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.
Biller T, Yosepovitch Z, Gedalia I. Effects of topical fluoride in the healing rate of experimental calvarial defects in rats. J Dent Res 1977;56:53–56.
“Bone gain was achieved after topical application of fluoride. Fluoride has a strong promoting effect on osteogenesis and accelerates the repair process of defects in membranous bone. No major histological differences are evident in the newly formed bone.”
Materials and Methods:
“In one half of the rats that underwent the procedure, a cotton wool swab soaked in 2% acidulated (0.1 M H3PO4) NaF solution was placed in the defect for 20 minutes. The area was then irrigated again with physiological saline solution. The scalp was then sutured. The remaining rats underwent the same local treatment with saline solution and served as controls.”
Is this a positive or negative results paper? Is there any explanation, other than the effect of fluoride ions, that could explain the results?
Little JW, Wilson JC, Bickley HC, Bickley C. Effects of parathyroid extract on the rupture strength of intact skin of the rat. J Dent Res 1977;56:46–47.
“Rats were injected with parathyroid extract (PTE) to search for possible effects on connective tissue of the skin. Rupture-strength analysis of skin samples showed a significant increase in strength of skin from PTE-treated rats. The explanation for this effect is not understood at present.”
From the Results:
“PTE-treated rats lost weight during the 3-day experimental period. The mean starting weight in grams for the PTE-TREATED groups was 149.75; for the vehicle-treated group, the mean was 148.20; and for the saline solution–treated group, the mean was 153.80. There were no significant differences among groups. At the time of death, the mean weight in grams for the PTE-treated group was 127.63; for the vehicle-treated group it was 162.50; and for the saline solution–treated group, the mean was 163.20. The mean weight at death of the PTE-treated group was significantly different from that of the two control groups . . . (ie, the vehicle-treated group and saline solution–treated group).”
Are there any problems with the interpretation of the increase in rupture strength as a specific effect of PTE?
Nacht M. A devitalizing technique for pulpotomy in primary molars. J Dent Children 1956;22:45–47.
“A review of literature revealed some interesting work done by several men with mummifying pastes. In 1929 Dr Hess, of the University of Zurich, reported negative results in a bacterial analysis of 62 pulps mummified with formaldehyde paste. Dr H. R. Foster of Oakland in 1936 describes a successful treatment using formocresol and paste. Again in 1939 Dr K. A. Easlick used the same treatment substituting paraformaldehyde. In the Handbook of Dental Practice—1948, Dr Charles Sweet describes a treatment using zinc oxide, cresolated formaldehyde and eugenol. Since the principle of mummification had been used by so many of these eminent men at various times, it was decided that this might be the answer to our problem.”
Identify the main form of argument used in this paragraph.
Brekke JH, Bresner M, Reitman MJ. Effect of surgical trauma and polylactate cubes and granules on the incidence of alveolar osteitis in mandibular third molar extraction wounds. J Can Dent Assoc 1986;4:315–319.
“The polylactic acid surgical dressing material, in either cube or granular form, substantially reduces the incidence of alveolar osteitis in healthy patients if all other principles of careful surgical technique are observed.”
Identify the technique used in this sentence that could deflect possible criticism of the major findings on the dressing material.
Cipes MH, Miraglia M, Gaulin-Kremer E. Habits, monitoring and reinforcement to eliminate thumbsucking. ASDC J Dent Child 1986;53:48–52.
“Although contingency contracting is a widely used strategy for involving parents in modifying their children’s behavior, this approach has apparently not been applied to the elimination of thumbsucking. . . . This paper explores monitoring and contingency contracting as alternative treatments for the persistent thumbsucker.”
Identify the logical technique used in constructing this approach and the investigational strategy involved in adopting this approach to the problem.
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?
Robinson PJ, Shapiro IM. Effect of diphosphonates on root resorption. J Dent Res 1966;55:166.
“These results indicate that under the conditions of this in vivo model system, diphosphonate does not retard the rate of root resorption. In addition, 1.0% pyrophosphate or 2% sodium fluoride are no more effective than physiological saline in inhibiting root resorption.”
Are these positive or negative results? What questions would you want answered when you read the paper?
Grenby TH, Desai T. A trial of lactitol in sweets and its effects on human dental plaque. Br Dent J 1988;164:383–387.
“Thirty subjects aged 18–20 years ate boiled sweets made with either sucrose or lactitol in addition to their normal diet over a 3-day experimental period and ceased all oral hygiene. Plaque accumulating on the teeth over the 3 days was assessed by three different methods, all of which showed lower values on the lactitol than on the sucrose sweets (P < 0.005 by the photographic method; P = 0.025 by the gravimetric method). Plaque collected from the lactitol-sweets group contained less soluble carbohydrate, glucose and sucrose, but was relatively higher in protein, calcium and phosphorous, than that from the sucrose-sweets group. There were unfavorable reactions to the texture and gastric effects of the lactitol sweets. . . .”
Materials and Methods:
“Sweets: These were the popular mint-humbug type, black-and-white striped boiled sweets, weighing approximately 3 g. The conventional sweets were made from a blend of sucrose and glucose syrup, which after boiling, contained 90% sucrose and 10% glucose. The experimental sweets contained 100% lactitol by weight, with additional sweetening by acesulfam-K. They were supplied in 4 oz (113 g) packs, which were identified by the experimental subjects according to color-coding only, not by composition or sweetening agent.”
Are there any alternative hypotheses to explain these data?
Kawazoe Y, Kotani H, Hamada T, Yamada S. Effect of occlusal splints on the electromyographic activities of masseter muscles during maximum clenching in patients with myofacial-pain-dysfunction syndrome. J Prosthet Dent 1980;43:578–580.
“If the elimination of occlusal interferences causes a decrease in the degree of tactile afferent impulses from periodontal receptors, the masseter muscle activity during maximum clenching with the splint should be reduced more than without a splint (intracuspal clenching) in patients with MPD syndrome having occlusal interferences.”
Identify the form of the deductive argument used and, if relevant, any additional premises that might be added to make the argument valid.
Eggleston DW. The interrelationship of stress and degenerative diseases. J Prosthet Dent 1980;44:541–544.
“If dental plaque were the only etiologic factor for caries and periodontal disease then all people with dental plaque would have these diseases. Such is not the case. Primitive humans on their natural diet have the lowest incidence of dental caries and periodontal disease even though they have no devices for removal of plaque.”
Identify the form of deductive argument used here and any additional rhetorical technique that contributes to the force of the argument.
Following up on the argument on chalones presented in chapter 5: Iversen OH. Comments on chalones and cancer. Mech Ageing Dev 1980;12:211–212.
“The correct syllogism is:
Chalones cause proliferation decay and thus tumor regression.
Tumor regression is most often not followed by cure in human cancer cases.
Ergo: Chalones will most often not cure cancer.”
Is this syllogism valid?
Sussman MI. Tooth reimplantation when it follows unintentional evulsion utilizing synthetic bone. Oral Health 1986;76:29.
“Since all 32 teeth were present, it was decided to attempt to save this tooth via periodontal surgery.”
Comment on the logic used in this sentence.
Kontturi-Närhi V, Markkanen S, Markkanen H. Effects of airpolishing on dental plaque removal and hard tissues as evaluated by scanning electron microscopy. J Periodontol 1990;61:334–338.
In this paper, the following scale was described.
“The condition of enamel surface was classified into three groups on the basis of photographs.
- No abrasion: Smooth normal enamel surface.
- Mild abrasion: Few micropits or prism ends (ameloblastic pits) visible between perikymata lines.
- Severe abrasion: Distinct perikymata lines with many prism ends and/or micropits visible on the whole surface occasional fracturing of perikymata edge.”
Discuss this measurement and indicate the type of statistical test that would be used to compare surfaces before and after airpolishing.
Henderson CW, Schwartz RS, Herbold ET, Mayhew RB. Evaluation of the barrier system, an infection control system for the dental laboratory. J Prosthet Dent 1987;58:517–521.
“On that particular day a different technician was used and the results did not agree with the rest of the data…. If the results on that day were eliminated from the data, after the first cleansing there would be no positive cultures for sodium hypochlorite, and after the second cleansing only one positive culture. This would improve the results of 3.25% sodium hypochlorite.”
Identify the type of error alluded to by the author in this excerpt.
Meinig DA. Removable partial dentures without rests. J Prosthet Dent 1994;71:350–358.
“Very poor—could lose their remaining teeth in two to three years
Poor—could lose their remaining teeth in 3 to 5 years
Fair—could lose several teeth but not all of them
Good—probably will keep all of their teeth for their lifetime.”
Comment on the classification system for periodontal condition used in this study. Is this an operational definition?
Stach DJ, Cross-Poline GN, Newman SM, Tilliss TS. Effect of repeated sterilization and ultrasonic cleaning on curet blades. J Dent Hyg 1995;69:31–39.
“The blades pretreated with the anticorrosive and then autoclaved were the most difficult to evaluate via SEM photographs because the product itself appears to leave a visible residue on the blade surface.”
Identify the type of measurement problem experienced in this study.
Novak MJ, Polson AM, Adair SM. Tetracycline therapy in patients with early juvenile periodontitis. J Periodontol 1988;59:366–372.
“1. The distance from the cementoenamel junction (CEJ) to the alveolar bone crest. The CEJ was designated as that point where the outer edge of the crown intersected the outer edge of the dentin of the root. The alveolar bone crest for a specific tooth surface was defined as the most coronal point of bone adjacent to the tooth surface where the periodontal ligament space had a uniform width. If an oblique flaring of the periodontal ligament space occurred coronally, the alveolar crest was taken as the point immediately subjacent to the flare, where the ligament space still exhibited uniform width.”
Comment on this measurement. Does it meet Wilson’s criteria (see page 122)?
Murray ID, McCabe JF, Storer R. Abrasivity of denture cleaning pastes in vitro and in situ. Br Dent J 1986;16:137–141.
“The six-month abrasion scores . . . show a similar result to that recorded at one month except that differences between materials have diminished. This is due to the fact that the maximum possible abrasion score is 4 and a number of G and K dentures reached this value well before six months.”
Identify the experimental tactical problem that occurred in this study.
Triol CW, Mandanas BY, Juliano GF, Yraolo B, Cano-Arevalo M, Volpe AR. A clinical study of children comparing anticaries effect of two fluoride dentifrices. A 31-month study. Clin Prev Dent 1987; 9:22–24.
“A negative control dentrifice (nonfluoridated) was not used in this program, since the water supply was below [optimal] levels of fluoridation, and total abstention from fluoride was considered not to be good dental practice. ”
Comment on the use of controls in this study.
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. ”
|Parameter||Chlorhexidine gel||Placebo gel|
|P/A sequence (9)||1.03||1.11|
|All patients (20)||.93||1.22|
|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?
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.
Addy M, Moran J, Davies RM, Beak A, Lewis A. The effect of single morning and evening rinses of chlorhexidine on the development of tooth staining and plaque accumulation. J Periodontol 1982;9:134–140.
From the Materials and Methods:
“Verbal and written instructions were given at the commencement of each period. Thus, during the rinsing period subjects refrained from all forms of oral hygiene and excluded from their diet coffee, red wine and port. Each was provided with a supply of a branded tea in bags and re-quested to consume eight cups per day. An attempt to standardize the teas was made by suggesting that one bag should be placed in a cup of boiling water for 2 min. The resulting infusion was then sweetened to taste and all volunteers agreed to add milk.”
Identify the experiment tactic used in this study on tooth staining.