Stress-Induced Depression and Its Effects on Tooth Wear in Rats: A 3D Dental Scan Imaging Perspective

Abstract

Background: In addition to behavioral and biochemical abnormalities, a parafunction associated with temporomandibular joint disorders (TMDs) resulted in stress-induced depression in rats. Exploring how chronic stress influences molar wear in rodents provides insights into the understanding of depression, TMD, and oral health. This study aimed to conduct a three-dimensional (3D) analysis of first molar wear in an animal model of depression by comparing molar attrition and cusp variation between stressed male rats and control groups.

Methods: After obtaining a validated model of depression in male rats, we obtained 3D scans of lower molars to analyze wear patterns. The 3D analysis was applied to quantify cusps' volume and the difference in first molar cusp morphological structure. The data were then compared to identify significant morphological differences between groups side by side.

Results: The analysis revealed the reduction of cusps' volume in the depression groups. Rats exposed to depression exhibited significantly greater occlusal table wear than their control counterparts (p < 0.05).

Conclusions: As dentistry moves towards greater digital imaging, understanding the impact of psychological factors on TMD becomes increasingly necessary. This study shows that stress-induced depression in rats can result in significant tooth wear, as investigated using a 3D dental scanner.

Keywords: bruxism; dental digital scanner; depression; restraint stress; temporomandibular disorder; three-dimensional analysis; tooth wear.

Figure 1

Diagram of the experimental design. After a 7-day acclimatization period, rats were randomized and assigned to the depression group, which was subjected to restraint stress (2 h/day) for 2 weeks. Depression-like behavior was evaluated using the Forced Swim Test (FST) on days 15 and 16. Following behavioral assessments, rats were sacrificed, and tissue samples were collected for analysis.

Figure 2

Physical changes and eating behaviors in control and stress-induced depression rats. Changes in the levels of (A) staring and (B) final body weight (BW), (C) daily weigh gain (DWG), (D) daily food intake (DFI), and (E) daily water intake (DWI) were assessed and compared between the two groups. (* p < 0.05, ** p < 0.01).

Figure 3

Hormonal and adrenal structural responses in control and stress-induced depression rats. (A) Changes in urinary corticosterone (urine CORT) levels, (B) the relative wet weight of the adrenal gland to body weight, and histological features of adrenal gland layers—(C) adrenal subregion cortex, (D) zona glomerulosa (ZG), (E) zona fasciculata (ZF), (F) zona reticularis (ZR), and the medulla (M)—were assessed and compared between groups. Photograph of histological adrenal gland sections stained with H&E of the control group (G) compared to depression group (H). (** p < 0.01).

Figure 4

Changes in the level of depression-like behaviors in stressed male rats were assessed using the forced swimming test (FST) by recording time spent in immobility (A), climbing (B), and swimming (C), as well as the number of fecal pellets (D) in control and stress-induced depression rats (* p < 0.05, ** p < 0.01).

Figure 5

Representative illustration of structural comparisons of lower molars. (A) Control–control, (B) depression–depression, and (C) control–depression. Green indicates slight to no difference between the two samples (p < 0.05 mm), while yellow and blue indicate a difference greater than 0.05 mm.

Figure 6

Representative 3D segmentation of cusp volumes in the first to third molars (M1–M3). Comparison of cusp morphology between the (A) control group and (B) depression group. Quantitative analysis of mean cusp volumes for the (C) left and (D) right sides. (* p < 0.05, ** p < 0.01).

Figure 7

Representative illustration of morphological analysis of the left first molar (M1). The six landmark points of the left M1 (A), which were used to calculate the distance differences. The distance difference analysis of the cusp of the M1 shows the difference between 2 groups on the left side (Left) and right side (Right) (B).

Figure 8

The nanostructure of the cusp tip surface revealed scratch lines in the depression group (red arrow).