Dental enamel micro-hardness for permanent central incisors in two beef cattle genotypes

Objective. To evaluate the microhardness of tooth enamel from creole steers of Patagonian origin and from indicus cross raised in different environments. Materials and methods. Right central incisors from adult steers were used: eight Patagonian Creole (PCG) and seven indicus cross (ICG). For each tooth was defined a central transect crossing the tooth from the outer edge of the enamel into the dentin, and hardness was measured at three equidistant depths: 30 μ from the outer edge (P1), 30 μ prior to the dentin-enamel junction (P3), and P2 between P1 and P3. Microhardness measurements were performed with a Shimadzu microdurometer model HMV-2 and were expressed in Vickers units. Data were analysed using a random regression model. Akaike information criterion was used for the election of the structure of the matrix associated to random effects. For the statistical analysis was used SAS PROC MIXED procedure, at a 5% significance level. Results. No lack of parallelism was detected between groups (p>0.05), and lines of equal slope were adjusted in each group. The average hardness of enamel decreased with increasing depth of measurement for both genotypes. Heterogeneity was observed in the variability of the groups. Conclusions. Not only PCG showed more hardness but also had the highest variability. Decrease in average hardness with increasing depth in enamel regardless of genotype and environment was confirmed.