A SCANNING ELECTRON-MICROSCOPIC STUDY OF IN-VITRO ABRASION OF MAMMALIAN TOOTH ENAMEL UNDER COMPRESSIVE LOADS

Microscopic tooth-wear (microwear) patterns can be an important tool f or assessing modes and rates of abrasive tooth wear, but their analysi s and interpretation is complicated by the fact that microwear is infl uenced by many factors. Three of these factors were here tested under conditions of compressive loading: (I) species differences in enamel s tructure, (2) abrasive particle size and (3) magnitude of force. Teeth of four species (Homa sapiens, Lemur fulvus, Ovis aries and Crocodylu s rhombifer) were abraded in vitro using three sizes of abrasive silic on-carbide grit (average diameters 73, 23 and 14 mu m), at two loads ( 50 and 100 kg). Microwear features were assessed by scanning electron microscopy of lightly etched enamel surfaces and epoxy replicas. Micro wear pits (length:width <4:1) were the predominant feature type. Facto rial analysis of variance of rank-transformed, feature-area measuremen ts demonstrated that, under conditions of compressive loading, the siz e of abrasive particles was the primary determinant of microwear size. These results contrast with previous experimental tests of abrasion b y predominantly shearing loads, where feature size was influenced by i nteraction among experimental factors, including the microscopic orien tation of enamel crystallites. Although magnitude of compressive force was not a factor in microwear size variation, it may be a critical fa ctor in explaining the presence or absence of microwear on tooth surfa ces. The relatively small compressive bite force generated during typi cal chewing may not consistently produce abrasive pitting. These exper iments demonstrate that, as the same abrasive regime can produce both large and small pits, the mechanism by which wear features are formed (i.e. compression or adhesion) cannot be determined from the size of f eatures alone. Nevertheless, the dependence of pit size on abrasive pa rticle size demonstrates that metrical variation in wear features can elucidate important attributes of an animal's diet.