Introduction
The aim of this study was to evaluate in vivo the effect of saliva contamination at different stages of the bonding procedure on the bond failure rate and the adhesive remaining on teeth after debonding brackets bonded with a hydrophilic self-etching primer (Transbond Plus self-etching primer [TSEP], 3M Unitek, Monrovia, Calif).
Methods
This was a prospective controlled clinical trial. The sample consisted of 46 patients with similar treatment plans and mechanotherapies. Stainless steel brackets (n = 531) were bonded with TSEP. The patients were divided into 2 groups: contamination with saliva before TSEP application and contamination with saliva after TSEP application. In both groups, saliva was applied in a split-mouth design. Diagonally opposite quadrants were allocated to either the contaminated group (contamination before [153 teeth] or after [115 teeth] TSEP application) or to the uncontaminated control group (263 teeth). Recording of failed brackets involved only first-time failures, and the observation period was a minimum of 6 months.
Results
The chi-squared test showed no significant differences ( P = 0.11) in bracket failures between the groups. Kaplan-Meier survival analysis detected no significant differences in the survival rates between the 3 groups ( P = 0.51). Most bond failures occurred during the first 3 months. In all 3 groups, the adhesive remaining on teeth after debonding tended to be less than half.
Conclusions
These findings suggest that saliva contamination before or after application of self-etching primer does not increase the clinical risk of bond failure.
Ever since Newman bonded brackets directly to tooth enamel, there have been many attempts to determine the causes and to reduce the incidence of bracket loss. Zachrisson cited contamination as an important cause of bond failure. The critical moment in the bonding process occurs just after the enamel has been etched; thus, controlling and isolating contamination at that stage is vital.
Oral contaminants can be grouped as follows: macroscopic and intrinsic to the mouth (oral fluids), microscopic and intrinsic (bacteria), extrinsic introduced by the subject (from diet and oral hygiene practices), and extrinsic introduced by the practitioner (lubricants used with rotatory instruments and latex). Much literature deals with contamination by oral fluids. Oonsombat et al and Sfondrini et al studied contamination from blood; both studies concluded that blood contamination greatly reduces bond strength. Also, contamination from plasma leads to reduced bond strength.
Of the oral fluids, saliva is the most common during clinical procedures. One reason why studies have tried to evaluate the effect of saliva on etched enamel is that the enamel, left clean and dry after etching, is a highly energized surface, a circumstance that facilitates the dispersion of polar organic fluids. Silverstone et al found that, when enamel has been exposed to saliva for half a second, the saliva can be removed successfully with water, whereas exposure time longer than 1 second allows the deposit of a surface layer that resists washing. They also found that the capacity for saliva contamination is independent of the area of enamel exposed to it. It has also been observed that bond strength values are significantly lower when brackets are bonded with the enamel still damp from saliva than when the enamel had been dried or reetched after contamination. It is estimated that saliva contamination reduces bond strength by 50% or more, because it fills the microporosities of the etched enamel, affecting the mechanical retention of the bonding material.
Self-etching adhesives have been developed as one of many attempts to reduce chair time and the number of intermediary procedures. In addition, the hydrophilic monomers in self-etching primers could be advantageous in the control of saliva contamination. Chemical reaction of self-etching primers with enamel takes place concomitantly with the chemisorption of the self-etching primers on the enamel surfaces. Phosphoric acid esters can not only decalcify hydroxyapatite, but also chemically adhere to the hydroxyapatite. Chemical adhesion could explain their tolerance to moisture. Another possible explanation might be the water in its composition. Water is necessary to activate the self-etching primer and obtain an adequate pH. Several in-vitro studies have evaluated the effect of saliva contamination on bond strength of brackets bonded with self-etching adhesives, with disparate results; for this reason, in-vivo studies are needed to clarify these findings.
Our objectives were to determine in vivo the effect of saliva contamination, introduced at different stages during the bonding process, on both the bond failure rate and the adhesive remaining on teeth for brackets bonded with a self-etching primer.
Material and methods
Our subjects were patients at the Department of Orthodontics of the Faculty of Medicine and Dentistry at the University of Valencia in Valencia, Spain. The study was approved by the Science and Ethics Committee at Valencia University Hospital. Forty-six patients were selected, all requiring treatment with fixed apparatus according to the following criteria: a malocclusion as symmetrical as possible; teeth free of caries, reconstruction, or enamel disorders; and no antagonistic contact between teeth and brackets and similar projected mechanotherapies.
Before the study, informed consent was obtained from each patient. A total of 531 standard metal brackets (Rocky Mountain Orthodontics, Denver, Colo) were bonded with Transbond Plus self-etching primer (TSEP, 3M Unitek, Monrovia, Calif) according to the manufacturer’s instructions. TSEP was applied to the vestibular surface for 5 seconds with the applicator. Then it was dried with a jet of air. Transbond XT resin (3M Unitek) was applied to the bracket base, which was then placed on the tooth surface and pressed firmly. Excess resin was removed around the bracket with a probe, and it was polymerized by positioning an Ortholux XT lamp (3M Unitek) on each interproximal side for 10 seconds. Ten minutes after bracket bonding, the corresponding arch was positioned. First, we placed a twisted 3-strand archwire (Tri-Flex stainless steel, 0.0155 in, Rocky Mountain Orthodontics) or a 0.012-in stainless steel archwire (Tru-Chrome, Rocky Mountain Orthodontics) to be replaced later by the corresponding sequence of arches.
Distribution of the sample proved to be fairly homogeneous; the numbers of brackets bonded on each type of tooth were similar, with a minimum of 23 brackets cemented to the maxillary canines (4.33%) and a maximum of 32 on the maxillary central incisors (6.2%).
The patients were divided into 2 groups: saliva contamination before TSEP application, and saliva contamination after TSEP application. Saliva was applied in both groups by using a split-mouth design. Diagonally opposite quadrants were allocated to either the contaminated group (contamination before,153 teeth, or after TSEP application, 115 teeth) or to the uncontaminated control group (263 teeth). Bracket bond failures were recorded only for first-time failures, and the observation period was a minimum of 6 months.
The patient’s own saliva was used for contamination. When the bond area had been isolated, a cotton swab soaked up saliva from the area around the Stenon duct opening. Patients were asked not to eat or drink for an hour before their appointment to ensure that saliva was not stimulated, and they were also asked to clean their teeth before bonding. Once saliva had been obtained, the swab was applied to the vestibular surface of the tooth so that it became completely contaminated.
When brackets failed, the adhesive remnant index (ARI) score was calculated according to the criteria of Årtun and Bergland : 0, no adhesive on the tooth; 1, less than half of the adhesive on the tooth; 2, more than half of the adhesive on the tooth; and 3, all adhesive left on the tooth, with an impression of the bracket base.
Only first-time failures were recorded, and the observation period was a minimum of 6 months (range, 6-16 months).
Statistical analysis
Data were analyzed with the SPSS statistical program for Windows (version 14.0, SPSS, Chicago, Ill).
The failure rates and ARI scores over the 6-month period were analyzed with the chi-squared test. Significance was predetermined at α = 0.05.
Bracket survival rate was analyzed with the Kaplan-Meier survival analysis by using the Breslow statistic at α = 0.05 level of significance. In order not to lose information about brackets observed beyond the 6-month point, the Kaplan-Meier test was carried out with 16 months as the observation period.
Results
Table I shows the numbers and rates of bracket failures over 6 months. The chi-squared test showed no significant differences ( P = 0.11) in bracket failures between the groups.
| Group | Brackets (n) | Failures (n) | Failure rate (%) |
|---|---|---|---|
| Control | 263 | 16 | 6.08 |
| Contamination before | 153 | 16 | 10.46 |
| Contamination after | 115 | 5 | 4.35 |
The Kaplan-Meier survival analysis detected no significant differences in bracket survival rates among the 3 groups ( P = 0.51). The 3 groups had the same pattern, with more bracket failures during the first 3 months; the survival rate was approximately 95% ( Fig ).
