Standard veterinary examination of teeth in sheep would be an essential part of the clinical investigation procedures which enables age estimation or poor productive potential indication [9]. Even though simple clinical dental examination requires relatively small costs, it is less informative and provides basic information on number, size, shape and structure of teeth and their occlusion with dental pad.
This study presents basic morphological, densitometric and mechanical properties of completely developed deciduous teeth such as mandibular incisors, canine and the second premolar in sheep at the age of 5 months of life for the first time. The analyses performed have shown significant differences of weight of teeth between all incisors reaching the highest value for the first incisors and diminishing gradually in i2 and i3 to the lowest value in i4 (canine). The differentiated weight of the teeth resulted from analogical differences of the length and total tooth volume of the incisors. Considering significant difference of weight, length and tooth volume, it is surprising that total enamel volume was comparable in i1 and i2 as well as in i3 and i4, even though i1 and i2 possess approximately 40 – 68% more enamel than i3 and i4. Gradual reduction of total dentine volume was observed between i1 – i2, i2 – i3 and i3 – i4, that reached 23%, 32% and 25%, respectively. However, densitometric analysis has shown similar values for all the evaluated deciduous teeth in this study when analyzing both MvTMD and vEMD. The only one difference obtained from densitometric evaluation of teeth in sheep has shown significantly higher vDMD in i1 when compared to i3 and i4. Thus, the performed densitometric measurements in both compartments have not shown considerable differences of volumetric tooth mineral density between several deciduous teeth, confirming similar course of mineralization processes of hard dental tissues in all the investigated teeth. Thus, it may be postulated that proper mineral metabolism and mineralization processes during first months of life in sheep lead to comparable mineral density threshold attainment in hard dental tissues of all teeth. The results of densitometric analysis in our study are in accordance to the other reports confirming significantly higher mineral density in enamel than in dentine. It was shown that enamel consists of 95% inorganic substance, 4% water and 1% organic substance, while in dentine all these constituents represent 70%, 20% and 10%, respectively [19–21]. Analogically to results of tooth weight, length and volume, consequent reduction of Wy was observed between i1 – i2, i2 – i3 and i3 – i4 and it reached 23%, 20% and 34%, respectively. Similar decrease of Wf was stated evaluating deciduous incisors and the differences between i1 – i2, i2 – i3 and i3 – i4 reached 24%, 25% and 21%, respectively. In case of the second premolar, its large crown and multi-root anatomical structure contributed to significantly higher values of tooth weight, volume (both in enamel and dentine) and ultimate force when compared to these parameters in incisors and canine. However, tooth length, MvTMD, vEMD and vDMD of p2 were similar when compared with the other investigated teeth. It should also be explained here that mechanical analysis of i1 – i4 and p2 was performed with two different methods such as three point bending and compressive tests and thus the assessment of Wy for p2 was not possible. Even though the current study was not performed on large animal population, the obtained values of morphological, densitometric and mechanical parameters may be deemed as reference data for deciduous teeth in sheep since the investigated teeth were completely developed and their growth was finished. In case of the other deciduous mandibular teeth that were not evaluated in this study, longer breeding procedure is required to finish their growth and development and receive meaningful data [22].
Precise evaluation of teeth properties in terms of morphology, microstructure and mechanical properties would be much more effective than simple clinical examination to provide data on whole body and calcified tissues metabolism during crucial periods of life. Considering very rapid growth rate during neonatal and postnatal development in sheep, morphometric (both on macro- and microstructural levels), densitometric and mechanical evaluation of deciduous teeth would be informative in terms of physiological, nutritional, pharmacological, toxicological and environmental conditions taking place during first months of life. Experimental studies on growing sheep have shown that advantageous nutritional manipulations during early stages of neonatal development positively influence mineral metabolism and bone tissue properties. Oral administration with alpha-ketoglutarate (AKG) during the first two weeks of life induced improved morphological traits (weight and length), volumetric bone mineral density (vBMD) and mechanical properties (maximum elastic strength and ultimate strength) of ribs in 5 month old ram lambs [23]. Similar effects of neonatal administration with AKG were observed in studies on femur properties, where vBMD of the trabecular and cortical bone compartments and ultimate strength were significantly increased when compared to the controls receiving standard diet [24]. Three week long neonatal administration with β-hydroxy-β-methylbutyrate (HMB) in lambs significantly increased serum concentrations of bone-specific alkaline phosphatase (BAP) and osteocalcin (OC) – the bone tissue formation markers reflecting osteoblastic activity. Moreover, growth hormone (GH) and insulin-like growth factor-1 (IGF-1), the hormonal factors inducing improved bone tissue metabolism and mineralization, were significantly increased as the consequence of 21-day neonatal administration with HMB. All these effects were associated with permanent changes of bone morphology, mineral density and mechanical endurance. β-hydroxy-β-methylbutyrate administered in young lambs improved bone weight, length, volume, vBMD of the cortical bone as well as geometrical and mechanical properties of femur and lumbar spine [25]. Even though teeth properties were not evaluated in all these experiments, structural and functional changes of hard dental tissues on macro- and microstructural levels would be expected, especially when one considers significant role of osteoblasts in hard dental tissues formation. Furthermore, previous studies have shown interferences between tooth development and alkaline phosphatase, osteocalcin, bone morphogenetic proteins (BMP) and bone sialoproteins involved in signaling functions and mediating hard dental tissue interactions during development [2, 26].