The effect of an air polishing device on sealant bond strength

Lois Scott, M.S.,* and Dale Greer, D.D.S., M.A.** University of Missouri-Kansas City, School of Dentistry, Kansas City, MO.

n L/ental sealants are considered an important compo- nent for the prevention of occlusal caries. Although the occlusal surface accounts for only 12% of the tooth surface, occlusal caries now accounts for 50% to 54% of dental caries.’ Considerable progress has been made in sealant technique and materials since the inception of the acid-etch technique.* Retention of the adhesive material is the major factor in assessing the success of bonding procedures and sealants.2

Retention of bonded material is enhanced if a high- energy enamel surface is created by removing oral contaminants. Current technique for removal of these contaminants uses a pumice-water slurry, rubber cup or brush in a slow-speed rotary handpiece followed by acid etching. Occlusal anatomy is such that cleaning of the deeper pits and fissures is difficult and the effect is primarily limited to the inclined planes.3-6 Even though acid etching removes additional contaminants on the surface enamel, the effect is again primarily on the inclined planes. Successful retention of the sealant and protection of the pit or fissure seems to be dependent on bonding of the resin to the inclined planes, forming a bridge of resin over the pit or fissure.’

The air polishing device has shown encouraging results in stain and debris removal from occlusal sur- faces.’ A surface free of stain and debris may allow a greater degree of surface contact with an acid-etching solution in and near the fissure and possibly also between the fissure and the resin material. This may enhance sealant retention and/or decrease dependence of bonding to inclined planes.

Sealant retention potential in laboratory studies is assessed by using tensile bond strength tests and evalua- tion of tag formation. Studies by Brockmann and Scott* substituting air polishing for traditional pumice-water slurry cleaning showed higher bond strengths and great- er numbers of tag formation although there was not a statistically significant difference between the means of the two groups. The studies did not include testing tensile bond strength after periods of water immersion. Additional testing after such immersion is a logical step

*Associate Professor, Division of Dental Hygiene. **Associate Professor, Department of Operative Dentistry.

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in studying this cleansing technique. Seotopo9 has shown high bond strengths after short periods of water immer- sion in samples that have minimal or no tag formation. He postulated that the tags become more critical in mechanical interlocking at the resin/enamel interface in a fluid environment as the immersion time increases.

The current studies were designed to build on the Brockmann and Scott* study with the addition of water immersion before tensile bond strength tests and with the addition of samples of sealed pits or fissures as well as smooth surfaces.

Specifically the studies evaluated whether substitution of traditional tooth-surface cleaning by use of the Prophy- Jet (Dentsply Int., York, Pa.) air-polisher resulted in equal or greater tensile bond strength of dental sealants on smooth surfaces and on occlusal fissures after water immersion for 7 days and 28 days as tested with the Instron Universal testing device (Instron Corp., Canton, Mass.).

MATERIAL AND METHODS Airpolishing device

The device used in this study was the Prophy-Jet component of the Cavi-Jet (Dentsply Int.) unit. This device uses a handpiece, controlled by a foot switch, that emits an air-propelled suspension of sodium bicarbonate in a water spray. The recommended working distance between nozzle and tooth surface is 4 to 5 mm. The device operates on a 115 volts, uses an operative air pressure of 50 to 55 psi, and an inlet water pressure of 25 to 60 psi. The Prophy-Jet device was evaluated and placed in the Acceptable category under Devices for Stain Removal by the American Dental Association in 1983. Caution is recommended in the use of sodium bicarbonate for patients who are on physician-recom- mended low-sodium diets, are hypertensive, or exhibit a severe respiratory disease. Because the device produces aerosols, eye protection is recommended for patients, dentists, and hygienists. Those operating the equipment should also use masks.

Permanent human teeth obtained from the Depart- ment of Oral Surgery, and from oral surgery practice in the Kansas City area were used. The teeth were stored in distilled water or an equal mixture of 10% formalin and

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EFFECT OF AIR POLISHING DEVICE

Exposed 3mm dia. site

Top View Fig. 1. Diagrams showing isolation of surface strength.

glycerine at room temperatures. There were no available histories on these samples. Incisors were used in the smooth-surface bonding study and premolars and molars were used in the pit and fissure study.

Study design

Thirty anterior teeth were paired, matching as many characteristics such as size, anatomical form, and general condition as possible, for the 7-day sample and 30 for the 2%day sample in the smooth-surface study. Sixty occlu- sal fissures were likewise selected and matched by using posterior teeth for the 7- and 28-day fissure study. A coin toss randomly assigned matched samples to the experi- mental or control group.

Preparation off specimens

In both studies, the teeth were stabilized in acrylic resin blocks to facilitate tensile-testing procedures. By using a carbide bur and high-speed handpiece, sites 3 mm in diameter were isolated on the facial surface of each tooth in the smooth-surface study. In the fissure- surface study, the deepest pit or fissure was identified and a site 3 mm in diameter was selected for testing. Isolating the site also eliminated a major portion of the accompanying inclined planes. Crown and bridge wax was flowed around and level with each site to prevent contact outside the test area by the bonding materials (Fig. 1).

The experimental surfaces were then cleansed either by the traditional method or by using the Prophy-Jet device. Pumice and water with a bristle brush in a slow-speed hand,piece were used in the traditional clean- ing process for 20 seconds unless the surface was inordinately stained. For such teeth, an additional 10 seconds were added. In the experimental group, the air polishing device was set at a standardized setting between medium and high. A millimeter ruler was

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Sectional View of fissure for testing tensile bond

Fig. 2. Alignment of composite-filled acrylic resin tube to tooth surface.

attached to the nozzle to assure a distance of 4 mm between the nozzle end and the site. The stream of the air polishing device was directed at a 90-degree angle for 20 seconds, with an additional lo-second exposure for a few teeth with exceptionally heavy stain.

The specimens were thoroughly rinsed and acid- etched according to manufacturer’s instructions. If a tooth did not exhibit adequate etching after I minute, the etching procedure was repeated. After a thorough rins- ing with tap water, the samples were dried by using an air syringe with a moisture-control attachment to elimi- nate moisture contamination. The specimens were placed in the lower arm of a holding apparatus. Visible light-cured dental sealant (Delton, Johnson & Johnson Dental Products, Co., E. Windsor, N. J.) was applied to the test site. An acrylic resin tube with a 3 mm internal diameter containing 5 to 6 mm of composite was placed in the upper arm of the apparatus and lowered to firmly

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Fig. 3. Specimen in holder ready for attachment of crosshead of Instron machine.

Table I. Analysis of variance for occlusal fissure eriamel study

DF ss MS F

Main effects Treatment 1 6590.269 6590.269 6.239’ Time 1 1043.376 1043.376 0.988

Two-way interactions Treatment time 1 211.834 211.834 0.201 Error 47 49648.203 1056.345

*P = .05.

RESULTS

Table II. Means and standard deviations* in occlusal fissure enamel study

A two-factor analysis of variance was performed for each study. There were no significant differences among the smooth-surface groups for treatment effects or time in water. In the fissure-surface study, there was a significant difference at the p < .05 level for treatment effects (Table I). The air polishing group demonstrated greater mean bond strength (46.94 kg/cm2) than the control group (23.91 kg/cm2) (Table II). There was no significant difference among the fissure-surface groups based on length of time of water immersion before bond testing. The coefficient of variation and standard devia- tions were high for all sample groups in both studies for time and for treatment effects.

Time 1 Time 2

Traditional 1 (n = 13) 26.46 k 20.04 Traditional 2 (n = 13) 21.35 zt 26.61 Air polishing 1 (n = 11) 53.58 I!X 32.91 Air polishing 2 (n = 14) 40.30 * 41.31

*Coefficient of variation of all samples combined = 97%.

DISCUSSION

contact the test surface (Fig. 2). The sealant was then cured by using visible light for 20 seconds from three directions around the site. The specimens were then immersed in distilled water at 37” C and stored for the assigned time period until tested.

Sample testing

All specimens were tested on the Instron Universal testing device, set to run at 0.2 in/min until the bond was severed. The pattern of tensile force and fracture was recorded on the Instron strip chart to the nearest .Ol kg. A specimen holder was designed to assure a perpendicu- lar force by the moving crosshead (Fig. 3).

These studies were developed to compare traditional cleaning procedures and air polishing with respect to sealant bond strength after 7- and 28-day water immer- sion. In the fissure study, a substantial amount of the cusps and inclined planes was removed to measure bond strength at the fissure. On smooth-surface enamel where access by the cleansing method was not impeded by tooth anatomy, the two methods resulted in comparable bond strength. However, a difference was found among the fissure samples. Even though removal of cuspal anatomy allowed greater access to the fissure area by both methods, there was a statistically significant difference in mean bond strength. The ability of the air-driven slurry to penetrate and clean more deeply in the fissure may have contributed to this difference. Comparison of the extent of penetration of the sealant into the fissure and bonding to the fissure enamel will be made through examination of the enamel/sealant interface via the scanning electron microscope at a later time.

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Both cleaning methods resulted in means close to the range suggested by Low et al.” for adequate clinical bond strength (126 to 36 kg/cm*). Means for the total population of each study were within that range, 34.80 kg/cm2 and 34.81 kg/cm2, in the smooth-surface study and fissure study, respectively. However, the traditional group mean in the fissure-surface study dropped slightly lower, 23.91 kg/cm2, whereas the air polishing mean was considerably higher, 46.14 kg/cm2.

3. Removal of the inclined planes of the cusps in the air polishing group resulted in mean bond strength well above that recommended for clinical use, suggesting that there was adequate bonding in the fissure site alone. A combination of bonding at the fissure and on the inclined planes would seem to enhance sealant retention. Clinical trials need to be conducted before clinical significance can be stated.

In the fissure study, only 26% of the samples in the traditional group were within or over the suggested kg/cm2 range compared with 57% of the air polishing groups. The difference then between bond strength was not only statistically significant but possibly a difference between being a.dequate or inadequate for clinical use. The results tenad to support a technique that ensures occlusal plane (coverage and bonding to the inclined planes when cleaning with the traditional method. Results suggest further study to determine whether such would continue to be essential with use of an air polishing device

CONCLUSIONS

1. In the fissure enamel study, mean sealant bond strength of the air polishing group was higher than that of the traditional group at the alpha .05 level of significance.

2. There was no difference between groups for time in water in either study or in treatment effects in the smooth-surface study.

These results must be considered tentative. The stan- dard deviations were large, resulting in high coefficients of variation with all groups. Low et al.‘O had suggested caution in attem.pting to rank differences in techniques or materials when the coefficient of variation is high. Studies that he reviewed in 1975 and other published studies showed ranges of 20% to 60%, indicating the difficulty of reducing such variability in studies with human enamel.‘O,” In this study, teeth were obtained from a wide range of subjects over a long period of time, which contributed to the variability. The method of preparation of the specimens, although patterned after previous studies, required untested variations. Most previous studies used a method that allowed creating a flat surface for the test area. In the present studies, to test the surface cleaning ability of the two methods, the natural surface with the normal anatomy had to be maintained. Selecting matching tooth samples from the same individual, such as those removed for orthodontic purposes, and refining the sample preparation method would help redu’ce the variability of the samples and the variability of the results.

3. The coefficient of variation of test samples in both studies was higher than that recommended for deter- mination of a rank order between groups.

4. Data support continued laboratory and clinical inves- tigation as to the effect of use of an air polishing device on sealant bond strength at the fissure site and on clinical retention.

REFERENCES

After consideration of the limitations and difficulties associated with testing the bond strength of sealants applied to occlu:sal fissure enamel, the results of these laboratory studies suggest:

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Gwinnett AJ. Scientific rationale for sealant use and technical aspects of application. J Dent Educ 1984;48:56-9. Ripa LW. Occlusal sealants: an overview of clinical studies. J Public Health Dent 1983;43:216-25. Mertz-Fairhurst EJ. Current status of retention and caries prevention. J Dent Educ 1984;48:18-26. Galil KA. Scanning and transmission electron microscopic exam- ination of occlusal surface plaque following toothbrushing. J Can Dent Assoc 1975;41:499-503. Newburn E. Cariology. 5th ed. Baltimore: William & Wilkins Co, 1983;234-5. Gwinnett AJ, Buonocore MG. A scanning electron microscope study of pit fissure surfaces conditioned for adhesive sealing. Arch Oral Biol 1972;17:415-23.

1. The air polishing device affects the fissure enamel in a manner that enhances bond strength at the fissure.

Taylor GL, Gwinnett AJ. A study of the penetration of sealants into pit fissures. J Am Dent Assoc 1973;87:1181-9. Brockmann S, Scott L. The effect of an airpolishing device on enamel-resin interface and bond strength. Unpublished. Soetopo. Mechanisms of adhesion of polymers to acid-etched enamel. J Oral Rehabil 1978;5:69-80. Low T, David EH, van Fraunhofer JH. A method of determin- ing the tensile bond strength of fissure sealant materials. J Oral Rehabil 1975;2:341-7. Young KG, Hussey M, Gillespie FC, Stephen KW. In vitro studies of physical factors affecting adhesion of fissure sealant to enamel. Proc Int Symp Acid-etch Tech. St Patti: North Central Publishing Co, 1975;50-61.

2. Removal of the inclined planes of the cusps in traditional groups resulted in mean bond strength below the range recommended by Low et al.‘O for clinic use, verifying the need for adequate inclined plane bonding when using the traditional method.

Reprint requests to: ASSCMXATE PROFESSOR LOIS SCOTT UNIVERSITY OF MISSOURI-KANSAS CITY

SCHOOL OF DENTISTRY KANSAS CITY, MO 64108

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