Abstract
Molar-incisor hypomineralisation (MIH) has been labelled as an ongoing problematic condition for both the affected children and dentists managing this condition. Several studies have investigated the biochemical properties of enamel affected with MIH. Assessing severity is considered at the present time to be a major determinant of the management of MIH. Based on the clinical presentation, the defects have been described as mild: white/opaque demarcated defects with no structural loss; moderate: defects with post-eruptive enamel breakdown (PEB) limited to enamel; severe: presence of atypical restorations with or without PEB involving enamel and dentine. Studies have shown that it is not always possible to grade the severity of MIH lesions based on their clinical presentation and/or mineral content.
The overall purpose of this research project was to investigate how the molecular and elemental composition of MIH enamel would influence the infiltration of a low viscosity resin proven to be able to infiltrate non-cavitated interproximal caries lesions.
The objectives of this research were two fold: to investigate the biochemical properties of enamel affected with MIH using Raman spectroscopy and scanning electron microscopy equipped with energy dispersive X-ray spectroscopy (EDS-SEM) and also to investigate the penetrability of a commercially available low viscosity resin infiltrant into MIH enamel using these two spectroscopic techniques.
After obtaining ethical approval and informed consent, extracted first permanent molars diagnosed clinically as affected by MIH were collected from different dentists throughout New Zealand. These teeth were received and sectioned with a water-cooled diamond saw and the pairs of lesion halves were subjected to a series of in vitro experiments.
Initially three first permanent molars with differing severities of MIH (brown, yellow, and white lesion type) were subjected to the following tests; laser fluorescence (LF), Raman spectroscopy, and EDS-SEM.
The molecular components of MIH enamel were analysed by means of Raman spectroscopy for three teeth, while the corresponding elements present were analysed using EDS-SEM.
Qualitatively, the enamel from the cervical region of MIH-affected teeth was always spared and the cuspal areas appear to be less severely affected. The MIH defect tissue involved bands that extended the full thickness of enamel but also followed the natural incremental lines of Retzius. Raman spectral maps revealed increased concentrations of protein and carbonate in MIH-affected enamel compared to cervical normal enamel. The results show a common trend of decreasing severity of MIH from brown to yellow and creamy white lesions respectively. The protein content tends to decrease from the surface layer toward the DEJ in all lesion types. Quantitatively, no significant differences were noted in the calcium to phosphorus ratio between hypomineralised and normal enamel areas within the MIH-affected tooth. These findings have implications for aetiology.
Seven permanent molars showing brown demarcated opacities without post-eruptive breakdown were sectioned perpendicular to the lesion surfaces giving two halves of each lesion. A total of sixteen lesion halves were obtained from seven teeth. One half of the paired lesion halves was subjected to resin treatment and the other half served as control. After taking laser fluorescence (LF) readings using DIAGNOdent, samples (lesion halves) were then allocated to four treatment groups (n=2 per group) and a resin infiltration procedure was carried out according to four different treatment protocols. The resin used in this study is the Icon caries infiltrant (DMG, Hamburg, Germany). Four out of eight samples in the control group were subjected to EDS-SEM analyses and comparisons were made with resin-infiltrated lesions.
Group 1: Standard treatment (as per manufacturer’s instructions)
Group 2: 5% Sodium hypochlorite (NaOCL) pre-treatment group
Group 3: 5% Sodium hypochlorite (NaOCL) mid-treatment group
Group 4: 30% H2O2 pre-treatment group
Group 5: Control group (non-treatment group)
The LF readings were taken to support the subjective classification of the study teeth based on the colour of enamel (brown). This study is a preliminary attempt to infiltrate enamel lesions in MIH with a commercially available light-activated low viscosity resin with a high penetration coefficient. Based on available background on the structure and chemistry of MIH enamel, this approach was considered logical and feasible. The results of this in vitro study, using the Raman spectroscopy and EDS-SEM revealed no significant differences between the groups or treatment protocols in terms of penetration depth of the resin infiltrant. Resin infiltration is possible in MIH enamel but the pattern of infiltration is inconsistent and variable. The current pilot investigation was limited by the fact that the study involved a small number of samples and future investigations should ensure a larger sample size.
In conclusion, Raman spectroscopy and EDS-SEM are useful tools for probing the chemical composition of MIH and normal enamel and can be used as additional tools to study changes in MIH enamel following treatment with different agents designed to further mineralise or to infiltrate enamel. The findings from this study add further useful insight into the aetiology of MIH; resin infiltration into MIH enamel has shown that infiltrant resin material is capable of penetrating MIH enamel but the pattern and depth of penetration is variable and less compared to those reported in carious lesions. A future study investigating the effect of etching agents with different viscosities on the pattern of resin infiltration in MIH enamel would be interesting. More research using large number of samples is required before they can be recommended for management of MIH-affected enamel.