The impact of perforation at different locations of the disc on TMJ stressStress distribution on the discs of the affected side

The results of stress distribution on the discs of the affected side are shown in Fig. 3. A, B and Fig. 4. A, B. In the normal state of the affected-side disc, the maximum equivalent stress (Maximum von Mises stress, MVMS) experienced by the affected-side disc is 4.3794 MPa, while the MVMS in the bilaminar region is 0.073212 MPa. The high-stress areas in the disc are mainly distributed in the middle band and posterior band. The high-stress areas in the bilaminar region are primarily located in the anterior-central portion of the bilaminar region. After the occurrence of anterior displacement of the affected-side disc, there is a sharp increase in MVMS for both the affected-side disc and the bilaminar region, reaching 7.7477 MPa and 0.2386 MPa, respectively. The high-stress areas in the disc exhibit a significant posterior shift, primarily distributed in the posterior-lateral region of the disc. The high-stress areas in the bilaminar region also show a posterior shift.

Fig. 3

Stress distribution on affected-side TMJ impaired by disc perforated at different locations (MPa). A: discs, B: bilaminar regions, C: condyles

Fig. 4

Peak value of the stress on the TMJ affected by perforated disc at different sites (MPa). A: affected-side discs; B: affected-side bilaminar regions; C: affected-side condyles; D: normal-side discs; E: normal-side bilaminar regions; C: affected-side condyles

When perforation occurs in the anterior and middle band of the affected-side disc, there are no significant changes observed in the MVMS and stress distribution areas of both the affected-side disc and the bilaminar region compared to the anteriorly displaced disc. When perforation occurs in the medial and lateral bands of the affected-side disc, there is an increase in MVMS for the affected-side disc. The MVMS for the medial perforation is 8.2254 MPa, while the MVMS for the lateral perforation is 8.8317 MPa. However, there are no significant changes observed in the stress distribution. Compared to the anteriorly displaced side, The MVMS and stress distribution of the affected-side bilaminar region does not show any significant differences.

After perforation occurs in the posterior band of the affected-side disc, there is a significant increase in the MVMS, reaching 13.247 MPa. High-stress concentration areas are observed around the site of perforation. The MVMS in the affected-side bilaminar region also shows a significant increase, reaching 0.36855 MPa. The high-stress areas are distributed at the junction between the disc and the bilaminar region. After the occurrence of perforation at the junction between the affected posterior band and the bilaminar region, the MVMS of the affected-side disc reaches a peak value of 15.668 MPa. The stress in the bilaminar region is 0.30213 MPa, also indicating a relatively higher state. The high-stress regions in both the disc and the bilaminar region are located around the perforation site. The occurrence of perforation in the bilaminar region has a less noticeable impact on the MVMS and stress distribution of the affected-side disc. The stress in the bilaminar region is relatively high, measuring 0.25953 MPa, with the high-stress regions mainly distributed around the perforation site.

Stress distribution on the condyles of affected side

The results of stress distribution on the condyles of the affected side are shown in Fig. 3. C and Fig. 4. C. When the disc on the affected side is in a normal state, the MVMS experienced by the condyle is 3.445 MPa, with a uniform stress distribution and no significant stress concentration. However, after the occurrence of disc displacement, the MVMS in the affected condyle increases to 6.4715 MPa, and the stress distribution starts to shift towards the anterior part of the condyle. When perforation occurs at the junction between the disc and the bilaminar region, the MVMS in the condyle reaches its peak at 7.2234 MPa. However, no significant regular patterns of MVMS change are observed when perforations occur in other locations. After the occurrence of perforation in the posterior band and at the junction between the disc and the bilaminar region, the high-stress distribution area in the condyle becomes smaller, indicating a more concentrated stress distribution.

Stress distribution on the discs of normal side

The results of stress distribution on the discs of the affected side are shown in Fig. 5. A, B and Fig. 4. D, E. In the normal state of the disc on the unaffected side, the MVMS experienced by the normal-side disc is 4.3924 MPa, while the MVMS in the bilaminar region is 0.069512 MPa. The high-stress areas in the normal-side disc are primarily distributed in the middle band and posterior band. In the normal-side bilaminar region, the high-stress areas are mainly distributed in the anterior-middle portion of the bilaminar region. After the occurrence of disc displacement on the affected side, there is a significant increase in MVMS in the normal-side disc, reaching 4.9622 MPa, and in the bilaminar region, reaching 0.076212 MPa. However, when perforations occur in the anterior band, middle band, and medial region of the affected-side disc, there are no significant changes in MVMS in the normal-side disc and bilaminar region compared to the disc displacement condition.

Fig. 5

Stress distribution on normal-side TMJ impaired by disc perforated at different locations (MPa). A: discs, B: bilaminar regions, C: condyles

After the occurrence of perforation in the lateral band of the affected-side disc, there is an increase in MVMS in the normal-side disc and bilaminar region, reaching 5.0098 MPa and 0.076618 MPa, respectively. Perforation in the posterior band of the affected-side disc results in a significant increase in MVMS in the normal-side disc, reaching 5.405 MPa, and the MVMS in the normal-side bilaminar region also increases to 0.080442 MPa.

When perforation occurs at the junction between the posterior band and the bilaminar region, the MVMS in the normal-side disc and bilaminar region reach their peaks, with the disc reaching 5.5432 MPa and the bilaminar region reaching 0.081781 MPa. The impact of perforation occurring in the bilaminar region on the MVMS in the normal-side disc is not significant. When observing the influence of pathological changes in the affected-side disc on the stress distribution in the normal-side disc tissue, no significant changes in stress distribution are observed in the normal-side disc and bilaminar region.

Stress distribution on the condyles of normal side

The results of stress distribution on the discs of the affected side are shown in Fig. 5. C and Fig. 4. F. In the normal state of the disc on the unaffected side, the MVMS experienced by the normal-side condyle is 3.7358 MPa, with a uniform stress distribution and no significant stress concentration. After the occurrence of disc displacement, the MVMS in the affected condyle increases to 4.2059 MPa. When perforations occur in the anterior, middle, posterior, lateral, and bilaminar region of the affected-side disc, there are no significant changes in MVMS in the normal-side condyle. However, significant increases in stress are observed in the normal-side condyle when there are perforations in the posterior band and at the junction between the disc and the bilaminar region, reaching 4.502 MPa and 4.5959 MPa, respectively. When observing the influence of disc pathology on the stress distribution in the normal-side condyle, no significant changes in stress distribution are observed in the normal-side disc and bilaminar region.

The impact of different sizes of perforations of the disc on TMJ stressStress distribution on the affected TMJ

The results of stress distribution on the TMJ of the affected side are shown in Fig. 6. A and Fig. 7. A, B, C. As the disc undergoes displacement accompanied by an increasing perforation size, the MVMS in the affected-side disc and bilaminar region gradually increases. At the 1/2 perforation size, the stress in the disc and bilaminar region reaches its peak, measuring 16.854 MPa and 0.34661 MPa, respectively. The stress distribution area also decreases with the expansion of the perforation size, leading to significant stress concentration, particularly around the perforation site.

Fig. 6

Stress distribution of the affected-side TMJ (A) and normal-side TMJ (B) impaired by disc perforated with different apertures (MPa)

Fig. 7

Peak value of the stress on the TMJ affected by perforated disc with different apertures (MPa). A: affected-side discs; B: affected-side bilaminar regions; C: affected-side condyles; D: normal-side discs; E: normal-side bilaminar regions; F: normal-side condyles

However, the MVMS in the condyle does not increase proportionally with the perforation size. As the affected-side disc progresses from a normal state to anterior displacement and further to the 1/4 perforation stage, the MVMS in the condyle gradually increases. At the 1/4 perforation, the condyle reaches its peak MVMS, measuring 9.0282 MPa. However, as the perforation size expands to 1/3 and 1/2, the maximum stress in the condyle shows a continuous decrease. These findings indicate that as the perforation size increases, the MVMS in the affected-side disc and bilaminar region progressively rises, reaching a peak at the 1/2 perforation size. Meanwhile, the condyle’s maximum stress varies during disc displacement and perforation progression, peaking at the 1/4 perforation size and decreasing thereafter when the perforation size expands to 1/3 and 1/2.

Stress distribution on the normal TMJ

The results of stress distribution on the TMJ of the affected side are shown in Fig. 6. B and Fig. 7. D, E, F. On the normal side, the MVMS experienced by the articular disc, bilaminar region, and condyle all increase continuously with the expansion of the perforation size in the articular disc. The stress peaks are measured at 5.8317 MPa for the articular disc, 0.0861 MPa for the bilaminar region, and 4.7862 MPa for the condyle. However, the stress distribution in these structures does not show significant changes despite the increase in MVMS.