What is the effect of preterm birth on permanent tooth crown dimensions? A systematic review and meta-analysis

Background The permanent tooth formation process may be disrupted in preterm infants with potential discrepancies in size and subsequent occlusal disturbances. Objective To systematically analyse and quantitively synthesize the available evidence regarding the impact of preterm birth on permanent tooth crown dimensions. Search methods Unrestricted searches in 6 databases and manual searching of the reference lists in relevant studies were performed up to March 2021 (Medline via PubMed, CENTRAL, Cochrane Database of Systematic Reviews, Scopus, Web of Science, ProQuest Dissertations and Theses Global). Selection criteria Observational studies investigating permanent tooth crown dimensions in preterm and control full-term born individuals. Data collection and analysis Following study retrieval and selection, relevant data were extracted, and the Newcastle-Ottawa scale was used to assess the selection, comparability, and outcome domains. Exploratory synthesis and meta-regression were carried out using the random effects model. Results Three studies were located from the initially retrieved records and the assessments with the Newcastle-Ottawa scale identified issues regarding the selection and comparability domains. Overall, the mesiodistal and the buccolingual dimensions of the permanent teeth in both dental arches tended to be smaller in children born prematurely than full term children. Subgroup analyses showed statistically significant differences for the extremely preterm to control group comparisons for the incisors and the first molars. Meta-regression showed a modificatory effect of gestational age and racial background but not of birth weight and gender on tooth size. The quality of available evidence was rated at best as moderate. Conclusions Premature birth could potentially be associated with reduced tooth-crown dimensions in some permanent teeth especially in children born extremely preterm. Although the results from these observational studies should be approached with caution until more information becomes available, the possible clinical implications in terms of diagnosis and treatment planning should be considered. Registration PROSPERO (CRD42020182243).

Sexual Dimorphism in Maxillary First Molar among Nepalese Population of Eastern Nepal

Introduction: Sexual dimorphism refers to differences in size, stature and appearance between male and female. It is a known fact that tooth crown is formed to full size in childhood even before eruption into oral cavity. The shape and size of the teeth permits an interesting dimension of study for sexual dimorphism, we aimed to delineate the sexual dimorphism by measuring the mesiodistal (MD) and buccolingual (BL) diameters of permanent maxillary first molar in Nepalese population of Eastern Nepal. Objectives: The aim of this study was to evaluate the sexual dimorphism in maxillary first molar among Nepalese population of eastern Nepal Methodology: 100 participants of either sex (50 males & 50 females) aged between 17 to 25 years were enrolled in the study. After thorough dental examination, impression of the maxillary arch was made and MD diameter and BL diameters were measured with the help of vernier caliper. A P value of <0.05 was considered as statistically significant. Results: Sexual dimorphism was found in MD and BL diameters of maxillary first molar in males measuring higher than females. Right mesiodistal showed the highest sexual dimorphism, whereas right buccolingual showed the least. Conclusions: This study confirms that permanent maxillary first molar shows significant sexual dimorphism, out of which mesiodistal measurement stands out to be the best parameter in Nepalese population of Eastern region.

New Middle Eocene proboscidean from Togo illuminates the early evolution of the elephantiform-like dental pattern

Africa has played a pivotal role in the evolution of early proboscideans (elephants and their extinct relatives), yet vast temporal and geographical zones remain uncharted on the continent. A long hiatus encompassing most of the Eocene (Ypresian to the Early Priabonian, around 13 Myr timespan) considerably hampers our understanding of the early evolutionary history of the group. It is notably the case with the origin of its most successful members, the Elephantiformes, i.e. all elephant-like proboscideans most closely related to modern elephants. Here, we describe a proboscidean lower molar discovered in Lutetian phosphate deposits from Togo, and name a new genus and species, Dagbatitherium tassyi . We show that Dagbatitherium displays several elephantiform dental characteristics such as a three-layered Schmelzmuster, the presence of a mesoconid, transversely enlarged buccal cusps and the individualization of a third lophid closely appressed to a minute distal cingulid. Dagbatitherium represents a stem Elephantiformes, pushing back the origin of the group by about 10 Myr, i.e. a third of its currently known evolutionary history. More importantly, Dagbatitherium potentially unlocks the puzzle of the origin of the unique elephantiform tooth crown organization by bridging a critical temporal and morphological gap between early bunodont incipiently bilophodont proboscidean taxa and more derived elephantiforms.

A histological investigation of dental crown characters used in mosasaur phylogenetic analyses

Mosasaur researchers have used varieties of tooth crown ornamentation as diagnostic and phylogenetic characters for decades. Such tooth crown features include facets, flutes, striations, serrated carinae, and coarse anastomosing texture. This study investigates the relative contribution of dentine and enamel to the development of these dental characters and assesses possible homologies between these structures. Histological analysis of isolated mosasaur teeth revealed that flutes and facets develop initially from the dentine, and the external enamel morphology we observe macroscopically mirrors the shape the underlying dentine. Striations combine underlying contributions from the dentine with additional and irregular enamel deposition that results strictly from amelogenesis. In both serrated carinae and anastomosing texture the border between the dentine and the enamel is smooth, and these external ornamentations form through variations in enamel development. Based on these observations, we infer that flutes and facets are part of a morphological spectrum and should not be treated as separate phylogenetic characters. Conversely, striations develop differently than flutes and facets, and should therefore be treated as a distinct character. We recommend referring to the “serrations” on mosasaur carinae as crenulations to differentiate these enamel-only structures from true denticles possessing a dentine core. Anastomosing texture can also coincide with significant apical thickening, both of which could be adaptations for processing hard-shelled prey. Care must be taken when using tooth crown features as diagnostic or phylogenetic characters because seemingly different morphologies can have similar developmental origins, and tooth morphology can be more closely tied to diet than to common ancestry.

Equatorial pliosaurid from Venezuela marks the youngest South American occurrence of the clade

Pliosaurids were the dominant macropredators in aquatic environments at least since the Middle Jurassic until their extinction in the early Late Cretaceous. Until very recently, the Cretaceous record of Pliosauridae has been poor and difficult to interpret from the taxonomic and phylogenetic perspective. Despite that the knowledge of Cretaceous pliosaurids improved in recent years, numerous aspects of their evolutionary history still remain only poorly known. Here, we report the first pliosaurid material from Venezuela. The taxon is most likely earliest Cenomanian in age, thus representing the youngest occurrence of Pliosauridae from South America. The Venezuelan taxon is based on a well-preserved tooth crown whose morphology and outer enamel structural elements appear to resemble especially those observable in the giant pliosaurid Sachicasaurus vitae from the Lower Cretaceous of Colombia. The new discovery extends the pliosaurid record on the continent by more than 10 million years and likely marks the southernmost Upper Cretaceous occurrence of Pliosauridae, worldwide. We also briefly discuss the affinities of the enigmatic Venezuelan elasmosaurid Alzadasaurus tropicus and highlight similarities to elasmosaurids from the Western Interior Seaway.

DETERMINATION OF CHEWING EFFICIENCY IN PATIENTS WITH RESTORED TOOTH CROWN PART

Supporting teeth preservation at the restoration of dentition defects with the help of fixed porcelain fused metal dentures is considered one of the most important issues of prosthodontics. Margin line preparation strategies are still disputable nowadays. In most cases preparation is confined to the ledge creation. Its function is to provide a smooth transition of orthopedic restoration to a tooth root and prevent the traumatization of marginal paradontium. These issues are gaining a momentum when the possibility of manufacturing fixed prosthesis with the use of partially or completely ruined teeth with the preserved root as a support appears. Since the opportunities of thermal method for gingiva retraction and marginal line formation around the supporting teeth are not studied enough in modern scientific sources, our research aims to define the mastication efficiency state in patients of sample groups after the fixation of dentures on the supporting teeth prepared for prosthesis with the help of diathermocoagulation and mechanical retraction. The authors of the article have determined the mastication efficiency in the patients with the restored tooth crown. Altogether 54 patients of two sample groups aged from 20 to 60 years and above with completely ruined tooth crowns were examined. Their soft tissues around the supporting teeth were prepared for the fixed prosthesis manufacturing. The first sample group involved 29 patients that made up 53.7% of general studied population. Their supporting teeth gingiva margins were retracted with the help of diathermocoagulation while preparing them for the fixed dentures. While the gingiva margins of the patients of the second sample group, consisting of 25 people (46.3% of general studied population), were retracted with the help of cotton Ultrapak cord, produced by Ultradent (the USA). It is offered in several size options. Mastication efficiency state after prosthesis was determined with the help of mastication test (Ukrainian Utility Patent # 94841). In this case, mastication index was the main diagnostic tool. It was received with the help of computer analysis of digital samples in software “Adobe Photoshop Extended”. The analysis of the dynamics of mastication test indices of the patients of sample group 1 delivered typical results. In a week after the fixation of fixed porcelain fused metal dentures, the reduction of the mean value of mastication test index by 0.2 was fixed. The verification of these changes according to the statistical significance showed positive result (at p = 0.0004). At the same time, the verification of the changes, occurred during the period from the 7th to the 30th day after the fixation of dentures in patients of sample group 1, with the help of Wilcoxon test showed that at p = 0.9 the reduction of the mean value to 5.148 had no statistical significance. While the dynamics of mastication test changes in sample group 2 looked as follows. The reduction of the mean values of mastication test index from 5.184 to 5.112 was observed. So, the spread between the values received before the retraction and in seven days after crown fixation made up 0.072. The conducted statistical verification of these changes (at p = 0.01) proved their statistical significance. In contrast, the collation of the indices received after seven days of denture fixation and in 30-days period after it (from 5.112 to 5.132) at p = 0.961 demonstrated changes at the level of statistical error. According to the received research results, prosthesis with the fixed porcelain fused metal dentures promotes patients’ mastication efficiency restoration. That is traced in the reduction of the mastication test index values received after the 7th day of crown fixation in both sample groups. It should be noted here, that statistically significant difference between the indices of the patients of sample group 1 and 2 was not found. On the 30th day of denture fixation, mastication efficiency indices remained almost the same.

MINERALIZATION OF TEETH ENAMEL AFTER ERUPTION

The aim: The paper was aimed at the study of the processes of mineralization of the enamel of the permanent tooth after its eruption. Materials and methods: To study the structure of the enamel of permanent teeth has been carried out using light and electron microscopy. The study of the process of the development of the primordia of the permanent teeth involved 10 culled puppies of 30-40 days of age. Microscopic, electron microscopic, immunohistochemical methods of research have been used to study the processes of histogenesis. Results: The studies show that in the postnatal period, the formation of the crown, externally covered with cuticular epithelium, marks the formation of the primordium of the permanent tooth at the follicle stage. After eruption of a tooth, different parts of its crown have three individual structural and functional barriers to enamel biomineralization. The first one is provided by the cuticular epithelium of the pitted areas of the crown, which ensures filtering of the salivary fluid from the protein deposit in the form of a pellicle. The second barrier is defined on the lateral and cuspidate surfaces of the enamel, where the cuticle is erased or poorly expressed. The third structural and functional barrier of enamel biomineralization is located in the cervical portion of teeth of different classes. Conclusions: Different areas of the enamel in the tooth crown have specific filtration barriers, which can be distinguished as follows: pit-and-fissure-and-groove, cuspidateand-approximal, and cervical barriers. The cuticle is poorly expressed or totally absent on the cusps of the tooth crowns in contrast to pitted areas.