Use of analysis of covariance in periodontal clinical trials

Statistical Power for Analyses of Changes in Randomized Controlled Trials

Randomized controlled trials (RCTs) are widely recommended as the most useful study design to generate reliable evidence and guidance to daily practices in medicine and dentistry. However, it is not well-known in dental research that different statistical methods of data analysis can yield substantial differences in study power. In this study, computer simulations are used to explore how using different univariate and multivariate statistical methods of analyzing change in continuous outcome variables affects study power, and the sample size required for RCTs. Results show that, in general, analysis of covariance (ANCOVA) yields greater power than other statistical methods in testing the superiority of one treatment over another, or in testing the equivalence between two treatments. Therefore, ANCOVA should be used in preference to change score or percentage change score to reduce type II error rates.

Influence of Soluble Pyrophosphate on Calculus Formation in Adults

The purpose of this double-blind, longitudinal clinical study was to assess the efficacy of a dentifrice containing 3.3% soluble pyrophosphate in inhibiting calculus formation and its effect upon the oral soft tissues. A total of 265 adult volunteers was given a dental prophylaxis. Each was examined for dental calculus and oral soft tissue pathology. The volunteers were then randomly assigned to use either a dentifrice containing soluble pyrophosphate and sodium fluoride or a placebo sodium fluoride formulation for ad libitum home usage. At the two-month completion of the study, 217 subjects were available for examination. The results showed that the group using the dentifrice containing soluble pyrophosphate experienced a significant 26% decrease in calculus formation as compared with the placebo group, with both dentifrices being equally well-tolerated by the oral soft tissues.

A controlled 6-month clinical trial to study the effects of a stannous fluoride dentifrice on gingivitis

OBJECTIVES

This study was conducted to assess anti-plaque and anti-gingivitis benefits of a stabilized stannous fluoride (SnF(2))/sodium hexametaphosphate (SHMP) dentifrice versus a negative control.

MATERIAL AND METHODS

This was a randomized, 6-month, stratified, single-centre, double-blind, parallel group, clinical study conducted in harmony with the guidelines for evaluating chemotherapeutic products for the control of gingivitis outlined by the American Dental Association. A stabilized 0.454% SnF(2)/SHMP dentifrice was tested against a commercially available negative control dentifrice. Following baseline measurements, subjects received a dental prophylaxis. Subjects were instructed to brush twice daily for 60 s using their assigned product. Efficacy measurements were obtained at baseline, 3 and 6 months post treatment using the Modified Gingival Index, Gingival Bleeding Index and the Turesky Modified Quigley-Hein Plaque Index. Oral tissue examinations were performed at all visits.

RESULTS

A total of 140 subjects were enroled and 128 completed the study. RESULTS after 6 months showed the SnF(2) dentifrice delivered a 16.9% reduction in gingivitis (p<0.001), a 40.8% reduction (p<0.001) in gingival bleeding, and an 8.5% reduction in plaque (p=0.001) versus the negative control. Both treatments were well tolerated.

CONCLUSIONS

Twice daily use of the SnF(2)/SHMP dentifrice over 6 months provided statistically significant anti-plaque and anti-gingivitis benefits relative to a negative control.

Anti-gingivitis efficacy of a stabilized 0.454% stannous fluoride/sodium hexametaphosphate dentifrice. A controlled 6-month clinical trial

OBJECTIVE

Stannous fluoride is a broad-spectrum anti-microbial agent that has been used in dentistry as a chemical adjunct to prevent dental caries and gingivitis. The objective of this study was to assess the anti-gingivitis efficacy of a stabilized 0.454% stannous fluoride/sodium hexametaphosphate dentifrice relative to a negative control.

METHODS

This was a randomized, 6-month, double-blind, parallel-group gingivitis study conducted according to the guidelines for evaluating chemotherapeutic products for the control of gingivitis outlined by the American Dental Association. A stabilized 0.454% stannous fluoride/sodium hexametaphosphate dentifrice was tested against a commercially available negative control dentifrice. Following baseline measurements, subjects received a dental prophylaxis. Subjects were then instructed to brush twice daily for 60 s using their assigned product. Oral soft-hard-tissue examinations and clinical examinations using the Modified Gingival Index, Gingival Bleeding Index, and the Turesky modification of the Quigley-Hein Plaque Index were performed at baseline, 3 and 6 months post-treatment.

RESULTS

A total of 143 subjects were enrolled and 130 of them completed the 6-month study. After 6 months of product usage, the experimental group had 21.7% less gingivitis (p<0.001), 57.1% less bleeding (p<0.001), and 6.9% less plaque (p=0.01) on average compared with the negative control group. No adverse oral soft-hard-tissue effects or extrinsic tooth staining was observed in the study.

CONCLUSION

The results demonstrate that use of the stabilized 0.454% stannous fluoride/sodium hexametaphosphate dentifrice over a 6-month period provided statistically significant reductions in gingivitis, gingival bleeding, and plaque when compared with a negative control dentifrice.

The Comparative Efficacy of Stabilized Stannous Fluoride/Sodium Hexametaphosphate Dentifrice and Sodium Fluoride/Triclosan/Copolymer Dentifrice for the Control of Gingivitis: A 6-Month Randomized Clinical Study

BACKGROUND

Antimicrobial agents such as stannous fluoride and triclosan have been incorporated into dentifrice formulations and have been shown to be effective in reducing gingivitis. The objective of this study was to compare the anti-gingivitis efficacy of a 0.454% stannous fluoride/sodium hexametaphosphate dentifrice to a positive control triclosan/copolymer dentifrice.

METHODS

This was a 6-month, randomized, double-masked, parallel-group study conducted according to the American Dental Association guidelines for evaluating chemotherapeutic products for the control of gingivitis. A 0.454% stannous fluoride/sodium hexametaphosphate dentifrice was tested against a commercially available positive control dentifrice (0.30% triclosan/2.0% Gantrez copolymer). Following baseline measurements, subjects received a dental prophylaxis. Subjects were then instructed to brush twice daily for 60 seconds using their assigned product. Tooth brushing was supervised for 3 days of each week. Clinical examinations using a gingival index were performed at baseline and at 3 and 6 months.

RESULTS

A total of 199 subjects were enrolled and 186 completed the 6-month study. Average baseline gingivitis and bleeding scores were similar for the two treatment groups. After 6 months, the experimental group had statistically significantly less gingivitis (25.8%) and statistically significantly less bleeding (27.4%) on average compared to the control group. Neither adverse oral soft tissue effects nor tooth staining were reported.

CONCLUSION

Within the limits of the study protocol, the results demonstrated superior therapeutic benefits for the stabilized 0.454% stannous fluoride/sodium hexametaphosphate dentifrice in reducing gingivitis compared to the triclosan/copolymer control in this partially supervised study.

A clinical comparison of antibacterial mouthrinses: effects of chlorhexidine, phenolics, and sanguinarine on dental plaque and gingivitis

This study compared the clinical efficacy of three mouthrinses containing either 0.12% chlorhexidine, phenolic compounds, or sanguinarine, which were used unsupervised, in a placebo-controlled, double-blind study of 6 months' duration. The study was conducted according to ADA clinical guidelines for evaluation of antigingivitis agents and was completed by 481 adults. Following baseline exams and a prophylaxis, subjects were randomly divided into treatment groups matched for age, gender, and gingivitis severity, and were instructed to use the rinses in accordance with manufacturer's directions. Followup examinations evaluated supragingival plaque, gingivitis, and gingival bleeding. Compared to placebo at 6 months, the group rinsing with 0.12% chlorhexidine had significantly less gingivitis (31% reduction), gingival bleeding (39% reduction), and plaque (49% reduction) and was significantly better than any of the other treatment groups (P less than 0.05). Both the phenolic and sanguinarine groups showed moderate, yet significant, reductions in plaque compared to placebo (24% and 12% respectively) yet were significantly less effective than the 0.12% chlorhexidine rinse (P less than 0.05). However, neither the phenolic nor sanguinarine rinses were significantly different than placebo in their effects on gingivitis or gingival bleeding. These results support previous published results on the superiority of 0.12% chlorhexidine when used in conjunction with professional care and as an adjunct to routine oral hygiene practices.

The use of chlorhexidine in the management of gingivitis in children

Two double-blind studies were conducted in 191 children in Mexico. Following a dental prophylaxis, either a 0.12% chlorhexidine gluconate mouthrinse or a placebo was used under supervised conditions in comparable groups twice per day. The chlorhexidine treatments resulted in a significant decrease of gingivitis when compared to the placebo rinse. Although superficial mucosal desquamations were seen in some chlorhexidine users, they were transient and without discomfort. The increase of cosmetic side effects, e.g., dental stain and supragingival calculus, was without consequence to the gingival health of the subjects. The use of a chlorhexidine rinse twice per day and as adjunct to regular oral hygiene procedures achieved a considerable benefit against gingivitis in children in two studies extending over ten and 12 weeks.

A comparison of 3 clinical indices for measuring gingivitis

A clinical study was conducted among 200 adult males and females to compare the intrusive gingival index (GI) for estimating gingivitis with the nonintrusive and only visually applied papillary-marginal-gingivitis index (PMGI). The GI examinations were performed by a senior examiner with long experience and a junior examiner, while the PMGI was graded by only a senior examiner with long experience. A 4th examiner was included for grading bleeding sites by gentle intrusion at the orifice of the gingival crevice. Following the baseline examination by all examiners, the subjects were randomly assigned to either a group that received an oral prophylaxis immediately or to a group that received an oral prophylaxis 6 weeks after the baseline. All subjects were regraded by all examiners 4 days after the 2nd group received a prophylaxis. This delayed prophylaxis design created a difference in the responses between treatment groups. Both the GI examiners and the PMGI examiner concluded there was significantly less gingivitis in the group receiving a prophylaxis second. There were also significantly fewer bleeding sites in the group receiving a prophylaxis second as determined by both GI examiners and the bleeding-sites examiner.

A clinical procedure for determining the proficiency of gingivitis examiners

The purpose of the present study was to evaluate a clinical procedure for determining the proficiency of gingivitis examiners. After 4 examiner trainees were instructed by and participated in practice examination sessions with a senior examiner, the 5 examiners participated in a 2-group clinical study which employed appropriately timed-staggered dental prophylaxes to create a gingivitis treatment effect between the 2 groups. The 1st group received dental prophylaxes 30 days before the 2nd group. 10 days after the 2nd group had received dental prophylaxes, both groups were examined independently by all 5 examiners. Baseline examinations had been made on all subjects by all 5 examiners independently to serve as a covariable in the statistical analyses. During this clinical exercise, the examiners did not know at what time prophylaxes had been given nor did they have access to the previous examination records. The expected presence of a treatment effect, as confirmed by the senior examiner, was found by all of the examiner trainees in this exercise. The treatment effect for all examiners was statistically significant.

The effect of soluble pyrophosphates on dental calculus in adults

A sodium fluoride dentifrice, containing a mixture of soluble pyrophosphates, was used ad libitum in an adult population for 6 months after receiving a dental prophylaxis. In comparison with the control group, who used the sodium fluoride formula without the pyrophosphates, the test group had significantly less calculus by occurrence and severity. Thus, a significant reduction in newly forming calculus was obtained with the experimental dentifrice when used as an adjunct to regular professional care and personal oral hygiene procedures.

The effect of verbal information and demonstration on denture hygiene in elderly people

The purpose of the present study was to investigate the effect of two oral hygiene information programs on denture hygiene. The programs were provided individually to healthy elderly denture wearers. Totally, 150 edentulous persons between 67 and 89 years of age were selected and randomly assigned to two experimental groups and one control group. In one test group (INFO) the participants were only given individual verbal information on how to remove denture plaque. The participants of the second test group (DEMO) received individual demonstration of denture cleaning in addition. One hundred and thirty-eight persons completed the study. The percentage plaque covering the maxillary denture base was assessed by a morphometric point-estimator scoring method at the start of the study and after 14 and 180 days. Verbal information resulted only in a short-term effect (14 days), whereas demonstration on how to remove denture plaque gave long-term (180 days) improvement of denture hygiene.

Why covariance analysis should replace increment analysis of variance in caries studies

Consider a caries study where experimental units are a) randomly assigned to groups, b) premeasured on DMFS, c) administered a specified treatment depending on group membership, and d) postmeasured on DMFS. Traditional analysis of these data consists of analysis of variance of the increment scores (increment ANOVA). In the place of increment ANOVA, others have suggested analysis of covariance with the postmeasure as criterion and the premeasure of covariate (ANOCOV). The present paper examines and documents the following: 1) Increment ANOVA and ANOCOV test the same null hypothesis. 2) Increment ANOVA and ANOCOV have exactly the same assumptions. 3) Increment ANOVA is usually less precise than ANOCOV. 4) The same concern for violations of assumptions must be expressed with increment ANOVA as with ANOCOV (see No. 2 above). 5) ANOCOV should replace increment ANOVA in caries studies (see points 1-4).

The use of analysis of covariance to increase precision wtih DMFS measures

For an experimental study with pre- and post-DMFS measures two methods of analysis were compared with respect to precision. It is shown that for large sample size, the analysis of covariance with the post-DMFS measure as criterion and the pre-DMFS measure as the covariate will be more precise than the analysis of variance of increment scores as the value of beta differs from 1. When beta is approximately 1, the two techniques will have essentially the same precision. The dental researcher interested in precision is advised, therefore, to use analysis of covariance with the pre-DMFS measure as the covariate and the post-measure as criterion rather than the traditional analysis of variance of increment scores. For large sample size, the precision of the former will tend to be at least that of the latter. The researcher is not encouraged to use analysis of covariance with the increment as the criterion; if the procedure increases precision over analysis of variance of the increments, it merely indicates that analysis of covariance (with the post-measure as criterion) should have been used originally.