An inverse relationship between dental fluorosis and Molar Incisor Hypomineralization in Mexican schoolchildren in an area with a high concentration of fluoride in drinking water: A cross-sectional study.

AIM: To evaluate the association between the frequency and severity of dental fluorosis and Molar Incisor Hypomineralization (MIH) in 8-12-year-old schoolchildren living in an area with a high concentration of fluoride in the drinking water. METHODS: The present cross­sectional study was conducted on Mexican children (n = 573) selected from one community presenting a drinking water fluoride concentration of 1.39 ppm/F. The prevalence of dental fluorosis was ascertained using the Thylstrup and Fejerskov Index (TFI). The presence and severity of MIH was evaluated using the European Academy of Pediatric Dentistry (EAPD) criteria. A multinomial regression model was used to estimate the odds ratio (OR) and the 95% confidence intervals (CI), using the severity of MIH as the result. RESULTS: The prevalence of MIH was 37.7% and, by severity, was 16.1% mild, 14.3% moderate, and 7.3% severe. The prevalence of dental fluorosis in permanent dentition was 70.9% (TFI ≥1) and, by severity, was 29.2% (TFI = 0), 45.6% (TFI 1-3) and 25.3% (TFI ≥4), while 54.5% of subjects were found to have poor oral hygiene. Schoolchildren with fluorosis (TFI ≥4) were 49% less likely [OR = 0.51; p = 0.025] to present mild MIH than children with fluorosis (TFI <4). Similarly, children with fluorosis (TFI ≥4) were 53% [OR = 0.47; p = 0.019] and 62% [OR = 0.38; p = 0.036] less likely to present moderate and severe MIH than children with fluorosis (TFI <4). CONCLUSION: An inverse relationship between the presence of fluorosis and MIH was found. The results obtained by the present study may contribute to both the early identification of disorders affecting the enamel and the creation and implementation of long-term oral health prevention, promotion, and intervention programs in the affected population.

Factors Associated with Hypersensitivity, Management, and Treatment Options for Teeth with Molar Incisor Hypomineralisation.

Tooth hypersensitivity is a common symptom in molar incisor hypomineralisation (MIH) patients and can affect children's quality of life. During daily routine, children with MIH often report sensitivity to various thermal and mechanical stimuli, and difficulty in achieving effective analgesia is a common issue becoming a challenge for dentists. Research has focused on the possible pathophysiological mechanisms behind this phenomenon, which, in turn, have not been determined. Even with the apparently intact enamel of MIH-teeth, the porosity of the hypomineralised enamel acts as an open door for the invasion of oral microorganisms, which reach the dentinal tubules, and stimulate subclinical inflammatory reactions in the pulp. Tissue inflammation may, in turn, lead to morphological and cytochemical changes within sensory neurons, resulting in sensitization of these nerve fibers. This phenomenon is complex, and the treatment modalities focus on inflammation management followed by tubule obliteration by using different materials and technologies. In conclusion, this chapter reviews the concept and etiology of hypersensitivity in teeth with MIH and summarizes the clinical management according to the best evidence available.

Molar Incisor Hypomineralisation as a Dental Caries Risk Factor - Is It True?

The development of the human dentition is susceptible to disruption owing to its intricate and delicate nature, encompassing variations in tooth number, anatomical configuration, and the characteristics of enamel, dentine, and cementum. This chapter will specifically address the prevalent defect of molar incisor hypomineralisation (MIH), which can impose a significant treatment burden on individuals. MIH is linked to deleterious alterations in the properties of affected enamel, which can lead to rapid enamel breakdown and carious lesion formation in those at a heightened caries risk. In addition, MIH is associated with tooth sensitivity, dental anxiety, difficulty eating, aesthetic concerns, and negative influence during the child's psychological growth, especially when the MIH is severe. Regarding dental caries, it is essential to note that MIH does not directly increase the risk of caries. However, MIH can alter the way the caries process manifests by creating niches where biofilm can accumulate, complicating oral cleaning efforts. Additionally, MIH adversely modifies the physicochemical properties of enamel, influencing how this "hardest of tissues" responds to cariogenic challenges.

Challenges of Using Scoring Systems for the Assessment of Molar Incisor Hypomineralisation.

The dental professional is exposed to complex challenges daily, posed by molar incisor hypomineralisation (MIH). These range from understanding its etiology through to determining the most effective strategies for clinical management of the problem. Beyond any doubt, the choice of the diagnostic scoring system to be used for recording the condition is included among these challenges. To a certain degree, this is understandable since the development of specific diagnostic tools for recording the occurrence of MIH takes place parallel to the ongoing discoveries about the problem. Therefore, the aim of this chapter is to present different MIH scoring systems that have previously been proposed in the literature for detecting MIH and discuss their applications, advantages, and limitations.

Molar Incisor Hypomineralisation Patient Assessment: Comprehensive Oral, Clinical Records and Behavior Evaluation.

Comprehensively evaluating molar incisor hypomineralisation (MIH) involves the integration of anamnesis and clinical data to diagnose, create a care plan, and predict prognoses. Anamnesis reveals relationships between defects and time, patient expectations, and impacts on the quality of life. Clinical studies emphasize posteruptive breakdown in yellow-brown opacities, highlighting the importance of identifying risk factors. The classification and recording of the clinical features associated with MIH are essential and allow for the longitudinal follow-up of the patient. Assessment of dental caries lesions, oral hygiene, and pain guides the care plan. Depending on the severity of MIH and associated symptoms, intraoral radiographs and cone beam computed tomography may be necessary. In cases of scheduled extractions, extraoral radiographs, photographs, and study models are indicated. Evaluations of the quality of life, aesthetic perception, and dental fear and anxiety provide valuable insights into the patient's emotional status and guide empathetic practice. A positive dental experience is based on communication with the patient, trust, and the proper use of behavior guidance techniques.

Prevalence of Enamel Hypomineralisation/Molar Incisor Hypomineralisation: A Scoping Review.

The aim of this scoping review was to provide an up-to-date assessment of the prevalence of enamel hypomineralisation (EH) and, in particular, molar incisor hypomineralisation (MIH). Epidemiological studies published from 2010 to 2023 were analyzed. After screening the primary literature, a total of 139 studies were included. According to the available epidemiological trials of children and adolescents from Europe (n = 39), the average prevalence of EH/MIH was 16.74%. The data from Asian studies (n = 50) showed an average prevalence of 15.6%. For South America (n = 33 studies), the mean prevalence of EH/MIH was 16.7%. The mean prevalence rates for North America (N = 9 studies), Africa (N = 6), and Australia (N = 2) were 25.9%, 11.4%, and 16.8%, respectively. Taken together, these data indicate that EH/MIH is a prevalent condition worldwide. With the aim of standardizing and generating comparable prevalence data, the use of the currently established criteria by the European Academy of Paediatric Dentistry (EAPD) for the detection of EH/MIH may support consistent reporting in epidemiological trials. However, other EH/MIH indices and phenotypes do exist. As the determination of EH/MIH prevalence depends on the correct use of index teeth, meticulous attention must be given to their correct application.

Genetic Theory behind the Molar Incisor Hypomineralisation.

Much effort has been spent in the identification of an environmental factor that explains the occurrence of molar incisor hypomineralisation (MIH). The best explanation, however, is accepting that MIH has a complex or multifactorial mode of inheritance. This chapter provides an analysis of how multifactorial inheritance operates in determining MIH, an explanation that accommodates the variation seen in the phenotype and the frequency of the problem around the world.

Understanding the Enamel Disintegration and Posteruptive Breakdown of Demarcated Opacities on Molar Incisor Hypomineralisation.

This review aims to present scientific knowledge regarding the demarcated opacities of molar incisor hypomineralisation (MIH) and factors that clarify the occurrence of posteruptive enamel breakdown. The demarcated opacities have distinct boundaries with the adjacent nonaffected enamel and may vary in color among white, creamy, yellow, and brownish. The hypomineralised enamel is more porous and less organized than the nonaffected enamel. As a result of the reduced mineral content and higher protein content, the hypomineralised enamel shows a progressive reduction in its mechanical properties according to the opacity feature. Chemically, the protein content of MIH opacities is abnormally high, mainly composed by albumin, which is a serum protein usually not found in mature enamel. The highest protein content is seen in brown opacities, followed by yellow and white opacities, both with higher protein content than nonaffected enamel. The fact that the hypomineralised enamel is more fragile than the nonaffected enamel is supported not only by laboratorial findings but also by clinical prospective studies that observed an aggravation of MIH over time, as well as the correlation between the color of the demarcated opacities and the risk of posteruptive enamel breakdown. A better understanding about the microstructure of the hypomineralised enamel has relevant implications for the clinical approach of the condition. In the clinic, besides a comprehensive assessment of anamnesis and clinical data, it is advisable to record the color and the location of the opacities by tooth surface in order to support the treatment decisions and estimate a prognosis for MIH patients.

Re-Establishing the Esthetics of Incisors in Patients with Molar Incisor Hypomineralisation.

The awareness of molar incisor hypomineralisation (MIH) has led to its increased clinical detection, consequently drawing more attention to its associated complications. This text offers an overview of the esthetic management of anterior teeth affected by MIH, a condition characterized by enamel defects that present significant cosmetic challenges. The focus is on the clinical presentation of MIH characteristics, considering the depth of lesions and the clinical aspects, and the treatment protocols available, despite a lack of extensive scientific evidence. To the best of the current scientific knowledge, the text evaluates the potential of minimally invasive procedures, as well as the use of traditional composite resin techniques and their possible combinations, highlighting the critical role of esthetic considerations for the impacted anterior teeth. The chapter is augmented with five illustrative clinical cases that display the practical application of these treatment approaches. These examples articulate the clinical decision-making process and personalized restorative strategies, aiming to balance function with enhanced esthetic results. The described cases act as a roadmap for clinicians tackling the complexities of MIH treatment in the context of limited empirical evidence, providing insights into achieving both satisfactory and esthetically pleasing outcomes for patients suffering from this condition.

Systemic and Environmental Risk Factors Associated with Molar Incisor Hypomineralisation.

The etiology of molar incisor hypomineralisation (MIH) has been attributed to systemic and environmental factors since 2001. The identification of MIH etiology is fundamental to better understand this condition, for differential diagnosis, and to identify the patient group at risk of MIH. Although the etiology of MIH is still unclear, it is stated as a multifactorial origin, with an overlap of systemic and genetic risk factors. The aim of this chapter was to discuss the systemic and environmental factors associated with MIH according to scientific evidence in the literature, relating it to the basic knowledge of amelogenesis and tooth development chronology. In this chapter, amelogenesis is described and illustrated in detail. Some characteristics of the amelogenesis process could explain some clinical features of the developmental defect of enamel, especially MIH. The chronology of tooth development was also referred to as a characteristic for the occurrence of MIH. Finally, the literature about systemic and environmental risk factors was revised, and the prenatal, perinatal, and postnatal factors associated with MIH were discussed. During the prenatal period, maternal health status, including illnesses during pregnancy and maternal smoking, are the main investigated factors associated with MIH. Prematurity (<37 weeks), low birth weight, and cesarean delivery are the factors associated with MIH during the perinatal period. Moreover, postnatal factors, such as common childhood illnesses, respiratory disease, infections, and antibiotic use, have been associated with MIH. New longitudinal studies that consider the synergy between exposure to environmental factors and biological susceptibility are likely to provide a new understanding of the etiology of MIH.

Impact of Molar Incisor Hypomineralisation on Quality of Life.

Oral health-related quality of life (OHRQoL) is a multifaceted concept that surpasses an exclusively clinical perception and includes functional, social, emotional, and environmental issues. The measure of OHRQoL represents a holistic approach for research and clinical practice. Negative impacts of oral conditions on OHRQoL in childhood can reflect on health development, especially in a life stage marked by social and cognitive maturation. Therefore, such problems can impact negatively on the daily lives of the individuals and their families. Individuals with molar incisor hypomineralisation (MIH) experience more frequent posteruptive breakdown, an elevated risk of tooth decay, filling failures, the need for recurrent dental treatment, and a higher prevalence of dental hypersensitivity. Children with severe MIH may struggle with everyday activities, such as brushing their teeth, speaking, smiling, chewing, and consuming hot or cold foods. MIH-affected incisors may exhibit opacities that can impact the aesthetics of their smiles. This condition may discourage children from smiling and can indirectly affect their parents as well. The management modalities are focused on solving functional, aesthetic, and hypersensitivity problems and to evaluate OHRQoL values before and after therapies. Therefore, this chapter aims to discuss how MIH affects the OHRQoL of children and the questionnaires that can be used to evaluate that impact.

Molar Incisor Hypomineralisation: A Recent Condition or a New Perception?

The condition known as molar incisor hypomineralisation (MIH) has been featured in the dental literature for some time. However, the condition itself, characterized by demarcated opacities, had been observed and documented in various forms before the official terminology was coined. The awareness and understanding of MIH have increased over the years, and there has been ongoing research to explore its prevalence, etiology, clinical implications, care, and treatment. In summary, MIH is not a recent condition, but the terminology and recognition of this dental phenomenon have been refined and formalized in the relatively recent past. This chapter reflects on our clinical experience, juxtaposing it with information from scientific literature and personal insights, as well as identifying gaps in understanding this enamel defect. Furthermore, another aim was to foster contemplation for potential research advancements in the MIH field.

Clinical Characteristics and Differential Diagnosis of Hypomineralised Second Primary Molars and Molar Incisor Hypomineralisation.

Molar incisor hypomineralisation (MIH) and hypomineralised second primary molars (HSPMs) are commonly seen dental developmental problems with a mean prevalence of around 14% and 9%, respectively, but with a large variability in the reported prevalences. From the dental development, we know that the enamel mineralisation of the second primary molar is taking place between the 19th week of pregnancy until 1 year of age. For the first permanent molars (FPMs) and incisors, the enamel mineralisation is taking place between birth until the age of 3-5. When there is a disturbance during this period, HSPM and/or MIH can occur. There is an overlap in the development of the second primary molars and the FPMs and incisors; the period between birth and the first birthday of the child. A disturbance in this period could cause both HSPM and MIH. There is a relation found in the occurrence of HSPM and MIH. Diagnosing HSPM and MIH can be challenging. All teeth present in the mouth need to be examined. The use of the European Association of Paediatric Dentistry scoring criteria is a good help. In these criteria also, the most common differential diagnoses are included.

Is It Possible to Remineralise Hypomineralised Enamel Lesions in Patients with Molar Incisor Hypomineralisation?

Molar incisor hypomineralisation (MIH) is characterized with reduced enamel mineral quantity, especially in the calcium and phosphate content, with increases in the carbonate and protein contents. Albumin is the main protein that accumulates pre-eruptively, leading to defective initiation of mineralisation. Other oral-fluid proteins are found in cases of posteruptive enamel surface breakdown. Most of the lesions extend through the full thickness of enamel. Due to the lower mineral quantity and increased carbon and protein content, MIH teeth are more prone to fractures once exposed to mastication. In addition, susceptibility to dental caries is increased and hypersensitivity is common in MIH patients. For these reasons, MIH-affected teeth might benefit from exposure to remineralising agents that will decrease caries susceptibility and reduce sensitivity. Several in vitro, in situ, and in vivo studies have shown that improving the mineralisation of MIH teeth after eruption is possible, especially at the surface. However, complete resolution is difficult due to the depth/thickness of these lesions. In fact, the process is similar to posteruptive maturation. Thus, this nomenclature should be used instead of remineralisation. The evidence available so far indicates that among the several available remineralising agents, casein phosphopeptide-amorphous calcium phosphate (CPP-ACP) cream and fluoride (F) varnish show the best results and are equally effective in remineralising MIH-affected teeth. Fluoride varnish demands no patient adherence, while CPP-ACP cream can be applied at home. However, it is important to consider that fluoride varnish is generally more economical than CPP-ACP cream. Consequently, the choice between these agents can be tailored to the patient's specific requirements.

External validation of an artificial intelligence-based method for the detection and classification of molar incisor hypomineralisation in dental photographs.

OBJECTIVES: This ex vivo diagnostic study aimed to externally validate an open-access artificial intelligence (AI)-based model for the detection, classification, localisation and segmentation of enamel/molar incisor hypomineralisation (EH/MIH). METHODS: An independent sample of web images showing teeth with (n = 277) and without (n = 178) EH/MIH was evaluated by a workgroup of dentists whose consensus served as the reference standard. Then, an AI-based model was used for the detection of EH/MIH, followed by automated classification and segmentation of the findings (test method). The accuracy (ACC), sensitivity (SE), specificity (SP) and area under the curve (AUC) were determined. Furthermore, the correctness of EH/MIH lesion localisation and segmentation was evaluated. RESULTS: An overall ACC of 94.3 % was achieved for image-based detection of EH/MIH. Cross-classification of the AI-based class prediction and the reference standard resulted in an agreement of 89.2 % for all diagnostic decisions (n = 594), with an ACC between 91.4 % and 97.8 %. The corresponding SE and SP values ranged from 81.7 % to 92.8 % and 91.9 % to 98.7 %, respectively. The AUC varied between 0.894 and 0.945. Image size had only a limited impact on diagnostic performance. The AI-based model correctly predicted EH/MIH localisation in 97.3 % of cases. For the detected lesions, segmentation was fully correct in 63.4 % of all cases and partially correct in 33.9 %. CONCLUSIONS: This study documented the promising diagnostic performance of an open-access AI tool in the detection and classification of EH/MIH in external images. CLINICAL SIGNIFICANCE: Externally validated AI-based diagnostic methods could facilitate the detection of EH/MIH lesions in dental photographs.

Which are the clinical consequences of Molar Incisor hypomineralization (MIH) in children and adolescents? Systematic review and meta-analysis.

OBJECTIVE: This systematic review was conducted to address the following research question: "What are the clinical consequences (outcome) of Molar Incisor Hypomineralization (MIH) (exposure) in children and adolescents (population/patient)?". MATERIAL AND METHODS: After defining the strategy, a search was performed in different databases (MEDLINE via Pubmed, Cochrane Library, BBO, LILACS, Scopus, Web of Science, Embase) and Grey literature in August 2023. Cross-sectional observational studies that identified clinical consequences of MIH (dental caries, post-eruptive structural loss, atypical restorations, hypersensitivity and tooth extraction) were included. The risk of bias was assessed following the Joanna Briggs Institute protocol for cross-sectional studies. Meta-analyses were conducted for each outcome, taking into account the number of patients and teeth. The effect measure considered was the prevalence; random-effects model was adopted. Heterogeneity was assessed using I2 statistics and prediction intervals (PI). RESULTS: A total of 903 studies were identified; 41 were selected for qualitative analysis and 38 for quantitative analysis. Twenty eight studies were classified as presenting uncertain risk of bias, 11 as low risk and 3 as high risk of bias. The prevalence levels, ranked from highest to lowest and considering the tooth and patient units, respectively, were: caries lesions (0.252 - 95% CI 0.158-0.375; 0.512 - 95% CI 0.385-0.639); hypersensitivity (0.286 - 95% CI 0.190-0.407; 0.417 - 95% CI 0.197-0.674), post-eruptive fracture (0.125 - 95% CI 0.099-0.158; 0.257 - 95% CI 0.145-0.412); atypical restorations (0.048 - 95% CI 0.030-0.077; 0.167 - 95% CI 0.096 - 0.274); tooth extraction (0.012 - 95% CI 0.007-0.019; 0.090 - 95% CI 0.019 - 0.331). All meta-analyses resulted in heterogeneity greater than 85%, with the exception of the outcome "tooth extraction" according to the tooth unit (I2 = 57.83). This heterogeneity may be attributed to factors such as differences in the location where the study was realized, the socioeconomic conditions of the studied population, the asymmetric nature of MIH, and patient age. CONCLUSION: The most common consequences of MIH are caries lesions, hypersensitivity, and post-eruptive breakdown. (PROSPERO:CRD42020201410).

Effectiveness of resin infiltration in the management of anterior teeth affected by molar incisor hypomineralisation (MIH): A systematic review and meta-analysis.

OBJECTIVES: To evaluate the effectiveness of resin infiltration in improving the aesthetic appearance of anterior teeth affected by molar-incisor hypomineralisation (MIH). DATA SOURCES: PubMed, Scopus, EMBASE, Web of Science, ScienceDirect, and Cochrane Central Register of Controlled Trials (CENTRAL) were searched from 2009 to 2024. The protocol was registered in the International Prospective Database of Systematic Reviews (PROSPERO CRD42023461909). STUDY SELECTION: Interventional or comparative studies comparing resin infiltration and other treatments in MIH-affected anterior teeth were included. The risk of bias was evaluated using the Risk Of Bias In Non-randomised Studies of Interventions (ROBINS-I tool) and the Risk of Bias 2 (RoB 2.0) tool. Meta-analysis utilized a random-effects model. DATA: Eighteen studies met the inclusion criteria, and twelve were included in the meta-analysis. Resin infiltration showed a higher color difference (ΔE) before and after treatment (mean difference 2.21, 95 % confidence interval [CI] 0.04-4.38, p < 0.001, I2 = 98.61 %, p < 0.001) and better optical improvement (standardised mean difference [SMD] 2.68; 95 %CI 0.30-5.06; p = 0.027, I2 = 97.8 %, p < 0.001) compared to controls. The estimated success rate based on dentist assessment was 92 % (95 %CI 88-95 %, I2 = 17.92 %, p = 0.06). Non-randomised trials showed high (8/14) or moderate (6/14) risk of bias, mainly from confounding and selection issues. Randomised trials had high risk (1/3) or some concerns (2/3) due to missing data. CONCLUSIONS: The findings suggest that resin infiltration significantly improves aesthetic outcomes in MIH-affected anterior teeth, as evidenced by higher colour difference and optical improvement compared to controls. CLINICAL SIGNIFICANCE: While our study shows promising results for resin infiltration, including high success rates and aesthetic improvements, larger-scale studies with longer follow-up periods are necessary to confirm these findings and assess its long-term efficacy.

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

PURPOSE: The aim of this study was to explore the potential to profile and distinguish varying clinical severity grades of MIH, compared to normal enamel, using proteomics. METHODS: Liquid chromatography-mass spectrometry analyses were conducted on enamel samples of extracted teeth, from 11 children and adolescents, spanning an age range of 6-18 years. Enamel powder samples were collected from extracted, third molars (n = 3) and first permanent molars diagnosed with MIH (n = 8). The MIH tooth samples were categorized into subgroups based on clinical severity grade. The data were statistically analyzed using ANOVA and Welch's t test. RESULTS: Teeth affected by MIH exhibited a diverse array of proteins, each with different functions related to dental enamel, distinguishing them from their normal enamel counterparts. The application of microdissection combined with LC-MS techniques has revealed the potential to discern unique proteomic profiles among MIH-affected teeth, characterized by varying clinical severity grades. Both analyzed MIH groups displayed consistent trends in the presentation of biological processes, including underabundance of proteins primarily associated with cell organization and biogenesis. Furthermore, proteins linked to cell death were overabundant in both MIH groups. CONCLUSION: Proteomics enabled the detection and differentiation of various proteins across different clinical severity grades of MIH.

Traumatic dental injuries and molar incisor hypomineralization: a cross-sectional study of schoolchildren from southern Brazil.

PURPOSE: To describe the prevalence and the variables associated with TDIs in schoolchildren aged 8 to 14 years in Estância Velha city in southern Brazil, placing emphasis on molar incisor hypomineralization. METHODS: Students enrolled in public schools of a medium-sized city in the southern Brazil were selected using cluster random sampling. Clinical examinations assessed molar incisor hypomineralization-MIH (European Academy of Pediatric Dentistry criteria), dental caries (DMFT index), and TDIs (O'Brien's criteria). Socioeconomic and demographic variables were assessed using a standardized questionnaire. Prevalence ratios were estimated using Poisson regression (p < 0.05). RESULTS: 513 students (54.8% female), with a mean age of 11.6 (± 1.9) years, participated in the study. The prevalence of TDIs was 11.3%, with enamel fracture representing 90.4%. The high prevalence of traumatic dental injuries was associated with MIH (PR: 2.22 CI: 1.27; 3.87; p < 0.01) and overjet > 3 mm (PR: 2.03 CI 1.19; 3.45; p < 0.01). CONCLUSION: The sample of schoolchildren from southern Brazil had a low prevalence of traumatic dental injuries. Molar incisor hypomineralization and increased overjet were associated with the higher prevalence of traumatic dental injuries.

Influence of different pre-treatments on the resin infiltration depth into enamel of teeth affected by molar-incisor hypomineralization (MIH).

OBJECTIVES: This in vitro pilot study aimed to evaluate whether different pre-treatments (demineralization, deproteinization, (chemo-)mechanical reduction of the surface layer) influence the penetration depth of a resin infiltrant into MIH-affected enamel compared to initial carious lesions. METHODS: Thirty extracted human permanent molars with non-cavitated initial carious lesions (n = 5) or MIH (n = 25) were chosen and randomly assigned to six experimental groups: IC: initial caries; M: MIH; MN: MIH, 5.25% sodium hypochlorite; MM: MIH, microabrasion; MA: MIH, air abrasion; MAN: MIH, air abrasion and 5.25% sodium hypochlorite. A modified indirect dual fluorescence staining method was adopted to assess the penetration depth (PD) of the resin infiltrant and the lesion depth (LD) by confocal laser scanning microscopy (CLSM). Exemplarily, scanning electron microscopic (SEM) images were captured. The relationship between group assignment and penetration/lesion depth was estimated using a linear mixed model incorporating the tooth as random effect (two observations/tooth). The significance level was set at p < 0.05. RESULTS: For MIH-affected molars, the mean PD (in µm; median, [minimum-maximum]) were M (178.2 [32.5-748.9]), MN (275.6 [105.3-1131.0]), MM (48.7 [0.0-334.4]), MA (287.7 [239.4-491.7]), and MAN (245.4 [76.1-313.5]). Despite the observed differences in PD between the groups, these could not be statistically verified (Bonferroni, p = 0.322). The percentage penetration was significantly higher for IC than for MIH groups (Bonferroni, p < 0.05). SIGNIFICANCE: Compared to IC, resin infiltration into MIH-affected enamel ist more variable. Different pre-treatments influence the resin penetration into developmentally hypomineralized enamel to a fluctuating level.