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Identical 13-year-old twin boys with Class II, division 2 malocclusions are treated at the same time, one with a full complement of teeth and the other with extraction of the first bicuspids.
Eighty-three percent of hamsters inoculated at birth with JC virus, a human papovavirus isolated from brain tissue of a case of progressive multifocal leukoencephalopathy, developed malignant gliomas within 6 months. Three brain tumors have been serially transplanted as subcutaneous tumors. JC virus was isolated from five of seven tumors tested. Cells from four tumors were cultivated in vitro. These cells contained an intranuclear antigen with the characteristics of a T antigen, and this antigen was antigenically related to SV40 T antigen. Although virus was not recovered from extracts of serially cultured tumor cells, JC virus was rescued when one tumor cell line was fused with permissive cells.
The classical tripartite concept of time divided into past/present/future components, has been applied to the analysis of the functional cerebral substrate of conscious awareness. Attempts have been made to localize and to separate the neuronal machineries which are responsible for the experience of a past, a present, and a future. One's experience of a past is obviously related to one's memories. Memory mechanisms (in the conventional sense) have a well known functional relation to superficial and deep parts of the temporal lobe. Some such mechanisms presumably have a more widespread distribution. The experience of a present or a "Now-situation" is mediated by the sensory input. This input also exerts a role for conscious awareness of an inner Now-situation, independent of current afferent impulses, as shown by numerous observations on sensory deprivation. The main discussion is devoted to the experience of a future. Evidence is summarized that the frontal/prefrontal cortex handles the temporal organization of behaviour and cognition, and that the same structures house the action programs or plans for future behaviour and cognition. As these programs can be retained and recalled, they might be termed "memories of the future". It is suggested that they form the basis for anticipation and expectation as well as for the short and long-term planning of a goal-directed behavioural and cognitive repertoire. This repertoire for future use is based upon experiences of past events and the awareness of a Now-situation, and it is continuously rehearsed and optimized. Lesions or dysfunctions of the frontal/prefrontal cortex give rise to states characterized by a "loss of future", with consequent indifference, inactivity, lack of ambition, and inability to foresee the consequences of one's future behaviour. It is concluded that the prefrontal cortex is responsible for the temporal organization of behaviour and cognition due to its seemingly specific capacity to handle serial information and to extract causal relations from such information. Possibly the serial action programs which are stored in the prefrontal cortex are also used by the brain as templates for extracting meaningful (serial) information from the enormous, mainly non-serial, random, sensory noise to which the brain is constantly exposed. Without a "memory of the future" such an extraction cannot take place.
Concern about claims that premolar extractions may put patients at risk for temporomandibular disorders (TMD) led to this study. We report first findings from a longitudinal study of orthodontic patients begun in 1983. By using the methods of Helkimo, we collected TMD data before initiation of orthodontic treatment, between 0 and 12 months after debanding, and 12 to 24 months after debanding. Analyses related Helkimo scores with premolar extractions in 65 patients for whom orthodontic treatment had been completed. Twenty-six patients were treated without premolar extractions, 25 had four premolars extracted, and 14 had two upper premolars extracted. Tests for significance of differences between mean Helkimo scores were conducted for the nonextraction group compared with the extraction groups, and between pretreatment and posttreatment Helkimo scores for each group. Results included: (1) no significant intergroup differences between mean pretreatment or posttreatment scores, and (2) small but statistically significant (p less than 0.05) differences (in the direction of improvement) between mean pretreatment and posttreatment scores for both the nonextraction group and for the four premolar extraction group.
The purpose of this study was to examine the results of a treatment regimen involving the extraction of four second molars followed by a combination of sagittal, Bionator, and fixed appliance therapy. The pretreatment and posttreatment cephalometric and dental cast records of 30 consecutively treated Class II, Division 1 cases were evaluated. Results showed that the Class II skeletal correction was achieved by a "headgear" effect inhibiting maxillary growth in conjunction with normal forward mandibular growth. No significant distal bodily movement or tipping of either maxillary or mandibular first molars was found. Significant increases were seen in maxillary arch length, maxillary intercanine and intermolar width, and mandibular intermolar width as a result of treatment. Maxillary third molar position tended to improve following second molar extraction; mandibular third molar changes were more variable.
1. Cephalometric tracings of thirty Class II, Division 1 cases without extraction and twenty-five Class II, Division 1 cases with extraction were evaluated and statistically compared by means of the overbite depth indicator (ODI) and the anteroposterior dysplasia indicator (APDI). 2. The mean ODI in the nonextraction group, in particular, was significantly higher than that of the extraction group. 3. Three clinical examples were presented to demonstrate the values of ODI and APDI as adjuncts to cephalometric differential diagnosis. 4. With respect to the vertical component it may be concluded that the lower the ODI value from the normal mean a case presents, the greater the incidence of an extraction procedure as a compromise for the poor skeletal pattern. 5. With respect to the horizontal component the initial APDI reading indicates the severity of skeletal discrepancy. When the posttreatment APDI reading falls below the normal mean, a relapse is probable: the lower the figure a case possesses, the greater the chance of relapse. In such incidences an extraction procedure must be provided to ensure the stability of occlusion.
There is no orthodontic indication for the extraction of sixth-year molars. Nevertheless, one-third of all permanent teeth extracted by us in orthodontic cases terminated within one year were first molars. The indication for the extraction of these permanent first molars was based exclusively on caries incidence. The resultant disadvantages to the course of treatment are discussed from medical and economic aspects.
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Discriminant analysis was used to assess the anatomical basis of the extraction/nonextraction decision in 238 former Saint Louis University Class II edgewise patients. The resulting discriminant scores (based on six measures of protrusion and crowding) were used to divide this parent sample into three prognostic subgroups: clear-cut extraction, clear-cut nonextraction, and a borderline stratum containing both extraction and nonextraction patients. The "clear-cut" patients--those at the tails of the distribution--were then contacted and asked to return for follow-up records (cephalograms, models, clinical examination); in the end, 62 (33 extraction and 29 nonextraction) were recalled. The average post-treatment interval was about 15 years. Premolar extraction produced a significantly greater reduction in hard- and soft-tissue protrusion. During the post-treatment period, however, both groups underwent essentially the same change: decreased profile convexity and a pattern of dental change/relapse that was correlated with antero-posterior mandibular displacement. Because of their greater initial crowding and protrusion, the various effects summed to make the extraction patients significantly more protrusive at recall. Both treatments produced mesial mandibular displacement, extraction significantly more than nonextraction; however, at recall the two groups did not differ with respect to the signs and symptoms of dysfunction. The present findings, therefore, fail to support the common, influential belief that premolar extraction frequently causes "dished in" profiles, "distalized" mandibles, and, ultimately, craniomandibular dysfunction.
The aim of this study was to observe longitudinally the anterior region of the lower jaw when treating only the upper jaw. A comparison was made between a group of 35 children treated with extraction of the maxillary first premolars and a fixed appliance in the upper jaw and a control group of 19 untreated children. The treatment group was studied with plaster models on five occasions: before treatment, at the end of active treatment, at the end of retention, after one year out of retention and at the last registration, in total over about a seven year period. Cephalometric registrations were made before treatment and at the last registration. The control group was studied with plaster models and lateral head films during a period of nine years and their age at the last registration was the same as for the treatment group. The space loss in the anterior region of the lower jaw increased from a mean of 0.4 mm (s.d. 0.82) to 2.5 mm (s.d. 1.52) in the treatment group and from 0.1 mm (s.d. 0.16) to 0.5 mm (s.d. 0.81) in the control group: an extra space loss of 2.0 mm for the treatment group. The main increase was registered during treatment and after retention. Subjective ranking of the plaster models from the final registrations according to the amount of crowding in the lower anterior region also showed a significant difference between the treatment group and the control group, the treatment group showing the largest of crowding. In cases where maxillary protrusion is treated by extraction in the maxilla only, stabilization of the lower arch with fixed orthodontic appliances seems justified.
The present study was undertaken to assess the long-term periodontal status adjacent to teeth that had been moved orthodontically into extraction sites. Twelve persons with a mean age of 29.2 +/- 5.7 (SD) years, who had completed orthodontic therapy at least 10 years previously, were examined. The orthodontic treatment had included bilateral premolar extraction in only the maxilla. Interproximal tooth surfaces in the maxilla adjacent to the extraction sites (study group) were compared to corresponding tooth surfaces in the mandible (control group) with respect to plaque, visual inflammation, bleeding after probing, pocket depth, gingival recession, loss of connective tissue attachment, radiographic bone height, and root resorption. Statistical comparisons were made via analyses of variance and t tests. There were no differences between the groups for any clinical parameter except the presence of less visual inflammation in study subjects. Radiographically, there were no differences in crestal alveolar bone levels measured from the cementoenamel junction. Bone height evaluation by the Bjorn method showed less alveolar support in the study group. However, this was due to the influence of root resorption rather than an effect on crestal height. It was concluded that orthodontic movement of teeth into extraction sites had been without detrimental effect upon the adjacent periodontal status.
Third molars, both upper and lower, do usually erupt into the place of electively removed second molars. None of the third molars in this study group became impacted during the observation period. Second molars in this study were removed before the roots had formed on the third molars. The bifurcation line appears to be a stable reference on the panoramic radiograph. It is the Author's conclusion that the extraction of permanent second molars is best for many patients, and when judiciously applied it is a reasonably safe and conservative modality in orthodontic care.
Forty patients in active retention following orthodontic tooth movement into premolar extraction sites were examined for the occurrence and distribution of interdental gingival clefts, defined as an invagination of interproximal tissue with definite mesial and distal peaks having a depth of at least 1 mm. Fourteen of the forty orthodontic patients demonstrated clefts in one or more of the premolar extraction sites. No clefts were observed in premolar areas of orthodontic patients who did not require premolar extraction or in patients without previous orthodontic treatment. Interdental clefts occurred most frequently at the buccal aspect of mandibular first premolar extraction sites. The presence of the cleft appears to have clinical implications, both in terms of orthodontic relapse, and maintenance of gingival health.
A high-performance liquid chromatographic method has been developed for the determination of urinary tetrahydro-beta-carbolines. When standing tryptamine with formaldehyde and acetaldehyde under extraction conditions, the significant amounts of artefact 1,2,3,4-tetrahydro-beta-carboline (TBC) and 1-methyl-1,2,3,4-tetrahydro-beta-carboline (MTBC) were formed in a short time. Urine samples added with 2-ethyl-1,2,3,4-tetrahydro-beta-carboline (an internal standard) were treated with fluorescamine, and then with glycine, followed by serial solvent extractions. Such a pretreatment using two-step reactions removed a precursor (trypamine) by extracting its fluorescamine derivative, and enhanced the detection response by consuming excess fluorescamine. It solved the analytical problem that artefact TBC and MTBC are formed during analysis. Reversed-phase ion-pair chromatography using a C8-column and trifluoroacetic acid as a counter ion completed a base-line separation of three analytes within 10 min. The calibration graphs showed a good linearity in the range 0.1-50.0 ng ml-1 of urine samples spiked with standard TBC and MTBC. In the spike experiment, the recovery and relative standard deviation were almost 100% and less than 3.0%, respectively, for both TBC and MTBC. The proposed method enables the determination of the genuine urinary concentrations of TBC and MTBC without involving their artefacts.
The purpose of the study was to evaluate the result in adults of Class I malocclusion cases who had all their first premolars extracted as the sole treatment of space deficiency in the mixed or early permanent dentition. The mean age at premolar removal was 10 1/2 years. Forty-two out of 44 cases were re-examined at a mean age of 30 years and 4 months. Observations of dental occlusion and oral health were compared to observations of control samples. The average malocclusion in the adults, as judged by a score method, was similar to that reported for an appliance-treated sample. Marked spontaneous arch alignment and residual space closure with age was seen in most cases. Despite earlier tooth removal, on average crowding developed to about the same degree as that of an non-extraction normal occlusion sample. No detrimental effects were seen with regard to overjet or overbite. Neither did the figures for lower incisor position at the follow-up examination differ from that of the normal occlusion sample. Although tipping of adjacent teeth towards the extraction site was frequent, especially in the mandible, no effect on marginal bone height was evident as judged by comparison with a non-extraction control sample. The results reveal a significant capacity for spontaneous improvements with age in dental arch morphology and relationship in extraction cases, provided that specific features have been looked for in case selection.
Residual lower first premolar extraction space was examined in 43 subjects, 16 male and 27 female, 5 years after extraction; 16 subjects were treated mechanically, 27 had no active treatment. Forty per cent of extraction sites had residual spaces averaging 0.62 mm left and 0.71 mm right. Various parameters were measured to try to establish reasons for non-closure of spaces. These included buccal space condition and incisal space condition measured on the pre-extraction models, and alveolar atrophy assessed on final models. The angulation of second premolars and canine to the maxillary plane and molar space were measured on 60 degrees cephalograms. Changes in these three parameters were measured after superimposing a tracing of the pre-extraction film on the final film. Angulation of lower incisors to the maxillary plane was measured on pre-extraction 90 degrees cephalograms, and change in lower incisor angulation and position measured after superimposing a tracing on the final 90 degrees film.
A retrospective cephalometric study was made of the hard tissue changes in a group of 90 Class III, Skeletal III children, diagnosed as suitable for treatment by orthodontic means alone. Thirty-two were treated by a combination of upper incisor proclination and headgear to an intact mandibular dentition (Group 1), while in 28 the overjet was corrected with mid-arch extractions and Edgewise mechanics (Group 2). The remaining 30 children acted as controls (Group 3). Children were initially examined as male and female subgroups, and where no significant differences were seen data were pooled. In order to standardize the results, treatment/observation effects were presented as average changes per year. The three groups were essentially comparable pretreatment. Following overjet correction, the lower incisors uprighted in both groups, with an improved relationship to the A-Po line: the upper incisors were proclined in Group 1 only. Underlying skeletal changes were restricted to the mandible, which showed a downward and backward hinging, and an increase in lower face height. The improved mandibular position was significantly greater in the non-extraction group and was accompanied by an improvement in facial convexity. In addition, treatment could be started earlier and was completed in a significantly shorter time (Table 1). It would, therefore, appear that, in the short term at least, a non-extraction/headgear approach has advantages over a standard mid-arch extraction/Edgewise technique.