The Introduction

The Introduction section should define the purpose of the investigation and review the literature that is relevant to the study. The purpose should include the research question(s) that will be answered by the investigation or the hypothesis(es) that will be tested. An example of a research question is: "Does the use of prizes and rewards improve the behavior of children in the dental office?" A hypothesis is a statement that predicts the relationship between two or more variables,5 such as: "The use of an ultrasonic scaling instrument for calculus removal results in a greater reduction in periodontal pocket depth than hand scaling instruments." In this case, the two variables are (1) type of scaling instrument and (2) pocket depth. The literature review should include the theoretical basis for the research, the current knowledge available on the research question and current gaps in knowledge.3

Below is an example of the Introduction section:

The Clinical Effect of Dentifrices Containing Stabilized Stannous Fluoride on Plaque Formation and Gingivitis - A Six-Month Study with Ad libitum Brushing4

Introduction
The anticaries effects of stannous fluoride have been known for over thirty years.1 Due to its antimicrobial properties, stannous fluoride has also been examined for its effects on plaque and gingivitis; however, efficacy against these conditions has not been as clearly defined.2,3 Over the past 20 years, the plaque and gingivitis effects of stannous fluoride have been studied in seven clinical trials involving six or more months of topical application.4-10 This work covered a variety of oral care formulations, clinical populations, and methodologies. In several of the studies, significant reductions in gingivitis and gingival bleeding were reported following the extended use of stannous fluoride. In a study evaluating the effect of fluoride mouth rinses on caries, gingivitis, and salivary S. mutans levels in caries prone adults, Klock et al.4 showed that after one year, subjects using a stannous fluoride rinse had about 50% fewer bleeding sites than subjects using a sodium fluoride rinse. This difference was statistically significant at p = 0.05. After two years, subjects in the stannous fluoride group continued to have less than half as many bleeding sites as those in the sodium fluoride group; however, the difference was no longer statistically significant. The authors attributed the lack of statistical significance in the second year of the study to the loss of subjects from one to two years. Boyd et al.5 demonstrated that subjects using a 0.4% stannous fluoride gel with "highly available Sn2+" ion, significantly reduced gingivitis and gingival bleeding following nine months of twice-daily application. Similar beneficial effects on gingival health were observed following the extended use of 0.4% stannous fluoride gels by Derkson et al.6 who demonstrated a reduction in gingivitis on the periodontium of overdenture abutment teeth, and by Tinanoff et al.7 who demonstrated reductions in gingivitis and gingival bleeding in subjects with fixed or removable dental prostheses. Zimmermann et al.8 reported that following seven months of use, an amine fluoride/stannous fluoride mouth rinse significantly reduced gingivitis and gingival bleeding.

In contrast to the clinical trials demonstrating antigingivitis effectiveness, Leverett et al.9 and Wolff et al.10 reported the results of stannous fluoride studies, which failed to detect reductions in gingivitis. In the Leverett study, students rinsing daily (on school days only) with a 0.1% stannous fluoride solution had consistently lower gingivitis scores at all examination points than students rinsing with a 0.05% sodium fluoride solution; however, this difference was modest in magnitude (less than 10%) and was not statistically significant. Results from this study suggest that intermittent daily dosing of a 0.1% stannous fluoride solution may not be sufficiently frequent enough to observe a gingivitis effect. In Wolff et al., close inspection of the results suggest that failure of subjects to comply with the brushing instructions for the stannous fluoride gels may have contributed to the negative results for gingivitis. Examination of the percentage of subjects self-reporting compliance in this trial reveals that by the end of the study (18 months), 33% of the subjects in the stannous fluoride group reported not using the test product, or using it less frequently than once a day. In contrast, only about 20% of the subjects in both the placebo and sodium fluoride groups reported this level of usage.

Further complicating the clinical situation is stannous fluoride's relative lack of stability in aqueous environments where hydrolysis and oxidation of the stannous ion is favored.2,3,11-13 One approach which has proven successful in stabilizing stannous fluoride is the use of non-aqueous gel formulations. These products, which are available commercially, have been clinically shown to possess antigingivitis efficacy. However, a limitation of the stannous fluoride gels is that they do not provide the cleaning and aesthetic benefits associated with conventional dentifrices and, therefore, require the adjunctive use of such dentifrices.10 This could potentially lead to poor compliance as patients' oral hygiene regimens become increasingly complicated as a result of their having to apply the stannous fluoride gel following brushing with a conventional dentifrice. It is reasonable to assume that in such a situation, the product, which will see a decline in use over time, would be the stannous fluoride gel. Therefore, it would be advantageous to develop conventional dentifrice products which stabilized stannous fluoride to the degree required to inhibit gingivitis.

This double-blind clinical study was designed to assess the clinical effects of products containing 0.454% stannous fluoride stabilized in conventional dentifrice formulations on gingivitis, gingival bleeding, plaque, stain, and microbiological parameters. The effects of the stabilized stannous fluoride dentifrices on the microbiological parameters are published separately.