Morris Povar

The dental polymer implant concept

lh e replacement of man’s wornout or depleted parts with human or animai tissues or synthetic materials has been in man’s mind and imagination for centurks. In the early 1900’s, Alexis Carrel1 transplanted every major organ in animals. His famous two-headed dog was proof that transplant failures were not the result of surgical or technical difficulties. The built-in immune mechanism, a specificity that permits the prevention oi certain diseases by vaccination, also acts to prevent the success of transplants, and immunologic rejection results. This is a fundamental biologic reaction and was adequately demonstrated by the outstanding research of Medawar’ on rabbit skin transplants. He demonstrated that there was an immunization of the animal with the first graft and subsequent accelerated rejection of the second graft. It wab now clear that homologous and heterologous transplants failed due to an immunologic response. Transplant failures result from the ability of the host to identif) another tissue as containing a foreign protein and to be able to reject this tissue through the development of specific antibodies. Lymphocytes are instrumental in this phenomenon, since they are responsible for the elaboration of antibody. To overcome this, scientists have tried to control the immune response bysuppressing the bone marrow by the use of radiation. globulins, immunosuppressivt drugs, and cortisone-type drugs. All these methods seriously endanger the life of the transplant recipient. placing him in a delicate balance between immunologic rejection and death from uncontrollable infection, since one of the body’s major defensive mechanisms a,%ainst pathogenic microorganisms has been removed.

Implants of acrylic teeth in human beings and experimental animals: Clinical and microscopic studies

A gnew and Fong,l who studied the histologic features of transplanted teeth and their supporting tissues, found that some of their transplants were successful and some were exfoliated or ankylosed and subsequently exfoliated. On the basis of experiences with implants of natural teeth, Flohr,6 Waerhaug and Zander,20 Iwaschenko13 and Tobon WhiteI explored plastic material as a possible substitute for natural teeth. Flohr, using the technique of Rottenberg, placed screwtype acrylic roots into surgically created alveolar sockets. Later, histologically normal connective tissue formed against the acrylic, and only minimal inflammatory infiltration occurred. Yet, Iwaschenko,13 in spite of careful splinting, found epithelial proliferation and subsequent exfoliation of acrylic teeth. Waerhaug and ZanderzO studied the reaction of the periodontal tissues to the implantation of acrylic roots into the alveoli of dogs. These acrylic roots were made of denture base material modeled from the extracted teeth. Indentations were made on the root to enhance retention; some of the roots were polished, whereas others were finished with a coarse Carborundum stone. The root implants were pounded into the alveolus with a hammer until they were firmly fixed; having no coronal portion, their surfaces were level with the surface of the gingiva. New bone formation occurred within 13 days, with no inflammation, and there was wellformed connective tissue. In all cases, however, epithelial sheets grew down along the implant, and all implants eventually fell out. These experiences prompted Waerhaug and Zander to conclude that the “lifetime of an implant is limited and

Neonatal hypoglycemia in the rhesus monkey: Effect on development and behavior☆

Abstract Neonatal hypoglycemia has been implicated as a cause of brain damage that may lead to cognitive, sensory, psychomotor, or behavioral deficits in children. Because nonhuman primates can serve as useful models of many aspects of human behavior, we have produced neonatal hypoglycemia in newborn rhesus monkeys to identify the specific nature of the deficits produced. Neonatal hypoglycemia was produced by the continuous subcutaneous delivery (begun in utero) of insulin for up to the first 4 hours after birth. A cognitive and behavioral testing program was begun under blind conditions when each animal reached 8 months of age. None of the measures of cognitive abilities or behavior distinguished experimental animals with 6.5 hours of hypoglycemia from controls. Ten hours of hypoglycemia resulted in motivational and adaptability problems that made it impossible for some animals to learn even the simplest tasks, but, when provided with additional attention and adequate motivation, these experimental animals performed as well as controls in tests designed to measure cognitive ability. We conclude that neonatal hypoglycemia of 10 hours duration results in adaptive difficulties in rhesus monkeys but, if special attention is devoted to these animals, there are no enduring cognitive or behavioral deficits.

Polymethacrylate-coated Vitallium pins as endosteal dental implants in papio and gelada baboons

Abstract 1. 1. A report of early clinical success with polymethacrylate-coated Vitallium pins inserted endosteally into edentulous areas of baboons in tripod or quadripod arrangements and united coronally with autopolymerizing polymethacrylate is submitted. Twelve nonanatomic endosteal implants have been placed into mandibular and maxillary areas for periods up to and over 6 months, with good clinical and x-ray success. A complementary histologic report will follow. 2. 2. A flask for molding polymers under pressure and heat has been devised and described. 3. 3. Vitallium pins have been designed to receive polymers. The results are pins that are strong, will not flake, and are resistant to abrasion. 4. 4. A technique for placing these implants has been described. 5. 5. Gross and microscopic study revealed successful adaptation of the tissues to the implants.

Measurement of eye orientation of monkeys during visual discrimination

This paper describes apparatus and procedures for measuring eye orientation in the rhesus monkey without restraining the head. The main components of the apparatus are (a) a helmet on which are mounted the discriminative stimuli and the optical and other devices for obtaining a corneal reflection, (bj a special restraining chair that allows the monkey to respond to pushbuttons in front of him, yet prevents him from reaching the equipment mounted on the helmet, and (c) systems for presenting stimuli, monitoring choice responses, and recording eye orientation, which are controlled by a LINC-8 computer. The initial findings on eye orientation during performance on both a hard and an easy brightness discrimination problem are also presented.

Eye movements of stumptailed monkeys during discrimination learning: VTE revisited

Eye movements of stumptailed monkeys were measured during learning of a pattern discrimination problem. Amount of scanning (shifts in visual fixation from one pattern to the other) increased once learning began and reached a maximum either at about the point that frequency of correct responses reached asymptote or just after that. These results, taken together with earlier findings on vicarious trial and error and operant observing behavior, suggest that this is the characteristic pattern of change in frequency of observing during visual discrimination learning. A change in information processing strategy is proposed as one explanation for these results. Duration of the last fixation on a discriminative stimulus during a trial showed similar, though not identical, changes with practice. The decrease in duration of the last fixation following learning contrasts with results of prior studies involving more complex tasks, and supports our conclusion that the duration of the last fixation is particularly sensitive to the cognitive processing requirements of the discriminative task.

The Dentition of Papio anubis

The dentition of Papio anubis was studied in 50 male and female animals; gross observation, study casts, radiographs, and histologic preparations were used. An overall general similarity to the dentition of human beings was observed in size, morphology, and occlusion. Notable differences in the baboon dentition were a more elongate arch form, prominent maxillary canine crowns, and second and third molar crowns of greater size than first molar crowns.

Behavioral consequences of neonatal hypoglycemia in the rhesus monkey: A preliminary report*

Three behavioral tests were conducted on each of two young rhesus monkeys, one of which (Animal 1-80) had 6–12 hr. of symptomatic neonatal hypoglycemia, and the other (Animal 315-80) not more than one hr. Animal 1-80 took considerably longer to adapt to the behavioral test apparatus than either Animal 315-80 or a group of 16 control animals. Animal 1-80 was also much slower than either 315-80 or the control animals at learning two complex visual discrimination tasks, the learning set, and delayed matching to sample tasks. The performance of animal 315-80 was indistinguishable from that of the control animals on all tests. The results suggest long-term effects of prolonged symptomatic neonatal hypoglycemia on aspects of emotional behavior and complex cognitive functions.

The clinical use of polymer-coated metal pins as endosteal implants

Abstract The polymer-coated metal pin, its fabrication, and use for treating patients have been described. It gives promise of being the most effective and safe type of implant that can be used for long-term fixed partial denture support.

Effects of goodness and other properties of patterns on discriminative performance of monkeys

Stumptailed monkeys were given a series of pattern discrimination problems of the type used in studies with humans to test Garner’s information-theoretic theory of figural goodness. Unlike humans’, the monkeys’ learning and response latency were not faster for problems involving good patterns (coming from small rotation-and-reflection equivalence sets) than for problems involving poor patterns (coming from large rotation-and-reflection equivalence sets). Like humans, the monkeys found problems involving patterns from the same equivalence set, regardless of the size of the set, to be much harder to learn than problems involving patterns from different sets. Learning was faster, the greater the number of unique elements distinguishing a pair of patterns. Effects of specific types of reflection and rotation were also analyzed. The results suggest that there are both similarities and differences in the processing of patterns by monkeys and humans, and that the processing can, at the same time, involve both whole patterns and elements or features of patterns.