BACKGROUND: Tooth intrusion easily leads to root resorption. Previous studies regarding orthodontic treatment-caused tooth root resorption or retrospective clinical studies based on X-ray films have great errors in outcome evaluation because of intrusion force which cannot be precisely controlled. OBJECTIVE: This study established dog models of mini-implant anchorage for incisor intrusion to observe the histological changes of tooth root and periodontal tissue and to evaluate the feasibility and safety of mini-implant anchorage for incisor intrusion. METHODS: Nine dogs were assigned to one control group (n = 1) and four experimental groups per time to sacrifice (1, 2, 4 and 12 weeks; n = 2 dogs for each experimental group). No force was added to the control group. In the experimental groups, mini-implant as an anchorage was placed in the buccal alveoli between maxillary second and third incisors on each side. A traction force of 100 g was imposed to each side to intrude the maxillary first and second incisors on each side. At 1, 2, 3, and 4 weeks (traction force was imposed for 4 weeks and after withdrawal of extraction force, mini-implant was retained in place for 8 weeks), dogs were sacrificed. The first and second incisors together with gingival and alveolar bone were completely resected to prepare histological specimens. Following hematoxylin-eosin staining, histological changes of tooth root and periodontal tissue were observed. RESULTS AND CONCLUSION: Compared with the control group, in the 1-week group, histological changes were primarily at the root tip and alveolar ridge crest, alveolar bone and cementum were absorbed and peridental membrane presented glassy degeneration in local region; in the 2-week group, bone resorption degree and range were obviously enlarged, and bone resorption developed from root tip, root middle part to cervical part; in the 4-week group, bone resorption was still active and the glassy degeneration of peridental membrane disappeared; in the 12-week group, significant improvement in alveolar bone and cemental surface was observed, bone lacuna had deposition of newly formed bone, and peridental membrane was orderly arranged. These findings reveal that in the mini-implant anchorage for dog incisor intrusion, early histological changes primarily appear in the root tip and alveolar ridge crest, presenting as alveolar bone and cemental resorption and the glassy degeneration of the peridental membrane. Bone resorption extent and range expand with the persistence of traction force. After withdrawal of traction force, tooth root and periodontal tissue were gradually repaired

Objectives:To investigate the risk factors and short-term prognosis of early pulmonary hypertension (PH) in preterm infants.Methods:A retrospective case-control study was performed in preterm infants (gestational age <32 weeks) in the neonatal intensive care unit (NICU) of the Children′s Hospital, Zhejiang University School of Medicine from January 2012 to December 2019. Eighty preterm infants with a diagnosis of PH between 3 and 14 days (early PH group) were matched in gestational age and sex with the controls (1∶2) of the same period in NICU. Perinatal clinical records, complications, echocardiography and early outcomes were collected. Characteristics and outcomes were compared between the two groups with t-test, nonparametric test or Chi-square test. Multivariate Logistic regression was used to analyze the predictive factors of early PH. Results:The gestational age of the early PH group and the control group were both (27.9±1.4) weeks, and 52 (65.0%) and 104 (65.0%) were males in each group, respectively. Univariate analysis showed that birth weights were lower in the early PH group than those in the control group (1 030 (850, 1 200) vs. 1 110 (1 000, 1 278) g, Z=-3.27, P=0.001). The early PH group had higher rates of pregnancy-induced hypertension, prolonged rupture of membranes (PROM) >1 week, born by caesarean, small for gestational age (SGA), 1 and 5 min Apgar score ≤7 scores, neonatal respiratory distress syndrome (RDS) and hemodynamic significant patent ductus arteriosus (hsPDA) (12.5% (10/80) vs. 3.8% (6/160), 11.2% (9/80) vs. 3.8% (6/160), 48.8% (39/80) vs. 28.8% (46/160), 10.0% (8/80) vs. 1.9% (3/160), 70.8% (51/72) vs. 51.7% (74/143), 50.0% (36/72) vs. 20.3% (29/143), 88.8% (71/80) vs. 59.4% (95/160), 85.0% (68/80) vs. 22.5% (36/160), χ 2=6.56, 5.12, 3.31, 8.05, 7.17, 20.05, 21.58, 84.84, all P<0.05). Multivariate Logistic regression analysis showed that the independent predictive factors of early PH were PROM >1 week, SGA, 5 min Apgar score ≤7 scores, nenonatal RDS and hsPDA ( OR=10.40, 18.61, 4.47, 4.13, 20.10, 95% CI 1.93-56.12, 2.82-122.76, 1.91-10.46, 1.50-11.39, 8.28-48.80, all P<0.05),respectively. Infants with early PH had higher incidence of bronchopulmonary dysplasia (BPD), BPD associated PH, severe intraventricular hemorrhage (IVH), extrauterine growth retardation (EUGR), laser treatment for retinopathy of prematurity (ROP) and mortality than the controls (all P<0.05). The duration of invasive mechanical ventilation was also longer in the early PH group than that in the control group ( P<0.05). Conclusions:Risk of early PH will be increased in preterm infants with PROM >1 week, SGA, 5 min Apgar score ≤7 scores, and comorbidities of nenonatal RDS and hsPDA. Early PH is associated with increased mortality, BPD, BPD associated PH, severe IVH, EUGR and laser treatment for ROP.