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Studies have explored occlusal marking interpretation, repeatability and accuracy. But, when an occlusion detection product is interposed between teeth, direct tooth-tooth occlusal contact relationships are replaced by tooth-material-tooth structures. Thus, the marks cannot reflect the original contacts. This has been shown for single tooth pair contacts. The purpose of this laboratory study was to similarly examine full dentitions. A dentiform was set into Class I centric occlusion with the mandible supported by a load cell. The maxillary arch was guided by precision slides. As the weighted (~52 N) upper assembly was lowered onto and raised off the mandibular arch, the loads on the mandible were measured. With and without (control) occlusal marking material, the steps were as follows: (cleaning - control 1 - material 1) … (cleaning - control 6 - material 6). The six materials were as follows: Accufilm I and II, Rudischhauser Thick and Thin, Hanel Articulating Silk and T-Scan. Then, the six sets of (cleaning - control - material) measurements were repeated with the mandibular assembly shifted, in turn, by 0·1 mm in the Anterior, Posterior, Right and Left directions. The five (Centric and four 0·1 mm shifted) occlusal relationships produced grossly different tooth-tooth (control) load profiles. And, in general, these controls were affected, in different ways, by the marking products. Among the five conventional products, the Rudischhausers fared the worst and the electronic T-Scan was an extreme outlier. Thus, in general, popular occlusal detection products alter the occlusal contact forces, and therefore, their markings cannot characterise the actual occlusion.

SUMMARY The occlusal conditions of periodontitis patients were investigated by using a computerized monitoring device. Thirty-three mild to severe periodontitis patients were enrolled in the study and they were categorized into three groups by their periodontitis severity. Each subject answered a preliminary questionnaire, received routine dental examinations, and underwent MKG/EMG tests using the K6 Diagnostic System. Clinical manifestations of periodontitis were confirmed by the questionnaire and the routine clinical examinations. According to the MKG tests, the traces of maximum opening distance and vertical freeway space showed no significant statistical difference among the groups. However, the velocity of terminal tooth contact was significantly delayed in the severe periodontitis group. According to the EMG tests, there was no significant difference in the rest mode EMG activities, but the function mode EMG activities significantly weakened in the severe periodontitis group. These results showed that severe periodontitis patients had poor occlusal conditions that might have been triggered by the instability of centric occlusion due to attachment loss.

summary The aim was to compare normal overjet versus large overjet cases with clinically healthy temporomandibular joints (TMJ); to establish normative data regarding the difference between condylar positions in centric occlusion (CO) and maximum intercuspation (MI) and deflective CO contacts. Two study groups of normal overjet and large overjet cases consisted each of 33 subjects with no detectable clinical signs of temporomandibular disorder (TMD). CO-MI differences were recorded using the SAM® Mandibular Position Indicator. Deflective contacts were examined on models mounted in CO. There was a significant difference between groups in the vertical (P = 0·030) and transverse (P = 0·008) range of movement from CO to MI, but not in the antero-posterior direction. There were no differences in the location of deflective contacts. Results of this study showed that patients with increased overjet show some differences compared with normal overjet patients, even in the non-patients. Further research on TMD patients is needed to find out about the role these features play in the aetiology and treatment of temporomandibular disorder (TMD). This study indicates that the clinician should be paying special attention to the TMJ status of patients with a large overjet.

Electromyographic activity of anterior temporal and masseter muscles was measured in 92 young healthy men and women with sound dentitions during rest position, contact in centric occlusion and clench. Male and female mean potentials were similar except in clench, where males had higher electromyographic levels. Mean pooled electromyographic potentials were 1.9 microV (TA) and 1.4 microV (MM) during rest position, 6.5 microV (TA) and 2.8 microV (MM) during contact in centric occlusion. Mean maximum voluntary clench potentials were 181.9 microV (TA) and 216.2 microV (MM) in men, 161.7 microV (TA) and 156.8 microV (MM) in women. Examined muscles were more asymmetric at low electromyographic activity (rest and centric occlusion) with the temporal muscle less asymmetrical than the masseter. In females temporal muscle activity tended to dominate at every contraction level, while in males masseter activity was stronger in clench, and temporal activity in centric occlusion and in rest position.

Analyses of the relationship between centric relation and centric occlusion were performed using the Mandibular Kinesiograph to show the abnormality of mandibular positions of the TMJ dysfunction patients. The distance between centric relation and centric occlusion in antero-posterior, left, and linear direction showed significant differences between the normal subjects and the TMJ dysfunction patients. In the TMJ dysfunction patients, the number of the subjects who showed larger deviation between centric relation and centric occlusion increased remarkably when compared with normal subjects. It is suggested that the slide between centric relation and centric occlusion can be one of the causes of the TMJ dysfunction.

An overview is presented of the mandibular reference positions of centric occlusion, centric relation and centric relation occlusion, and the position of rest. Clinical applications of the different positions are discussed on the basis of the physiology of the mandibular locomotor system.

Young adults (Md 24) and Adults (Md 41) were examined with respect to the distribution of occlusal contacts in molars, premolars and anterior teeth when exerting light and hard pressure respectively in the habitual intercuspal position. There was no difference between the right and left side and the number of contacts per tooth was low. In all groups of teeth there was a smaller number of contacts at light pressure. The lower number of contacts at light pressure in Adults when comparing with Young adults was related only to the anterior teeth. The increase of the number of contacts at hard pressure was greater for the anterior teeth than for the molars. In cases where there was a greater number of contacts present on one side, the distribution did not alter significantly when changing from light to hard pressure. Neither did the articulator-adjusted intercuspal position differ significantly in this respect from the clinically recorded intercuspal position at hard pressure. A further result was that about 50% of the individuals had 60% or more contacts on one side at light pressure. These findings stress the importance of meticulous care when performing occlusal adjustment, as the number of contacts per tooth is low and indicates the need for observing the difference between light and hard pressure.