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PubMed1992

Vectorial analysis of the instantaneous equilibrium of forces between incisal and condylar guidances.

Protrusive functional relationships between the upper and lower jaws are constrained by the structures of the temporomandibular joints (TMJs) and the opposing contacting surfaces of the anterior teeth. To check these biomechanical relationships, the link quadrilateral bell crank model was assumed in order to compute the instantaneous equilibrium of forces using vectorial analysis. Four anterior teeth configurations were analyzed to study the distribution of force components. The first represented normal bite (used as control), the second represented long anterior overjet, the third represented deep anterior overbite, and the fourth one represented freedom in centric. When three different interincisal contact positions were assumed, functional compromises concerning load/reaction between the TMJ and anterior dentition were found. In centric occlusion there was a tendency toward less loading in the joints and increased loading on the dentition. In intermediate positions and close to the edge-to-edge position, the mechanical tendencies were toward increased loading in the joints and decreased loading on the dentition.

Bite Force↗

PubMed1997

Initial TMJ disk recapture with anterior repositioning appliances and relation to dental history.

Fifty-eight consecutive patients in a referral based practice seeking treatment for complex chronic painful temporomandibular joint (TMJ) disease were enrolled in a prospective study to assess the recapture of displaced disks by anterior repositioning appliances (ARA) and the improvement in disk position in those disks that did not fully recapture. After standard clinical workup, including assessment of pain, maxillary and mandibular ARAs were constructed which repositioned condyles to the Gelb 4/7 position as determined by cephalometrically-corrected linear tomograms. Multi-planar magnetic resonance imaging (MRI) was performed immediately before and after insertion of the mandibular ARA, showing three-dimensional recapture of disks in 85% and improved disk position in 6% of reducing displacements. Disk position was improved in 28% of nonreducing joints, but none were totally recaptured. Recapture or improvement was achieved in 91% of reducing, 28% of nonreducing, and 63% of all joints with internal derangements. Initial disk position, reduction on opening and recapture by ARA were statistically independent of patient age, number of teeth missing, number of third molars missing, malocclusion (Angle's class), overjet, overbite, prosthetic appliances, and previous orthodontic treatment. It was concluded that ARA therapy provided effective recapture of displaced TMJ disks that reduce upon mouth opening. In this population of patients with chronic TMJ pain, previous dental treatment had no statistically significant effect on the incidence of internal derangement or on disk recapture by ARA therapy. There was no evidence of adverse effect from orthodontics, prosthetics, or any other dental care.

Adult↗

PubMed2002

Study of the signs and symptoms of temporomandibular dysfunction in individuals with normal occlusion and malocclusion.

The signs and symptoms of temporomandibular dysfunctions were studied in a well-defined sample, divided into one group with normal occlusion and a second group with malocclusion, where the primary characteristic was Angle Class II a malocclusion with moderate to deep overbite. Each group comprised 30 individuals with a mean overall age of 22.6 years. The following were evaluated in both groups: tenderness to palpation of the muscles involved in the joint; presence of articular noises; subjective symptoms obtained via a questionnaire; and mandibular movements. The data gathered was subjected to statistical analysis and no significant differences were detected between the groups in the majority of variables studied. However, it was found that those individuals with malocclusion had a wider range of lateral movement and also complained of greater discomfort in the TMJ when compared to individuals in the normal occlusion group. The lack of uniformity between the results of this work and those of other authors may be attributed in particular to variations in age of the sample populations studied.

Adult↗

PubMed2003

Maximal bite force and its association with signs and symptoms of TMD, occlusion, and body mass index in a cohort of young adults.

The purpose of this population-based cohort was to measure maximal bite force (MBF) in the molar and incisal regions and to examine whether MBF was associated with TMD, gender, occlusion (in terms of overjet, overbite, and total number of occluding contacts), and body mass index (BMI). MBF in the molar and incisal regions was measured using a calibrated method in 384 (196 males, 188 females) and 357 (181 males, 176 females) subjects, respectively. Two attempts in each region (right molar, left molar, and incisal) were made in random order. The subjects completed a multiple-choice questionnaire including subjective symptoms of TMD and were subsequently clinically examined. Helkimo's clinical dysfunction index and BMI were calculated. The mean MBF value in the molar region was significantly higher in males (878 N, SD 194) than in females (690 N, SD 175) (p < 0.001). The incisal forces were 283 N (SD 95) and 226 N (SD 86) (p < 0.001), respectively. According to multiple linear regression, TMJ discomfort was significantly negatively associated with MBF in the molar region (p < 0.05) and overjet was significantly negatively associated with maximal incisal bite force (p < 0.05). No significant associations between MBFs and body mass were found. The results demonstrate that in a population-based cohort of young adults signs, and symptoms of TMD and studied occlusal factors, unlike body mass, associate independently with MBF.

Adult↗

PubMed1991

Face height and tooth eruption in adults--a 20-year follow-up investigation.

A longitudinal roentgen cephalometric investigation of vertical craniofacial and dentoalveolar changes during 20 years of adulthood, was performed in 15 men and 15 women. Two lateral cephalograms taken at the average ages 25 and 45 years, were available of each subject. Skeletal and dental changes were described by 13 linear and four angular cephalometric measurements. The analysis of the linear variables showed that total anterior face height increased by 1.60 mm on average. Approximately one-fifth of this increase occurred in the upper and four-fifths in the lower face. In the dentoalveolar region, significant increments of all dimensions except overjet and overbite were found, indicating an eruptive movement of the teeth and a vertical development of their investing tissues. The analysis of the angular measurements showed that posterior rotation of the mandible and uprighting of the upper incisors had occurred during the period of investigation.

Adult↗

PubMed1991

Association between morphology of the first cervical vertebra, head posture, and craniofacial structures.

In order to test the assumption of an association between the anatomy of the first cervical vertebra, the atlas, and dentofacial build, roentgen-cephalograms of 78 young adults with either a markedly high or a low atlas dorsal arch were analysed with regard to head posture, and cervicovertebral and dentofacial anatomy. The high and low dorsal arch groups each comprised 22 women and 17 men. The head was more extended in the low arch groups and particularly so among the women, in whose low arch group there was a tendency for the cervical spine to be inclined more forward. Both the dorsal arch and the dens of the second vertebra were vertically smaller in the low arch groups, and more so among the men. Vertebral length was reduced more in the women, however. The clival plane was more parallel to the foraminal plane in the low arch groups and the gonial angle was more obtuse. Furthermore, the women with low arches showed a steepened mandibular plane, a backward-rotated condylar head, a decrease in the ratio of posterior to anterior face height, smaller vertical overbite and reduced proclination of the lower incisors. The prevalence of severe malocclusions was higher than in the corresponding high arch group.

Adult↗

PubMed1992

Effect of the vertical force component of Class II elastics on the anterior intrusive force of maxillary archwire.

Class II elastics are usually employed in the treatment of excessive overbite and overjet with the Begg technique. The effect of Class II elastics on bite opening and the extent of such an effect is uncertain. This article, based on measurements of 30 cases, illustrates that the effect of the vertical component of force from Class II elastics in reducing the intrusive force generated by the anchor bands in the upper archwire is less than previously believed. The position of the circles in the archwire for intermaxillary elastics has the greatest influence on the anterior intrusive force of the upper archwire. The direction of the Class II elastics and the length of the dental arch (a negative correlation) came second, while the force actually exerted by the elastics had the smallest influence. It is, therefore, suggested that the position of the intermaxillary elastic circles should be located according to the differing clinical objectives.

Dental Stress Analysis↗

PubMed1993

Anterior open bite malocclusion: a follow-up study of orthodontic treatment effects.

Treatment response and stability of the anterior open bite malocclusion were evaluated in 20 open bite patients (17 females, 3 males), who were treated with the Edgewise appliance. The overbite, the number of teeth in occlusion, the functional occlusal contacts of the incisors and the cephalometric characteristics were studied before treatment (T1), at the end of retention (T2), and at least 1 year out of retention (T3). The apical root resorption of the upper incisors was analysed before and after treatment. The mean age at the follow-up control was 17 years 10 months. In 15 patients at least two occlusal contacts of the incisors were possible at the end of the retention period as well as at the follow-up control. The number of teeth in occlusion mesial to the second molars, expressed in percentage of the maximum possible, increased from 40 to 70 per cent during treatment with a positive tendency from T2 to T3. Apical root resorption of the upper incisors exceeded 10 per cent of the original root length in 4 out of 19 measurable cases. One of these patients had a history of trauma and the three others displayed atypical root form. Cases with an increased facial convexity, in which the uprighting of the incisors was possible, seemed to have a favourable treatment prognosis.

Adolescent↗

PubMed1993

A cephalometric comparison of medieval skulls with a modern population.

Thirty-one medieval skulls, mostly dating from the Black Death in 1348, were compared with 32 modern, untreated adults. The medieval population was unusual because the skulls could be so closely dated. Lateral skull radiographs were used for the comparison, based on the method of Seddon (1984). A method error study indicated that the measurements could be treated with reasonable confidence, although possible difficulties with the material are discussed. The findings suggest that the modern group have the longer face and longer palate. The medieval group were found to have more retroclined upper incisors and more proclined lower incisors as well as reduced overbites. The results also suggest changes in mandibular shape over time together with cranial base changes: the modern mandible has a more obtuse gonial angle and is generally longer and thinner. It was not possible to reach a firm conclusion regarding chin prominence. The cranial base saddle angle has become more acute since the medieval period, and the length S-N is greater in the modern group. Depending on interpretation, the skull material could be said to have a more prominent maxilla. Possible reasons for the differences are discussed.

Adolescent↗

PubMed1993

Vertical height differences in subjects with severe dental wear.

The present study aims to determine differences in vertical facial dimensions as a result of severe dental wear. The sample consisted of 35 subjects (mean age 48.4 years) who had advanced dental wear recognized by loss of more than one-third of the estimated original incisor crown length. The control group comprised 40 subjects (mean age 26.1 years) with acceptable occlusions and no signs of severe generalized tooth wear. Lateral skull radiographs were taken for both the study sample and the control group with the mandible in the maximum retruded position, from which measurements were made using a digitizer. The results showed no significant differences for total face height (n-gn) between the groups (P > 0.05) although for the study sample, upper face height was greater (P < 0.05) and lower face height was smaller (P < 0.05). Smaller values for tooth length were found in the wear sample, with the mean differences in tooth length being 5.0 mm for upper incisors and 3.3 mm for lower incisors. The overbite was smaller in the wear sample and the lower incisor position differed from controls in this group. It is concluded that the differences in face height together with differences in lower incisor position through dento-alveolar development contribute to maintenance of total facial height, so compensating for loss of vertical height through severe dental wear.

Aging↗

PubMed1995

Long-term evaluation after chincap treatment.

The purpose of this study was to investigate the skeletal changes occurring during and after chincap therapy. The subjects of this study, with a mean age of 9 years 3 months, consisted of 27 patients; all of whom possessed an anterior crossbite. Of these patients, 15 had skeletal Class III and the remaining 12 had skeletal Class I malocclusions with anterior crossbites. The applied total force with the chincap was 600 grams and the mean treatment period was 12 months. The changes during and after treatment were analysed by using linear and angular cephalometric measurements. The result obtained in this investigation was that in skeletal Class I and Class III cases, successfully treated by a chincap appliance, where the necessary overjet and overbite relationship was obtained, the abnormality tended to return to the original position during the period following chincap removal.

Cephalometry↗

PubMed1995

A cephalometric investigation of the effects of the Elastic Bite-block in the treatment of Class II division 1 malocclusions.

The purpose of this study was to investigate cephalometrically, the effects of a functional appliance-headgear combination, the Elastic Bite-block (EBB). Of 50 Class II division 1 subjects who participated in this study, 30 made up the treatment group and 20 the control group. All of the selected cases exhibited mandibular retrognathism, facial growth pattern either along the Y-axis or in the horizontal direction, and were all at the peak of the prepubertal growth spurt. Whilst the EBB was applied to the treatment group for 1 year, no treatment was performed on the control group. Measurements made on the lateral cephalograms, obtained at the beginning and end of the study were statistically evaluated. The following changes took place as a result of EBB treatment: sagittal growth of the maxilla was inhibited, the upper molars were distalized and intruded, sagittal growth of the mandible was stimulated and the lower molars erupted in a mesio-occlusal direction. As a result of downward and backward rotation of the mandible, the vertical dimension showed incremental changes. The upper and the lower incisors were both uprighted and intruded, and overjet and overbite decreased.

Activator Appliances↗

PubMed1995

A comparative study of the effects of customized facemask therapy or headgear to the lower arch on the developing Class III face.

This retrospective, cephalometric study examined the effects of treatment in a group of 83 Class III, Skeletal III children, who were considered suitable for orthodontic correction of their malocclusions. All children completed therapy successfully: 44 individuals were treated with headgear to the mandibular dentition and for 39 a customized facemask was prescribed. These two groups were compared with 30 untreated Class III controls. Data were examined at the beginning and end of active treatment for the treated groups, and over a similar time interval for the controls. Where differences between the sexes were apparent, data for each sex are given separately. Where no significant differences were seen, data are pooled. In order to standardize the results, treatment (or observation) effects are presented as average changes per year. Surprisingly, despite the very different methods of applying the extra-oral force, the two treated groups showed strikingly similar therapeutic effects. The reverse overjet was corrected with little alteration in overbite. Upper incisors proclined whilst the lowers retroclined, becoming less prominent in relation to APo. The mandible hinged downwards and backwards, whilst the maxillary complex advanced. Lower face height increased more than would be expected by growth alone. Mirroring the hard tissue changes, the soft tissue profile improved and the relationship between the upper and lower lips became more harmonious. For only three parameters did the facemask children demonstrate a significantly better performance than their headgear peers: the overjet and the antero-posterior position of the lower lip and chin in females. It was concluded that, despite their differing approaches, the customized facemask and headgear to the mandibular dentition have very similar treatment effects. Both are clinically effective. However, treatment can begin earlier, and both the skeletal and profile changes are marginally superior when a facemask is worn.

Adolescent↗

PubMed1996

Occlusal morphology in Turner syndrome.

The prevalence of malocclusion in 32 Turner syndrome patients, age 7-16.7 years, was investigated. The sample was subdivided according to karyotype, and 72 normal girls, aged 7.1-16.1 years, served as controls. Compared with normal girls overjet did not differ significantly while overbite was significantly reduced in 45X patients. The prevalence of distal molar occlusion, anterior and lateral open bite and lateral crossbite was significantly increased. Most significant differences were found between 45X patients and controls. Mosaic and isochromosome for the long arm of X karyotypes showed the same pattern of malocclusion, but with greater variation. No significant differences were found comparing 45X patients with mosaic and isochromosome for the long arm of X karyotypes. The results indicate that patients with structural and/or numerical aberration of the X chromosome, develop a specific pattern of malocclusion with deviations in sagittal, vertical and transversal directions.

Adolescent↗

PubMed1996

Agenesis of mandibular second premolars. Spontaneous space closure after extraction therapy: a 4-year follow-up.

The aim of this study was to investigate the space closure and occlusal changes in 11 subjects (mean age 11.8 years) with normal occlusion and agenesis of the mandibular second premolar, after extraction of the mandibular secondary primary molar and the maxillary second premolar on the side of the agenesis. The treatment started when the first premolars came into occlusion and the subjects were followed for 4 years. Dental casts were taken at the start of treatment and after 1, 2 and 4 years, and lateral cephalograms were taken at the start of treatment and after 2 and 4 years. Space closure, sagittal movements, rotational movements, and tipping of the first molars and first premolars and dental midline shift were measured on photographs of dental casts. Sagittal movement of the incisors was measured on lateral cephalograms. The results showed that most of the extraction space closed during the first year (55 per cent in the maxilla, 46 per cent in the mandible) and at the end of the follow-up period 89 per cent of the extraction space closed in the maxilla and 80 per cent in the mandible, leaving a mean residual extraction space of 0.9 and 2 mm respectively. In the maxilla, 70 per cent of the extraction space closed by mesial and rotational movements of the first molars. Maxillary premolars moved distally, rotated and tipped only during the first year of observation. In the mandible, the space closure occurred by mesial/rotational movements and tipping of first molars and distal movement and tipping of the first premolars. Unilateral extraction had no influence on the maxillary midline while it caused a statistically significant mandibular dental shift to the extraction side. Extraction therapy had no impact on the overjet, overbite or incisor inclination.

Adolescent↗

PubMed1998

Functional occlusion after fixed appliance orthodontic treatment: a UK three-centre study.

This study aimed to assess the prevalence of functional occlusal contacts in cases treated to a Class I incisor relationship by upper and lower fixed appliance therapy. Helkimo's dysfunction indices were used by one examiner to assess mandibular mobility, clinical dysfunction and occlusal status. One-hundred-and-eighty-eight subjects participated in three UK orthodontic centres; Cardiff, Newport and Liverpool. The results show that RCP (CR)-ICP (CO) discrepancies occurred in 33 (18 per cent) cases, non-working side contacts were present in 31 per cent and posterior contacts on protrusion occurred in 44 (23 per cent) subjects. These interferences were significantly more frequent in cases treated by postgraduate students compared with those treated by staff clinicians (P < 0.05). An overbite greater than 2.4 mm resulted in a highly significant reduction in the occurrence of non-working side contacts and posterior protrusive contacts (P < 0.001). The prevalence of functional occlusal discrepancies in this UK sample of orthodontic cases is similar to that reported in the American literature.

Adolescent↗

PubMed1999

Long-term effect of the chincap on hard and soft tissues.

The short- and long-term effects of the chincap used in combination with a removable appliance to procline upper incisors were analysed cephalometrically in 23 patients with Class III malocclusions. The overall changes were compared with growth changes in a closely matched control sample of untreated Class III patients. There was no evidence that the chincap retarded growth of the mandible. During treatment, there was an increase in mandibular length and facial height. The lower incisors retroclined and the upper incisors proclined. The incisor relationship was corrected. Soft tissue changes included an increase in nasolabial angle and improvement in soft-tissue profile, including the nose. Skeletal post-treatment changes included further mandibular growth associated with an increase in angle SNB and Wits measurement. Facial height also increased significantly. The Class I overjet was maintained, although slightly diminished. The soft tissue nose, upper and lower lip, and chin moved anteriorly, and the nasal tip and chin moved inferiorly. At the end of the study period there were no significant skeletal or soft tissue differences between the treated and control groups. The only significant contrasts were in the overjet and the overbite. Chincap therapy combined with an upper removable appliance to procline the upper incisors is effective in producing long-term correction of the incisor relationship by retroclination of lower incisors, proclination of upper incisors, and redirection of mandibular growth in a downward direction. The direction of growth at the chin is maintained subsequent to treatment, as are the changes in incisor inclination, although in diminished form. There are corresponding improvements in the soft tissue profile.

Case-Control Studies↗

PubMed2000

The retraction of upper incisors with the PG retraction system.

The aim of this study was to evaluate the effect on the dentoalveolar structures of the application of PG springs for retraction of upper incisors and to compare the outcome with the effect of a closed coil spring retraction system. Thirty-six subjects with Angle Class I or Class II malocclusions were selected for the study. Each subject had the two upper first premolars extracted and presented a symmetrical extraction space of at least 3 mm distal to the lateral incisors after canine retraction. The subjects were divided into two groups, the PG group with 17 subjects and the coil group with 19 patients. One group had the incisors retracted by PG universal retraction springs, whereas in the other a closed coil spring system was used. The average chronological ages were 18 years 4 months for the PG group, and 18 years 7 months for the coil group. In both groups the springs were activated to produce an initial force of 150 g per side. To examine the type of movement of the anterior and posterior teeth, and the time and rate of space closure, 20 parameters were measured and evaluated statistically with Wilcoxon and Mann-Whitney U-tests. In both groups the incisor retraction was accompanied by mesial movement of the buccal segments. Distal movement of the root apex of the incisors was observed in both groups, although more pronounced in the PG group (P < 0.01). A significant incisor intrusion resulting in a decrease in overbite was found in the PG group, whereas the deep bite increased significantly in the coil spring group. The PG spring produced a three-dimensional control in the movement of the upper incisors, so that application of additional intrusive mechanics after completion of the incisor retraction became unnecessary.

Adolescent↗