Cellular, molecular, and genetic determinants of tooth eruption

How do teeth erupt?

The development of normal occlusion requires eruptive migration of teeth from their developmental position in the jaw into a functional position within the oral cavity. This process involves significant and coordinated movement in an axial direction and appropriate eruption through the gingival tissues. The mechanisms regulating these developmental events are poorly understood, and teeth retain eruptive potential throughout their lifespan. In recent years, the use of mouse models has helped to elucidate some of the underlying molecular and biological mechanisms of mammalian tooth eruption. Here, we outline our current understanding of tooth eruption mechanisms and discuss their relevance in terms of known human disorders of tooth eruption.

Radiological assessment of periodontal ligament space visibility on third molars for forensic age assessment - a comparison study of three different staging scales

Various staging scales have been proposed for the assessment of the visibility of the periodontal ligament space of mandibular third molars on dental panoramic radiographs (PANs) for forensic age assessment in living individuals. However, up to now, there has been no systematic comparison between these staging scales available. We directly compared the 2010 staging scale proposed by Olze et al. with the 2017 staging by Lucas et al. and the 2020 staging by Guo et al. in a German study population. We evaluated 233 PANs from 115 females and 118 males aged 20.0 to 40.9 years using three independent examiners, with one examiner conducting two assessments. We examined the correlation between age and stage, as well as the inter- and intra-rater reliabilities. While the point estimates for the correlation coefficient and the reliability measures were lowest for the Guo scale and highest for the Olze scale, confidence intervals showed a large overlap, particularly for the scales of Olze et al. and Lucas et al. The correlation coefficients between stage and age were consistently lower in females than in males across all methods. In summary, we showed that the staging scales of Olze et al. and Lucas et al. were very similar. The Olze method showed higher point estimates across all analyses, and because there are more reference data available for this method, we argue that it should be preferred as the method of choice for further studies in the field. However, Guo method could be considered for instances, in which the inter-radicular periodontal ligament is not evaluable.

Metabolic Bone Diseases Affecting Tooth Eruption: A Narrative Review

Tooth eruption is an essential process for the development of the oral and maxillofacial system. Several inherited and acquired diseases might affect this tightly regulated process, resulting in premature, delayed, or even failed tooth eruption. The purpose of this article is to review the literature and the clinical parameters of metabolic bone diseases that affect tooth eruption. It examines the physiological aspects of tooth eruption and the pathophysiological changes induced by metabolic bone diseases, including changes in bone metabolism, density, and structure. The search strategy for this review included an electronic search in PubMed, Google Scholar, Medline, Scopus, and the Cochrane Library using the following keywords: "metabolic bone diseases", "tooth eruption", "delayed tooth eruption", and each reported disease in combination with "tooth eruption disorders", covering publications up to March 2024 and limited to English-language sources. Understanding the influence of metabolic bone diseases on tooth eruption is crucial for managing both dental and skeletal manifestations associated with these disorders. This review suggests that a multidisciplinary approach to treatment may significantly improve oral outcomes for patients suffering from such conditions. Clinicians should be aware of the specific dental abnormalities that may arise and consider comprehensive evaluations and individualized treatment plans. These findings underscore the need for further research into targeted therapies that address these abnormalities.

Proteomic profiling of human dental enamel affected by molar incisor hypomineralisation of different clinical severity grades: an in vitro study

PURPOSE

The aim of this study was to explore the potential to profile and distinguish varying clinical severity grades of MIH, compared to normal enamel, using proteomics.

METHODS

Liquid chromatography-mass spectrometry analyses were conducted on enamel samples of extracted teeth, from 11 children and adolescents, spanning an age range of 6-18 years. Enamel powder samples were collected from extracted, third molars (n = 3) and first permanent molars diagnosed with MIH (n = 8). The MIH tooth samples were categorized into subgroups based on clinical severity grade. The data were statistically analyzed using ANOVA and Welch's t test.

RESULTS

Teeth affected by MIH exhibited a diverse array of proteins, each with different functions related to dental enamel, distinguishing them from their normal enamel counterparts. The application of microdissection combined with LC-MS techniques has revealed the potential to discern unique proteomic profiles among MIH-affected teeth, characterized by varying clinical severity grades. Both analyzed MIH groups displayed consistent trends in the presentation of biological processes, including underabundance of proteins primarily associated with cell organization and biogenesis. Furthermore, proteins linked to cell death were overabundant in both MIH groups.

CONCLUSION

Proteomics enabled the detection and differentiation of various proteins across different clinical severity grades of MIH.

Prevalence and local causes for retention of primary teeth and the associated delayed permanent tooth eruption

BACKGROUND

This study aimed to evaluate the prevalence of retained primary teeth (RPT) associated with delayed permanent tooth eruption and the factors associated with this condition in German children.

METHODS

This is a cross-sectional retrospective study that evaluated panoramic radiographs from orthodontic patients. The diagnosis of RPT was established according to Nolla developmental stage. The primary tooth was considered retained when its successor permanent tooth was in Nolla stage 8, 9, or 10. Statistical analysis was performed with an α of 5% (p < 0.05).

RESULTS

A total of 102 children (48 girls and 54 boys), and 574 primary teeth and their respective permanent successor teeth were evaluated. We classified 192 teeth as RPT. Sixty-one (59.8%) children presented one or more RPT. Gender was not significantly different between RPT and control teeth (p = 0.838; odds ratio 0.95, confidence interval 95% 0.44-2.16). In the majority of the RPT cases (68.7%), no clear cause to explain the prolonged retention was identified. The pathological problems most commonly observed with RPT were dental fillings (19.3%), followed by dental caries (4.6%), and ectopic tooth eruption (2.1%).

CONCLUSIONS

The incidence of RPT associated with delayed permanent tooth eruption in German children was high and the most common pathological condition associated with RPT was dental caries.

Risk factors and treatments for impacted permanent second molars

Background/purpose

Impaction of permanent second molar (PM2) is found occasionally. This study tried to explore the risk factors associated with the impacted PM2 teeth and show how to use different treatment modalities to correct the impaction of PM2 teeth.

Materials and methods

This study used three cases of PM2 impaction to show how to identify the risk factors of PM2 impaction and how to remove these risk factors to facilitate the eruption of impacted PM2 teeth to the correct occlusal positions.

Results

The first and second cases both showed delayed eruptions of two maxillary PM2 teeth. After resection of the dense fibrotic gingival tissues on the tooth eruption pathway, these two impacted maxillary PM2 teeth finally erupted to the normal occlusal positions by their inherent tooth eruption potential. The second case also had mesioangular impaction of two mandibular PM2 teeth. After odontectomy of teeth 38 and 48, the two impacted mandibular PM2 teeth also erupted to the normal occlusal positions by their inherent tooth eruption potential. The third case had impaction of teeth 17, 27 and 47. After extraction of four third molars and four selected premolars, orthodontic mesialization of four permanent first molars, and orthodontic traction using a mini-screw, the three impacted teeth finally erupted to the normal occlusal positions.

Conclusion

We conclude that after removing the obstacles on the tooth eruption pathway, the impacted PM2 teeth usually can erupt to their normal occlusal positions by their inherent tooth eruption potential with or without the assistance of orthodontic traction.

Dental abnormalities in rare genetic bone diseases: Literature review

Currently, over 500 rare genetic bone disorders are identified. These diseases are often accompanied by dental abnormalities, which are sometimes the first clue for an early diagnosis. However, not many dentists are sufficiently familiar with phenotypic abnormalities and treatment approaches when they encounter patients with rare diseases. Such patients often need dental treatment but have difficulties in finding a dentist who can treat them appropriately. Herein we focus on major dental phenotypes and summarize their potential causes and mechanisms, if known. We discuss representative diseases, dental treatments, and their effect on the oral health of patients and on oral health-related quality of life. This review can serve as a starting point for dentists to contribute to early diagnosis and further investigate the best treatment options for patients with rare disorders, with the goal of optimizing treatment outcomes.

Dental age assessment in the living: a comparison of two common stage classifications for assessing radiographic visibility of the root canals in mandibular third molars

After dentition is complete, degenerative tooth characteristics can be used for dental age assessment. Radiological assessment of the visibility of the root canals of the mandibular third molars in dental panoramic radiographs (DPRs) is known to be one such suitable feature. Essentially, two different stage classifications are available for evaluating the visibility of the root canals of mandibular third molars in the DPR. The aim of this study was to determine if one method outperforms the other. Therefore, the 2010 method of Olze et al. was directly compared to the 2017 method of Lucas et al. in the 2020 modification of Al Qattan et al. To this end, 233 DPRs from 116 females and 117 males aged 20.0 to 40.9 years were evaluated by three independent experienced examiners. In addition, one examiner ran two independent evaluations. Correlation between age and stage was investigated, and the inter- and intra-rater reliability was estimated for both methods. Correlation between age and stage was higher with the Olze method (Spearman rho 0.388 [95% CI 0.309, 0.462], males and 0.283 [95% CI 0.216, 0.357], females) than the Lucas method (0.212 [95% CI 0.141, 0.284], males and 0.265 [95% CI 0.193, 0.340], females). The intra-rater repeatability of the Olze method (Krippendorff's α = 0.576 [95% CI 0.508, 0.644], males and α = 0.592 [95% CI 0.523, 0.661], females) was greater than that for the Lucas method (intra-rater α = 0.422 [95% CI 0.382, 0.502], males and α = 0.516 [95% CI 0.523, 0.661], females). Inter-rater reproducibility was also greater for the Olze method (α = 0.542 [95% CI 0.463, 0.620], males and α = 0.533 [95% CI 0.451, 0.615], females) compared to the Lucas method (α = 0.374 [95% CI 0.304, 0.443], males and α = 0.432 [95% CI 0.359, 0.505], females). The method of Olze et al. was found to present marginal advantages to the Lucas et al. method across all examinations and may be a more appropriate method for application in future studies.

TMEM119 (c.G143A, p.S48L) Mutation Is Involved in Primary Failure of Eruption by Attenuating Glycolysis-Mediated Osteogenesis

Primary failure of eruption (PFE) is a rare oral disease with an incidence rate of 0.06%. It is characterized by abnormal eruption mechanisms that disrupt tooth eruption. The underlying pathogenic genetic variant and mechanism of PFE remain largely unknown. The purpose of this study was to explore the role of a novel transmembrane protein 119 (TMEM119) mutation in two PFE patients in a Chinese family. Information collection was performed on the family with a diagnosis of PFE, and blood samples from patients and healthy family members were extracted. Whole-exome sequencing was performed. Bioinformatics analysis revealed that a heterozygous variant in the TMEM119 gene (c.G143A, p.S48L) was a disease-associated mutation in this family. Recombinant pcDNA3.1 plasmid-containing wild-type and mutant TMEM119 expression cassettes were successfully constructed and transfected into MC3T3-E1 cells, respectively. The results of in vitro analysis suggested that the subcellular distribution of the TMEM119 protein was transferred from the cell cytoplasm to the nucleus, and the ability of cells to proliferate and migrate as well as glycolytic and mineralized capacities were reduced after mutation. Furthermore, rescue assays showed that activating transcription factor 4 (ATF4) overexpression rescued the attenuated glycolysis and mineralization ability of cells. Results of in vivo analysis demonstrated that TMEM119 was mainly expressed in the alveolar bone around the mouse molar germs, and the expression level increased with tooth eruption, demonstrated using immunohistochemistry and immunofluorescence. Collectively, the novel TMEM119 mutation is potentially pathogenic in the PFE family by affecting the glucose metabolism and mineralized function of osteoblasts, including interaction with ATF4. Our findings broaden the gene mutation spectrum of PFE and further elucidate the pathogenic mechanism of PFE.

MCP-5 suppresses osteoclast differentiation through Ccr5 upregulation

Human monocyte chemoattractant protein-1 (MCP-1) in mice has two orthologs, MCP-1 and MCP-5. MCP-1, which is highly expressed in osteoclasts rather than in osteoclast precursor cells, is an important factor in osteoclast differentiation. However, the roles of MCP-5 in osteoclasts are completely unknown. In this study, contrary to MCP-1, MCP-5 was downregulated during receptor activator of nuclear factor kappa B ligand (RANKL)-induced osteoclast differentiation and was considered an inhibitory factor in osteoclast differentiation. The inhibitory role of MCP-5 in osteoclast differentiation was closely related to the increase in Ccr5 expression and the inhibition of IκB degradation by RANKL. Transgenic mice expressing MCP-5 controlled by Mx-1 promoter exhibited an increased bone mass because of a decrease in osteoclasts. This result strongly supported that MCP-5 negatively regulated osteoclast differentiation. MCP-5 also prevented severe bone loss caused by RANKL.

Appropriate timing of treatment contributes to better root development of impacted anterior teeth in children

INTRODUCTION

This study investigated the effects of different timings of orthodontic treatment on the root development of impacted anterior teeth in children.

METHODS

The cone-beam computed tomography (CBCT) data of 45 children with impacted anterior teeth were divided into unformed root (UR) group or basically formed root (BFR) group to evaluate root length (RL) and root growth length (RGL) of impacted teeth and contralateral nonimpacted teeth pretreatment and posttreatment. In addition, 22 patients with impacted dilaceration were selected to assess the effects of the crown-root angle and root development stage on RL and RGL. The Student t test, Wilcoxon test, analysis of variance, and multiple linear regression analysis were used for statistical evaluations.

RESULTS

The RL of treated impacted teeth pretreatment and posttreatment was significantly shorter than contralateral nonimpacted teeth values (P <0.05). Posttreatment, the RL and RGL of impacted teeth of the UR group were significantly greater than those of the BFR group (P <0.05). The RGL of the dilacerated root in the UR group was considerably higher than in the BFR group (P <0.05). The larger crown-root angle group had a longer posttreatment RL (P <0.05). Multiple linear regression analysis revealed that the Nolla stage of impacted teeth and RL of contralateral teeth pretreatment significantly influenced the RL of impacted teeth posttreatment.

CONCLUSIONS

Prompt orthodontic treatment is necessary for children with impacted anterior teeth to release the impacted state and achieve better root development. The root length of a dilacerated tooth continued to develop under treatment, but the crown-root angle partly constrained it.

Evaluation of Current Studies to Elucidate Processes in Dental Follicle Cells Driving Osteogenic Differentiation

When research on osteogenic differentiation in dental follicle cells (DFCs) began, projects focused on bone morphogenetic protein (BMP) signaling. The BMP pathway induces the transcription factor DLX3, whichh in turn induces the BMP signaling pathway via a positive feedback mechanism. However, this BMP2/DLX3 signaling pathway only seems to support the early phase of osteogenic differentiation, since simultaneous induction of BMP2 or DLX3 does not further promote differentiation. Recent data showed that inhibition of classical protein kinase C (PKCs) supports the mineralization of DFCs and that osteogenic differentiation is sensitive to changes in signaling pathways, such as protein kinase B (PKB), also known as AKT. Small changes in the lipidome seem to confirm the participation of AKT and PKC in osteogenic differentiation. In addition, metabolic processes, such as fatty acid biosynthesis, oxidative phosphorylation, or glycolysis, are essential for the osteogenic differentiation of DFCs. This review article attempts not only to bring the various factors into a coherent picture of osteogenic differentiation in DFCs, but also to relate them to recent developments in other types of osteogenic progenitor cells.

Outcome of Surgical Extraction of Linguoverted Deciduous Mandibular Canine Teeth, Performed as an Interceptive Orthodontic Procedure in Puppies, on Permanent Occlusion

Linguoversion of deciduous mandibular canine teeth can be a painful condition, interferes with the development and growth of the jaws, and potentially leads to further malocclusions affecting permanent dentition. Extraction of linguoverted deciduous mandibular canines is considered an interceptive orthodontic procedure that would allow unimpeded development of the jaws and permanent teeth. This study assessed clinical records of 124 dogs that had linguoverted deciduous mandibular canine teeth surgically extracted between October 2010 and September 2019 in a veterinary dental referral clinic. Seventy-seven cases fulfilled the study criteria. Fifty-one percent of these patients required further orthodontic treatment of the permanent occlusion and forty-nine percent demonstrated atraumatic permanent occlusion. The study found no correlation of the outcome with age at the time of surgery. The class of malocclusion (class 1 or class 2) at the time of surgery was also not associated with the outcome.

Salivary Protein and Electrolyte Profiles during Primary Teeth Eruption: A Cross-Sectional Study

This study aimed to assess the qualitative changes in the saliva during the process of primary teeth eruption. This cross-sectional study was conducted on 147 children from 2 to 48 months, of which 49 were in group A (no erupted primary teeth), 53 were in group B (at least one active erupting primary tooth), and 45 were in group C (eruption of all 20 primary teeth was completed). Salivary proteins were evaluated by sodium dodecyl sulfate electrophoresis with polyacrylamide gel, while the concentrations of salivary sodium, potassium, chloride, and calcium ions were evaluated by ion selective electrodes. The data were analyzed using ANOVA and Bonferroni tests (alpha = 0.05). The concentration of proteins with molecular weights of 20-30 KDa was significantly higher in group A, and it gradually decreased with age. The concentration of proteins with molecular weights of 50-60 KDa in group B was significantly lower than those of groups A and C. The calcium ion concentration in group A was significantly higher than that of the other groups. The concentration of potassium ions was minimal in group C. The proteins and electrolyte profiles of the subjects' saliva changed in the process of primary tooth eruption. The highest concentrations of proteins such as statherin, histatin, P-B peptide, and cystatin and the lowest concentrations of proteins such as amylase were present in group B.

Third molar eruption in orthopantomograms as a feature for forensic age assessment-a comparison study of different classification systems

Evaluation of third molar eruption represents an established method for age assessment of living individuals. Different classification systems are available for the radiological assessment of third molar eruption. The aim of this study was to identify the most accurate and reliable classification system for the mandibular third molar eruption on orthopantomograms (OPG). We compared the method of Olze et al. (2012) with the method of Willmot et al. (2018) and a newly derived classification system using OPGs from 211 individuals aged 15-25 years. The assessments were performed by three experienced examiners. One examiner evaluated all radiographs twice. The correlation between age and stage was investigated and the inter- and intra-rater reliability was estimated for all three methods. Correlation between stage and age was similar between classification systems, although higher in the data from males (Spearman's rho ranging from 0.568 to 0.583) than from females (0.440 to 0.446). Inter- and intra-rater reliability measures were similar across methods and invariant on sex, with overlapping confidence intervals, although the highest point estimates for both intra- and inter-rater reliability were for the method by Olze et al. with Krippendorf's alpha values of 0.904 (95% confidence interval 0.854, 0.954) and 0.797 (95% confidence interval 0.744, 0.850). It was concluded that the method of Olze et al. from 2012 is a reliable method for practical application and future studies.

Effect of Neonatal Factors on the Eruption of Primary Teeth in Children: A Longitudinal Prospective Cohort Study

Introduction

Eruption of first primary teeth is a normal physiological process. Antenatal nutritional deficiency and prenatal and neonatal factors play an important role in eruption of primary teeth. Neonatal factors, such as gestational age (GA), degree of prematurity, severity of neonatal illness, and birth weight are primarily related to eruption of primary teeth. The relation between neonatal factors and the timing of eruption of primary teeth has not been studied prospectively among Indian preterm infants.

Aims

To evaluate the influence of neonatal factors on the eruption of primary teeth in children born preterm.

Materials and methods

A prospective longitudinal cohort study design was adopted. A total of 150 subjects were recruited by simple random sampling. Each child was followed up from birth up to 36 months. Intraoral examination was done and the teeth present in each visit were recorded. Data were statistically analyzed and interpreted.

Statistical analysis used

Descriptive statistics, t-tests for independent sample, and Pearson's chi-squared tests were applied. Tooth showing statistically significant difference in mean age of eruption between term and preterm categories was studied for the effect of maternal and neonatal characteristics on eruption using multivariate regression analysis.

Results

The mandibular central incisor was the first tooth to erupt. Significant determinant of eruption of mandibular incisor in term children was found to be parity, weight for GA, and complementary feeding, whereas for preterm children, significant determinants were parity, birth weight birth length, weight for GA, and complementary feeding.

Conclusion

Neonatal factors, such as birth weight, birth length, weight for GA, and introduction of complementary feeding have a strong significant association with the eruption of primary teeth.

Clinical significance

The findings of this study will guide in the preventive management of oral health in preterm children.

How to cite this article

Indira MD, Nandlal B, Narayanappa D, et al. Effect of Neonatal Factors on the Eruption of Primary Teeth in Children: A Longitudinal Prospective Cohort Study. Int J Clin Pediatr Dent 2023;16(2):321-326.

Time and sequence of the replacement of the deciduous by the permanent dentition in dogs and its applicability for age estimation

This study investigated the influence of several covariates on the time and sequence of permanent dentition emergence following exfoliation of the deciduous teeth in puppies. The aim was to determine whether the emergence of permanent dentition can be used to assess whether a puppy that is traded across borders in the EU has reached the legally required minimum age of 15 weeks. The events were evaluated in a longitudinal study, with some cross-sectional observations, of 440 puppies belonging to 82 breeds. No significant differences were found between the left and right sides of a puppy's dentition nor between male and female puppies. Breed size and skull type had a significant impact: both the appearance and the completion of tooth eruption occurred considerably later in small or toy breeds and brachycephalic skull type breeds. The sequence of emergence differed little between maxillary or mandibular quadrants or between breeds. The first emerging elements were the maxillary first premolars or first incisors or the mandibular first incisors. The emergence of a permanent tooth usually occurred within 3 days before or after exfoliation of its precursor, except for the canines, which demonstrated a wider tooth replacement interval. This study presents standards for age assessment based on the emergence of permanent dentition for breeds of different sizes, using median ages or cumulative emergence percentages. However, the legal age determination of puppies with an assumed age of 15 weeks cannot be performed based on permanent dentition emergence, as this occurred at a later age in a large proportion of dogs (at least 95%) in our studied population. The probability of being at least 15 weeks old when at least one maxillary tooth has emerged was at least 72.25%, depending on breed size.

Prevalence of Delayed Eruption of Permanent Upper Central Incisors at a Tertiary Hospital in Riyadh, Saudi Arabia

Tooth eruption is defined as the axial movement of the tooth from its site of development in the alveolar bone to its functional position in the oral cavity. A delay in eruption can directly affect the accurate diagnosis, overall treatment planning, and timing of treatment. Thus, Delayed Tooth Eruption can have a significant impact on a patient’s proper health care. This study aimed to estimate the prevalence of delayed eruptions of permanent upper central incisors in Riyadh, Saudi Arabia. A retrospective study assessed panoramic radiographs of children between the ages of 6–10 years old who attended the Dental University Hospital clinics at King Saud University in Riyadh, Saudi Arabia between 2014 and 2020. The radiographs were collected and examined to detect any delayed eruption of the permanent upper central incisors. Panoramic radiographs with delayed erupted permanent upper central incisors were identified by tooth developmental stages and eruption sequence. Of the 745 radiographs, 23 (3.09%) presented at least one delayed erupted permanent upper central incisor of which boys and girls comprised 16 (69.5%) and 7 (30.4%), respectively. Retained primary teeth was the most causative factor of delayed eruption (43.4%), followed by the early loss of primary teeth (21.7%) and insufficient arch space. The present study is the first to assess the prevalence of delayed eruption of the permanent upper central incisors on a Saudi population. Boys were found to have more prevalence of delayed eruption of the permanent upper central incisors compared to girls. Clinicians should be aware of such a condition as early diagnosis of delayed eruption is essential for providing optimal dental care.

A Novel lncRNA Mediates the Delayed Tooth Eruption of Cleidocranial Dysplasia

Delayed eruption of permanent teeth is a common symptom of cleidocranial dysplasia (CCD). Previous studies have focused on the anomaly of osteogenesis resulting from mutations in the Runt-related transcription factor-2 gene (RUNX2). However, deficiencies in osteoclastogenesis and bone resorption, and the epigenetic regulation mediated by long non-coding (lnc)RNAs in CCD remain to be elucidated. Here, a novel osteoclast-specific lncRNA (OC-lncRNA) was identified during the osteoclast differentiation of RAW 264.7 cells transfected with a RUNX2 mutation expression cassette. We further confirmed that OC-lncRNA positively regulated osteoclastogenesis and bone resorption. The OC-lncRNA promoted the expression of CXC chemokine receptor type 3 (CXCR3) by competitively binding to microRNA (miR)-221-5p. The CXCR3–CXC-motif chemokine ligand 10 (CXCL10) interaction and nuclear factor-κB constituted a positive feedback that positively regulated osteoclastogenesis and bone resorption. These results demonstrate that OC-lncRNA-mediated osteoclast dysfunction via the OC-lncRNA–miR-221-5p–CXCR3 axis, which is involved in the process of delayed tooth eruption of CCD.

Multiple roles of Runt-related transcription factor-2 in tooth eruption: bone formation and resorption

OBJECTIVE

The aim was to provide a comprehensive review of the current knowledge of the multiple roles of Runt-related transcription factor-2 (RUNX2) in regulating tooth eruption, focusing on the molecular mechanisms regarding tooth eruption mediated by RUNX2.

DESIGN

Relevant literatures in PubMed, Medline, and Scopus database were searched, and a narrative review was performed. The multiple roles of RUNX2 in regulating tooth eruption was reviewed and discussed.

RESULTS

Aberrant RUNX2 expression leads to disturbed or failed tooth eruption. Tooth eruption involves both the process of bone formation and bone resorption. RUNX2 promotes osteogenesis around the radicular portion of the dental follicle that provides the biological force for tooth eruption through inducing the expression of osteogenesis-related genes in dental follicle cells/osteoblasts. On the other hand, through indirect and direct pathways, RUNX2 regulates osteoclastogenesis and the formation of the eruption pathway.

CONCLUSION

RUNX2 exerts a pivotal and complex influence in regulating tooth eruption. This review provides a better understanding of the function of RUNX2 in tooth eruption, which is beneficial to illuminate the precise molecular mechanism of osteogenesis and bone resorption, aiding the development of effective therapy for the failure of tooth eruption.

Review and case report of the treatment in a young girl with primary failure of eruption

Any localized non‐eruption of teeth can be attributed to myriad of factors. A failure of a permanent tooth to erupt or cessation of initial eruption with no obvious local/systemic causative factor is said to be primary failure of eruption (PFE). The etio‐pathogenesis of PFE is due to the mutation of PTH1R gene. Clinical features such as infra‐occluded teeth, posterior open bite, lack of any cause or habit are usually attributed to diagnosing the condition, and a confirmatory diagnosis is done by the gene analysis of PTH1R gene. Treatment of such a condition is tricky as any application of orthodontic traction to teeth affected by PFE will not be successful and may cause ankylosis. This correspondence reviews and demonstrates the treatment of a case of PFE to restore function and esthetics to the best possible outcome.

Evaluation of the eruption of permanent teeth and their association with malocclusion

Objectives

This study was done to determine the timing of eruption of permanent teeth by sex and the number of permanent teeth erupted at different ages and to assess its association with malocclusion.

Material and Methods

The sample for this study consisted of 633 healthy subjects (317 boys and 316 girls) aged between 5.0 and 15.0 years. The subjects were divided into subgroups considering an age interval of 1 year.

Results

The mean eruption times were lower for girls compared with boys except for the maxillary and mandibular second premolars and second molars, which were found to erupt earlier in boys. All the permanent mandibular teeth, except the second premolars, tended to erupt earlier than their maxillary antagonists in both sexes. The sequence of eruption differs between girls and boys in the maxillary canine and maxillary second premolars. In Class III malocclusion, all the permanent mandibular teeth erupt earlier than their maxillary antagonists. In the entire sample, the correlation between the number of erupted teeth and age was strong (p < .05), but the differences between sexes were not significant.

Conclusions

It is important to know the normal eruption time of permanent teeth in the population due to diagnosis and better treatment planning in pediatric dentistry and orthodontics.

Vitamin D deficiency is a risk factor for delayed tooth eruption associated with persistent primary tooth

OBJECTIVE

To verify the association between 25(OH)D level and polymorphisms in the vitamin D receptor gene (VDR) with the disturbance in the dental development and eruption.

DESIGN

A total of 183 children from two datasets were evaluated. The first dataset was a case-control (15:15) designed to assess if persistent primary tooth (PPT) is associate with serum 25(OH)D level and with genetic polymorphisms in VDR. The second dataset of genomic DNA samples from 54 children with delayed tooth eruption (DTE) and 99 controls were analysed to verify if genetic polymorphisms in VDR (rs2228570 and rs739837) are associated with DTE. The 25(OH)D and the genotyping/allele distribution were analysed using the T-test and chi-square test, respectively.

RESULTS

The level of 25(OH)D in the PPT group (24.9 ± 6.4 mg/mL) was significantly lower than the control (30.0 ± 7.0 mg/mL) (p=.047). Our data show that children with 25(OH)D deficiency are more likely to present PPT (OR = 2.36; 95%CI: 1.51, 3.70). The rs739837 and rs2228570 polymorphisms were not associated with DTE (OR = 1.44; 95%CI: 0.87, 2.39 and OR = 0.80; 95%CI: 0.45, 1.44, respectively).

CONCLUSIONS

Vitamin D deficiency is a risk factor for PPT.

Symmetry and Aesthetics in Dentistry

Animal bodies in general and faces in particular show mirror symmetry with respect to the median-sagittal plane, with exceptions rarely occurring. Bilateral symmetry to the median sagittal plane of the body also evolved very early. From an evolutionary point of view, it should therefore have fundamental advantages, e.g., more effective locomotion and chewing abilities. On the other hand, the recognition of bilaterally symmetric patterns is an important module in our visual perception. In particular, the recognition of faces with different spatial orientations and their identification is strongly related to the recognition of bilateral symmetry. Maxillofacial surgery and Dentistry affect effective masticatory function and perceived symmetry of the lower third of the face. Both disciplines have the ability to eliminate or mitigate asymmetries with respect to form and function. In our review, we will demonstrate symmetric structures from single teeth to the whole face. We will further describe different approaches to quantify cranial, facial and dental asymmetries by using either landmarks or 3D surface models. Severe facial asymmetries are usually caused by malformations such as hemifacial hyperplasia, injury or other diseases such as Noma or head and neck cancer. This could be an important sociobiological reason for a correlation between asymmetry and perceived disfigurement. The aim of our review is to show how facial symmetry and attractiveness are related and in what way dental and facial structures and the symmetry of their shape and color influence aesthetic perception. We will further demonstrate how modern technology can be used to improve symmetry in facial prostheses and maxillofacial surgery.

Revisiting the human dental follicle: From tooth development to its association with unerupted or impacted teeth and pathological changes

Dental follicles are involved in odontogenesis, periodontogenesis, and tooth eruption. Dental follicles are unique structures, considering that their remnants can persist within the jawbones after odontogenesis throughout life if the tooth does not erupt. Pathological changes may occur in these tissues as individuals age. The changes range from benign to life threatening. Thus, the assessment of age-related changes in dental follicles associated with unerupted teeth is of paramount importance. In this review, we summarize the physiological roles and changes in dental follicles in odontogenesis, tooth eruption, and aging, in addition to the pathological changes associated with these structures. We encourage investigators to consider this peculiar tissue as a unique model and explore its potential to clarify its importance from the viewpoints of developmental biology, tissue physiology, and pathology.

Age-Related Metabolic Pathways Changes in Dental Follicles: A Pilot Study

Aging is not a matter of choice; it is our fate. The “time-dependent functional decline that affects most living organisms” is coupled with several alterations in cellular processes, such as cell senescence, epigenetic alterations, genomic instability, stem cell exhaustion, among others. Age-related morphological changes in dental follicles have been investigated for decades, mainly motivated by the fact that cysts and tumors may arise in association with unerupted and/or impacted teeth. The more we understand the physiology of dental follicles, the more we are able to contextualize biological events that can be associated with the occurrence of odontogenic lesions, whose incidence increases with age. Thus, our objective was to assess age-related changes in metabolic pathways of dental follicles associated with unerupted/impacted mandibular third molars from young and adult individuals. For this purpose, a convenience sample of formalin-fixed paraffin-embedded (FFPE) dental follicles from young (<16 y.o., n = 13) and adult (>26 y.o., n = 7) individuals was selected. Samples were analyzed by high-performance liquid chromatography-mass spectrometry (HPLC-MS)-based untargeted metabolomics. Multivariate and univariate analyses were conducted, and the prediction of altered pathways was performed by mummichog and Gene Set Enrichment Analysis (GSEA) approaches. Dental follicles from young and older individuals showed differences in pathways related to C21-steroid hormone biosynthesis, bile acid biosynthesis, galactose metabolism, androgen and estrogen biosynthesis, starch and sucrose metabolism, and lipoate metabolism. We conclude that metabolic pathways differences related to aging were observed between dental follicles from young and adult individuals. Our findings support that similar to other human tissues, dental follicles associated with unerupted tooth show alterations at a metabolic level with aging, which can pave the way for further studies on oral pathology, oral biology, and physiology.

Nicotinamide Improves Delayed Tooth Eruption in Runx2+/- Mice

Patients with cleidocranial dysplasia (CCD) caused by mutations in RUNX2 have severe dental anomalies, including delayed or absent eruption of permanent teeth. This requires painful and expensive surgical/orthodontic intervention because of the absence of medicine for this condition. Here, we demonstrate that nicotinamide, a vitamin B3 and class III histone deacetylase inhibitor, significantly improves delayed tooth eruption in Runx2^+/- mice, a well-known CCD animal model, through the restoration of decreased osteoclastogenesis. We also found that Csf1 mRNA and protein levels were significantly reduced in Runx2^+/- osteoblasts as compared with wild type whereas RANKL and OPG levels had no significant difference between wild type and Runx2^+/- osteoblasts. The nicotinamide-induced restoration of osteoclastogenesis of bone marrow-derived macrophages in Runx2^+/- mice was due to the increased expression of RUNX2 and CSF1 and increased RANKL/OPG ratio. RUNX2 directly regulated Csf1 mRNA expression via binding to the promoter region of the Csf1 gene. In addition, nicotinamide enhanced the RUNX2 protein level and transacting activity posttranslationally with Sirt2 inhibition. Taken together, our study shows the potential and underlying molecular mechanism of nicotinamide for the treatment of delayed tooth eruption by using the Runx2^+/- murine model, suggesting nicotinamide as a candidate therapeutic drug for dental abnormalities in patients with CCD.

The Role of Autophagy in Osteoclast Differentiation and Bone Resorption Function

Autophagy is an evolutionary conserved and highly regulated recycling process of cellular wastes. Having a housekeeping role, autophagy through the digestion of domestic cytosolic organelles, proteins, macromolecules, and pathogens, eliminates unnecessary materials and provides nutrients and energy for cell survival and maintenance. The critical role of autophagy and autophagy-related proteins in osteoclast differentiation, bone resorption, and maintenance of bone homeostasis has previously been reported. Increasing evidence reveals that autophagy dysregulation leads to alteration of osteoclast function and enhanced bone loss, which is associated with the onset and progression of osteoporosis. In this review, we briefly consolidate the current state-of-the-art technology regarding the role of autophagy in osteoclast function in both physiologic and pathologic conditions to have a more general view on this issue.

The regulatory role of the RANKL/RANK/OPG signaling pathway in the mechanisms of tooth eruption in patients with impacted teeth

BACKGROUND

Tooth impaction is a common problem in orthodontic practice and in some cases accompanied by pain and pathological changes of surrounding teeth. Understanding the cellular and molecular mechanisms underlying tooth impaction allows finding the most effective orthodontic treatment for patients with impacted teeth (IT). RANK (receptor activator of NF-κB) / RANKL (RANK ligand) / OPG (osteoprotegerin) signaling pathway controls bone resorption and may be involved in the regulation of tooth eruption. The study aimed to evaluate bone remodeling based on the assessment of the RANKL/RANK/OPG status in patients with IT.

METHODS

Bone samples from 18 patients (mean age 25.27 ± 3.34) were divided into 3 groups: 1 - bone tissue of healthy persons (control group); 2 - bone tissue, that was taken near the healthy tooth in patients with tooth impaction; 3 - bone tissue, that was collected near the IT. Levels of RANKL, RANK, OPG, osteocalcin (OC), NF-κB p65 subunit, NFATc1, and caspase-3 were determined by western blotting. The difference between groups was assessed using ANOVA followed by Tukey's post-hoc test. P-value ≤0.05 was considered statistically significant.

RESULTS

We established a 1.73-fold elevation of RANK level in the IT area vs. control, indicating the recruitment of preosteoclasts. An increase in RANKL, OPG, and OC content was demonstrated (1.46-, 1.48-, and 1.42-fold respectively), reflecting the high activity of osteoblasts near the IT. Despite the activation of the RANKL/RANK/OPG system in the impaction area, NF-κB and NFATc1 levels did not change compared vs. control, indicating a blocked/delayed process of osteoclastogenesis. We found a decrease in the content of procaspase-3 (1.28-fold), while the level of its active form p17 increased by 2.26 folds near the healthy tooth in patients with IT compared with control. In the area of ​​IT, we observed an increase in procaspase-3 and p17 levels (1.32 and 1.78 folds). This reflects impairments of caspase-3 activation and accumulation of its inactive form in the IT area that may contribute to the tooth eruption failure.

CONCLUSIONS

Tooth impaction may be associated with the disturbances in the caspase-3 cascade activation and the imbalance in the RANKL/RANK/OPG system, and as a result, blocked bone resorption.

Retained primary teeth in STAT3 hyper-IgE syndrome: early intervention in childhood is essential

BACKGROUND

STAT3 hyper-IgE syndrome (STAT3-HIES) is a rare primary immunodeficiency that clinically overlaps with atopic dermatitis. In addition to eczema, elevated serum-IgE, and recurrent infections, STAT3-HIES patients suffer from characteristic facies, midline defects, and retained primary teeth. To optimize dental management we assessed the development of dentition and the long-term outcomes of dental treatment in 13 molecularly defined STAT3-HIES patients using questionnaires, radiographs, and dental investigations.

RESULTS

Primary tooth eruption was unremarkable in all STAT3-HIES patients evaluated. Primary tooth exfoliation and permanent tooth eruption was delayed in 83% of patients due to unresorbed tooth roots. A complex orthodontic treatment was needed for one patient receiving delayed extraction of primary molars and canines. Permanent teeth erupted spontaneously in all patients receiving primary teeth extraction of retained primary teeth during average physiologic exfoliation time.

CONCLUSIONS

The association of STAT3-HIES with retained primary teeth is important knowledge for dentists and physicians as timely extraction of retained primary teeth prevents dental complications. To enable spontaneous eruption of permanent teeth in children with STAT3-HIES, we recommend extracting retained primary incisors when the patient is not older than 9 years of age and retained primary canines and molars when the patient is not older than 13 years of age, after having confirmed the presence of the permanent successor teeth by radiograph.

4-Hexylresorcinol Administration Increases Dental Hard Tissue Formation and Incisor Eruption Rate in Rats

Dental hard tissue formation and bone turnover are required for tooth eruption. 4-Hexylresorcinol (4HR) accelerates tooth movement by increasing bone turnover in orthodontic treatment. This study aimed to evaluate the following: (1) the effect of 4HR application on the expression of proteins associated with tooth formation, and (2) the effect of 4HR application on mandibular incisor eruption rate in a rat model. Primary cultured pulp cells received either 4HR (1 to 100 µM) or solvent only; western blotting was performed for transforming growth factor-beta 1 (TGF-β1), bone morphogenic protein-2/4 (BMP-2/4), runt-related transcription factor 2 (Runx2), osterix (OSX), dentin sialophosphoprotein (DSPP), and parathyroid hormone-related protein receptor (PTHrP-R). In in vivo study, rats (15 males and 15 females) received either solvent or 0.128 mg/kg or 12.8 mg/kg of 4HR via subcutaneous injection; mandibular incisor eruption rate was subsequently recorded. Immunohistochemical staining and western blotting for TGF-β1, BMP-2/4, Runx2, OSX, DSPP, and PTHrP-R were performed in the mandibular tissue samples. 4HR administration was found to increase TGF-β1, BMP-2/4, Runx2, OSX, DSPP, and PTHrP-R expression in both cell culture and tissue samples. Immunohistochemical staining of some markers showed site-specific expression, thereby indicating programmed differentiation of odontoblasts and ameloblasts. The eruption rate was significantly higher in the 12.8 mg/kg 4HR-administered group than in the untreated control (p = 0.001 and 0.010 for males and females, respectively). Collectively, 4HR administration increased the expression of markers related to dental hard tissue formation and accelerated the eruption rate of incisors in rats.

Soluble silica stimulates osteogenic differentiation and gap junction communication in human dental follicle cells

Several studies have indicated that dietary silicon (Si) is beneficial for bone homeostasis and skeletal health. Furthermore, Si-containing bioactive glass biomaterials have positive effects on bone regeneration when used for repair of bone defects. Si has been demonstrated to stimulate osteoblast differentiation and bone mineralisation in vitro. However, the mechanisms underlying these effects of Si are not well understood. The aim of the present study was to investigate the effects of soluble Si on osteogenic differentiation and connexin 43 (CX43) gap junction communication in cultured pluripotent cells from human dental follicles (hDFC). Neutral Red uptake assay demonstrated that 25 μg/ml of Si significantly stimulated hDFC cell proliferation. Dosages of Si above 100 μg/ml decreased cell proliferation. Alizarin Red staining showed that osteogenic induction medium (OIM) by itself and in combination with Si (25 μg/ml) significantly increased mineralisation in hDFC cultures, although Si alone had no such effect. The expression of osteoblast-related markers in hDFC was analysed with RT-qPCR. OSX, RUNX2, BMP2, ALP, OCN, BSP and CX43 genes were expressed in hDFC cultured for 1, 7, 14 and 21 days. Expression levels of BMP-2 and BSP were significantly upregulated by OIM and Si (25 μg/ml) and were also induced by Si alone. Notably, the expression levels of OCN and CX43 on Day 21 were significantly increased only in the Si group. Flow cytometric measurements revealed that Si (50 μg/ml) significantly increased CX43 protein expression and gap junction communication in hDFC. Next-generation sequencing (NGS) and bioinformatics processing were used for the identification of differentially regulated genes and pathways. The influence of OIM over the cell differentiation profile was more prominent than the influence of Si alone. However, Si in combination with OIM increased the magnitude of expression (up or down) of the differentially regulated genes. The gene for cartilage oligomeric matrix protein (COMP) was the most significantly upregulated. Genes for the regulator of G protein signalling 4 (RGS4), regulator of G protein signalling 2 (RGS2), and matrix metalloproteinases (MMPs) 1, 8, and 10 were also strongly upregulated. Our findings reveal that soluble Si stimulates Cx43 gap junction communication in hDFC and induces gene expression patterns associated with osteogenic differentiation. Taken together, the results support the conclusion that Si is beneficial for bone health.

Alveolar bone morphology in patients with a unilateral palatally displaced maxillary lateral incisor: A cone-beam computed tomography study

INTRODUCTION

Lingual displacement of the maxillary anterior teeth is 1 of the most common forms of malocclusion. The labial alveolar bone is thinner for the maxillary lateral incisor than for the central incisor and canine; however, the alveolar bone width at the actual position of the maxillary lateral incisor has not been examined. We investigated the morphologic characteristics of the alveolar bone around palatally displaced maxillary lateral incisors using cone-beam computed tomography and a split-mouth model.

METHODS

Twenty-seven patients with a unilateral palatally displaced maxillary lateral incisor were included. Axial, sagittal, and horizontal measurements were recorded at 3 levels (ie, 25%, 50%, and 75% of the root length) using cone-beam computed tomography. All obtained data were statistically analyzed using paired t tests.

RESULTS

The labial alveolar bone width at 25% of root length was significantly lesser on the affected side. At all 3 levels, the distance between a line tangential to the labial alveolar bone of the central incisor and canine and the position of the labial alveolar bone of the lateral incisor was significantly greater on the affected side. At 50% and 75% of root length, the horizontal distance between the posterior nasal spine and the labial alveolar bone of the lateral incisor was significantly lesser on the affected side.

CONCLUSIONS

Palatal displacement of maxillary lateral incisors is significantly associated with decreased alveolar bone width at the apical level and asymmetry. However, a further elaborate investigation is necessary to determine the clinical relevance of the study.

A three-dimensional analysis of primary failure of eruption in humans and mice

OBJECTIVES

Primary failure of eruption (PFE) is a genetic disorder exhibiting the cessation of tooth eruption. Loss-of-function mutations in parathyroid hormone (PTH)/parathyroid hormone-related peptide (PTHrP) receptor (PTH/PTHrP receptor, PPR) were reported as the underlying cause of this disorder in humans. We showed in a PFE mouse model that PTHrP-PPR signaling is responsible for normal dental follicle cell differentiation and tooth eruption. However, the mechanism underlying the eruption defect in PFE remains undefined. In this descriptive study, we aim to chronologically observe tooth eruption and root formation of mouse PFE molars through 3D microCT analyses.

SETTING AND SAMPLE POPULATION

Two individuals with PFE were recruited at Showa University. A mouse PFE model was generated by deleting PPR specifically in PTHrP-expressing dental follicle and divided into three groups, PPR^fl/fl ;R26R^tdTomato/+ (Control), PTHrP-creER;PPR^fl/+ ;R26R^tdTomato/+ (cHet), and PTHrP-creER;PRR^fl/fl ;R26R^tdTomato/+ (cKO).

MATERIALS AND METHODS

Images from human PFE subjects were acquired by CBCT. All groups of mouse samples were studied at postnatal days 14, 25, 91, and 182 after a tamoxifen pulse at P3, and superimposition of 3D microCT images among three groups was rendered.

RESULTS

Mouse and human PFE molars exhibited a similar presentation in the 3D CT analyses. The quantitative analysis in mice demonstrated a statistically significant decrease in the eruption height of cKO first and second molars compared to other groups after postnatal day 25. Additionally, cKO molars demonstrated significantly shortened roots with dilacerations associated with the reduced interradicular bone height.

CONCLUSIONS

Mouse PFE molars erupt at a much slower rate compared to normal molars, associated with shortened and dilacerated roots and defective interradicular bones.

A novel nonsense PTH1R variant shows incomplete penetrance of primary failure of eruption: a case report

BACKGROUND

Aim of this work was to describe a rare inheritance pattern of Primary Failure of Eruption (PFE) in a small family with incomplete penetrance of PFE and a novel nonsense PTH1R variant.

CASE PRESENTATION

The proband, a 26 year-old man with a significant bilateral open-bite, was diagnosed with PFE using clinical and radiographic characteristics. DNA was extracted from the proband and his immediate family using buccal swabs and the entire PTH1R coding sequence was analyzed, revealing a novel heterozygous nonsense variant in exon 7 of PTH1R (c.505G > T). This variant introduces a premature stop codon in position 169, predicted to result in the production of a truncated and non-functional protein. This variant has never been reported in association with PFE and is not present in the Genome Aggregation Database (gnomAD). Interestingly, the c.505G > T variant has also been identified in the unaffected mother of our proband, suggesting incomplete penetrance of PFE.

CONCLUSIONS

In this study, we report a new PTH1R variant that segregates in an autosomal dominant pattern and causes PFE with incomplete penetrance. This underlines the diagnostic value of a thorough clinical and genetic analysis of all family members in order to estimate accurate recurrence risks, identify subtle clinical manifestations and provide proper management of PFE patients.

Mesenchymal Progenitor Regulation of Tooth Eruption: A View from PTHrP

Tooth eruption is a unique biological process by which highly mineralized tissues emerge into the outer world, and it occurs concomitantly with tooth root formation. These 2 processes have been considered independent phenomena; however, recent studies support the theory that they are indeed intertwined. Dental mesenchymal progenitor cells in the dental follicle lie at the heart of the coupling of these 2 processes, providing a source for diverse mesenchymal cells that support formation of the highly functional tooth root and the periodontal attachment apparatus, while facilitating formation of osteoclasts. These cells are regulated by autocrine signaling by parathyroid hormone-related protein (PTHrP) and its parathyroid hormone/PTHrP receptor PPR. This PTHrP-PPR signaling appears to crosstalk with other signaling pathways and regulates proper cell fates of mesenchymal progenitor cell populations. Disruption of this autocrine PTHrP-PPR signaling in these cells leads to defective formation of the periodontal attachment apparatus, tooth root malformation, and failure of tooth eruption in molars, which essentially recapitulate primary failure of eruption in humans, a rare genetic disorder exclusively affecting tooth eruption. Diversity and distinct functionality of these mesenchymal progenitor cell populations that regulate tooth eruption and tooth root formation are beginning to be unraveled.

Risk factors for bone loss in juvenile-onset systemic lupus erythematosus: a prospective study

OBJECTIVE

Juvenile-onset systemic lupus erythematosus (JoSLE) is associated with low bone mass for age and fractures; nevertheless, risk factors for bone impairment are poorly understood. The aim of this study was to evaluate risk factors for bone mass loss in JoSLE patients.

METHODS

Forty-nine female JoSLE patients were evaluated at baseline and after a 3.5-year follow-up regarding clinical, laboratory (including bone turnover markers), areal bone mineral density (aBMD) and bone microarchitecture parameters using high-resolution peripheral quantitative computed tomography (HR-pQCT). Based on the difference between final and baseline aBMD value, the patients were divided into three groups: aBMD gain (BG), aBMD loss (BL) and aBMD no change (NC).

RESULTS

The mean patient age was 18.7 ± 3.3 years. Sixty-one percent of patients presented with aBMD gain, 18.4% aBMD loss, and 20.4% remained stable during this follow-up period. Comparing the BL with the BG group, there was a higher frequency of alcohol consumption (p = 0.009), a higher frequency of inadequate calcium intake (p = 0.047) and lower levels of baseline procollagen type 1 amino-terminal propeptide (P1NP) (p = 0.036) in the BL group. Moreover, worsening of HR-pQCT parameters trabecular volumetric density (p = 0.003) and cortical thickness (p = 0.009) was observed in the BL group. In addition, a higher frequency of renal activity was observed comparing the BL + NC with the BG group (p = 0.036).

CONCLUSIONS

This is the first longitudinal study that has analyzed the risk factors of bone loss in JoSLE patients. The authors emphasize the importance of evaluating lifestyle habits and renal disease activity in these young women. Furthermore, this study suggests that trabecular and cortical compartments deteriorated, and low levels of P1NP may be a predictor of bone impairment in JoSLE.

Scintigraphic evaluation of cheek teeth in clinically sound horses

Dental disorders are one of the top-ranking clinical domains in equine practice. Scintigraphy has emerged as a useful diagnostic imaging modality for equine dental diseases. There is a paucity of the normal scintigraphic uptake and its correlation with age. This prospective, cross-sectional, descriptive and pilot-designed study aimed to describe the radioisotope uptake (RU) patterns of the reserved crown and periodontal bone of the maxillary and mandibular cheek teeth (CT) in clinically sound horses and to evaluate the age effect on RU. For this purpose, 60 horses that underwent a bone scintigraphy for reason unrelated to head were included and divided equally into four age groups. Regions of interests (ROIs) were positioned around alveolar and periodontal bone of each maxillary and mandibular CT including their reserve crown, and a reference ROI positioned at the mandibular ramus. The count per pixel of each ROI was measured using a dedicated software and the RU ratio relative to the reference region was calculated. The results showed that the maxillary and mandibular CT had a standard RU pattern, where it increased from rostral to caudal, and peaked in the middle of dental arcades and decreased slightly towards the last CT. The maxillary CT had a higher RU compared with the mandibular CT, and there was no significant difference in the maxillary and mandibular CT uptake between age groups. This information may aid veterinarians evaluating potentially abnormal dental scintigraphy.

Distribution of glutamate receptor, ionotropic, kainate 1 and neuropeptide calcitonin gene-related peptide mRNAs during formation of the embryonic and postnatal mouse molar in the maxilla

The neuropeptide calcitonin gene-related peptide (CGRP) is a well-characterized neurotransmitter. Glutamate receptor, ionotropic, kainate 1 (Grik1) has also been demonstrated to generate high-affinity kainate receptors. However, little is known about the roles of CGRP and Grik1 during the developmental formation of teeth. In this study, we endeavoured to analyse the expression and localization of CGRP and Grik1 mRNAs using in situ hybridization on the mouse maxilla during development from the embryonic stage (E18.5) to after birth (P10, P15 and P20). We found that hybridization with an anti-sense probe for CGRP clearly localized in the maxilla at E18.5 in contrast to that of P15 and P20. Hybridization with an anti-sense probe for CGRP was not detected in the dental pulp of molars in the maxilla at P10, which is in contrast to Grik1 mRNA at the same developmental stage. Hybridization with an anti-sense probe for Grik1 mRNA was detected in the basal region of the dental pulp of molars at P10 and P15. Finally, these markers were not detected in molars in the mouse maxilla at P20. The ratio of positive cells for the hybridization signals of Grik1and CGRP in the dental pulp decreased from E18.5 (p<0.001). These features in CGRP and Grik1r mRNAs may indicate roles of function during tooth development between embryonic and postnatal stages with root formation and erupted movements.

[Effects of post-natal inhibition of RANKL on molar eruption and root formation in C57BL/6 mice]

INTRODUCTION

Recent observations performed in the orthodontic department of La Pitié-Salpêtrière hospital in Paris reported an increase of non-familial eruption defects of permanent molars. Our recent data have evidenced the involvement of osteoclasts (OC) in both the eruption and the dental retention processes through the RANKL/RANK/OPG signaling pathway. These facts are at the origin of the hypothesis of the existence of an environmental etiology for those eruption defects that would correspond to the perturbation of cellular autocrine/paracrine signaling pathways as the RANKL/ RANK/OPG.

MATERIALS AND METHODS

C57BL/6 mice were submitted to repeated injections with anti-RANKL neutralizing antibody during the nine days following birth. A phenotypic comparison with transgenic mice overexpressing RANK was performed for the functional characterization of the RANKL/RANK/OPG pathway. The dento-alveolar complex was analyzed using micro-CT for bone density and Masson's trichrome staining for histological examination.

RESULTS

The RANKL transient invalidation of RANKL stopped the molar root development and tooth eruption contrary to transgenic mice overexpressing RANK. The recruitment and the OC activity were strongly impacted.

DISCUSSION

This research is of direct clinical interest in understanding the pathology of eruption as indirect in establishing orthodontic treatment protocols for particular cases.

Alteration of circular RNA expression in rat dental follicle cells during osteogenic differentiation

Circular RNAs (circRNAs) are novel noncoding RNAs and play crucial roles in various biological processes. However, little is known about the functions of circRNAs in osteogenic differentiation. The current study aimed to investigate the differential expression of circRNAs in rat dental follicle cells (rDFCs) during osteogenic differentiation, identified by RNA high-throughput sequencing and quantitative real-time polymerase chain reaction. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses were performed to further explore the biofunctions of circRNA biofunctions. Two hundred sixty-six differentially-expressed circRNAs that are involved in several important signaling pathways, including mitogen-activated protein kinases (MAPK) and transforming growth factor-β (TGF-β) signaling pathways were revealed. Among these, circFgfr2 and its predicted downstream targets, miR-133 and BMP6 (bone morphogenetic protein-6), were identified both in vivo and in vitro. For further validation, circFgfr2 was overexpressed in rDFCs, the results showed that the expression of miR-133 was downregulated and the expression of BMP6 was upregulated. Taken together, the results revealed the circRNA expression profiles and indicated the importance of circRNAs of rDFCs. In addition, circFgfr2 might promote osteogenesis by controlling miR-133/BMP6, which is a potential new target for the manipulation of tooth regeneration and bone formation.

Multiple impacted permanent teeth, an indicator for early detection of hypoparathyroidism: A rare case report

Eruption is a process of continuous movement of the developing tooth bud from its developmental location to functional location. Teeth that cease to erupt before emergence to their functional position in the oral cavity are termed as impactions. In permanent dentition, third molars are the most frequently impacted teeth followed by the canines. When impaction involves few teeth, the condition is localized but when it involves multiple teeth, the condition becomes generalized and is often associated with some derangement of the normal physiological processes. Factors causing impactions may be localized, pertaining to the area or, systemic or, generalized including bone disorders such as cleidocranial dysplasia and/or some sort of endocrinological disturbance such as hypoparathyroidism. Hypoparathyroidism is a rare endocrinological disorder accompanied by anomalies of various systems including bones and teeth. The dental defects due to hypoparathyroidism may present as hypocalcemia, aplasia and/or hypoplasia, defects of mineralization, short and blunted roots, delayed eruptions, and clinically missing or impacted teeth. This report describes an interesting and unusual case where multiple impacted permanent teeth and retained primary teeth accompanied by other clinical manifestations in a 16-year-old female patient probed the clinicians for further investigations which, eventually, aided in early diagnosis of hypoparathyroidism.

Bone resorption deficiency affects tooth root development in RANKL mutant mice due to attenuated IGF-1 signaling in radicular odontoblasts

The tooth root is essential for normal tooth physiological function. Studies on mice with mutations or targeted gene deletions revealed that osteoclasts (OCs) play an important role in tooth root development. However, knowledge on the cellular and molecular mechanism underlying how OCs mediate root formation is limited. During bone formation, growth factors (e.g. Insulin-like growth factor-1, IGF-1) liberated from bone matrix by osteoclastic bone resorption stimulate osteoblast differentiation. Thus, we hypothesize that OC-osteoblast coupling may also apply to OC-odontoblast coupling; therefore OCs may have a direct impact on odontoblast differentiation through the release of growth factor(s) from bone matrix, and consequently regulate tooth root formation. To test this hypothesis, we used a receptor activator of NF-κB ligand (RANKL) knockout mouse model in which OC differentiation and function was entirely blocked. We found that molar root formation and tooth eruption were defective in RANKL^-/- mice. Disrupted elongation and disorganization of Hertwig's epithelial root sheath (HERS) was observed in RANKL^-/- mice. Reduced expression of nuclear factor I C (NFIC), osterix, and dentin sialoprotein, markers essential for radicular (root) odontogenic cell differentiation indicated that odontoblast differentiation was disrupted in RANKL deficient mice likely contributing to the defect in root formation. Moreover, down-regulation of IGF/AKT/mTOR activity in odontoblast indicated that IGF signaling transduction in odontoblasts of the mutant mice was impaired. Treating odontoblast cells in vitro with conditioned medium from RANKL^-/- OCs cultured on bone slices resulted in inhibition of odontoblast differentiation. Moreover, depletion of IGF-1 in bone resorption-conditioned medium (BRCM) from wild-type (WT) OC significantly compromised the ability of WT osteoclastic BRCM to induce odontoblast differentiation while addition of IGF-1 into RANKL^-/- osteoclastic BRCM rescued impaired odontoblast differentiation, confirming that root and eruption defect in RANKL deficiency mice may result from failure of releasing of IGF-1 from bone matrix through OC bone resorption. These results suggest that OCs are important for odontoblast differentiation and tooth root formation, possibly through IGF/AKT/mTOR signaling mediated by cell-bone matrix interaction. These findings provide significant insights into regulatory mechanism of tooth root development, and also lay the foundation for root regeneration studies.

Graphene-Based Nanomaterials for Tissue Engineering in the Dental Field

The world of dentistry is approaching graphene-based nanomaterials as substitutes for tissue engineering. Apart from its exceptional mechanical strength, electrical conductivity and thermal stability, graphene and its derivatives can be functionalized with several bioactive molecules. They can also be incorporated into different scaffolds used in regenerative dentistry, generating nanocomposites with improved characteristics. This review presents the state of the art of graphene-based nanomaterial applications in the dental field. We first discuss the interactions between cells and graphene, summarizing the available in vitro and in vivo studies concerning graphene biocompatibility and cytotoxicity. We then highlight the role of graphene-based nanomaterials in stem cell control, in terms of adhesion, proliferation and differentiation. Particular attention will be given to stem cells of dental origin, such as those isolated from dental pulp, periodontal ligament or dental follicle. The review then discusses the interactions between graphene-based nanomaterials with cells of the immune system; we also focus on the antibacterial activity of graphene nanomaterials. In the last section, we offer our perspectives on the various opportunities facing the use of graphene and its derivatives in associations with titanium dental implants, membranes for bone regeneration, resins, cements and adhesives as well as for tooth-whitening procedures.

Primary failure of eruption: Clinical and genetic findings in the mixed dentition

OBJECTIVE

To test the hypothesis that mutations in the parathyroid hormone 1 receptor ( PTH1R) include effects in both primary and permanent teeth.

MATERIALS AND METHODS

DNA was extracted from saliva samples of 29 patients (8 familial and 21 sporadic) who presented with clinical evidence of infraoccluded teeth, and their unaffected relatives (N = 22). Sequencing followed by mutational analysis of the coding regions of PTH1R gene was completed for all individuals (N = 29).

RESULTS

Eight of 29 cases revealed a heterozygous pathogenic variant in the PTH1R gene; five of eight variants represented distinct mutations based on comparison with the dbSNP, HGMD, and ESP databases. One mutation (c.1765 T>C p.Trp89Arg) was found to segregate within a family (n = 3). In silico analyses for all variants revealed a putative pathogenic effect. A genotype-phenotype correlation was reported as defined by a functional mutation in PTH1R and corresponding effects on one or more posterior teeth only; unilateral or bilateral involvement, infraoccluded primary teeth.

CONCLUSIONS

Novel mutations were reported in the PTH1R gene that included PFE-affected primary molars, thus providing the basis for using a genetic diagnostic tool for early diagnosis leading to proper management.