Production of a nasoantral window with an Ar+-laser.

In vitro experiments on perforating and cutting 14 human nasoantral walls using an argon laser are described. The drilling velocity is proportional to the power density up to 100 W/mm2. The cutting velocity is measured using focussed spots of 40 micrometer diameter and powers from 5 to 40 W. Histological studies were performed at the edges of the lesion. The experiments show that the technical problem for producing a window in the nasoantral wall using a laser can be solved.     

Relationship between dietary habits and caries increment assessed over two years in 405 English adolescent school children

The study was conducted in seven schools on children initially aged 11.5 years. They recorded their diet on five occasions, each of three days, and received an annual dental examination, including radiography. Caries increments were low, mostly (58 per cent) in fissure surfaces. Correlations between caries increment and dietary factors were low due to the low caries increments observed and the large error associated with dietary data where analyses attempt to discriminate between individuals. The highest correlation was between caries increment and weight of daily intake of sugars (+ 0.143, p < 0.01). Multivariate analyses revealed that this relationship could not be explained by differences in sex, social class, tooth-brushing habits or level of plaque as measured by gingival inflammation. Weight of sugar intake appeared to be more strongly correlated to caries than frequency of intake; concentration of sugars in foods was positively related, and sugars in snacks were more strongly related to caries than total dietary sugars. The 31 children who consumed most sugar (> 163 g/day) developed 5.0 DMFS during the 2 years, 0.9 DMFS per year more than the 31 children (3.2 DMFS during 2 years) who had the lowest sugar intake (< 78 g/day).     

Maxillary dental arch growth in different types of cleft

A total of 45 subjects, 15 complete unilateral cleft lip and palate (UCLP), 15 complete bilateral cleft lip and palate (BCLP), and 15 cleft palate only (CPO) were studied. Measurements of alveolar points on maxillofacial models were taken of each subject at 5 months, 19 months and 4 years of age. The results revealed different types of growth retardation among the cleft groups. A comparison with 10 controls at 4 years of age showed that the dimensions of the three cleft groups were smaller than the controls, especially at the anterior region of the maxilla. These findings suggest that the relation of the nasal septum to the palatal processes may play an important role in the underdevelopment of the maxilla in the cleft lip and palate patients.     

Interface effects on mechanical properties of particle-reinforced composites.

OBJECTIVES: Effective bonding between the filler and matrix components typically improves the mechanical properties of polymer composites containing inorganic fillers. The aim of this study was to test the hypothesis that composite flexural modulus, flexure strength, and toughness are directly proportional to filler-matrix interfacial shear strength. METHODS: The resin matrix component of the experimental composite consisted of a 60:40 blend of BisGMA:TEGDMA. Two levels of photoinitiator components were used: 0.15, and 0.5%. Raman spectroscopy was used to determine degree of cure, and thermogravimetry (TGA) was used to quantify the degree of silane, rubber, or polymer attachment to silica and glass particles. Filler-matrix interfacial shear strengths were measured using a microbond test. Composites containing glass particles with various surface treatments were prepared and the modulus, flexure strength, and fracture toughness of these materials obtained using standard methods. Mechanical properties were measured on dry and soaked specimens. RESULTS: The interfacial strength was greatest for the 5% MPS treated silica, and it increased for polymers prepared with 0.5% initiator compared with 0.15% initiator concentrations. For the mechanical properties measured, the authors found that: (1) the flexural modulus was independent of the type of filler surface treatment, though flexural strength and toughness were highest for the silanated glass; (2) rubber at the interface, whether bonded to the filler and matrix or not, did not improve toughness; (3) less grafting of resin to silanated filler particles was observed when the initiator concentration decreased. SIGNIFICANCE: These findings suggest that increasing the strength of the bond between filler and matrix will not result in improvements in the mechanical properties of particulate-reinforced composites in contrast to fiber-reinforced composites. Also, contraction stresses in the 0.5 vs 0.15% initiator concentration composites may be responsible for increases in interfacial shear strengths, moduli, and flexural strengths.