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Notes: Abstract. Several publications have reported an increased susceptibility for root caries after periodontal therapy. It has been suggested that newly exposed roots were less resistant to cariogenic species. This study examined the hypothesis that the increased susceptibility could also be related to an intra-oral microbial shift during the initial phase of the periodontal therapy from a perio-pathogenic to a more cariogenic flora. 10 patients with severe periodontitis were followed for 8 months after thorough scaling and root planing in combination with optimal plaque control. At baseline and after 4 and 8 months, samples were taken from the saliva, the tongue dorsum and the supragingival interdental spaces. These samples were cultured both aerobically and anaerobically in order to determine the total number of colony forming units (CFU) per sample as well as the number of CFU of Streptococcus mutans and Lactobacillus species. Oral hygiene parameters were recorded at the same visits. Finally, at baseline and at the 8 months follow-up, changes in caries activity and periodontal health were registered. Although the total number of aerobic and anaerobic CFU in samples from the tongue and the saliva remained nearly constant over the entire observation period (variations within 0.5 log), significant (p≤0.05) increases in the number of S. mutans could be detected, especially at month 8. The significant decrease in the total number of anaerobic CFU in samples from the teeth was not associated with a reduction in the number of S. mutans, so that also for this niche the relative proportion of the latter increased. The number of lactobacilli species for the different niches showed only negligible changes (within 0.5 log values), except for samples from the teeth for which a small (1 log), but statistically significant (p〈0.01), reduction could be detected. The periodontal conditions improved for all patients, but the caries activity could not be arrested. These findings seem to indicate that the increased caries susceptibility after periodontal therapy might partially be explained by a significant increase in the number of S. mutans due to ecological changes within the oral cavity. The clinical consequence of this observation would be to advocate a more strict caries preventive program during initial periodontal therapy.

Notes: Abstract. Tetracyclines are frequently used in the treatment of periodontitis; however, emergence of resistant bacterial strains has decreased the utility of these drugs. At present, there are a lot of data in the literature from which one can draw conclusions regarding the use of local drug delivery. This paper reviews the utility and different systems of local delivery of minocycline, a semisynthetic tetracycline, in the treatment of periodontitis.

Notes: The ultrastructure of sensory nerve endings in the human periodontal ligament from 43 extracted teeth was studied using serial sections. Three types of nerve endings were found: free nerve endings (FNE), Ruffmi-like endings and lamellated corpuscles. Free nerve endings stem from unmyelinated or from myelinated nerve fibers. The endings contain neurotubuli, neurofilaments and vesicles. Ruffini-like receptors were mostly found in the apical part of the periodontal ligament. In these Ruffmi-like receptors a particularly abundant concentration of mitochondria appears. In some cases desmosome-like junctions are present between neurite and ensheathing cell. Lamellated corpuscles were also found in the periodontal ligament. The lamellae are extremely endocytotic and are in close contact with each other.

Notes: The utility of a planimetric method for measuring in vivo plaque growth on teeth within 24 hours was tested. A reproducible photographic technique was developed. With this technique color slides were made after plaque disclosure with neutral red 0.5% and enlarged up to 25 times natural size for tracing on paper. The percentage of tooth surface covered by plaque was calculated with a planimeter. To obtain a stable and interpretable staining of the plaque three dye applications were applied. The interpretation of the slides was only reproducible when the slides were examined the same day and with the use of a tooth outline. Under these conditions an intra-examiner correlation coefficient of 0.999 was found. Furthermore, it was possible to detect significant differences in rate of plaque growth between two subjects within a time interval of four hours.

Notes: The histology of periodontal innervation in man and of the neural endings in the periodontal ligament in particular remains a controversial matter. Quantitative ultrastructural studies are needed and would help clarifying some functional characteristics of periodontal mechanoreceptors. Most of these characteristics are comparable to those of tegumental receptors elsewhere in the body. Some discrepancies exist however between the findings in perpheral afferent nerves and the findings in the intra-crainal centres.Concerning the functional significance of periodontal reeceptors, the jaw-opening reflex and the silent period in jaw muscle activity are related to each other, and their importance is questioned. Although much work has been accomplished on the silent period, the concurrent monosynaptic reflex has been mostly neglected and it has not been demonstrated whether periodontal receptors are the only origin of these reflexes.The perdominant role of periodontal receptors in detecting and discriminating forces acting on a tooth and in the control of the mandibular position when an occlusal contact is present has been proven.

Notes: The development and reproducibility of maximal clenching forces developed between two antagonistic teeth on a gnathodyamometer were examined. All the occlusal surface of the two teeth was used by adapting acrylic bite blocks on the dynamometer. It appeared that the maximal clenching force is a reproducible value. Itwas also noted that the developed force increases progressively when a maximal clenching effort is exerted successively every fiften seconds, even after a pause of five minutes. After about ten clenching efforts the developed force became stabilized. However, when the subject paused for ten minutes, the clenching force he developed immediately afterwards, returned to the level at the beginning of the experiment.

Notes: The tactile function of the human periodontal mechanoreceptors has mostly been studied by psychophysical approaches. It was concluded that periodontal mechanoreceptors play a major role in the tactile function of teeth. It must be noted however that the interocclusal tactile threshold is not solely determined by periodontal mechanoreceptors but also by pulpal, muscular or articular receptors. While temporomandibular joint receptors play a minor role, muscular receptors are important in the discriminatory ability for a mouth opening of 5 mm and more. To discriminate between the contribution of periodontal and other receptors in the oral tactile function, future studies should use appropriate psychophysical methodologies and well-defined stimulus parameters.

Notes: Determinations of interocclusal tactile threshold levels so far have involved neither appropriate psychophysical approaches nor an assessment of the mechanical and thermal properties of the foils used. Twenty subjects (12 females) aged 18 to 50 (mean age 35) were tested for their absolute threshold level (RL). Both the method of limits and the staircase method were applied to determine the active or passive RL. For the active RL assessment, foils of different thicknesses were placed between edge-to-edge opposed incisors during gentle biting. Inner ear receptors of the blindfolded subjects were blocked by broad band noise applied through earphones, because vibrations induced by occlusal contact and conducted through bone might be perceived by these receptors. The foils presented were aluminum (Al), tin (Sn), polyester (PE) and calibrated steel (St) (thickness ranging from 8 to 50 μm) which offer different physical and thermal properties. The range of RL of the group varied between 8 μm for aluminum to 46 μm for polyester for 50% correct assessments. Increasing the foil temperature from room temperature (20°C) to body temperature (35°C) significantly increased the RL for conducting materials (one-way blocked ANOVA). These results indicate that temperature exchange takes place while presenting conducting foils at 20°C (cold stimulus) interocclusally, which influences the RL by activating thermosensitive receptors. The passive RL determination with classical von Frey-hairs resulted in a mean axial RL of 3.0 g. Both psychophysical RL assessments (method of limits, staircase method) gave reproducible and similar results as ascertained by ANOVA. Furthermore, a positive correlation was established between active and passive RL (Pearson correlation test). It is concluded that the physical and thermal properties of the foils need careful consideration in future experiments on threshold determination. Although active RL determination may involve the activation of non-periodontal receptors, it remains a realistic parameter to monitor tactile function of teeth.

Notes: With local anaesthesia seven out of nine volunteers developed increased clenching forces during successive efforts with two antagonistic teeth. The magnitude of the increase could not be evaluated, as most subjects had to be prevented from clenching any harder, in order to avoid damage.When a dynamometer was adapted bilaterally to several premolar and molar teeth, greater forces were developed than with the dynamometer adapted to two antagonists. This could be a result of decreased periodontal and/or pulpal receptor stimulation. In the former case, maximum clenching value was reached immediately, and the force remained almost constant during following clenching efforts.Both experiments substantiate the hypothesis that periodontal and/or intradental receptors have a negative feed-back on the activity of jaw closing muscles.

Notes: The following comments are given on the guidelines suggested by Türker (1988) for studies on oral reflexes using the surface EMG of the masseter muscles in man, including the silent period.(i) Attention should not be confined to electrical stimulation since mechanoreceptors in the periodontium, especially in the periodontal ligament, can only be activated by mechanical stimulation of a tooth. Furthermore, different modes of stimulation and stimulation sites do not yield equivalent reflex complexes. Weak and transient mechanical stimulation of a tooth while clenching at a low level of 5 or 10% MVC is a selective model (89%) to study the influence of periodontal receptors.(ii) Statistical criteria should be applied on rectified and averaged EMG records to prevent any subjective bias in the measurements of reflex variables. Whether a period of increased EMG activity is due to clustering of action protentials of motor units firing of which was delayed by a preceding inhibition, or to a real excitatory influence, can be assessed by applying statistical criteria on averaged and subsequently rectified records.(iii) The clenching level should be less than 25% of MVC to avoid muscle fatigue, and to elicit pronounced reflexes with a weak and therefore more selective stimulus.(iv) The stimulus intensity should be much less than six times the threshold if selectivity for mechanoreceptors is desired. Furthermore, periods of increased activity in surface EMG resulting from a weak stimulus are probably due to real excitatory influences and not to clustering of motor unit action potentials after an inhibition.(v) Jaw separation and the use of a force transducer are not always advantageous. If mechanical stimulation is applied to a tooth, clenching in full habitual occlusion causes a complete suppression of the influence of muscle spindles. A shift in activity between the various elevator muscles, and hence a change in activity of the muscle studied, may occur during an experimental session if biting force is used as a feedback. Such a shift is not relevant if feedback is carried out on rectified and lowpass filtered (1.6 Hz) EMG of the muscle studied.