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Background: Following root planing and scaling many studies have implied an association between a loss of clinical attachment at sites with initially shallow pockets (1 to 3 mm) and gains in attachment level for deeper probing depths. However, these effects are also consistent with a statistical phenomenon referred to as regression towards the mean. This principle suggests that extreme values will moderate the next time they are recorded. The purpose of this report was to estimate the effect that regression towards the mean has on perceived changes in attachment level after root planing and scaling., Methods: During the initial examination, 2 different investigators conducted 2 full-mouth probings. Two quadrants were randomly selected to be root planed and scaled until the root surfaces were smooth by tactile touch of an explorer. The 2 remaining quadrants were not treated. At 4 to 6 weeks after treatment, another full mouth probing was done. An examiner who was blind to the quadrants that had been scaled measured attachment level and probing depth after therapy. This study design provided periodontal measurements before and after root planing and scaling, measurements before and after a period of 4 to 6 weeks of no therapy, and duplicate measurements at the beginning of the study., Results: Using the repeat examination when no true change could occur, shallow sites (< or =3 mm of probing depth) showed average negative differences between repeat attachment level measurements (-0.23 mm), which mimicked loss of periodontal attachment. Deep sites, (>6 mm) showed average positive values (0.40) mimicking gain in attachment level. These results suggest that regression towards the mean is a significant effect in this data set. Both shallow non-scaled and scaled sites had similar differences in repeat measures (-0.28 mm, -0.25 mm) which were also similar to and not statistically different from changes after therapy for both non-scaled (-0.21 mm) and scaled sites (-0.08 mm). Thus not only does this data set exhibit regression towards the mean, but it explains the majority of perceived loss of periodontal attachment after scaling at sites that have minimal probing depth., Conclusions: These results suggest that the majority of perceived loss of attachment due to scaling at sites of minimal probing depth that have been reported in many studies may be due a statistical phenomenon called regression towards the mean.

This report is an example of tumor metastasis to the temporomandibular joint and its effect on pain, restriction of jaw movement, and the subsequent inability of the patient to function normally. Neoplasm is not the usual etiology of myofascial pain dysfunctionsyndrome and the muscle sparm component of this patient's jaw dysfunction was emphasizedby the relief of symptoms from the use of symptomatic reversible type therapy (tranquilizer, muscle relaxant, and heat). There was an overlay of stress-tension factors in this case history that contributed to the muscle spasm symptoms of the patient. There canbe other etiological factors in jaw dysfunction associated with TMJ pathology such asdevelopmental anomalies, trauma, arthritis, and neoplasm, but as a group they comprise only about 5% of TMJ dysfunction problems (D.M. Laskin, personal communication).