The present study compared the dental-treatment outcomes, oral-hygiene improvement, and patient co-operation during follow-up visits between children treated under GA and NP from dental records during 2008 –2020. The results demonstrated that at baseline, the GA group had a significantly higher caries experience (dmft and dmfs), number of cases with definitive negative behaviour, and mean OHI-S than the NP group. The extensive dental treatment (e.g. stainless-steel crown, pulp therapy, and extraction) was significantly higher in the GA group than the NP group, which suggests that uncooperative children with extensive dental caries tended to receive dental treatment under GA. These finding were similar to those in Grindefjord (2018), who reported that children treated under GA had more decayed teeth and more restorations.

Dental treatment under GA is recommended as an effective behaviour management technique for unco-operative children with ECC, especially for children with extensive dental caries that requires extensive and multiple restorations without the need for their co-operation. Moreover, the number of complete cases was higher in patients treated by GA interventions (Baakdah et al. 2021) that was similar to the finding of the present study. However, the number of Thai children with S-ECC who received dental treatment under NP behaviour management was much higher than the GA group. This finding is possibly due to the limited facilities and government dental fee support in Thailand. Moreover, many parents of children with S-ECC are concerned about the pharmacological management procedures, related complications, financial issues, and long waiting time. This problem is possibly due to the multiple treatment visits required for patients who lacked psychological or emotional maturity. Therefore, this study used age-matched pairs between GA and NP groups to minimise the different outcomes and bias.

The result of this retrospective study revealed that ~ 70% of the children in both groups were maintained on a regular follow-up schedule. However, 6.7–18.9% of the patients in both groups dropped out from the follow-up appointment in each follow-up period (6, 12, 18, and 24 months). At the 24-month follow-up, there were 123 patients (58.5%) in the GA group and 146 patients (69.5%) in the NP group. There was no significant difference in outcomes between groups until the 24-month follow-up.

The percentage of new caries in the GA group was 6.6–9.9% within 6 − 24 months that was higher compared with Baseggio et al. (2010), who reported 3.13% new caries at the 24-month follow-up. However, our results were similar to a study by Jiang et al. (2019) that reported 8.5% and 18.8% of new carious cases at the 6-and 12-month follow-up, respectively. Although the preventive intervention was applied individually using the same standard guidelines in both GA and NP groups, the number of new carious teeth at the 6-month follow-up in the NP group was significantly greater than the GA group. This finding is explained by the different treatment planning between the NP and GA interventions. The NP group had more teeth prone to developing new caries than the GA group because many patients, whose parents preferred non-painful dental procedures, received minimal invasive techniques. In contrast, the treatment plans in the GA group was traditional restorations that contained a high number of painful dental procedures, such as a stainless-steel crown and extraction.

Furthermore, although the oral hygiene of both groups improved, the new caries in both groups were still quite high. These results indicated that Thai children with S-ECC have a high risk of dental caries. These results were supported by Boonyawong et al. (2022), who reported that 80.8% of preschool children had dental caries with a mean dmft of 8.2. They also found that older age, higher visible dental plaque score, and lower mother’s education level were significant risk factors for dental caries in preschool children. There was significant oral-hygiene improvement between before and after treatment in the GA group. Therefore, a caries-risk assessment and individual preventive approach during follow-up visits are necessary for preschool children.

We found that dental-treatment failure was not significantly different between the GA and NP groups from the 6–24-month follow-up. The restoration failure rate in this study ranged from 3.2 to 6.2% in the GA group and 3.6 − 12.7% in the NP group. More than 90% of the class II restorations in this study were restored with resin-modified glass ionomer cement (RMGIC). Previous studies demonstrated a wide range in the failure rate of class II restorations in primary posterior teeth with RMGI (2.58 – 16%) within 3 years in patients receiving NP treatment (Dermata et al. 2018; Webman et al. 2016). Furthermore, the composite and glass ionomer restoration failure rate under GA ranged from 9.9– 44.4% within 6 –24 months (Jiang et al. 2019; Biria et al. 2012). Therefore, the outcome of the dental restorations in this study was similar to those in previous studies.

The number of teeth with sealant loss within 24 months in the GA group was 3.3 –9.1% compared with the NP group at 5.7–8.5%. The rate of sealant loss in the GA group was similar to that in Jiang et al (2019) who reported a sealant loss of 7.1% at 6 months, and 10.7% at 12 months after being treated under GA. In the present study, the number of SSC dislodgements in both groups were low (less than 1%) compared with previous studies that reported a failure rate of SSCs placed under GA of 0.5% − 8% during the 6 − 36-month follow-up period (Jiang et al.2019; Biria et al. 2012; Al-Eheideb and Herman 2004; Tate et al. 2001; Sabbahi et al. 2022). In contrast, the failure rate of SSCs placed under NP in a previous study ranged from 2% − 25% during the 2 − 10-year follow-up periods (Randall 2002).

Pulp therapy was performed significantly more often in the GA group than the NP group, and pulpectomy was done more frequently than pulpotomy in both groups. The pulpotomy failure rate in this study (4.3% − 16.7%) was slightly higher than in previous studies that found a low-pulpotomy failure rate (1.1 – 14%) in teeth treated under GA within 6 −–36 months (Khodadadi et al. 2018; Biria et al. 2012; Al-Eheideb and Herman 2004; Sabbahi et al. 2022). However, the pulpotomy failure rate in this study was similar to other studies that reported a 1.9 –25.8% failure rate of pulpotomy with formocresol within 6 − 36 months (Trairatvorakul and Koothiratrakarn 2012; Dhar et al. 2017), and the pulpotomy with ferric sulphate failure rate was 15.4 –18.1% within 12 –24 months (Dhar et al. 2017). In contrast, the pulpectomy failure rate of in the present study (0– 7.4%) was lower than in previous studies that reported pulpectomy failure in the GA ranging from 0.8% − 9.5% in 6 − 33 months (Khodadadi et al. 2018; Jiang et al. 2019; Biria et al. 2012). However, it is difficult to compare the outcome of pulp treatment amongst different studies due to the variety of root canal materials used. Previous studies found that the pulpectomy failure rate in primary teeth with ZOE was 0% − 8% within 6 –18 months (Coll et al. 2020; Chen et al. 2017a,b ), and that of pulpectomy with Vitapex was 0% − 28.6% within 6 − 18 months (Chen et al. 2017b, a; Rasi et al. 2019; Trairatvorakul and Chunlasikaiwan 2008).

Both groups demonstrated improved patient co-operation during the follow-up visits. The NP group had significantly better co-operation than the GA group at all follow-up visits. Moreover, the GA group had a significantly twofold higher use of protective stabilisation during the follow-up visits (p = 0.001) (data not shown). These findings may be related to the baseline behaviour of children in the GA group who had more negative behaviour compared with the NP group. Furthermore, the children in the NP group received more behaviour management by dentists during treatment than the GA group who completed dental treatment in a single visit.

Although ECC treatment can be performed using GA and NP interventions, it has been reported that children with ECC had a poorer oral health-related quality of life compared with caries-free children (Singh et al. 2020). Therefore, providing prenatal oral-health care knowledge during pregnancy to prevent early acquisition of mutans streptococci, raising awareness of ECC with caregivers and health care professionals, limiting free-sugar consumption and daily fluoride exposure for young children are essential to prevent the development of ECC (Pitts et al. 2019; Xiao et al. 2019).

The limitation of this study was that some information could not be obtained from the dental chart records, such as the socioeconomic status of the caregivers. Moreover, the accuracy of retrospective data may not be as high as in a prospective study. Future prospective studies that evaluate dental-treatment outcomes are suggested.