Search

As is shown by Figs. 1 to 4, those second premolars in which calcification was retarded at the initial examination (63 to 74 postnatal months) kept up the same trend in subsequent examination and their root formations were markedly less than normal, the tendency being more pronounced with boys. With boys, these teeth were found to have attained to relatively poor roots even at the final stage of our study (171 to 182 postnatal months). Therefore, it may be reasonably assumed that the same trend would be more or less carried into the subsequent stage of development even though we lack concrete data to substantiate the assumption. Generally speaking, the chronological assessment of the development of individual teeth should be compre-hensively made by taking into consideration such factors as the physical stature, weight [8], girdle of chest, bone age [9, 10, 11], sex maturity [12], as well as local factors including pathologic lesions of the root of precursor teeth [13, 14, 15] and effect of dental extraction [16]. Concerning the amount of root formation and eruption of teeth, GRoN [17] maintains that the degree of root formation has closer bearings on the eruption of teeth than postnatal or bone age and when a root has been formed by 3/4, a tooth erupts clinically. According to HAVVIKKO [18], the bone eruption is distinguished from the clinical eruption of teeth and though admitting certain variations among teeth, a root has been formed by 1/2 at bone eruption and 3/4 at clinical eruption. The authors hold the view [1] that the average root at the period of normal replacement process is about 1/2 of what will be at perfection and roughly corresponds to the long diameter of crown. Even if normal calcification is retarded, the amount of root formation at bone eruption is more or less normal as long as the precursor suffers from no pathologic lesion of some kind. In other words, even with successors in which retarded calcification is observed the bone eruption will take place when the amount of root formed comes to correspond to the length of crown. This is equally true of the mandible and maxilla.The mean period of bone eruption of calcification-retarded premolars is as late as 19 months in boys and 6 months in girls. This discrepancy is more pronounced in the mandible than in the maxilla..Hitherto, the growth pattern of human teeth by MASSLER and SCHOUR [4] has been accepted as standard. According to this growth pattern, the crown of first premolar begins its calcification in 1 1/2 to 2 years reaching the perfection in 5 to 6 years, while that of second premolar begins in 2 to 2 1/2 years and reaches the perfection in 6 to 7 years. Therefore, both the beginning and perfection of first premolar is sooner by one year.In our present study, however, not a few of the samples in the initial examination (5 yr. 3 mos. to 6 yr. 2 mos.) were observed to reveal mere traces of calcification of their roots. On the other hand, no retarded calcification of first premolars to such a great degree was noted. In addition, a large measure of variation was observed relative to the degree of calcification of upper and lower second premolars. It follows then that the above standard data do not necessarily represent reliable information in clinical environment. The study material of MASSLER and SCHOUR is not exactly known and they have drawn on the previous data by LOGAN and KRONFELD [19]. The latter based their findings on the corpses of children and, for thisreason, they cannot be said to be consecutive or vertical in any sense. SATO and others [20, 21] pointed out that it was not proper to cite these data as if standard.On the other hand, the vertical study by GARN, LEWIS and POLACHECK [6] established the existence of large individual variations in the eruption of mandibular premolars and molars, and also pointed lack of recognition of this fact at large. Other investigators including FANNING [15], HAVVIKKO [18], KANEDA [22]

Increasing attention has been given to human monkeypox since the achievement of global smallpox eradication. Monkeypox, which was first described in Central Africa in 1970, resembles smallpox clinically but differs from it epidemiologically. Forty-seven cases of human monkeypox have occurred since 1970 in 5 Central and West African countries; 38 of these cases have been reported from Zaire. The evolution of the illness and the sequelae of monkeypox and smallpox are the same; monkeypox has a case-fatality rate of about 17%. Children below 10 years of age comprise 83% of the cases. All cases have occurred in tropical rainforest areas and clustering of cases has been observed in certain zones within countries and within families. Person-to-person spread may have occurred in 4 cases; the secondary attack rate among susceptible, very close family members was 7.5% (3 cases/40 contacts) and among all susceptible contacts was 3.3% (4 cases/123 contacts)-much lower than the 25-40% secondary attack rate that occurs with smallpox. Although the low transmission rate and the low frequency of disease indicate that monkeypox is not a public health problem, more data are needed.Whilst many animals near human monkeypox cases have been demonstrated to have orthopoxvirus antibodies, the natural reservoir(s) and the vector(s) of monkeypox virus are unknown. Studies are in progress to identify the natural cycle of monkeypox virus and to define better the clinical and epidemiological features of this disease.

Prospects for the eradication of smallpox are now highly encouraging. With the cessation of man-to-man transmission, the question of possible animal reservoirs of smallpox becomes increasingly important. During the period 1970-1975, 20 cases of a smallpox-like disease were detected in smallpox-free areas of tropical rain forest in West and Central Africa. Epidemiological and virological investigations revealed that the disease was caused by an animal poxvirus termed monkeypox virus, a member of the orthopox virus group. The disease spread with difficulty even among susceptible close contacts and does not appear to be sufficiently transmissible to permit continuing infection to become established in man. During the investigations, four orthopox viruses termed whitepox viruses were isolated from rodents and monkeys. The isolates were not distinguishable from variola virus with currently available laboratory techniques, but there is no evidence so far that viruses of this group have infected man. Although there is now substantial and accumulating evidence that there is no animal reservoir for smallpox, continued surveillance and studies in West and Central Africa are warranted.

In 1980, the World Health Assembly declared the global eradication of smallpox and recommended the universal discontinuation of smallpox vaccination; nevertheless, it recommended that surveillance and research on orthopoxvirus infections should continue. By early 1982, all except 8 countries in the world had stopped routine vaccination programmes and all except 1 no longer required an international certificate of smallpox vaccination for travellers. Since 1978, as a result of continuing active surveillance, 176 smallpox rumours have been investigated in 60 countries. Two of these concerned the two laboratory-associated cases that occurred in the United Kingdom in 1978; all the others were false alarms. Special surveillance programmes for human monkeypox have been developed in West and Central Africa. The number of laboratories retaining variola virus stocks has been reduced to four. Investigations to determine the identity and origin of the six known isolates of "whitepox" virus have continued. Research on mapping of variola DNA and on monoclonal antibodies against certain orthopoxvirus antigens is continuing. All these measures are aimed at ensuring that the achievement of smallpox eradication is permanent.

In considering global eradication of smallpox the absence of an animal reservoir is important. Present knowledge of experimental infection of non-human primates with variola virus and of a related virus infection in monkeys, termed monkeypox, is examined.From the literature review and the results of a survey of captive monkeys in 26 major biological institutions it is concluded that outbreaks of supposed smallpox and monkeypox are not frequent and that man may be comparatively insusceptible to monkeypox. A natural reservoir of smallpox in non-human primates is thought to be unlikely although further studies are warranted since the survey reveals that certain species of monkeys can be infected with smallpox and that infected monkeys can transmit infection to others.