Herbst Therapy Research Articles

Prevalence of temporomandibular disorders diagnosis in patients treated with Herbst appliance: a systematic review and meta-analysis

BackgroundThe Herbst appliance is an excellent therapy for treating class II malocclusions with increased overjet. Its mechanics involve propelling the mandibular bone using two pistons the patient cannot remove. The so-called bite-jumping keeps the mandible in a more anterior position for a variable period, usually at least 6 months. This appliance does not inhibit joint functions and movements, although there are scientific papers in the literature investigating whether this appliance can lead to temporomandibular disorders. This systematic review aims to evaluate whether Herbst’s device can cause temporomandibular diseases by assessing the presence of TMD in patients before and after treatment.MethodsA literature search up to 3 May 2023 was carried out on three online databases: PubMed, Scopus and Web of Science. Only studies that evaluated patients with Helkimo scores and Manual functional analysis were considered, as studies that assessed the difference in TMD before and after Herbst therapy. Review Manager version 5.2.8 (Cochrane Collaboration) was used for the pooled analysis. We measured the odds ratio (OR) between the two groups (pre and post-Herbst).ResultsThe included papers in this review were 60. Fifty-seven were excluded. In addition, a manual search was performed. After the search phase, four articles were considered in the study, one of which was found through a manual search. The overall effect showed that there was no difference in TMD prevalence between pre-Herbst and post-Herbst therapy (OR 0.74; 95% CI: 0.33–1.68).ConclusionHerbst appliance seems not to lead to an increase in the incidence of TMD in treated patients; on the contrary, it appears to decrease it. Further studies are needed to assess the possible influence of Herbst on TMDs.

Comparisons of soft tissue changes after Herbst appliance treatment in three different growth phases

This study aimed to compare the soft tissue effects of Herbst appliance in Class II malocclusion patients treated in three different craniofacial growth phases: prepubertal (PRE), circumpubertal (CIR), and postpubertal (POS). In total, 95 patients with Class II Division 1 malocclusion previously treated with a Herbst appliance were analyzed. Through the cervical vertebral maturation stages method, patients were allocated into three groups depending on the growth craniofacial phase at the beginning of treatment: PRE, CIR, and POS. Seventeen cephalometric measures were evaluated from each lateral radiograph before and after Herbst therapy using the Radiocef 2 software (Radio Memory, Belo Horizonte). Intragroup and intergroup treatment changes were compared statistically using a paired t test and MANOVA test, respectively. Soft tissue thickness changes were related only to mandible; all three mandibular measurements (L1_LL, B_B', and Pog_Pog') showed thickening for the PRE group ranging from 0.92 mm (Pog_Pog') to 2.02 mm (B_B'), and only lower lip thickened overtime for the POS group (L1_LL = 0.99 mm). Soft and hard tissue pogonion displaced anteriorly, but only the soft tissue showed differences among groups; PRE group presented more anterior displacement than POS group (3.61 mm and 1.39 mm, respectively). Hard and soft tissue facial convexity decreased more in the PRE and CIR groups than in the POS group. Mentolabial sulcus depth reduced more in the PRE (1.07 mm) and CIR (1.29 mm) groups than in the POS (0.55 mm) group. Horizontal movement of the skeletal and soft pogonion presented a moderate-high positive correlation (r = 0.783), and hard and soft facial convexity showed a moderate-low positive correlation (r = 0.403). Herbst appliance therapy produces soft tissue improvements in the three phases of craniofacial growth, being greater in patients in the PRE and CIR phases.

Dental changes induced by a modified Herbst appliance followed by fixed appliances: A digital dental model analysis.

Herbst therapy is an effective treatment for Class II malocclusions. However, the maintenance of the effects after fixed appliances treatment remains questionable. This retrospective study aimed to assess, using digital dental models, the sagittal and transverse dental arch changes in young patients during two Class II Division 1 treatment phases, first with modified Herbst appliance (HA) and then with fixed appliances. The treated group (TG) comprised 32 patients (17 boys, 15 girls; mean age, 12.85 ± 1.16 years) treated with HA and fixed appliances. The control group comprised 28 patients (13 boys, 15 girls; mean age, 12.21 ± 1.35 years) with untreated Class II malocclusions. Digital models were obtained immediately before and after HA therapy and after fixed appliances. Data were statistically analyzed. Compared with the control group, the TG showed an increase in maxillary and mandibular arch perimeters and in intercanine and intermolar arch widths, a decrease in overjet and overbite, and an improvement in canine and molar relationships. In the time after HA therapy until the end of fixed appliances treatment, the TG showed a decrease in maxillary and mandibular arch perimeters, overjet, upper and lower intermolar widths; an increase in molar Class II relationship; and no changes in canine relationship, overbite, and upper and lower intercanine widths. In this sample of patients treated with HA, on average, there was an improvement in the Class II relationship, which seemed to remain after fixed appliances. The transverse dental changes achieved in HA phase relapsed after treatment with fixed appliances.

Long-term evaluation of soft tissue profile changes induced by Herbst appliance followed by fixed appliances

The present investigation aimed to evaluate, by cephalometric analysis, the soft tissue profile changes in adolescents with Class II Division 1 malocclusion, treated with Herbst appliance (Stage I) and fixed appliances (Stage II), followed-up for an average of 4 years (Stage III). The adolescents were divided into two groups: treated group (TG) - 33 adolescents with Class II malocclusions (17 boys and 16 girls) consecutively treated with Herbst appliance and fixed appliances; control group (CG) - 28 adolescents (13 boys and 15 girls) with untreated Class II malocclusions. Lateral cephalograms were obtained immediately before (T1) and after (T2) Herbst treatment, after fixed appliances (T3), and on average, 4 years after orthodontic treatment. Intergroup comparison was evaluated by t or Mann-Whitney tests. The TG was evaluated by analysis of variance followed by Tukey test or Friedman test followed by Dunn’s test. Compared to the CG, the TG showed significant favorable changes at Stage I: decrease in facial convexity, upper lip retrusion, lower lip protrusion, improvement of soft tissue pogonion and increase in mentolabial angle. The total posttreatment period (T2-T4) of the TG showed: increase in H line-Prn, and upper and lower lips retrusion, while the others variables remained stable. This study suggests that Herbst therapy improved features of soft tissue facial profile, which were maintained after fixed appliances and for an average of 4 years posttreatment, although the convex facial characteristic has prevailed.

Treatment and posttreatment effects of Herbst appliance therapy on trabecular structure of the mandible using fractal dimension analysis.

This controlled study aimed to evaluate the effects of Herbst therapy on the trabecular structure of the condyle and angulus mandible using fractal dimension analysis (FD-A) accompanied by skeletal cephalometric changes. The panoramic and cephalometric radiographs of 30 patients with skeletal Class II malocclusion treated with the Herbst appliance (C II-H group, mean age: 15.23 ± 1.08), 30 patients with skeletal Class II malocclusion that received fixed orthodontic treatment (C II-C group, mean age: 15.73 ± 1.38), and 30 patients with skeletal Class I malocclusion (C I-C group, mean age: 15.90 ± 1.30) were selected. FD-A was performed on the superoposterior region (C-SP) and centre of the condyles (C-C) and the mandibular angulus (Ang) on the panoramic radiographs taken at the pretreatment (T0), intermediate stage of treatment (T1), and posttreatment (T2) timepoints just like cephalometric analysis. Herbst therapy provided a statistically significant increase in SNB, ANS-Me, Na-Me, S-Go, Co-Gn and a decrease in ANB and overjet (P < 0.05). All skeletal changes remained stable during the fixed appliance treatment after Herbst. The FD values in C-C increased (P < 0.05), and C-SP values decreased (P < 0.05) during Herbst therapy, while after removal of the Herbst appliance, no significant change was observed despite an increase in C-SP. The Ang value did not change during Herbst treatment, but then increased significantly (P < 0.05). There was no significant change in the FD values of the C I-C and C II-C groups at any stage of treatment. The C-C and C-SP changes at T1-T0 period, C-SP and Ang changes at T2-T1 period, and C-C, C-SP, and Ang values at T2-T0 period were found higher in C II-H group compared with the C II-C group significantly (P < 0.05). Herbst therapy changed the trabecular structure of the condyles in different directions at the superoposterior and central regions of the condyles, while the structural complexity of the angulus mandible, which did not change during the Herbst treatment, increased during the fixed orthodontic treatment after Herbst.

English

BACKGROUND Skeletal malocclusions occur because of the defect in the underlying skeletal structure. Mandibular skeletal retrusion is the most common characteristic of class II malocclusion. The purpose of this study was to evaluate pharyngeal airway dimension in Class II patients treated with Herbst appliance and fixed mechanotherapy using cone beam computed tomography (CBCT). METHODS This comparative study was conducted among 30 Class II patients (9 to 15 years of age) selected from the outpatient department of orthopaedics. They were divided into 2 Groups; Group I (15 patients) was treated by Herbst appliance; Group II (15 patients) was treated by fixed mechanotherapy. Pharyngeal airway volume, length and width evaluation were done using CBCT in vivo dental software 5.1 (ANATOMAGE, San Jose, CA). Intergroup comparison was done using independent t tests and level of significance (P &lt; 0.05). Correlation of parameters were carried out using Pearson’s correlation test. RESULTS Significant increase in nasopharyngeal, velopharyngeal, glossopharyngeal, laryngopharyngeal, and total airway volume in Herbst group was observed. Velopharyngeal length, glossopharyngeal length and nasopharyngeal airway width showed significant increase in Herbst group. CONCLUSIONS Treatment of Class II patients with Herbst appliance resulted in increase in pharyngeal airway volume. Herbst therapy induced repositioning of tongue resulting in increased length due to posterior fall of uvula, and hence airway volume increased drastically. KEY WORDS Airway Volume, Herbst Appliance, Class II Malocclusion, Retrognathic Mandible

Three-dimensional skeletal mandibular changes associated with Herbst appliance treatment.

Three-dimensional evaluation of skeletal mandibular changes following Herbst appliance treatment. Retrospective case-control study, based on a sample size calculation. Twenty-five pubertal patients treated with Herbst appliance (HAG), and 25 matched Class II patients who received other non-orthopaedic dental treatments (CG). Three-dimensional models were generated from pre-treatment (T0) and post-treatment (T1) cone beam computed tomograms. Volumetric registration on the cranial base was used to assess mandibular displacement; volumetric regional registration was performed to evaluate mandibular growth. Quantitative measurements of X, Y, Z and 3D Euclidian changes, and also qualitative visualization by colour-mapping and semi-transparent overlays were obtained. Downward displacement of the mandible was observed in both HAG and CG (2.4mm and 1.5mm, respectively). Significant forward displacement of the mandible was observed in the HAG (1.7mm). HAG showed greater 3D superior and posterior condylar growth than the CG (3.5mm and 2.0mm, respectively). Greater posterior growth of the ramus was noted in the HAG than in CG. Immediately after Herbst therapy, a significant mandibular forward displacement was achieved, due to increased bone remodelling of the condyles and rami compared to a comparison group. Three-dimensional changes in the direction and magnitude of condylar growth were observed in Herbst patients.

Herbst appliance effects on pharyngeal airway ventilation evaluated using computational fluid dynamics.

To evaluate the effect of a Herbst appliance on ventilation of the pharyngeal airway (PA) using computational fluid dynamics (CFD). Twenty-one Class II patients (10 boys; mean age, 11.7 years) who required Herbst therapy with edgewise treatment underwent cone-beam computed tomography (CBCT) before and after treatment. Nineteen Class I control patients (8 boys; mean age, 11.9 years) received edgewise treatment alone. The pressure and velocity of the PA were compared between the groups using CFD based on three-dimensional CBCT images of the PA. The change in oropharyngeal airway velocity in the Herbst group (1.95 m/s) was significantly larger than that in the control group (0.67 m/s). Similarly, the decrease in laryngopharyngeal airway velocity in the Herbst group (1.37 m/s) was significantly larger than that in the control group (0.57 m/s). The Herbst appliance improves ventilation of the oropharyngeal and laryngopharyngeal airways. These results may provide a useful assessment of obstructive sleep apnea treatment during growth.

Signs and symptoms of TMJ disorders in adults after adolescent Herbst therapy: a 6-year and 32-year radiographic and clinical follow-up study.

To analyze radiographic signs of temperomandibular joint (TMJ) osteoarthritis and clinical TMJ symptoms in patients 6 years and 32 years after treatment with a Herbst appliance. Fourteen patients were derived from a sample of 22 with Class II division 1 malocclusions consecutively treated with a banded Herbst appliance at the age of 12-14 years old (T1-T2). The subjects were reexamined after therapy at the ages of 20 years (T3) and 46 years (T4). The TMJs of the 14 patients were analyzed radiographically (conventional lateral tomography at T3 and cone-beam computed tomography at T4) and clinically/anamnestically at T3 and T4. Six years after Herbst therapy, signs of osteoarthritis were seen in one patient. At the 32-year follow-up, two additional patients had developed signs of osteoarthritis. At the 6-year follow-up, TMJ clicking was present in two patients, though none of the patients reported TMJ pain. At the 32-year follow-up, six patients had TMJ clicking and one patient had TMJ pain. This longitudinal very-long-term follow-up study after Herbst therapy revealed only minor problems from the TMJ. The TMJ findings 6 years and 32 years after Herbst treatment corresponded to those in the general population. Thus, in the very long term, the Herbst appliance does not appear to be harmful to the TMJ.

Late adult skeletofacial growth after adolescent Herbst therapy: A 32-year longitudinal follow-up study

The aim of this longitudinal 32-year follow-up investigation was to analyze the very long-term effects of Herbst treatment on the dentoskeletal structures. We followed 14 patients from a sample of 22 with Class II Division 1 malocclusions who were consecutively treated with the banded Herbst appliance at ages 12 to 14 years. The subjects were reexamined after therapy at the ages of 20 years (when the radius epiphysis/diaphysis plate was closed) and 46 years. Lateral head films were analyzed from before (T1) and after (T2) treatment, and at 6 years (T3) and 32 years (T4) after treatment. (1) In the standard analysis (angular measurements) during the T2 to T3 period of 6 years, significant skeletal changes were the following: increase of the SNB (1.0°; P <0.01), decrease of the ANB (0.9°; P <0.01), and decrease of the ML/NSL (2.5°; P <0.001). During the T3 to T4 period of 24 years, no further significant angular changes occurred. (2) In the analysis of the sagittal changes in the occlusion (linear measurements) during the T2 to T3 period of 6 years, the mandible (6.1 mm; P <0.001) and the maxilla (3.0 mm; P <0.01) grew forward. During the T3 to T4 period of 24 years, the mandible (2.8 mm; P <0.01) and the maxilla (3.1 mm; P <0.01) continued to grow forward. Thus, during the total posttreatment (T2-T4) period of 32 years, there was continuous forward growth of the mandible (8.9 mm; P <0.001) and the maxilla (6.1 mm; P <0.001). (3) The analysis of superimposed lateral head films showed in all 14 subjects large amounts of sagittal and vertical skeletofacial growth during T3 to T4. In all 14 subjects, large amounts of sagittal and vertical skeletofacial growth occurred after the age of 20 years. However, the question of when, during the period from 20 to 46 years, growth had come to an end remains open. Closure of the radius epiphysis/diaphysis plate is not useful as an indicator for completed skeletofacial growth. Our findings indicate the importance of considering late adult skeletofacial growth in dentofacial orthopedics, orthognathic surgery, and tooth implantology with respect to treatment timing, posttreatment retention, and relapse.

Three-dimensional cone-beam computed tomography analysis of enlargement of the pharyngeal airway by the Herbst appliance

Pharyngeal airway size is increasingly recognized as an important factor in obstructive sleep apnea. However, few studies have examined the changes of pharyngeal airway form after dental procedures for treating obstructive sleep apnea during growth. The purpose of this study was to evaluate the effect of the Herbst appliance on the 3-dimensional form of the pharyngeal airway using cone-beam computed tomography. Twenty-four Class II subjects (ANB, ≥5°; 11 boys; mean age, 11.6years) who required Herbst therapy with edgewise treatment had cone-beam computed tomography images taken before and after Herbst treatment. Twenty Class I control subjects (9 boys; mean age, 11.5years) received edgewise treatment only. The volume, depth, and width of the pharyngeal airway were compared between the groups using measurements from 3-dimensional cone-beam computed tomography images of the entire pharyngeal airway. The increase of the oropharyngeal airway volume in the Herbst group (5000.2mm(3)) was significantly greater than that of the control group (2451.6mm(3)). Similarly, the increase of the laryngopharyngeal airway volume in the Herbst group (1941.8mm(3)) was significantly greater than that of the control group (1060.1mm(3)). The Herbst appliance enlarges the oropharyngeal and laryngopharyngeal airways. These results may provide a useful assessment of obstructive sleep apnea treatment during growth.

Mandibular incisor inclination, tooth irregularity, and gingival recessions after Herbst therapy: A 32-year follow-up study

The aim of this study was to analyze the very long-term results after Herbst treatment with respect to changes in the mandibular incisor segment: incisor inclination, incisor alignment, and gingival status. Fourteen patients were derived from a sample of 22 consecutive patients with Class II Division 1 malocclusions treated with the banded Herbst appliance. Intraoral photographs, mandibular dental casts, and lateral head films were analyzed from before (T1, age 12.5years) and after (T2, age 14years) treatment, and at 6years (T3, age 20years) and 32years (T4, age 46years) after treatment. At T1, incisor inclination in the 14 subjects was, on average, 100.1°. From T1 to T2, the incisors were proclined in 11 (79%) of the 14 patients, with an average value of 5.2°. Maximum proclinations of 10° were found in 2 subjects. From T2 to T4, tooth inclination recovered completely in 7 (63%) of the 11 patients. Incisor irregularity values were, on average, 3.4mm at T1 and 3.0mm at T2. These increased from T2 to T4 by 40% and had an average value of 5.0mm at T4. Clinically insignificant labial gingival recessions on single front teeth were registered in 1 subject at T2 and in 8 subjects at T4. Gingival recessions were seen especially on bodily displaced incisors. In Herbst patients followed for 32years after therapy, proclined mandibular incisors generally rebounded. The increase in posttreatment incisor tooth irregularity was not thought to be related to incisor tooth inclination changes but more likely resulted from physiologic processes occurring throughout life. Minor gingival recessions (especially on bodily displaced and crowded canines and incisors) seen in a few patients, 32years after treatment, seemed not to be related to the posttreatment tooth inclination changes.

Facial-profile attractiveness changes in adult patients treated with the Herbst appliance.

The goal of this study was to compare facial profile attractiveness changes of adult patients treated with the Herbst appliance assessed by orthodontists and laypeople. The patient sample comprised 28 adult Herbst patients. Facial profile photographs of the patients were randomly divided into two evaluation sets (before T0, after treatment T1). Ten members of the Angle Society of Europe (orthodontists) and 10 dental students in their third semester (laymen) rated both sets of photographs using Visual Analog Scales (VAS) with an interval of 1 day between the ratings. On average, both orthodontists and students found an improvement in facial profile attractiveness through Herbst appliance treatment (VAS T1-T0 = 0.3 ± 1.9 cm). However, the interindividual perception of profile attractiveness varied greatly in the two rater groups. For both time periods (T0, T1), lower VAS ratings were given by students than by orthodontists. Herbst therapy in adult patients generally improves facial profile attractiveness. Students rated facial profiles more critically than orthodontists.

Thirty-two-year follow-up study of Herbst therapy: A biometric dental cast analysis

The aim of this study was to analyze the very long-term effects of Herbst treatment on toothposition and occlusion. Fourteen patients from a sample of 22 with Class II Division 1 malocclusions consecutively treated with the banded Herbst appliance were reexamined 32 years after therapy. Dental casts were analyzed from before (T1) and after (T2) treatment, and at 6 years (T3) and 32 years (T4) after treatment. Minor changes in maxillary and mandibular dental arch perimeters and arch widths were seen during treatment (T1-T2) and posttreatment (T2-T4). Mandibular incisor irregularity remained, on average, unchanged from T1 to T2 but increased continuously during the 32-year follow-up period (T2-T4). Class II molar and canine relationships were normalized in most patients from T1 to T2. During the early posttreatment period (T2-T3), there was a minor relapse; during the late posttreatment period (T3-T4), molar and canine relationships remained, on average, unchanged. Overjet and overbite were reduced to normal values in all subjects during treatment (T1-T2). After treatment (T2-T4), overjet remained, on average, unchanged, but overbite increased insignificantly. Thirty-two years after Herbst therapy, overall, acceptable long-term results were seen. Stability was found in 64% of the patients for sagittal molar relationships, in 14% for sagittal canine relationships, in 86% for overjet, and in 86% for overbite. A Class II relapse seemed to be caused by an unstable interdigitation of the occluding teeth, a persisting oral habit, or an insufficient retention regimen after treatment. Most posttreatment changes occurred during the first 6 years after treatment. After the age of 20 years, only minor changes were noted. Long-term posttreatment changes in maxillary and mandibular dental arch perimeters and widths as well as in mandibular incisor irregularity seemed to be independent of treatment and a result of physiologic dentoskeletal changes throughout adulthood.

The Herbst appliance updated

The aim of this paper is to analyze the evolution that the Herbst appliance has experienced in the last 30 years. In particular the different designs proposed for the Herbst appliance are examined and the related differences in clinical management, indications, and treatment effects are also illustrated. The two major challenges in the clinical management of the Herbst appliance are represented by the choice of the type of stabilization and by the control of the proclination of the lower incisors. The use of acrylic splints presents a set of relevant advantages: the construction technique is simple, the appliance can be worn easily by the patients, and the height of the splint can be adjusted to the growth pattern. Moreover, the acrylic splint Herbst can be used to reposition the mandible in cases with temporomandibular disorders. As for the proclination of the lower incisors, an accurate assessment of the neuromuscular pattern of the individual patient before treatment can provide the clinician with reliable criteria to evaluate the risk for incisor proclination during Herbst therapy.

Occlusal stability of adult Class II Division 1 treatment with the Herbst appliance

During recent years, some articles have been published on Herbst appliance treatment in adult patients, an approach that has been shown to be most effective in Class II treatment in both early and late adulthood. However, no results on stability have yet been published. Our objective was to analyze the short-term occlusal stability of Herbst therapy in adults with Class II Division 1 malocclusions. The subjects comprised 26 adults with Class II Division 1 malocclusions exhibiting a Class II molar relationship > or =0.5 cusp bilaterally or > or =1.0 cusp unilaterally and an overjet of > or =4.0 mm. The average treatment time was 8.8 months (Herbst phase) plus 14.7 months (subsequent multi-bracket phase). Study casts from before and after treatment and after an average retention period of 32 months were analyzed. After retention, molar relationships were stable in 77.6% and canine relationships in 71.2% of the teeth. True relapses were found in 8.2% (molar relationships) and 1.9% (canine relationships) of the teeth. Overjet was stable in 92.3% and overbite in 96.0% of the patients; true relapse did not occur. Herbst treatment showed good occlusal stability 2.5 years after treatment in adults with Class II Division 1 malocclusions.

Reduced mandibular cast splints an alternative in Herbst therapy? A prospective multicentre study

The aim of this study was to analyse anchorage loss with reduced, in comparison with total mandibular cast splints during Herbst treatment. Lateral head films of 32 Class II division 1 patients (15 females, 17 males) aged 13.0 years with reduced mandibular cast splints (RMS: second premolar to second premolar) and of 34 Class II division 1 patients (19 females, 15 males) aged 13.9 years with total mandibular cast splints (TMS: molar to molar) were analysed before (T1) and directly after (T2) Herbst treatment. Anchorage loss was assessed considering mandibular incisor proclination, changes of lower incisor edge position, and changes of occlusal plane inclination. To assess possible group differences, Student's t-tests were applied. The lower incisors proclined more in the RMS (11.8 degrees) than in the TMS (9.3 degrees) group. However, the amount of incisal edge advancement was less in the RMS (2.9 mm) than in the TMS (3.7 mm) group. The occlusal plane tilted insignificantly less in the RMS (5.7 degrees) than in the TMS (6.3 degrees) group. Reduced and total mandibular casted splint anchorage seemed to be similarly effective. Anchorage loss, measured by mandibular incisor proclination, was greater in the reduced anchorage group, whereas measured by lower incisor edge advancement, it was larger in the total anchorage group. Therefore, RMS can be recommended for Herbst treatment since they are less expensive than total splints.

Herbst appliance therapy and temporomandibular joint disc position: A prospective longitudinal magnetic resonance imaging study

The objective of this prospective study was to verify changes in the position of the temporomandibular joint (TMJ) disc by means of magnetic resonance images (MRIs) in adolescent patients treated with the Herbst appliance. Twenty consecutive Class II Division 1 patients treated with Herbst appliances were selected for the study. MRIs were analyzed at 3 stages: immediately before Herbst treatment (T1), 8 to 10 weeks after appliance placement (T2), and at the end of the 12-month Herbst treatment, immediately after appliance removal (T3). Class I or overcorrected Class I dental-arch relationships were observed after Herbst therapy. The qualitative evaluation showed that each patient had the disc within normal limits at T1. At T2, a slight tendency toward disc retrusion because of mandibular advancement was observed, but, at T3, the disc returned to normal, similar to T1 values. By using a quantitative evaluation, parasagittal MRIs (central, medial, and lateral slices) of the TMJs showed that there was no change of disc position from T1 to T3, except in the central slice, which had a retrusive position of the articular disc at T3. During the 12-month period of Herbst appliance treatment, mild changes in the position of the disc occurred in patients whose articular discs were within normal limits at T1. These changes were within normal physiological limits when evaluated in the short term.

Période optimale pour le traitement par appareil de Herbst

This article endeavours to answer the question of whether treatment at an early or a later age is the ideal time for Herbst therapy. We discuss this topic by summarizing and evaluating the short and long-term effects of the Herbst appliance on the dentofacial complex. We place special emphasis on treatment outcomes in relation to the patient's somatic and skeletal maturity at the time of therapy. We also address the long-term stability of the treatment results. The available knowledge in the literature demonstrates that the ideal period for Herbst treatment is in the permanent dentition at or just after the peak of pubertal growth.

Comparison of Class I and Class II Treatment Duration Among Three Different Orthodontic Practices

The purpose of this investigation was to assess the relative treatment time difference (months/appointments) between Class II Division 1 patients and Class I patients from 3 different orthodontic offices. In addition, we also compared the estimated treatment length with the actual treatment length to determine how accurate the orthodontists were in predicting treatment duration. A total sample of 237 patients representing 3 observational groups (Angle Class I nonextraction, and Class II Division I extraction and nonextraction) were selected from the active retention files of each office. Pretreatment ANB angle, pretreatment overjet, and the pre- and posttreatment PAR scores (weighted) were measured. The results of this investigation indicated that among the 3 orthodontic offices, Class II Division 1 cases took an average of 5 more months than Class I cases. There was no significant treatment time difference (months) between the Class II extraction and nonextraction groups. Class II treatments including Herbst therapy were significantly longer (around 8 months) than treatments including headgears. The treatment length in 4 of the 9 observational groups was significantly underestimated and our data demonstrated no association of pretreatment PAR scores and percentage PAR reduction with treatment duration.