Insights into molar-incisor hypomineralisation in past populations: A call to anthropologists

OBJECTIVE

Molar incisor hypomineralisation (MIH) is a developmental defect of enamel affecting the first permanent molars and often the incisors and affecting approximately 13% of the current population worldwide. Here, we aim to highlight potential differential diagnoses of MIH in archaeological collections (taphonomic discoloration, amelogenesis imperfecta, fluorosis, rachitic teeth, etc.).

METHODS

Causative factors of dental discolourations are identified through a literature review.

RESULTS

In an archaeological context, the sediments contained in the burial soil can lead to tooth discoloration. Taphonomic staining of the dentition may have a similar appearance to enamel hypomineralisation, and thus is a confounding factor that has the potential to cause miscalculation of the true prevalence of MIH within archaeological collections. Some rare medieval cases are reported in the modern literature but without microanalysis, misdiagnosis is possible. The aetiological factors of MIH are unknown but probably follow the multifactorial model involving systemic medical and genetic factors.

CONCLUSIONS

Systematic detection and diagnosis of MIH during anthropological studies is therefore of great interest.

SIGNIFICANCE

The hypotheses that only contemporary agents are causative factors of MIH could be refuted by the discovery of individuals living before medication or pollutants. The identification of MIH in a group of individuals also provides information regarding the health status of a population and reflects stress occurring during the period of mineralisation of the first permanent molars after secretion of the enamel matrix.

LIMITATIONS

Taphonomic alterations of archaeological remains prevent MIH diagnosis.

SUGGESTIONS FOR FUTURE RESEARCH

MIH diagnosis can be difficult in archaeological series and further non-destructive methods (microtomography, elemental analyses, etc.) are required.

Prevalence of Molar-Incisor Hypomineralization and Caries in Eight-Year-Old Children in Croatia

The aim of this study was to detect molar–incisor hypomineralization (MIH) and caries prevalence in eight-year-old children with early mixed dentition in Eastern Croatia. There is a lack of data on MIH in Croatia. There were 729 children examined in total: 356 (48.83%) were female and 373 (51.16%) were male. The presence of MIH was found in 95 children, the prevalence of MIH was 13%, and the remaining 634 (87%) did not have any changes associated with MIH. The prevalence of caries overall in the population of examined children was 11.48%. In the group of children with MIH, the prevalence of caries was 24.14%, while in the group of children with no MIH, the prevalence of caries was 11.18%. Teeth had a Decayed, Missing, and Filled Teeth (DMFT) index of 1.2, the value of the SiC index was 1.4, and the decayed, missing, and filled teeth (dmft) index for deciduous teeth was 5.8. Children with MIH had a caries index of DMFT 2.1, and the value of the SiC index was 2.6. The index of caries for non-MIH children was DMFT 1.1 and the SiC index was 1.2. MIH prevalence in Croatia is more common in girls than in boys. MIH has a significant impact on children’s development and is a major factor in the occurrence of caries.

Japanese nationwide survey of hypophosphatasia reveals prominent differences in genetic and dental findings between odonto and non-odonto types

Hypophosphatasia (HPP) is a rare and intractable metabolic bone disease caused by mutations in the ALPL gene. Here, we undertook a nationwide survey of HPP in Japan, specifically regarding the prominent genetic and dental manifestations of odonto (n = 16 cases) and other (termed “non-odonto”) (n = 36 cases) types. Mean serum alkaline phosphatase (ALP) values in odonto-type patients were significantly greater than those of non-odonto-type patients (P<0.05). Autosomal dominant and autosomal recessive inheritance patterns were detected, respectively, in 89% of odonto-type and 96% of non-odonto-type patients. The ALPL “c.1559delT” mutation, associated with extremely low ALP activity, was found in approximately 70% of cases. Regarding dental manifestations, all patients classified as odonto-type showed early exfoliation of the primary teeth significantly more frequently than patients classified as non-odonto-type (100% vs. 56%; P<0.05). Tooth hypomineralisation was detected in 42% of non-odonto-type patients, but not in any odonto-type patients (0%; P<0.05). Collectively, these results suggest that genetic and dental manifestations of patients with odonto-type and non-odonto-type HPP are significantly different, and these differences should be considered during clinical treatment of patients with HPP.

Molar incisor hypomineralization: Analysis of asymmetry of lesions

Clinically, Molar-Incisor Hypomineralization (MIH) lesions are not distributed symmetrically, and their severity varies even within the same arcade.

AIM

To estimate the frequency of asymmetries in hypomineralized lesions on permanent molars and incisors of children with MIH.

METHODS

Three pediatric dentists, calibrated following the diagnostic criteria of Mathu-Muju and Wright (2006) (Kappa 0.87) identified presence and severity of opacities on molars and incisors of patients with MIH. Six pairs of teeth (permanent maxillary and mandibular first molars, central and lateral incisors) were evaluated in each patient. Degree of lesion severity (0-none, 1-mild, 2-moderate, 3-severe) was recorded for each tooth. For each pair containing any affected teeth, asymmetry of presence (one tooth in the pair with lesion and the other intact), asymmetry of severity (both teeth with lesions but with different degrees of severity) or symmetry of severity (both affected teeth with the same degree of severity) were evaluated. The recorded values were entered into a database to calculate percentages, 95% confidence intervals and Chi-Square test for comparisons.

RESULTS

The sample consisted of475 of the 1032 pairs of teeth evaluated in the 172 patients included in the study, mean age 11±2.2 years, and 50% female. Asymmetry was found for 67.5% (63.1 - 71.7) of the pairs of the studied teeth. There was a significant relationship between asymmetries and symmetries (p=0.038). A total 50.1% of the pairs were asymmetrical for presence of opacities. Of these, 62.2% scored severity 1 (mild). Symmetry of severity was found for 32.5% of the lesions. Among the pairs of affected teeth, the most frequently observed degrees of lesion severity were mild and moderate, with the exception of lower molars, in which 49% had severe lesions.

CONCLUSIONS

In this study, MIH lesions were asymmetrical both in presence and severity for all tooth types.

The influence of different types of brackets and efficacy of two chlorhexidine mouthwashes on oral hygiene and the incidence of white spot lesions in adolescents during the orthodontic therapy

BACKGROUND

To detect the effect of two different types of brackets (ceramic and stainless steel) and investigate the effectiveness of two chlorhexidine mouthwashes 0.2% (CHX) on oral hygiene status and incidence of white spot lesions (WSLs) in adolescents wearing fixed orthodontic appliance.

SUBJECTS AND METHODS

One hundred and twenty subjects (aged 11 to 18 years, mean age 14.5 years) were divided into six equal groups according to brackets type and to different mouthwashes: Group 1: metal brackets and conventional CHX, Group 2: metal brackets and CHX with anti-discoloration system (CHX-ADS), Group 3: ceramic brackets and conventional CHX, Group 4: ceramic brackets and CHX-ADS, Group 5: metal brackets and water correction flavors mouthwash (placebo), Group 6: ceramic brackets and placebo. Four weeks after the placement of fixed orthodontic appliance the subjects were provided with three different mouthwashes for use during the next two weeks. Assessment was carried out according to oral hygiene index-simplified (OHI-S) and WSL index performed: prior to placement of the appliance (baseline), four weeks, six weeks, eighteen weeks, and thirty weeks after the placement. The data were then subjected to statistical analysis.

RESULTS

Group 4 showed reduction in the OHI-S scores when compared to the Group 5 (in the 6^th week), and Group 6 (in the 6^th and 18^th week), which was statistically significant, P<0.05. Group 4 showed decrease in the WSLs scores when compared to the Group 1 (in the 4^th, 6^th, 18^th and 30^th week), Group 5 (in the 18^th and 30^th week) and Group 6 (in the 6^th, 18^th and 30^th week), which was statistically significant, P<0.05.

CONCLUSION

The ceramic brackets and the usage of CHX-ADS resulted in better oral hygiene status and lower incidence of WSLs.

Pre- and postnatal determinants of deciduous molar hypomineralisation in 6-year-old children. The generation R study

BACKGROUND

Deciduous Molar Hypomineralisation (DMH) and Molar Incisor Hypomineralisation (MIH) are common developmental disturbances in pediatric dentistry. Their occurrence is related. The same determinants as suggested for MIH are expected for DMH, though somewhat earlier in life. Perinatal medical problems may influence the prevalence of DMH but this has not been studied sufficiently.

OBJECTIVE

This study aimed to identify possible determinants of DMH in a prospective cohort study among 6-year-old children.

STUDY DESIGN

This study was embedded in the Generation R Study, a population-based prospective cohort study from fetal life until young adulthood. The the data were used to identify the determinants of DMH. Clinical photographs of clean, moist teeth were taken with an intra-oral camera in 6690 children (mean age 6.2 years; 49.9% girls). Data on possible determinants that had occurred during pregnancy and/or the child's first year of life were on the basis of manual standardized measurements (like length and weight) and questionnaires. Multivariate analyse with backward and forward selection was performed.

RESULTS

A number of factors in the pre-, peri- and postnatal phase were found to be associated with DMH. After multivariate logistic regression analyses, Dutch ethnic background, low birth weight, maternal alcohol consumption during pregnancy, and fever episodes in the first year of the child's life were found to play a role in the development of DMH in 6-year-old children.

CONCLUSION

This study shows that Dutch ethnicity, low birth weight, alcohol consumption by the mother during pregnancy and any fever in the first year of the child's life are associated with DMH. Not only childhood factors but also prenatal lifestyle factors need to be taken into account when studying determinants for DMH.

Oral manifestations of suspected eating disorders among women of 20-25 years in Bangalore City, India

To detect the presence of eating disorders (EDs) and clinical findings in 20-25 years old women residing in professional college hostels in Bangalore city, India, a cross-sectional study was conducted. One hundred seventeen women of the 128 selected randomly participated in the study. SCOFF [Sick, Control, One-stone (14 lbs/6.5 kg), Fat, Food] Questionnaire was used for screening suspected cases of anorexia nervosa (AN) and bulimia nervosa (BN). Examination was done for systemic findings, extra-oral and intra-oral manifestations of EDs. Data obtained were analyzed using SPSS (version 13.0). The response rate was 71.3%, of which 42.7% were suspected to have EDs by SCOFE Examination showed significantly higher prevalence of periomylolysis (p = 0.004), dental caries (p = 0.004), and tooth sensitivity (p = 0.001) in suspected cases. The study succeeded at 'case-finding' of EDs with a significant prevalence of oral manifestations in suspected cases. Thus, dentists play a major role for early detection and prompt further referral of co-morbid disorders, like EDs.

Assessment of non-cavitated and cavitated carious lesions among 12- to 15-year-old government and private school children in Pune, Maharashtra, India

PURPOSE

The present cross-sectional study was conducted to assess and compare the mean number of non-cavitated (initial lesions, IL) and cavitated carious lesions (WHO criteria) per child in the permanent dentition and to correlate it with the plaque index among 12- to 15-year-old government and private school children.

MATERIALS AND METHODS

481 schoolchildren aged 12-15 years were selected randomly by multistage random sampling from two government and two private schools. Demographic details were collected at the time of examination. Baseline plaque scores were recorded using the Silness and Löe plaque index. Immediately after brushing and drying the teeth, cavitated lesions were recorded based on WHO recommendations and non-cavitated lesions were recorded using the IL criteria of Nyvad et al and Fyffe et al.

RESULTS

The mean number of surfaces with cavitated and non-cavitated lesions for government school children was 2.13 ± 2.98 and 3.21 ± 2.97, respectively, and 1.24 ± 1.86 and 3.08 ± 2.33 for private school children, respectively. WHO + IL surfaces among private school children were 4.33 ± 3.48 and in government school children 5.35 ± 4.45. There was a positive correlation of plaque score with IL (r = 0.63) and WHO+IL (r = 0.73).

CONCLUSION

Non-cavitated lesions are about twice as common as cavitated carious lesions in school children. Government school children had a higher number of cavitated and non-cavitated carious lesions when compared with private school children.

The prevalence and aetiology of molar-incisor hypomineralisation in a group of children in Istanbul

AIM

To our knowledge, the prevalence and aetiology of molar-incisor hypomineralisation has not been discussed nor investigated in Turkish children in Istanbul. Therefore the aim of the present study is to investigate the prevalence and aetiology of MIH in a group of children in Istanbul.

DESIGN

Between April and July 2007, a retrospective clinical study was initiated at the Dept. of Paediatric Dentistry, School of Dentistry, Yeditepe University, Istanbul, Turkey. A total of 147 children aged 7-9 years visiting our clinic were examined by two calibrated paediatric dentists (kappa: 0.89). The examiners used the criteria for the diagnosis of demarcated opacities, post-eruption breakdown, atypical restorations, and extracted PFMs due to MIH developed by Weerheijm et al.

RESULTS

In the present study, prevalence of MIH was 14.9%. Of the 22 children affected with MIH, 17 (77.2%) had only demarcated opacities, but no breakdown or atypical restorations. Regarding diseases in the first 3 years of life, 55% of MIH and 19.4% of non-MIH children had a disease history. 27% of MIH children had suffered from upper and lower respiratory tract infections including bronchitis. This was significantly different from non-MIH children (p<0.001).

CONCLUSION

MIH was common among a group of 7-9 years old children, Istanbul.

Prevalence and severity of molar incisor hypomineralization in a region of Germany -- a brief communication

OBJECTIVES

Molar incisor hypomineralization (MIH) is a developmental disturbance concerning permanent incisors and first permanent molars. The aim of this study was to ascertain the frequency of MIH in the region of central Hesse, Germany.

METHODS

1,022 children aged 6 to 12 years were surveyed during routine school-based dental examinations, which were conducted by the regional public health department. Symptoms of MIH were recorded and a DMF-T evaluation was carried out.

RESULTS

Approximately 6 percent (5.9 percent) of all examined children showed at least one ill-structured first permanent molar in terms of MIH. Furthermore, 57.9 percent of these children with hypomineralized first molars also showed changes in the enamel structure of the permanent incisors. Altogether, children with MIH showed a significantly higher DMF-T value for permanent teeth than children without MIH.

CONCLUSIONS

A carefully managed recall program for children affected by MIH is essential with regard to the increasing importance of preventive and restorative measures.

Enamel Demineralization during Fixed Orthodontic Treatment – Incidence and Correlation to Various Oral-hygiene Parameters

OBJECTIVE

To investigate the incidence of white spot lesions (WSLs) around brackets and molar bands during orthodontic therapy, and establish whether a correlation to indices of dental and gingival health, fluoride application and oral hygiene could be demonstrated.

PATIENTS AND METHODS

Fifty-three patients with fixed orthodontic appliances were included at random in this study at the Department of Orthodontics of Erlangen-Nuremberg University. Dental health (DMFS), plaque index, papillary bleeding index, sulcus probing depth (SPD), gingival recession (GR), clinical attachment level (as sum of SPD and GR), oral hygiene, and fluoride use were evaluated. WSLs were graded from intraoral photographs taken before and after treatment.

RESULTS

97.5% of teeth before and 73.6% after treatment were free of WSLs. Of all teeth, 24.9% developed new WSLs or a rise in their number. New or more numerous WSLs were more common in upper and lower premolars (34.4%) and front teeth (28.1%) than molars (11.8%). WSL incidence during therapy correlated with clinical attachment level, and the oral hygiene and fluoride-use scores.

CONCLUSIONS

Despite improvements in materials and preventive efforts, orthodontic treatment continues to carry the considerable risk of enamel demineralization. Each patient's prophylactic efforts, including fluoride use, are of paramount importance in preventing WSLs.

Molar incisor hypomineralization: review and prevalence data from the study of primary school children in Kaunas/Lithuania

AIMS

These were to determine the prevalence of MIH in a group of primary school children in Kaunas, Lithuania and to compare the prevalence of MIH in Lithuania with the prevalence in other countries using published data.

METHODS

First permanent molars and all permanent incisors were examined in 1277 children, aged 7 to 9 years and having at least one erupted permanent molar, for demarcated opacities, post-eruptive enamel breakdown, atypical restorations and extractions due to MIH, according to the criteria, provided by the EAPD experts. Examinations were performed by two calibrated observers (k=0.829).

RESULTS

Of all the children 190 (14.9%) had hypomineralization defects in at least one index tooth, 124 (9.7%) had at least one affected molar and were considered as having MIH. Only demarcated opacities were present in 68 (54.8%) of children with MIH, 35 (28.2 %) had at least one tooth with breakdown, 21 (16.9%) had atypical restorations. No teeth had been extracted due to MIH. Children with 3-6 affected teeth were 3.5 times more likely to have enamel breakdown and/or atypical restorations when compared with the children having only one or two affected teeth. Of the 124 children with MIH 96 (77.4%) had lesions only in molars, 28 (22.6%) had both - molars and incisors - affected.

CONCLUSIONS

MIH was common among 7-9 years old Lithuanian children; majority of the affected children were affected mildly. Severity of the lesions was increasing with the number of affected teeth. Compared to the other studies MIH in Lithuania was moderately prevalent.

[Molar incisor hypomineralisation in the first permanent teeth]

The aim of this study was to point out the prevalence of hypomineralised molars and incisors and emphasize importance of this condition in paediatric dentistry. This condition is defined as hypomineralisation of one or more first permanent molars frequently affecting incisors and referred to as molar incisor hypomineralisation (MIH). Aetiology of MIH has not been fully clarified and numerous aetiological factors have been cited. Hypomineralised molars are more prone to caries, cause severe restorative problems and are frequently extracted due to serious damage and caries complications. Incisors can present demarcated enamel opacities, while enamel breakdown is uncommon. Considering the fact that permanent first molars with severe defects demand complex treatment, they represent a serious problem for the patient as well as for the dentist.

[Dentin demineralization in situ during frequent exposures to bananas or sucrose]

The aim of the study was to compare sucrose solution and bananas on demineralizing potential in situ, and to address the question if fluoride toothpaste is equally effective in preventing dentin demineralization at open, smooth surfaces and at plaque stagnation sites (grooves). Four volunteers wore an appliance containing bovine dentin specimens with narrow grooves and a smooth surface for two 1-week in situ periods, with 8 1-minute exposures daily: either by a rinse with 10% sucrose, or by consumption of a piece of banana. Twice daily, the appliance was dipped in toothpaste slurry of a fluoride-free toothpaste at one side and a fluoride toothpaste at the contralateral side. Demineralization was assessed by tranversal microradiography. No difference in dentin demineralization was found after frequent exposure to either sucrose solution or bananas. Fluoride toothpaste effectively protected dentin only at the smooth surfaces. In the grooves, fluoride affected the demineralization pattern; it drove lesions towards the bottom of the groove.

[Some causes of systemic demineralization of dental solid tissues in children of early age]

Among the risk factors causing generalized demineralisation of dental solid tissues in young kids (disturbances during antenatal development of embryo, frequent sickness of infant, etc.) the most important factor is the type of breath feeding of infant. Such factors as the good balance of calcium and phosphor in mother's milk contribute to the maintenance of healthy dental tissues. As our data shows in majority of kids (98%) with artificial feeding type, calcium and phosphorus levels in the blood serum and their rate (<1.30) were decreased, along with that hydrogen ion concentration in oral fluids was also decreased. All above mentioned has influence on physical-chemical reactions occurring in tooth enamel, increases enamel penetration and reduces buffer characteristics of oral fluids. Those problems are especially important for Georgia, where the level of fluoride in the drinking water is very low (0.35-0.45 mg/l).

Prevalence of enamel defects and MIH in non-fluoridated and fluoridated communities

AIM

This was to study the prevalence of enamel defects and molar incisor hypomineralisation (MIH) in children attending Leeds Dental Institute (UK) and Westmead Dental Hospital, Sydney (Australia).

METHODS

Prospective dental examinations were carried out on 25 children referred to two orthodontic departments. A questionnaire was completed to obtain background information and about previous fluoride (F) exposure followed by an oral examination. First permanent molars and permanent incisors were examined for presence, type and severity of enamel defects using the modified DDE screening index. Chi square tests were used to compare results.

RESULTS

Data for 24 children in Sydney and 20 in Leeds presented with at least one enamel defect. Of 300 teeth examined, 155 in Sydney and 82 in Leeds had a defect (p < 0.005). Severity of enamel defects was higher in Sydney. The children presenting with any type of enamel defect in at least one incisor or molar were 21 in Sydney and 10 in Leeds. However, if only demarcated defects were considered, the number in Sydney dropped to 11 and in Leeds remained at 10.

CONCLUSIONS

There was a higher prevalence of enamel defects in those children living in F Sydney than in non-F Leeds, but the prevalence of MIH was the same supporting the view that F is not associated with the aetiology of MIH.

The prevalence of Molar Incisor Hypomineralisation (MIH) in a group of Italian school children

AIM

This epidemiological study in a group of Italian children was undertaken in order to increase our knowledge of the prevalence of Molar Incisor Hypomineralisation (MIH) in different European countries.

METHOD

A population of school children aged 7.3 - 8.3 years, living in Lissone, Northern Italy, was examined for the presence and severity of MIH.

RESULTS

Of a total of 227 children (113 females), 31 (13.7%) had MIH, the tooth prevalence in the permanent first molars being 5.8%. Fifteen children (6.6%) had demarcated opacities in the incisors with a tooth prevalence of 2.1%. The defects in the molars were mild with the exception of one child who had severe defects.

CONCLUSION

MIH was quite common in this Italian town, and the prevalence figures were near those reported in Scandinavian countries but clearly higher than those from Dresden, Germany.

Early childhood caries and risk factors in rural Puerto Rican children

A sample of 167 Puerto Rican children whose ages ranged from six months to forty-seven months (mean = 23 months) were studied. Children were examined for Early Childhood Caries with light and mirror and a structured interview was administered to parents and caretakers to identify risk factors. Results indicated that only 37.4 percent of the children were free of decalcification lesions or frank decay. While 53.9 percent of the children had lesions on maxillary incisors, 40.0 percent had molars affected by decalcification lesions and caries. Analysis of risk factors indicate that giving the baby a bottle when crying at night, number of adults and children in the family, use of fluoridated dentifrice, and age of the child were associated with the caries process in these children. Bottle and breast feeding, per se, were not risk factors. Disease patterns suggest other dietary risk factors, such as frequent snacking on food/drinks with sugar.

How useful are cross-sectional data from surveys of dental caries?

Surveys are projects involving systematic data collection without a specific hypothesis to be tested and hence without a specific research design. This paper reviews their uses, and some of the issues involved with measuring dental caries in surveys. The principal benefits of surveys are in (a) monitoring trends in oral disease when the surveys are repeated periodically: and (b) giving dental health a visibility it might otherwise not get among policy-makers. On the other hand, they are of limited use in determining treatment needs for a population, evaluating treatment outcomes, and evaluating prevention programs. Some major issues in caries surveys today include difficulties with the DMF index; the use of exclusively visual versus visual-tactile criteria; "hidden" caries; and the appropriate role for early, non-cavitated carious lesions. The DMF index suffers from its mixing of disease and treatment, and more research is needed to determine the most appropriate role for exclusively visual criteria in surveys. Trade-offs, such as weighing the benefits of exclusively visual criteria against the probable greater difficulty in finding "hidden" caries, have not been determined. Inclusion of non-cavitated lesions in a survey will increase its cost. Organizers should therefore be clear before the survey on how this additional information will be used to justify the additional expense.

Prevalence of hidden caries

Clinical evaluations of the first and second permanent molars were compared with radiographic evaluations of the same teeth, for 359 patients (between six and eighteen years old) of the pediatric department of the Academic Centre for Dentistry Amsterdam (ACTA). The teeth were professionally cleaned and dried before the clinical evaluation. Despite the thorough examination, taking into account the fact that all discolorations and/or decalcifications were noted, 15 percent of the teeth that did not show signs of enamel caries clinically, showed a dentine lesion on the bitewing radiograph. These 15 percent of teeth with hidden caries were found in 7.5 percent of the population studied. The absence of clinical signs of occlusal enamel caries or dentine caries does not guarantee a sound dentition. Sealant treatment of teeth that are sound (both clinically and radiographically) is justified, therefore, soon after tooth eruption.

Morphometric computerized analysis on the dentinal tubules and the collagen fibers in the dentine of human permanent teeth

A morphometric analysis has been performed on important components of human dentine using an image computerized analyzer. The dentinal tubule diameter and their area percentage were calculated. Moreover the area percentage of the collagen fibers in the dentinal matrix was measured. These parameters have been evaluated in different areas of the coronal and the radicular dentine in permanent teeth. Measurements have been performed on undecalcified and decalcified teeth and on teeth treated with enzymatic digestion to remove the organic non collagen matrix and to evidentiate the collagen fiber network. The values obtained in different areas of the tooth and in samples submitted to different treatments were evaluated by statistical analysis. Dentinal tubule diameter and area percentage significatively decrease from the inner to the peripheral dentine both in the undecalcified teeth as in the decalcified ones and in the samples undergone to enzymatic digestion. The collagen fiber percentage in the organic matrix is significatively lower in the mantle dentine.