OBJECTIVETo study the effect of bleaching on the mechanical properties of human dentin.

METHODSThe finite element method (FEM) based the cohesive zone model had been employed to study the fracture resistance of human dentin. There types of dentin were considered, i.e. original dentin, dentin after direct-bleaching and indirect-bleaching.

RESULTSThe bleaching treatments had large impact on the crack growth resistance of human dentin. The initiation toughness (1.48 MPa x square root of m), growth toughness (3.90 MPa x square root of m x mm(-1)) and plateau toughness (3.25 MPa x square root of m) of human dentin were reduced to 1.29 MPa x square root of m, 3.45 MPa x square root of m x mm(-1) and 2.71 MPa x square root of m respectively after indirect-bleaching. The worst case was the direct-bleaching which causes significant reductions in the growth toughness (0.14 MPa x square root of m x mm(-1)) and plateau toughness (1.63 MPa x square root of m) respectively, while the initiation toughness remained the same as that after indirect-bleaching.

CONCLUSIONThe cohesive zone modeling is an effective tool in characterizing the fracture behavior of human dentin. Bleaching treatments reduce the crack growth resistance of human dentin and increase the risk of fracture of teeth.

Dentin ; Humans ; Tooth Root

Objective:To explore the efficacy and safety of transvaginal anterior pelvic floor reconstruction with mesh in treatment of patients with cystocele and lower urinary tract symptoms.Methods:A retrospective analysis of 32 patients who underwent transvaginal anterior pelvic reconstruction with mesh from June 2015 to February 2019 was performed. The age of the patients was 57-86 years old, with an average of (67.8±7.6) years; body mass index(BMI) (22.6±3.0) kg/m 2; mean duration of disease (2.9±2.3) years; delivery 1-7 times, mean(3.0±1.5) times. All patients underwent transvaginal anterior pelvic reconstruction. The anterior wall of the vagina was incised, and the space between the pelvic floor and the bladder was bluntly separated. The mesh was placed under the guidance of the puncture needle after locating marks of body surface. Patients underwent the American Urological Association Symptom Scoring (AUASS) with (14.2±3.5) points, the residual urine (71.3±53.0) ml and the maximum urine flow rate (16.9 ± 3.8) ml/s were measured preoperative. The Pelvic Organ Prolapse Distress Inventory(POPDI-6), Urogenital Distress Inventory(UDI-6) and Pelvic Floor Impact Questionnaire(PFIQ-7) were recorded as the value of (48.0±7.3) points, (41.7 ± 8.2) points and (62.5 ± 16.4) points, respectively. Thirty-two patients were divided into 2 groups as the group of urinary storage symptom (22 patients) and the group of voiding symptom (10 patients) according to the preoperative lower urinary tract symptoms. The operative time, intraoperative bleeding volume and average hospital stay were recorded. The patients were followed up with AUASS, maximum urine flow rate, residual urine, POPDI-6, UDI-6, PFIQ-7 and complications during and after operations. Results:All the operations of 32 cases were successfull. The average operation time was (61.1±18.6) min, the average intraoperative blood loss was (41.5±12.3)ml, and the average hospital day was (9.1±1.8)d. There were no major organ injuries such as bladder, ureter, iliac vessels and rectum. 27 patients were followed up for 3 to 36 months, with an average of (24.7±10.8) months. There significant improvement of LUTS. At the last follow-up, the AUASS storage phase score (3.4±1.9) points in the urinary storage symptom group(19 patients) and the AUASS urinating phase score (3.9±1.7) points in the voiding symptom group(8 patients) were compared with the preoperative AUASS scores (11.6±1.9) points and (13.9±1.2) points which were significantly reduced. By the last follow up of all the 27 patients, residual urine (23.4±11.0)ml, POPDI-6(3.1±5.4) points, UDI-6 (3.2±5.1) points and PFIQ-7 (12.4±1.7) points were significantly lower than preoperative data. The maximum urinary flow rate(22.4±4.1)ml/s, was significantly higher than that before the operation. All the differences were statistically significant ( P<0.05). All patients had no recurrence of cystocele. One patient had anterior vaginal wall mesh exposure 3 months after surgery. After removing excess mesh in the outpatient clinic, she was cured by smearing with estrogen ointment. One patient experienced frequent urination and urgency who was cured by oral tolterodine tartrate. One patient with de novo mild SUI during the 1-year follow-up. The symptoms were improved in the outpatient clinic after pelvic floor muscle exercise. At 2-year follow-up, one patient was observed de novo mild posterior wall prolapse with no clinical manifestations and no treatment was carried out. Conclusions:Transvaginal anterior pelvic reconstruction with mesh could be effective in treating cystocele with lower urinary tract symptoms with less surgical trauma, fewer complications and lower recurrence rate. It could effectively improve lower urinary tract symptoms such as frequent urination, urgency and difficulty urinating.However, safety issues such as the incidence of long-term de novo SUI and mesh exposure still require further long-term follow-up.