Various changes have been made in the chemistry and formulation of primers and adhesives. Conventionally, priming and bonding (after etching) required the application of two different solutions in two separate steps—hence the two-bottle adhesive. Recent developments have combined primer and bonding agent into a single solution, resulting in the one-bottle adhesive. Using the one-bottle adhesive obviously should improve efficiency and simplicity by eliminating one step, but this advantage should not be offset by any reduction in clinical performance and durability.

We conducted an investigation to evaluate and compare the 36-month clinical performance of two-bottle and one-bottle adhesives with Class V resin-based composite restorations on NCCLs. In addition, we compared water-based, ethanol-based and solvent-free adhesives. We evaluated the restorations in terms of retention, marginal integrity, marginal discoloration and sensitivity. We also analyzed pretreatment lesion properties, tooth features and patient demographics to discover any predisposition to retention failure.

	BACKGROUND: CERVICAL LESIONS

TOP ABSTRACT BACKGROUND: CERVICAL LESIONS METHODS, SUBJECTS AND MATERIALS DATA COLLECTION AND ANALYSIS RESULTS DISCUSSION CONCLUSION REFERENCES

 
The prevalence of cervical lesions has been reported to be from 5 to 85 percent.^1,2,4–9 They often occur at the cementoenamel junction, an area of structural weakness where the enamel layer is at its thinnest,¹⁰ and occur more frequently in dentin and cementum than in enamel, challenging the restorative material’s ability to bond to it adequately. Bonding to cementum and dentin is less predictable than bonding to enamel.^11,12 Erosion, abrasion and abfraction (stress flexure) are believed to be causative in the formation of NCCLs in this vulnerable area of enamel.^13,14 It has been postulated that the cervical area of a tooth is subject to unique stress, torque and moments resulting from occlusal function.^14–17 It is likely that the etiology is multi-factorial in nature, perhaps interacting in a synergistic manner.^3,5,6,10,13 In addition, there are patient-derived factors such as parafunctional habits, diet and poor home oral care that are especially detrimental to Class V restorations.^{13–15,17–19} In lieu of effective preventive treatments, the focus has been on improving the outcomes of restorative procedures. Thus, modified preparations, improved adhesives and specialized materials have been suggested as a means to improve the clinical success of cervical restorations.^14,17

The ability to better estimate success and longevity of restorations will be a factor in treatment decision making so that care in this aspect of dentistry can become more evidence-based.

The adhesive layer is the weak link in composite restoration retention²⁰—hence the constant effort to modify and improve on it.²¹ The early approaches to adhesive restorations involved etching with acids and bonding agents in various forms; however, early bonding agents proved to be weak and unreliable.²² This eventually led to the evolution of modern bonding agents, which contain three major components: etchant, primer and adhesive.^21,23 In the 1980s, the so-called "fourth-generation" bonding agents (or two-bottle adhesives) were used widely with great success, and they definitely were an improvement on the previous generation of bonding agents.²⁴ The primer’s function is to prepare the tooth surface, much like a surfactant, for coating and infiltration by the adhesive, which then provides retention for the resin-based composite restoration. Thus, changing the type of primer solvent could affect the overall quality of the bonding agent. The next innovation was the fifth-generation bonding agents (or one-bottle adhesives), approximately 10 years later, which combined the primer and adhesive into a single solution.^22,25

The true test of any adhesive is its clinical performance under function over time. The evolution of bonding agents already has progressed to the next generation—the sixth—which has eliminated even the etching step, combining etching, priming and adhesive into one solution.^22,25 On the basis of what little evidence there is, the sixth-generation bonding agents have a shallow etch²⁶ and worse microleakage in comparison with those of the fifth-generation bonding agents.²⁷ The viability and potential of the fifth- (and sixth-) generation bonding agents in laboratory evaluations can be confirmed or refuted by long-term clinical studies. Knowing the quality of various adhesives enables practitioners to choose the most appropriate adhesive for the clinical situation and desired result. The ability to better estimate success and longevity of restorations will be a factor in treatment decision making, or at least provide realistic expectations of outcomes, so that care in this aspect of dentistry can become more evidence-based.

	METHODS, SUBJECTS AND MATERIALS

TOP ABSTRACT BACKGROUND: CERVICAL LESIONS METHODS, SUBJECTS AND MATERIALS DATA COLLECTION AND ANALYSIS RESULTS DISCUSSION CONCLUSION REFERENCES

 
Design. We designed the study as a longitudinal, double-blinded, randomized clinical trial, with descriptive analysis of clinical evaluation criteria and failure characteristics. Patient screening and pretreatment selection of teeth with NCCLs, identified visually or tactilely, were performed by two clinical investigators (T.C.A., hereafter "Clinician A," and X.L., hereafter "Clinician B"). The same two investigators also placed restorations and performed posttreatment evaluation of restorations. The patient was unaware of which tooth was being treated with which adhesive.

With crossover evaluation, each investigator evaluated only the restorations that the other investigator had placed. The evaluators thus were blinded as to treatment rendered during recall evaluation, resulting in a double-blind situation. The investigators screened the patients initially to determine if they met the study entry criteria (described below). They enrolled the qualified patients in the study for the evaluation visit. Qualified patients were recruited in the order in which they reported for the screening session, thus forming a convenience sample.

Procedure. The investigators carried out the evaluations using a mouth mirror, an explorer and a periodontal probe. They used air from the air-water syringe to administer the thermal sensitivity test. The investigators selected patients who had a high incidence of NCCLs, specifically those who had at least three lesions, each on a separate vital tooth with opposing occlusion that required restorations. They deemed the lesions to require restoration if they were more than 1 millimeter in depth, had patient-reported thermal sensitivity or both. They screened all teeth in each subject; if more than three teeth qualified, they selected those with the largest or most sensitive lesions. With three adhesives per patient and one adhesive per tooth, the experimental groups were balanced, enabling a fair comparison.

The other inclusionary criteria were that subjects were older than 18 years of age and in good general health (American Society of Anesthesiologists²⁸ physical status classification P1 or P2). Patients were excluded if they had active, untreated periodontal disease or rampant, uncontrolled caries; had xerostomia; were undergoing orthodontic treatment; were undergoing bleaching treatment; or used supplemental fluoride.

The investigators selected 57 subjects, ranging in age from 29 to 75 years, with a mean age of 51 years. They recorded pretreatment lesion characteristics such as shape, size, sclerosis, sensitivity and occlusion, as well as tooth location and patient demographics, as described and analyzed in an earlier article.²⁹ These factors have been identified as possible covariables in NCCL formation, as well as in retention or lack thereof of Class V resin-based composite restorations.³⁰

The investigators used three types of restoration/adhesive combinations: Silux Plus (3M ESPE, St. Paul, Minn.) microfill resin-based composite with the Scotchbond Multipurpose (SM) (3M ESPE) water-based, two-bottle adhesive; Silux Plus microfill resin-based composite with the Single Bond (SB) (3M ESPE) ethanol-based, one-bottle adhesive; and Synergy Duoshade microhybrid resin-based composite (Coltène Whaledent, Cuyahoga Falls, Ohio) with One Coat Bond (OCB) (Coltène Whaledent) solvent-free, one-bottle adhesive. They used the same resin-based composite (Silux Plus) with SM and SB, whereas they used a different resin-based composite (Synergy) with OCB, to ensure compatibility between bonding agent and resin for a given manufacturer. The SM primer consists of water, hydroxyethyl methacrylate (HEMA) and polycarboxylic acid copolymer, and the SM adhesive contains bisphenol glycidyldimethacrylate (bis-GMA), HEMA and photoinitiators. The SB adhesive is composed of ethanol, bis-GMA, HEMA, dimethacrylate resins, polyalkenoic acid copolymer, water and photoinitiators. The OCB adhesive is made up of HEMA, hydroxypropyl methacrylate, methacrylated polyalkenoate, urethane dimethacrylate, silica and photoinitiators. The investigators placed three restorations in each subject, resulting in a total of 171 restorations. The choice of adhesive and lesion was randomized within the subject.

First, the clinician placed topical anesthetic gel on a cotton tip on the buccal gingiva to reduce patient discomfort. Procedures usually were performed without local anesthesia. The clinician cleaned the lesions with a light prophylaxis, using a slurry of nonfluoridated flour of pumice and water. He beveled the incisal or occlusal margin of enamel 0.5 to 1.0 mm at approximately a 45-degree angle to the external cavosurface, using a high-speed, water-cooled, rotary handpiece with a medium-grit diamond bur. The purposes of the bevels were to increase the enamel surface area for adhesion and to improve the esthetic outcome by creating a gradual transition from tooth to restoration at a highly visible part of the margin.³¹ Although there are clinical protocols whereby no cavity preparation is performed, there exists sufficient evidence that the presence of a bevel improves microleakage and retention^32–35 to the extent that it was felt omitting this step would be less than optimal treatment. To achieve a consistent bevel, the clinician used a Brasseler 8248S-012 (Brasseler, Savannah, Ga.) conical-tip diamond.

He then isolated the teeth with absorbent shields, cotton rolls and braided surgical silk (as retraction cord) soaked in a hemostatic agent (Nephrostat, Nephron, Tacoma, Wash.). The clinician then placed the adhesives and resin-based composites exactly according to the manufacturers’ directions (Box). He then trimmed and polished the restoration using hand instruments, carbide finishing burs, safety-tip fine diamonds, polishing disks (Sof-Flex, 3M ESPE), and rubber finishing points (Dialite, Brasseler). The procedures followed with each of the studied adhesives are detailed in the box.

View larger version (83K): [in this window] [in a new window]   Figure 1. Cervical lesion before restoration (in tooth no. 5) adjacent to a similar lesion after restoration (in tooth no. 4) with resin-based composite.

Marginal integrity. The clinicians measured marginal integrity by visual and tactile inspection of the margins of the restoration, to determine if there were any gaps in the tooth-restoration interface. They categorized their observations in an ordinal scale as "undetectable/slightly detectable," "detectable without penetration" and "detectable with penetration."

Marginal discoloration. The investigators evaluated marginal discoloration by visually inspecting the margins of the restoration to determine if there was any stain or discoloration and, if so, whether it was merely at the surface or had penetrated deep, between the tooth-restoration interface. They categorized their observations in an ordinal scale as "none," "superficial" and "deep."

Sensitivity. The investigators evaluated sensitivity by applying a blast of air from an air-water syringe at a distance of approximately 1 inch, with adjacent teeth under rubber dam isolation. The application of air was for a maximum of five seconds. They recorded the subjective patient response of level of sensitivity (discomfort) on a 10-point continuous visual-analog ratio scale, ranging from "no discomfort" (0) to "extreme discomfort" (10). On this scale, a score from 0 through 3 is categorized as no or mild sensitivity, from 4 through 6 as moderate sensitivity and from 7 through 10 as extreme sensitivity. We compared these responses with the preoperative responses to determine if sensitivity to air blast increased, decreased or remained the same.

Compared with baseline retention rates of 100 percent, the overall average retention rate was 86 percent after three years.

	DATA COLLECTION AND ANALYSIS

TOP ABSTRACT BACKGROUND: CERVICAL LESIONS METHODS, SUBJECTS AND MATERIALS DATA COLLECTION AND ANALYSIS RESULTS DISCUSSION CONCLUSION REFERENCES

 
We recorded the frequency distribution for each characteristic. We compared the retention rate after three years among the three adhesives using logistic regression, which we implemented using generalized estimating equations to account for the dependence between observations owing to multiple lesions per subject and the unequal number of observations per subject.³⁸ Given that only one restoration was recorded as a partial loss, we combined the "partial loss" and "total loss" categories for the logistic regression analyses.

We performed similar analyses using logistic regression to compare marginal integrity, marginal discoloration and sensitivity after three years among the three adhesives. Given that these outcomes are not observed after a restoration has failed, we did these comparisons using only observed outcomes at three years. For these comparisons, owing to the small number of restorations in some of the outcome categories, we dichotomized the outcomes as follows:

– discoloration: none versus superficial or deep;

– marginal integrity: none/slightly detectable versus detectable with or without penetration;

– sensitivity: none/mild versus moderate/extreme.

We performed an odds ratio analysis on the pretreatment characteristics of the subgroup of retentive failures after 36 months. Additional logistic regression analyses helped us assess whether any of the pretreatment lesion characteristics were predictive of retention after three years. We conducted all significance testing using two-sided generalized score tests from generalized estimating equation–derived logistic regression. Also, to describe the longitudinal trends, Figures 2 through 5 (Figures 4 and 5 are on page 317) graphically present frequencies for each outcome at baseline, six months, one year, two years and three years after initial restoration placement.

View larger version (50K): [in this window] [in a new window]   Figure 2. Restoration retention over time. SM: Scotchbond Multipurpose (3M ESPE, St. Paul, Minn.). SB: Single Bond (3M ESPE). OCB: One Coat Bond (Coltène Whaledent, Cuyahoga Falls, Ohio). ADA: Standard established by the ADA Council on Dental Materials, Instruments and Equipment37 for dentin and enamel adhesive materials.

View larger version (49K): [in this window] [in a new window]   Figure 3. Restorations’ marginal integrity over time. SM: Scotchbond Multipurpose (3M ESPE, St. Paul, Minn.). SB: Single Bond (3M ESPE). OCB: One Coat Bond (Coltène Whaledent, Cuyahoga Falls, Ohio).

View larger version (50K): [in this window] [in a new window]   Figure 4. Restorations’ marginal discoloration over time. SM: Scotchbond Multipurpose (3M ESPE, St. Paul, Minn.). SB: Single Bond (3M ESPE). OCB: One Coat Bond (Coltène Whaledent, Cuyahoga Falls, Ohio).

View larger version (55K): [in this window] [in a new window]   Figure 5. Restorations’ sensitivity over time. SM: Scotchbond Multipurpose (3M ESPE, St. Paul, Minn.). SB: Single Bond (3M ESPE). OCB: One Coat Bond (Coltène Whaledent, Cuyahoga Falls, Ohio).

	RESULTS

TOP ABSTRACT BACKGROUND: CERVICAL LESIONS METHODS, SUBJECTS AND MATERIALS DATA COLLECTION AND ANALYSIS RESULTS DISCUSSION CONCLUSION REFERENCES

Outcomes. Table 1 (page 318) shows the breakdown of the outcomes by type of adhesive.

Marginal integrity. Of the retained restorations, namely in 127 teeth and 50 patients, SB had the greatest marginal integrity (82 percent undetectable or slightly detectable), then OCB (60 percent undetectable or slightly detectable), followed closely by SM (59 percent undetectable or slightly detectable), but we did not find the differences to be statistically significant (P > .05). Most margins that were detectable had no penetration, with only a small proportion detectable with penetration. The baseline marginal measurements were 87 percent undetectable or slightly detectable; after treatment, the overall average was 66 percent with undetectable or slightly detectable margins after three years.

Marginal discoloration. SB had the least marginal discoloration (71 percent having no discoloration), compared with OCB (60 percent with no discoloration) and SM (50 percent with no discoloration), but the differences were not shown to be statistically significant (P > .05). Most margins that were discolored had superficial discoloration, with a small proportion having deep discoloration. The baseline marginal measurements were 94 percent with no discoloration; after treatment, the overall average was 60 percent with no marginal discoloration after three years.

Sensitivity. In terms of sensitivity, SM, OCB and SB were virtually the same, with 91 percent, 91 percent and 89 percent of the restorations, respectively, having no or mild sensitivity. The differences were not statistically significant (P > .05). Most restorations that were sensitive had moderate sensitivity, with a small proportion having extreme sensitivity. The pretreatment sensitivity measurements were 73 percent having no or mild sensitivity (Figure 5); the overall average after treatment was 91 percent with no or mild sensitivity after three years. The calculated power is 0.93, 0.74 and 0.41 to detect a 20 percent, 15 percent or 10 percent difference, respectively, in retention between groups at a .05 significance level.

Failure analysis. Table 2 (page 319) shows the pretreatment lesion characteristics of restorations not retained in this period. With the restorations that were partially or totally lost—in this case 20 of 146 (14 percent)—we evaluated the characteristics of the lesions, teeth and patients to see if there were any trends relating to retention. Lesion shape tended toward the larger angles (in 16 of 20 restorations), with no failures in the below–45-degree category. Seventeen of the 20 lesions had axial depth in the 1- to 2-mm range, with three more than 2 mm. Fifteen lesions had occlusogingival width in the 1- to 3-mm range, with smaller numbers more than 3 mm. Thirteen lesions had mild sclerosis, with none in the "heavy" category. Fifteen lesions had no or mild sensitivity. Thirteen teeth were in Class I occlusion, with 14 having group or mixed guidance. All 20 teeth had mobility of either type 0 or type I, with wear facets present in 18 teeth. Fourteen of the 20 were maxillary teeth, and 17 were posterior teeth, with slightly more premolars than molars. Fifteen of 20 restorations were found in patients who were 41 years of age or older, and 15 found in patients who were male. Clinician B’s restorations experienced slightly more failures (12 of 20) than did Clinician A’s (eight of 20). However, under odds ratio analysis, only obtuse angle, group function, lack of mobility, posterior molars and male sex were more prevalent than expected. Under logistic regression analysis, only the association with posterior teeth was statistically significant (P < .05).

Longitudinal trends. For all evaluation criteria, we measured baseline at one week postoperatively.

Retention. In general, retention failures seemed to occur early, then slowed and stabilized at three years. SM and OCB were retained at slightly higher rates (though not significantly higher) than SB at three years after restoration placement. SB retention failures occurred at a consistently higher rate than did SM and OCB failures during the entire recall period, almost in a linear fashion (Figure 2). These retention rates compare favorably with the ADA Acceptance program criteria.³⁷

Marginal integrity. In general, marginal integrity seemed to degrade appreciably within the first six months, then stabilize for 18 months, followed by a rather steep decline between 24 and 36 months. SB had slightly greater (but not significantly greater) marginal integrity than did SM and OCB at three years after restoration placement. SB’s marginal integrity stabilized at two years and remained steady up to three years, without the decline demonstrated by SM and OCB (Figure 3).

Marginal discoloration. In general, marginal discoloration seemed to occur at a fairly steady rate, almost in a linear fashion, over three years. SB had slightly less (but not significantly less) marginal discoloration than SM and OCB at three years after restoration placement. SB’s marginal discoloration occurred at a consistently slower rate than did that of SM and OCB during the entire recall period (Figure 4).

Postoperative sensitivity. In general, postoperative sensitivity seemed to be highest at six months, then improved and reached a plateau for the next 30 months. SM had slightly less (but not significantly less) sensitivity than SB and OCB after six months, and also at three years after restoration placement. After six months, rates of postoperative sensitivity of SM, SB and OCB restorations at every recall period were very close, if not identical (Figure 5). Substantial improvement has been achieved compared with preoperative sensitivity levels.

Summary. In summary, retention failures tended to occur early, marginal integrity declined intermittently over time, marginal discoloration increased steadily over time, and postoperative sensitivity increased slightly initially and then decreased quickly to a low level that remained steady over time, much better than preoperative sensitivity levels.

	DISCUSSION

TOP ABSTRACT BACKGROUND: CERVICAL LESIONS METHODS, SUBJECTS AND MATERIALS DATA COLLECTION AND ANALYSIS RESULTS DISCUSSION CONCLUSION REFERENCES

 
In attempting to restore lost tooth structure, the clinician aims to place dissimilar materials in close proximity and obtain the best adherence possible. This is achieved by overcoming the surface energy of both materials and minimizing the gap between them. Adhesive bonding agents have been developed expressly for this purpose, to create mechanical and chemical bonds between the tooth and the resin. However, the interface between tooth and restorative material remains an area of potential weakness.²⁰ The solvent-free adhesive can result in a thicker adhesive layer that may offer better thermal protection³⁹ and reduce shear stress⁴⁰ but, if too thick, may have a weaker bond.³⁹

Retention. Failure of retention can occur owing to cohesive failure or adhesive failure. Cohesive failure occurs because of a rupture within tooth structure or within restorative material. More typically, failure occurs at the weakest link, namely the tooth-resin interface (specifically at the adhesive layer).²⁰ Adhesion between tooth and composite is achieved primarily by the adhesive, and in this study, after three years, all three adhesives performed well in this regard. Most restorations were retained, with an overall average of 14 percent experiencing displacement and loss in that time. Other clinical trials of one-bottle adhesives have found comparable retention rates of 75 to 98 percent,^41,42 with one substantially worse at 51 percent,⁴³ after three years. Clinical performance and shear bond strength have been found to be no different between ethanol- or acetone-based one-bottle adhesives,⁴¹ indicating that the solvent may play less a role than does the actual chemistry of the adhesive.⁴⁴ The retention rates found in other clinical trials of two-bottle adhesives range from 40 to 95 percent after three years,^45–50 consistent with our finding that one- and two-bottle adhesives might be similar in terms of retention.

Marginal integrity. Failure of marginal adaptation occurs because of the loss of tooth structure, loss of restorative material or breakdown of adhesion at the interface, or a combination of all three. Marginal gaps can occur over time—especially at the marginal surface—primarily because of exposure to the oral environment, which leads to microleakage, wear and stress fatigue. It also can occur immediately during placement, owing to faulty technique, or during light curing, when resin shrinkage can occur. The adhesive plays a large role in resisting these forces. In our study, after three years, all three adhesives performed well in this regard. Several had detectable margins and a few had margins detectable with interfacial penetration, with an overall average of 21 percent of restorations undergoing marginal degradation in that time. Other clinical trials have found better rates of excellent marginal integrity of 90 to 100 percent, for both one- and two-bottle adhesives, after three years.^41,42,45,50

Marginal discoloration. Marginal staining occurs primarily because of the infiltration of colored molecules into the interface. Microleakage begins at the marginal surface, and as adherence breaks down, interfacial gaps grow larger, leading to macroleakage, interfacial staining and visible marginal discoloration. The adhesive plays a large role in resisting this process. In our study, after three years, all three adhesives performed adequately in this regard. There was notable superficial discoloration and some deep discoloration, with an overall average of 34 percent of restorations sustaining marginal discoloration in that time. Other clinical trials of one- and two-bottle adhesives have found better rates of no marginal discoloration of 88 to 90 percent after a three-year period.^41,45 In vitro microleakage studies have found SM and SB to be equivalent,⁵¹ with sealing good for enamel but not as good for dentin and cementum.^52,53 The simplified one-bottle adhesives appear comparable with the two-bottle adhesives in terms of microleakage.^54–56 Long-term marginal discoloration always has been a problem^57,58 and may remain a significant problem even for the newer adhesives such as SB and OCB.^52,59

Sensitivity. Postoperative sensitivity has been attributed variously to operative trauma, desiccation, leakage, air entrapment and other causes.^60–64 To avoid such sensitivity, occlusion of open dentinal tubules is paramount in the restorative procedure. The shielding of exposed enamel and dentin by the composite material itself should reduce the thermal and mechanical stimuli of the oral environment. However, since it is the adhesive that has direct contact with the tooth surface, the ability of this layer to coat and bond to the tooth plays a key role in reducing sensitivity. In our study, after three years, all three adhesives performed well in this regard. A small number had moderate sensitivity and few had extreme sensitivity, with an overall average of 18 percent of restorations attaining markedly alleviated sensitivity in that time. Dentin adhesives are known to be effective in reducing or alleviating NCCLs’ sensitivity.^60–62 Other clinical trials of one- and two-bottle adhesives have found similar rates of no or mild posttreatment sensitivity of 90 to 100 percent, with significant reduction over baseline rates.^41,42,45 Long-term reduction in sensitivity has never been an issue, even with third-generation adhesives,^63,64 and should remain successful, especially for the newer adhesives with simplified procedures.

Certain characteristics may predispose a restoration toward retentive failure, such as obtusely angled lesions with group function in posterior immobile teeth in male patients.

Failure analysis. From the subgroup of restorations with retentive failure, there appear to be some pretreatment lesion characteristics that stand out, such as obtuse angle, small axial depth, small vertical width, presence of sclerosis, lack of sensitivity, Class I occlusion, group function, wear facets, lack of mobility, posterior, maxillary teeth, older age and male sex. However, on closer analysis of the pretreatment group, we saw that many findings of the failure subgroup reflect only the overall group characteristics, which could be expected by chance alone.

– There were more failures within the obtusely angled (> 135 degrees) group of lesions than expected, with increased divergence of opposing occlusal and gingival walls resulting in a less retentive preparation.

– In terms of occlusion, there were more failures with group guidance, and more with no mobility, than expected. Restorations on teeth that are under occlusal stress or flexure are more likely to result in loss of retention, a tendency that has been well-documented.^15,16

– As far as tooth location, more of the affected teeth than we expected were posterior teeth, and more of them were molars than we expected. This could be explained by the fact that greater occlusal forces, and hence lateral forces, are exerted in the posterior teeth, especially in molar teeth. The association of retention to posterior location is the only one to be statistically significant.

– More failures occurred with men than expected, but it remains speculative that any sex-related behavioral effects are responsible.¹³

Not surprisingly, these characteristics by and large coincide with the findings of our earlier study²⁹ on the etiology of NCCL formation, leading to the postulate that the same factors associated with lesion formation are likely to cause retention failure as well.³⁰ However, there are differences in that greater retention failure occurs in molars (rather than premolars), in obtusely angled lesions (rather than right-angled lesions) and in men (rather than equivalence between the sexes). This dichotomy likely is caused by the differing impact of these factors and the fact that there are overlapping but not identical factors associated with lesion formation and with retention failure. In addition, since the sample size of retentive failures is rather small (20), the absence of a difference does not necessarily imply a lack of association, which is difficult to prove definitively. However, a difference might indicate that a true association does exist.

The results of this study appear to suggest no difference in clinical performance after three years between the two-bottle, fourth-generation adhesives and the one-bottle, fifth-generation adhesives, nor among the water-based, ethanol-based and solvent-free adhesives. However, there were differences that appeared to be clinically notable and that might have been shown to be statistically significant with a larger sample size. For instance, retention rates were slightly better for OCB than SM or SB, SB had better marginal integrity than SM or OCB, and SB had better marginal discoloration than OCB, which in turn was better than SM. Hence, we can assert only that even though statistical differences could not be demonstrated, there were trends to suggest that minor differences might exist for these evaluative criteria. The adhesives’ clinical performance certainly is an improvement on the third and earlier generations of adhesives.²² The retention rates were moderately high, and the rate of marginal integrity was predominantly clinically acceptable, with a definite, enduring reduction in thermal sensitivity during three years of clinical service. However, there was a steady increase in marginal discoloration during that period that was likely to continue over time.

Preliminary results seem to suggest that certain characteristics may predispose a restoration toward retentive failure, such as obtusely angled lesions with group function in posterior immobile teeth (especially molars) in male patients. To maximize clinical success, the clinician might consider more retentive preparations, occlusal adjustments, resin-based composites with low elastic moduli, and encouraging the patient to modify diet and dental hygiene behavior.^13,14,17,19 Interesting trends for these NCCL restorations are detectable after comparison of evaluation criteria over the short term⁶⁵ and the medium term. Any differences between the various adhesives may become even more apparent after extended clinical function. Long-term data are necessary to determine if the observed trends get worse, better or remain the same, perhaps at five years from baseline. This type of information enables judicious case selection and appropriate modification of treatment protocols,^14,17 where necessary, for long-term clinical success.

	CONCLUSION

TOP ABSTRACT BACKGROUND: CERVICAL LESIONS METHODS, SUBJECTS AND MATERIALS DATA COLLECTION AND ANALYSIS RESULTS DISCUSSION CONCLUSION REFERENCES

 
Within the limitations of this investigation, we found that the three adhesives—SM, SB and OCB—had minor differences in terms of retention, marginal integrity, marginal discoloration and sensitivity over the three-year evaluation period. No statistically significant differences were demonstrated between one- or two-bottle systems, nor among water-based, ethanol-based and solvent-free adhesives, although the statistical power of the study might be modest. The overall retention rate was moderately high, with a distinct, sustained reduction in air sensitivity. NCCL restorations in posterior teeth may have a greater tendency for retention failure. Marginal quality remained acceptable in terms of marginal integrity, degrading at a low level, whereas there was a noteworthy steady increase in marginal staining after three years. Restorations that have poor marginal integrity tend to have increased marginal discoloration as well. The small differences in outcomes between the various adhesives after three years means that under the conditions of this in vivo clinical trial, the newer adhesive systems could provide an acceptable level of medium-term clinical service.