Perinatal factors contributing to intellectual impairment in a cohort of Japanese children with very low birth weight.

BACKGROUND: To determine whether prematurity, intrauterine growth restriction (IUGR), or neonatal stress affects intellectual impairment in children with very low birth weight (VLBW). METHODS: This national historical cohort study evaluated children with VLBW cared for in perinatal medical centers throughout Japan. Factors assessed included three latent variables (prematurity, IUGR, and stress during the neonatal period) and eight observed variables during perinatal period. The primary endpoint was intellectual or developmental quotient (IQ/DQ) at age ≥3 years. Structural equation model (SEM) was used to examine factors associated with IQ/DQ. RESULTS: The study included 248 VLBW children, who were of mean age 5.7±2.0 years and mean IQ/DQ of 85.5 at last encounter. SEM showed that stress during the neonatal period (ß=-0.37) contributed more to IQ/DQ than intrauterine malnutrition (ß=0.25) and prematurity (ß=0.15) and that the duration of mechanical ventilation was an important contributor to stress during the neonatal period. CONCLUSIONS: Neonatal stress was more harmful to future intellectual impairment of VLBW neonates, with IUGR contributing more than prematurity. Duration of mechanical ventilation was an important risk factor in neonatal stress. Neonatologists should minimize neonatal stress in VLBW neonates, and obstetricians should monitor fetal growth restriction to prevent intellectual impairment in later life.

Minimization of dental implant diameter and length according to bone quality determined by finite element analysis and optimized calculation.

PURPOSE: The purpose of this study was to investigate the influences of bone quality and implant size on the maximum equivalent elastic strain (MES) in peri-implant bone using finite element (FE) analysis, and to minimize implant size via optimized calculation based on MES. METHODS: Three-dimensional FE models consisting of a mandible and a titanium implant with a superstructure were constructed and applied a vertical load or an oblique load of 60N. We investigated the effects of four variables: the thickness of the cortical bone (C), Young's modulus of the trabecular bone (T), and the diameter (D) and length (L) of the implant. According to the variables determined using Latin hypercube sampling, 500 FE models were constructed and analyzed under each of the loads following the construction of response surfaces with the MES as a response value. D and L were minimized by optimized calculation with the MES limited to the physiological limit with reference to the mechanostat theory. RESULTS: The MES was significantly influenced by D more than L, and could be restricted to the physiological limit unless both C and T were small. Larger MES than physiological limit was observed around the bottom of implants. CONCLUSIONS: From the viewpoint of the mechanostat theory, we calculated minimum size of implants according to the bone quality. However, the results should be verified with more detailed FE models made using CT data, animal studies and clinical prognoses.

Effect of bite force in occlusal adjustment of dental implants on the distribution of occlusal pressure: comparison among three bite forces in occlusal adjustment.

BACKGROUND: The purpose of this study was to investigate the influence of occlusal forces (the contractile force of masticatory muscles) exerted during occlusal adjustment on the distribution of the forces among teeth, implants, and temporomandibular joints (TMJs) in intercuspal clenching in cases with bilateral missing molars and premolars by using finite element analysis. METHODS: A three-dimensional finite element model of the mandible with eight implants in the premolar and molar regions was constructed. Linearly elastic material properties were defined for all elements except the periodontal ligament, which was defined as nonlinearly elastic. The TMJs and antagonists were simplified and replaced with nonlinear springs. Antagonists were assumed to be natural teeth or implants and had two- or three-stage displaceability. We constructed finite element (FE) models in which occlusal adjustment with three kinds of occlusal force (40 N as a light bite, 200 N as a hard bite, and 400 N as a maximum biting force) was performed. The clearance by occlusal adjustment was decided beforehand with a trial-and-error method so that the occlusal forces were distributed similarly to the distribution of the natural dentition. Each model was evaluated under loads of 40, 100, 200, 400, and 800 N to determine the distribution of occlusal forces on the teeth and implants. RESULTS: The occlusal forces were concentrated on the most posterior implants while the load was larger, and the percentage of bearing force at the TMJ was small, and vice versa. CONCLUSIONS: Maximum biting force was better for occlusal adjustment to prevent overloading of the most posterior implant.