Author: Dr. Shirish M. Bapat.
Class II Division 1 malocclusion is one of the most commonly found malocclusion. It is characterized by Class II molar relationship, increased overjet, narrow dental arches with crowding of anterior teeth. The overbite is increased in horizontal growers and decreased in vertical growers. There may be maxillary excess, or mandibular deficiency or both. This malocclusion has anteroposterior, transverse, and vertical components. If the maxillary arch is narrow in relation to the mandibular arch, the mandible cannot close normally, but gets retruded to occlude in a distal relationship with the opposing arch. In the vertical growers, the excess vertical growth of maxilla and eruption of the posterior teeth in both arches causes mandible to rotate backward accentuating horizontal discrepancy. This opens anterior bite. For every 1 mm eruption of teeth in the posterior region, the bite opens anteriorly by 2 mm.1
Various factors have been described to contribute to the etiology of this malocclusion. They include: heredity, genetic disorders, trauma to the mandible, habits, and various syndromes affecting growth of mandible. As the vertical growth worsens this malocclusion, it seems natural that the control of the vertical growth of maxilla and eruption of the upper and lower posterior teeth will improve the occlusion by causing anterior rotation of the mandible.
CONTROL OF THE VERTICAL GROWTH AND ERUPTION
Control of vertical growth of the maxilla and eruption of the upper and lower posterior teeth can be done by various treatment approaches as stated below.
Functional Appliances with Bite blocks and Headgear
The most effective approach to growth modification involving vertical maxillary excess(VME) and Class II relationship is a combination of extraoral force in the form of high-pull headgear to the maxilla(fig. 1), and a functional appliance with posterior bite blocks to anteriorly reposition the mandible and control eruption.1,2 The extraoral force increases the control of the maxillary growth and functional appliance allows the force to be delivered to the whole maxilla rather than simply to the permanent first molars. The high-pull headgear improves retention of the functional appliance. The outer bow is turned up to pass the force close to the estimated center of resistance of maxilla. The head cap is connected with the outer bow and the force is adjusted to 400-500 g per side in upward and backward direction. The functional appliance provides the possibility of enhancing the sagittal mandibular growth while controlling the eruption of posterior teeth by bite block effect.
|Fig 1: High Pull Headgear.
While registering the bite for construction of the functional appliance, the mandible is brought downward 4-5 mm and forward 5-6 mm. The bite must be opened past the normal resting vertical dimension if molar eruption is to be affected. The viscoelastic forces resulting from stretch of the soft tissues, including muscles, exert a vertical intrusive force on the posterior teeth. In children with anterior openbites, the bite block covers only the posterior teeth and the anterior teeth are allowed to erupt. Whereas, in long face patients without openbite, bite block covers all teeth. As the vertical growth of the maxilla and eruption of the posterior teeth are controlled, the mandible would rotate in an upward and forward direction i.e. anti clockwise.1
As the maxillary anterior teeth are subjected to a distal force by the functional appliance, the incisors tend to tip backward. If this needs to be prevented, the torquing springs(fig. 2) may be incorporated as described by Stockli and Teuscher3 for bodily retraction of the maxillary incisors. Langerstrom et al2 studied 40 subjects with Class II Division 1 malocclusion with at least 5 mm overjet treated with high-pull headgear-activator combination. All patients were instructed to wear the activator-headgear only during sleeping hours. The headgear was adjusted to provide about 300 g force to the maxilla and the upper dentition. The results showed that Class II correction was achieved by distal repositioning of the maxillary teeth(mean, 0.07 mm) and mesial repositioning of the mandibular teeth(mean, 3.3 mm) with wide range of variation. The mean total Class II correction was 3.29 mm + 2.16 mm. The maxillary prognathism often remained unchanged with a slight vertical lowering of the maxilla. Mandibular prognathism was often found to increase during treatment. The mean anterior relocation of pogonion was 2.81 mm + 1.70 mm. The mandibular plane inclination showed no statistically significant change. Kurosava et al4 obtained 3.10 counterclockwise rotation of the mandible in a Class II division 1 malocclusion case with high mandibular plane angle corrected by 2 phase treatment. The first phase involved treatment with quad-helix appliance followed by high-pull headgear with bionator. The second phase involved treatment with fixed edgewise appliance after extractions of four first premolars. Mesial movement of the upper and lower molars was carried out, which accounted for the mandibular forward rotation.
High-pull Headgear to a Maxillary Splint
|Fig. 2: Activator with headgear tubes and torquing springs.
A more effective headgear approach for children with excessive vertical development is the use of a plastic occlusal splint(fig. 3) to which a facebow is attached. This allows vertical force to be directed against all the maxillary teeth- not just the molars- and appears to have a substantial maxillary dental and skeletal effect with good vertical control.1,5
The maxillary splint limits dental eruption better than the headgear just to the maxillary first permanent molars. Unfortunately, this type of appliance allows mandibular posterior teeth to erupt freely. This effect will prevent the upward and forward rotation of the mandible. Hence a posterior bite block may be added to the maxillary splint to prevent molar eruption by forces generated by stretch of the facial soft tissues created by the bite block, and a lingual arch may be placed in the lower arch to prevent compensatory eruption of the lower molars. To achieve both skeletal and dental correction, the patient must be compliant throughout what could be a long treatment period, if not, a fixed maxillary splint is preferred instead of a removable splint.1,5
|Fig. 3: Maxillary splint with headgear tubes.
Fotis et al6
used full coverage maxillary splint for treatment of Class II Division1 cases. Splint formed a bite plate occlusally with even contact on all lower teeth. A Kloehn type face bow was inserted in the tubes embedded in the splint in the molar region. A 500 g headgear force was applied 450 upward and backward in relation to the occlusal plane on each side. They observed a slight anterior rotation of the mandible in most of the cases with 4.9 mm improvement in the molar relationship. In a study of 47 patients with a mean age of 10.19 years for girls and 11.23 years for boys with maxillary dentoalveolar protrusions and Class II, Division 1 malocclusions treated with high-pull headgear attached to a full coverage heat cured plastic maxillary occlusal splint, Caldwell et al 7
found significant inhibition of vertical development of the maxilla, and slight intrusion of the maxillary dentition with no significant increase in the mandibular plane angle. Only the mandibular anterior teeth contacted the splint, which encouraged eruption of the mandibular posterior teeth and leveling of the curve of Spee. Patients were instructed to wear the appliance 24 hours a day except while eating and during sports activities. The ANS moved down 1.52 mm and PNS moved down 1.07 mm in the matched control group, whereas a decrease of 0.1 mm and 0.55 mm was registered in the treatment group. The palatal plane was observed to rotate clockwise only 0.160 in the control group, and 10 clockwise in the traction splint group. SNA angle remained the same in the control group, but it decreased 1.310 in the treatment group. Whereas the mean SNB value increased 0.220 in the controls, it decreased 0.300 in the treated sample. The mean ANB angle decreased 0.210 in the control sample and 0.870 in the treatment sample. The upper incisor retroclined 7.80 in relation to the SN plane, and retracted 1.28 mm in the treatment group, but proclined slightly in the controls. Overbite decreased an average 2 mm in the treated sample, whereas no significant change in overbite was demonstrated in the controls. Maxillary incisor extruded 2.3 mm in the controls but intruded 0.25 mm in the treatment group. The maxillary molar moved an average 1.4 mm distally in relation to point A in the treatment group, but mesially an average 0.24 mm in relation to point A in the control group. In the vertical plane, maxillary molar elongated by 2.4 mm in the controls, but it intruded by 0.4 mm in the treatment sample. The maxillary molar tipped mesially 0.70 in the controls, but tipped distally 3.30 in the treatment group relative to the palatal plane. The palatal plane rotated clockwise 0.840 more in the treatment group than due to growth in the short period. The high-pull traction holds the anterior part of the palate in position while the posterior part is displaced superiorly. The lower molar erupted 1.1 mm to maintain occlusal contact as the upper molar was intruded in the treatment sample. There was significant inhibition of vertical development of the mandibular incisors which can be attributed to the contact of these teeth on the splint serving to retard their eruption. The lower incisor erupted 1.09 mm in the controls as against only 0.24 mm in the treatment group. The treatment resulted in effective vertical control of the maxilla and maxillary molars. Mandibular plane opened only slight by 0.340. Overbite decreased an average 2 mm in the treated patients, whereas no significant change in overbite was demonstrated in the controls. Treatment group showed significant overjet reduction averaging 4.24 mm in the treatment period ranging from 4-20 months.
Stuani Sasso et al8
used high-pull headgear applied to a modified Thurow appliance, which was an occlusal splint covering canine to last molar with expansion screw. The inner bow of the face bow was incorporated in acrylic covering the occlusal surfaces of the posterior teeth. The mandibular plane angle reduced by 50
and facial axis angle increased by 40
, indicating change in the facial growth from vertical to horizontal probably due to the control of the maxillary vertical growth. High-pull Headgear to the Maxillary First Permanent Molars
Early use of a high-pull headgear has been proposed for treating patients with high angle Class II Division 1 malocclusion. It causes restriction of the horizontal and vertical maxillary growth and also causes distal movement of the maxillary molars. Firouz et al9
treated 12 adolescent patients with Class II Division 1 malocclusion, having skeletal age of 9.5 to 12.5 years, with a high-pull headgear force applied to the maxillary first permanent molars. A force of 500 g was used for each side so that the resultant force was directed through the level of trifurcation of the maxillay molars, approximately at a 200
angle to the occlusal plane. Thus the appliance generated a force including intrusive, as well as distally directed component. The intrusive force on the molars was estimated as 500 g., sin 200
. Each patient wore the headgear for a 6-month period, minimum 12 hours a day. A 0.032x0.032 stainless steel passive transpalatal arch was tied to the lingual brackets welded to the first permanent molar bands to maintain symmetry and prevent molar rotation. After 6 months of treatment maxillary molars were distally displaced an average 2.56 mm and intruded an average of 0.54 mm. In contrast, the maxillary molars in the control group were mesially displaced on the average 0.23 mm and erupted 0.42 mm. The distal molar movement in the treatment group significantly contributed to the correction of the Class II molar relationship. Overall, the displacement of the maxillary molars was in the form of translation-like tooth movement. In fact, the roots of these molars were displaced slightly further 2.50
distally than the crowns. The lower molars did not show a compensatory eruption in response to the maxillary molar intrusion. Anteroposterior growth of the maxilla was reduced in the treatment group relative to the control group by 0.5 mm. Horizontally, the maxilla in the treatment group moved distally by an average of 0.33 mm. Whereas in the controls, A point moved forward (mean 0.5 mm). The headgear not only restricted or redirected the anteroposterior growth of the maxilla, but also exerted an orthopedic effect by moving the maxilla distally. In the vertical plane the palate grew downward less than half the amount of downward growth that was observed in the controls. In a female patient aged 9 years of age with Class II Division1 malocclusion, 16 mm overjet, anterior openbite, bilateral crossbite, excessive gingival display, and high mandibular plane angle with short ramus, Sabri10
started phase1 treatment with high-pull headgear therapy using 16 ounce force per side through the center of resistance of the permanent maxillary first molars. Definite intrusion of the maxillary first molars was noticed after 10 months of headgear wear. Phase II, which started at 10 years of age, was initiated with rapid maxillary expansion for 3 weeks and 10 mm of arch expansion was achieved. The same appliance was continued for stabilization for 4 months after giving a double tie through screw holes. After that the expander was removed and high-pull headgear was reinitiated. By 11 years of age, openbite and overjet were significantly reduced and the cross bite was corrected. The headgear was continued in phase III of the treatment which involved nonextraction treatment with 0.022x0.028” edgewise fixed orthodontic appliance. Class I occlusion was achieved at the end of the treatment. The mandibular plane angle reduced by 20
which indicated that the mechanics used controlled the vertical movement of the teeth. The angle SNA reduced by 20
and angle SNB increased by 20
. Cozza et al11 treated 12 year 6 months old boy with skeletal Class II Division 1 malocclusion with severe gummy smile with high-pull headgear to the maxillary first permanent molars and achieved Class I molar relationship after 6 months of treatment. Spontaneous distal drifting of the maxillary premolars occurred. This was followed by a fixed orthodontic appliance therapy. Anterior rotation of the mandibular plane was observed with 30
reduction of the mandibular plane angle and palatal plane rotated anteriorly downward by 50 Trans-Palatal Arch(TPA)
Transpalatal Arches are aimed to cause molar rotation, molar expansion, molar stabilization, reinforcement of molar anchorage and molar intrusion in the maxillary arch. For all functions except the last, the palatal arch is placed 1-2 mm away from the palate(fig. 4). For molar intrusion, the palatal arch is placed further away to transmit intrusive forces of tongue on the molars. Kydd and Toda12
reported that tongue pressure on the hard palate during swallowing has a range of 37-240 g/cm2
) with an average of 112g/cm2
). Yuhi et al13
found that the tongue pressure exerted on TPA during swallowing showed a tendency to increase when the loop of the palatal arch was positioned more distally. The tongue pressure on the TPA placed between first permanent molars was 1.57 and 1.71 N/cm2 for distances of 4 mm and 6 mm from the palate. Maximum pressure was noted when the loop of the TPA was placed in the palatal midline between the right and left second permanent molars. The maximum tongue pressure was seen when the loop of TPA was 6 mm from the palatal mucosa in the second molar region(2.23 N/cm2
). The difference in force level between the 6 mm position and 4 mm position (1.96 N/cm
) of the loop of TPA from the palate was not significant. Hence they recommended positioning the loop of the TPA 4 mm from palate for practical application.
|Fig. 4: Transpalatal arch.
S pena and Gracco14
inserted a transpalatal arch between maxillary first permanent molars with an acrylic button added to improve patient comfort and increase tongue contact surface in an 8 year old patient with skeletal openbite. A high-pull headgear was used to generate vertical intrusive force on the maxillary molars. TPA was progressively lowered in the palatal vault to increase the action of the tongue in intruding or, at least, counteracting the extrusion or eruption of the molars. Loss of the occlusal contact occurred in the molar region. Hence deciduous molar cusps were ground with a diamond bur to reestablish contact of permanent molars. This was continued until the anterior openbite closed by forward rotation of the mandible.
A vertical-pull chin cup(fig. 5) has been successfully used with conventional orthodontic appliances for openbite malocclusions.1,15
decrease in the mandibular plane angle in 20 patients treated with the extraction of 4 premolars and a vertical pull chin cup for 9 months. Redlich et al16
treated an 8 year old female patient with severe high-angle Class II Division1 malocclusion having vertical maxillary excess and gummy smile in two phases. Phase 1 treatment which lasted 14 months consisted of maxillary expansion with Hyrax appliance followed by removable expansion plate to hold expansion achieved by the Hyrax appliance. This was followed by a high-pull headgear in conjunction with a chin cup which was continued in an intermediate phase of 2 years. The phase 2 treatment which started at the age of 13 years involved fixed orthodontic appliance therapy with high-pull headgear for vertical control. The high-pull headgear with chin cup decreased the mandibular plane angle by 30
at the end of phase1 and further reduced it by 10
at the end of phase2. Chin cup has also been used during active RPE therapy to minimize the vertical displacement of the maxilla, control the opening of the mandibular plane angle, and reduce the gonial angle.17,18
Sankey et al,18
using a high-pull chin cup in combination with a bonded palatal expander that infringed on the freeway space by 2-3 mm and activated slowly by 1/4
tuen per week, in combination with a high-pull chin delivering 16-20 ounces of force per side at 450
to the occlusal plane at least 14 hours per day for 6 month in the children with mean age of 8.2 years demonstrated relative intrusion of the maxillary molars, vertical control of the mandibular molars, and increased eruption of the maxillary incisors that contributed to the improvement of occlusion. There was no increased vertical displacement of ANS or PNS. Condylar growth of 3.8 mm occurred which was in a more anterosuperior direction, and the posterior face height increased significantly. The mandible showed almost three times more forward rotation than expected and the chin moved forward almost twice as much as in the controls. The Gonial angle reduced by 1.20
. Mandibular Crozat appliance controlled vertical eruption of the lower molars while expanding the lower arch. There was improvement in all three planes of space. The authors stated that their results support the axiom, “the whole is greater than the sum of its parts.”
Posterior Bite Blocks
|Fig. 5: Chin cup with High-pull headgear.
Posterior bite blocks(fig. 6) have been shown to effectively modify vertical skeletal patterns to control anterior facial heights in animal models and humans.18,19
However, they hinge the mandible open beyond its resting position which tends to increase the gonial angle.19
Animal studies evaluating repelling magnets embedded in the bite block appliances show superoanterior maxillary displacement and molar intrusion. However, they also show greater potential for root resorption due to excessive intrusive forces and deviated mandibular jaw posture that could produce skeletal asymmetries and unilateral crossbites due to the shearing forces created by the repelling magnets.18,19
Iscan and associates18,19
compared the effects of a spring loaded bite blocks worn for 6 months to a passive bite block with a vertical chin cup worn for 8 months. Both groups showed similar amounts of forward maxillary displacement, increase in the mandibular length, posterior molar intrusion, forward mandibular autorotation, increased overbite, and reduction of the anterior facial height. Dellinger21
used active vertical corrector comprising repelling magnets embedded in the bite blocks and acrylic shields to prevent lateral jaw deviations in conjunction with a vertical chin cup. He found intrusion of the posterior teeth, forward mandibular autorotation and reduction of the anterior face height after 4-7 months of treatment.
|Fig. 6: Maxillary appliance with Posterior bite blocks.
It has been found that the short face individuals have higher and long face persons have lower biting forces than those with normal vertical dimension.1
In the cases with muscle weakness syndrome, there is a downward and backward rotation of the mandible associated with excessive eruption of the posterior teeth.1
However, Proffit and Fields1
found that there was no difference in the amount of bite force in the children with long face, normal face and short face. Hence they stated that the different biting force is an effect rather than a cause of the malocclusion. Buschang et al19
stated that there is a considerable evidence showing smaller and less active muscles and weaker biting forces among hyperdivergent subjects. Garcia-Morales et al22
found that greater hyperdivergence was related to poorer mechanical advantage and lower maximum bite force among children, as reported among adults. Patients with myotonic dystrophy have been found to have 2-3 times less EMG activity of the temporalis and masseter muscles during maximum clenching, lower maximum bite forces, anterior openbite malocclusions, and hyperdivergent growth patterns.23,24 These findings support the hypothesis that reduced muscle function may cause changes in the craniofacial morphology.
English and Olfert25
used masticatory muscle exercises as an adjunctive treatment for open bite malocclusions. They treated these cases at an average age of 9.3 years. First, expansion of the narrow maxilla was done with bonded rapid palatal expander. It was followed by a TPA with an acrylic button of 15 mm diameter, 2-3 mm off the palatal shelf. High-pull headgear was then used 12 hours per day with 500 g force per side. Fixed lower lingual arch was placed to maintain arch length and avoid molar extrusion in the lower arch. After expansion, patients in the expansion group were instructed to clench a soft bite wafer for 1 minute 5 times a day. Each 1 minute session included 5 seconds of isometric clenching followed by 5 seconds of rest and repeated six times for a total 1 minute. The exercise regimen was continued for one year. Exercise in combination with high-pull headgear produced favourable results. Gonial angle reduced by average 1.30
, and the mandibular plane angle reduced by average 4.80
. Thus chewing exercises helped to control the vertical dimension and the mandible autorotated anteriorly. Kondo26
treated adult patient with Skeletal Class II openbite by maxillary expansion plate initially to expand tongue space. This was followed by a fixed edgewise appliance treatment with myofunctional therapy consisting of masticatory and cervical muscle training which involved chewing gum exercises and neck muscle massage from start to the end of the treatment. Increased masticatory muscle activity by biting exercises caused intrusion of the overerupted mandibular molars. This facilitated anterior movement and upward and forward rotation of the mandible. This demonstrates the usefulness of the excellent treatment method of “muscle wins” philosophy i.e. restoring normal muscle function by muscle exercises. The malocclusion was corrected in a short period of 25 months. Role of Extractions in the Vertical Control
Garlington and Logan27
showed that second premolar extractions could be useful in treating anterior openbite by reducing the posterior vertical dimension. Aynur28
reported that in the subject with skeletal openbite extending to the posterior teeth treated with extractions of the second premolars or the first permanent molars led to a closing rotation of the mandible by -1.060
respectively. This occurred because the posterior teeth were protracted out of the palato-mandibular wedge. The difference was probably due to the fact that the molars in first molar extraction cases had a greater forward movement compared with those in the second premolar extraction cases. However, there was no decrease in the mandibular plane angle when molars were protracted forward in the first premolar extraction cases. Martina et al29
reduction in the mandibular plane angle in a case of skeletal openbite treated by protraction of upper and lower second molars with closing loop arch wires following extractions of hypoplastic maxillary and mandibular first permanent molars. The extraction treatment has been reported to cause supraeruption of molars during space closure which prevents forward mandibular rotation and reduction in or even maintenance of the vertical facial and dentoalveolar heights. Combined high-pull headgear and extraction treatment produces similar results. The vertical movements of the upper molar are better controlled, but the lower molar shows even greater compensatory supraeruption.19
This effect should be controlled for better results. Orthodontic implants have recently enabled orthodontist to control eruption or even cause active intrusion of the posterior teeth during this phase of treatment. CONCLUSION
Effective vertical control during treatment of Class II Division1 cases produces improvement in the sagittal discrepancy of the upper and lower dental arches. There is individual variation in the treatment response in different patients. All cases do not respond positively. As the vertical growth ceases the last, this control needs to be maintained for a prolonged duration, preferably till end of the mandibular growth. The relapse of the correction of the mandibular plane angle and the gonial angle due to reverting of the growth trend after treatment to the pretreatment pattern necessitates such a prolonged control. Early treatment is critical as it gives a psychological benefit to the child and reduces need for invasive surgical procedures like corticotomy and orthognathic surgery later in the postadolescent phase. REFERENCES
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