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5 Class I Malocclusion

5.1 Definition

The lower incisor edges occlude with or lie immediately below the cingulum plateau of the upper central incisors.

5.2 Prevalence

Fifty per cent of Caucasians present with this type of occlusion.

5.3 Aetiology of Class I

5.3.1 Skeletal Factors

 Patients can present with either a skeletal Class I, II, or III.

 They can present with dento‐alveolar compensation, when they will have the following features:Can be a skeletal II or III.Skeletal II = upper incisors retroclined and lower incisors proclined.Skeletal III = upper incisors proclined and lower incisors retroclined.

 Average, increased, or decreased lower anterior facial height (LAFH).

 Mandibular asymmetry or narrow maxilla can result in crossbites.

5.3.2 Soft Tissue Factors

 Patients usually have favourable soft tissues.

 They could present with bimaxillary proclination, a term used to describe the proclination of the upper and lower incisors.

 Features found with bimaxillary proclination are:Weak muscular toneIncompetent lipsForward tongue positionMacroglossia tongue.

5.3.3 Local Factors

 Dento‐alveolar disproportion can result in crowding or spacing.

 Early loss of deciduous teeth can result in a centreline displacement.

 When there is crowding, teeth can become impacted, such as maxillary canines, maxillary central incisors, first permanent molars or premolars due to early loss of deciduous first molars (Ds) and secondary molars (Es).

 When there is spacing, the ‘ugly duckling’ stage can be seen when maxillary canines are not erupted. Once the canines have erupted this is usually self‐correcting. Patients can present with a diastema due to:Missing lateralsMicrodontSupernumeraryLow fraenal attachment

 Proclined incisors.

5.4 Treatment of Class I

There are five ways in which a class I malocclusion can be treated.

5.4.1 No Treatment

 Leave the malocclusion and accept the teeth, and their discrepancies, as they are.

 All patients must be informed of all the risks if they wish to take the no treatment option.

5.4.2 Removable Appliance

 Create space:An upper removable appliance (URA) can be used to create space.For example, distalization of the posterior segment can be achieved by the use of a nudger appliance with or without headgear.

 Maintain space:A URA can be used as a space maintainer.For example, its use in early loss of deciduous teeth will allow eruption of permanent teeth.

 Aligning:A URA can be used to align the dentition by use of a labial bow.Only tipping movements can be achieved with the use of URAs.

 Correct deepbite:A URA can be useful for patients presenting with deepbites.By incorporating a flat anterior bite plane (FABP) onto the URA, you can achieve incisor intrusion and passive lower molar eruption, which will help to open the patient’s bite.

5.4.3 Fixed Appliance

 Extractions can be considered to relieve crowding in class I malocclusions:Maxillary and mandibular second premolars for mild–moderate crowding.Maxillary and mandibular first premolars for moderate–severe crowding.Second premolars are considered for extractions if mild–moderate crowding is present. The reason they would be considered in this case is because extracting these teeth provides less space within the arch. However, first premolars are considered for moderate–severe crowding, as these provide more space anteriorly.

 Non‐extractions can be considered for the following:Self‐ligating appliances.Using an appliance that has low friction on the teeth.Gaining upper arch expansion to create space, limiting the need for extraction.Achieving a big wide smile creates space‐enabling tooth alignment.

5.4.4 Headgear

Headgear can be used for the following reasons:

 Creating space:Many different types of pull can be considered:Cervical low pullHigh pullCombi pull.Creating space can be achieved by distalising the molars.

 Correcting a deepbite:A cervical low pull would be considered.This type of headgear pulls below the occlusal plane.By pulling below the occlusal plane, distalisation of the molars and extrusion of the molars occur.Extrusion of the molars helps to reduce the deepbite in the anterior region.

5.4.5 Surgery

Rapid maxillary expansion (RME) is used in the upper arch only. It consists of molar bands on U4s and U6s, with rigid arms extending from molar bands with a Hyrax screw. It achieves skeletal expansion by splitting the mid‐palatine suture. Patients can activate the appliance up to four times a day by the use of a key, producing 1 mm of expansion movement a day. The appliance is left in situ for three months to allow for the bony infill of the mid‐palatine suture (expanded suture).