Long-term stability of posterior crossbite correction, treated in the mixed or permanent dentition of growing children: A systematic review and meta-analysis.

When treating posterior crossbite, the primary goal is to achieve long-term crossbite correction. The majority of studies however focus on relapse of the increase in the transverse dimension, but not relapse of the crossbite itself, which is an essential outcome. The aim of the present study was to determine long-term stability (2 years minimum post-treatment) of posterior crossbite correction, treated in mixed or early permanent dentitions of growing children. Following registration in PROSPERO (CRD42022348858), an electronic literature search including PubMed, Embase, Web of Science, the Cochrane Library, and a manual search were conducted up to January 2023, to identify longitudinal studies looking into the long-term stability of crossbite correction in growing children. Data extraction and risk of bias assessment were carried out, and subsequently, a random-effects meta-analyses models were used to calculate estimates for relapse of the crossbite and relapse at the transverse level. Twenty-two studies were included, of varying designs and quality, representing 1076 treated patients, with different expansion appliances and protocols. Meta-analysis results showed that 19.5% (95% CI: 15%; 25%) of patients present with relapse of posterior crossbite at long-term follow-up. At the transverse level, 19.3% of the total expansion (including overexpansion) relapsed (95% CI: 13%; 27%) regardless of whether there a was relapse of the crossbite itself. Data from existing studies, with a moderate level of evidence, indicate that the long-term stability of posterior crossbite correction in growing children is unfavourable in roughly 1 in 5 growing children, with crossbite relapse long-term. On average, 19% of the maxillary expansion performed (including overexpansion) relapses long-term, which may occur in cases with or without relapse of the crossbite.

Headgear therapy in children with Class II malocclusion and the role of compliance on treatment outcome: A nine-month randomized controlled trial.

OBJECTIVES: To evaluate three-dimensional movements of maxillary teeth during headgear treatment in Class II growing children, using digital analytical tools, and to determine the effects of compliance on these movements. MATERIALS AND METHODS: A 9-month parallel-group randomized controlled trial was carried out on 40 children with Class II malocclusion, aged 8-12 years, half assigned to receive a cervical headgear and half to a no-treatment group, using block randomization. Subjects in the treatment group were instructed to wear the headgear for 12 hours daily and monitored using an electronic module. After 9 months, the following dental outcomes were measured: first maxillary molar distalisation, rotation, tip and torque, arch depth, and interpremolar and intermolar distances. Caregivers and participants were not blinded to group assignments, but those assessing outcomes were. Linear regression models were used to detect differences between groups and correlation coefficients to find correlations between compliance and dental outcomes. RESULTS: All 40 included patients were analysed. A significant difference in molar distalisation was observed between the treatment (1.2 mm) and control groups (-0.2 mm). Arch depth change was also increased to a larger extent in the treatment groups (1.3 mm vs 0.1 mm), as was the interpremolar distance (1.9 mm vs 0.4 mm). In contrast, no significant differences in molar rotation or torque change were observed. With regard to compliance, average compliance was 55%. A significant correlation was found between molar distalisation and compliance in the treatment group. CONCLUSIONS: Headgear therapy has significant effects on molar distalisation, arch depth, and arch width. Compliance has a significant positive effect on molar distalisation.

Effects of age and diet consistency on the expression of myosin heavy-chain isoforms on jaw-closing and jaw-opening muscles in a rat model.

BACKGROUND: Skeletal craniofacial morphology can be influenced by changes in masticatory muscle function, which may also change the functional profile of the muscles. OBJECTIVES: To investigate the effects of age and functional demands on the expression of Myosin Heavy-Chain (MyHC) isoforms in representative jaw-closing and jaw-opening muscles, namely the masseter and digastric muscles respectively. METHODS: Eighty-four male Wistar rats were divided into four age groups, namely an immature (n = 12; 4-week-old), early adult (n = 24; 16-week-old), adult (n = 24; 26-week-old) and mature adult (n = 24; 38-week-old) group. The three adult groups were divided into two subgroups each based on diet consistency; a control group fed a standard (hard) diet, and an experimental group fed a soft diet. Rats were sacrificed, and masseter and digastric muscles dissected. Real-time quantitative polymerase chain reaction was used to compare the mRNA transcripts of the MyHC isoforms-Myh7 (MyHC-I), Myh2 (MyHC-IIa), Myh4 (MyHC-IIb) and Myh1 (MyHC-IIx)-of deep masseter and digastric muscles. RESULTS: In the masseter muscle, hypofunction increases Myh1 (26, 38 weeks; p < .0001) but decreases Myh4 (26 weeks; p = .046) and Myh2 (26 weeks; p < .0001) expression in adult rats. In the digastric muscle, hypofunction increases Myh1 expression in the mature adult rats (38 weeks; p < .0001), while Myh2 expression decreases in adult rats (26 weeks; p = .021) as does Myh4 (26 weeks; p = .001). Myh7 expression is increased in the digastric muscle of mature adult rats subjected to hypofunction (38 weeks; p = <.0001), while it is very weakly expressed in the masseter. CONCLUSION: In jaw-opening and jaw-closing muscles, differences in myosin expression between hard- and soft-diet-fed rats become evident in adulthood, suggesting that long-term alteration of jaw function is associated with changes in the expression of MyHC isoforms and potential fibre remodelling. This may give insight into the role of function on masticatory muscles and the resultant craniofacial morphology.

Mandibular condyle changes in rats with unilateral masticatory function.

OBJECTIVE: Certain malocclusions or unilateral tooth loss can lead to asymmetric functional load of the two mandibular sides during mastication and induce skeletal asymmetries to the condylar process of growing individuals. However, in adults, asymmetric function may have a different impact. The aim of the present study was to investigate three-dimensionally the effects of unilateral masticatory function on the condylar process morphology in growing and adult rats and the adaptive processes to differential condylar loading. MATERIALS AND METHODS: Fifty-six growing and adult Wistar rats aged 4 and 26 weeks respectively were obtained. The maxillary right molars of the experimental animals were extracted and all animals were followed for 12 weeks. Three-dimensional images were obtained by an in-vivo microcomputed tomography (micro-CT) examination. The following measurements were studied: condylar process height, condylar base width, and condylar cross-sectional surface. RESULTS: While no differences were found with regards to condylar process height and base width, the cross-section of the condyle on the extraction side did not increase during growth in the young rats. No such differences were found in adults. Young rats had statistically significantly shorter condylar height, base width and cross-sectional surface than the adult rats and showed significant growth of these structures during the experimental period. CONCLUSION: Condylar height and base width growth are not hindered by reduced occlusal function, contrary to the average cross-sectional surface, which implies that the condyle form of growing individuals becomes thinner while maintaining its length, in the absence of occlusal stimuli. The condyle of adult rats with extractions is less affected by occlusion changes.

Longitudinal changes of the insertion of the maxillary labial frenum in children and adolescents undergoing orthodontic treatment.

INTRODUCTION: This study aimed to evaluate potential vertical changes in the position of the maxillary labial frenum (MLF) insertion in growing children and to compare these changes to the vertical growth of the dentoalveolar process and lower facial third. METHODS: This retrospective longitudinal study investigated records of 33 healthy children. Dental casts, lateral cephalograms, and photographs were evaluated at pretreatment (T0), posttreatment (T1), and 3-5 years into retention (T2). To evaluate the vertical changes of MLF insertion in relation to the vertical growth of the dentoalveolar process, the palatal plane (PP) was used as a reference. These changes were also compared between different MLF typologies (ascribed as thin or fibrous). RESULTS: The distance from MLF to PP only slightly increased from T0 to T2 by 0.6 ± 0.5 mm (P <0.001), whereas the distance between the incisal edge and PP increased significantly from T0 to T2 by 2.6 ± 0.8 mm (P <0.001). A positive correlation was found (r = 0.94; P <0.001) between the changes from the incisal edge to the PP and the MLF to the incisal edge between T0 and T2. No correlation was found between the change from the incisal edge to the PP and MLF to PP between T0 and T2. Thin MLF types showed a larger increase in distance from their insertion to the incisal edge (2.6 ± 0.8 mm) than thick MLF types (1.8 ± 0.7; P <0.03). CONCLUSIONS: The MLF remains stable compared with the PP, whereas the maxillary incisal edge moves away from the PP, indicating increased vertical growth of the alveolar process. Dentists should be aware of those changes before performing interventions such as unnecessary frenectomies.

Spontaneous correction and new development of posterior crossbite from the deciduous to the mixed dentition.

AIM: To determine (a) the prevalence of spontaneous correction of posterior crossbites from the deciduous to the mixed dentition and (b) the development of new posterior crossbite cases during the eruption of the first permanent molars, in orthodontically untreated children. MATERIALS AND METHODS: A cohort of pupils aged 4-12 years participated in annual dental screenings, from 2001 to 2019. Data were collected prospectively but examined retrospectively. Children were selected who had been initially screened in their deciduous dentition and on at least one consecutive year, presenting with a posterior crossbite in the deciduous or mixed dentition. Those with a posterior crossbite in the deciduous dentition were evaluated to see whether the crossbite persisted in the mixed dentition, and vice versa. RESULTS: Of the 2571 children participating in the annual dental screenings, 1076 children were in the deciduous dentition at their first screening appointment, with 693 having attended at least two screening appointments. Of these 693 children, 70 had a posterior crossbite in the deciduous dentition (10.1%). The crossbite persisted in the mixed dentition in only 16 out of these 70 children. Twenty-six out of the 623 children who did not have a posterior crossbite in the deciduous dentition developed one in the mixed dentition. LIMITATIONS: The retrospective data collection, multiple examiners carrying out the dental screenings, and the absence of data on para-functions and oral habits were some of the limitations of the present study. CONCLUSIONS: In the present sample, 1 in 10 children have a posterior crossbite in the deciduous dentition, which is however autocorrected in about three-quarters of cases. On the other hand, 4% of children developed a new crossbite in the mixed dentition. It may thus be reasonable in cases with posterior crossbite in the deciduous dentition to wait for the first permanent molars to erupt before initiating treatment.

Evaluation of natural head position over five minutes: A comparison between an instantaneous and a five-minute analysis with an inertial measurement unit.

BACKGROUND: Head posture is a balance of several positions and therefore shows inherent variation. Most methods available to quantify this are however instantaneous, not providing information about its variation over time. A dynamic recording of head posture would thus be beneficial. OBJECTIVES: The purpose of this study was to evaluate the variation in natural head position (NHP) over 5 min using an inertial measurement unit (IMU). METHODS: Fifteen healthy young volunteers were asked to sit on a chair and keep their head in the self-balanced position for 5 min. A mirror was then revealed in front of them, and they were asked to look at their eyes for 20 s. This procedure was undertaken on two separate occasions with a one-week interval. This was compared to an instantaneous measurement of head position at a specific time point corresponding to the 15th second of the recording. RESULTS: During the 5 min of recording, the participants tended to elevate their head progressively by a mean of 1.5°, which is then corrected by looking at oneself in the mirror. Most participants tended to rotate their head to the left and continued that progressive rotation despite looking in the mirror. The roll axis had no systematic changes observed between the self-balanced position and the mirror-guided position and was the most reproducible axis. Moderate to good correlations were found comparing both sessions for each axis. CONCLUSION: The comparison between the five-minute analysis and the instantaneous measurement showed a systematic difference on the pitch axis but no differences for the yaw and roll. These results suggest that the variation in the NHP during a period of 5 min is generally specific to each participant with a head elevation and rotation to the left in most cases.

Effect of masseter muscle mass on the rate of experimental tooth movement in rats.

BACKGROUND: Previous clinical observational studies have suggested that orthodontic tooth movement (OTM) is related, at least partly, to the mass and/or capabilities of the masticatory muscles. OBJECTIVES: Our study aimed to examine the influence of masticatory muscle mass on the OTM in an animal experimental model in which the masseter muscle was modulated by botulinum neurotoxin type A (BTX) injection. METHODS: Eighteen Wistar rats were equally divided into two groups: BTX injection and control. BTX was injected bilaterally into the masseter muscles. Three days after the injection, the maxillary left first molars were orthodontically moved for 14 days. At the end of the experiment, micro-computed tomography was performed to evaluate the rate of OTM and bone morphometry. The masseter muscles were weighed and prepared for histological analyses. RESULTS: The masseter muscle mass in the BTX group was less than that in the control group, and histological findings showed atrophy of muscle fibres. The rate of OTM was significantly higher in the BTX group than in the control group. Furthermore, a negative correlation was detected between masseter muscle mass and OTM in the BTX group. Bone morphometry showed no difference between the control and BTX groups. CONCLUSION: Decreased masseter muscle mass was found to be closely related to an increase in the rate of OTM in rats using BTX injection to modify the masseter muscle mass. Masseter muscle mass could be a predictive factor for OTM in rats injected with BTX.

Airway changes after fixed functional appliance treatment in children with and without morphologic deviations of the upper spine: A 3-dimensional CBCT study.

INTRODUCTION: Functional appliances (FA) have a positive effect on the upper airway volume and minimal cross-sectional area (MCA) in children. An association between morphologic deviations of the upper spine (MDUS) and reduced treatment response was found in appliances used to treat adults with obstructive sleep apnea. This study aimed to: (1) compare airway changes after FA treatment in children with and without MDUS and controls; (2) identify if MDUS causes a smaller upper airway. METHODS: Pretreatment and posttreatment cone-beam computed tomography scans were included from 21 children with MDUS and 42 without MDUS treated with a fixed FA, along with a pair-matched control group (matched for chronological age, skeletal age, gender, and mandibular inclination) who received orthodontic treatment for minor malocclusions without an FA. The influence of MDUS on changes in upper airway volume and MCA were evaluated with 3-dimensional cone-beam computed tomography scans using standardized, previously validated methods and mixed-effects linear regression. RESULTS: There was a significantly increased volume and MCA in the FA groups with and without MDUS compared with control (P = 0.003 and P = 0.049) and in the FA group without MDUS compared with the MDUS group (P = 0.008 and P = 0.011) after treatment. There was no significant pretreatment difference in airway dimensions between the MDUS and non-MDUS FA groups. CONCLUSIONS: The airway response with fixed FA is significantly reduced in MDUS children. MDUS caused no significant pretreatment airway differences in children. However, MDUS may be important in predicting airway changes in FA treatment.

Indirect vs direct bonding of mandibular fixed retainers in orthodontic patients: Comparison of retainer failures and posttreatment stability. A 5-year follow-up of a single-center randomized controlled trial.

INTRODUCTION: This 2-arm parallel trial aimed to assess the number of failures of mandibular fixed retainers bonded with direct and indirect bonding methods at a 5-year follow-up and investigate the stability of intercanine and interpremolar distances. METHODS: Consecutive patients from the clinic of the University of Geneva (Switzerland) were randomly allocated to either direct or indirect bonding of a mandibular fixed retainer at the end of orthodontic treatment. Inclusion criteria included the presence of all mandibular incisors and canines; and the absence of active caries, restorations, fractures, or periodontal disease of these teeth. The patients were randomized in blocks of 4 using an online randomization service, with allocation concealment secured by contacting the sequence generator for assignment. Two and 5 years (T5) after bonding the retainers, the patients were recalled, and impressions were taken. The primary outcome was the 5-year survival of the mandibular fixed retainer bonded with both bonding methods. The secondary outcomes were the intercanine and interpremolar distances and the assessment of unexpected posttreatment changes (ie, changes in torque and/or rotations of the mandibular incisors and canines). Blinding was applicable for outcome assessment only. Kaplan-Meier curves were generated, and a Cox proportional hazard regression model was fitted for bonding type, age, and treatment. Linear mixed models were fitted to intercanine and interpremolar distances: bonding type, time, age, and treatment were modeled as outcomes. RESULTS: Sixty-four patients were randomized in a 1:1 ratio. At T5, 6 patients without previous failure were lost to follow-up from each group. At T5, the fixed retainer was debonded in 14 patients (54%) for each group. The hazard ratio of indirect bonding to direct bonding was 1.09 (95% confidence interval, 0.26-4.60; P = 0.91); there was no statistically significant difference in survival between the groups. Regarding intercanine and interpremolar distances, none of the tested prognostic factors reached statistical significance. Unexpected posttreatment changes were observed in 6 failure-free patients, all bonded with the direct bonding method. Only 1 patient required debonding of the fixed retainer. No other serious harms were observed. CONCLUSIONS: The 5-year survival rate for both direct and indirect bonding methods was 46%, without a statistically significant difference between bonding methods. Bonded retainers were effective in maintaining intercanine and interpremolar distances. Unexpected posttreatment changes were only observed with retainers bonded with the direct bonding method. REGISTRATION: The trial was not registered. PROTOCOL: The protocol was not published before trial commencement. FUNDING: No funding or conflict of interest to be declared.

Measuring the difference in natural head position between the standing and sitting positions using an inertial measurement unit.

AIMS: The purpose of this study was to compare the natural head position (NHP) in the sitting position to the NHP in a standing position using inertial measurement unit (IMU) and lateral photographs. MATIERIALS & METHODS: Twenty healthy young adult volunteers were asked to look at a mirror located at 1 metre in front of their eyes while being recorded with the IMU system. Lateral photographs were also taken. This procedure was undertaken for the standing and sitting positions, on two separate occasions within a one-week interval. RESULTS: A strong correlation was found between the IMU system and the lateral photographs (r > .99) with regard to the pitch axis, the absolute mean difference was 0.4 ± 0.5 (p = .99) for both standing and sitting positions. We found that in the sitting position the head was elevated by 2.5 ± 2.4 (p < .05) more than in the standing position, but no significant differences were observed for the other two axes (roll and yaw). CONCLUSION: The IMU system is comparable to lateral photographs for pitch assessment. Except for a slight elevation of the head in the sitting position, no clinical differences were observed for the NHP when comparing the standing and sitting positions.

Does age influence self-perception of the soft-tissue profile in children?

INTRODUCTION: Appreciation of the soft-tissue profile is important in orthodontic diagnosis and treatment. However, are the patients themselves aware of their profile appearance? We aimed to evaluate if age influences self-perception of the soft-tissue profile in children. METHODS: The study population for this prospective cross-sectional investigation consisted of 3 groups of 60 patients, classified according to age (<12 years; 12-15 years; >15 years). Each subject's right-sided facial profile was photographed to obtain a silhouette. Facial profile silhouette templates were created to represent the local population. Each subject's photograph was inserted into the corresponding template, and the subjects were asked to identify themselves. Facial profile self-recognition was recorded as a binary variable (yes or no). Other recorded variables included age, sex, and sexual maturity rating (using Tanner staging). Chi-square tests were used to analyze facial profile self-recognition between different subgroups, and stepwise multiple regression was used to predict the probabilities of facial profile self-recognition, with age, sexual maturity rating, and other recorded variables as independent variables. RESULTS: Eighty percent of subjects aged >15 years recognized their own profile, compared with only 55% and 50% of subjects aged 12-15 years and <12 years, respectively. Subjects aged >15 years were significantly more likely to recognize their profile than younger subjects (P = 0.001). Similarly, subjects with the most advanced sexual maturity rating (stage V) were significantly more likely to recognize their profile (85% self-recognition) than those in groups I-IV (P <0.001). Girls were more likely to recognize their profiles than boys (P = 0.028). When using multiple regression analysis, sexual maturity rating appears to be the only significant predictor for facial profile self-recognition (R2 = 0.25; P <0.001). CONCLUSIONS: Facial profile self-recognition seems to improve with age and sexual maturity (sexual maturity rating stage V). Because orthodontic treatment planning takes possible soft-tissue changes into account, it is important to evaluate the degree of self-perception of the patients to adapt our goals and treatment discussions.

Prevalence, distribution, and age at clinical detection of missing permanent incisors.

OBJECTIVES: To determine the prevalence and distribution of clinically missing permanent incisors, and the age at which they are detected, in school-aged children. METHODS: A total of 2573 children aged 4-13 underwent oral health screening on at least one occasion between 2001 and 2017. In order to define a threshold age, after which permanent incisor agenesis could be suspected clinically with reasonable certainty, children who had been seen for at least three consecutive years, with any clinically missing permanent incisor were selected (n = 19). The maximum age of detection among these children was chosen as the threshold age. Based on this, a total of 766 children at or above the threshold age were screened for a cross-sectional epidemiological survey. Chi-squared tests were used to compare the prevalence of clinically missing permanent incisors among boys and girls, comparing unilateral versus bilateral, and right- versus left-sided missing teeth. RESULTS: Roughly 2% of the sample presented with at least one clinically missing maxillary lateral incisor. This was bilateral in half of cases. Clinically missing mandibular incisors were found in 0.5% of children. Finally, the threshold age for clinical suspicion of maxillary lateral incisor agenesis was set at 11.5 years. Agenesis was confirmed in all of the children attending a follow-up radiographic visit. CONCLUSIONS: Approximately 1 in 50 children present with a clinically missing maxillary lateral incisor. The age at suspicion of maxillary lateral incisor agenesis can sometimes be several years after its expected eruption, perhaps due to significant variation in eruption times.

Perception of pain in Class II malocclusion children treated with cervical headgear: a randomized controlled trial.

OBJECTIVES: The aims of this study were: 1. to evaluate the experience of pain perceived by children during separator placement and headgear wear; 2. to find possible associations between the perceived intensity of pain and the levels of Substance P (SP) and interleukin-1 beta (IL-1ß) in the gingival crevicular fluid (GCF) during these procedures; 3. to identify other factors, such as previous pain experience, which could be associated to the patients' perceived discomfort or pain during treatment. TRIAL DESIGN: Nine-month parallel-group randomized controlled trial. METHODS: Forty Class II malocclusion children (8-12 years) were included, half of which received a cervical headgear while the other half did not receive any treatment during the study period. Baseline pain data were recorded including previous experience to general and dental pain, Corah's Dental Anxiety Scale, and baseline pain using a visual analogue scale (VAS). Elastic separators were placed in children for 1 week, followed by molar band and cervical headgear placement. Children were seen at various time points throughout the 9-month period where at each appointment, a VAS assessment of pain as well as GCF sampling was carried out to quantify the levels of SP and IL-1ß. Multiple regression analysis was performed to ascertain the influence of factors including sex, age, time, headgear wear, and baseline pain data on pain severity. RESULTS: Pain severity and SP and IL-1ß levels in the GCF follow a similar pattern, with peaks being observed 1 day after orthodontic elastic separator placement. Pain was more severe after the placement of orthodontic separators than following cervical headgear wear. With regard to pain predictors, pain is more severe in older children, those with a worse previous general pain experience, and those with higher levels of IL-1ß, particularly after elastic separator placement. CONCLUSIONS: Orthodontic pain and discomfort following orthodontic separator placement and cervical headgear wear depends on factors including age, previous pain experience, and the level of IL-1ß in the GCF.

Occlusal traits and longitudinal dental changes in children and adolescents with congenital or childhood onset myotonic dystrophy.

BACKGROUND/OBJECTIVES: This research aimed to study the malocclusions of children and adolescents with myotonic dystrophy type 1 (DM1), in respect to healthy individuals, and trace the occlusal changes that occurred in these individuals during growth. MATERIALS/METHODS: Thirty-six dental casts, from children and adolescents with DM1 living in western and southern Sweden, were compared with a control group of 50 healthy individuals. To identify potential changes in occlusal traits, 26 casts were assessed and followed-up over a median time of 9 years. Independent samples t-tests were used to compare the two groups and their changes over time. Paired samples t-tests tested changes over time within each group (P < 0.05). RESULTS: DM1 patients had a higher prevalence of anterior open bite, posterior crossbite, and Class III malocclusions. When compared to controls, patients presented smaller upper and lower intermolar as well as intercanine widths. In both groups, the individuals revealed longitudinal changes with a decrease in both upper and lower arch lengths and an increase on the palatal vault height. During the follow-up period, the prevalence of malocclusions remained almost the same, only significantly differing regarding the changes that occurred between groups referred to the upper intermolar width, which decreased among DM1 patients. CONCLUSIONS/IMPLICATIONS: In comparison to healthy controls, children and adolescents with DM1 have shown already at an early age a higher prevalence of both anterior open bite and posterior crossbite. These occlusal traits did not change with time apart from the upper narrow intermolar width, which further decreased with time.

Spontaneous eruption of impacted maxillary incisors after surgical extraction of supernumerary teeth: a systematic review and meta-analysis.

OBJECTIVES: To evaluate the spontaneous eruption potential of impacted human permanent teeth localized in the anterior part of the maxilla, after the surgical extraction of obstacles in their eruption pathway, by means of a systematic review and meta-analysis. MATERIALS AND METHODS: A systematic literature search was carried out to locate studies reporting on the percentage of anterior permanent teeth erupting after surgical removal of the obstacle, without other interventions. Eruption potential of impacted teeth was calculated using a random-effects meta-analysis. Information about the sex proportion, follow-up duration, age and years during which the study was carried out was used for subgroup analyses. RESULTS: A total of twelve studies were included, with a total sample size of 960 cases and a follow-up period of up to 36 months. The results show that more than 65.5% of impacted teeth erupt spontaneously following surgical extraction of the obstacle, with an odds ratio of 4 (95% CI 1.9, 8.2) (p < 0.001) favouring spontaneous eruption. CONCLUSIONS: When faced with an impacted maxillary anterior tooth, surgical extraction of the obstacle can lead to spontaneous eruption of the impacted tooth in the majority of cases, with better success with a longer follow-up for up to 3 years. CLINICAL RELEVANCE: Based on the present meta-analysis, clinical recommendation would be to surgically remove the obstacle impeding the eruption of a maxillary anterior permanent tooth and wait for the eruption of the tooth for a period of 12-36 months, depending on the age of the patient.

The effect of retraining hypofunctional jaw muscles on the transverse skull dimensions of adult rats.

OBJECTIVE: To experimentally investigate the effects of increased masticatory muscle function on the transverse cranial dimensions on adult rats with an earlier reduced masticatory muscle function. MATERIAL AND METHOD: Sixty young male rats were used. The experimental group received soft diet for a prolonged period, so that the animals developed weak masticatory muscles. A control group received ordinary hard food during the whole experimental period (27 weeks). After 21 weeks when the animals had nearly ceased their body growth the rats in the experimental group were divided into two groups. One group continued with soft diet until the end of the experiment (hypofunctional group). The other group received ordinary hard food to get the possibility to retrain their masticatory muscles (rehabilitation group). At week 21 and at the end of the experimental period (week 27), axial cephalograms were taken. Fourteen landmarks were defined to measure seven transverse distances of the skull. RESULTS: The increase of the anterior zygomatic arch width and interzygomatic width during the experimental period were larger in the rehabilitation group compared to both the normal and the hypofunctional group. CONCLUSION: Retraining of masticatory muscles in adult rats leads to increase of some transverse cranial dimensions.

Class II functional appliance treatment and dynamic three-dimensional mimic muscle evaluation.

BACKGROUND: Functional appliances have skeletal and dentoalveolar treatment effects, but knowledge on their effect on facial expressions is limited. OBJECTIVE: To analyse changes in facial expressions, using three-dimensional (3D) mimic muscle evaluation, in growing children with Class II malocclusion and large overjet, undergoing functional appliance treatment. METHODS: Fifteen growing children with Class II division 1 malocclusion, selected prospectively, had dynamic 3D recordings of facial expressions prior to and 12 months after commencing functional appliance treatment. Facial expressions recorded were smile and lip pucker, and the movements of the oral commissures were analysed, as well as mouth width and its symmetry. A control group of fifteen age- and sex-matched growing children without immediate need for orthodontic treatment had similar recordings prior to and after a 12-month observation period. RESULTS: In the treatment group, the Class II malocclusion in all children improved after 12 months of functional appliance wear. With regard to movements of the oral commissures, the initial recordings of the treatment group did not show any significant differences to the control group for neither smile nor lip pucker. Differences were noted however when looking at mouth width asymmetry, where this tended to become more symmetrical in the functional appliance treatment group, during rest and during smiling, while it became more asymmetrical in the untreated control group. CONCLUSION: The use of removable functional appliances in children with Class II division 1 malocclusion may have a positive effect on mouth width symmetry when smiling, making it more symmetrical.

Changes in facial expressions following functional orthopaedic treatment for Class II division 1 malocclusion: a prospective controlled study.

OBJECTIVE: The aim of this study was to quantify changes in facial expressions in children with Class II division 1 malocclusion treated with functional appliances. MATERIALS AND METHODS: A prospective controlled study was carried out evaluating 20 children with Class II division 1 malocclusion (ages 9-13) treated with a functional appliance for 12 months (treatment group). Age- and gender-matched children without immediate orthodontic treatment need were followed up without treatment for 12 months (control group). A frame-mode video sequence was taken of each subject at the beginning and end of the 12-month study period, during which 5 distinct facial expressions (posed smile, spontaneous smile, aggressive smile, lip pucker, and maximal mouth opening) were recorded. Frames at which each facial expression was at its peak were analysed. Changes in horizontal and vertical facial anthropometric distances brought about by performing each facial expression were measured. Intragroup differences following treatment were assessed using paired t-tests, whereas intergroup differences were assessed using unpaired t-tests. RESULTS: All treated children showed an improvement in dentoalveolar relationships. Initial facial expressions differed between groups, with the treatment group showing less marked changes during lip pucker and more marked changes during maximal mouth opening. In contrast, no statistically significant differences were found between groups for the final facial expressions. CONCLUSIONS: This study suggests that functional appliance use in growing children with Class II division 1 malocclusion tends to normalize soft-tissue movements during facial expressions.

Headgear compliance as assessed by a temperature-sensitive recording device: a prospective clinical study.

OBJECTIVE: To accurately describe compliance in headgear wearing time by using a temperature- and force-sensitive device over an 8 month period of use in a prospective clinical manner. MATERIALS AND METHODS: Twenty children with Class II malocclusion aged 8-12 years were randomly selected for treatment with cervical headgear. The headgears were equipped with an electronic module, which measured temperature and force, and patients were instructed to wear the headgear 12 hours daily. The recorded values were analysed to determine the number of days the headgear was used, the number of hours per day it was worn, and the percentage of compliance (100 per cent corresponding to 12 hours daily). RESULTS: The average treatment period was 8.4 months with 5.8 months of effective use. When effectively used, headgear was worn 8.7 hours a day (compliance of 73 per cent). Including days where it was not worn, compliance was 6.4 hours (54 per cent). The appliance was used on average 0.5 hours during the day (8 am-8 pm) and 5.9 hours during the night (8 pm-8 am). Very low compliance was recorded during July and August. CONCLUSION: The average compliance with cervical headgear use was 54 per cent of the 12 hour prescription. The headgear was effectively used only 5.8 months over the study period, with roughly 30 per cent of no use. Headgear was used almost exclusively during evening and night-time. During the summer period, compliance was particularly poor.