22 – Exercises in Critical Thinking


Exercises in Critical Thinking

It is difficult to overstate the value of practice. For a new skill to become automatic or for new knowledge to become long-lasting, sustained practice, beyond the point of mastery, is necessary.

—Daniel T. Willingham
from Practice makes perfect perfect—
But only if you practice beyond the point of
perfection. Am Educator 2004; Spring:31.


The following excerpts from the dental literature are intended to illustrate some of the concepts introduced in the preceding chapters. To keep the section reasonably brief, the examples have been extracted from papers, and much detail has been omitted. In some instances, the authors discuss the weaknesses or strengths of the particular approach they employed in their article, which is not included here. The intent in presenting these examples is not to criticize or commend the articles in question, but rather to show how the arguments, strategies, and ideas discussed in this book appear in the dental (or popular) literature. To provide a wide range of examples in a reasonable amount of space, only select material was extracted from the papers. Often the problems contain a conclusion drawn from the abstract or summary of the paper and select material from other sections of the paper, such as Materials and Methods and Results, relevant to the conclusion. In approaching these problems, you should assume that the aspects of the conclusions that are not concerned with the information presented in the Materials and Methods and Results extracts are not problematic. For example, in Problem 1 assume that bone gain was actually achieved, even though it is not clear from the material that is presented how bone gain was measured, the time fluoride was applied, and so forth.

Problem 6

Hoad-Reddick G. Gagging: A chairside approach to control. Br Dent J 1986;161:174–176.

“An attempt was made to help people who were unable to wear dentures owing to an exaggerated gagging reflex. Nineteen patients (7 women and 12 men) were taught a controlled method of breathing based on that recommended by the National Childbirth Trust for use by women in labor. The technique is described and this approach to control is related to work done elsewhere. Fourteen of the patients now wear dentures full time.

“In this study, patients who . . . were unable to wear dentures at all owing to retching problems were encouraged to make one further attempt at denture-wearing, using a breathing technique based on that recommended by the National Childbirth Trust for use by women in labor.

“Landa suggests that the majority of patients show a history of a precipitating cause. In an examination of personalities of dental patients who retched while attempting to wear dentures, Wright used Eysenck Personality Questionnaires. There was no evidence to suggest that retching patients were more neurotic than the control group. Most workers agree that retching is multifactorial in origin.

“All patients were instructed in controlled rhythmic breathing and told to practice it for one or two weeks before prosthetic treatment commenced….

Identify the logical technique used in constructing this approach and the investigational strategy involved in adopting this approach to the problem. Are there any negative results reported here?

Problem 20

Cao CF, Aeppli DM, Bloomquist WF, Bandt CL, Wolff LF. Comparison of plaque microflora between Chinese and Caucasian population groups. J Clin Periodontol 1990;17:115–118.

From the Abstract:

“This investigation was designed to compare the predominant plaque micro-organisms from a Chinese group of patients exhibiting periodontitis with an age-, sex- and periodontal disease–matched Caucasian group of patients. In addition to race, the 2 population groups differed with respect to diet and oral hygiene habits, or effectiveness at removing plaque. Clinical measurements were determined along with an evaluation for micro-organisms in supragingival and subgingival plaque. Although the Chinese and Caucasian population groups were similar with respect to composition of micro-organisms in subgingival plaque, notable differences were observed in supragingival plaque. The microbial differences observed in supragingival plaque may be explained at least in part, if not totally, by the higher plaque index scores of the Chinese versus Caucasian population groups. ”

Table P-1 Mean severity scores of ulcers*

Parameter Chlorhexidine gel Placebo gel
A/P sequence .84 1.31
P/A sequence (9) 1.03 1.11
All patients (20) .93 1.22
Adjusted means 0.94 1.21
Difference in means = 0.27
SE of the difference = 0.115
*Used with permission from Addy M, Carpenter R, Roberts WR. Br Dent J 1976;141:118.

From Materials and Methods:

“10 visiting male Chinese students or scholars at the University of Minnesota, aged 25 to 40 years (mean age + SD = 31.3 + 4.4 years), with symptoms of gingival bleeding, were evaluated for periodontal disease. The criteria for selection of Chinese patients included less than 2.5 years residence in the USA. . . . Caucasians were selected from previous studies for comparison…. There was no statistically significant difference between Chinese and Caucasians in this study with respect to the gingival index.”

From the Results:

“The proportions of spirochetes, motile rods and cocci in plaques are shown . . . . The 2 groups differ significantly with respect to all three microbial forms in supragingival plaque. . . .”

From the Discussion:

“The greater amount of plaque in the Chinese subjects can probably best be explained by differences in oral hygiene habits. Differences in the microbial composition of supragingival plaque between Chinese and Caucasians is likely attributable to the age and quantity of plaque, since old plaque is inhabited by a more complicated microflora…. However, the general similarity of subgingival cultivatable flora in the two population groups suggests that subgingival plaque is more dependent on its microenvironment than on the composition of the adjacent supragingival plaque, race or diet.”

How would you classify this study design? What are some of the difficulties in coming to definitive conclusions with this approach?

Problem 21

Addy M, Carpenter R, Roberts WR. Management of recurrent aphthous ulceration: A trial of chlorhexidine gluconate gel. Br Dent J 1976;141:118–120.

Some relevant information extracted from the paper includes:

“Thirty patients agreed to participate in the trial. They were chosen from a larger group of aphthous-ulcer sufferers who regularly attended dental school and who experienced regular and frequent ulceration. The trial was conducted in a double-blind crossover manner employing an active gel containing 1 percent chlorhexidine gluconate in an aqueous base. Each gel was used for a period of 35 days with 14 days between the two preparations to avoid carry-over effects. At the commencement of the trial each patient was examined and then verbally instructed on the use of gels. Thus, each gel was to be used 3 times a day after meals. The patients were requested to place approximately 2.5 cm of the gel on the index finger, carry it to the mouth and allow the gel to distribute itself throughout the mouth, any residue being swallowed. The patients were also instructed to record the number and duration of the ulcers and to describe the discomfort experienced according to an arbitrary scale of: 1 = uncomfortable; 2 = fairly painful; 3 = very painful.”

See the results in Table P-1. The difference in means of 0.27 between the chlorhexidine treatment and the placebo treatment was significant (P < .05).

From the Discussion:

“Chlorhexidine gluconate as a 1 percent gel produced a significant reduction in the duration and discomfort of ulcers in a group of 20 patients when compared with a placebo gel.”

Identify the experimental design and discuss any problems that there might be in the analysis of the data.

Jan 4, 2015 | Posted by in General Dentistry | Comments Off on 22 – Exercises in Critical Thinking
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