Abstract
Background
Molar-incisor hypomineralization (MIH) is a qualitative defect in enamel formation with a multifactorial etiology. Studies indicate a high prevalence of MIH across the Americas, yet the prevalence in Mexico remains uncertain.
Aim
This study aimed to review the literature on the prevalence of MIH in the Mexican population and its associated factors.
Methods
Six electronic databases were searched for relevant studies: PubMed, Scopus, Dentistry & Oral Science, Science Direct, Web of Science, and Google Scholar, covering the period from March 10th, 2024. Cross-sectional studies were assessed for risk of bias using the Joanna Briggs Institute (JBI) tool.
Results
Nine studies met the inclusion criteria, encompassing 5039 children aged 6–12 years, with a mean age of 9.02 ± 1.19 years; 50.1% were boys, and 49.9% were girls. The overall prevalence of MIH was 23%, with a higher prevalence in boys (34.1%) than in girls (30.4%). MIH was more common in molars (30.7%) than in incisors (10.8%), with no cases reported in permanent second molars. Five studies (55.5%) noted dental caries in MIH-affected individuals, with 78.7% showing caries and 21.3% caries-free. The JBI analysis found 33.3% of studies with moderate risk and 66.7% with low risk of bias.
Conclusion
The prevalence of MIH in Mexico aligns with rates reported in Brazil and Venezuela. The evidence indicates no significant gender differences in MIH distribution, with molars being more frequently affected than incisors. A substantial proportion of Mexican children with MIH also present with dental caries.
1
Introduction
Weerheijm et al., in 2001, proposed the term Molar-Incisive Hypomineralization (MIH) to describe the first permanent molars with idiopathic enamel defects, known as “cheese molars” [ ]. Subsequently, in 2003, the European Academy of Paediatric Dentistry (EAPD) characterized this condition as a hypomineralization of systemic origin with an unknown cause, affecting one to four first permanent molars and possibly involving the permanent incisors [ ].
Clinically, teeth affected by MIH exhibit asymmetrical opacities that are white, cream, yellow, or brown on the buccal surface or the incisal/occlusal third of the crown, with varying degrees of extent and severity. Moreover, MIH can result in significant issues, including hypersensitivity, pain, post-eruptive breakdown, difficulties with chewing and eating, as well as aesthetic and treatment challenges [ ].
The etiology of MIH is multifactorial, as several genetic and prenatal, perinatal and postnatal factors have been proposed that can affect the maturation of tooth enamel, from the last trimester of pregnancy to the third year of the child’s life. Genetic factors are single nucleotide polymorphisms of different genes expressed at the secretory, transitional, or maturation stage of amelogenesis [ ]. Prenatal factors include, diseases and/or complications during pregnancy, alcohol, tobacco and antibiotic use. Perinatal factors include type of birth such as preterm birth, hypoxia or respiratory problems and low birth weight [ ]. Postnatal factors include long-term breastfeeding, asthma, high fever, infections, varicella, diarrhea, and pneumonia [ ].
MIH generally affects children aged 6–17 years, has no gender or racial predilection, and shows a worldwide prevalence of about 2.8%–44% [ ]. This depends on the country, region and age group under study. Low and middle-income countries and children with poor general health during the first three years of life are more likely to have MIH [ ]. A recent systematic review showed a higher prevalence of MIH in the American Continent (15.3%), followed by Oceania (14.7%), Africa (14.5%), Europe (14.4%) and Asia (10.7%) [ ]. The prevalence of MIH in the Mexican population remains to be elucidated about the American continent. For these reasons, a new systematic review on the topic would be convenient and relevant worldwide. Therefore, the overall objective of the present study was to conduct a comprehensive review of the literature on the prevalence of MIH in the Mexican population, as well as its associated factors.
2
Materials and methods
2.1
Protocol and registration
The design of this study was performed following the guidelines of the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) [ ] and was registered in Open Science Framework (OSF): 10.17605/OSF.IO/A6ZS4.
2.2
Focused question
Our objective was to answer the PECO question, “What is the prevalence of MIH in the Mexican population?” The respective statements were.
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(P) Population: Human clinical or epidemiological studies.
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(E) Exposure: Children diagnosed with MIH.
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(C) Comparison: Children without MIH.
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(O) Outcome: Prevalence of MIH.
The general objective was to determine the prevalence of MIH in the Mexican population. The secondary objectives were to evaluate the prevalence of MIH by gender (boys and girls), tooth involvement (molars and incisors), and the presence of dental caries. In addition, we carried out a comprehensive review of the literature to compare the prevalence of MIH in the countries that make up the American continent.
2.3
Eligibility criteria
Studies that were eligible for inclusion had to meet the following criteria: Cross-sectional clinical studies reporting the prevalence of MIH in the Mexican population, studies written in English and Spanish language, studies published after 2003, studies clearly reporting the diagnosis of MIH, children of both genders and without systemic alterations. Studies with incomplete data, without the possibility of access by the authors, narrative, comprehensive, systematic reviews, meta-analyses, and book chapters were excluded.
2.4
Search strategy
Six electronic databases were used for study identification for this systematic review: PubMed, Scopus, Dentistry & Oral Science, Science Direct, Web of Science, and Google Scholar, from March 10th, 2024. For PubMed, our search strategy was based on the following algorithm: (“Molar Hypomineralization” [Mesh]) AND (“Prevalence” [Mesh]). For the rest, the following keywords were used: Molar-incisor AND Hypomineralization AND Prevalence AND Mexican. Also, to further enrich our search strategy, a comprehensive hand search was conducted in the following journals: Community Dentistry and Oral Epidemiology, Journal of Public Health Dentistry, Operative Dentistry, Oral Health & Preventive Dentistry, Pediatric Dentistry and American Journal of Dentistry.
2.5
Study selection
Study selection was independently evaluated by two investigators (M.A.A.S and J.S.B.R), who performed the evaluation of the titles and/or abstracts of the retrieved studies. Any disagreement was resolved by discussion in consultation with a third expert reviewer (C.C.A.S).
2.6
Data extraction process
Data extraction was performed by two investigators (C.C.A.S and S.I.V.J) independently. The following information was collected: author, year, type of work funding, inclusion and exclusion criteria, age, gender, sample size, classification of MIH, total prevalence of MIH, prevalence of MIH by gender, description of severity of MIH, percentage of affected molars and incisors, description of other symptoms and the percentage of children with MIH affected by dental caries or free of caries.
2.7
Summary measures and synthesis of results
Data analysis was performed using descriptive statistics. Predefined tables were prepared in Microsoft Excel to collect continuous data, mean age ± standard deviation (SD), minimum-maximum range and frequency distribution (%). The data were analyzed in STATA V18 software (Stata Corp, College Station, TX, USA). The graphs were made in Graphpad Prism 8 software.
2.8
Risk of bias
Two reviewers (M.A.A.S and A.H) independently assessed the risk of bias of the included studies. The Joanna Briggs Institute (JBI) tool was used to assess cross-sectional studies [ ]. Eight items were assessed, and the final score was obtained. If the score was between 1 and 3 there was a high risk of bias; between 4 and 6 there was a moderate risk and ≥7 a low risk of bias assessment. A third investigator (J.S.B.R) verified the ratings obtained, and the group discussion resolved any discrepancies.
2.9
Statistically analysis
Forest plots were utilized to display odds ratios (OR) and 95% confidence intervals (CI). The I 2 statistic assessed the heterogeneity among the studies included. A random-effects model was employed to aggregate the primary outcomes when heterogeneity exceeded 50% and was statistically significant. Furthermore, a funnel plot and Egger’s regression analysis were performed to evaluate potential publication bias.
3
Results
3.1
Study selection
In the identification phase, 531 articles were found from the six databases included (PubMed 43 records; Scopus 6 records; Dentistry & Oral Science 5 records; ScienceDirect 24 records; Web of Science 6 records; and Google Scholar 447 records). The manual search identified no records relevant to this study. Duplicates (31 records) were then removed giving a total of 500 articles. Then, in the screening phase, based on title and abstract, 491 records were excluded because they did not focus on the research topic. After analyzing the full text of the remaining articles, no articles were excluded. Thus, a total of 9 articles were assessed for eligibility and included in systematic review and meta-analysis. Details of study selection are shown in Fig. 1 .
3.2
Sociodemographic and clinical characteristics of the studies
In this study, 9 articles with a cross-sectional design were reviewed [ ]. The total number of children studied in the included investigations was 5039. The ages of the children ranged from 6 to 12 years; the mean ± SD age of the patients studied was 9.02 ± 1.19 years, of whom 50.1% were boys and 49.9% were girls. Most of the articles were published after 2019 (7:77.7%) [ ]. The oldest study was from 2016 [ ], whereas, the most recent was from 2022 [ ] ( Table 1 ).
| Author/Year | Ethical | Funding | Inclusion criteria | Exclusion criteria | Age (years) | Gender B o /G i |
Sample size |
|---|---|---|---|---|---|---|---|
| García-Pérez et al., 2022 [ ] | Yes | None | Schoolchildren of either gender aged 8–10 years; written parental authorization to participate; the four upper and lower incisors and the first four permanent molars fully erupted; the parents/guardians of the participant residing at the same address | Declining to cooperate with OHRQoL questionnaire; the presence of a craniofacial deformity; a history of dental trauma; current orthodontic treatment; not cooperating during the oral examination | 9.2 8–10 |
318/315 | 633 |
| Sosa-Soto et al., 2021 [ ] | Yes | NR | Children aged 8 years who exhibited the first four permanent molars and the eight lower and upper permanent incisors | Wearing fixed orthodontic appliances; or a chronic systemic disease | 8.6 | 327/303 | 630 |
| García-Vázquez et al., 2020 [ ] | NR | NR | Children 10 and 11 years of both gender; whose parents authorize participation in the study | Children with orthodontic or maxillary orthopedic appliances; with unerupted first molars and permanent incisors and with molars affected by other enamel defects | 11.3 10–11 |
21/14 | 35 |
| Irogoyen-Camacho et al., 2019 [ ] | Yes | None | Children has at least one erupted or partially erupted first permanent molar | Children with fixed orthodontic appliances; or children who were absent during the days of oral evaluation | 7.1 6–8 |
262/287 | 549 |
| Villanueva-Gutiérrez et al., 2019 [ ] | Yes | Self-funded | Schoolchildren aged 8–12 years presenting the eruption of at least one first permanent molar | Children with orthodontic attachments that prevented the examination of tooth surface | 9.7 8–12 |
250/256 | 506 |
| Villanueva-Gutiérrez et al., 2019 [ ] | Yes | NR | Schoolchildren aged 8 to 10 presenting the eruption of at least one first permanent molar | Children with orthodontic attachments that prevented the examination of the tooth surface | 8.9 8–10 |
217/194 | 411 |
| Villanueva-Gutiérrez et al., 2019 [ ] | Yes | CONACYT | The parents signed a consent form for the participation of their children in the study and that the child assented to an oral examination; the children were also required to be present during the days of the oral examination | Children in whom the first permanent molars had not erupted or who had no more than one-third of the anatomical crown visible on any first permanent molar; children who had not attended school during the days of the study | 9 | 321/365 | 686 |
| Gurrusquieta et al., 2017 [ ] | Yes | NR | Children with first four erupted permanent molars; whose parents had provided written consent and completed the medical history questionnaire | NR | 8.4 | 574/582 | 1156 |
| Murrieta-Pruneda et al., 2016 [ ] | Yes | FES Zaragoza | Schoolchildren aged 8 to 12 presenting the eruption of at least one first permanent molar | Children whose parents did not authorize their inclusion in the study had premature loss of the teeth of interest to the study for reasons other than those caused by the presence of MIH of any of the teeth of interest to the study; were undergoing orthodontic treatment; were uncooperative at the time of the examination; or had a physical disability | 9.8 8–12 |
235/198 | 433 |
The 77.7% of the included studies used the MIH classification proposed by the EAPD [ , ], the remaining 11.15% used the system proposed by Ghanim et al. [ , ] and Mathu-Muju and Wright [ , ]. With respect to the classification proposed by the EAPD, it was found that 19.45% of the affected teeth had mild MIH [ , ], 28.5% had moderate MIH [ , ] and 12.53% had severe MIH [ , ].
The prevalence of MIH in boys was 34.1% and in girls was 30.4% [ , , ]. The prevalence of MIH was higher in molars (30.7%) than in incisors (10.8%). No study reported involvement in permanent second molars [ ].
Only one (11.11%) study [ ] reported that children had symptoms such as sensitivity and pain. Five (55.5%) studies reported the prevalence of dental caries in children affected by MIH [ , ]. A total of 78.7% had dental caries, while 21.3% had no caries ( Table 2 , Fig. 2 , panel A–C).
