Objective:To analyse the stress distribution of the tooth and inlay with the restoration of resin,porcelain,gold alloy,co-balt chromium materials respectively.Methods:3-D finite element models of mandibular first molar with meiso-occlusal (class II) cavity and different inlays were established.Von-mises stress distribution on the tooth and inlay with vertical load and lingual load at 45°were analyzed.Results:After restoration peak stress of high elastic module materials and dental inlays was higher than that of the low elastic module material inlays,however,the restorations of the different elastic module materials had the similar stress distribution trend.The stress under of lateral load(lingual at 45°)to the teeth inlays was significantly higher than that under vertical load.Peak stress concentration of tooth was on the bottom of the cavity near the pulp chamber dentin;inlay peak stress distribution is mainly in its corresponding to the gingival wall.In the tooth tissues stress level of the contact surface of inlay restoration,the strength was as the fol-lowing:Composite resin inlay >ceramics inlay >the gold alloy ceramics inlay >cobalt chromium alloy inlay.The stress level of the inlay of the four kinds of inlay restoration materials was just opponent with the tooth tissues.Conclusion:Gingival wall is the weakest part of meiso-occlusal(class II)cavity inlay restoration,while near the pulp chamber at the bottom of the cavity is the weakest part of the tooth.Among the 4 materials Under the same load condition,composite resin inlay restoration has minimal tooth stress and uniform stress distribution,and can reduce the posibility of odontoschism and microleakage.

ABSTRACT:Objective To analyze the stress changes of tooth tissues in the medial-occlusal (Class Ⅱ)cavity restored with different kinds of inlay materials by the three-dimensional (3-D)finite element.Methods The inlay restored 3-D finite element model of medial-occlusal (Class Ⅱ)cavity was established by CBCT scanning method and reverse engineering software Mimics,Geomagic Studio,Pro/E5.0 software,and finite element analysis software. The Von-mises stress and change tendency of tooth tissues and four different kinds of inlay materials were compared after taking vertical loading and tongue 45°to loading.Results There were different stress levels of tooth tissues among different inlays of medial-occlusal (MO)Class Ⅱ cavity.The stress level of the cobalt chromium alloy inlay was the largest,the stress level of the gold alloy inlay was lower,and the stress level of the composite inlay was the lowest.Dental tissues stress distribution was similar for the four different restorative materials,and focused on hole bottom of dentin near the pulp in dentin.Conclusion Compared with ceramics,gold alloy and cobalt chromium inlay restoration,restoration with composite resin inlay can reduce the organization stress of the remaining tooth in the medial-occlusal (Class Ⅱ)cavity type.

Objective:To compare the efficacy of double thread elastic locking intramedullary nail (ELIN) and threaded elastic intramedullary nail (TEIN) in the treatment of mid-shaft clavicular fracture.Methods:From August 2017 to September 2020, 33 patients with mid-shaft clavicular fractures were treated with ELIN (double threaded nail group), including 14 males and 19 females, age 52.09±16.32 years old; Robinson classification: 20 cases of type 2A2, 6 cases of type 2B1, and 7 cases of type 2B2. Thirty-two patients were selected as the control group with TEIN fixation (single threaded nail group) during the same period, including 13 males and 19 females; age 43.25±15.03 years old; Robinson classification: 19 cases of type 2A2 and 5 cases of type 2B1, 8 cases of 2B2 type. The operation time, intraoperative incision length, fracture healing time, internal fixation removal time, Constant-Murley shoulder joint score, disabilities of the arm, shoulder, and hand (DASH) score, fracture reduction and postoperative complications were compared between the two groups.Results:The patients in both groups were followed up after operation, the double-threaded screw group was followed up for 16-48 weeks (average, 23.7 weeks), and the single threaded nail group was followed up for 15-51 weeks (average, 22.9 weeks). The operation time of the double threaded nail group and the single threaded nail group were 19.45±6.74 min and 19.59±4.98 min, and the length of the incision was 1.70±0.79 cm and 1.73±0.84 cm. The fracture healing time were 12.12±1.29 weeks and 13.88±1.84 weeks. The internal fixation removal time was 13.09±1.31 weeks and 15.69±1.94 weeks. The Constant-Murley shoulder score was 93.18±3.78 points and 90.09±4.03 points, and the DASH scores were 1.49± 0.49 points and 3.85±1.13 points; There was no significant difference in operation time and incision length between the two groups ( t=0.01, 0.19; P>0.05), while fracture healing ( t=3.70, P<0.001), internal fixation removal time ( t=6.34, P<0.001), Constant-Murley shoulder score ( t=3.19, P<0.001), DASH score ( t=10.95, P<0.001) differences were statistically significant. The length of the clavicle on the healthy side was 16.38±1.09 cm in the double threaded nail group, and the length of the clavicle on the affected side after internal fixation removal was 16.33±1.12 cm. There was no obvious shortening deformity on the affected side, and there was no significant difference in the length of the clavicle between the two sides ( t=1.57, P=0.127). The clavicle lengths of the healthy side and the affected side after internal fixation removal in the single threaded nail group were 16.55±1.12 cm and 15.12±1.18 cm, and the difference was statistically significant ( t=8.02, P<0.001). The postoperative shortening values of the double-threaded screw group and the single-threaded screw group were 9.47±2.12 mm and 17.41±2.42 mm, and the difference was statistically significant ( t=14.07, P<0.001). Postoperatively, 5 cases of bursitis and 2 cases of skin irritation occurred in the double threaded nail group; While 6 cases of bursitis, 3 cases of skin irritation, 4 cases of shortening malunion, and 1 case of broken nail occurred in the single threaded nail group (fracture delayed union after replacement of internal fixation); the other patients did not experience screw retraction, wound infection, delayed fracture union or nonunion, neurovascular injury, and achieved osseous union. Conclusion:Both elastic intramedullary nails are effective surgical methods for the treatment of middle clavicle fractures, and the operation time is short and minimally invasive. However, compared with the TEIN, the fracture healing time of the double-threaded ELIN is shorter, the internal fixation removal time is earlier, the shoulder joint and upper limb function is better, and the shortening deformity is less likely to occur.