Mesial migration and loss of first molars among young adolescents in Kuwait.

OBJECTIVE: Our aim was to determine the prevalence of and factors associated with mesial migration and/or loss of first molars in 13-14-year-old school children in Kuwait. METHODS: A population-based sample of 1,583 eighth grade students of mean age 13.23 +/- 0.42 yrs, representing about 7% of the target population, were selected using multistage cluster sampling methods. Information on nationality, family income, and number of siblings was collected through subject and family interview. Any mesial migration or loss of first molars as well as visible caries was recorded in a well lit classroom. RESULTS: The prevalence of mesial migration and/or loss was 11.4%. Almost 70% of this occurred only in the mandible, and the majority (75.7%) had only one tooth affected (p < 0.01). Although the prevalence differed with residential geographical regions (p < 0.01), there were no gender differences (p > 0.05). The prevalence also differed with family income (p < 0.05), increased (p < 0.05) with increasing number of siblings, and was higher (p < 0.001) in subjects with presence of caries lesions (22.2%) than in those without (9.6%). CONCLUSIONS: About 12% of current age cohorts of school children in Kuwait are likely to experience mesial migration and/or loss of one or more first molars. The conditions are associated with presence of untreated caries lesions. Private school attendance and high as well as low family income are associated with a decreased level of mesial migration and/or loss of one or more first molars. Increased number of siblings is a risk factor.

Is the postretention relapse of maxillary and mandibular incisor alignment related?

Previous studies suggest a poor association between initial and postretention pattern of incisor irregularity. One explanation may be that the incisor movements are limited by the boundaries provided by the incisors in the opposite arch. If so, postretention malalignment of the maxillary and mandibular incisors may be related. To test this hypothesis, long-term postretention study models of 96 patients with acceptable occlusion at the time of appliance removal were examined. The occlusal surfaces of the postretention study models were photocopied, and tooth anatomical contact points were digitized. An algorithm was used to fit the dental arch to the digitized points. The amount of incisor rotation and anatomical contact point displacement of maxillary and mandibular anterior teeth, relative to their respective dental arches, were computer generated. Overbite, the number of occlusal contact points in the anterior segment, and concavity of the lingual surfaces of the maxillary incisors were recorded manually. Statistical analyses demonstrated a significant association (P <.05) between the overall irregularity of the maxillary and mandibular incisors. The association did not differ among subgroups that were stratified according to overbite or number of occlusal contacts. No associations were found for the overall amount of incisor rotation in the 2 arches (P >.05). The amount and direction of displacement of antagonistic pairs of maxillary and mandibular central incisors were also associated (P <.05), but not the amount and direction of rotation (P >.05). The lingual configuration of the maxillary incisors did not affect the pattern of mandibular incisor malalignment.

Periodontal status of mandibular incisors after pronounced orthodontic advancement during adolescence: a follow-up evaluation.

The purpose of this study was to analyze whether pronounced orthodontic advancement of the mandibular incisors during Class II correction in the mixed dentition results in gingival recession. Through mandibular superimposition of the pretreatment and posttreatment cephalograms of 67 Class II patients who were treated with reverse headgear to the mandibular dentition, 45 patients with a minimum of a 1-mm advancement of the cementoenamel junction (CEJ; mean, 2.18 +/- 0.87) and a minimum of a 2-mm advancement of the incisal edge (mean, 3.87 +/- 1.34) were identified. Using the same protocol in Class II patients, 30 individuals who finished treatment at a similar time and age, but without reverse headgear and with no advancement of the CEJ (mean -0.43, SD 0.53) and a maximum of 1-mm advancement of the incisal edge (mean -0.26, SD 1.15) were identified. Before treatment, the mandibular incisors were more retruded, relative to the line from point A to pogonion and relative to the mandibular plane in the patients with pronounced advancement than in those with no advancement of the mandibular incisors; no differences were found at the time of appliance removal. A total of 30 patients with pronounced advancement and 21 patients with no advancement could meet for a follow-up examination a mean period of 7.83 years (SD, 4.44) and 9.38 years (SD, 4.39) after treatment, respectively. Clinical examinations at the time of follow-up revealed no differences in the amount of recession, the width of attached gingiva, the length of supracrestal connective tissue attachment, the probing pocket depth, and gingival bleeding index or visible plaque index of the mandibular incisors between the patients in the 2 groups. An examination of color slides demonstrated no differences in the number of mandibular incisors that developed recession from before treatment to after treatment and from after treatment to follow-up. Measurement of mandibular incisor crown height on the study models demonstrated no difference in the increase in clinical crown height from after treatment to follow-up between the patients in the 2 groups. It was concluded that pronounced advancement of the mandibular incisors may be performed in adolescent patients with dentoalveolar retrusion without increasing the risk of recession.

Long-term profile changes associated with successfully treated extraction and nonextraction Class II Division 1 malocclusions.

This study was undertaken to compare the post-treatment and long-term soft tissue profiles of successfully managed and stable Class II, division 1 malocclusions treated with either 4 first premolar extractions or nonextraction therapy. It was hypothesized that, if sound extraction decisions were made according to accepted treatment objectives and successful treatment outcomes were achieved, there should be no differences between groups in soft tissue profiles post-treatment and long-term post-retention. The sample consisted of 63 Caucasian adolescents (23 extraction, 40 nonextraction). Correction of the malocclusion was achieved using a combination of cervical headgear concurrent with mandibular growth and maxillary incisor retraction. Pretreatment, post-treatment, and long-term post-retention lateral cephalometric radiographs were evaluated. The soft tissue facial profiles of the extraction and nonextraction samples were the same following active treatment and long-term post-retention. Progressive flattening of the facial profile was observed in both samples. This flattening was attributed to the maturational changes associated with continued mandibular growth and nasal development and was not influenced by whether or not teeth were removed. Long-term lip positions were more retrusive than the ideals suggested by Ricketts and Steiner, but close to the values reported for normal, untreated adults of similar ages. The pretreatment position and thickness of the lower lip as well as the initial maxillomandibular skeletal relationship may be predictors of post-treatment or long-term lower lip position.

Evaluation of friction during sliding tooth movement in various bracket-arch wire combinations.

Frictional forces during simulated sliding tooth movement were measured with a model that was representative of the clinical condition. The model allowed tipping of the tooth until contact was established between the arch wire and diagonally opposite corners of the bracket wings; it also allowed rotation until the wire contacted opposite corners of the ligature tie, or the buccal shield with self-ligating brackets, and the base of the slot. Conventional and self-ligating stainless steel brackets as well as conventional ceramic brackets, and ceramic brackets with a stainless steel slot, all with 0.022 inch bracket slot, were tested with 0.019 x 0.025 inch arch wires of stainless steel, nickel titanium, and beta titanium. Each of the 12 bracket-arch wire combinations was tested 10 times. No significant interaction was detected between brackets and arch wires (P = .89), but the bracket and arch wire effects were significant (P < .001). The pairwise differences between conventional and self-ligating stainless steel brackets and ceramic brackets with stainless steel slot were not significant. However, the conventional ceramic brackets generated significantly higher friction than the other brackets tested. Beta titanium arch wires produced higher frictional forces than nickel titanium arch wires, but no significant differences were found between each of the two and stainless steel arch wires. Attempts to identify differences in surface scratches of the arch wires produced by the different brackets were unsuccessful.

Are dental anomalies risk factors for apical root resorption in orthodontic patients?

Regression analyses suggest a weak prediction power of identified risk factors for apical root resorption in orthodontic patients, indicating the presence of etiologic or causative factors that have not yet been disclosed. To investigate the possible significance of dental anomalies as risk factors, pretreatment and posttreatment periapical radiographs of 84 patients with presence of at least one dental anomaly and of 84 patients without such anomalies were compared. The patients in the two groups were matched according to age, gender, Angle Class, extraction therapy, overbite, and treatment time. Apical root resorption was calculated by subtracting posttreatment tooth length measurements from the corresponding pretreatment measurements. Two sample t tests revealed no differences in mean root resorption between the patients in the two groups (P = .88). Stepwise regression analyses did not identify any of the individual anomalies as risk factors. In addition, patients with more than one anomaly did not appear to be at increased risk.

Relapse after orthodontic correction of maxillary median diastema: a follow-up evaluation of consecutive cases.

An evaluation of 96 treated orthodontic patients with maxillary median diastema ranging from 0.50 mm to 5.62 mm (mean 1.22, SD 0.85) was performed 4.0 to 9.0 years after completion of active treatment. Pre- and posttreatment data were gathered from available records. Follow-up data were gathered from records and interviews of 37 patients, and from phone interviews of 59 patients. The incidence of diastema relapse was 49% when scored as either presence of a measurable space at follow-up, a history of orthodontic or prosthetic retreatment to close a reopened space, or continued use of a retainer to control relapse tendency. Logistic regression analysis revealed that pretreatment diastema size and presence of a family member with a similar condition were the only significant risk factors for relapse (p<0.05), while pretreatment spacing in the maxillary anterior dentition approached significance (p = 0.10). No association was found between relapse and presence of an abnormal frenum or an osseous intermaxillary cleft, although patients with an abnormal frenum had a wider pretreatment diastema than those with a normal frenum (p<0.05). Fremitus of the maxillary incisors was the only parameter at follow-up associated with space reopening (p<0.01).

Associations between initial, posttreatment, and postretention alignment of maxillary anterior teeth.

Contradictory findings from studies on pretreatment malalignment as a risk factor for relapse of maxillary incisor alignment may be due to inappropriate sample selection and measurement technique. In an attempt to clarify the issue, 745 sets of study models made before (T1) and after (T2) orthodontic treatment and at long-term out of retention (T3) were screened. On the basis of the configuration of the maxillary anterior teeth on the T3 study models, three groups were established: one with significant spacing (group 1, n = 30); one with significant irregularity (group 2, n = 49); and one with perfect alignment (group 3, n = 28). The occlusal surfaces of the 321 maxillary study models at T1, T2, and T3 were photocopied and the tooth anatomic contact points digitized. An algorithm was used to fit the dental arch to the digitized points. Amount of incisor rotation and anatomic contact point displacement of the maxillary anterior teeth relative to the dental arch were computer generated. Interdental spaces in the maxillary anterior segment, as well as overjet and overbite, were measured manually. Nonstructural data were collected from the charts. Logistic regression analyses revealed that irregularity was associated with greater anatomic contact displacement and with greater incisor rotation both at T1 and T2 (P < 0.01). Similar analyses also revealed that spacing was associated with greater interdental spaces at T1 and T2 (P < 0.01). Correlation analyses revealed that the pattern of pretreatment rotational displacement has a strong tendency to repeat itself after retention (P < 0.001), as opposed to the pattern of contact point displacement and interdental spacing.

A 3-year follow-up study of various types of orthodontic canine-to-canine retainers.

The present study was performed to test the tendency for plaque and calculus build-up along the wire of different types of bonded orthodontic canine-to-canine retainers, whether the presence of such retainers causes any damage to the teeth involved, the failure rate of the retainers, and any changes in incisor alignment during a 3-year period of retention. The four test groups received either retainers made of thick plain wire bonded only to the canines (n = 11); thick spiral wire bonded only to the canines (n = 13); thin, flexible spiral wire bonded to each tooth (n = 11); or removable retainers (n = 14). Accumulation of plaque and calculus along the gingival margin, gingival inflammation and probing attachment level were scored in lingual areas from canine to canine at the time of fixed appliance removal and again 3 years after retainer insertion. Incisor irregularity was measured on plaster models made at the same time periods. Accumulation of plaque and calculus and development of caries along the wire were scored at follow-up. Retainer failures were recorded whenever they occurred. The results revealed no intergroup differences in changes between baseline and follow-up examinations or status along the retainer wire for any of the variables. Gingival inflammation and plaque accumulation were scored less frequently after 3 years in retention than at the time of debonding. No signs of caries were seen adjacent to the wire. Failures were observed of one, four and three of the fixed retainer types, respectively. These patients showed a greater increase in incisor irregularity than the other patients.

Reaction strains on the condylar neck during mastication and maximum muscle stimulation in different condylar positions: an experimental study in the miniature pig.

Most researchers agree that the primate temporomandibular joint (TMJ) is loaded compressively during function and that condylar position must play a role in mediating such loads. However, the precise nature of that role remains unclear. Using a pig model in this study, we attempted to analyze strain on the neck of the condyle during normal mastication and during simulated function in different condylar positions. Miniature three-element rosette strain gauges were bonded to the lateral surface of the condylar neck in 4 female miniature pigs (one per condyle). Measurements of strain were made during normal mastication and with the pigs under general anesthesia during maximum stimulation of the masseter and temporalis muscles in each of five condylar positions--centric occlusion, centric relation, anterior, relaxed and wide open--established through use of acrylic splints. Condylar position was evaluated by superimposition of lateral and dorsoventral cephalograms, with measurement of horizontal and vertical changes in location of implants placed on the zygomatic arch. As in primates, the TMJ was found to be load-bearing during mastication, with compressive strain oriented approximately perpendicular to the occlusal plane. In 3 pigs, strain was higher during balancing than during working function. During stimulation, the TMJ reaction strains were significantly lower with the condyles in the anterior position compared with the other positions, and the compressive strain was directed more anteriorly along the neck of the condyle in that position.

A post-treatment evaluation of multibonded ceramic brackets in orthodontics.

The purpose of this study was to perform a clinical evaluation of ceramic brackets with silane-coated bases for chemical (Transcend) and microcrystalline bases for mechanical (Transcend 2000) retention. The sample consisted of 49 consecutive patients; the first 30 were treated with brackets with chemical retention and the following 19 with brackets with mechanical retention. For each patient the brackets on one side of the mouth were assigned at random to be bonded with Concise and the other with Transbond as recommended by the manufacturers. Levelling and alignment of severely displaced roots was initiated with superelastic wires and completed with stainless steel wires. Any space closure or correction of interarch discrepancy was performed with rectangular stainless steel wires. The brackets with chemical retention were removed with a torsional rotation debonding wrench, and those with mechanical retention with a tensile debonding plier. The bond failure rate was low, with no difference between the two bracket types or between brackets bonded with Concise and Transbond. Bracket fracture was a significant clinical problem, both during active treatment and at the time of appliance removal. New teeth with formation of pronounced enamel cracks were seen in 20.6 and 10.5 per cent of the teeth treated with brackets with chemical and mechanical retention, respectively (P < 0.001), with no difference between teeth bonded with Concise and Transbond. Enamel tear-outs were seen in 3 of the 544 and in 1 of the 344 teeth treated with the respective types of bracket. These teeth were bonded with Concise.

Changes in condylar postition and occlusion associated with maxillary expansion for correction of functional unilateral posterior crossbite.

The purpose of this study was to confirm that correction of functional posterior crossbite through maxillary expansion is associated with a change in condylar position and occlusal relationships, and to determine whether maxillary expansion is associated with autonomous increase in mandibular arch width. Pretreatment and posttreatment study models of 61 patients ages 4.1 to 12.0 years (mean 8.5 years, SD 1.5) were available after maxillary expansion with a Quad Helix or a Haas expander for correction of a functional posterior crossbite. Pretreatment and posttreatment tomograms were available for 22 of the patients. Tomographic evaluation revealed that the condyles moved posteriorly and superiorly on the noncrossbite side from before to after treatment (p < 0.05). No differences were observed on the crossbite side. Superior joint space was greatest on the noncrossbite side before treatment, whereas, conversely, it was greatest on the crossbite side after treatment (p < 0.05). Relative condylar position was more anterior on the noncrossbite side before treatment (p < 0.05), but similar on both sides after treatment. Molar and canine relationships were more Class II on the crossbite side before treatment (p < 0.01 and < 0.05, respectively) and similar on both sides after treatment. A significant reduction in midline deviation was seen from before to after treatment (p < 0.001). A small, but significant autonomous increase in mandibular intermolar width (p < 0.001) occurred concomitant with the maxillary expansion.

Alveolar bone loss of maxillary anterior teeth in adult orthodontic patients.

The purpose of this study was to evaluate prevalence and severity of alveolar bone loss in adult orthodontic patients, and to identify risk factors for such bone loss. Standardized periapical radiographs of maxillary anterior teeth and cephalograms made before (T-1) and after (T-2) treatment and treatment charts of 343 adults aged 20.0 to 70.1 years (mean 34.5, SD 9.0) before treatment, representing groups of consecutively treated patients from four orthodontic practices, were examined. Alveolar bone loss was calculated by subtracting the distance from the cementoenamel junction (CEJ) to the alveolar crest (AC) at each interproximal tooth surface from the mesial of one maxillary canine to the mesial of the other. Changes in bone level were calculated by subtracting the distance CEJ-AC at T-1 from the corresponding distance at T-2. Tooth movement was calculated from measurements of superimposed tracings of pretreatment and posttreatment cephalograms. Hygiene level was scored subjectively as adequate or inadequate on the basis of gingival appearance on posttreatment intraoral color slides. Sample means of averaged bone loss of all six anterior teeth and of the surface with the most severe bone loss per patient were 0.54 mm (SD 0.62) and 1.82 mm (SD 1.01), respectively. Only 2.5% of the patients had averaged bone loss of > or = 2 mm, whereas 36% of the patients had one or more surfaces with bone loss of > or = 2 mm. Multiple linear regression analyses revealed a positive relationship between age and bone loss, and a negative relationship between initial bone level and subsequent bone loss. No association was found between bone loss and length of treatment, posttreatment gingival appearance, amount of horizontal or vertical tooth movement, or treatment with maxillary osteotomy.

Risk of pulp damage due to temperature increase during thermodebonding of ceramic brackets.

The purpose of this study was to perform in vitro measurements of the temperature increase at the enamel-dentine interface during electrothermal removal of ceramic brackets, and to analyse, in vivo, whether signs of pulp damage can be observed 4 weeks after the procedure. In vitro study: a total of 29 caries-free human teeth were cut into buccal and lingual halves. The buccal halves were bonded with ceramic brackets, and miniature thermocouples were placed from the pulpal side into holes drilled to the enamel-dentine interface under the centre of the bracket slot. From the onset of thermodebonding, the temperature increase relative to room temperature was recorded for a period of 43 seconds. The maximum temperature increase at the enamel-dentine interface was 6.9 degrees C. In vivo study: a total of 12 human premolars scheduled for extraction for orthodontic reasons were bonded with ceramic brackets. Electrothermal debonding was performed the following day. After 4 weeks, the teeth were extracted and prepared for histological examination. Following demineralization, sections were prepared for light microscopic examination. No signs of pulpal inflammation were observed.

Long-term stability of mandibular incisors following successful treatment of Class II, Division 1, malocclusions.

The purpose of this study was to evaluate the long-term stability of mandibular anterior alignment in a large group of Class II, Division 1, patients who demonstrated successful occlusal results at the end of active treatment. The specific aim was to search for predictors of relapse and associations between relapse and other post-retention changes. The sample of 78 adolescents was limited to successfully treated cases as judged by subjective evaluation of intercuspation and incisor occlusion of posttreatment study models. Neither cephalometric characteristics nor post-retention occlusion were considered in sample selection. Of these patients, study models and cephalograms were available pretreatment, at the end of active treatment, and a mean of 14 years post-retention. The results demonstrated an increase of incisor irregularity and a reduction of intercanine width and arch length post-retention. At post-retention, 9.0% had irregularity index values of 6.5 mm or more and 47.4% had values equal to 3.5 mm or less. Stepwise backward multiple regression analyses revealed that narrow pretreatment intercanine width and high pretreatment incisor irregularity were significant predictors of relapse. Treatment increase of intercanine width and post-retention decrease of intercanine width and arch length were associated with relapse.

Changes following the use of protraction headgear for early correction of Class III malocclusion.

The purpose of this study was to evaluate treatment effects and posttreatment changes following the application of elastic forces from a facemask to the dentition for the early correction of Class III malocclusion. Cephalograms made before and after treatment and at a minimum of 1 year follow-up (mean 3.57 years, S.D. 2.07) of 16 patients were compared with those of 13 untreated matched controls. Pretreatment age ranged from 4.58 to 8.25 years (mean 6.80 years, S.D. 1.13), and mean active treatment time was 0.61 years (S.D. 0.15). Available study models at the three time periods were also analyzed. Treatment resulted in a significant improvement in the maxillomandibular relationship and overjet (P < 0.001). The major treatment effect was a downward and backward movement of the mandible and retroclination of the mandibular incisors. However, any skeletal and dentoalveolar advancement of the maxilla contributed to the clinically significant improvement. No differences were observed between the patients and the controls during the posttreatment follow-up. Despite some relapse, the patients demonstrated a net improvement in maxillomandibular relationship and overjet at the end of follow-up relative to the controls. Overcorrection of the overjet during treatment may be important for maintaining a successful correction.

A postretention study of patients presenting with a maxillary median diastema.

The purpose of this study was to assess postretention stability of maxillary midline diastema closure, to search for predictors of relapse, and to test for associations between relapse and other postretention changes. The sample consisted of 35 patients with pretreatment diastemas ranging from 0.9 mm to 3.0 mm (mean 1.4, SD = 0.5) following eruption of the maxillary canines. Data were gathered from treatment charts, study models, periapical radiographs, and cephalograms taken pretreatment, posttreatment, and 1 to 26 years postretention (mean 11.4, SD = 6.4). Measurable diastema relapse was observed in only 12 cases. The majority of the relapse was 0.6 mm or less, and maximum relapse was 3.0 mm. Abnormal frenums and/or intermaxillary osseous clefts did not appear to be risk factors for relapse, and no pretreatment predictors of relapse could be established. The only posttreatment change associated with diastema relapse was proclination of the maxillary incisors (p < 0.01).

Effects of Le Fort I osteotomy on human gingival and pulpal circulation.

The maxillary blood flow during the first 24 h following Le Fort I osteotomy was evaluated by laser Doppler flowmetry. Pulpal blood flow was recorded from two maxillary incisors and gingival blood flow was assessed from a site slightly apical to the interdental papilla of the maxillary central incisors of 12 patients receiving Le Fort I osteotomy, nine control patients receiving mandibular osteotomy, and 10 nonsurgical control subjects without orthodontic appliances. Measurements were made before surgery and at time intervals between 0-8, 8-16, and 16-24 h after surgery. The nonsurgical controls were tested at similar intervals. Gingival and pulpal blood-flow measurements did not change over time in the nonsurgical control group. Presurgical blood-flow values did not differ between the two surgical groups. Following surgery, mean gingival (but not pulpal) blood flow was significantly lower for patients treated with Le Fort I osteotomy than for patients treated with mandibular osteotomy. Follow-up examinations revealed that one patient receiving Le Fort I osteotomy experienced loss of gingiva and bone around both central incisors. This patient had one of the largest reductions in gingival blood flow.

Risk factors for apical root resorption of maxillary anterior teeth in adult orthodontic patients.

The purpose of this study was to identify risk factors for apical root resorption in adult orthodontic patients. Standardized periapical radiographs of maxillary anterior teeth and cephalograms made before and after treatment and treatment charts of 343 adults, representing groups of consecutively treated patients from four orthodontic practices, were examined. Apical root resorption was calculated by subtracting posttreatment tooth length measurements from the corresponding pretreatment measurements. Root width was measured from the mesial to the distal outline of the roots 4 mm from the apex. Root form was scored subjectively as normal, pointed, eroded, blunt, bent, and bottle shaped. Root movement was calculated from measurements of superimposed tracings of pretreatment and posttreatment cephalograms. Proximity of the central incisor roots to the palatal cortical bone was scored subjectively as present or absent. Severity of initial malocclusion and treatment variables were collected from the charts. Multiple linear regression analyses revealed that amount of root movement, long roots, narrow roots, abnormal root shape, and use of Class II elastics were significant risk factors. However, the statistical model had a low explained variance, strongly suggesting a weak prediction power. No association was found between type of initial malocclusion, treatment time, use of rectangular arch wires, proximity of the root to the palate or treatment with maxillary osteotomy, and root resorption. Endodontic treatment was a preventive factor.