Measurement of Tooth Wear by Means of Digital Impressions: An In-Vitro Evaluation of Three Intraoral Scanning Systems

This in-vitro study aimed to investigate whether intraoral scanners (IOS) are suitable for wear measurement compared to optical profilometry (WLP). A zirconia cast representing the teeth (24–28) was fabricated. It was digitized six times using three different intraoral scanners, Cerec Omnicam AC (OC), Trios 3 (Tr3), and True Definition (TD). The scans were conducted at baseline (t0) and at three different stages of simulated wear (t1–t3), each at one wear-facet on FDI 26 and FDI 27. WLP was used as a reference method. Within each acquisition system, the maximum wear at each facet was analyzed by superimposing the STL data of t0 with t1–t3. A power analysis was performed (G*Power), and the Wilcoxon-signed-rank-test was used to evaluate whether there were statistically significant differences between the groups (Bonferroni corrected) (α = 0.05). At wear-facet FDI 27, differences from +4% t1 TD up to +19% t2 OC, corresponding to a metric value of 8 µm and 45 µm, were measured. At FDI 26 deviations between −2% t1 Tr3, and +10% OC and Tr3, were observed. Considering some limitations, the IOS are a promising alternative to wear measurement based on WLP due to its simple application to capture surface changes in a reasonable and quick way.

Dental microwear of a basal ankylosaurine dinosaur, Jinyunpelta and its implication on evolution of chewing mechanism in ankylosaurs

Jinyunpelta sinensis is a basal ankylosaurine dinosaur excavated from the mid Cretaceous Liangtoutang Formation of Jinyun County, Zhejiang Province, China. In the present study, its dental microwear was observed using a confocal laser microscope. Jinyunpelta had steep wear facets that covered most of buccal surfaces of posterior dentary teeth. Observation of dental microwear on the wear facet revealed that scratch orientation varied according to its location within the wear facet: vertically (i.e. apicobasally) oriented scratches were dominant in the upper half of the wear facet, and horizontally (i.e. mesiolaterally) oriented ones were in the bottom of the facet. These findings indicated that Jinyunpelta adopted precise tooth occlusion and biphasal jaw movement (orthal closure and palinal lower jaw movement). The biphasal jaw movement was widely observed among nodosaurids, among ankylosaurids, it was previously only known from the Late Cretaceous North American taxa, and not known among Asian ankylosaurids. The finding of biphasal jaw movement in Jinyunpelta showed sophisticate feeding adaptations emerged among ankylosaurids much earlier (during Albian or Cenomanian) than previously thought (during Campanian). The Evolution of the biphasal jaw mechanism that contemporaneously occurred among two lineages of ankylosaurs, ankylosaurids and nodosaurids, showed high evolutionary plasticity of ankylosaur jaw mechanics.

Comparative anatomy of selected basal ceratopsian dentitions

The dental structure of basal ceratopsians is described. Evolutionary trends in maxillary and dentary teeth of basal ceratopsians include decrease and possible loss of enamel on the occluding side of tooth crowns, increase in the angle of wear facet, development of a prominent primary ridge and deep indentations on mesial and distal sides of the primary ridge, and increase in tooth size in neoceratopsians. Premaxillary teeth in the basalmost ceratopsian Yinlong and basal neoceratopsian Archaeoceratops oshimai exhibit wear facets and denticles along the carina, which imply use for feeding. Maxillary and dentary teeth of basal ceratopsians were probably not as effective in feeding as those in ceratopsids because of the relatively less prominent primary ridges. Some dental characters can be used to identify taxon and tooth position of isolated basal ceratopsian teeth.

Jaw movement, dental function, and diet in the Paleocene multituberculate Ptilodus

The shape and arrangement of cusps and crests and the orientation of wear striations on the cheek teeth of fossil mammals can be used to reconstruct occlusal patterns. Occlusal patterns have been documented previously in a variety of therian mammals and also in triconodonts and docodonts among nontherians. This is the first detailed analysis of patterns of jaw movement and dental function in a member of the highly specialized nontherian order Multituberculata (Allotheria). Ptilodus, a Paleocene multituberculate, appears to have had two cycles of mastication that followed different paths of movement and utilized different sets of teeth. The first cycle, the slicing-crushing cycle, occurred as the large, laterally-compressed fourth lower premolar (P4) sliced orthally into food items held primarily against the fourth upper premolar (P4). Food items sliced in this manner passed down both the labial and lingual sides of P4, forming subparallel striations in valleys between the nearly vertical enamel ridges. The second cycle is the grinding cycle in which the mandible was retracted while the molars were in tight occlusion, thus producing longitudinal striations on the molars. Unlike the pattern in therians, triconodonts, and docodonts, there is no transversely triangular masticatory orbit in the grinding cycle of multituberculates. The generally accepted idea that the labial aspect of P4 in ptilodontoid multituberculates sheared orthally against the lingual aspect of P4 is not supported. Instead, predominantly horizontal striations developed on the posterolabial wear facet of P4, and on a conjoined facet posterolingually on P4 and anterolingually on the first upper molar (M1), indicate that relative movement between these surfaces was largely palinal (i.e., the jaw moved from front to back), rather than orthal and occurred during the grinding cycle of mastication.In considering the dietary preferences of ptilodontoid multituberculates, it appears that most members were not folivorous. The small size of many species of Ptilodontoidea suggests that they could not have subsisted on a folivorous diet, which is rich in structural carbohydrates. The length of striations on the sides of P4 of Ptilodus, one of the largest of the Ptilodontoidea, indicates that large, hard food items were ingested. The presence of both smooth and highly-striated enamel on homologous dental wear facets in different individuals of Ptilodus mediaevus from a single quarry sample suggests a varied diet. The recent suggestion that ptilodontoids were omnivorous is supported.

The Morphology and Occlusion of the Molariform Cheek Teeth in Some Macropodinae (Marsupialia: Macropodidae).

The morphology and functional occlusion of the cheek teeth of Wallabia bicolor and Macropus giganteus are compared. W. bicolor seems to be essentially a browser and M. giganteus is predominantly a grazer. W. bicolor has a large sectorial premolar, weakly developed links, a plane tooth row with all the teeth in occlusion simultaneously in the adult, and no molar progression. M. giganteus has a reduced premolar, strongly developed links, a curved lower tooth row which meets the upper tooth row at a tangent allowing only a few teeth to be in occlusion at one time, and molar progression. The reconstruction of the occlusal cycles is interpreted mainly by examination of wear facet development and striae patterns. Occlusion in W. bicolor involves a strong anteroposterior action bringing the opposing surfaces together across a broad area. M. giganteus teeth occlude with an initial forward motion, followed by a lateral movement which avoids large surface-area contact. M. giganteus teeth seem to be more adapted to cutting fibrous, abrasive material. Species of Dorcopsis, Dorcopsulus, Dendrolagus, Thylogale and Setonix show the same general masticatory features as W. bicolor, but species of Macropus and Megaleia more approximate the M. giganteus condition.