Hercules C. Karkazis

Dimensional stability of dentures processed in boilable acrylic resins: A comparative study

An investigation was conducted to evaluate and compare the dimensional stability of three fast boilable denture resins with a conventional and a high-impact denture resin processed with a long-curing cycle. Although the boilable denture resins have been introduced to the dental profession and offer merits such as faster processing, saving time for the dentist, patient, and technician, reduction of energy costs, and dramatic increase in denture laboratory production without adding personnel or purchasing new equipment, the relevant dental literature is sparse. The results of this investigation indicate that all five denture resins produced dentures that shrink. Also measurements between certain teeth showed shrinkages. Linear shrinkages of denture bases and teeth distances were less than 1%. Flange-to-flange and molar-to-molar changes were less than 0.5 mm and 0.2 mm respectively. Maxillary complete dentures processed in boilable resins presented less distortion in the midpalatal area across the posterior section than dentures processed in the conventional heat-cured resin. Although linear changes reported in this investigation were thought to be clinically insignificant, clinical studies should be conducted to establish correlation with laboratory findings.

Cephalometrically predicted occlusal plane: Implications in removable prosthodontics

Although the determination of the occlusal plane is crucial in clinical removable prosthodontics, none of the existing methods gives sufficient guidelines for that purpose. The aim of this investigation was to check the hypothesis that the angulation of the occlusal plane is generally related to the skeletal base of the maxillae. Statistical analysis revealed (1) no strong linear correlation (p greater than 0.05) between the following variables: (a) the length of Cooks plane to Cooks occlusal plane angle, (b) the length of the maxillary plane to the maxillary occlusal plane angle, and (c) the Po Na ANS angle to the occlusal Frankfort plane angle; (2) no parallelism between the occlusal and HIP plane with a mean angle of 4.57 degrees, SD 2.57 degrees, and range of 0 to 9.5 degrees; and (3) no correlation between the predicted and clinically determined occlusal planes (r0.267, t1.797, p greater than 0.05).

Changes in the mandibular rest position after removal of remaining teeth and insertion of complete dentures.

A 24-month study was conducted to determine changes in the mandibular rest position after removal of the remaining teeth and insertion of complete dentures. A total of 24 patients with at least 10 teeth acting as occlusal stops were included in this study. Serial lateral cephalometric radiographs were made for each patient on four occasions (1) before extraction (2) 7 to 10 days after the initial denture insertion (3) 12 months later, and (4) 24 months later. Two angular measurements and one linear measurement were made for each radiograph and compared. A statistically significant increase in the face rest height with a tendency for posterior mandibular rotation was recorded between stages 1 and 2. This initial posterior rotation was followed by a gradual forward and upward movement, which finally brought the mandibular rest position even below the preextraction levels. The findings confirm the concept of the variability of posture and suggest that the mandibular rest position is an unreliable means of reestablishing the vertical dimension of occlusion that existed before extraction of the natural teeth.

Variation in the masseteric silent period in older dentate humans and in denture wearers

The masseteric silent period was elicited by chin taps at 40% clenching in the masseter muscle of the preferred chewing side in 22 younger dentate individuals, in 22 older dentate individuals, in 22 older experienced denture wearers and in 7 older inexperienced denture wearers. One simple and three combined types of silent period (combination of early and late phases of depression) were recorded in all groups. An early silent period was always elicited, the only exception being in some inexperienced denture wearers. Both the age and the extent of rehabilitation with dentures in the trained denture wearers affected reflex latencies (p < 0.05), while the variation in duration was not significant (p > 0.05). The duration of the silent period was, however, affected by the type of silent period, thus by the measuring technique (p < 0.05). Increased variation was observed in the inexperienced denture wearers, who were in a period of adaptation.

Reproducibility of the human masseteric jaw-jerk reflex in association with the menstrual cycle

The jaw jerk was elicited by chin taps in the relaxed masseter muscle of the preferred chewing side in five young females. Recordings were made during three randomized sessions and under standardized conditions: two sessions between the seventh and the 15th day of the female menstrual cycle and the third within the last 5 days of the cycle. Both latency and duration of the reflex were generally reproducible over time. Individual between-session variation was occasionally present, with a general tendency for lower values in the end-cycle session, but this did not affect the overall results. Systematic subject variation, such as central excitatory-state variance of the timing of the experiments, and possibly some other uncontrolled technical error, may have contributed to the observed variation.

Random variation in the masseteric silent period after chin taps

Although the silent period duration has often been evaluated as a potential indicator of stomatognathic system dysfunction, there is still some uncertainty as to its normal biologic variation. This study investigated the subject variation in the silent period in a group of 22 young and healthy subjects under standardized conditions. Electromyographic recordings were obtained from the masseter muscle at 40% clenching after chin taps. Four different patterns of the silent period were recorded: one simple and three combined. Although the latencies of the early and late phases of depression were generally consistent, the results for duration were more variable and depended on the pattern of the silent period.

The effect of intercuspal clenching on the masseteric jaw-jerk reflex in humans.

Although several studies have been conducted regarding the jaw-jerk reflex and its various modifying parameters, the effect of intercuspal clenching still remains poorly understood. Evidence of both excitatory and inhibitory influences of periodontal receptors on jaw muscle activity has been reported. It is also suggested that a level of background activity in the stimulated muscle facilitates the reflex response. It was therefore the purpose of this study to investigate the effect of simultaneously activated periodontal receptors on the various parameters of the masseteric jaw-jerk reflex during moderate masseter muscle activation. Electromyographic recordings were obtained from the masseter muscle of the preferred chewing side at rest and at intercuspal clenching in 10 men, by use of a computerized recording and analysis system. In the clenching trials the level of muscular activity was set at 40% of the maximum value obtained through visual feedback. The results showed that at 40% clenching the occurrence of the reflex was reduced as compared with that obtained at rest. Moreover, when present during clenching, its latency and duration were shorter, whereas its amplitude was higher. It was suggested that the simultaneous activation of periodontal receptors may occasionally inhibit the masseteric monosynaptic excitation.