Time-dependent microbiome dynamics in orthodontic thermoplastic materials: comparing PETG and TPU

Abstract

Objectives: This study compares the effects of thermoplastic polyurethane (TPU) and polyethylene terephthalate glycol (PETG) aligners on the oral microbiome and salivary pH during orthodontic treatment.

Materials and methods: Ten participants wore TPU and PETG aligners for 24 h. At five time points (1 min, 4, 8, 12, and 24 h), saliva was collected for pH analysis, and microbial samples were taken from both aligner and supragingival plaque surfaces for 16S rRNA sequencing. Statistical analyses included repeated Measures ANOVA for pH, Kruskal-Wallis test for alpha diversity, PERMANOVA for beta diversity, and two-way ANOVA for microbial composition.

Results: In Group PETG, salivary pH significantly decreased from T0 to T4 (p < 0.05). No significant changes in alpha or beta microbiota diversity were observed in either group. Microbial shifts in supragingival plaque microbiomes were detected at T8 in Group PETG, while in Group TPU, these changes became evident between T12 and T24. In aligner microbiomes, Group TPU showed significant reductions in Veillonella, Actinomyces, and Fusobacterium at T24 (p < 0.05). In contrast, Group PETG exhibited significant increases in Streptococcus from T4 to T24 (p < 0.05) and Fusobacterium from T0 to T4 (p < 0.05), followed by a decline from T4 to T24 (p < 0.01).

Conclusions: PETG aligners caused significant reductions in salivary pH at T4 and triggered pronounced fluctuations at T8 in supragingival plaque microbiomes. TPU aligners caused a delayed decline in salivary pH between T8 and T12 and drove distinct structural shifts during prolonged wear from T12 to T24.

Clinical relevance: Material choice based on microbial impact highlights the need for personalized aligner materials and cleaning cycles.

Keywords: 16S Rrna; Clear aligners; Dentistry; Oral microbiome; Orthodontics; Thermoplastic materials.

Fig. 1

Line graphs generated based on the pH values of saliva at T0, T4, T8, T12, and T24. *Statistically significant difference: pH value of PETG: T0–T4, p = 0.0202

Fig. 2

Alpha diversity indices of the aligner microbiomes of Group TPU-T at T0, T4, T8, T12, and T24, assessed by Kruskal–Wallis test. The panels show: (a) Chao1 index, (b) Observed Species, (c) Shannon’s diversity, and (d) Simpson’s diversity. Data was presented using median and interquartile ranges. The order of the five lines in each set of data from the bottom to top indicates the minimum, first quartile, median, third quartile, and maximum

Fig. 3

Alpha diversity indices of the aligner microbiomes of Group PETG-T at T0, T4, T8, T12, and T24, assessed by Kruskal–Wallis test. Panel definitions and boxplot representation are identical to those described in Fig. 2

Fig. 4

Alpha diversity indices of the aligner microbiomes of Group TPU-A at T0, T4, T8, T12, and T24, assessed by Kruskal–Wallis test. Panel definitions and boxplot representation are identical to those described in Fig. 2

Fig. 5

Alpha diversity indices of the aligner microbiomes of Group PETG-A at T0, T4, T8, T12, and T24, assessed by Kruskal–Wallis test. Panel definitions and boxplot representation are identical to those described in Fig. 2

Fig. 6

Beta diversity analysis based on weighted UniFrac distance metrics of Group TPU-T (a), PETG-T (b), TPU-A (c), and PETG-A (d) at T0, T4, T8, T12, and T24. The order of the five lines in each set of data from the bottom to top indicates the minimum, first quartile, median, third quartile, and maximum

Fig. 7

Principal coordinates analysis (PCoA) visualization of the structural variation in microbial communities for Group TPU-T (a), PETG-T (b), TPU-A (c), and PETG-A (d) at T0, T4, T8, T12, and T24. Each point represents the bacterial community of an individual sample

Fig. 8

Temporal changes in bacterial abundance at the phylum level for Group TPU-T (a), PETG-T (b), TPU-A (c), and PETG-A (d) at T0, T4, T8, T12, and T24

Fig. 9

Temporal changes in the relative abundance of the Saccharibacteria phylum. All data are expressed as mean ± standard deviation by ANOVA. *p < 0.05; **p < 0.01

Fig. 10

Temporal changes in bacterial abundance at the genus level for Group TPU-T (a), PETG-T (b), TPU-A (c), and PETG-A (d) at T0, T4, T8, T12, and T24. All data are expressed as mean ± standard deviation by ANOVA. *p < 0.05; **p < 0.01

Fig. 11

15 most abundant bacterial genus in the supragingival plaque microbiomes (a) and the aligner microbiomes (b) at T0, T4, T8, T12, and T24

Fig. 12

Temporal changes in the relative abundance of major pathogenic-related genera of Group TPU-T (a), PETG-T (b), TPU-A (c), and PETG-A (d) at T0, T4, T8, T12, and T24. All data are expressed as mean ± standard deviation by ANOVA. *p < 0.05; **p < 0.01

Fig. 13

Temporal changes in bacterial abundance at the species level for Group TPU-T (a) and PETG-T (b), and the relative abundance of major pathogenic-related species of Group TPU-A (c) and PETG-A (d) at T0, T4, T8, T12, and T24. All data are expressed as mean ± standard deviation by ANOVA. *p < 0.05; **p < 0.01