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PubMed2003

The effects of commonly prescribed premolar extraction sequences on the curvature of the upper and lower lips.

The potential for premolar extractions to produce adverse facial effects after orthodontic treatment is still controversial. Detailed documentation of the predictability, or otherwise, of various soft tissue treatment effects would obviously be of assistance to clinical orthodontists in day-to-day treatment planning, by potentially refining the criteria for appropriate selection of various premolar extraction sequences. With this in mind, a retrospective lateral cephalometric study of 80 premolar extraction cases was undertaken to assess whether different patterns of premolar extraction do in fact produce predictably different lateral profile effects. A comparison was made of the changes in lip curvature after the extractions of all first premolars (4/4), all second premolars (5/5), or upper first and lower second premolars (4/5). Changes in the depths of curvature of both the upper and lower lips were not solely dependent on the selection of a particular premolar extraction sequence. Instead, there were wide ranges of individual variation in the changes in the depths of the lip curves. Therefore, in addition to the inherent soft tissue morphology of the lips in individual patients, it is the combined effect of the lip response to various dental and skeletal changes and the competent clinical management of extraction spaces that apparently affects the shapes of the lips within the lateral profile during treatment. In other words, it would seem possible for the clinician to carefully manage either first or second premolar extraction spaces while still protecting the facial profile.

Adolescent↗
PubMed1997

Efficacy of intraarch mechanics using differential moments for achieving anchorage control in extraction cases.

A prospective survey was conducted to test the hypothesis that maximum anchorage can be achieved in the maxillary arch by controlling forces and moments using intraarch mechanics while retracting canines into first premolar extraction sites. The sample consisted of 24 patients (mean age 18 years, 9 months) who required the extraction of two maxillary first premolars, with or without extractions in the mandibular arch. Movements of the first molars, canines, and incisors were evaluated with 6 cephalometric variables and 10 study model variables. T tests were used to assess differences between pretreatment and postretraction tooth positions. Cephalometrically, the maxillary first molars (left and right sides combined) moved mesially ONLY 0.7 mm (SD 0.43; p < 0.008). All other cephalometric variables showed no significant differences between the two time points. From the study models, the molars moved mesially ONLY 0.5 mm on both the right and left sides (right side SD = 0.43 and left side SD = 0.38; p < 0.005), while the canines were retracted on average 5.8 mm on the right side and 5.6 mm on the left. The molars and canines showed significant mesiopalatal and distolingual rotations, respectively. Many of the study model and cephalometric variables were significantly correlated to one another. This study questions the need to use adjunctive appliances, which directs a distal force to the posterior teeth, if horizontal molar anchorage control is a treatment objective. By controlling forces and moments, using intraarch mechanics while retracting maxillary canines into first premolar extraction sites, minimal molar anchorage loss occurred.

Adolescent↗
PubMed1973

Human papovavirus (JC): induction of brain tumors in hamsters.

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.

Animals↗
PubMed1998

Verbal and visuospatial short-term memory in children: evidence for common and distinct mechanisms.

This study was designed to identify whether verbal and visuospatial short-term memory performance in children is served by common or distinct mechanisms. Five- and 8-year-old children were tested on their verbal recall of spoken letter names and digits, and on their recall of tapped sequences of blocks. The performance of the children on the verbal and visuospatial serial recall tasks was largely unrelated, extending evidence for dissociable memory systems found in adults. Detailed characteristics of recall, such as serial position functions, migration patterns, and distribution of error types, were similar in the tasks requiring recall of letters and of blocks, although order errors predominated in the block but not the letter recall task for the older children. These results appear to reflect the application of common processes specialized for the extraction of serial order information from the phonological and visuospatial components of short-term memory.

Adult↗
PubMed1996

The effects of extracting upper second permanent molars on lower second permanent molar position.

There is some controversy over whether the extraction of upper second permanent molars as part of orthodontic treatment leads to the over eruption of unopposed lower second permenent molars. A study was established to investigate the presence of any over-eruption in a group of subjects who had upper second permanent molars extracted as part of a previous course of orthodontic treatment. These subjects (the experimental group) were compared with a control group of subjects, matched for age and sex. Upper and lower impressions were taken, and the vertical positions of the posterior teeth were objectively assessed from the study models using the travelling microscope. Measurements from the study models showed that the distal aspect of the lower second permanent molar had over erupted in the experimental group when compared to the control (P < 0.001 right, P < 0.05 left). The degree of over-eruption was influenced on the mesial aspect by the distal position of the upper first permanent molar (P < 0.01), but the distal aspect was not. Eruption of the upper third molar did not affect the over-eruption of the lower second permanent molar in the experimental group. The majority of upper third molars had erupted at least 3 years since the upper second molars had been extracted, but the majority had erupted into an unfavourable contact position with the first permanent molar.

Adult↗
PubMed1985

"Memory of the future": an essay on the temporal organization of conscious awareness.

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.

Awareness↗
PubMed1992

Orthodontic risk factors for temporomandibular disorders (TMD). I: Premolar extractions.

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.

Adult↗
PubMed1997

Comparison of the changes in facial profile after orthodontic treatment, with and without extractions.

A study was made of 31 patients with Angle Class II malocclusion. Fifteen patients did not undergo extraction of teeth (Group A), while 16 underwent extractions of four premolars (Group B). Data was obtained from the corresponding lateral radiographs of the head taken both before and after orthodontic treatment. The main aim of the study was to compare the response of the soft and hard tissues of the facial profile in Class II malocclusion treated with the extraction of four premolars and the response of borderline cases presenting with similar malocclusions, but not subjected to extraction. In this latter group reasonable doubt existed as to whether or not to remove teeth in order to solve the occlusal and aesthetic problems. It is concluded that significant hard tissue differences between the groups at the end of treatment were limited to a more retruded position of the incisors and a reduced overbite amongst those patients subjected to extraction. The main soft tissue differences between the groups at the end of treatment were a more retruded lower lip and a more pronounced lower labial sulcus in those patients subjected to extraction.

Adolescent↗
PubMed1987

An evaluation of combination second molar extraction and functional appliance therapy.

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.

Activator Appliances↗
PubMed1979

A comparative cephalometric study of Class II, Division 1 nonextraction and extraction cases.

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.

Adolescent↗
PubMed1978

[The extraction of the 6-year molars in orthodontic practice].

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.

Bicuspid↗
PubMed1997

Condyle displacement associated with premolar extraction and nonextraction orthodontic treatment of Class I malocclusion.

This study assessed condyle position change with premolar extraction and nonextraction orthodontic treatment in Class I malocclusions. Axially corrected pretreatment and posttreatment tomograms were obtained in 22 extraction and 13 nonextraction cases. Tomographic images were randomized and blinded for joint space measurement. A total of 27 linear anterior, superior, and posterior joint spaces were obtained from each tomogram and averaged. Comparisons of pretreatment and posttreatment joint spaces between groups were done by t test (pool variance estimate) with p < 0.05. Left and right anterior joint spaces were significantly increased during orthodontic treatment of the nonextraction group. No other significant changes in condyle position were determined in either group. There were no significant correlations between mean joint space changes with length of Class II elastic wear. There was no significant difference in condyle position change with extraction space closure using closing arch wires compared with elastic chain.

Adolescent↗
PubMed1999

The effect of first premolar extraction on vertical dimension.

The purpose of this study was to evaluate the vertical changes occurring in Class I patients treated orthodontically with first premolar extraction and to compare these changes with those occurring in Class I patients treated orthodontically without extractions. Records of 40 Class I nonextraction cases (24 girls, 16 boys) and 40 Class I maxillary and mandibular first premolar extraction cases (23 girls, 17 boys) were obtained. The pretreatment and posttreatment cephalograms were digitized, and 6 linear and 8 angular cephalometric measurements were selected to evaluate vertical changes. Evaluation of the treatment results of the extraction and nonextraction cases showed that the vertical changes occurring after the extraction of maxillary and mandibular first premolars were not different than those occurring in the nonextraction cases.

Bicuspid↗