Lawrence Furstman

The effect of loss of occlusion upon the mandibular joint

Abstract An investigation was made to determine whether the removal of selected quadrants of molar teeth would create a morphologic change in the mandibular joint that could be considered a causative factor in the mandibular joint pain-dysfunction syndrome. Fifty-one white male rats were used in this study. Thirty-six rats were subjected to various surgical procedures when they were 2 months of age; one, two, or four quadrants of molar teeth were extracted. Rats were killed at intervals of 2, 4, and 6 months after the surgical procedures. Fifteen rats were used as littermate controls and were killed in groups of five at intervals of 4, 6, and 8 months for a comparative study of normal and experimental morphology. Each squamosomandibular articulation of each animal, both normal and experimental, was examined individually by means of x-ray as well as microscopic techniques. Following the removal of selected quadrants of molar teeth, the following changes were seen: 1. 1. The squamosal portion of the joint was considerably denser than normal and showed a large increase in thickness of fibrous connective tissue as well as large additional increments of osteoid bone on the articular surface. 2. 2. The articular disc increased in thickness, and disorientation of the fibers of the disc was seen. 3. 3. A thinning of the cartilaginous cap of the condyle was observed, as well as severe osteosclerotic changes in the condyle. Changes were the same in both mandibular joint areas, even though the operative procedures were unilateral. No differences between normal and experimental animals of the same age group could be found by x-ray study. All films were magnified four times for this purpose. Clinical implications are significant enough to warrant a reconsideration of some areas of orthodontic thinking.

Normal Age Changes in the Rat Mandibular Joint

SYNOPSIS IN INTERLINGUA ALTERATIONES NORMAL DE INVETULATION IN LE ARTICULATION MANDIBULAR DEL RATTO.—Esseva studiate le normal crescentia e morphologia del articulation mandibular del ratto. Le articulationes studiate includeva specimens ab 15 differente gruppos de etate ab 1 die ad 2 annos. Le alterationes causate per le processos normal del invetulation es describite pro le areas principal del articulation, i.e., le fossa del articulation, le disco articular, e le condylo mandibular. Marcate alterationes esseva observate in le osso del fossa articular e del condylo. Alterationes de character plus subtil esseva notate in le disco articular. Le consta tation le plus remarcabile esseva le constantia del spissitate del cartilagine condylar post le cinquantesime die del vita.

The early development of the human temporomandibular joint

Abstract 1. 1. The early development of the human temporomandibular joint was examined and studied by microscopic techniques. Eighty fetal specimens plus one 2 1 2 -month postterm infant were used in this study. 2. 2. The critical time area in the formation of the human temporomandibular joint is from the eighth to the tenth weeks of fetal life. During this 2 week period proliferation and histodifferentiation of the embryonic mesenchyme take place and the condyle of the mandible assumes its mature morphologic pattern. 3. 3. The critical time area for the formation of the articular disc is from the twelfth to the fourteenth weeks of fetal life. Small clefts appear and coalesce to form the inferior and superior compartments. The articular disc has assumed its mature morphologic shape by the fetal age of 14 weeks, when it consists of a thin central area which increases in thickness as the peripheral regions of the disc are reached. The articular disc is composed of fibrous connective tissue and exhibits a high degree of vascularity except in the thin central area. No evidence of cartilage was found. 4. 4. First evidence of the temporal bone is seen in the 8-week specimen. Formation of the entire glenoid fossa and the articular eminence can be followed easily in this series. Both the articular eminence and the glenoid fossa are well formed by the twenty-second week of fetal life. 5. 5. Meckels cartilage plays no part in the actual development of the temporomandibular joint. It is thought that its early function is to act as a framework or scaffolding for the developing mandible. 6. 6. The ramus of the mandible is formed of membrane bone. This grows only by surface apposition. The continued endochondral bone formation at the head of the mandibular condyle is the major contributing factor in the increase in height of the ramus of the mandible. 7. 7. The early attachment of the muscles of mastication is first noted in the 8-week fetus when the external pterygoid muscle is plainly demonstrated. Attachment of the internal pterygoid muscle is demonstrated at 13 weeks, and the masseter muscle is clearly evidenced at the fourteenth week. It is quite probable that the last two muscles were attached earlier, but no specific study was made to determine their attachment date.

Postnatal development of the mandible of the cat

Summary The growth of the mandible was studied by a histologie analysis of frontal and horizontal sections through the mandibles of sixteen kittens varying in postnatal age from 1 to 90 days. Meekels cartilage, which appeared as an inactive polyspheroid bar at the posterior and inferior third of the mandibular symphysis, completely disappeared by the fourteenth postnatal day and did not contribute to the development of the mandible in this area. A growth center at which the endochondral type of bone formation occurred was present in the symphysis of a 1-day-old kitten and continued to be active until the sixtieth day, at which time eruption of the deciduous canines into the oral cavity was complete. Upon cessation of the growth of this cartilage, it persisted at the midline in the adult cat as fibrocartilage. Calcified cartilage was observed in the primary trabeculae as far laterally as the deciduous first molar, which indicated that the development of the alveolus in this region may have been due to the growth of the symphyseal cartilage. A system of anastomosing veins, for which the term venous lakes has been suggested, occurred at the midline, separating the two heads of cartilage from one another, and also surrounded the remnants of Meckels cartilage. It has been postulated that the purpose of these venous lakes may have been to separate the two halves of the mandible, allowing the development of this anterior growth center. The increase of intercanine width for the deciduous canine in cats was brought about by the development of an endochondral type of bone formation at the mandibular symphysis. The cartilage in the mandibular symphysis not only served as a center of growth but, by its directional growth, determined the shape and form of the anterior portion of the mandible.

Postnatal development o f the cat palate

Abstract 1. 1. A histologic study of the palatal components was conducted in cats from 1 to 90 days of age. 2. 2. The hard palate of the cat consisted of three distinct bilateral growth areas—the premaxillary, maxillary, and palatine portions. 3. 3. Bone formation at the midpalatal suture of the premaxillary portion of the hard palate was limited to the intramembranous type of bone formation. No cartilage was observed at any time in the midpalatal suture of the premaxilla. 4. 4. Cartilage associated with the endochondral type of bone formation was observed at the midpalatal suture in the maxillary and palatine portions of the hard palate. This endochondral type of bone formation was active from the ages of 1 to 60 days. There were no remnants of cartilage in the suture at 90 days. 5. 5. Cartilage was observed on the maxillary surface of the premaxillomaxillary transverse suture and on both maxillary and palatine surfaces of the maxillopalatine transverse suture. There was no evidence of cartilage in the transverse sutures at 90 days. 6. 6. The posterior border of the hard palate consisted of two rounded heads of cartilage similar to the mandibular condyle. Bone growth of the endochondral type was markedly reduced by 60 days, and no evidence of any cartilaginous activity remained at 90 days. 7. 7. The endochondral type of bone growth in the palatal sutures and at the posterior border appears to be at least partially responsible for the dimensional changes produced during early postnatal palatal growth. 8. 8. The cessation of the endochondral type of bone growth appears to be related to completion of the eruption of the deciduous dentition.

Postnatal development of the mouse palate

Abstract 1. 1. The postnatal development of the palatal complex from birth to maturity was studied in the mouse. In addition, the midpalatal suture was examined histologically to determine whether or not endochondral bone formation took place in this area. Animals ranging in age from birth to maturity were prepared for nitrocellulose embedding in the usual manner. The area of study was limited to a symmetrical coronal section of tissue bounded anteroposteriorly by the mesial and distal surfaces of the first molar teeth. 2. 2. As the palate grew in width, there was a progressive proportional decrease in height of the palatal vault. The middle third of the palate assumed a more inferior position in relation to the lateral thirds. 3. 3. Endochondral bone formation was active in varying degrees in the midpalatal suture of the mouse from birth until the twentieth day. 4. 4. At birth there was a condensation of mesenchymal cells in the midline. Lateral to the midline the mesenchymal cells differentiated into chondroblasts. As the chondroblasts matured, they increased in size and PAS-positive droplets appeared in their cytoplasm. Surrounding the chondroblasts was an amorphous ground substance. The chondroblasts divided and gave rise to clusters of chondrocytes separated by a matrix. 5. 5. At 5 days the midline showed three zonal layers of cells—the resting zone, the proliferating zone, and, most laterally, the hypertrophic zone with larger chondrocytes and conspicuous glycogen storage prior to their degeneration. Degeneration of the chondrocytes was characterized by increased glycogen storage, intracellular edema, and matrix breakdown. 6. 6. Growth in width and thickness of the palate was most rapid between birth and 5 days and between the ages of 10 and 15 days. Growth in width and thickness of the palate was slowest between the fifth and the tenth days. 7. 7. By the fifteeth day a layer of bone was present at the calcifying zone, beginning the “sealing-off” process. 8. 8. By the twentieth day growth in width of the palate ceased. Chondrocytes within the subcapsular layers appeared inactive; they were uniform in size and exhibited little glycogen content. However, growth in thickness of the palate increased threefold from the twentieth day to the thirty-fifth day. 9. 9. At the thirty-fifth day the chondrocytes were almost devoid of any glycogen and appeared totally inactive. The midpalatal suture resembled the cartilage of the mandibular condyle. 10. 10. Hyaline cartilage was still present as a narrow band that extended along the entire height of the midpalatal suture in the adult mouse. 11. 11. The presence of cartilage in the midpalatal suture was shown not to be specific.