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Оглавление6 Class II Div I Malocclusion
6.1 Definition
The lower incisor edges occlude posterior to the cingulum plateau of the upper central incisors.
The upper central incisors are often proclined and there is an increased overjet.
6.2 Prevalence
Thirty‐five per cent of Caucasians present with this type of occlusion.
6.3 Aetiology of Class II Div I
6.3.1 Skeletal Factors
Patients will present with a skeletal Class II with retrognathic mandible.
Dento‐alveolar compensation:Patients may be presenting with a skeletal Class II, however they could be presenting with class I incisors.Patients who have retroclined upper incisors and proclined lower incisors are compensating for a class I incisor relationship; however, when these teeth have been decompensated patients will be turned into a class II div I malocclusion.
Normal, increased or decreased lower anterior facial height (LAFH).
6.3.2 Soft Tissue Factors
Patients could be presenting with incompetent lips for the following reasons:They could be presenting with reduced coverage of the lower lip line, which results in proclined incisors.Patients could present with a retrognathic mandible, resulting in incompetent lips. A retrognathic mandible is found when a patient presents with abnormal posterior positioning of the mandible. Another easier term used to describe this is a backwards positioning of the mandible (the mandible is sat further back relative to the maxilla).Patients could be using excessive muscular activity, which is needed to achieve an oral seal.
Adaptive tongue thrust:An adaptive tongue thrust is a tongue thrust that will cease once the incisors are in the correct position.It is the habit of forcing the tongue between the teeth.Common features found with a tongue thrust are an overjet and anterior open bite (AOB).
Lower lip trap:A lower lip trap can result in upper incisor proclination and lower incisor retroclination.It is seen when the lower lip is drawn up behind the upper incisors.
Strap‐like lower lips:Strap‐like lower lips are also known as tight lips.They cause retroclination of the lower incisors, making a class II div I look worse.
Endogenous tongue thrust:This is a tongue thrust that cannot be ceased once the teeth are in the correct position.It is the habit of forcing the tongue between the teeth.It can cause upper incisor proclination and AOB.A patient with an endogenous tongue thrust will relapse once treatment is complete due to the habit continuing.
6.3.3 Local Factors
Crowding:Crowding can lead to incisors being proclined out of the arch labially, which can result in an increased overjet.Teeth are pushed out of the arch due to there not being enough space for them.
Spacing:A diastema could be present.This could be due to a digit sucking habit which has caused an increased overjet.An underlying mesiodens may be present between the upper central incisors, erupted or unerupted.
Anterior mandibular extractions:Can lead to uprighting of the lower incisors under lip pressure and an increase in the overjet and overbite.
6.3.4 Habit
A persistent digit sucking habit can cause:Increased overjetNarrow upper archProclined upper incisors – class II div ILow tongue positionIncomplete overbiteRetroclined lower incisorsBuccal crossbites.
6.4 Treatment of a Class II Div I
There are six ways to treat a class II div I malocclusion.
6.4.1 No Treatment
Leave the malocclusion and accept the teeth and their discrepancies.
All patients must be informed of the risks if they wish to take the no treatment option.
6.4.2 Removable Appliance
Labial bow:An upper removable appliance (URA) used with a labial bow incorporated.This labial bow is used to retract the upper incisors, which will reduce an overjet.When using a URA to reduce an overjet, it is important to make sure the acrylic which is positioned palatal to the upper anterior teeth is removed, if it is not the overjet will not reduce.
Midline expansion screw:A URA may be used with a midline expansion screw.A class II div I case may present with buccal crossbites.Expansion of the upper arch with a midline expansion screw will help to correct crossbites.
Correct deepbite:Patients could be presenting with a deepbite.A URA can incorporate a flat anterior bite plane (FABP).Incorporating this will allow passive lower molar eruption and lower incisor intrusion, which will help to open the deepbite.
Create space:Space may sometimes need creating.Space can be created by incorporating two unilateral screws to help distalise the posterior segment.
6.4.3 Functional Appliance
A functional appliance may be any of these six appliances:
Clark’s twin block
Herbst
Bionator
Medium opening activator (MOA)
Clip‐on fixed functional (COFF)
Frankel.
A functional appliance postures the mandible forward, reducing the upper anterior segment and proclining the lower anterior segment to reduce the overjet.
6.4.4 Fixed Appliances
Extractions can be considered to relieve crowding in class II div I malocclusions:Maxillary first premolars only:This is considered in a mild–moderate crowded case with a well‐aligned lower arch.In this case the maxillary first premolars are considered because more space is gained from these teeth; due to the need for more space anteriorly to reduce an overjet, this will help to retract the upper incisors.Maxillary first premolars and mandibular second premolars:This is considered in a mild–moderate case with crowding in both arches.Maxillary first premolars would be considered to help retract the upper incisors to reduce an overjet. These teeth are considered because more space is needed anteriorly for retraction.Mandibular second premolars would be considered for moderate crowding on the lower arch, because less space is needed to align the dentition due to there only being mild–moderate crowding.Maxillary and mandibular first premolars:This is considered in a moderate–severe crowded case in both arches.Due to more space being needed in both arches, more space is gained by extracting the first premolars, therefore this would be a consideration in severe cases.Mandibular first premolars are to be extracted if a patient has severe crowding in the lower arch.
Intermaxillary elastics:With a class II div I case, elastics will be considered.Class II intermaxillary elastics would be used.Class II elastics will help to retract the upper anterior segment and procline the lower anterior segment, which will help to reduce the overjet.Class II elastics also work in our favour if a patient also presents with a deepbite, as this allows molar extrusion which will help to open the patient’s bite.
Space closure:Fixed appliances will close all remaining spaces once the overjet has reduced.For example, a patient has had upper first premolars and lower second premolars extracted. In the upper arch, lacebacks will be placed from the upper canines to the upper first permanent molars to achieve a class I canine relationship. Once the canines are in class I, chain elastic will be placed U2–2 to retract the remaining overjet. In the lower arch, lacebacks are used to relieve lower anterior crowding; once teeth are aligned the back teeth will be brought forwards (mesially) to close the remaining spaces.
Correct deepbite:A patient presenting with a deepbite can be corrected in this stage.There are numerous ways of correcting a deepbite with fixed appliances:Bond and engage 7s on archwirePosition anterior brackets more incisallyReverse curve archwiresComposite/metal bite turbosFixed FABPClip‐on FABPIntermaxillary elastics – class IIHeadgear – cervical low pull.
Correct AOB:A patient presenting with an anterior openbite can be corrected in this stageThere are a numerous ways of correcting a AOB with fixed appliances:Posterior bite blocks – intrudes posterior segmentPositioning anterior brackets more gingivallyReverse curve archwires (upside down)Anterior box elasticsIncisor extrusionTemporary anchorage devices (TADs)Kim mechanicsHeadgear – high pull.
6.4.5 Headgear
Create space:Headgear can be used to create space.The type of headgear that would be used is the combi straight pull headgear.This type of pull is level with the occlusal plane, which is used to distalise the maxillary molars.
Correct deepbite:Headgear can be used to correct a deepbite.The type of headgear that would be used is the cervical low pull headgear.This type of pull is below the occlusal plane, which is used to distalise and extrude the maxillary molars. By doing this it encourages a backward growth rotation, which will reduce the deepbite.
Correct AOB:Headgear can be used to correct an AOB.The type of headgear that would be used is the high pull headgear.This type of pull is above the occlusal plane, which is used to distalise and intrude the maxillary molars and achieve maxillary restraint. By doing this it encourages a forward growth rotation, which will reduce the AOB.
6.4.6 Surgery
Surgery can be given as a treatment option to some patients. The majority of patients who have surgery are severe cases. Patients presenting with a severe retrognathic mandible would be considered. The type of surgery would be a bilateral sagittal split osteotomy (BSSO), which achieves mandibular advancement.
