10 Dental Anthropology 2018 │ Volume 31 │ Issue 01 Technical Note: The Definition of New Dental Morphological Variants Related to Malocclusion Marin A. Pilloud 1,* 1 Department of Anthropology, University of Nevada, Reno, NV 89557 The Arizona State University Dental Anthropology System (ASUDAS) has been the standard in defin- ing morphological variants of the teeth for over 25 years (Turner et al., 1991). This publication outlines 36 traits of the dentition as well as rocker jaw, and mandibular and palatine tori. This original work is based on a rich literature defining morphological variation of the teeth (e.g., Dahlberg ,1956; Haniha- ra ,1961; Harris and Bailit, 1980; Hrdlička ,1921; Morris, 1970; Morris et al., 1978; Scott, 1977; Scott, 1980; Tomes, 1914; Turner ,1970; Turner, 1971). However, since its publication, there have only been a handful of additional traits defined, includ- ing the canine mesial ridge (Irish and Morris, 1996), maxillary premolar accessory ridges (Burnett et al., 2010), deciduous morphological var- iants (Sciulli, 1998), and molar crenulations (Pilloud et al., 2017). There is room to expand our current under- standing of dental morphological variation and to create definitions of additional traits. This paper broadens the current suite of traits and defines var- iants that may be of interest in bioarchaeological and forensic studies of dental variation that sur- round issues of malocclusion: canine/midline dia- stema, dental crowding, and maxillary and man- dibular overjet. While these variants are not new to those working with teeth or the human skeleton (e.g., Alt and Türp, 1998; Lasker, 1950), a working definition and scoring system has not yet been cre- ated within dental anthropology, with the excep- tion of the midline diastema. Each trait is discussed below and a definition and scoring system is pro- vided. Diastema While the midline diastema has been defined in the new volumes by Scott and Irish (2017) and Edgar (2017), their definitions differ as to what exactly constitutes a diastema, they do not offer grades of expression, nor do they incorporate a canine dia- stema. The definition presented here is based on the definitions provided in these two works as well as several other preceding studies. Further, the incorporation of a canine diastema is included. Therefore, diastemata can occur in the maxillary midline or on either side of the mandibular or max- illary canine. The proposed scoring system incor- porates both types of diastemata; however, they are discussed separately below. Midline maxillary diastema Midline maxillary diastemata have been reported on extensively in the clinical literature (e.g., Chu et al., 2011; Kamath and Arun, 2016; Shashua and Årtun, 1999). Anthropological research on midline maxillary diastemata has identified population, sex, and age differences in the occurrence of this trait (Edgar, 2007; Horowitz, 1970; Lavelle, 1970; McVay and Latta, 1984; Nainar and Gnanasundaram, 1989; Richardson et al., 1973). This discussion focuses on the adult dentition, as midline diastemata can commonly be found in pri- mary and mixed dentition, and can be lost as the ABSTRACT Since the codification of the Arizona State University Dental Anthropology System over 25 years ago, few additional morphological traits have been defined. This work serves to expand the cur- rent suite of traits currently collected by biological anthropologists. These traits surround various issues of malocclusion and follow clinical definitions of these traits as well as incorporate observed population variation in character states. These traits include issues of spacing (i.e., diastema and crowding) as well as mandibular and maxillary occlusion (i.e., overbite, underbite). A discussion of the etiology and utili- ty of these traits in bioarchaeological and forensic anthropological research is also given. *Correspondence to: Dr. Marin A Pilloud, Department of Anthropology, University of Nevada, Reno mpilloud@unr.edu Keywords: dental crowding, midline diastema, canine diastema, overbite, underbite, overjet 11 Dental Anthropology 2018 │ Volume 31 │ Issue 01 permanent teeth erupt (Gkantidis et al., 2008). There are many definitions of diastemata that incorpo- rate various space sizes and grades of expression. In a joint publication by the World Health Organization (WHO) and the International Dental Federation (IDF), a midline diastemata is defined as a space of more than 2.0 mm (Bezroukov et al., 1979). In their new volume on den- tal morphology, Scott and Irish (2017) define the midline maxillary diastema as any space greater than 0.5 mm (following Lavelle, 1970), and see no need to further de- fine the trait beyond present or absent (based on Irish, 1993). Edgar (2017) also defines midline diastema; how- ever, in her scoring system, 1.0 mm of space is required for presence. None of the current scoring systems allow for different grades of expression and only focus on presence/absence. However, in their study of nearly 6,000 radiographs, McVay and Latta (1984) found a statistically significant difference in midline diastema size between their sample groups of White, Black, and “Oriental” (sizes defined as <0.49, 0.5-1.49, >1.5 mm). A study of 759 American Black and White children also found there to be size differences, with 19% of Blacks and 10% of Whites having a midline diastema over 2 mm (Horowitz, 1970). Differences in size of midline diastemata were also reported among a sample in South India (Nainar and Gnanasundaram, 1989). It may therefore be useful to separate out grades of expres- sion in global studies of diastema. Canine diastema Canine diastemata can occur in the maxilla (sometimes referred to as premaxillary diastema) between the maxil- lary canine and the lateral incisor (Schultz, 1948), or be- tween the canine and third premolar (Mongtagu, 1989). Canine diastemata also occur on the mandibular canine, again on either side of the tooth. Lavelle’s (1970) study of diastemata among 656 individuals found the majority of diastemata were between the maxillary third premolar and canine and the maxillary second incisor and canine. A study by Keene (1963) evaluating midline and canine diastemata (>0.5 mm) among 183 white males found the most common diastema location was between the maxil- lary canine and the third premolar (even more common than midline diastema). Keene also found that the majori- ty of diastemata were between 1 and 3 mm in size. These studies highlight the potential role of canine diastemata in defining human population variation. Definition and Scoring System: Diastema In this proposed system, a diastema is defined as any gap between the teeth with a separation of 0.5 mm or more. Diastemata can be scored in three locations: 1) maxillary central incisors, 2) maxillary canines, and 3) mandibular canines (Figure 1). Among the canines, the separation can occur on either side, between the canine and the lateral incisor, or the canine and the third premolar. The current scoring system does not differentiate between the two locations. 0 – absent (< 0.50 mm) 1 – low-grade diastema 0.5-1.49 mm 2 – high-grade diastema ≥1.5 mm Affected teeth: maxillary central incisors, mandibular ca- nine, maxillary canine Dental Crowding and Occlusion In this discussion, it is important to define occlusion and note the ideal model of occlusion to identify deviations from normal (i.e., malocclusions). Occlusion “relates to the arrangement of maxillary and mandibular teeth and to the way in which teeth contact” (Türp et al., 2008:446). An ideal form of occlusion occurs when the “skeletal ba- ses of maxilla and mandible are of the correct size relative to each other and the teeth [are] in correct relationship in all three planes of space at rest” (Hassan and Rahimah, 2007:3). The three planes being anteroposterior, vertical, and transverse. Therefore, malocclusion would be any deviation from this norm to include malpositioning of teeth within the dental arcade (i.e., displacement or rota- tion.), or a disassociation between the dental arches in any of the three planes of direction (Proffit, 1986). While there are many references regarding the treat- ment of malocclusion in the clinical literature (Angle, 1907; Dahiya et al., 2017; Singhal et al., 2015), there is little consensus on how it is quantified or fully defined (Tang and Wei., 1993). The earliest and still commonly used classification of malocclusion is that offered by Angle (1899). In this work, three types of malocclusion are de- scribed, all in relation to the position of the upper and lower first molar. Class I describes normal positions of the molars, and can be further subdivided into Class I - normal and Class I - malocclusion. Class I - malocclusion Figure 1. Individual with a midline maxillary diaste- ma (score of 1), and a canine diastema (score of 1) (photo courtesy of G. Richard Scott). 12 Dental Anthropology 2018 │ Volume 31 │ Issue 01 includes crowding, spacing, and rotations of the anterior teeth, even though the molars may be in normal alignment (Silva and Kang, 2001). Class II is a retrusion of the jaw (i.e., overbite) in which the mandibular teeth occlude pos- terior to normal (i.e., lower first molar occludes posterior to the upper first molar). Class III is a protrusion of the lower jaw (i.e., underbite) in which the mandibular teeth occlude mesial to normal, typically by the length of one premolar, but may be a larger distance in severe cases. Since 1899, various other methods have been proposed to quantify malocclusion (e.g., Baume and Maréchaux, 1974; Björk et al., 1964; Little, 1975). In the late 1960’s, re- search out of the University of Toronto developed the Or- thodontic Treatment Priority Index to quantify various types of malocclusion (Grainger, 1967). In the late 1970’s, the World Health Organization (WHO) and the Interna- tional Dental Federation (Fédération Dentaire Internatio- nale– FDI, now called the World Dental Federation) de- vised a simple method to record malocclusion. This sys- tem includes crowding and diastemata as “space condi- tions”. In this system, crowding is defined as present when > 2 mm of space deficiency is observed between the size of the dental arch and the anterior teeth (i.e., incisors, canine, and both premolars). Deviations from normal oc- clusion in this system include maxillary and mandibular overjets, openbites, and midline shifts, among others (Bezroukov et al., 1979). As malocclusion can include crowding and malposition of the jaws, the following definitions of malocclusion are offered, generally following the definitions of Angle (1899) and those of the WHO/FDI (Bezroukov et al., 1979). Definition and Scoring System: Dental Crowding Dental crowding (Angle’s Type I – malocclusion) is de- fined as the presence of any tooth that deviates from ideal alignment through either rotation or displacement. The system proposed here is based on that described by Van Kirk and Pennell (1959). Rotation and displacement can be categorized into two types: major or minor. Minor rotation is under 45o, where major rotation is defined as 45o or greater from ideal alignment. Minor displacement is under 1.5 mm, and major displacement is 1.5 mm or greater from ideal alignment either labially or lingually (Figure 2). In the original system outlined in Van Kirk and Pennell (1959), each tooth is scored and scores are summed to as- sess the level of malocclusion. This system could be cum- Figure 2. Scoring of rotation and displacement as part of dental crowding for lateral teeth. Based on Van Kirk and Pennell (1959). 13 Dental Anthropology 2018 │ Volume 31 │ Issue 01 bersome in the work of the biological anthropologist and could be impossible when faced with teeth that may be missing ante- or post-mortem. Therefore, the system below is proposed for use in forensic anthropo- logical or bioarchaeological settings. Crowding is subdivided into incisal and (first and second incisors) and lateral (canine and premolars). The molars are not considered in this system. If all teeth in each class are not present, the level of crowd- ing cannot be scored; allowing for some, but not a lot of missing teeth. If bilateral winging is observed and no other crowding is present in the incisal region, crowding should not be scored (i.e., leave the entry blank for crowding and score winging in its place to avoid redundant data). Incisal (first and second incisor) 0 – absent – both teeth are in ideal alignment (no ro- tation and no displacement) 1 – slight – one or both teeth show slight deviations from ideal alignment (rotation between 1o and 44o and/or displacement between 0.1 and 1.4 mm) 2 – moderate – at least one tooth shows major malalignment (rotation ≥ 45o and/or displace- ment ≥ 1.5 mm), the other may be in ideal align- ment or show slight deviation 3 – severe – both teeth show major malalignment (rotation ≥ 45o and/or displacement ≥ 1.5 mm) Affected areas: mandibular and maxillary incisors Lateral (canine and third and fourth premolar) 0 – absent – all three teeth are in ideal alignment (no rotation and no displacement) 1 – slight – one or all three teeth show slight devia- tions from ideal alignment (rotation between 1o and 44o and/or displacement between 0.1 and 1.4 mm) 2 – moderate – at least one tooth shows major malalignment (rotation ≥ 45o and/or displace- ment ≥ 1.5 mm), the others may be in ideal align- ment or show slight deviation 3 – severe – all three teeth show major malalignment (rotation ≥ 45o and/or displacement ≥ 1.5 mm) Affected areas: mandibular and maxillary canines and premolars To illustrate this scoring method, two worked exam- ples are presented. In Figure 3, there is a set of man- dibular teeth that illustrate crowding and can be scored as follows: Incisal Right and Left – 0 – there is no rotation or dis- placement of teeth on the right or left sides Lateral Left – 2 – the fourth premolar shows slight rotation (< 45o) but shows major displacement (≥ 1.5 mm) Lateral Right – 2 – the right canine shows minor rota- tion (< 45o) and the third premolar shows major displacement (≥1.5 mm) Figure 4 illustrates a set of maxillary teeth with crowd- ing that can be scored as follows: Incisal Right – 2 – the right second incisor shows ma- jor displacement (≥1.5 mm) and the central incisor shows minor rotation (< 45o) Incisal Left – 2 – the left second incisor shows major displacement (≥1.5 mm) and the central incisor shows minor rotation (<45o) Lateral Left and Right – 0 – there is no rotation or dis- placement of teeth on either side Figure 3. Mandibular teeth that illustrate crowding (photo courtesy of G. Richard Scott and Christy G. Turner, II). Figure 4. Maxillary teeth that illustrate crowding (photo courtesy of G. Richard Scott and Christy G. Turner, II). 14 Dental Anthropology 2018 │ Volume 31 │ Issue 01 Discussion Diastema There may be a number of causes for a midline dia- stema, to include a large superior labial frenum, su- pernumerary teeth, missing teeth, peg teeth, digit sucking, abnormal arch size, muscular imbalances in the oral region (Huang and Creath, 1995), ossifying fibroma of the palate (Kamath and Arun, 2016), or even a tongue piercing (Tabbaa et al., 2010). Howev- er, genetics may also play a role. A familial study on the maxillary midline diastema reported the herita- bility to be 0.32 ± 0.14 among a white sample and 0.04 ±0.16 in a black sample. The researchers con- cluded that among the white sample there was a stronger genetic basis for midline diastema and that the environment could be playing a larger role in trait expression among the black sample (Gass et al., 2003). While this study reports low heritabilities, many studies have documented population differ- ences in the expression of the trait (Huang and Creath, 1995; Lavelle, 1970; McVay and Latta, 1984; Scott and Irish, 2017), which suggests the utility of the trait in bioarchaeology and forensic anthropolo- gy. Further, as several studies have illustrated prev- alence rates of canine diastemata in different popula- tions (e.g., Keene, 1963), this trait may have value in biological anthropological studies as well. Malocclusion Dental crowding and malocclusion are often dis- cussed in relation to the adoption of agriculture and the introduction of soft foods as part of the mastica- tory-functional hypothesis (Carlson and Van Ger- ven, 1977; Corruccini, 1984; Corruccini et al., 1983; Larsen, 2015). In this discussion, malocclusion en- compasses two distinct features: malalignment of the teeth (i.e., crowding) and malalignment of the jaws (i.e., overbite and underbite). While these are related conditions of occlusion, they may have sepa- rate etiologies. While over- and under-bites have not been traditionally recorded in bioarchaeological or forensic anthropological research, their heritabil- ity is well documented in the clinical literature (Chen, 2006; Lee and Goose, 1982; Lundström, 1948; Walker, 1951). There is, however, considerable debate in the clin- ical and anthropological literature as to the exact cause of dental crowding. Mossey (1999) argues that while the phenotype is ultimately the result of the environment and genes working together, there is evidence to suggest a strong genetic component to various traits of malocclusion. While there is a docu- mented increase in crowding over human evolution, it is generally the result of a disproportion of the dental arches and the size of the teeth (Proffit, 1986), both of which are largely the result of genes. In fact, a study of tooth size of “North American Cauca- sians” found that individuals with larger teeth also had more evidence of crowding (Doris et al., 1981). Further, work on Amazonian populations by Nor- mando and colleagues (Normando et al., 2013; Nor- mando et al., 2011) has argued for a strong genetic component to crowding and malocclusions; alt- hough, differing opinions exist (see McKeever, 2012). Hughes and colleagues (2001) also document- ed high heritabilities of spacing (crowding and dia- stemata) among Australian children. In a clinical setting, the role of external forces such as resting or chewing pressures (Proffit, 1986), and various skeletal, soft tissue, dento-alveolar fac- tors as well as habits (i.e., thumb or finger sucking) (McDonald and Ireland, 1998) have a documented influence on dental development and malocclusion. While many of these factors that lead to crowding (e.g., size of teeth, supernumerary teeth) may be un- der genetic control, it is difficult to point to one ge- netic cause for crowding. As such, many studies have highlighted the role of environment in dental crowding and are largely dismissive of a genetic contribution (Harris and Johnson, 1991; Harris and Smith, 1982; King et al., 1993). Proffit (1986), on the other hand, combines both genetics and environ- ment by arguing that slight crowding is likely relat- ed to genetic factors, whereas in cases of severe mal- occlusion, external factors play a larger role. While the etiology of dental crowding may not be clear, its occurrence may still be important to study in terms of understanding changes in stresses upon the masticatory system, dental reduction, and chang- es in diet in the evolutionary past of humans. Until now there has not been a way to quantify or define this trait that could be applicable outside of a clinical setting. The system proposed herein to record den- tal crowding can be systematically recorded in ar- chaeological and medicolegal settings to evaluate questions of anthropological interest. Finally, these traits of malocclusion (crowding and maxillary and mandibular overjet) may have relevance as traits that are heritable and could have importance in biological distance analyses as well as studies in the estimation of ancestry within forensic anthropology. A recent study on dental morpholog- ical variation collected data on dental crowding among modern samples and found that dental crowding could successfully differentiate popula- tions (Maier, 2017). Moreover, there has already been a substantial amount of work exploring popu- lation variation in terms of the three types of maloc- clusion as defined by Angle: Class I normal, Class I malocclusion (anterior crowding), Class II malocclu- sion (maxillary overjet), and Class III malocclusion (mandibular overjet). Table 1 outlines the various 15 Dental Anthropology 2018 │ Volume 31 │ Issue 01 TABLE 1. Population variance of malocclusion Study Ancestry n Class I normal % Class I mal- occlusion % Class II mal- occlusion % Class III mal- occlusion % (Horowitz 1970) White 321 53.6 NA 33.6 4.7 Black 397 76.8 NA 11.4 6.3 (Garner and Butt 1985) Black American 445 27.0 44.0 16.0 8.7 Kenyan 505 16.8 51.7 7.9 16.8 (Onyeaso 2004)) Nigerian 663 24.5 50.0 13.7 11.8 (Altemus 1959) African American 3289 16.48 66.4 12.3 4.9 (Lew et al. 1993) Chinese 1050 58.8 52.7 21.5 12.6 White 1000 44.3 61.1 52.2 3.5 (Silva and Kang 2001) Latino 507 6.5 62.9 21.5 9.1 studies that immediately highlight population differ- ences in the various types of malocclusion, thereby il- lustrating their relevance to anthropological studies of population variation. Orthodontic Considerations Modern orthodontia can impact observations of all of these traits. While braces may seem ubiquitous, they are a relatively new development. In the United States orthodontic work made a marked appearance in the 1950s as the “baby boom” created a larger sample of potential patients. However, the practice did not really take off until the 1970s when the number of qualified orthodontists nearly tripled from the decade before (Asbell, 1990). According to the American Association of Orthodontists (2016), nearly 5,000,000 people were receiving orthodontic care in the United States in 2016, and they estimated that half of the U.S. population could benefit from orthodontic work. In studying traits of malocclusion and the possibility of orthodontic work, it is important to consider various factors that may limit access to treatment. Multiple studies have documented economic and social barriers to receiving orthodontic treatment (Germa et al., 2010; Krey and Hirsch, 2012), as well as ethnic differences in desires for orthodontic treatment (Reichmuth et al., 2005). Addi- tionally, cultural practices and views on beauty can also interfere. For example, in a Nigerian sample of 141 individuals, a study found that 48 (34%) had artificially created a midline diastema for the “enhancement of personal beauty and aesthetic” (Umanah et al., 2015:226). While orthodontic work could erase many of these traits, there are various factors to consider when studying a set of remains such as socioeconomic or social status, ancestry, and antiquity of the remains (i.e., death prior to 1970 is less likely to have had ortho- dontic care). Conclusions These traits of malocclusion all figure prominently in clinical discussions of occlusion and are broadly related to conditions that include spacing issues (i.e., diastema and crowding), and deviations from normal occlusion (i.e., maxillary and mandibular overjet). While the midline diastema has been embraced by the ASUDAS and other dental morphologists, the other traits de- scribed herein have not. The reason for this finding is likely related to a lack of understanding of the etiology of these conditions; however, it is argued here that these traits show a degree of genetic heritability and could be relevant to studies of population variation. Yet, the environmental component of these traits of occlusion cannot be ignored and may therefore serve as a means to quantify the degree of malocclusion over human evolution. It is hoped that this definition of a scoring system will generate further discussions of traits of malocclusion and that comparative population studies can be generated to further our understanding of population variation and human evolution. Acknowledgments I thank G. Richard Scott for always being supportive and for helping me work through this scoring system. He is always there to talk teeth with me. 16 Dental Anthropology 2018 │ Volume 31 │ Issue 01 REFERENCES Alt K. W., and Türp J. C. (1998). Hereditary Dental Anomalies. 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