E. Preston Hicks

Reliability of the Bolton tooth-size analysis when applied to crowded dentitions

The Bolton tooth-size analysis is widely taught and used in orthodontics. However, its reliability has not been documented. The purpose of this study was to evaluate the reliability of the analysis when performed with needle-pointed dividers and a Boley gauge. Four clinicians measured the teeth on 15 sets of casts with two instruments at two sessions. The measurements were used to calculate tooth-size excess. To evaluate the measurement error, the difference between the two analyses made by the same investigator on the same set of casts was calculated. More of the same-investigator analyses were significantly correlated when the Boley gauge was used than when the needle-pointed dividers were used. Between-investigator analyses revealed significant correlations for each measurement session with both instruments. Every investigator was found to have at least one measurement error for each analysis and with each instrument that was as large as a clinically significant result of a Bolton analysis. The results of this study demonstrate that clinically significant measurement errors can occur when the Bolton tooth-size analysis is performed on casts with at least 3 mm of crowding. The Boley gauge demonstrated a higher frequency of significantly correlated repeated measures and thus may be somewhat more reliable for this analysis than the needle-pointed dividers.

Third molar management: A case against routine removal in adolescent and young adult orthodontic patients

In the nearly two decades since the National Institutes of Health conference, controversy and uncertainty have continued with respect to the diagnosis and treatment of impacted, nondiseased third molars in adolescents and young adults. Articles published over the past 10 years have studied the issue from the vantage point of risk management. Those who favor prophylactic removal justify this action on three premises: 1. All impacted third molars are potentially pathologic; therefore, prophylactic removal reduces or eliminates risk of future disease. 2. The presence of third molars can cause late crowding. 3. Removal during adolescence and young adulthood reduces risks of operative and postoperative complications compared with older patients. Those who favor conservative management offer three counter arguments: 1. Although impacted third molars do pose a risk of a pathologic condition, the risk is relatively small in comparison with the risks of operative and postoperative complications and the costs of unnecessary removal. 2. Although some investigators have shown a statistical association of third molars and late anterior crowding, the association is not strong enough to allow prediction of patients at risk. This is due principally to the high degree of individual variability, suggesting that many other factors interact in the development of postadolescent crowding. 3. Although studies have shown that morbidity is reduced when impacted, nondiseased third molars are removed during adolescence or young adulthood, the cost-risk-benefit data do not justify routine removal. Proponents of prophylactic removal argue that the benefits outweigh the risks. Proponents of conservative management argue that the scientific evidence is inconclusive in support of prophylactic removal. Unfortunately, much of the clinical research has been flawed. This has led to contradictory interpretations that have not fully clarified the relative risks and benefits of early intervention. Untrustworthy data have served only to fuel the debate and controversy concerning proper protocols. However, careful analyses of the published research show that routine removal of impacted or unerupted, disease-free third molars cannot be justified. A case-by-case management protocol that requires monitoring development represents the consensus of most researchers in this field.

Heuristic reasoning and cognitive biases: Are they hindrances to judgments and decision making in orthodontics?

Studies show that our brains use 2 modes of reasoning: heuristic (intuitive, automatic, implicit processing) and analytic (deliberate, rule-based, explicit processing). The use of intuition often dominates problem solving when innovative, creative thinking is required. Under conditions of uncertainty, we default to an even greater reliance on the heuristic processing. In health care settings and other such environments of increased importance, this mode becomes problematic. Since choice heuristics are quickly constructed from fragments of memory, they are often biased by prior evaluations of and preferences for the alternatives being considered. Therefore, a rigorous and systematic decision process notwithstanding, clinical judgments under uncertainty are often flawed by a number of unwitting biases. Clinical orthodontics is as vulnerable to this fundamental failing in the decision-making process as any other health care discipline. Several of the more common cognitive biases relevant to clinical orthodontics are discussed in this article. By raising awareness of these sources of cognitive errors in our clinical decision making, our intent was to equip the clinician to take corrective action to avoid them. Our secondary goal was to expose this important area of empirical research and encourage those with expertise in the cognitive sciences to explore, through further research, the possible relevance and impact of cognitive heuristics and biases on the accuracy of orthodontic judgments and decision making.

The essential work of fracture of thermoplastic orthodontic retainer materials.

OBJECTIVE To investigate whether oral cleansing agents affect the essential work of fracture (EWF) and plastic work of fracture (PWF) for two types of orthodontic thermoplastic retainer materials. MATERIALS AND METHODS Polyethylene-terephthalate-glycol (PETG; Tru-Tain Splint) and polypropylene/ethylene-propylene rubber (PP-EPR) blend (Essix-C+) sheets were compared. For each material, six sets of 25 sheets were thermoformed into double-edge-notched-tension specimens; subsets of five specimens were formed with internotch distances (L) equal to 6, 8, 10, 12, or 14 mm, respectively. Sets were stored (160 hours, 25 degrees C) in air (DRY), distilled water (DW), Original Listerine (LIS), mint Crest ProHealth (CPH), 3% hydrogen peroxide (HP), or Polident solution (POL). Specimens were fractured in tension at 2.54 mm/min. Areas under load-elongation curves were measured to determine total work of fracture (W(f)). Linear regressions (W(f) vs L [n = 25]) yielded intercepts (EWF) and slopes (PWF). Ninety-five percent confidence intervals were used to evaluate differences in EWF and PWF estimates. RESULTS PP-EPR blends showed higher EWFs after storage in HP vs storage in DW. PP-EPR blend showed higher EWFs after storage in CPH vs PETG. After HP storage, PP-EPR exhibited lower PWFs than with any other storage conditions. PP-EPR exhibited higher PWFs than PETG after storage in DRY, DW, and LIS. CONCLUSIONS Compared with DW, none of the cleansers decreased the energy to initiate fracture. With one exception, no cleanser decreased the energy to continue plastic fracture extension. In PP-EPR blend, increased resistance to fracture initiation was observed with CPH and HP, yet, surprisingly, HP decreased resistance to plastic fracture growth.