Impact of the Veneering Technique and Framework Material on the Failure Loads of All-Ceramic Computer-Aided Design/Computer-Aided Manufacturing Fixed Partial Dentures.

OBJECTIVES: Zirconia (Y-TZP) ceramics are considered as posterior fixed partial denture (FPD) materials; however, their applications are limited due to chipping. The use of monolithic lithium disilicate (LiDi) glass ceramics in posterior FPDs can be advantageous. This in vitro study aims to compare the loads until failure of posterior Y-TZP-FPDs and LiDi-FPDs before and after aging.

Effects of supercritical fluid CO2 and 25 kGy gamma irradiation on the initial mechanical properties and histological appearance of tendon allograft.

Tendon allografts, when autograft options are limited or when obtaining an autograft is not aligned with the patients' best interest, play an important role in tendon and ligament reconstruction. To minimize the risk of infectious disease transmission tissue banks perform screening tests and the allografts cleaned are sterilized. The current study examines and compares the initial mechanical properties and histological appearance of supercritical CO2 (SCCO2)-treated and gamma-irradiated porcine extensor tendons. Thirty intact porcine forelimb extensor tendons randomized equally into three groups: control group, gamma-irradiation group, and SCCO2-treated group. Once treated, histological assessment and histomorphologic measurements were made on the histological sections obtained from each tendon while stiffness and ultimate failure loads were evaluated from tensile testing. Histological evaluation of gamma-irradiated tendons showed significant disruption to the hierarchical morphology of the fascicle bundles, which was not evident in SCCO2-treated specimens. Histomorphologic measurements showed a significant increase for measured dead space (void) between tendon fibrils of the gamma-irradiated group comparing to both control and SCCO2 treated groups (p < 0.01). There was a significant reduction in the ultimate failure load for tendons treated by gamma-irradiation compared to the control group (p < 0.05). No statistically significant difference was detected between control and SCCO2-treated tendons in the ultimate failure load. Stiffness values were not significantly different between three-study groups. This study suggests that while gamma-irradiation has a deleterious effect on mechanical properties of tendon tissue, SCCO2 does not alter the biomechanical properties and the histological structure of porcine extensor tendons.

Biomechanical comparison between triple Endobutton technique and modified Weaver Dunn procedure for anatomical reconstruction of coracoclavicular ligament / 医用生物力学

Objective To compare the biomechanical behavior of a triple Endobutton technique for anatomic reconstruction of coracoclavicular ligament and with a modified Weaver-Dunn procedure. Methods Twelve fresh frozen cadaveric shoulders were applied with 70 N in superior, anterior and posterior direction, respectively, to measure displacement of the acromioclavicular joint. The failure test with the load at the rate of 25 mm/min was conducted to record the failure load and failure mode. The specimens were then randomly assigned to 2 groups: the triple Endobutton technique group and the modified Weaver-Dunn procedure group for reconstruction and to conduct displacement test and failure test again. The stability and mechanical strength of acromioclavicular joints after reconstruction under different states were then compared. Results The triple Endobutton technique group had significantly less anterior ((8.72±1.41) mm vs (37.03±5.05) mm) and posterior ((8.03±3.68) mm vs (14.85±1.89) mm) displacement than that in the modified Weaver-Dunn procedure group after reconstruction (P<0.05), and the former had similar displacement ((7.81±2.22) mm anterior and (7.16±1.95) mm posterior) as compared to the intact state. There were no significant differences in superior displacement among the groups. The modified Weaver-Dunn procedure group had significantly smaller failure loads ((172±9) N) than that in the triple Endobutton technique group ((687±115) N) and the intact ligament group ((685±234) N) (P<0.05). Conclusions The triple Endobutton technique has less anterior and posterior displacement and its stability is more closely approximate to the intact ligament; meanwhile, it has similar strength as coracoclavicular ligaments, which can better restore the function of coracoclavicular ligaments.

Biomechanical study of compressive strength distribution on the whole spine endplates / 医用生物力学

Objective To study distributions of the compressive strength on the whole spine endplates by measuring the compressive strength at different locations of the whole spine endplates. Methods Indentation tests were performed at 49 locations in 225 bony endplates of intact human vertebrae (C3 S1) from 5 fresh male specimens to record the failure loads. Results (1) For the whole spine endplates, failure loads of the cervical and lumbar spine were found to be higher than those of the thoracic spine (P<0.01).The failure load was first decreased from C3 to C7 before increasing to T1, and then dropping through T7 and rising again from T8, reaching the maximum at L4, and dropping at L5 before increasing again at S1. (2) The failure load at inferior cervical endplates was significantly higher than that at superior endplates except at C5 and T1 (P＜0.05). (3) Within the intervertebral space, the cranial endplates had a higher yield stress than the caudal endplates except at C5/6, T12/L1 and L5/S1. (4) Failure loads were generally increased from the central to peripheral zones (P＜0.05). (5) For different angular points, failure load distributions were found among the endplates (P<0.01). (6) Distributions of the compressive strength on the endplates varied significantly within the whole spine（P<0.01）. It was found that at C3/4, the failure load at posterior was higher than that at anterior, but at C5/6, the failure load at posterior and anterior was balanced. At T1, the failure load was found to be higher at posterior again, until passing through T2 5, and at T6 L3, the failure load at anterior was higher than that at posterior, and balanced between the anterior and posterior again at L4. At L5 S1, the failure load at posterior was higher than that at anterior. Conclusions The strength distributions on the endplates varied significantly at different locations within the whole spine, which was closely correlated with the physiological curve of the spine. The failure load at inferior endplates was higher than that at superior endplates and it was increased from central to peripheral zones. Within the intervertebral space, the compressive strength at cranial endplates was higher than that at caudal endplates.