Poly-(L-lactic) acid membranes in palatal surgery in beagle dogs: clinical and histologic evaluation

This article reports on the histologic findings from a larger study that was designed to investigate whether the attachment of scar tissue to underlying bone, which is normally found after palatal surgery, can be prevented by using biodegradable poly-(L-lactic) acid membranes. Von Langenbeck's procedure was simulated in 12-week-old beagle dogs without clefts. In one group normal wound healing was allowed. In two groups, membranes were inserted immediately after surgery or 3 weeks thereafter. Sham and control groups were also included. Histologic evaluation was carried out at regular intervals. Reports have been published on other aspects, such as clinical wound healing, contraction and maxillary arch development in beagle dogs following this treatment. After direct implantation of membranes, wound healing was retarded. Disintegration of the membranes started soon after implantation and remaining particles were surrounded by a fibroblastic sheath and a fibrous capsule. At sites where membrane particles persisted, attachment of the scar tissue to the underlying bone by Sharpey's fibers was prevented.     

Biodegradation of non-porous films after submucoperiosteal implantation on the palate of Beagle dogs

The aim of this study is to investigate the in vivo behaviour of five different biodegradable films after submucoperiosteal implantation on the palate of Beagle dogs. Non-porous films of poly-(L-lactic) acid (=PLLA), high molecular weight poly-(L-lactic) acid (=HMW-PLLA), poly-(DL-lactic) acid (=PDLLA), poly(-caprolactone) (=PCL) and a copolymer of poly hydroxybutyrate 80%-hydroxyvalerate 20% (=PHB-co-HV 80/20) were implanted submucoperiostally on the palate of Beagle dogs. After 2, 4, 8 and 12 weeks in situ, the structure of the films and the tissue reactions were studied histologically. In terms of mechanical properties and tissue response, the PHB-co-HV film is the most suitable for use on dogs.     

Selective reduction of nitrobenzene to nitrosobenzene on oxidic catalysts

Pure unpromoted Mn₃O₄ appears to be a very suitable catalyst for the selective reduction of nitrobenzene to nitrosobenzene; the oxygen vacancies required to split off oxygen atoms can be created both by the phenyl group of nitrobenzene itself and by an additional reducing agent like e.g. methane.     

Mixed oxides as catalysts for the selective reduction of nitrobenzene

The catalytic behaviour of the PbO-Mn₃O₄ and the Bi₂O₃-MoO₃ systems was investigated in the selective reduction of nitrobenzene to nitrosobenzene. Lead compounds appeared to be good catalysts, and co-catalysts when used with Mn₃O₄. Different from oxidations by di-oxygen, Bi₃O₃ alone is a good catalyst and formation of mixed Bi-Mo-O compounds does not enhance the catalytic activity. It is suggested that the difference between these catalysts in the mentioned reaction is related to the way in which the oxygen vacancy is represented by the oxygen donor.     

Behavior of Eucalyptus Kraft Pulp Extractives Components across ECF Bleaching and Their Impact on Brightness Reversion

Abstract

This study investigated the chemical composition of the dichloromethane and acetone extracts of eucalypt pulp across D(EP)DP and AZDP bleaching sequences by gas chromatography-mass spectrometry (GC-MS). The bleaching stages led to the partial removal and to several oxidative transformations of fatty acids and sterols, the main lipophilic extractives found in the unbleached pulp. The pulp samples were bleached to 90–91% ISO by D(EP)DP and AZDP sequences and their brightness stability and chemical characteristics determined. The effect of aging on brightness was investigated. The AZDP bleaching sequence resulted in pulps of higher brightness stability. Furoic structures representing the main acid degradation products of HexA are suggested as the actual intermediates that cause yellowing by forming colored compounds. The AZDP process removed larger amounts of HexA across bleaching.     

Time-dependent mechanical behaviour of the periodontal ligament

The process of tooth displacement in response to orthodontic forces is thought to be induced by the stresses and strains in the periodontium. The mechanical force on the tooth is transmitted to the alveolar bone through a layer of soft connective tissue, the periodontal ligament. Stress and/or strain distribution in this layer must be derived from mathematical models, such as the finite element method, because it cannot be measured directly in a non-destructive way. The material behaviour of the constituent tissues is required as an input for such a model. The purpose of this study was to determine the time-dependent mechanical behaviour of the periodontal ligament due to orthodontic loading of a tooth. Therefore, in vivo experiments were performed on beagle dogs. The experimental configuration was simulated in a finite element model to estimate the poroelastic material properties for the periodontal ligament. The experiments showed a two-step response: an instantaneous displacement of 14.10 +/- 3.21 microns within 4 s and a more gradual (creep) displacement reaching a maximum of 60.00 +/- 9.92 microns after 5 h. This response fitted excellently in the finite element model when 21 per cent of the ligament volume was assigned a permeability of 1.0 x 10(-14) m4/N s, the remaining 97 per cent was assigned a permeability of 2.5 x 10(-17) m4/N s. A tissue elastic modulus of 0.015 +/- 0.001 MPa was estimated. Our results indicate that fluid compartments within the periodontal ligament play an important role in the transmission and damping of forces acting on teeth.     

The healing process of palatal tissues after palatal surgery with and without implantation of membranes: an experimental study in dogs

The aim of this study was to evaluate the wound-healing process clinically and histologically in growing beagle dogs after palatal repair according to von Langenbeck, with and without implantation of membranes of a copolymer of polyhydroxybutyrate 80%–hydroxyvalerate 20% (=PHB-co-HV 80/20). Von Langenbeck's repair was performed in 12 dogs (age 12 wk), while von Langenbeck's repair followed by implantation of PHV-co-HV membranes was carried out in 11 dogs (age 12 wk). Four dogs (age 12 wk) served as unoperated controls. Standardized intra-oral slides of the palate were taken and measurements of the wound surface areas were carried out. Histological sections were prepared at three different ages. The animals were studied until the age of 25 wk. It was found that wound closure after the von Langenbeck's procedure took about 3 wk, while the use of PHB-co-HV membranes after von Langenbeck's repair resulted in complete wound closure after approximately 7 wk after the membranes had sequestered. At the age of 25 wk, the histologic results after the von Langenbeck procedure showed that the entire scar tissue covering the former denuded bony areas was attached to the bone by means of Sharpey's fibres, while after implantation of the membranes only local scar tissue attachment by means of Sharpey's fibres was found. Further research is necessary to develop a membrane which allows wound closure without sequestration of it. © 1998 Chapman & Hall