Variability of exostoses on human jaws during the past six millennia in Northern China / Variabilidad de las exostosis en las mandíbulas humanas durante los últimos seis milenios en el norte de China

SUMMARY: The aim of this study was to survey oral exostoses in human populations that belonged to the same region encompassing five periods over 6000 years, to determine the prevalence and its changing trend over time. A total of 306 human jaws belonging to the modern Xi'an region and four archeological sites, Banpo (6700-5600 years BP), Shaolingyuan (3000 years BP), Shanren (2200 years BP) and Chang'an (1000-1300 years BP), were investigated. The degree of buccal exostosis (BE), torus mandibularis (TM) and torus palatinus (TP) and the TP shape were recorded. The prevalence of BE, TM, and TP in the five groups was 20.8 %-62.5 %, 17.5 %-71.5 %, and 31.7 %-74.2 %, respectively. The differences in the three types of exostoses among the five groups were all statistically significant, but only TM and TP showed a decreasing trend over time. A high and quite diverse prevalence of oral exostoses was found in the five groups of samples. Decreasing trends in relation to time for TM and TP were detected.

RESUMEN: El objetivo de este estudio fue sondear las exostosis orales en poblaciones humanas que pertenecían a la misma región abarcando cinco períodos durante 6000 años, para determinar la prevalencia y su tendencia cambiante a lo largo del tiempo. Un total de 306 mandíbulas humanas pertenecientes a la moderna región de Xi'an y cuatro sitios arqueológicos, Banpo (6700-5600 años AP), Shaolingyuan (3000 años AP), Shanren (2200 años AP) y Chang'an (1000-1300 años AP) BP), fueron investigados. Se registró el grado de exostosis bucal (EO), torus mandibular (TM) y torus palatino (TP) y la forma de TP. La prevalencia de EO, TM y TP en los cinco grupos fue 20,8 % -62,5 %, 17,5 % -71,5 % y 31,7 % -74,2 %, respectivamente. Las diferencias en los tres tipos de exostosis entre los cinco grupos fueron todas estadísticamente significativas, pero solo TM y TP mostraron una tendencia decreciente con el tiempo. Se encontró una prevalencia alta y bastante diversa de exostosis oral en los cinco grupos de muestras. Se detectaron tendencias decrecientes en relación al tiempo para TM y TP.

The Effects of Diamond-Like Carbon Films on Fretting Wear Behavior of Orthodontic Archwire-Bracket Contacts.

This study aims to assess the effects of diamond-like carbon (DLC) films on fretting wear behavior of orthodontic archwire-bracket contacts. 'Mirror-confinement-type electron cyclotron resonance (MCECR) plasma sputtering' was utilized to deposit carbon films on stainless steel archwires and brackets. Nanostructure of carbon films such as the bonding structure, cross-sectional thickness and surface roughness were studied. The fretting wear behavior of various archwire-bracket contacts were investigated by using a self-developed tester in ambient air and artificial saliva. The results indicated that DLC-coated wires showed significantly low friction coefficient than the uncoated wires independently of the applied environments. Nevertheless, the DLC-coated and uncoated brackets showed no significant differences in the friction coefficient. Microscopic analysis showed that low wear took place for the DLC-coated surfaces. It is proposed that the application of DLC coating on archwires can decrease the orthodontic fretting wear and coefficient of friction. Unfortunately it does not affect the frictional properties for brackets at present.

Traumatic loss of a maxillary central incisor treated with nonextraction orthodontics.

This case report describes the orthodontic treatment of a girl who lost her maxillary left central incisor from trauma. The patient had a concave profile, a Class I molar relationship on the right side and a Class II molar relationship on the left side, with a slight maxillary retrusion, an anterior edge-to-edge bite, and a posterior crossbite. Therefore, the treatment consisted of rapid palatal expansion to widen the maxilla in a transverse direction along with reverse headgear to improve the incisor relationship. The crown of the left canine was modified to resemble the left lateral incisor, and a porcelain veneer was placed to make the left lateral incisor resemble the left central incisor. This case report illustrates how orthodontics alone can be used to treat a missing central incisor, without a bridge or an implant.

Variability in permanent tooth size of three ancient populations in Xi'an, northern China.

OBJECTIVES: This paper compares permanent dental dimensions between three ancient populations that belonged to the same biological population throughout a temporal range of 2000 years to detect temporal trends and metric variation in dentition. MATERIALS AND METHODS: The samples analysed were dental remains of 4502 permanent teeth from 321 individuals, which were excavated from three archaeological sites: Chang'an (1000-1300 years BP), Shanren (2200 years BP) and Shaolingyuan (3000 years BP) in the Xi'an region (northern China). For each tooth three standard measurements were taken: Mesiodistal (MD) diameter of crown, labiolingual or buccolingual (BL) diameter of crown and length of root (LR). RESULTS: Three ancient population samples generally displayed the same dental dimensions (p>0.05), whereas some tooth types varied. The Shaolingyuan had larger canine and the smallest maxillary second molars and the Chang'an had the largest mandibular first molars in the MD dimension. The Shanren had the smallest maxillary third molars and mandibular central incisors, and the Chang'an had the smallest maxillary lateral incisors in the BL dimension. In the LR measures, statistically significant differences of five tooth types showed that the Chang'an were smaller than the Shaolingyuan and the Shanren. Comparisons of coefficients of variation for teeth showed that the length of root and third molar usually displayed greater variation. CONCLUSIONS: Decreasing or increasing trend for crown size does not occur between the ancient populations, while changes in crown size of a few tooth types fluctuate. The root size is more variable than the crown size and is likely to reflect a degenerated trend in a few tooth types.