Turner and Harris 2004.3 74 75 This communication describes the unusual morphol- ogy of maxillary second premolars (Fig. 1) that were encountered in an otherwise normal young adult. These teeth are distinctive because of the large accessory cusp that occurs bilaterally on the buccal surface of each max- illary second premolar. We present this case in hopes of stimulating discussion about similar teeth that other researchers have encountered and to solicit suggestions of likely causes of this variant. The case is an 18-4 year old African American male who presented for routine orthodontic treatment. By our inspection (Figs. 1, 2) this young male is phenotypically normal aside from the uncommon premolars. All 32 permanent teeth are present, including the third molars where the maxillary teeth have initiated root formation and the mandibular teeth have their crowns mostly formed (Fig. 3). The orthodontic issues were (1) a palatally impacted right canine with just 2.5 mm of space between the lateral incisor and first premolar in this quadrant, (2) an anterior openbite with the right central and left lateral incisors in crossbite, and (3) tongue-thrust on swallowing. There is a Class I molar relationship (Angle) bilaterally. The young man was unaware of his unusual premolars. He did not have a regular dentist, though there are occlusal amalgams on his left and right mandibular first molars (all other teeth are noncarious). These accessory cusps arise from the buccal cingulum. Apart from lingual cingula on the lingual aspects of incisors and canines, basal developments are uncommon in humans. The obvious exception is Carabelli’s trait that occurs on the protocone of maxillary molars. Carabelli’s complex has been amply described (e.g., Kraus, 1959; Korenhof, 1960; Turner and Hawkey, 1998), and it is one of the few morphological variants commonly discussed in clinical dental texts (Zeisz and Nuckolls, 1949; Ash, 1993). Other cingular traits include (1) the paramolar tubercle of Bolk (Dahlberg, 1945) and (2) and talon cusps that arise from the lingual cingulum of incisors (e.g., Harris and Owsley, 1991; Lorena et al., 2003; Segura-Egea et al., 2003; Dash et al. 2004). Dahlberg Brief Report: Maxillary Second Premolars with Paramolar Tubercles Robert A. Turner and Edward F. Harris* Department of Orthodontics, The Health Science Center, University of Tennessee, Memphis, TN 38163 *Correspondence to: Edward Harris, Department of Orthodontics, College of Dentistry, The Health Science Center, University of Tennessee, Memphis, TN 38163 E-mail: eharris@utmem.edu (1950) suggests that paramolar cusp is a term applied to “any stylar or anomalous cusps, supernumerary inclusion or eminence occurring on the buccal surfaces of both upper and lower premolars and molars. Dahlberg used the term protostylid to distinguish just those cusp-like features occurring on the protoconid of lower molars near the buccal groove. Various authors have commented on the association between Carabelli’s cusp and size of the crown of the rest of the tooth (Garn, 1977; Hsu et al., 1997). Scott has reported positive statistical associations between various cingular elements, notably (1) among the expressions of lingual tubercles on the maxillary incisors and canines Fig. 1. Occlusal intraoral view of the young adult African-American described here. By our inspection, the accessory cusps on the second premolars are the only dental features outside normal limits. 76 77 (Scott, 1977), (2) between Carabelli’s complex and size of the hypocone (Scott, 1979; also see review in Keene, 1968), and (3) between Carabelli’s complex—on the lingual aspect of maxillary molars—and the protostylid—on the buccal aspect of mandibular molars (Scott, 1978). Noteworthy features of the accessory cusps (Fig. 2) are their size and bilateral symmetry. There is no trace of this feature on the first premolar. Crown diameters (Table 1) were compared to a sample of American blacks (Richardson and Malhotra, 1975) but these standards are only available for mesiodistal diameters (Fig. 4). Comparisons also were made to the American white standards reported by Harris and Burris (2003). Our case possesses small mandibular incisors and large mandibular molars, but the UP2 with the accessory cusps is unremarkable in these comparisons. This suggests, along with the raw data, that the accessory cusp constitutes part of the normal tooth’s buccolingual width; the cusp is not simply added on to it. This agrees with the observation (Fig. 2) that the occlusal tables of the P2s are somewhat compressed buccolingually. Normally, the P2 dimension is at least as large as the Fig. 2. Close-up occlusal views of the second premolars. Arch lengths are different in the two quadrants because of the unerupted (impacted) canine on the man’s right. Fig. 3. Panoramic radiograph. The palatally impacted right canine is noteworthy, but other features appear to be within normal limits. � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � �� �� � �� �� �� �� �� �� � �� �� �� �� �� �� �� � � � � � �� � � � � � �� � � �� �� � � � � �� ��������� � �� ��������� � �� ��������� ������� �������� Fig. 4. Plots of z-scores for this case compared to mesiodistal diameters of American blacks (Richardson and Malhotra, 1975) and mesiodistal and buccolingual dimensions of American whites (Harris and Burris, 2003). TABLE 1. Crown dimensions1 Mesiodistal Buccolingual Tooth Right Left Right Left Maxilla I1 9.4 9.4 6.7 6.6 I2 7.7 7.4 6.4 6.4 C U 7.9 U 8.4 P1 8.5 8.2 10.7 10.7 P2 7.6 7.8 11.3 11.0 M1 11.1 11.1 12.4 12.5 M2 11.4 11.5 12.1 11.4 Mandible I1 6.0 6.0 4.5 4.8 I2 6.8 6.8 5.8 5.8 C 7.4 7.9 7.5 7.5 P1 8.4 8.1 8.3 8.6 P2 8.3 7.8 9.1 9.6 M1 13.5 13.0 12.2 12.3 M2 IE 12.4 11.6 11.8 1U = unerupted; IE = incompletely erupted. R.A. TURNER AND E.F. HARRIS 76 77 P1, but, on the left, the paracone-protocone distance is 6.0 mm on P1 and 5.9 on P2. On the right where the accessory cusp is slightly larger, the intercusp distance is 6.8 mm on P1 but just 5.8 on P2—again indicating that part of the normal tooth mass has been recruited for production of the extra cusp. Periapical radiographs of these premolars (Fig. 5) are unremarkable. Both of these second premolars possess just one root, as is the norm (Ash, 1993), and there appears to be just a single, normal pulp chamber. Crown morphology of the second premolars is not unusual. There are two main cusps separated by a central developmental groove. There are moderate- size mesial and distal ridges. The right UP2, that is slightly larger than its antimere, has a distal protocone ridge that is absent on the left tooth. The accessory cusp has a lunate (curvilinear) cross-section; it is so large mesiodistally that it essentially “wraps onto” the curvature of the buccal margin of the paracone (buccal cusp). The buccal aspect of the cusp itself is smooth and featureless, descending straight to the cementoenamel junction. The accessory cusp has a single elevation (cusp) with the apex located exactly buccal of the paracone’s apex. Distance between these cusp tips is 1.25 mm on both the right and left tooth. Notably, these accessory cusps would never enter occlusion. That is, one might suppose that the cusp might be adaptive by contributing to the crown’s overall occlusal area. As is normal, though, the paracone (buccal cusp) of the maxillary premolar overhangs the buccal cusp of the lower premolar and the maxillary premolar ’s lingual cusp (protocone) occludes into the lower premolar ’s central fossa. Consequently, regardless of how worn these premolars might become, the accessory cusp will always be buccal of the mandibular tooth—with nothing to occlude against. It seems doubtful, then, that this morphological variant has any adaptive significance, at least functionally. Heights of the accessory cusps are about 1⁄2 mm short of the apices of the paracones, and these cusps have free apices that jut about 2 mm occlusal of where the accessory cusp melds into the paracone. This anatomy is relevant because it means that the cusp developed from its own enamel knot rather than proliferating at a later time from the paracone. Enamel knots are sites of nondividing cells that form during the bell stage of tooth formation. They occur in the stellate reticulum as projections from the inner enamel epithelium (Bhaskar, 1980). Enamel knots have been recognized for over a century (reviewed in Butler, 1956), though their function was unknown. Recent work by molecular biologists (Jernvall et al., 1994; Thesleff et al., 2001) has shown that knots produce substances that promote mitotic growth in the adjacent IEE. Since the knots themselves are nondividing, this creates irregularities in the IEE that become cusps (Jernvall et al., 1994, 1998; Jernvall, 2000). It seems that the primary enamel knot, which is the most obvious on light microscopy and the earliest to form, determines the site of the tooth’s occlusal table (or its counterpart in the simpler anterior teeth), while later-forming ‘secondary’ enamel knots coincide with formation of the individual cusps (Thesleff and Jernvall, 1997; Thesleff et al., 2001; Thesleff, 2003). Separate enamel knots seem to coincide with separate centers of enamel formation since amelogenesis invariably progresses gingivally (Hillson and Bond, 1997). In the present case, it seems that an “accessory” enamel knot developed buccal to the presumptive paracone on the left and right second premolars, but not on the earlier- forming first premolars mesial to them. We have contacted a few experts in the field concerning these teeth. Some have not encountered such a variant. Others stated that they have seen similar cases, but did not bother to record them. Certainly, the frequency of this variant is rare. Readers who have seen similar cases—or have comments on this report—are encouraged to contact the authors. LITERATURE CITED Ash MM Jr. 1993. Wheeler’s dental anatomy, physiology and occlusion, 7th ed. Philadelphia: WB Saunders. Bhaskar SN. 1980. Orban’s oral histology and embryology, 9th ed. St Louis: CV Mosby Company. Butler PM. 1956. Ontogeny of the molar pattern. Biol Rev 31:30-70. Dahlberg AA. 1945. The paramolar tubercle (Bolk). Am J Phys Anthropol 3:9-103. Dahlberg AA. 1950. The evolutionary significance of the protostylid. 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