the Catholic University of Leuven. Essentially, the teeth were randomly assigned for restoration either following the CSE-NE or CSE-E application procedure using randomization tables. 50 restorations per group were placed in cervical non-carious erosion/abrasion/abfraction lesions of incisives, canines and premolars. Only maximum two restorations per group were placed in one patient so that per patient restorations prepared following the two different protocols were mutually compared.

The restorations were placed from September 2000 to January 2001 by two specially instructed and experienced dentists from the university dental school. All restorative procedures were done under rubberdam isolation. Regarding tooth preparation, the dentin walls of the lesions were superficially roughened with a coarse diamond and a short enamel bevel (1–2 mm) was made. The restorative procedure is described in detail in the 2-year report .

After 13 years, the clinical performance of the restorations was recorded in terms of (1) restoration retention, (2) enamel and dentin marginal integrity, (3) marginal discoloration, (4) caries occurrence, (5) post-operative sensitivity and (6) preservation of tooth vitality following a modified USPHS index system . The first four parameters were considered the key parameters for overall clinical success. Retention loss, severe marginal defects and/or discoloration that needed intervention (repair or replacement) and occurrence of caries along the restoration margins were considered as clinical failures.

Marginal integrity was evaluated using a sharp probe and mirror. Post-operative sensitivity was measured by blowing a stream of compressed air at a distance of 2–3 cm from the cervical restoration for 3 s while shielding the adjacent teeth with fingers and by moving the probe over the restored tooth surface. A persistent reaction after air-blowing or probing the restored tooth surface was recorded as post-operative sensitivity. Clinical photographs were taken at this recall. Statistical analysis compared the ratings of retention, marginal integrity, marginal discoloration and overall clinical success on a pair-wise basis between the experimental and the control group using the McNemar test ( p < 0.05).

3

Results

The 1, 5, 8 and 13-year clinical data for the various parameters evaluated are summarized in Table 2 .

Table 2

Evaluation results in percentage at 1, 5, 8 and 13 years.

	1 Year		5 Years		8 Years		13 Years
	CSE-E	CSE-NE	CSE-E	CSE-NE	CSE-E	CSE-NE	CSE-E	CSE-NE
Recall rate (restoration)	96	96	84	84	76	76	62	62
Retention rate	100	100	100	98	97	97	96	96
Absence of marginal defects	70	72	52	17	16	8	16	4
Enamel marginal defect	9	13	34	64	65	86	72	86
Small enamel marginal defect	9	13	34	64	65	86	68	86
Severe enamel marginal defect	0	0	0	0	0	0	4	0
Dentin marginal defect	22	15	29	41	54	62	77	65
Small dentin marginal defect	22	15	29	41	54	62	77	54
Severe dentin marginal defect	0	0	0	0	0	0	0	11
Absence of marginal discoloration	96	100	83	68	72	56	47	41
Superficial localized marginal discoloration	4	0	17	32	28	44	53	55
Deep generalized restoration discoloration	0	0	0	0	0	0	0	4
Absence of post-operative sensitivity	98	98	100	100	100	100	100	100
Absence of caries occurrence	100	100	100	100	100	100	100	96
Overall clinical success rate	100	100	100	100	97	97	93	86

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