Molar-incisor hypomineralisation (MIH) is a delimited qualitative developmental defect, which is known to be associated with several dental complications like hypersensitivity, increased caries risk, and aesthetic impairment leading to a significant reduction in OHRQoL (Solinas et al. 2021). Up-to-date, several clinical trials have been conducted recently to evaluate the remineralisation and desensitising effect of various products e.g. fluoride varnish, casein-amorphous calcium phosphate (CPP-ACP), hydroxyapatite containing and arginine containing toothpastes in addition to silver diamine modified atraumatic restorative technique (SMART) and sealant application (Bakkal et al. 2017; Biondi et al. 2017; Restrepo et al. 2016). Though the management of hypersensitivity is still a huge challenge in daily practice (Rapaso et al.,2019). Thus, this clinical prospective study provides more insight and evidence on the management and the extend of hypersensitivity reduction in MIH molars with and without enamel breakdown (MIH TNI- 3 & 4).

This study involved 25 patients with a mean age of 8.6 (± 1.85) years, which is slightly higher than those of a similar previous study as shown in Table 1 (Bekes et al. 2022). This might be explained by the fact that this study included not only newly erupted hypersensitive MIH molars but also patients with persisting hypersensitivity after prior desensitising treatments and one adolescent patient with 2nd permanent molar. The presence of enamel hypomineralisation on the second permanent molar is not unusual, this can be supported by the finding of a previous study, which concluded that the occurrence of enamel hypomineralization in the permanent second molar is generally more prevalent when the permanent first molar exhibits molar incisor hypomineralization (MIH) especially with severe defect (De Farias et al., 2021).

The assessment of hypersensitivity is known to be subjective, which is difficult to measure. Evaporative stimuli (Schiff air cold sensitivity score) and visual analogue scale (VAS) are the most popular methods to induce and measure pain intensity in dentine hypersensitivity (Bijur et al. 2001). Since the pain intensity in the air test is higher the than tactile test, the Schiff air cold sensitivity score (SCASS) test was used as the primary outcome parameter in this study (Bekes et al. 2017). However, the additional subjective assessment of hypersensitivity was done using the Wong-baker faces scale (WBFS) instead of the visual analogue scale (VAS). This was decided as WBFS was originally created for children to communicate pain through facial expressions (Facial scales) and the most preferred way for children to report pain (Wong & Baker, 1998; Keck et al. 1996). Furthermore, this study included children with a history of previous desensitising treatments, but no desensitising treatment should have been performed within 4 weeks. This can be explained by the assumption that a minimum period of 2–4 weeks “wash-out phase” is required to eliminate or at least reduce the desensitising effect of a previously applied treatment (Vano et al. 2018).

According to baseline characteristics of the study sample, a slightly higher number of hypersensitive lower molars were observed (n = 20, 46.5% upper quadrants vs. n = 23, 53.5% lower quadrants). This is similar to the observed characteristics of hypersensitive MIH-affected molars in a previous study (Bekes et al. 2017), whereas the slight majority of the included hypersensitive MIH molars were of high grade of sensitivity SCASS 3 (n = 24, 55.8%) as shown in Table 3. This supports the conclusion of previous findings, that hypersensitivity in MIH molars is significantly affected by the quality of mineralisation and degree of hypomineralisation rather than the size of the MIH defect (Linner et al. 2021). Hence, in this study hypersensitive MIH molars with and without enamel breakdown (MIH-TNI 3 & 4a/b) were included.

Regarding the degree of hypersensitivity and its pain intensity, the results of this study showed a mean SCASS of 2.56 (± 0.50) and a mean WBFS of 5.86 (± 2.50). This is similar to a previous study, which involved a mean SCASS of 2.4 (± 0.50) but a higher mean of WBFS 7.1 (± 1.7) as depicted in Table 3 & 4 (Bekes et al 2022). According to a previous epidemiological study, MIH molars of high intensity of hypersensitivity are mostly represented by maximum scores of SCASS (Raposo et al. 2019).

This clinical trial was able to report a hypersensitivity relief, which is evident by a significant decrease (P < 0.001, paired t test) in the SCASS score, which reduced from 2.56 (± 0.50) to 1.14 (± 0.96) immediately after 15 min and even further to 0.71 (± 0.89) in the following 12 weeks period as shown in Table 4. A similar significant results were observed with a prolonged use of 8% arginine and calcium carbonate paste over 8 weeks, in which SCASS scores dropped from 2.1 (± 0.3) to 0.8 (± 0.9) (Bekes et al. 2017). Moreover, two other previous studies reported the use of an experimental paste based on zinc-hydroxyapatite which was shown to be effective in reducing hypersensitivity in MIH molars as well. They concluded the non-inferiority of a toothpaste containing microcrystalline hydroxyapatite compared to amino fluoride containing toothpaste (Ehlers et al. 2021; Butera et al. 2023). However, the major problem of hydroxyapatite-containing toothpaste is the lack of fluoride, which is known to be essential for caries prevention (AAPD, 2023). Importantly, this study involves assessing the effect of a single application of GIC sealant (Ionostar Plus + Easy Glaze, VOCO). Hence an assessment of immediate effect (15 min after application) was not only possible but showed a clear clinical benefit.

In this study, for the majority of MIH molars the hypersensitivity SCASS score were reduced to ≤ 1 immediately (15 min post application; 65.1%) and to a SCASS score of 0 over a period of 12 weeks (52.4%, Table 3). This means that the majority of patients (n = 34, 80.9%) didn’t show pain or hypersensitivity to the air stimulus anymore. This can be verified through the subjective assessment of pain intensity via WBFS, which showed a significant reduction in the mean WBFS score (P < 0.01, paired t test, Table 4) from 5.86 (± 2.50) to immediately after the application of 3.00 (± 2.28) and after 3 months to 2.95 (± 2.17). The result of this study is in a way different than those of a previous study, which aimed to assess hypersensitivity relief of 2 different sealing techniques (resin-based sealant & GIC-based sealant) in different times point. It showed a drastic decrease of the mean SCASS from 2.3 (± 2.17) at baseline to 0.4 (± 0.7) immediately after the treatment and to 0.1 (± 0.41) after a time span of 12 week. Whereas, the results from a randomised control trial (RCT aimed to assess hypersensitivity reduction of silver-modified atraumatic restorative technique SMART (SDF + GIC), which showed a significant reduction from 1.77 (± 0.83) to 0.08 (± 0.28) for SMART, in which SMART showed a slightly more reduction in MIH hypersensitivity than SDF (Balikaya et al. 2022). This difference in the end-point SCASS score may be explained by the fact that the baseline SCASS in this study was initially higher than those of the two mentioned studies. Moreso MIH molars with persistent hypersensitivity referring to teeth which were in a way unreceptive to received previous desensitising treatments were also included (n = 13) (Bekes et al. 2022).

A recent study showed an improved oral health-related quality of life (OHRQol) in children with hypersensitive MIH molars after receiving an application of sealant coverage (Bekes et al. 2021). Thus a sealant coverage might be a helpful and simple tool to improve OHRQoL, due to the fact that a higher severity of MIH-TNI correlated significantly with impaired OHRQoL (Sekundo et al. 2024).

In this study, hypersensitive MIH molars of a baseline SCASS score of 2 & 3 reported a statistically significant reduction of hypersensitivity immediately and in 12 weeks period (P < 0.05, Mann–Whitney U test). Though still some of the hypersensitive MIH molars with baseline 2 (n = 2, 10.5%) and SCASS 3 (n = 13, 54%) reported a persistent hypersensitivity (SCASS ≥ 2) as shown in Table 5. Based on a recent systematic review, due to difficulty in assessing subjective pain intensity, which is affected by the inherently subjective and intricate nature of pain, the clinical management of hypersensitivity is mainly defined as a contemporary approach through utilising a combination of in-office application adjacent with home-based desensitising agents such as toothpaste containing potassium salt, fluoride and hydroxyapatite (Dionysopoulos et al. 2023).

However, the effect is more prominent after a 12 weeks period, in which hypersensitive MIH molars with a baseline SCASS of 2 showed a statistically higher reduction in the mean SCASS than those of baseline SCASS 3 (P = 0.03, t test; Table 5). This difference can be explained by the fact that all hypersensitive MIH molars with baseline SCASS of 2 included in the study showed no post-treatment hypersensitivity (SCASS < 2) while some of the MIH molars with high intensity of hypersensitivity (SCASS 3; n = 8, 34.8%) reported a persistent hypersensitivity (Table 5). Based on previous studies, in almost all the patients, who received desensitisation treatments independent of the material used, an improvement in the SCASS values was observed., This emphasizes the hypothesis of starting from very high sensitivity values and a decrease over time. Repeating or combining desensitisors and enhancing sensory changes will stabilise the situation with time (Murri Dello Diago et al. 2021).

In addition, the study analysis involved assessing the effect of GIC sealant application (Ionostar Plus + Easy Glaze, VOCO) on hypersensitivity reduction of MIH molars with (n = 13, 30%) and without a history of desensitizing treatment (n = 30, 70%) as shown in Table 6. Furthermore, this study included hypersensitive MIH molars with at least no history of desensitizing treatment prior to 1 month before the GIC sealant application. Previous studies investigating various treatment modalities on MIH hypersensitivity showed a significant end-point desensitizing effect within 4 weeks (Bekes et al 2022, 2017). Nevertheless, the study results didn’t show any statistically significant difference in hypersensitivity reduction in MIH molars with and without prior desensitizing treatment (p < 0.05). Whereas, hypersensitive MIH molars with no history of pre-treatment showed a higher rate of post-GIC-sealant hypersensitivity (SCASS ≥ 2; n = 9, 40.9%) than those without a history of pre-treatments (SCASS ≥ 2; n = 3, 23.1%) after 12 weeks post GIC sealant application (Table 6). Interestingly in this study, the pre-treatment group showed a statistically significant reduction in desensitization in the time frame of 15min – 12 weeks (p < 0.05). This supports the fact that the frequency of desensitisation treatment on MIH molars is also important for the longevity of the desensitising effect and that this technique is effective irrespective of the type of pre-treatment (Balikkaya et al., 2022).

One secondary aim of the study involved the evaluation of the retention rate of GIC (Ionostar Plus + Easy Glaze, VOCO) on hypersensitive MIH molars over a period of 12 weeks. Based on the study results, fourteen GIC sealants (33.5%) were completely lost over a period of 12 weeks. In two of these cases there were even the presence of dentine caries (4.8%, Table 7). This retention rate is slightly lower than those of a similar study, which observed partial loss of the GIC sealant in 8 teeth (21.1%) but no caries presence over a period of 12 weeks (Bekes et al. 2022). This lower performance rate of the GIC sealant in this study might be explained by the fact that the study involved MIH molars with enamel breakdown to some extent more than the surface coverage of a conventional GIC sealant, which could be still used as an initial quick treatment until definitive restoration is placed (Fragelli et al., 2015). However, both studies showed comparable domains of deteriorations, which were marginal integrity and tactile surface texture (Bekes et al. 2022).

According to a retrospective analysis of the retention of resin-based sealant on MIH molars, the retreatment rate was higher within 2 years and the failure risk was three times more than molars without MIH (Kotsanos et al. 2005). Based on the findings of 4-years follow-up study, a significant enhancement in the retention of fissure sealants in hypomineralised molars was observed when a single bottle adhesive system was applied prior to the placement of the resin-based sealant (Lygidakis et al. 2009). Whereas according to another clinical study, loss of the retention of resin-based sealant in MIH molars was observed in three teeth out of 25 teeth within four weeks (Fragelli et al., 2017), this is lower than those of the present study, in which three out of 42 GIC sealant were lost after 12 weeks.

The fact that hypomineralised enamel has a higher porosity, reduced degree of hardness and elasticity with a change in carbon-carbonate ratios when compared to sound enamel (Elhennawy et al., 2017). This results in compromised bonding due to poor adhesion and reduced bonding strength in MIH-affected enamel (Lagarde et al. 2020). Thus the application of GIC sealant might be superior to resin-based sealants, which require optimal conditions such as excellent moisture control (Cvikl et al. 2018). On the contrary, glass ionomer cement sealants can serve as a suitable temporary treatment option in challenging clinical conditions where isolation is insufficient. This is due to their lower technique sensitive and their ability to set quickly without the need for intermediate steps like etching. This is particularly advantageous in cases where a sealing is necessary for a not fully erupted MIH molar, as well as for non-cooperative, anxious children or patients experiencing hypersensitivity and pain in their molars. The straightforward application procedure of glass ionomer cement sealants makes them a more convenient choice for children. Additionally, these sealants may offer the added benefit of fluoride release, making them a viable option for tooth preservation and caries protection (Elhennawy & Schwendicke 2016). It has been proposed that the use of a GIC sealant can provide protection for molars affected by MIH against post-eruption enamel breakdown (Lygidakis 2010). The prevailing theory suggests that the fluoride found in this material may permeate into the affected enamel and dentin, promoting mineralization of the hypomineralized areas (Lygidakis 2010).

The present study has some limitations, which included a higher sample size that would have been required for some secondary outcome variables, like the assessment of the retention rate of GIC sealant. A longer follow-up time frame would have been good to evaluate the domains of the deterioration and hypersensitivity relief over a longer period. In addition, the lack of untreated control, which would have been interesting for the interpretation of the study results. However, due to the high degree of hypersensitivity intensity, the lack of control (no in-office treatment) might have been not only unethical but also not feasible as parents would have refused in study participation. A comparative control group involving other standard desensitisation treatments, such as resin-based sealants, CPP-ACP pastes, sodium fluoride (NaF) varnish would have added more value to the results. Further investigations are required to assess hypersensitivity relief of combining GIC sealant with other standard desensitisation treatments such as CPP-ACP pastes, and sodium fluoride (NaF) varnish.