Byline: Andre. de Souza, Regina Claudia. Colares, Juliano. Mendonca, Lidiany Karla. Rodrigues, Sergio. Santiago

Context: Non-carious cervical lesions are usually associated with dentin hypersensitivity. The use of oxalic acid in restorations of these lesions could be beneficial in relieving pain. Aims: To evaluate the use of oxalic acid in restorations of non-carious cervical lesions. Settings and Design: A randomized clinical trial. Subjects and Methods: One operator placed 90 restorations in 20 volunteers of both sexes, with at least two lesions to be restored with the techniques: Control - Restoration with total-etch technique and Experimental - Restoration with pretreatment with oxalic acid followed by application of adhesive system. The restorative adhesive system used was XP Bond/Durafill. The restorations were directly assessed by two independent examiners using a modified United States Public Health Service (USPHS) method at baseline, 6 and 12 months, taking into account the following criteria: Retention (R), marginal integrity (MI), marginal discoloration (MD), postoperative sensitivity (S), caries (C), and anatomic form (AF). Statistical analysis used: The data were statistically analyzed using the Fisher exact and McNemar tests. The level of significance was set at 5%. Results: After 1 year, the results of restorations clinically satisfactory obtained for the control and experimental group respectively were: R (97% / 89%), MI (100% / 100%), MD (100% / 100%), S (100% / 100%), C (100% / 100%), and AF (100% / 100%). Conclusions: The use of oxalic acid as an agent of dentin pretreatment did not influence the clinical performance of restorations in non-carious cervical lesions after 1 year.

INTRODUCTION

The loss of hard tissue in the cervical area of teeth is currently a common clinical condition. [sup][1],[2] About a quarter of the population has these lesions and are significantly more prevalent at older ages, and may affect any tooth, but there was higher occurrence in canine and premolars. [sup][3]

The noncarious cervical lesions are usually associated with dentin hypersensitivity. Oxalate-based desensitizing agents act by obliterating the dentinal tubules, with a precipitation of calcium oxalate crystals on the surface and inside the dentinal tubules, and also by depolarizing the nerve endings. [sup][4] This mechanism explains why these agents usually act in the reduction of short- and long-term evaluation. [sup][5],[6] The obliteration is effective in reducing dentin sensitivity, but the obliteration effects are limited, because the surface crystals can be dissolved or removed by daily brushing.

The restoration of noncarious cervical lesions is indicated when there is presence of intolerable hypersensitivity; depth next to the pulp; weakening of tooth structure, loss of contour that affects hygiene and periodontal health; and esthetics. [sup][7] Composite resins and glass ionomer materials are the most suitable materials for noncarious cervical lesions. [sup][8] However, adhesive resin monomers that are in frequent contact with the dentinal fluid may experience a process of hydrolytic degradation. [sup][9] The association of adhesive restorations and oxalate-based agents could minimize contact of adhesives with the dentinal fluid, thereby reducing bonding degradation and improving the clinical success rate of restorations.

The application of potassium oxalate salts on dentin surface after acid etching shows similar immediate bond strength to dentin when compared to a no pretreatment with desensitizing agents, not interfering in the process of bond strength. [sup][10] However, it was observed a reduction in the bond strength to the teeth that received oxalic acid after aging. [sup][11]

Taking into consideration the lack of studies that assess the clinical performance of restorative procedures associated with oxalate-based desensitizing agents, the aim of this randomized, double-blind clinical trial was to evaluate the clinical success of restorations in non-carious cervical lesions with or without the application of oxalic acid. The null hypothesis tested was that both techniques have similar effectiveness after one year of clinical service.

SUBJECTS AND METHODS

Selection of patient and teeth

Twenty volunteers of both sexes (16 female, 4 male), aged between 24-55-years-old, were properly informed regarding the study and, in agreement, signed a term of acceptance. The present research was reviewed and approved by local Research Ethics Committee under the protocol n[degrees] 224/08. The criteria for inclusion in this study were: Appropriate oral hygiene, low decay index, absence of periodontal disease, bruxism, and traumatic occlusion, no wear facets, presence of at least two non-carious cervical lesions with a deep equal or greater than 1 mm, independently of their location in the dental arcade to be restored.

Anamnesis, photographs and radiographic examination were performed initially. The clinical evaluation was performed using a mouth mirror, an explorer and a periodontal probe.

The degree of hypersensitivity was determined according to the Verbal Rating Scale - VRS from 0-3, in which: 0 = no discomfort, 1 = minimum discomfort, 2 = mild discomfort, and 3 = intense discomfort. Each tooth received air blast stimuli with an air syringe for one second at the distance of 1 cm of the tooth surface and the presence of sensitivity was used to enrol in the study.

Restorative procedures

A total of 90 restorations were performed by one operator, and in 45 of these were done prior treatment with oxalic acid (Bisblok- BISCOInc. Schaumburg, IL, USA) after etching. The others were used as control following the total etch technique. The restorative technique and the materials used are described in [Table 1]. The treatment used for each tooth was set randomly using a table created in the system excel (Microsoft, Richmond, CA, USA). {Table 1}

The restorations were placed under cotton roll isolation and with gingival barriers (Top Dam, FGM Produtos Odontologicos, Joinville, SC, Brazil). The lesions were pumiced prior to all restorative procedures. Enamel margins were not beveled and no mechanical retention was performed. All restorations were light cure for at least 40 seconds with minimum light intensity of 500 mW/cm [sup]2 (VIP Junior, Bisco Inc., Schaumburg, IL, USA) calibrated with a curing radiometer. The immediate finishing with the removal of eventual excesses with a scalp blade n[degrees]12, while the mediate finishing and polishing were performed after one week, starting with 12-fluted tungsten carbide burs (Jet Burs, Sao Paulo, SP, Brazil), the Enhance polishing system (Dentsply, Petropolis, RJ, Brazil) and Diamond; Diamond Flex; Diamond Excel (FGM Produtos Odontologicos, Joinville, SC, Brazil).

Clinical evaluation

The restorations were evaluated at baseline, 6 months and 1 year post-insertion for retention, marginal adaptation, margin discoloration, caries, post-operative sensitivity and anatomic form using a modified United States Public Health Service (USPHS) criteria for clinical evaluation of dental restorative materials [Table 2].{Table 2}

Two experienced examiners, blind with regard to the applied techniques, performed the evaluation using a mirror and a double-ended probe after tooth prophylaxis with water and pumice in a low-speed hand piece. Each examiner independently evaluated the restoration once, when disagreement occurred, a consensus had to be made between the evaluators before the patient was dismissed in order to obtain only one score for each restored tooth. The intra-examiner Cohen?s Kappa statistics was 0.87.

The retention rates of restorations were calculated according to the American Dental Association (ADA) Guidelines [sup][12] as follows: Cumulative failure % = [(PF + NF)/(PF + RR)] x 100%, where PF is the number of previous failures before the current recall; NF the number of new failures during the current recall; and RR the number of restorations recalled for the actual recall.

The intra-group comparisons between baseline and other evaluation periods within the same material were performed using the McNemar test. The inter-group comparisons performed to identify differences between restorative materials at each period were conducted using the Fisher exact tests. Statistical procedures were performed using the Statistical Package for Social Sciences (SPSS 17.0) for Windows. The significance level for all statistical evaluations was set at 5%.

Results

Twenty research subjects were selected and 90 restorations were placed, 45 for each group, but three of these subjects could not complete the study: One move out and two for health reasons.

At 6 months we had a loss of two restorations for each group, and the recall of 1 year, a loss of one restoration to the control group and four for the experimental group, totalizing a cumulative loss in 12 months of 8% for the control group and 18% for the experimental group.

[Table 3] summarizes the clinical performance findings as frequency of Alfa, Bravo and, Charlie scores. No restorations exhibited postoperative sensitivity and caries at 12 months. There was no statistically significant difference between baseline and 1 year for all evaluated criteria.{Table 3}

Discussion

This study aimed to clinically evaluate the effect of the use of oxalic acid with a total-etch adhesive system on clinical success of restorations in non-carious cervical lesions. As well as important clinical trials that use similar methodologies, [sup][13],[14] this clinical study was a randomized, double-blind aiming for reliable results.

Many clinical studies that promote restorations in non-carious cervical lesions are conducted with the use of rubber dam; [sup][10],[14],[15] others have promoted that the use of cotton rolls does not diminish the performance of Class V restorations. [sup][16] This study used cotton rolls and gingival barriers by an operator preference and a greater flexibility of clinical procedures.

All restorations we replaced with microfilled composites aiming a better performance due to the low elastic modulus of these materials in comparison with hybrid composites, but in fact, the literature has not reached a consensus on whether or not low modulus materials can improve the clinical performance of Class V restorations. Clinical trials of 2-3 years of follow-up showed no difference in retention between retention rates of micro filled/hybrids and flow-able composites. [sup][15] However, Bayne et al ., [sup][17] have demonstrated that the elasticity modulus is an important property in the retention of restorations placed in non-carious cervical lesions. When a more rigid composite material such as a hybrid is used, the shear stress at the adhesive interface could exceed the compressive stress, thus acting primarily on the bond. The introduction of low modulus resin based materials has been promoted as possibly beneficial for restoring non-carious cervical lesions. In addition, it is suggested that the clinical retention of an adhesive restoration depends not only on the retention capacity of the adhesive system used but also on the viscoelastic properties of the restorative material tested. It has been claimed that flexural deformation of a tooth in the cervical region is at least partly absorbed by restorative material. The materials with a low modulus of elasticity when used in cervical restorations tend to bend more like a tooth structure when subjected to a masticatory load and may flex and be retained. [sup][17] The combination of these factors may have been responsible for the choice of microfilled composite in the present study.

Studies have shown that simplified total etching adhesives are considered full-permeable membranes that allow flow of liquids that comes both the external environment as dentinal tubules. This permeability is primarily responsible for the hydrolytic degradation of hybrid layer. [sup][18] Additionally, XP Bond is a one-bottle etch-and-rinse adhesive, composed of a pre-mixed solution of monomers dissolved in t-butanol. Due to an improved ability to diffuse through partially collapsed demineralized dentin, it is claimed to be less technique sensitive. [sup][19] However, in vitro results do not reflect the clinical behavior of the material and clinical studies showed controversial results when XP Bond is used as adhesive system in non-carious cervical lesions. [sup][20],[21] This way, more clinical evaluations with this adhesive system must be encouraged in order to prove its efficiency.

Aiming to reduce the effects caused by the permeability of the adhesives, some authors have suggested that the occlusion of dentinal tubules to block the flow of fluids responsible for adhesive failures. [sup][10],[22],[23] Among the substances for this purpose, the potassium oxalate is one of the most indicated, with excellent results in the reduction of hydraulic conductance in vitro . [sup][10],[22] The potassium oxalate reacts with ionized calcium in dentinal fluid, forming crystals of calcium oxalate that obliterate the tubules, reducing the permeability of dentin, [sup][22] and can be used before applying the adhesive. [sup][10],[11],[22],[23] However, some studies show that in vitro results, unhappily, do not reflect the clinical behavior of the material or technical, turning the clinical evaluations as fundamental method to prove the efficiency. [sup][11],[24],[25],[26],[27] Although there are clinical studies using Bis-block as desensitizing agents, [sup][28] we do not find clinical trials of these substances under restorations in non-carious cervical lesions, making this study relevant to complement and confront some laboratorial findings.

Analyzing marginal integrity, marginal discoloration, postoperative sensitivity, caries and anatomic form we had 100% of success (Alfa or Bravo scores) at one year, in agreement with other same clinical trials, [sup][8],[14] but in relation of anatomic form, although the results were clinically acceptable, we had an almost significant ( P = 0.058) values bravo to the experimental group, which allows us to suppose that in longer periods of evaluation, this difference may represent significant results.

In the recall of 6 months, we reevaluated 17 patients resulting in 80 of the 90 teeth examined in the baseline period. We observed a loss of four restorations, with two of the control group and two in the experimental group, that is less than 5% according to the standards of the ADA. [sup][12]

In recall of one year, we had accumulative loss of 8% for the control group and 18% for the experimental group. The high degree of sclerosis, absence of cervical enamel and exceed of compressive stress are factors that can increase the number of adhesive failures in restorations of non-carious cervical lesions. [sup][13],[18] Although no statistical difference, the greater degree of loss of retention of the restorations that had Bisblock as pretreatment could be explained by the decrease in permeability caused by desensitizing, which in this case, might compromise the dentin bond, since it is a complex region due to the factors mentioned above. According to the study by Silva et al ., [sup][11] that used the method of microtensile in the laboratory showed that after one year there was a reduction in this bond strength to the teeth that received potassium oxalate after acid etching.

In respect to marginal integrity, the large number of restorations of resin composite exhibiting a decline in rating (Alfa to Bravo) is probably due to no margins beveled and/or to the small fracture of the cavo-surface margin and material due to stress from polymerization shrinkage. Despite the improved bond strength of the materials, increased tooth flexure may still contribute to localized defects in marginal integrity for both materials. [sup][8]

In this study, there were no statistically significant differences between treatments; however, both were significantly important in reducing dentin hypersensitivity. Based on this, we can report that the use of oxalic acid in restorations of non-carious cervical lesions may represent an additional clinical step. However, further clinical studies should be performed with different degree of tooth sensitivity, as well as longer terms of recalls to a greater understanding of the results.

Conclusion

Within the limits of the current study, it may be concluded that the use of oxalic acid as an agent of dentin pre-treatment did not influence the clinical performance of restorations in non-carious cervical lesions after 1 year.

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