Uptake of 15N by macrophytes in subsurface-flow wetlands treating domestic wastewater.

Constructed subsurface-flow wetlands are becoming more common for on-site treatment of domestic wastewater to provide secondary quality effluent. Macrophytes are generally added to wetlands to increase treatment efficiency but their role in reducing N content is controversial. Our investigation utilized two subsurface-flow wetlands to determine the efficiency of different macrophytes in uptake of 15N labeled ammonium sulfate. Macrophytes in Wetland 1 recovered 35% of the added N in their shoots but only 5% of the added N was recovered in the shoots and roots in Wetland 2. A major difference for the two wetlands was N and hydraulic loadings. Wetland 1 received 7.5 Kg N ha(-1)d(-1) and Wetland 2 received 16.9 Kg N ha(-1)d(-1). Retention time for Wetland 1 based on pore volumes was 2.9 d and for Wetland 2 it was 1.2 d. The retardation factor for NH4+ was approximately 2.5 for both wetlands and the breakthrough curves indicated lack of plug flow. The importance of macrophytes in taking up NH4 appeared to dependent on N and hydraulic loadings.

The prevalence of overhanging dental restorations and their relationship to periodontal disease.

Overhanging dental restorations (ODR) are a major dental health problem. An ODR is defined as an extension of restorative material beyond the confines of a cavity preparation. They have been strongly implicated as an etiologic factor in the progression of periodontal disease and are alarmingly prevalent. In addition to promoting plaque accumulation, they change a nondestructive subgingival flora to a destructive one. There is good documentation that bleeding, gingivitis, and bone loss increase in tissues adjacent to ODR as compared to homologous teeth. Removal of ODR enhances the effectiveness of the hygienic phase of periodontal therapy. Many ODR, however, are not detected on radiographs and are evident only by use of an explorer directed subgingivally. For this reason and others, many are not removed. This literature review summarizes research concerning the prevalence, significance and removal of ODR.

Periodontal wound healing responses to varying oxygen concentrations and atmospheric pressures.

Oxygen effects on healing gingival wedge excisions were tested using Sprague-Dawley rats. 40 operated controls were maintained at normal pressure in room air. 3 experimental groups of 40 rats each were exposed for 90 min daily to one of the following: (1) 20.8% oxygen at 2.4 atmospheres pressure, (2) 100% oxygen at 1 atmosphere, or (3) 100% oxygen at 2.4 atmospheres. 5 animals in each group were sacrificed at the following times: 30, 54, 78 h and weeks 1, 2, 3, 6 and 12. Histometric analysis was performed using light microscopy. The connective tissue healing above a reference notch on the maxillary first molar mesial root was assessed. The controls failed to show healing comparable to experimental animals until the end of 2 weeks. Enhanced connective tissue healing above the notch was most significant (p less than or equal to 0.05) in the 2.4 atmospheres pressure groups at 3 and 6 weeks when compared to controls. However, by 12 weeks, no significant differences could be detected. New cementum formation was rare and occasional root resorption was observed. Early connective tissue adaptation does not imply eventual attachment as epithelial downgrowth progressively displaced the connective tissue adjacent to the root in both experimental and control groups of this study.

The long-term effectiveness of periodontal therapy in a clinical practice.

A retrospective study was conducted of 620 patients in a periodontal practice over the years 1960 to 1982. Various periodontal therapies were assessed by using careful office protocols, meticulous record-keeping and well-defined outcome criteria. Four treatment outcome categories were used: two representing satisfactory outcomes (referred to as "STABLE"), and two unsatisfactory outcomes ("UNSTABLE"). The percentages of patients in the STABLE categories following different therapies were: (1) nonsurgical treatment, 63.6%; (2) closed curettage, 73.1%; (3) open curettage, 95.0%; (4) modified Widman flap, 91.6%; (5) full flap and osseous surgery, 71.1%. The major conclusions were that the modified Widman flap and open curettage were more effective than flap and osseous surgery, and much more effective than closed curettage when it was employed as an alternative treatment (54.8% STABLE) to the osseous surgery (71.1% STABLE). Thus, moderate surgical therapies appear to be at least as effective as ostectomy procedures in the treatment of periodontal disease, while nonsurgical and closed curettage therapies appear to be less effective.

The relationship between periodontitis and the maxillary sinus.

This article presents a short review of the literature describing the relationship of periodontal disease and the maxillary sinus. This is followed by two case reports which demonstrate a close physical relationship between molar roots and the sinus and suggest that a sinusitis may develop from the extension of periodontal disease into the maxillary sinus. Further investigation of this hypothesis is necessary.

The pulpal response to topically applied citric acid.

Citric acid is currently being used to aid in the reattachment of periodontal tissues to tooth roots which have become separated as a result of periodontitis. The present study examines the effect of topically applied citric acid on the dental pulp. Citric acid, pH 1, was applied for 3 minutes on instrumented premolar teeth in six dogs. As a control, saline solution was applied on similarly instrumented premolars. The teeth were removed 1, 6, 24, 48, 72, and 144 hours after citric acid application. After histologic preparation, the pulps were examined for inflammatory cell infiltrates, odontoblast displacement into the dentinal tubules, hyperemic capillaries in the odontoblast layer, hemorrhage, abscess formation, irregular dentin, and the thickness of the dentin remaining beneath the treated area. There was no statistically significant response to the citric acid over the saline controls. Nor was the pulpal response, as examined above, correlated to the thickness of the remaining dentin. The results suggest that citric acid, pH 1, when applied to tooth roots during surgical reattachment therapy, does not adversely affect the pulp.

Gingival fenestration.

A pathologic entity, the gingival fenestration, has been described. The lesion is seen infrequently in clinical practice, probably due to the short time span of its existence and the lack of acute symptoms. It is possible that it occurs with greater frequency than generally realized. A hypothesis is presented as to the method of formation of the gingival fenestration and it is suggested that the area should be treated as gingival recession extending to the apical border of the fenestration.