M. M. Ash

Functional occlusal forces: An investigation by telemetry

In normal chewing the forces exerted on the occlusal surface seldom exceeded 10 to 15 pounds, as recorded by an eight-channel force transmitter in a removable fixed partial denture. Ninety-five percent of forces were less than 3.5 pounds for subject A, 2.0 pounds for subject B, and 10.0 pounds for subject C. The chewing frequency and the places of maximal force on the occlusal surface were relatively constant. The electromyographic chewing patterns could be considered normal in all circumstances. There was a remarkable statistically significant day-to-day variation in force values. The forces also changed for different kinds of food. The differences between maximum and minimum force values were highest in voluntary, nonfunctional movements.

Jaw muscle activity in complete denture wearers—A longitudinal electromyographic study

EMG study of subjects wearing immediate complete upper and lower dentures revealed marked alterations in activity of the jaw closing muscles during the biting actions recorded. This finding suggests that changes in jaw and occlusal relationships due to resorption of residual ridges and settling of the dentures also affects jaw muscle activity. The relations between EMG and morphologic findings will be analyzed further in a separate article.

“Myo-Monitor centric”: An evaluation

Abstract Ten patients had three “Myo-Monitor centric” records made at each of three appointments. Terminal hinge axis determination and interocclusal registration of centric relation were used to accurately mount maxillary and mandibular casts on a modified articulator. The characteristics of “Myo-Monitor centric” were investigated by: evaluation of the reproducibility of “Myo-Monitor centric” records; comparison of “Myo-Monitor centric” position to centric relation contact position and centric occlusion; comparison of the tooth contact on hinge closure from “Myo-Monitor centric” with centric relation contact; evaluation of the effect of the anteroposterior head position on the number and location of tooth contacts during “Myo-Monitor centric” mandibular closure; and a comparison of the anteroposterior relationships among “Myo-Monitor centric,” centric relation, and centric occlusion. Examination and appropriate statistical analysis of the data revealed several characteristics of “Myo-Monitor centric”: The axis of rotation determined by “Myo-Monitor centric” was always anterior and inferior to the patients terminal hinge axis; “Myo-Monitor centric” registrations within individuals were non-reproducible; with “Myo-Monitor centric” registrations, centric relation contacts on the mandible were anterior to both centric relation and centric occlusion contacts on the maxillae; variation of anteroposterior head position affected Myo-Monitor-produced mandibular closure; and eight of ten patients had “Myo-Monitor centric” contact anterior to their centric relation contact.

Scanning electron microscopy of mineralized cartilage in rat mandibular condyle

The pattern of mineralization was studied in the mandibular condyle of the young adult rat. Specimens were rendered anorganic in NaOCl and examined in a scanning electron microscope. A mineralized cartilage front was found to persist on the articular aspect of the condyle. The surface is characterized by closely approximating chondrocyte lacunae enclosed to different degrees within the mineralized front. The mineralized component itself is calcospheritic; larger calcospherites forming the inner concave wall and smaller calcospherites forming the outer convex wall. The calcospherites are comprised of irregular crystalline plates radiating from the center of the mass. The bony surface of the ramus immediately beneath the condyle is typified by Howships lacunae alternating with areas of forming bone indicating intense remodeling activity. The mandibular condyle has not been examined in this way before. The information is relevant to consideration of growth and development, functional adaptation, physiological aging, and pathological change.

Silent period in jaw elevator muscle activity during mastication

33. Belser, U. C., and Hannam, A. G.: Jaw elevator muscle activity logi, Ortofunktion. Copenhagen, 1974, <:h. V. Munksgaard, pp during controlled tooth clenching and unilateral chewing. J 173-2 18. PROSTHET DENT (Submitted for publication.) lZrp7nl reywfs lo: 34. Belser, L!. C., and Hannam, A. G.: The contribution of the deep DK. J. W. C. MACDONALD massewr muscle to functional and parafunctional jaw moveNo. 61 ESQUIRE BLDG. merits. Arch Oral Biol (Submitted for publication.) 10080 JASPER AVE. 35. Moller. E.: Tyggeapparatets naturlige funktionen. In KroghEDX~ONX)N, A~r.4. TS J lV9 Poulwn, W., and Carlscn, 0 , editors: Bidfunktioner, BettyfysioCAN\I)\

Occlusal stability following occlusal adjustment

Abstract An investigation of occlusal stability of teeth after occlusal adjustment was conducted. The eight patients who participated in this study presented occlusal prematurities and interferences (interceptive and deflective contacts) which were eliminated by selective grinding according to the principle of obtaining and maintaining occlusal stability. To measure changes in occlusal stability, reference points were scribed on the teeth; base-line, 45 day, and 90 day serial stone casts were obtained. Each cast had one point on each tooth involved in the occlusal adjustment (tooth point) and one or two different teeth not involved in the grinding procedure (reference points). Each cast was photographed from two camera positions. The stereopairs thus obtained were placed on the stage of a Mann comparator to determine X and Y coordinates. The Z coordinates were mathematically computed. Likewise, the measurements of the distances from reference points to tooth points were determined by means of analytical photogrammetry. The statistical analysis disclosed that the mean differences between the base-line and 45 day measurements and between the base-line and 90 day measurements were not statistically significant.

Ossification in adult rat mandibular coyndyle—SEM of chondroclasia

The morphology of the mineralized component at the osteochondral junction was studied in the mandibular condyle of 264-day-old rats. Specimens were rendered anorganic in NaOCl, cut open with a sculpel, and the resulting surfaces examined in a scanning electron microscope. The extent of the mineralized cartilage plate and its relationship to invading vascular channels were visualized. Areas of resorption of calcified cartilage were identified and compared to areas of bone resorption. A likely sequence of events was reconstructed from the exposed internal surfaces: from initial chondroclasia in individual lacunae to extensive resorption of the cartilage plate; and from initial deposition of bone over the resorbed calcified cartilage cores to the organization of osteocyte lacunae and bony trabecule. The mandibular condyle has not been examined in this way previously. Possible cellular mechanisms suggested by other studies to be operating at the osteogenic front are discussed in the light of the results.

Condylar cartilage: A scanning electron microscope study of anorganic mammalian condyles

The mandibular condyles of four mammalian species (sheep, cat, monkey, and human) were rendered anorganic in NaOCl and examined by SEM. A mineralized cartilage front was identified in all specimens on the basis of a comparable morphology of chondrocyte lacunae and a calcospheritic pattern of mineralization. Species-specific differences in the cartilage surfaces were found to exist. The role of this cartilage in condylar remodeling and pathology is discussed. Attention is drawn to the fact that mineralized cartilage was identified on the articular aspect of all adult mammalian anorganic condyles examined.