Interpretations of general problems in amelogenesis • 271 



Cusp growth, for the most part, terminates in the central 

 part of the occlusal surface, at grooves, pits, or at the advanc- 

 ing termini of the adjacent cusps. The size and shapes of 

 these cusps are detemiined to a considerable extent by the 

 rate and extent of growth of the neighboring cusps. In the 

 lower molars, for example, the grooves adapt to form a Y or 

 X configuration, with other minor adjustments. In most in- 

 stances in man, the lower molars present a larger prominence 

 of the central crest on the buccal surface of the metaconids 

 (mesiolingual cusps). This crest has been the subject of inter- 

 est to odontologists because of its size and its tendency to 

 deflect distally as it projects buccaly. This structure has been 

 labeled the "detlecting wrinkle" (T-19 64 and 1-1464B of 

 Figure 1 ), and varies in frequency and details of form and 

 direction in any given dentition, from dm2 to Ml to M2 and 

 to M3, following the succession patterns of Butler's Field 

 Concept of development (Butler 1939; Dahlberg 1945). 



The deflecting wrinkle variations are seen in other 

 sketches of Figure 1 as thickened and shorter ( in M2 of Al va 

 H, in Ml ofR.W.H.)andasdivided(inMl,M2,andM3of 

 7A). The wrinkle of Ml of R.D.H. shows a beginning of 

 separation but not a complete severance of the termini of the 

 wrinkle, as on the Mis of 1-1464B. The deflection of the 

 terminal end is almost always confined to the Mis, and is 

 very rare on the stubby, heavier or divided M2s. Additional to 

 the areas or pathways not open for the full expression of the 

 developing wrinkle, there is a deterrent of phylogenetic ori- 

 gin, the distal trigonid ridge or crest, a distal ridge remnant of 

 the original trigonid (three-cusp tooth formed in evolution) 

 (Korenhof 1978). Zoubov ( 1973) reports a high frequency of 

 distal trigonid ridges in lower molars of some eastern popula- 

 tions of the Soviet Union, and Hanihara (1966) records high 

 frequencies of deflecting wrinkles in mongoloid-complex 

 dentitions. However, a substantial number of terminal ends 

 of this wrinkle are physically separated as an enamel island, 

 especially on M2s and occasionally on M 1 s, as seen on M I of 

 BH, Ml of 1-1464B and Ml of R.D.H. of Figure 1. These 

 terminal enamel islands are similar to the islands seen in the 

 crenulations and wrinkles of some of the fossils discussed by 

 Weidenreich ( 1937) and Tobias (1986). Also, a similar sug- 

 gestion of some morphological changes induced by spiro- 

 chetes in the enamel islands and some other conformations 

 (Bradlaw 1953; Samat and Schour 1941-1942) can be seen 

 in Figure 2 (Dahlberg 1986; Mann et al. 1990). 



The major problem in understanding and interpreting ame- 

 logenesis arises from the fact that several separate processes 

 are going on at one time. These are involved in a recording 

 sequence of calcification and growth of other centers of simi- 

 lar activity. Also, there is an interplay of environment, genes, 

 and interactions with delays or arrests of procedures. This 



Figure 2. Bucco-lingual view of deciduous lower right sec- 

 ond molar showing many disorganized groupings of enamel 

 islands on occlusal surface. Buccal pit and protostylid seen 

 on buccal surface. Several divided islands visible on this 

 tooth from 5-year-old male American Indian, William and 

 Mary collection of the Chickahominy tribe. (Mann et al. 

 1990). 



works out well for the normal programming of tooth forma- 

 tion. However, it compounds the picture for observers (Boy- 

 de 1970) who already are faced with myriads of perfor- 

 mances of the polygenic tooth production scheme or 

 background. The introduction of insults or new factors of 

 major potential in themselves do not cause the same effects 

 on such things as islands of enamel, other tissues, or time- 

 and chemically regulated interactions. Not all morphologi- 

 cally similar productions of enamel rings, pits, or surface 

 enamel island arrays and patterns have the same causation. 

 Those affecting the ontogenetic sequences can be very mis- 

 leading. Many such cases have been considered the systemic 

 effects of congenital syphilis or other factors, without suffi- 

 cient substantiation. A simple example would be the occur- 

 rence of only one instance of a mulberry molar in a large 

 population. Other causes can be possible triggers for such 

 metabolic events. Pits and defects are good markers, but 

 need additional corroborating evidence for proper evalua- 

 tion. 



Zagreb Paleopathology Symp. 1988 



