Enamel hypomineralization viewed from the pattern of progressive mineralization of human and monkey developing enamel

Role of amelogenin phosphorylation in regulating dental enamel formation

Amelogenin (AMELX), the predominant matrix protein in enamel formation, contains a singular phosphorylation site at Serine 16 (S16) that greatly enhances AMELX's capacity to stabilize amorphous calcium phosphate (ACP) and inhibit its transformation to apatitic enamel crystals. To explore the potential role of AMELX phosphorylation in vivo, we developed a knock-in (KI) mouse model in which AMELX phosphorylation is prevented by substituting S16 with Ala (A). As anticipated, AMELXS16A KI mice displayed a severe phenotype characterized by weak hypoplastic enamel, absence of enamel rods, extensive ectopic calcifications, a greater rate of ACP transformation to apatitic crystals, and progressive cell pathology in enamel-forming cells (ameloblasts). In the present investigation, our focus was on understanding the mechanisms of action of phosphorylated AMELX in amelogenesis. We have hypothesized that the absence of AMELX phosphorylation would result in a loss of controlled mineralization during the secretory stage of amelogenesis, leading to an enhanced rate of enamel mineralization that causes enamel acidification due to excessive proton release. To test these hypotheses, we employed microcomputed tomography (µCT), colorimetric pH assessment, and Fourier Transform Infrared (FTIR) microspectroscopy of apical portions of mandibular incisors from 8-week old wildtype (WT) and KI mice. As hypothesized, µCT analyses demonstrated significantly higher rates of enamel mineral densification in KI mice during the secretory stage compared to the WT. Despite a greater rate of enamel densification, maximal KI enamel thickness increased at a significantly lower rate than that of the WT during the secretory stage of amelogenesis, reaching a thickness in mid-maturation that is approximately half that of the WT. pH assessments revealed a lower pH in secretory enamel in KI compared to WT mice, as hypothesized. FTIR findings further demonstrated that KI enamel is comprised of significantly greater amounts of acid phosphate compared to the WT, consistent with our pH assessments. Furthermore, FTIR microspectroscopy indicated a significantly higher mineral-to-organic ratio in KI enamel, as supported by µCT findings. Collectively, our current findings demonstrate that phosphorylated AMELX plays crucial mechanistic roles in regulating the rate of enamel mineral formation, and in maintaining physico-chemical homeostasis and the enamel growth pattern during early stages of amelogenesis.

Overexpression of ameloblastin in secretory ameloblasts results in demarcated, hypomineralized opacities in enamel

Introduction: Developmental defects of the enamel manifest before tooth eruption and include amelogenesis imperfecta, a rare disease of underlying gene mutations, and molar-incisor hypomineralization (MIH), a prevalent disease in children originating from environmental and epigenetic factors. MIH enamel presents as the abnormal enamel marked by loss of translucency, demarcation between the healthy and affected enamel, and reduced mineral content. The pathophysiology of opaque, demarcated enamel lesions is not understood; however, the retention of enamel proteins in the matrix has been suggested. Ameloblastin (Ambn) is an enamel protein of the secreted calcium-binding phosphoproteins (SCPPs) critical for enamel formation. When the Ambn gene is mutated or deleted, teeth are affected by hypoplastic amelogenesis imperfecta. Methods: In this study, enamel formation in mice was analyzed when transgenic Ambn was overexpressed from the amelogenin promoter encoding full-length Ambn. Ambn was under- and overexpressed at six increasing concentrations in separate mouse lines. Results: Mice overexpressing Ambn displayed opaque enamel at low concentrations and demarcated lesions at high concentrations. The severity of enamel lesions increased starting from the inner enamel close to the dentino-enamel junction (DEJ) to span the entire width of the enamel layer in demarcated areas. Associated with the opaque enamel were 17-kDa Ambn cleavage products, a prolonged secretory stage, and a thin basement membrane in the maturation stage. Ambn accumulations found in the innermost enamel close to the DEJ and the mineralization front correlated with reduced mineral content. Demarcated enamel lesions were associated with Ambn species of 17 kDa and higher, prolonged secretory and transition stages, a thin basement membrane, and shortened maturation stages. Hypomineralized opacities were delineated against the surrounding mineralized enamel and adjacent to ameloblasts detached from the enamel surface. Inefficient Ambn cleavage, loss of contact between ameloblasts, and the altered basement membrane curtailed the endocytic activity; thus, enamel proteins remained unresorbed in the matrix. Ameloblasts have the ability to distinguish between Ambn concentration and Ambn cleavage products through finely tuned feedback mechanisms. The under- or overexpression of Ambn in murine secretory ameloblasts results in either hypoplastic amelogenesis imperfecta or hypomineralization with opaque or sharply demarcated boundaries of lesions, similar to MIH.

Knowledge, experience, and perception of molar incisor hypomineralisation among dentists in the metropolitan area of Mexico City: a cross-sectional study

BACKGROUND

Molar-incisor hypomineralisation (MIH) is the most common developmental abnormality observed in teeth. Being a relatively new condition, its treatment can present a challenge for the dentist. There is currently no study available that has evaluated the knowledge of Mexican dental personnel. This study aimed to evaluate the knowledge, experience, and perceptions of dental surgeons regarding the detection, assessment, and treatment of MIH in the metropolitan area of Mexico City.

METHODS

A cross-sectional study was designed. Dentists from Mexico City and its metropolitan area were invited through social networks to answer a questionnaire of 30 questions related to MIH. Participants were classified into general practice dentists, paediatric dentists, and other speciality dentists. Pearson's chi-square test was used for data analysis.

RESULTS

The questionnaire was answered by 391 dentists. A total of 86% (338 out of 391) of them identified MIH lesions, while 84% of them reported having observed MIH lesions in their practice. The most frequently observed lesions were yellow-brown opacities which accounted for 47% of the lesions, 46% were white opacities, while only 7% were observed as post-eruptive fractures in the enamel as part of the manifestations of MIH. The most frequently reported problem in the management of teeth with MIH was insufficient training for treating children with MIH. A total of 84% of dentists stated that they would like more information on the treatment of MIH lesions.

CONCLUSIONS

Most of the surveyed dentists recognised MIH and reported having observed MIH lesions in their practice. Most of the dentists indicated that the main problem for the management of the MIH is the lack of training.

Molar-incisor hypomineralisation prevalence in a cohort of Australian children with type 1 diabetes

PURPOSE

Systemic diseases or drugs administered early in life may cause a disruption in amelogenesis and contribute to the qualitative defect of enamel described as molar-incisor hypomineralisation (MIH). Therefore, an increase in prevalence of MIH in children with type 1 diabetes (T1D) may be expected as this systemic disorder is commonly diagnosed in early childhood. The aim of this study was to determine the prevalence of MIH in a cohort of children with T1D and investigate diagnosis of MIH with T1D factors.

METHODS

Cross-sectional study of children with T1D recruited from paediatric diabetes clinics at the Women's and Children's Hospital (South Australia). A detailed medical history, comprehensive dental and MIH examination according to the European Academy of Paediatric Dentistry (EAPD) long form classification was collected for each child. All upper and lower first permanent molars and central incisors were scored.

RESULTS

A total number of 73 participants; 35 (47.95%) males were examined including 584 teeth. The mean age of the participants was 13.25 ± 2.58 years, with a mean age of diagnosis 7.75 ± 3.58 years, and a mean HbA1c of 8.5 ± 1.6%. 42 out of 73 children (54.8%) had enamel defects on at least one of the teeth examined. However, 19.2% met the criteria for MIH. Univariate and bivariate analyses were conducted but no significant associations were noted between MIH and risk factors including diabetes control (p > 0.1).

CONCLUSION

There was a high prevalence of enamel defects and MIH amongst children with T1D. More research is required to establish association between T1D and MIH.

Identification by whole-exome sequencing of new single-nucleotide polymorphisms associated with molar-incisor hypomineralisation among the Lebanese population

OBJECTIVE

Molar-incisor hypomineralization (MIH) is a developmental qualitative enamel defect, causing a worldwide challenging dental problem. The etiology of this defect remains unclear. Here we identify by whole-exome sequencing (WES) new single-nucleotide polymorphisms (SNPs) in genes expressed during enamel mineralization and in those modulating prenatal, natal and postnatal risk factors among the Lebanese MIH children: immune system and xenobiotic detoxification.

DESIGN

Dental examination for MIH was performed based on the MIH index for diagnostic criteria. Saliva samples were collected from 37 non-related, MIH-diagnosed subjects for DNA extraction. WES was performed on the Illumina HiSeq2000 platform. The χ² test and Fisher's exact test were used to determine relationship between SNPs frequencies and MIH. OR and its 95% CI were used to report the strength of association. The significance threshold was set at 0.05.

RESULTS

Among the Lebanese population, 37 SNPs presented a significant association with MIH in the following genes: AMTN, MMP-20, STIM1, STIM2, ORAI1, SLC34A2, SLC34A3, VDR, PVALB, HSP90B1, TRPM7, SLC24A4, CA6, SLC4A2, TNFRSF11A, IL10RB, ARNT, ESR1 and CYP1B1.

CONCLUSION

This is the first WES study conducted in patients with MIH. Yet, interactions between polymorphisms in different gene categories are to be investigated for a better assessment of MIH susceptibility.

A Breakthrough in Understanding the Pathogenesis of Molar Hypomineralisation: The Mineralisation-Poisoning Model

Popularly known as "chalky teeth", molar hypomineralisation (MH) affects over 1-in-5 children worldwide, triggering massive amounts of suffering from toothache and rapid decay. MH stems from childhood illness and so offers a medical-prevention avenue for improving oral and paediatric health. With a cross-sector translational research and education network (The D3 Group; thed3group.org) now highlighting this global health opportunity, aetiological understanding is urgently needed to enable better awareness, management and eventual prevention of MH. Causation and pathogenesis of "chalky enamel spots" (i.e., demarcated opacities, the defining pathology of MH) remain unclear despite 100 years of investigation. However, recent biochemical studies provided a pathomechanistic breakthrough by explaining several hallmarks of chalky opacities for the first time. This article outlines these findings in context of previous understanding and provides a working model for future investigations. The proposed pathomechanism, termed "mineralisation poisoning", involves localised exposure of immature enamel to serum albumin. Albumin binds to enamel-mineral crystals and blocks their growth, leading to chalky opacities with distinct borders. Being centred on extracellular fluid rather than enamel-forming cells as held by dogma, this localising pathomechanism invokes a new type of connection with childhood illness. These advances open a novel direction for research into pathogenesis and causation of MH, and offer prospects for better clinical management. Future research will require wide-ranging inputs that ideally should be coordinated through a worldwide translational network. We hope this breakthrough will ultimately lead to medical prevention of MH, prompting global health benefits including major reductions in childhood tooth decay.

Relation between molar-incisor hypomineralization (MIH) occurrence and war pollutants in bombarded regions: Epidemiological pilot study in Lebanon

Background

Molar-incisor hypomineralization (MIH), a developmental enamel defect affecting one or more first permanent molars (FPMs) and sometimes incisors (PIs), is one of the most common pandemic health problems in the world. MIH etiology is still unclear and has been suggested to be related to exposure to environmental toxicants during enamel mineralization.

Aims

To assess the susceptibility to MIH occurrence in regards to war pollutants through the investigation of the prevalence and the clinical characteristics of MIH in a group of Lebanese children whose FPMs and PIs enamel mineralization coincides with the 2006 Lebanese war.

Patients and Methods

This cross-sectional study was performed in schools from different regions of Lebanon. Schoolchildren born in 2004, 2005, 2006, and 2007 were examined for MIH. Clinical status, lesion type, extension, and severity were recorded using the short form chart of the MIH index. Pearson's Chi-square or Fischer's exact test were used to determine if there is a significant relationship between categorical variables.

Results

An overall MIH prevalence of 22.93% has been reported. Forty-seven point seventy-five per cent had both molars and incisors affected. Demarcated opacities were the most frequently observed clinical status. Most of the MIH FPMs and PIs were mildly affected with lesions extended on less than the third of the tooth surface.

Conclusions

MIH prevalence among children born around 2006 Lebanese war is high. The hypothesis of a relation between MIH susceptibility and war pollutants in bombarded regions is legible but requires to be elucidated via additional in vitro and in vivo studies for accurate risk assessment.

Molar Incisor Hypomineralization Prevalence in the Schoolchildren of Gannavaram Mandal, Krishna District, Andhra Pradesh, India: A Cross-sectional Study

AIM AND OBJECTIVES

To evaluate the prevalence of molar incisor hypomineralization (MIH) in schoolchildren of the ages between 8 and 14 years of Gannavaram Mandal, Krishna district, Andhra Pradesh, India.

MATERIALS AND METHODS

A total of 2,250 children of ages between 8 and 14 years were selected randomly from different schools. After obtaining requisite permissions from Mandal Educational Officer (MEO), children was screened for the prevalence of MIH according to European Academy of Paediatric Dentistry (EAPD) 2003 diagnostic criteria and severity for MIH was examined using Wetzel and Reckel scale.

RESULTS

Prevalence of MIH was observed to be 2.1% with higher cases of mild severity and with no sex predilection (p > 0.05).

CONCLUSION

Early diagnosis and treatment can significantly reduce complications associated with MIH. Very few studies have been conducted in India and studies encompassing extensive population are warranted to better understand its etiology.

CLINICAL SIGNIFICANCE

MIH lesions lead to carious development. Hence there is need to identify MIH in children as early as possible to reduce the clinical complications.

HOW TO CITE THIS ARTICLE

Tarannum, Ravichandra KS, Muppa R, et al. Molar Incisor Hypomineralization Prevalence in the Schoolchildren of Gannavaram Mandal, Krishna District, Andhra Pradesh, India: A Cross-sectional Study. Int J Clin Pediatr Dent 2021;14(6):737-740.

Diagnosis of Dental Fluorosis Using Micro-Raman Spectroscopy Applying a Principal Component-Linear Discriminant Analysis

Dental fluorosis is an irreversible condition caused by excessive fluoride consumption during tooth formation and is considered a public health problem in several world regions. The objective of this study was to evaluate the capability of micro-Raman spectroscopy to classify teeth of different fluorosis severities, applying principal component analysis and linear discriminant analysis (PCA-LDA), and estimate the model cross-validation accuracy. Forty teeth of different fluorosis severities and a control group were analyzed. Ten spectra were captured from each tooth and a total of 400 micro-Raman spectra were acquired in the wavenumber range of 250 to 1200 cm⁻¹, including the bands corresponding to stretching and bending internal vibrational modes ν₁, ν₂, ν₃, and ν₄ (PO₄³⁻). From the analysis of the micro-Raman spectra an increase in B-type carbonate ion substitution into the phosphate site of the hydroxyapatite as fluorosis severity increases was identified. The PCA-LDA model showed a sensitivity and specificity higher than 94% and 93% for the different fluorosis severity groups, respectively. The cross-validation accuracy was higher than 90%. Micro-Raman spectroscopy combined with PCA-LDA provides an adequate tool for the diagnosis of fluorosis severity. This is a non-invasive and non-destructive technique with promising applications in clinical and epidemiological fields.

Pathogenesis of Molar Hypomineralisation: Aged Albumin Demarcates Chalky Regions of Hypomineralised Enamel

Molar hypomineralisation (MH) is becoming globally recognised as a significant public health problem linked to childhood tooth decay. However, with causation and pathogenesis unclear after 100 years of investigation, better pathological understanding is needed if MH is to become preventable. Our studies have implicated serum albumin in an extracellular pathomechanism for chalky enamel, opposing longheld dogma about systemic injury to enamel-forming cells. Hypothesising that chalky enamel arises through developmental exposure to serum albumin, this study used biochemical approaches to characterise demarcated opacities from 6-year molars. Addressing contradictory literature, normal enamel was found to completely lack albumin subject to removal of surface contamination. Querying surface permeability, intact opacities were found to lack salivary amylase, indicating that “enamel albumin” had become entrapped before tooth eruption. Thirdly, comparative profiling of chalky and hard-white enamel supported a dose-response relationship between albumin and clinical hardness of opacities. Moreover, albumin abundance delineated chalky enamel from white transitional enamel at opacity borders. Finally, addressing the corollary that enamel albumin had been entrapped for several years, clear signs of molecular ageing (oxidative aggregation and fragmentation) were identified. By establishing aged albumin as a biomarker for chalky enamel, these findings hold methodological, clinical, and aetiological significance. Foremost, direct inhibition of enamel-crystal growth by albumin (here termed “mineralisation poisoning”) at last provides a cogent explanation for the clinical presentation of demarcated opacities. Together, these findings justify pursuit of an extracellular paradigm for the pathogenesis of MH and offer exciting new prospects for alleviating childhood tooth decay through medical prevention of MH.

Molar-incisor hypomineralisation in Lebanon: association with prenatal, natal and postnatal factors

BACKGROUND

Molar-incisor hypomineralisation is an enamel developmental defect highly prevalent in Lebanon. Literature suggests that perinatal conditions and childhood illnesses might be potential aetiological factors for this affection.

AIMS

This case-control study aimed to investigate the association of MIH with prenatal, natal and postnatal factors amongst 7-9 years Lebanese children and to end up with recommendations to overcome its occurrence.

METHODS

Self-administered, structured questionnaire including potential etiological factors was distributed to 659 MIH and non-MIH children's parents. The analysis of data was carried out using Statistical Package for Social Sciences Computer Software (SPSS 21.0, Inc., Chicago, IL, USA). For Statistical analysis, Pearson's chi-square, Fischer's exact test and multivariate regression model were used. A p value of less than 0.05 was considered statistically significant.

RESULTS

Children whose mothers had consumed food and drinks canned during pregnancy had 2.9 (CI: 1.367 to 6.187) times more likely to have MIH. Those who had history of taking antibiotics had 2.15 (CI: 1.186 to 3.909) times higher odds of MIH than those who did not have while those who had fever episodes during the early childhood years were 2.057 (CI: 1.149 to 3.683) times more likely to develop MIH.

CONCLUSION

During early childhood, careful handling of high fever, greater public awareness regarding misuse of antibiotics and education about bisphenol A and how to avoid it during pregnancy and breastfeeding are recommended to decrease the occurrence of MIH.

Forensic isoscapes based on intra-individual temporal variation of δ 18O and 206Pb/207Pb in human teeth

Isotopic signatures used in the georeferencing of human remains are largely fixed by spatially distinct geologic and environmental processes. However, location-dependent temporal changes in these isotope ratios should also be considered when determining an individual's provenance and/or trajectory. Distributions of the relevant isotopes can be impacted by predictable external factors such as climate change, delocalisation of food and water sources and changes in sources and uses of metals. Using Multi-Collector Inductively-Coupled Plasma Mass Spectrometer (MC-ICP-MS) analyses of ²⁰⁶Pb/²⁰⁷Pb in tooth enamel and dentin from a population of 21 ± 1-year-old individuals born circa 1984 and isotope ratio mass spectrometry (IRMS) of δ ¹⁸O in their enamel, we examined the expected influence of some of these factors. The resulting adjustments to the geographic distribution of isotope ratios (isoscapes) found in tooth enamel and dentin may contain additional useful information for forensic identification, but the shifts in values can also impact the uncertainty and usefulness of identifications if they are not taken into account.KEY POINTSIsoscapes of ²⁰⁶Pb/²⁰⁷Pb and δ ¹⁸O used for geolocation are not static.Within a few years, the enamel and dentin of a person may exhibit measurable differences in ²⁰⁶Pb/²⁰⁷Pb even without changing locations.Changes in climatic patterns tied to rising temperatures are more significant than the direct effect of increasing temperature on δ ¹⁸O fixed in tooth bioapatite.Third molar (M3) enamel mineralisation includes material incorporated from before formal amelogenesis takes place.

Pathogenesis of Molar Hypomineralisation: Hypomineralised 6-Year Molars Contain Traces of Fetal Serum Albumin

Molar Hypomineralisation (MH) is gaining cross-sector attention as a global health problem, making deeper enquiry into its prevention a research priority. However, causation and pathogenesis of MH remain unclear despite 100 years of investigation into “chalky” dental enamel. Contradicting aetiological dogma involving disrupted enamel-forming cells (ameloblasts), our earlier biochemical analysis of chalky enamel opacities implicated extracellular serum albumin in enamel hypomineralisation. This study sought evidence that the albumin found in chalky enamel reflected causal events during enamel development rather than later association with pre-existing enamel porosity. Hypothesising that blood-derived albumin infiltrates immature enamel and directly blocks its hardening, we developed a “molecular timestamping” method that quantifies the adult and fetal isoforms of serum albumin ratiometrically. Applying this novel approach to 6-year molars, both isoforms of albumin were detectable in 6 of 8 chalky opacities examined (corresponding to 4 of 5 cases), indicating developmental acquisition during early infancy. Addressing protein survival, in vitro analysis showed that, like adult albumin, the fetal isoform (alpha-fetoprotein) bound hydroxyapatite avidly and was resistant to kallikrein-4, the pivotal protease involved in enamel hardening. These results shift primary attention from ameloblast injury and indicate instead that an extracellular mechanism involving localised exposure of immature enamel to serum albumin constitutes the crux of MH pathogenesis. Together, our pathomechanistic findings plus the biomarker approach for onset timing open a new direction for aetiological investigations into the medical prevention of MH.

Evaluating the changes in molar incisor hypomineralization prevalence: A comparison of two cross-sectional studies in two elementary schools in Mexico City between 2008 and 2017

BACKGROUND

Little information is available on the trends over time of the prevalence of molar incisor hypomineralization (MIH). This condition may be preventing dental caries decline.

AIM

(a) To compare the prevalence of MIH, in Mexico City schoolchildren, evaluated in 2008 with a group evaluated in 2017, (b) to identify the association of MIH with dental caries, and (c) to assess the mother's perception of her child's oral health status.

DESIGN

Two cross-sectional studies performed in 2008 and in 2017 were compared. The oral examiner and the selected schools were the same in both surveys.

RESULTS

A total of 549 schoolchildren were evaluated. The prevalence of MIH in the first survey was 20.3%, and 31.9 % in the second survey, (p = .002). Children with MIH were more likely to have dental caries. The odds ratio was 2.24 (p = .036) and 4.18 (p ˂ .001) in the first and second surveys, respectively. Mothers of children with MIH perceived worse oral health status of their children than the mothers whose children did not have MIH (odds ratio = 4.47, p ˂ .001).

CONCLUSION

The findings portray a clear increase in prevalence of MIH and highlight the need for increased awareness about this condition among dentists and the general population.

Significance of oral health in adult patients with congenital heart disease

Due to improved diagnosis and treatment life expectancy of patients with congenital heart disease is steadily increasing resulting in a growing portion of adult patients. When entering, adulthood patients commonly show a shift in their specific needs for medical care. Since the treatment is mostly not curative many patients have life-long cardiovascular anomalies, among others, entailing high risk for the development of infective endocarditis. Several oral diseases, i.e., caries, apical periodontitis and periodontitis show a very high overall prevalence. These entities are primarily initiated by bacterial infections. Hence, they cause an inherent risk for bacteremia and subsequently for infective endocarditis in patients with congenital heart disease during professional dental care and various daily activities. Conversely congenital heart disease seems to be inevitably associated with considerable impairment of oral health resulting in a tight interrelation between both entities. Different preventive strategies are available to address the elevated risk for infective endocarditis due to oral diseases in patients with congenital heart disease during professional dental care and routine daily activities. This review delineates the current evidence regarding the issue of oral health in adult patients with congenital heart disease.

Antimicrobial photodynamic therapy on teeth with molar incisor hypomineralization-controlled clinical trial

BACKGROUND

Molar incisor hypomineralization (MIH) is a change in the formation of dental enamel of systemic origin that affects at least one of the first 4 permanent molars and usually affects incisors. During the eruption, the affected surfaces tend to fracture, exposing the dentin, which causes excessive sensitivity in addition to making the region very susceptible to the appearance of carious lesions. The objective of this research will be to evaluate the clinical effect of antimicrobial photodynamic therapy (aPDT) in permanent teeth with severe and sensitive MIH.

METHODS

The methodology will be based on the selection of patients from 6 to 12 years of age with permanent molar teeth, randomly divided in 2 groups. The selected teeth should have MIH on the occlusal surface, indicated for clinical restorative treatment. In Group 1, aPDT will be applied for the treatment of infected dentin. Afterward, the teeth will be restored with high viscosity glass ionomer cement. In Group 2, the removal of the softened dentin around the side walls of the cavity with sharp dentine curettes and posterior restoration with high viscosity glass ionomer cement will be performed. All patients will have clinical and radiographic follow-up with a time interval of 6 and 12 months. The data obtained will be submitted to descriptive statistical analysis to evaluate the association of categorical variables. Chi-square test and Fisher exact test will be applied, to analyze the correlation between the continuous variables, Pearson correlation test will be applied. For the analysis of dentin density in the scanned radiographic images and the microbiological results for colony-forming units, ANOVA and Kruskal-Wallis will be applied.

DISCUSSION

Often in the presence of severe MIH, the presence of dentin sensitivity is also associated with caries lesion, making it even more necessary to respect the principles of minimal intervention.

TRIAL REGISTRATION

NCT03904641.

Crystallographic texture and mineral concentration quantification of developing and mature human incisal enamel

For human dental enamel, what is the precise mineralization progression spatially and the precise timing of mineralization? This is an important question in the fundamental understanding of matrix-mediated biomineralization events, but in particular because we can use our understanding of this natural tissue growth in humans to develop biomimetic approaches to repair and replace lost enamel tissue. It is important to understand human tissues in particular since different species have quite distinct spatial and temporal progression of mineralization. In this study, five human central incisors at different stages of enamel maturation/mineralization were spatially mapped using synchrotron X-ray diffraction and X-ray microtomography techniques. From the earliest developmental stage, two crystallite-orientation populations coexist with angular separations between the crystallite populations of approximately 40° varying as a function of position within the tooth crown. In general, one population had significantly lower texture magnitude and contributed a higher percentage to the overall crystalline structure, compared to the other population which contributed only 20-30% but had significantly higher texture magnitude. This quantitative analysis allows us to understand the complex and co-operative structure-function relationship between two populations of crystallites within human enamel. There was an increase in the mineral concentration from the enamel-dentin junction peripherally and from the incisal tip cervically as a function of maturation time. Quantitative backscattered-electron analyses showed that mineralization of prism cores precedes that of prism boundaries. These results provide new insights into the precise understanding of the natural growth of human enamel.

Adhesion to Enamel of Teeth Affected by Molar Incisor Hypomineralization: Literature Review

Background/Aim: Molar incisor hypomineralization (MIH) is a qualitative defect of systemic origin, affecting permanent first molars and often permanent incisors. The treatment modalities can include, amongst others, fissure sealants for prevention of dental caries and composite restorations. Both require adhesion to tooth structure. The aim of this study was to review the literature on the adhesion to enamel affected by MIH.

Material and Methods: A search of PupMed/Medline, ResearchGate and Google Scholar was performed and limited between 2003, when the judgement criteria for MIH were set, and 2016. Thirty-three papers were considered relevant to the subject including five in vivo and six in vitro studies. Studies involving less than ten teeth were excluded.

Results: A four-year clinical trial showed that the application of a total-etch 2-step adhesive system prior to sealant placement is superior to the etch-seal technique. Despite the high success rate of composite restorations shown in three clinical longitudinal studies, there are conflicting results over self-etch being superior to total etch adhesive systems. Pretreating the enamel surface, prior to the adhesive system, with fluoride preventive solutions could reduce the mikroleakage under orthodontic brackets. Three in vitro studies provide inconsistent data about NaOCl pretreating potentials to improve adhesion of composite restorations. Resin infiltration, prior to resin restorations, could improve the microhardness of defected enamel, which may lead to increased bond strength, especially in combination with NaOCl pretreatment.

Conclusions: Adhesion to enamel affected by molar incisor hypomeralization is inferior compared to normal enamel. Sealants applied with the etch-bond-seal technique have greater retention than with the etch-seal technique. Further research is required to provide evidence of the effectiveness of the adhesive system and pretreatment to achieve optimal bonding to MIH.

Effectiveness of an oral health intervention program for children with congenital heart defects

Background

Children with congenital heart defects (CHD) are reported to have poorer oral health compared with healthy children. The aim of the present study was to evaluate the effectiveness of an intensive oral health care program among children with CHD followed from infancy to the age of 5 years, by comparing their oral health status at 5 years with a control group of children with CHD who had not received the program.

Methods

In this longitudinal study, children in western Norway with a need for lifelong follow-up due to congenital heart defects were invited to participate (n = 119). Children born in 2008–2011 were offered an oral health intervention program from infancy to the age of 5 years. The outcome measures for evaluating the intervention were dental caries prevalence, dental erosion, plaque index and gingival bleeding index. The data of the intervention group were compared with cross sectional oral health data of 5 year old controls with CHD born 2005–2007 (already published).

Results

Early oral health intervention did not affect the prevalence of caries (25.3% versus 25.4%) or dental erosion (22.2% versus 19.7%) of children with CHD assessed at 5 years. Children in the intervention group were less likely than those in the control group to present with both dental plaque and gingival bleeding at age 5 years. In spite of no difference in caries prevalence between the groups, caries affected children (d_1-5mft) in the intervention group had fewer teeth affected by caries than children in the control group (p = 0.06). The care index was reported to be higher in the intervention group compared with the control group, implying that fewer children in the intervention group suffered from untreated dentine caries. Parents in the intervention group were more likely to brush their children’s teeth twice a day than parents of children in the control group.

Conclusion

The oral health promotive program did not influence the prevalence of caries nor dental erosion. However, the findings indicated better oral hygiene, reduced gingival bleeding and less untreated dentine caries in the intervention compared with the control group.

Trial registration

ClinicalTrials.gov NCT03311438. Registration date: October 17th 2017, retrospectively registered.

Electronic supplementary material

The online version of this article (10.1186/s12903-018-0495-5) contains supplementary material, which is available to authorized users.

Synchrotron imaging and Markov Chain Monte Carlo reveal tooth mineralization patterns

The progressive character of tooth formation records aspects of mammalian life history, diet, seasonal behavior and climate. Tooth mineralization occurs in two stages: secretion and maturation, which overlap to some degree. Despite decades of study, the spatial and temporal pattern of elemental incorporation during enamel mineralization remains poorly characterized. Here we use synchrotron X-ray microtomography and Markov Chain Monte Carlo sampling to estimate mineralization patterns from an ontogenetic series of sheep molars (n = 45 M1s, 18 M2s). We adopt a Bayesian approach that posits a general pattern of maturation estimated from individual- and population-level mineral density variation over time. This approach converts static images of mineral density into a dynamic model of mineralization, and demonstrates that enamel secretion and maturation waves advance at nonlinear rates with distinct geometries. While enamel secretion is ordered, maturation geometry varies within a population and appears to be driven by diffusive processes. Our model yields concrete expectations for the integration of physiological and environmental signals, which is of particular significance for paleoseasonality research. This study also provides an avenue for characterizing mineralization patterns in other taxa. Our synchrotron imaging data and model are available for application to multiple disciplines, including health, material science, and paleontological research.

Enamel biorhythms of humans and great apes: the Havers-Halberg Oscillation hypothesis reconsidered

The Havers-Halberg Oscillation (HHO) hypothesis links evidence for the timing of a biorhythm retained in permanent tooth enamel (Retzius periodicity) to adult body mass and life history traits across mammals. Potentially, these links provide a way to access life history of fossil species from teeth. Recently we assessed intra-specific predictions of the HHO on human children. We reported Retzius periodicity (RP) corresponded with enamel thickness, and cusp formation time, when calculated from isolated deciduous teeth. We proposed the biorhythm might not remain constant within an individual. Here, we test our findings. RP is compared between deciduous second and permanent first molars within the maxillae of four human children. Following this, we report the first RPs for deciduous teeth from modern great apes (n = 4), and compare these with new data for permanent teeth (n = 18) from these species, as well as with previously published values. We also explore RP in teeth that retain hypoplastic defects. Results show RP changed within the maxilla of each child, from thinner to thicker enameled molars, and from one side of a hypoplastic defect to the other. When considered alongside correlations between RP and cusp formation time, these observations provide further evidence that RP is associated with enamel growth processes and does not always remain constant within an individual. RP of 5 days for great ape deciduous teeth lay below the lowermost range of those from permanent teeth of modern orangutan and gorilla, and within the lowermost range of RPs from chimpanzee permanent teeth. Our data suggest associations between RP and enamel growth processes of humans might extend to great apes. These findings provide a new framework from which to develop the HHO hypothesis, which can incorporate enamel growth along with other physiological systems. Applications of the HHO to fossil teeth should avoid transferring RP between deciduous and permanent enamel, or including hypoplastic teeth.

Evaluation of Mineral Content and Photon Interaction Parameters of Dental Enamel After Phosphoric Acid and Er:YAG Laser Treatment

OBJECTIVE

The purpose of this study was to evaluate the effects of laser and acid etching on the mineral content and photon interaction parameters of dental enamel in human teeth.

BACKGROUND DATA

The composition of dental enamel may vary, especially at the surface, depending on the reactions that occur during dental treatment.

MATERIALS AND METHODS

Forty maxillary premolars were divided randomly into 2 groups of 20 teeth. In the first group, half of teeth crowns were etched by using 37% phosphoric acid; in the second group, half of teeth crowns were etched by using an erbium:yttrium-aluminum-garnet (Er:YAG) laser. The remaining half crowns in each group were used as untreated controls. We characterized the calcium (Ca), phosphorus (P), magnesium (Mg), sodium (Na), and potassium (K) contents in each specimen by using wavelength dispersive X-ray fluorescence spectrometry. The total atomic cross-section ([Formula: see text]), effective atomic number ([Formula: see text]), and electron density (N_e) of the tooth samples were determined at photon energies of 22.1, 25, 59.5, and 88 keV by using a narrow beam transmission method. Data were analyzed statistically by using the Mann-Whitney U test.

RESULTS

The mineral contents after Er:YAG laser and phosphoric acid etching did not differ significantly (p > 0.05), and no significant variation in [Formula: see text], [Formula: see text], or N_e was observed.

CONCLUSIONS

Therefore, we conclude that the Er:YAG laser and phosphoric acid systems used in this study did not affect mineral composition or photon interaction parameters of dental enamel.

Association between Molar Incisor Hypomineralization in Schoolchildren and Both Prenatal and Postnatal Factors: A Population-Based Study

BACKGROUND

Although studies throughout the world have investigated potential factors involved in the occurrence of molar incisor hypomineralization (MIH), the findings are varied and inconclusive.

OBJECTIVE

The aim of the present study was to evaluate the prevalence of MIH and identify associated prenatal, perinatal and postnatal factors among Brazilian schoolchildren aged 8 and 9 years.

METHODS

A cross-sectional study was conducted with a randomly selected population-based sample of 1181 schoolchildren. Information on demographic and socioeconomic characteristics as well as prenatal, perinatal and postnatal aspects was obtained through questionnaires. The clinical examination included the investigation of MIH based on the criteria of the European Academy of Paediatric Dentistry. Dental caries in the permanent dentition and developmental defects of enamel (DDE) on the primary second molars were also recorded. Data analysis involved descriptive statistics, bivariate tests and Poisson regression with robust variance.

RESULTS

The prevalence of MIH was 20.4%. MIH was more frequent among children with dental caries in the permanent dentition (PR: 2.67; 95% CI: 1.98-3.61), those with DDE on the primary second molars (PR: 2.54; 95% CI: 1.87-3.45) and those who experienced asthma/bronchitis in the first four years of life (PR: 1.93; 95% CI: 1.45-2.56).

CONCLUSIONS

The prevalence of MIH was high and was associated with dental caries, the presence of DDE on primary second molars and the experience of asthma/bronchitis in early life. These findings could be useful in the identification of children in need of shorter recall intervals to prevent the consequences of MIH, such as enamel breakdown dental caries.

A comparison of the presentation of molar incisor hypomineralisation in two communities with different fluoride exposure

AIM

To compare the clinical presentation of two cohorts of children diagnosed with molar incisor hypomineralisation (MIH) and living in areas of low and high background fluoridation.

METHODS

The study population comprised 12-year-old children participating in the 2008-2009 National Dental Epidemiological Programme in five regions in Northern England. Participating dentists were trained and calibrated in the use of the modified Developmental Defects of Enamel Index. Children were examined at school under direct vision with the aid of a dental mirror. First permanent molars and incisors were recorded for the presence and type of enamel defects greater than 2 mm. A diagnosis of MIH was ascribed to any child with a demarcated defect in any first permanent molar. Risk ratios for the occurrence of demarcated, diffuse and hypoplastic defects were generated for MIH children in the fluoridated and non-fluoridated area.

RESULTS

3,233 children were examined. The prevalence of MIH in the fluoridated community was 11 % and in the non-fluoridated community was 17.5 %. Incisors in children with MIH were at greater risk of having demarcated defects (risk ratio 4.0, 3.6-4.5) and diffuse defects (risk ratio 2.2, 2.0-2.5). Molars in children with MIH were at greater risk of diffuse defects (risk ratio 4.4, 3.8-5.0). The teeth of children with MIH living in the fluoridated area were at greater risk of demarcated defects for both incisors (risk ratio 1.6, 1.3-2.0) and molars (risk ratio 1.3, 1.2-1.5) relative to the teeth of MIH children living in the non-fluoridated area.

CONCLUSIONS

Children with MIH were at increased risk of both diffuse and demarcated defects in their incisors. Children with MIH living in the fluoridated area were at increased risk of diffuse and demarcated defects relative to MIH children living in the non-fluoridated area.

XRMA and ToF-SIMS Analysis of Normal and Hypomineralized Enamel

Molar incisor hypomineralization (MIH) is a developmental disturbance of the enamel. This study presents analyses of hypomineralized and normal enamel in first molar teeth diagnosed with MIH, utilizing time-of-flight secondary ion mass spectrometry area analyses and X-ray microanalysis of area and spot profiles in uncoated samples between gold lines which provide electrical conductivity. Statistical analysis of mean values allows discrimination of normal from MIH enamel, which has higher Mg and lower Na and P. Inductive analysis using complete data sets for profiles from the enamel surface to the enamel-dentin junction found that Mg, Cl and position in the profile provide useful discrimination criteria. Element profiles provide a visual complement to the inductive analysis and several elements also provide insight into the development of both normal and MIH enamel. The higher Mg content and different Cl profiles of hypomineralized enamel compared with normal enamel are probably related to a relatively short period during the development of ameloblasts between birth and the 1st year of life.

Background factors of molar-incisor hypomineralization in a group of Finnish children

OBJECTIVE

Molar-Incisor Hypomineralization (MIH) is a common developmental enamel defect characterized by demarcated opacities in permanent molars and incisors. Its etiology still remains unclear. The aim of this retrospective cohort study was to assess if the socioeconomic environment of the child is associated with MIH.

MATERIALS AND METHODS

The study was located in two rural towns and three urban cities in Finland. A total of 818 children, between 7-13 years old, were examined for MIH using the evaluation criteria in line with those of the European Academy of Paediatric Dentistry, but excluding opacities smaller than 2 mm in diameter. The mothers filled in a questionnaire which included questions related to the family's way of living (e.g. area of residency, farming, day care attendance) and socioeconomic status (family income, number of mother's school years, level of maternal education).

RESULTS

The prevalence of MIH in the study population was 17.1%. Family income, urban residency and day care attendance were associated with MIH in the univariate analysis. In the multivariate analysis using binary logistic regression, only urban residency during a child's first 2 years of life remained associated with MIH. The prevalence of MIH in urban areas was 21.3% and in rural areas 11.5% (OR = 2.18, CI = 1.35-3.53, p = 0.001).

CONCLUSIONS

The prevalence of MIH was related to urban residency and could not be explained by any other factor included in the study.

Mapping the spatial and temporal progression of human dental enamel biomineralization using synchrotron X-ray diffraction

OBJECTIVE

The complex biological, physicochemical process of human dental enamel formation begins in utero and for most teeth takes several years to complete. Lost enamel tissue cannot regenerate, therefore a better understanding of the spatial and temporal progression of mineralization of this tissue is needed in order to design improved in vivo mineral growth processes for regenerative dentistry and allow the possibility to grow a synthetic whole or partial tooth.

METHOD

Human dental enamel samples across a range of developmental stages available through archaeological collections have been used to explore the spatial and temporal progression of enamel biomineralization. Position sensitive synchrotron X-ray diffraction was used to quantify spatial and temporal variations in crystallite organization, lattice parameters and crystallite thickness at three different stages in enamel maturation. In addition X-ray microtomography was used to study mineral content distributions.

RESULTS

An inverse correlation was found between the spatial variation in mineral content and the distribution of crystallite organization and thickness as a function of time during enamel maturation. Combined X-ray microtomography and synchrotron X-ray diffraction results show that as enamel matures the mineral content increases and the mineral density distribution becomes more homogeneous. Starting concurrently but proceeding at a slower rate, the enamel crystallites become more oriented and larger; and the crystallite organization becomes spatially more complex and heterogeneous.

CONCLUSION

During the mineralization of human dental enamel, the rate of mineral formation and mineral organization are not identical. Whilst the processes start simultaneously, full mineral content is achieved earlier, and crystallite organization is slower and continues for longer. These findings provide detailed insights into mineral development in human dental enamel which can inform synthetic biomimetic approaches for the benefit of clinical dentistry.

Putative factors associated with molar incisor hypomineralisation: an epidemiological study

AIM

The aim of the study was to examine the aetiological factors involved in the development of molar incisor hypomineralisation (MIH).

METHODS

The study population comprised 4,049 children (2,029 girls, 2020 boys) aged 7-12 years. Children were examined for MIH in the school environment. Putative aetiological factors were evaluated using a questionnaire sent to children's families. The questionnaire included questions on prenatal, perinatal, and postnatal systemic conditions. Multivariate analysis was performed using multiple logistic regression, and Pearson's Chi-square test was used to evaluate nominal or ordinal variables with Fisher's exact test used in cases of small sample sizes. A level of p < 0.05 was considered statistically significant.

RESULTS

MIH was observed in 7.7 % of the study population. A total of 3,827 completed questionnaires were returned, yielding a response rate of 95.3 %. MIH was found to be associated with prematurity (7 %), gastrointestinal problems (3.9 %), pneumonia (6.3 %), frequent fever (26.1 %), measles (14.7 %), and chickenpox (29.3 %) before age 4 years.

STATISTICS

Prevalence did not vary significantly between girls and boys (p > 0.05). Prematurity, gastrointestinal problems, pneumonia, frequent high fever, measles, and chickenpox before age 4 years were found to be significantly related with MIH (p < 0.05).

CONCLUSIONS

The aetiology of MIH is not clear yet, and the results of this study support the results of previous studies regarding the putative causal effect of several factors.

Molar incisor hypomineralisation: possible aetiological factors in children from urban and rural areas

AIM

To analyse factors potentially associated with molar incisor hypomineralisation (MIH) development. METH¬ODS: A population-based study was carried out with 903 children aged from 6-12 years old, born and residing in rural and urban areas of the town of Botelhos, State of Minas Gerais, Brazil. Their mothers completed a structured medical history questionnaire, from pregnancy to the child's 3rd year of life. Two examiners evaluated children for MIH according to criteria suggested by the European Academy of Paediatric Dentistry. Descriptive analyses of the data and odds ratios (OR) with 95% test-based confidence intervals (CI) were estimated. Chi-square test was used to evaluate the differences between groups.

RESULTS

The prevalence of MIH in children from rural area (RA) was significantly higher than those from the urban area (UA) (24.9% versus 17.8%, p= 0.01). In urban children, neither significant associations with MIH nor medical problems were found. In rural children, however, MIH was significantly more common among those whose mothers had experienced medical problems during pregnancy (OR=2.11; 1.01-4.37 CI 95%; p=0.04), who had throat infections (OR=2.93; 1.47-5.87 CI 95%; p=0.01), who had high fever (OR=1.91; 1.07-3.39 CI 95%; p=0.02), and who had used amoxicillin associated with other antibiotics (OR=1.92; 1.02-3.62 CI 95%; p=0.04) during the first 3 years of life.

CONCLUSION

This study suggests a link between MIH and health problems during pregnancy, as well as environmental factors.

Combined effect of fluoride and 2,3,7,8-tetrachlorodibenzo-p-dioxin on mouse dental hard tissue formation in vitro

Fluoride interferes with enamel matrix secretion and mineralization and dentin mineralization. The most toxic dioxin congener, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), also impairs dental hard tissue formation and mineralization in vitro and in vivo. Our aim was to investigate in vitro whether the combined effect of sodium fluoride (NaF) and TCDD on dental hard tissue formation is potentiative. For this purpose, mandibular first and second molar tooth germs of E18 mouse embryos were cultured for 5-12 days with NaF and TCDD alone at various concentrations (2.5, 5, 10, 12.5, 15, and 20 μM and 5, 10, 12.5, and 15 nM, respectively) to determine the highest concentrations, which alone cause no or negligible effects. Morphological changes were studied from the whole tooth photographs and histological tissue sections. The concentrations found were 15 μM for NaF and 10 nM for TCDD. While at these concentrations, the effects of NaF and TCDD alone were barely detectable, the effect of simultaneous exposure on dentin and enamel formation was overt; mineralization of predentin to dentin and enamel matrix secretion and mineralization were impaired. Immunohistochemical analysis revealed that the combined exposure modified amelogenin expression by odontoblasts. Morphology of ameloblasts and the expression of amelogenin indicated that ameloblasts were still secretory. The results show that NaF and TCDD have potentiative, harmful effects on the formation of dental hard tissues. Since children can be exposed to subclinical levels of fluoride and dioxins during early childhood, coincidently with mineralization of the first permanent teeth, this finding may have clinical significance.

Aetiology of Molar-Incisor Hypomineralisation: A systematic review

AIM

This was to review and assess the studies on aetiology of Molar-Incisor Hypomineralisation (MIH) or, as a proxy, of demarcated opacities in permanent first molars and to consider the potential factors involved with findings obtained in animal experiments.

METHODS

A systematic search by Medline online database was performed. Abstracts behind appropriate titles were studied and finally the full articles were evaluated for their strength of evidence in the aetiology of MIH.

RESULTS

From a total of 1,142 articles 28 were identified and selected for review. The selected papers covered medical problems in prenatal, perinatal and postnatal period, medication of the child during the first years of life, and exposure to fluoride or environmental toxicants (dioxins and PCBs) in the early childhood. Based on the assessment of the articles it was still not possible to specifically name those factors causing MIH although correlations between several potential factors and MIH were presented. Among the factors suggested and found to cause enamel defects in animal experiments were: high fever, hypoxia, hypocalcaemia, exposure to antibiotics (amoxicillin, a macrolide), and dioxins.

CONCLUSION

Despite increased knowledge on the aetiology of MIH insufficient evidence to verify the causative factors exists. Further studies, especially prospective ones, are needed to improve the level and strength of evidence of the role of the present putative factors and to reveal new factors that may be involved. Any combined effect of several factors should be taken into account. Experimental dose/response studies and research on the molecular mechanisms causing the abnormal function of the ameloblasts are also necessary to deepen our knowledge of MIH.

Organic and inorganic content of fluorotic rat incisors measured by FTIR spectroscopy

Details on how fluoride interferes in enamel mineralization are still controversial. Therefore, this study aimed at analyzing the organic contents of fluorosis-affected teeth using Fourier Transformation Infrared spectroscopy. To this end, 10 male Wistar rats were divided into two groups: one received 45 ppm fluoride in distilled water for 60 days; the other received distilled water only. Then, the lower incisors were removed and prepared for analysis by two FTIR techniques namely, transmission and micro-ATR. For the first technique, the enamel was powdered, whereas in the second case one fluorotic incisor was cut longitudinally for micro-ATR. Using transmission and powdered samples, FTIR showed a higher C-H content in the fluorotic enamel compared with control enamel (p<0.05, n=4 in the flurotic, and n=5 in the control group). Results from the micro-ATR-FTIR spectroscopic analysis on one longitudinally cut incisor carried out at six points reveal a higher C-H bond content at the surface of the enamel, with values decreasing toward the dentine-enamel junction, and reaching the lowest values at the subsuperficial enamel. These results agree with the morphological data, which indicate that in the rat incisor the fluorotic lesion is superficial, rather than subsuperficial, as in the case of human enamel. The results also suggest that the increased C-H bond content may extend toward the more basal enamel (intraosseous), indicating that fluorotic enamel may intrinsically contain more protein. Finally, particularly when coupled to ATR, FTIR is a suitable tool to study the rat incisor enamel, which is a largely used model of normal and abnormal amelogenesis. Further studies along this line may definitely answer some questions regarding protein content in fluorotic enamel as well as their origin.

Passports from the past: Investigating human dispersals using strontium isotope analysis of tooth enamel

Strontium isotopes are a powerful tool which provide information about provenance directly from the tissues of humans rather than the grave context and burial goods. Geographical variation in strontium isotopes is primarily controlled by the underlying geology but there are many other factors that need to be considered before migratory individuals can be identified. Consequently, despite many studies which have shown that the method works well, it is clear that much remains to be clarified and it will not work for every question or in every place. It rests on the assumption that people were sourcing their food locally and that there is a measurable strontium isotope difference between the place the person migrated from and the place they migrated to. As migrants may deliberately seek out familiar soil types and terrains in their new homeland, some questions surrounding major migration events may prove intractable for this technique. Other factors that can create heterogeneity or homogeneity leading to false positives or false negatives, such as human choices or coastal subsistence, are explored and the metabolism of strontium into human tooth enamel is discussed. Several models of land-use choices by humans are presented to highlight the subtleties inherent in the isotope data and these are used to interpret archaeological human isotope ratios from three studies.

Polarized light and scanning electron microscopic investigation of enamel hypoplasia in primary teeth

BACKGROUND

Enamel hypoplasia is a developmental disturbance during enamel formation, defined as a macroscopic defect in the enamel, with a reduction of the enamel thickness with rounded, smooth borders. Information on the microstructural level is still limited, therefore further studies are of importance to better understand the mechanisms behind enamel hypoplasia.

AIM

To study enamel hypoplasia in primary teeth by means of polarized light microscopy and scanning electron microscopy.

METHODS

Nineteen primary teeth with enamel hypoplasia were examined in a polarized light microscope and in a scanning electron microscope.

RESULTS

The cervical and incisal borders of the enamel hypoplasia had a rounded appearance, as the prisms in the rounded cervical area of the hypoplasia were bent. The rounded borders had a normal surface structure whereas the base of the defects appeared rough and porous.

CONCLUSIONS

Morphological findings in this study indicate that the aetiological factor has a short duration and affects only certain ameloblasts. The bottom of the enamel hypoplasia is porous and constitutes possible pathways for bacteria into the dentin.

Multilevel complex interactions between genetic, epigenetic and environmental factors in the aetiology of anomalies of dental development

Dental anomalies are caused by complex interactions between genetic, epigenetic and environmental factors during the long process of dental development. This process is multifactorial, multilevel, multidimensional and progressive over time. In this paper the evidence from animal models and from human studies is integrated to outline the current position and to construct and evaluate models, as a basis for future work. Dental development is multilevel entailing molecular and cellular interactions which have macroscopic outcomes. It is multidimensional, requiring developments in the three spatial dimensions and the fourth dimension of time. It is progressive, occurring over a long period, yet with critical stages. The series of interactions involving multiple genetic signalling pathways are also influenced by extracellular factors. Interactions, gradients and spatial field effects of multiple genes, epigenetic and environmental factors all influence the development of individual teeth, groups of teeth and the dentition as a whole. The macroscopic, clinically visible result in humans is a complex unit of four different tooth types formed in morphogenetic fields, in which teeth within each field form directionally and erupt at different times, reflecting the spatio-temporal control of development. Even when a specific mutation of a single gene or one major environmental insult has been identified in a patient with a dental anomaly, detailed investigation of the phenotype often reveals variation between affected individuals in the same family, between dentitions in the same individual and even between different teeth in the same dentition. The same, or closely similar phenotypes, whether anomalies of tooth number or structure, may arise from different aetiologies: not only mutations in different genes but also environmental factors may result in similar phenotypes. Related to the action of a number of the developmental regulatory genes active in odontogenesis, in different tissues, mutations can result in syndromes of which dental anomalies are part. Disruption of the antagonistic balance between developmental regulatory genes, acting as activators or inhibitors can result in dental anomalies. There are critical stages in the development of the individual tooth germs and, if progression fails, the germ will not develop further or undergoes apoptosis. The reiterative signalling patterns over time during the sequential process of initiation and morphogenesis are reflected in the clinical association of anomalies of number, size and form and the proposed models. An initial step in future studies is to combine the genetic investigations with accurate recording and measurement of the phenotype. They also need to collate findings at each level and exploit the accurate definition of both human and murine phenotypes now possible.

Nothing new under the heavens: MIH in the past?

AIM

This was to study an archaeological population of subadult teeth in 17th and 18th century skeletal material from a London (England) cemetery for enamel defects including molar-incisor-hypomineralisation (MIH).

METHODS

Dentitions of 45 sub-adults were examined using standard macroscopic methods and systematically recorded. A total of 557 teeth were examined with a *5 lens and photographed. Ages of the individuals were estimated from their dental crown and root development stages and not from charts that combine tooth eruption with development stages. The dental age of the individual and the approximate age of onset of enamel defects was then calculated on the basis of the chronological sequence of incremental deposition and calcification of the enamel matrix. Affected enamel was graded macroscopically as: - Mild: <30% of the tooth's enamel surface area visibly disrupted (this encompasses the entire range reported in most other studies), Moderate: 31-49% of the tooth's enamel surface area visibly disrupted and Severe: >50% of the tooth's enamel surface area visibly disrupted.

RESULTS

Of the total number of individuals 41 (93.2%) showed signs of enamel developmental dysplasia or MIH, 28 of them showing moderate or severe lesions of molars, primary or permanent (63.6% of the sample). Incisors and canines, though surviving much less often, showed episodes of linear hypoplasia.

CONCLUSION

The extensive lesions seen on many of the molars displayed cuspal enamel hypoplasia (CEH). Many of these teeth also exhibited Molar Incisal Hypomineralisation (MIH).

The developmental clock of dental enamel: a test for the periodicity of prism cross-striations in modern humans and an evaluation of the most likely sources of error in histological studies of this kind

Dental tissues contain regular microscopic structures believed to result from periodic variations in the secretion of matrix by enamel- and dentine-forming cells. Counts of these structures are an important tool for reconstructing the chronology of dental development in both modern and fossil hominids. Most studies rely on the periodicity of the regular cross-banding that occurs along the long axis of enamel prisms. These prism cross-striations are widely thought to reflect a circadian rhythm of enamel matrix secretion and are generally regarded as representing daily increments of tissue. Previously, some researchers have argued against the circadian periodicity of these structures and questioned their use in reconstructing dental development. Here we tested the periodicity of enamel cross-striations--and the accuracy to which they can be used--in the developing permanent dentition of five children, excavated from a 19th century crypt in London, whose age-at-death was independently known. The interruption of crown formation by death was used to calibrate cross-striation counts. All five individuals produced counts that were strongly consistent with those expected from the independently known ages, taking into account the position of the neonatal line and factors of preservation. These results confirm that cross-striations do indeed reflect a circadian rhythm in enamel matrix secretion. They further validate their use in reconstructing dental development and in determining the age-at-death of the remains of children whose dentitions are still forming at the time of death. Significantly they identify the most likely source of error and the common difficulties encountered in histological studies of this kind.

Transmission electron microscope characterisation of molar-incisor-hypomineralisation

Molar-incisor-hypomineralisation (MIH), one of the major developmental defects in dental enamel, is presenting challenge to clinicians due, in part, to the limited understanding of microstructural changes in affected teeth. Difficulties in the preparation of site-specific transmission electron microscope (TEM) specimens are partly responsible for this deficit. In this study, a dual-beam field emission scanning electron microscope (FESEM)/focused ion beam (FIB) milling instrument was used to prepare electron transparent specimens of sound and hypomineralised enamel. Microstructural analysis revealed that the hypomineralised areas in enamel were associated with marked changes in microstructure; loosely packed apatite crystals within prisms and wider sheath regions were identified. Microstructural changes appear to occur during enamel maturation and may be responsible for the dramatic reduction in mechanical properties of the affected regions. An enhanced knowledge of the degradation of structural integrity in hypomineralised enamel could shed light on more appropriate management strategies for these developmental defects.

Molar incisor hypomineralization: a study of aetiological factors in a group of UK children

OBJECTIVES

The objectives were to investigate the aetiology of molar incisor hypomineralization (MIH), and to discuss previously published studies.

SUBJECTS AND METHODS

One hundred and nine children attending the Department of Paediatric Dentistry at the Royal London Hospital were included in the study: 57 children with MIH and 52 controls. Their mothers completed a medical history interview.

RESULTS

No significant associations were found with MIH and delivery and birth complications, breastfeeding, immunization history, other illnesses and allergies, general anaesthetics, fluoride history, and trauma or abscesses affecting the primary predecessors. A family history of enamel defects was more commonly reported for MIH children, but the association was not statistically significant. However, MIH was significantly more common among those whose mothers had experienced problems during pregnancy (P = 0.025), those who had chickenpox between the ages of 3 and 3.99 (P = 0.047), and those for whom amoxycillin was the only antibiotic they had received (P = 0.028).

CONCLUSIONS

The aetiology of MIH remains unclear, and this study questions whether it is because of a lone aetiological insult. This study recommends further research looking at the links with chickenpox occurring around the third year of life and amoxycillin.

Gross enamel hypoplasia in molars from subadults in a 16th-18th century London graveyard

Dental Enamel Hypoplasia has long been used as a common nonspecific stress indicator in teeth from archaeological samples. Most researchers report relatively minor linear and pitted hypoplastic defects on tooth crown surfaces. In this work we report a high prevalence and early age of onset of extensive enamel defects in deciduous and permanent molars in the subadults from the post-medieval cemetery of Broadgate, east central London. Analysis of the dentition of all 45 subadults from the cemetery, using both macroscopic and microscopic methods, reveals disturbed cusp patterns and pitted, abnormal and arrested enamel formation. Forty-one individuals from this group (93.2%) showed some evidence of enamel hypoplasia, 28 of them showing moderate or extensive lesions of molars, deciduous or permanent (63.6% of the sample). Scanning Electron Microscope images reveal many molars with grossly deformed cuspal architecture, multiple extra cusps and large areas of exposed Tomes' process pits, where the ameloblasts have abruptly ceased matrix production, well before normal completion. This indented, rough and poorly mineralized surface facilitates both bacterial adhesion and tooth wear, and when such teeth erupt fully into the mouth they are likely to wear and decay rapidly. We suggest that this complex combination of pitted and plane-form lesions, combined with disruption of cusp pattern and the formation of multiple small cusps, should henceforth be identified as "Cuspal Enamel Hypoplasia."