Voleibol y boxeo

3.1. Specific Gaps Existing in Previous Studies on RCT Quality and Post-operative AP

Methodological flaws: First, for measurements of exposures, some studies simply scored RCT quality as “good / poor” or “adequate / inadequate”, according to a self- determined radiographic set of criteria (Ray and Trope, 1995; Siqueira et al., 2005). For measurements of outcomes, there is the lack of a clear definition for the success/failure of endodontic treatment; little has been done to distinguish outcomes that should be highlighted during different lengths of follow-up. Second, many studies did not adjust for important confounding factors when looking at the association of RCT quality and AP, e.g., person- level demographic factors such as socioeconomic status, BMI, smoking history, hypertension and diabetes were not accounted for. Third, in analyses of RCF teeth, correlations among teeth within the same individual are often ignored in the modeling process. Many previous studies simply lumped together all treated teeth into a group without regard to number of teeth contributed per individual, and such analyses that ignore the correlation structure may lead to incorrect inferences. Others randomly selected one observation per person for analysis, resulting in inefficient estimation because not all data were used (Kleinbaum and Klein, 2002; Chuang et al., 2002).

Limited populations studied: Most studies involved European populations. A recent review (Friedman, 2002) identified 11 observational cohort studies of at least mid-range level of evidence and only one study in the US was included (Trope et al., 1999). All of the previous studies conducted in the US used either highly selective patients from dental clinics of teaching hospitals (Ray and Trope, 1995; Buckley and Spangberg, 1995; Trope et al.,

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1999; Chugal et al., 2001; Chugal et al., 2003) or subjects from dental insurance programs (Salehrabi and Rotstein, 2004). None of them used a population-based sample.

Suboptimal study design: Most previous studies have cross-sectional designs, which thus reduce their ability to make inferences about the prognosis of endodontically treated teeth. Moreover, such studies are usually performed on selected patients treated by skilled or supervised specialists; they have in essence been case reports with groups of dental patients. Therefore, these studies demonstrated the potential outcomes of RCF teeth in dental institutions or specialist clinics rather than their realistic outcomes in the general population. Although some studies have longitudinal designs, they only included cases observed for about 6-12 months. Such short observation time does not reflect the complete change in outcomes of RCF teeth, and it is impossible to determine whether a periapical lesion is healing or expanding.

Difficult comparisons of study results: Previous studies differ from each other in material composition, treatment procedures and methodology. Due to their varying range of factors and lack of standardization, it is somewhat difficult to make direct comparisons and interpret the results.

In summary, further longitudinal epidemiological studies on North American populations are needed to assess the prevalence and incidence of post-operative AP, and its associations with RCT quality, after adjusting for potential confounding variables.

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In contrast with the research on post-operative AP related to RCT, research on tooth loss is relatively sparse. Besides the above gaps regarding methodology, study populations, study design and study results, there are a few other specific issues to consider.

Insufficient observation time: The majority of longitudinal studies on tooth loss followed up a group of dental patients only for a relatively short time period, for instance, at most 9-10 years. Interpretation of such studies is limited by insufficient follow-up time. A longer follow-up period is desirable in studies of tooth loss.

Failure to compare loss of RCF teeth and non-RCF teeth in the same study: Although attempts have been made to determine potential predictors for loss of RCF teeth, these studies usually focused on a group of RCF teeth only, and did not include non-RCF teeth. Thus they were unable to compare the survival status between teeth with and without RCT.

Failure to assess AP as a separate cause: AP has often been combined with caries as related to tooth loss, and little has been done to evaluate the role of AP as a separate reason. It would be interesting to assess how both RCT and AP would affect tooth survival in the same study.

Statistical approach: Some studies simply performed a logistic regression analysis with a dichotomous dependent variable: tooth extracted or not extracted. This analysis ignores information on the timing of tooth loss, which would provide important information (Weiger et al., 1998). Some studies simply discarded the information on teeth that were not extracted during the follow-up period, which could only work well if the proportion of such “censored” teeth is small. In short, conventional methods are inefficient for dealing with

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survival data. By contrast, survival analysis can accommodate these characteristics of survival data and should be used in the research of tooth loss.

In summary, studies of tooth loss should be designed in such a way that sufficient follow-up time is available for most teeth, and a proper analytical approach should be used to enable correct inferences of estimates.

CHAPTER III. RESEARCH QUESTIONS AND