Extractions as a form of interception in the developing dentition: a randomized controlled trial

Severe Crowding Associated with Lower Canine Premature Resorption: Interceptive Treatment with Clear Aligners-A Pilot Study

BACKGROUND

Early mixed dentition represents a critical phase since crowding conditions can occur. The interceptive resolution of dental crowding allows favorable arch and occlusal development. The aim of the present investigation was to evaluate dentoalveolar changes of clear aligner treatment planned to manage lower incisor crowding, loss of arch length, and midline deviation in early mixed dentition.

METHODS

A total of 13 patients (7 females, 6 males, 9.4 ± 1.2 age) treated with clear aligners were selected. Arch dimensions and incisor inclinations were evaluated before (T0) and at the end of interceptive treatment (T1). A paired t-test was chosen to compare T1-T0 changes. The level of significance was set at 5%.

RESULTS

The greatest significant increase in mandibular width was observed at the level of the first deciduous molars (+2.44 ± 1.4 mm), followed by the second permanent molars (+2.16 ± 1.4 mm). Lower arch length and arch depth showed a statistically relevant increase (2 ± 0.6 mm and 4.5 ± 1.6 mm, respectively). The mean lower dental midline changes were statistically significant (1.42 ± 0.73 mm).

CONCLUSIONS

Early treatment with clear aligners, including the combination of transversal arch development, maintenance of leeway space, and guidance of eruption, represents a valid treatment strategy in early mixed dentition to manage arch crowding and occlusion development.

Occlusion development after premature loss of deciduous anterior teeth: preliminary results of a 24-month prospective cohort study

OBJECTIVE

This study aimed to evaluate occlusion development after premature loss or extraction of deciduous anterior teeth, by means of a prospective cohort study.

METHODS

Fifteen infants and children aged 1 to 5 years old were longitudinally assessed (with loss or extraction of deciduous anterior teeth [n = 9], and without tooth losses [n = 6]). Photographs and dental casts at the baseline and after 24 months of follow-up were performed. Dental casts were scanned, and linear measurements were made on the digitalized models (missing tooth space, arch perimeter, arch length, arch width, intercanine length and intercanine width). The t-test was used for groups comparisons (α = 0.05).

RESULTS

Individuals' mean age at baseline was 2.93 (± 1.18) years. No statistically significant differences were observed in the missing tooth space in the group with tooth loss during the 24 months of follow-up (p > 0.05). Arch perimeter, arch length, arch width, intercanine length and intercanine width did not show differences between the groups (p > 0.05). Qualitative photographic evaluation revealed other changes in the dental arches and occlusion, such as exfoliation and eruption of deciduous teeth, eruption of permanent teeth, self-correction or establishment of malocclusion, among others.

CONCLUSION

The results suggest that the premature loss of deciduous anterior teeth does not affect the perimeter, length and width of the dental arches; however, other alterations that lead to malocclusion could be established.

Comparison between clear aligners and 2 × 4 mechanics in the mixed dentition: a randomized clinical trial

OBJECTIVES

To compare the efficacy and efficiency between clear aligners and 2 × 4 fixed appliances for correcting maxillary incisor position irregularities in the mixed dentition.

MATERIALS AND METHODS

The sample comprised 32 patients from 7 to 11 years of age randomly allocated into two parallel treatment groups: the clear aligners group, 14 patients (6 girls, 8 boys) with a mean initial age of 9.33 years (standard deviation [SD] = 1.01) treated with clear aligners; and the fixed appliances group, 13 patients (9 girls, 4 boys) with a mean initial age of 9.65 years (SD = 0.80) treated with partial (2 × 4) fixed appliances. Digital models were acquired before treatment and after appliance removal. Primary outcomes were incisor irregularity index and treatment time. Secondary outcomes were arch width, perimeter, length, size and shape, incisor leveling, incisor mesiodistal angulation, plaque index, and white spot lesion formation (International Caries Detection and Assessment System index). Intergroup comparisons were evaluated using t-tests or Mann-Whitney U-tests with Holm-Bonferroni correction (P < .05).

RESULTS

Treatment time was approximately 8 months in both groups. No intergroup differences were observed for changes in any of the variables. Similar posttreatment arch shapes were observed in both groups.

CONCLUSIONS

Clear aligners and 2 × 4 mechanics displayed similar efficacy and efficiency for maxillary incisor position corrections in the mixed dentition. The choice of appliance should be guided by clinician and family preference.

Very early orthodontic treatment: when, why and how?

Introduction:

Several orthodontic problems should already be treated at an early age to prevent the necessity of future complex and expensive procedures. Scientific evidence suggests that posterior crossbites, mild to moderate Class III, as well as certain Class II malocclusions, open bites and arch length discrepancies can benefit from simple, but efficient interceptive therapy.

Objective:

To summarize the existing evidence-based literature on early orthodontic treatment, and to illustrate its application and effectiveness by showcasing multiple clinical examples.

Conclusion:

Early short-term interceptive orthodontic treatment with simple appliances, in the deciduous or early mixed dentition phase, can efficiently correct certain malocclusions and help to either reduce the complexity or even avoid the necessity of complex and expensive procedures during puberty. For certain patients with significant arch length discrepancy the concept of serial extractions should be part of the orthodontic armamentarium.

Root and Root Canal Anatomy of Primary Mandibular Central Incisor, Lateral Incisor, and Canine in Indian Children: A Cone Beam Computed Tomography Study

Background. A thorough knowledge of root and root canal morphology in primary dentition is essential for success of endodontic therapy. This information also finds importance in anthropological research in reconstructing human population history. Lack of studies of root and root canal morphology in mandibular anterior teeth prompted us to the present study. Methods. A total of 109 extracted primary mandibular incisors and canines were collected, out of which 90 teeth were selected for this study and divided into 3 groups: CI, mandibular central incisor; LI, mandibular lateral incisor; C, mandibular canine. All the sample teeth were scanned using cone beam computed tomography (CBCT). Number of roots, number of root canals, length of root, mesiodistal (MD), and buccolingual (BL) width of canal, shape of canal, and presence of accessory canals were assessed. Collected data were statistically compared using one-way ANOVA and chi-square tests. Results. All teeth studied displayed single root with single root canal conforming to type I Vertucci’s classification. Root length of CI was significantly shorter than both LI and C, with no significant difference between LI and C. Straight root canals were more common in CI and LI, whereas curved canals were more common in C. S-shaped canals were seen in a few CI and C. BL canal width was more than MD width in all teeth, C showing significantly larger dimensions than both CI and LI. Conclusion. This study presents root and root canal characteristics of primary mandibular central incisor, lateral incisor, and canine in children from Indian ethnicity.

Orthodontic treatment for crowded teeth in children

BACKGROUND

Crowded teeth develop when there is not enough space in the jaws into which the teeth can erupt. Crowding can affect baby teeth (deciduous dentititon), adult teeth (permanent dentition), or both, and is a common reason for referral to an orthodontist. Crowded teeth can affect a child's self-esteem and quality of life. Early loss of baby teeth as a result of tooth decay or trauma, can lead to crowded permanent teeth. Crowding tends to increase with age, especially in the lower jaw.

OBJECTIVES

To assess the effects of orthodontic intervention for preventing or correcting crowded teeth in children. To test the null hypothesis that there are no differences in outcomes between different orthodontic interventions for preventing or correcting crowded teeth in children.

SEARCH METHODS

Cochrane Oral Health's Information Specialist searched four bibliographic databases up to 11 January 2021 and used additional search methods to identify published, unpublished and ongoing studies.

SELECTION CRITERIA

We included randomised controlled trials (RCTs) that evaluated any active interventions to prevent or correct dental crowding in children and adolescents, such as orthodontic braces or extractions, compared to no or delayed treatment, placebo treatment or another active intervention. The studies had to include at least 80% of participants aged 16 years and under.

DATA COLLECTION AND ANALYSIS

Two review authors, independently and in duplicate, extracted information regarding methods, participants, interventions, outcomes, harms and results. We resolved any disagreements by liaising with a third review author. We used the Cochrane risk of bias tool to assess the risk of bias in the studies. We calculated mean differences (MDs) with 95% confidence intervals (CI) for continuous data and odds ratios (ORs) with 95% CIs for dichotomous data. We undertook meta-analysis when studies of similar comparisons reported comparable outcome measures, using the random-effects model. We used the I² statistic as a measure of statistical heterogeneity.

MAIN RESULTS

Our search identified 24 RCTs that included 1512 participants, 1314 of whom were included in analyses. We assessed 23 studies as being at high risk of bias and one as unclear.  The studies investigated 17 comparisons. Twenty studies evaluated fixed appliances and auxiliaries (lower lingual arch, lower lip bumper, brackets, archwires, lacebacks, headgear and adjunctive vibrational appliances); two studies evaluated removable appliances and auxiliaries (Schwarz appliance, eruption guidance appliance); and two studies evaluated dental extractions (lower deciduous canines or third molars). The evidence should be interpreted cautiously as it is of very low certainty. Most interventions were evaluated by a single study. Fixed appliances and auxiliaries One study found that use of a lip bumper may reduce crowding in the early permanent dentition (MD -4.39 mm, 95% CI -5.07 to -3.71; 34 participants). One study evaluated lower lingual arch but did not measure amount of crowding. One study concluded that coaxial nickel-titanium (NiTi) archwires may cause more tooth movement in the lower arch than single-stranded NiTi archwires (MD 6.77 mm, 95% CI 5.55 to 7.99; 24 participants). Another study, comparing copper NiTi versus NiTi archwires, found NiTi to be more effective for reducing crowding (MD 0.49 mm, 95% CI 0.35 to 0.63, 66 participants). Single studies did not show evidence of one type of archwire being better than another for Titinol versus Nitinol; nickel-titanium versus stainless steel or multistrand stainless steel; and multistranded stainless steel versus stainless steel.  Nor did single studies find evidence of a difference in amount of crowding between self-ligating and conventional brackets, active and passive self-ligating brackets, lacebacks added to fixed appliances versus fixed appliances alone, or cervical pull headgear versus minor interceptive procedures. Meta-analysis of two studies showed no evidence that adding vibrational appliances to fixed appliances reduces crowding at 8 to 10 weeks (MD 0.24 mm, 95% CI -0.81 to 1.30; 119 participants). Removable appliances and auxiliaries One study found use of the Schwarz appliance may be effective at treating dental crowding in the lower arch (MD -2.14 mm, 95% CI -2.79 to -1.49; 28 participants). Another study found an eruption guidance appliance may reduce the number of children with crowded teeth after one year of treatment (OR 0.19, 95% CI 0.05 to 0.68; 46 participants); however, this may have been due to an increase in lower incisor proclination in the treated group. Whether these gains were maintained in the longer term was not assessed. Dental extractions One study found that extracting children's lower deciduous canines had more effect on crowding after one year than no treatment (MD -4.76 mm, 95 CI -6.24 to -3.28; 83 participants), but this was alongside a reduction in arch length. One study found that extracting wisdom teeth did not seem to reduce crowding any more than leaving them in the mouth (MD -0.30 mm, 95% CI -1.30 to 0.70; 77 participants).

AUTHORS' CONCLUSIONS

Most interventions were assessed by single, small studies. We found very low-certainty evidence that lip bumper, used in the mixed dentition, may be effective for preventing crowding in the early permanent dentition, and a Schwarz appliance may reduce crowding in the lower arch. We also found very low-certainty evidence that coaxial NiTi may be better at reducing crowding than single-stranded NiTi, and that NiTi may be better than copper NiTi. As the current evidence is of very low certainty, our findings may change with future research.

Impact of early extraction of the deciduous canine on relief of severe crowding

OBJECTIVES

To explore whether there were any differences in orthodontic treatment need, treatment complexity, treatment time, or the number of visits between a group of children receiving early intervention (extraction of upper and lower deciduous canines) and an age- and condition-matched control group without intervention.

MATERIALS AND METHODS

Patient records and study casts in the late mixed or early permanent dentitions of 46 subjects (20 from the extraction group and 26 from the control group) of an earlier prospective longitudinal study were retrieved. Orthodontic treatment need and complexity were assessed by the index of complexity, outcome, and need (ICON). Statistical calculations were performed by t-test for parametric outcome variables (treatment time, number of visits, and orthodontic treatment need) and Fisher exact test for the categorical variable (tooth extractions).

RESULTS

There were no statistically significant differences between the groups in ICON scores of orthodontic treatment need (extraction group, mean score 59.8; control group, mean score 52.8), number of visits (mean of about 15 visits for both groups), or treatment time (extraction group, mean 21.5 months; control group, mean 20.3 months). The extraction of permanent teeth was more prevalent in the deciduous canine extraction group (59%) as compared with the control group (28%); however, this was not statistically significant (P = .07) but showed a tendency toward worsening the crowding and the future need of orthodontic extractions.

CONCLUSIONS

Early removal of deciduous primary canines will reduce neither the need for later orthodontic treatment nor its complexity, nor will it shorten the treatment time.

The effect of extraction of lower primary canines on the morphology of dental arch: A systematic review and meta-analysis

BACKGROUND

The beneficial effect of the extraction of primary canines in the resolution of incisor irregularity and its side effects are controversial.

AIM

To systematically review the effects of the extraction of primary canines in incisor irregularity and dental arch morphology.

DESIGN

Controlled non-randomized (non-RCT) and randomized clinical trials (RCT) evaluating children treated with extraction of primary canines compared with those without intervention.

RESULTS

A total of 984 articles were found, of which two RCTs and one non-RCT met the inclusion criteria. Both had a low RoB. A high level of evidence was observed through GRADE. A meta-analysis showed the extraction of primary canines produced a significant decrease in incisor irregularity (95% CI: -3.56, -2.09 mm). This decrease, however, was associated with a reduction of arch length (95% CI: -1.58, -0.94 mm), intermolar width (95% CI: -0.61, -0.22 mm), and overjet (95% CI: -075, -018). A mild overbite increase was found (95% CI: 0.10, 0.76 mm).

CONCLUSION

A high level of evidence showed that the extraction of primary canines improved incisor irregularity in the mixed dentition. Side effects included reduced arch length and intermolar width. A slight reduction in overjet and a mild increase in overbite were also observed. When they are not part of the treatment goal, these occlusal changes can be prevented by installing a lingual arch.

Open and closed surgical exposure of palatally displaced canines: a cost-minimization analysis of a multicentre, randomized controlled trial

OBJECTIVE

To evaluate the costs of open and closed surgical exposure and subsequent orthodontic treatment for the correction of palatally displaced canines (PDCs).

TRIAL DESIGN

A multicentre, two-arm parallel group randomized controlled trial.

METHODS

One hundred twenty adolescents between 9 and 16 years of age, from three orthodontic specialist centres, were randomized to one of the two surgical exposure interventions. The randomization was conducted according to a two-arm parallel group 1:1 allocation ratio, using computerized lists with block randomization. In both the surgical techniques, whole mucoperiosteal flaps were raised, and bone covering the PDCs was removed. In the open technique, glass ionomer was built up on the PDC crown - reaching above the mucosa through a hole punched in the flap - to allow the canine to erupt autonomously. After eruption, the canine was orthodontically moved above the mucosa. In the closed technique, an eyelet was bonded onto the PDC, the flap was repositioned and the canine was orthodontically moved beyond the mucosa. The trial ended when the PDC was successfully aligned in the dental arch.Cost analysis was performed including costs for surgery, orthodontic treatment, emergency visits, and material, as well as costs for transports and time spent in connection with every appointment.

BLINDING

Patients and caregivers could not be blinded due to obvious limitations of the clinical setting, while outcome assessors and data analysts were blinded.

RESULTS

A cost-minimization analysis was performed since both exposure groups succeeded equally well in terms of treatment effects. The two different surgical exposures and following orthodontic treatments did not differ significantly in terms of costs.

GENERALIZABILITY AND LIMITATIONS

Costs are estimated in the Swedish setting, which needs to be considered if applying the results in other settings. Calculations of total cost do not include finishing, debonding, retention, and follow-up.

CONCLUSION

There is no significant difference in costs between closed and open surgical exposure with following orthodontic treatments in PDCs.

TRIAL REGISTRATION

ClinicalTrials.gov, ID: NCT02186548.

Open vs closed surgical exposure of palatally displaced canines: a comparison of clinical and patient-reported outcomes-a multicentre, randomized controlled trial

OBJECTIVES

To compare treatment time, patients' perceptions during orthodontic treatment, dental fear and side effects, between open and closed surgical exposures in patients with palatally displaced canines (PDCs).

TRIAL DESIGN

Multicentre, randomized controlled trial, with random 1:1 allocation of two parallel groups.

MATERIALS AND METHODS

One hundred and twenty patients from three different orthodontic centres were randomized into one of the two intervention arms, open or closed surgical exposure. Both techniques had mucoperiosteal flaps raised and bone removed above the PDCs. In open exposure, tissue was removed above the canine, and glass ionomer - reaching above soft tissue - was built on the crown. The canine was then left to erupt spontaneously, prior to orthodontic alignment. At closed exposure, a chain was bonded to the canine and orthodontic traction was applied under the mucosa until eruption. Orthodontic alignment of the canines was undertaken after eruption into the oral cavity, with fixed appliances in both groups. All participants were treated according to intention to treat (ITT).

BLINDING

Due to the nature of this trial, only outcome assessors could be blinded to the intervention group.

RESULTS

One hundred and seventeen patients completed the trial. All PDCs were successfully aligned. Total treatment time was equal in the two techniques, mean difference -0.1 months (95% CI -3.2 to 2.9, P = 0.93). The closed group experienced more pain and discomfort during the active orthodontic traction. Dental fear, root resorption and periodontal status did not show any clinically significant differences between the groups.

GENERALIZABILITY

Results of this randomized controlled trial (RCT) can be generalized only to a similar population aged 9-16 years, if exclusion criteria are met.

CONCLUSION

The closed exposure group experienced more pain and discomfort mostly during active orthodontic traction. All other studied outcomes were similar between the two exposure groups.

CLINICAL TRIAL REGISTRATION

ClinicalTrials.gov, ID: NCT02186548 and Researchweb.org, ID: 127201.

PLATOON: Premature Loss of bAby Teeth and its impact On Orthodontic Need - protocol

OBJECTIVE

To investigate the impact of premature extraction of primary teeth (PEPT) on orthodontic treatment need in a cohort of children participating in the Born in Bradford (BiB) longitudinal birth cohort.

DESIGN

Observational, cross-sectional cohort.

PARTICIPANTS

We aim to recruit 1000 children aged 7-11 years: 500 with a history of PEPT and 500 matched non-PEPT controls.

METHODS

After informed consent/assent, orthodontic records will be collected, including extra and intra-oral photographs and alginate impressions for study models. Participants will also complete a measure of oral health-related quality of life (COHIP-SF 19). The records will be used to quantify space loss, identify other occlusal anomalies and assess orthodontic treatment need using the Index of Orthodontic Treatment Need. For each outcome, summary statistics will be calculated and the data for children with and without PEPT compared. The records of the children identified to be in need of orthodontic treatment will be examined by an expert orthodontic panel to judge if this treatment should be undertaken at the time of the records or delayed until the early permanent dentition. Collecting robust records in the mixed dentition provides the clinical basis to link each stage of the causal chain and enable the impact of PEPT on orthodontic need to be characterised. This study is the first to provide the foundations for future longitudinal data collection allowing the long-term impact of PEPT to be studied.

The effect of premature extraction of primary teeth on the subsequent need for orthodontic treatment

AIM

This was primarily to examine the effect of premature extraction of primary teeth (PEPT) on subsequent malocclusion and need for orthodontic treatment in the permanent dentition. The secondary aim was to correlate the effect of PEPT with loss of space in the primary and mixed dentitions.

METHODS

A predefined protocol was developed and registered prospectively with PROSPERO database. The electronic databases, searched, were MEDLINE, EMBASE, PubMed, and Cochrane Central Register of Controlled Trials. The study designs considered for inclusion were controlled trials, cohort, and case-control studies. Risk of bias was assessed using a validated quality assessment tool.

RESULTS

513 studies were identified. Sixteen studies were included in the systematic review, one study reported on malocclusion, and 15 studies reported on space changes. Narrative synthesis was undertaken owing to the heterogeneity of the included studies. No study examined the effect of PEPT on orthodontic need. Most studies reported on space dimensions used a split-mouth design and were at a high risk of bias.

CONCLUSIONS

The included literature identified that PEPT led to various features of malocclusion and space loss in the mixed and permanent dentitions. No studies, that met the inclusion criteria, described the effect of PEPT on the subsequent need for orthodontic treatment.

Mandibular changes secondary to serial extractions compared with late premolar extractions and controls

INTRODUCTION

Variations in treatment times for serial extraction and late premolar extraction patients may be due to differences in the time needed to flatten the occlusal curves. In this study, we compared tooth tipping and occlusal curves in patients treated by serial extractions or late premolar extractions with untreated controls.

METHODS

Mandibular dental casts and cephalometric radiographs were collected from 90 subjects (30 Class I control subjects, 30 patients with serial extractions, and 30 with late premolar extractions) at 3 time points: T0, baseline for the controls and serial extraction patients; T1, after natural drift and preorthodontics for the controls and the serial extraction patients, and pretreatment for the late premolar extraction patients; and T2, after comprehensive orthodontic treatment for the serial extraction and the late premolar extraction groups. The long axes of the central incisor, canine, and first molar to the palatal plane were measured on digitized headfilms to determine the direction and the amount of tipping between the time points. Three occlusal curves were measured by sphere fitting cusp-tip landmarks on digitized mandibular casts.

RESULTS

From T0 to T1, incisors and canines in the patients with serial extractions tipped distally. Molars at T1 in the patients with serial extractions were tipped forward more than in the late premolar extraction patients and the controls. From T1 to T2, canines and molars in the patients with serial extractions were uprighted.

CONCLUSIONS

Serial extractions produce steeper occlusal curves and distal tipping of the incisors and canines after drift (T1). Posttreatment (T2) occlusal curves in the patients with serial extractions are steeper than in the late premolar extraction patients and controls (except for the curve of Spee). After the serial extractions, orthodontic treatment included incisor and canine proclination, with molar uprighting and occlusal curve flattening.

Infant dental enucleation: A literature review on a traditional remedial practice in East Africa

OBJECTIVE

To summarize and review the literature on infant dental enucleation, a traditional remedial procedure prevalent mainly in East Africa.

MATERIALS AND METHODS

Literature searches were made electronically using general and specialized search engines. The main search was performed through a systematic strategy in PubMed, comprising tabulated keywords, search codes, and translated and transliterated terms. Criteria for the selection of studies were designed to provide a general understanding of the procedure. The findings were synthesized into two sections: a summary of the population prevalence studies, and a thematic literature review.

RESULTS

An overview of the known prevalence and clinical specifications was established. Insight was gained into the purpose of the procedure and the factors influencing its performance. Diverging suggestions were seen with regard to the rationale for use of infant dental enucleation between different populations. Moreover, reports of complications and consequences involving the general health and the dentoalveolar structures of patients were examined.

CONCLUSIONS

Prevalence, clinical features and risks of infant dental enucleation point to a need for greater awareness of the procedure. Further, there is a need for specific guidelines regarding management of suspected cases within dental and healthcare communities.

Loss of deciduous teeth--is timing important to the GDP?

On a daily basis, GDPs encounter patients with prematurely lost deciduous teeth or, conversely, deciduous teeth retained well past their accepted exfoliaton date. The timing of deciduous tooth loss impacts on many aspects of the developing occlusion. The aim of the article is both to describe this impact and also to set out guidelines which should assist the general dental practitioner in the decision of when to lose deciduous teeth.

CLINICAL RELEVANCE

The timing of deciduous tooth loss is an important concept which, when outside the normal pattern, may have adverse or beneficial side-effects that general dental practitioners should fully understand.

Pain and fear in connection to orthodontic extractions of deciduous canines

BACKGROUND

Interceptive extractions of deciduous canines are, from a patient perspective, poorly investigated.

AIMS

To describe pain, discomfort, and dental fear in connection to extractions of the deciduous canines, indicated as an orthodontic treatment procedure.

DESIGN

Thirty-two Swedish children aged 7-9 years had all four deciduous canines extracted over three occasions. The children rated procedural and postoperative pain on visual analogue scales. Acceptance of injections and extractions was assessed by the treating dentists. Analgesic consumption and recovery time for drinking and eating was reported by parents. Dental fear was assessed using the Children's Fear Survey Schedule questionnaire.

RESULTS

Procedural pain showed low median levels, although some individuals reported high values. Boys reported significantly more pain at appointments when two (as opposed to one) canines were extracted. Postoperative pain levels were low and use of analgesics sparse. Dental fear paralleled norm values and did not increase from pre- to post-extraction.

CONCLUSIONS

Pain management routines during extractions of this kind should be revised. Single tooth extractions seem to be preferable to extractions of two canines at the same appointment. Extraction of four deciduous canines should not cause major postoperative inconvenience; these extractions neither triggered nor increased dental fear.