Abstract-
skeletal Class III malocclusion was originally thought to arise primarily from an overdevelopment of mandible,but now maxillary retrusion contributes 60% of the case.skeletal class III malocclusion with maxillary deficiency are among the most difficult to treat,and is often widely treated with protraction facemask.The mandibular growth prediction is difficult so, orthodontist was not willing to render early orthopedic treatment.serial cephalometric radiographs was taken a few years after facemask therapy, and growth treatment response vector(GTRV) was analysed to individualize and to facilitate the accuracy in predicting the excessive mandibular growth which is described and proposed in this article.
Among analyzing dozens of treatment methods and related issues,focussing on discussion of rationale for early “timely” treatment of skeletal class III malocclusion,indication and contraindication of early class III malocclusion treatment,and provides a method of predicting excessive mandibular growth.
Body:
Skeletal class III malocclusion is occur due to hereditary cause although environment factors like oral habbits and mouth breathing play an important role.The skeletal class III malocclusion due to genetic origin can occur due to – excessively large mandible,forwardly placed mandible,smaller than normal maxilla,retroposition maxilla,combination .
Prevalence varies among different ethnic groups.
Incidence- 5% Americans and much greater in Asiatic population.4-5% among Japanese and 4-14% among chinese population.
Individual; with class III malocclusion may have combination of skeletal
And dentoalveolar components.according to guyer and coworkers, 57% of
Patients with normal or prognathic mandible shows maxillary deficiency,so protraction facemask appliance effect on skeletal and dental are documented and also different cephalomeric variables such as position of mandible,corpus length,gonial angle,ramal height helps in predicting successful treatment ourcome have been shown.
Rationale or goals-
- To prevent irreversible soft tissue or bony change like anterior cross bite correction.
- To improve occlusal function
- To improve skeletal discrepancies,provide more favourable environment for future growth.
- To simplify phase II comprehensive treatment
- To provide good facial esthetics.
Indication and contraindication of early class III treatment-
Turpin recommends early treatment should be considered for patient that present positive characteristics like-
- Good facial esthetics
- Mild skeletal disharmony
- No hereditary prognatism
- Presence of anterioposterior functional shift
- Convergence facial pattern
- Symmetrical condylar growth.
- Good patients cooperation
And that present with negative characteristics treatment can be delayed until the growth is completed like-
- poor facial esthetics
- severe skeletal disharmony
- hereditary
- no anterioposterior shift
- divergent facial pattern
- asymmetric condylar growth
- growth complete
- poor patient cooperation
early treatment of skeletal classIII malocclusion-
chin cup therapy-
Skeletal class III malocclusion with normal maxilla and moderately protussive mandible can be treated with chin cup therapy and popular among Asian population as its effect is favourable on sagittal and vertical dimentions.
objectives-
To provide growth inhibition or redirection and posterior position of mandible.
Orthopedic effect-
- Redirection of mandibular growth vertically ,backward position(rotation) of the mandible.
- Remodeling of mandible with closure of gonial angle(angle of mandible)
Types-
occipital pull chin cup- mandibular protussive patients
vertical pull chin cup- steep mandibular angle, excessive anterior
facial height patients.
Orthopedic force- 300- 500g/side
Time- 14hours per day
Protraction facemask-
The protraction facemask used in growing patients having prognathic mandible and retrusive maxilla. It aids in pulling the maxillary structures forward and pushing the mandibular structures backward direction.the facemask has anterior wire with elastics.To minimize the tipping of palatal plane,the protraction elastics are attached near the maxillary canine with downward and forward pull of 30degree from the occlusal plane.
Orthopedic force- 300-600 gram/side depending upon age of patients.
Time- 12hours/day
In mixed dentition stage,maxillary expansion appliance should be fabricated as anchorage for maxillary protraction.
Activation-0.25mm/ turn twice daily for 7-10 days.
Also studies have found that the maxilla can be displaced anteriorly with significant changes in facial sutures.
Objective-
To enhance forward displacement of the maxilla by sutural growth.
According to melsen in her histologial findings found midpalatal suture was broad and smooth in “infantile” stage (8- 10 years),and sqmamous, overlapping in”juvenile” stage(10-13years).
Clinical studies shown,the maxillary protraction was effective in the primary,early mixed,early permanent dentition.optimal time intervene classIII malocclusion is initial eruption of incisors,a positive overjet and overbite at end of facemask treatment appears to maintain anterior occlusion.
In perspective clinical trials,treatment starts in the mixed dentition was stable 2yrs after the removal of appliance due to overcorrection,use of functional appliance as retainer for 1yr.
Random clinical trials shows,when the patient are followed until completion of pubertal growth, 67% will have favourable outcome.also due to unfavourable growth pattern,some need orthognathic surgery.
Growth perdiction of class III malocclusion-
Several investigator have attempted to predict progression of class III malocclusion.Response vector analysis to individualize,enhance the success of predicting excessive mandibular development.patients is then treated with maxillary expansion and protraction facemask to eliminate-
- Anterior crossbite.
- Centric occlusion/ centric relation discrepancy
- To maximize the growth potential of nasomaxillary complex.
To decide whether the malocclusion is camouflaged by orthodontic treatment, or surgical intervention requirement, when growth is completed, the growth treatment response vector (GTRV) is analysed.
The GTRV ratio was calculated by the formula:
GTRV = horizontal growth change in maxilla
Horizontal growth change in mandible.
The result of several experiment in class III with maxillary deficiency ,GTRV ratio falls below 0.33.0.88 can be successfully camouflaged with orthodontic treatment,below 0.38 should need orthognathic surgery.
wth using GTRV analysis.
Conclusion-
Early treatment of class III patients with maxillary deficiency can be performed with protraction facemask and GTRV analysis helps the clinician in predicting the patients with excessive mandibular growth that may not be camouflaged with orthodontic treatment.
protraction facemask is use to eliminate –
Anterior crossbite
Centric occlusion/ centric relation discrepancy
To maximize the growth potential of the nasomaxillary complex.
With orthopedic chin cup therapy, there is change in craniofacial pattern in treating the skeletal class III malocclusion in growing children with skeletal mandibular prognatism.
protraction facemask is ideally performed in early mixed dentition,follow up lateral cephalogram taken 2-3 yrs after treatment to determine horizontal growth of maxilla,mandible
GTRV ratio was calculated during early permanent dention period.
A myofunctional appliance like FRIII can also be used during growth to intercept class III malocclusion due to skeletal maxillary retrusion.
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