With the aim of establishing the role of interfacial free energy in pellicle formation in vivo, surface free energies of five polymers, dentine and enamel were determined after j, 2 and 48 hours exposure to the oral environment of beagle dogs. After exposure for j hour in the oral cavity of the dogs, the surface free energies of the substrata, originally ranging from 22 to 134 mJ-m" 2 . converged to values between 60 and 100 mJ-m -2 . Thermodynamically this is a very favourable situation, as the solid-liquid interfacial free energy during exposure is minimal for this range of substratum surface free energies. Changes in the adsorbed protein film most likely occurring during the later stages of the adsorption process, have not been observed from changes in surface free energy. It is therefore concluded that only the initial stages of protein adsorption and pellicle formation are interfacial free energy influenced.KEY WORDS: Acquired enamel pellicle, protein adsorption, interfacial free energy.

In a previous investigation, children with Down's syndrome (DS) showed an earlier, more rapid and more extensive gingival inflammation than normal healthy control children. These differences in gingival inflammation may be the result of aberrant morphology of the gingiva related to the genetic disorder in DS children. The aims of the present study were (i) to describe the structural composition of "normal" gingiva in DS compared to control children, (ii) to analyse the histological changes in the gingiva during plaque development and (iii) to investigate whether the clinical findings could be supported by morphological observations. The study was carried out in 8 DS and 8 matched control children. Their ages ranged from 5-10 years. Gingival normality was guaranteed by strict oral hygiene procedures. During a period of 21 days in which oral hygiene was abolished, gingival biopsies were taken from buccal sites of deciduous teeth following a predetermined schedule on days 0, 7, 14 and 21. Results on day 0 showed no morphological differences between the DS and control children regarding oral epithelium, junctional epithelium or connective tissue. During the experimental phase of the study, the amount of plaque accumulation in the DS children gave rise to a more extensive gingival inflammation than in the control children. The gingival inflammation in the DS group started earlier and included: (1) an acute inflammatory response, (2) an increase of the junctional epithelium area, (3) an increase of the infiltrated connective tissue area (ICT) and (4) a decrease in collagen fibre density of about 35-40% compared to day 0. The same phenomena were not seen until 7 days later in the control group. Conversely, the development of a perivascular lymphocyte infiltrate (LI) in the DS children was delayed compared to the control group. This may be caused by the impaired delayed-type hypersensitivity response in DS children. The development of 2 separate infiltrates (ICT and LI) in this age group and the different temporal development of ICT (day 7 for the DS and day 14 for the control group) and LI (day 14 for the DS and day 7 for the control group) does suggest different immunological mechanisms for both areas and both groups.

In a previous experimental gingivitis study, it was shown that in children with Down's syndrome (DS), gingival inflammation started earlier, was more extensive and developed faster, than in normal healthy control children. In both groups, the start of the process was accompanied by an acute inflammatory response and an increase of the infiltrated connective tissue area (ICT). The purpose of the present study was to investigate how these facts were reflected at a cytological level. The study was carried out in 8 DS and 8 matched control children. Their ages ranged from 5-10 years. A "normal" healthy gingiva was attained after strict oral hygiene procedures. During a period of 21 days in which oral hygiene was abolished, gingival biopsies were taken on days 0, 7, 14, and 21. In both groups, junctional epithelium (JE) and ICT contained low numbers of polymorphonuclear leucocytes (PMNs). The start of the inflammation (day 7 for the DS and day 14 for the control children) was marked by a significant positive correlation between the numbers of PMNs in the JE and the ICT, and a significant increase of the numbers of PMNs in ICT. In ICT, a concomitant decrease in collagen fibre density was observed. In the control group, the decrease correlated with the numbers of PMNs in ICT, which suggests that this collagen breakdown is caused by PMN products. After the initial decrease, the collagen fibre density remained fairly constant in this group throughout the study. In the DS group, there was a tendency to a further decrease in the ICT3 area, correlated with the numbers of PMNs in ICT.(ABSTRACT TRUNCATED AT 250 WORDS)

Calculus plays an important role in chronic inflammatory periodontal disease and tooth loss. Patients can suffer from calculus formation despite good oral hygiene. The strength of adhesion between calculus and the enamel surface, though not determinant for the formation of calculus itself, determines whether calculus remains on the teeth during eating and toothbrushing. In this study, the amount and the strength of adhesion of calcium-rich deposits formed in vivo on different materials are related to substrate surface free energies (sfe). In 4 beagle dogs, fenestrated crowns were made on the upper fourth premolars. Smooth facings of glass (sfe 120 mJ.m-2), polished bovine enamel (sfe 85 mJ.m-2), polymethylmethacrylate (PMMA sfe 56 mJ.m-2) and polytetafluorethylene (PTFE sfe 20 mJ.m-2) were inserted in the crowns for 1, 3, 7, 14 or 28 days. The amount of deposit was evaluated both gravimetrically and planimetrically using Alizarin Red S for staining. Adhesion of calcium-rich deposits was evaluated planimetrically by studying their removal in a brushing machine. Dry weight increased linearly with time (approximately 0.18 mg.cm-2 per day) and was slightly less on PTFE than on the other materials. After 1 to 3 days, staining already revealed a 100% coverage by calcium-rich deposits. The number of strokes required to reduce the planimetric scores by 63% was extremely small on PTFE and PMMA and related with substrate surface free energies. This study shows that a possible way to reduce calculus formation in vivo is to decrease the surface free energy of the enamel using appropriate surfactants in, e.g., toothpastes.

Artificial periodontal defects were evaluated clinically for 24 months in six beagle dogs. Defects were created bilaterally around the lower second, third and fourth premolars. The gingiva was separated from the teeth by intrasulcular incisions and copper bands were cemented around the teeth as far apically as possible. After 3 weeks the bands were replaced by cotton ligatures, which were kept in place deep subgingivally for 11 weeks. The dogs were placed on a soft diet, allowing plaque accumulation throughout the study. One week after removal of the ligatures, probing depths of around 4.5 mm were recorded. During the evaluation period of 24 months, plaque accumulation was abundant and subsequently the gingiva was heavily inflamed. However, a distinct healing tendency was evident clinically. Two years after removal of the ligatures, probing depth was reduced to approximately 3.5 mm and the attachment level as assessed clinically had changed in a coronal direction. Part of this recorded increase in periodontal attachment may have been the result of changes in composition and condition of the periodontal tissues resulting in differences in probing depths.