The Angle classification has prevailed over the last century as a simple, quantifiable method to test malocclusion prevalence within populations. However, what Angle defined as a “normal occlusion” should, in fact, be considered the “ideal” occlusion given the strict criteria he used in his classification. This ideal occlusion is rather uncommon and has driven researchers to disagree on how much deviation from the ideal should be accepted as normal [1].

According to the Angle classification, class III malocclusion is defined as the lower molar mesially positioned relative to the upper molar with no specifications in regards to the line of occlusion [1,2]. Nevertheless, as with all Angle’s classification of malocclusion, class III malocclusion comprises several skeletal and dental components that may differ from the concept of normality. For example, it can be characterized by presenting a mandibular skeletal protrusion (mandibular prognathism), a maxillary skeletal retrusion, a combination of both, or no anteroposterior skeletal imbalances [3].

Multiple studies have documented the prevalence of Angle class III malocclusion. However, there seems to be a wide range of prevalence rates reported, usually attributed to variation among samples [4-38]. For example, several studies have indicated that Asian races have a higher prevalence of Angle class III malocclusion than other races [4-10]. In some instances population data have shown conflicting reports, such as differing studies among Nigerian children reporting Angle class III malocclusion prevalence ranging from 1.2% (1993) up to 11.8% (2004) [11-13].

In spite of the continually increasing data on malocclusion prevalence, little has been done to consolidate this information in a comprehensive and critical way [14]. Further; to the best of our knowledge, there has not been a systematic analysis of the prevalence of Angle class III malocclusion among different populations. Meta-analysis is a systematic method that uses statistical techniques for combining results from different studies to obtain a quantitative estimate of the overall effect of a particular intervention or variable on a defined outcome; metaanalysis produces a stronger conclusion than can be provided by any individual study. Although no protocol has been enacted governing the methods of Angle class III malocclusion prevalence studies, a review and metaanalysis of the available literature will be helpful in establishing guidelines for future researchers.

The PubMed search returned 134 total articles, including 10 listed as review articles. ISI Web of Knowledge generated 52 total articles, 16 of which did not appear in the PubMed. The Cochrane search produced 2 articles.

Review of all articles produced 37 which were determined to be relevant to Angle class III malocclusion prevalence. A search of all references of these 37 articles produced an additional 42 articles that were also considered relevant. Applying the inclusion criteria for these 79 articles revealed 21 articles that were acceptable for the literature review. Two articles were excluded from the analysis because they reported the same population included in other articles (Figure 3).

The majority of articles analyzed data from African populations: Tanzania [13-15], Nigeria [10-12], Sudan [16], Senegal [17], and Kenya [18]. Four articles looked

at populations from Southeast Asia, including China [4, 5], Malaysia [7], and Singapore [8]. The articles from Singapore and Malaysia utilized a mix of Malaysian, Chinese, and Indian, which were analyzed separately in this study. Three articles reviewed populations from the Middle East: Egypt [19], Kuwait [20], and Turkey [21]. The remaining 3 articles analyzed Lithuanian [22], Italian [23], and Indian [24] populations.

The sample size of the populations ranged from 21 to 2329 and the prevalence of Angle class III malocclusion ranged from 0 to 26.67% (Table 1). The combined total sample size of all studies was 15,200 individuals, 1090 of whom exhibited Angle class III malocclusion, for an average prevalence of 7.04%.

Populations from Southeast Asian countries showed the highest Angle class III malocclusion prevalence rate

of 15.80%, based on 1874 individuals [4-8]. Middle Eastern nations had a mean prevalence of 10.18% out of 4127 individuals [19-21]. The European studies had an average prevalence rate 4.88% out of 1290 individuals [22,23]. The African data produced a prevalence rate of 4.59% out of 7017 individuals [10-17]. Indian populations had the lowest prevalence rate of 1.19% out of 1595 individuals [7,8,24].

The range of Angle class III malocclusion prevalence rates was between 1.22% and 19.72% among the African group [12,14]. Prevalence data varied most among Tanzanian populations, with prevalence rates of 1.81%, 5.23%, 8.00%, and 19.72% [13-15]. The prevalence rates were also variable among the Nigerian populations, with rates of 1.22%, 2.04%, and 11.79% reported [10-12].

The Southeast Asian group had a range of Angle class III malocclusion prevalence between 12.58% and 26.67% [7,8]. The Middle Eastern group showed a range of 9.48% and 11.38% [19,20]. The Indian group had a range of 0% [7] to 4.76% [8].

Meta-regression analysis showed no statistically significant association between prevalence rates and the method of assessment, age group and year of the study. However, much of the study-to-study variation (approximately 40%) could be explained by population when it was used as a parameter in the analysis. In fact, studyto-study variation dropped to 0.579 when population was taken into account.

Using the formula log(odds) = b₀ + (study)^δ, where b₀ is the regression constant and δ is study-to-study variation expressed as an odds ratio on the logit scale (in this case, δ = 0.979), we were able calculate the increase in the odds of malocclusion for a study at 1 SD (standard deviation) above the mean. This can be expressed as e^0.979 = 2.66, where e is the exponent constant. In other words, at 1 SD above the mean, the odds of malocclusion are 2.66 times greater than at the mean (Figures 1 and 2).

Analysis of the reported prevalence of class III malocclusion requires scrutiny of the methods employed in

collection of the data. Of particular interest is the subject of inclusion criteria. The quality of the inclusion criteria ultimately affects the reliability of the prevalence data.

The selection criteria for this literature search were chosen to minimize the number of confounding variables present in class III malocclusion prevalence data. Individuals under 11 years old were excluded from this study as younger children have a greater tendency for Angle class III malocclusion as compared to older children with more erupted permanent teeth. This is most likely explained by the presence of pseudo class III malocclusion, which is a habitual established crossbite of all anterior teeth, without any skeletal discrepancy, resulting from functional forward positioning of the mandible on closure [39]. Furthermore, a mesial step predisposition in the primary dentition is not a good predictor of class III malocclusion in the permanent dentition [25].

The large variation in Angle class III malocclusion prevalence rates in this study suggests a high level of variability across geographic regions and races. Chinese and Malaysian groups showed a much higher mean prevalence rate than other racial groups: 15.69% and 16.59%, respectively [4-8]. This is consistent with previous reports of higher rates of Angle class III malocclusion among Asian populations [26,27].

Angle class III malocclusion rates among the three Middle Eastern groups in this study are fairly similar. However, previous studies indicated a wide range of rates from 1.3% in Israeli Arabs [28] to 15.2% in Iranians [28]. Additionally, many different rates appear for Iranians: 2.1%, 7.8%, 9.2%, and 15.2% [29-32]. A study of Turks [33] in 2004 showed a prevalence rate of 11.5%, similar to the 10.30% reported in the 2007 study [21] included in this review. However, a 1969 study of Egyptians [34] showed a rate of 4%, which is not concordant with the 11.38% rate reported for the Egyptian population in this study [19]. Agreement of previously reported Angle class III prevalence data appears to be haphazard at best among Middle Eastern populations. Furthermore, major discrepancies appear to exist among populations within individual countries.

Most of the African populations showed a relatively low prevalence, although two populations each showed a much higher rate than the rest [10,14]. Furthermore, the range of rates among the Tanzanian populations varied considerably [13-15]. Previously studies from Kenya, Tanzania, and Nigeria also show a large level of variation in prevalence rates (between 1% and 16.8%) [35,36]. This suggests a large amount of local variability within and among African countries.

The lack of European populations in this study makes it difficult to draw any generalization about prevalence rates of Angle class III malocclusion. Recent studies excluded by the selection criteria show a range of 2% to 6% among European countries [37,38]. This suggests that Europeans have a relatively lower prevalence rate than other populations.

With respect to the prevalence of class III malocclusion in the Americas, two publications were identified. The first study, reported a prevalence of class III malocclusion of 9.1% among Mexican-American adolescents living in Los Angeles area [40]. This study was excluded as it evaluated a convenience sample. Data from the third National Health and Nutrition Examination Survey (NHANES III) showed that in the United States, only a fraction of a percentage of all adults presented class III. This type of malocclusion was more prevalent in Mexican-Americans and African-Americans compared to Whites [41]. Because this study did not distinguish between subjects that had previous orthodontic treatment, it was also excluded from the final selection.

Defining a population can be a difficult task. We found that most studies analyze a specific city or region of a country. Such a sampling may or may not represent the country as a whole. Genetic predisposition for Angle class III malocclusions may be present in certain groups, but these populations do not necessarily fall into neat geographic areas. Many countries, such as Singapore, represent a conglomeration of individuals from many different nationalities and races. Other countries, like Nigeria and China, may have numerous local ethnic groups that are divided by language, religious belief, and cultural practices, minimizing contact between groups. Although it is tempting to generalize the national status of Angle class III malocclusion in a particular country based on a few local population studies, a more representative sampling would be needed to draw more accurate conclusions.

Scoring malocclusions is generally a subjective decision based on the training and opinions of the clinician or researcher. Additionally, many researchers may be reporting different rates of malocclusion prevalence simply because they used different methods to measure the malocclusion. Ideally, a universal system for scoring Angle class III malocclusions should be employed to better standardize epidemiological studies in this area. Furthermore, researchers should be more careful in their selection criteria for their populations to eliminate any confounding variables.

It may ultimately be impossible to accurately sample every population for a general prevalence rate from both a logistical and theoretical standpoint. Populations can always be broken down into smaller groups which may or may not represent the population as a whole. However, given these limitations, it is important to remember the need for data of Angle class III malocclusion prevalence. Angle class III malocclusions can be both socially and functionally handicapping, and identifying populations that require greater attention may help clinicians and politicians in deciding how to best address helping them find treatment.

• Prevalence of Angle class III malocclusion varies greatly among and within populations.

• Chinese and Malaysian populations show a relatively higher prevalence of Angle class III malocclusion while Indian populations show a relatively lower prevalence, as compared to other races.

• A more standardized protocol for reporting malocclusion prevalence data would be helpful in drawing meaningful comparisons across geographic and racial groups in the future.