Class I Introduction PDF

# Class I ## Benjamin R. K. Lewis ### Chapter Contents: - Aetiology - Skeletal - Soft Tissues - Dental Factors - Crowding - Late lower incisor crowding - Spacing - Median diastema - Early loss of first permanent molars - Displaced Teeth - Vertical Discrepancies - Transverse Discr...

# Class I ## Benjamin R. K. Lewis ### Chapter Contents: - Aetiology - Skeletal - Soft Tissues - Dental Factors - Crowding - Late lower incisor crowding - Spacing - Median diastema - Early loss of first permanent molars - Displaced Teeth - Vertical Discrepancies - Transverse Discrepancies - Bimaxillary proclination - Trauma - Management following traumatic loss of an incisor ### Learning Objectives for this Chapter: - Gain an understanding of Class I malocclusion. - Gain an understanding of management of problems seen in Class I malocclusions. - Gain an understanding of the management of first permanent molars of poor prognosis. - Gain an understanding of orthodontic management following an episode of dental trauma. ### 8.1 Aetiology #### 8.1.1 Skeletal - Usually Class I, but it can be Class II or III with the inclination of incisors compensating for the underlying skeletal discrepancy. - Marked transverse skeletal discrepancies between the arches are more commonly associated with Class II or III occlusions, but milder transverse discrepancies are often seen in Class I cases. - Anterior open bite can occur where the anteroposterior incisor relationship is Class I. #### 8.1.2 Soft Tissues - The major exception is bimaxillary proclination. - This may be racial in origin, but can also occur because of lack of lip tonicity, which results in the incisors being moulded forwards under tongue pressure. #### 8.1.3 Dental Factors - The most common are tooth/arch size discrepancies, leading to crowding or spacing. - Size of the teeth is genetically determined and so, to a great extent, is the size of the jaws. - Environmental factors can also contribute to crowding or spacing. - Premature loss of a deciduous tooth can lead to a localization of any pre-existing crowding. - Local factors include displaced or impacted teeth. ### 8.2 Crowding - Crowding occurs where there is a discrepancy between the size of the teeth and the size of the arches. - Approximately 60% of Caucasian children exhibit crowding to some degree. - Elective extraction of teeth is one method of alleviating crowding. - When planning extractions to manage crowding: - Consider the position, presence, and prognosis of remaining permanent teeth - Consider the degree of crowding - Consider the patient's malocclusion - Consider the patient's age - Consider the patient's profile ### 8.3 Spacing - Generalized spacing is usually due to either hypodontia or small teeth in well-developed arches. - In milder cases, it may be wiser to encourage the patient to accept the spacing or just to gather the anterior teeth together. - Alternatively, if the teeth are narrower than average, acid-etch composite additions or porcelain veneers can be used to widen them. - In severe cases of hypodontia, a combined orthodontic-restorative approach to localize space for the provision of prostheses, or implants, may be required. - Localized spacing may be due to hypodontia; traumatic loss of a tooth; or because extraction was indicated due to displacement, morphology, or pathology. #### 8.3.1 Median Diastema - It is more common in the upper arch. - A normal physiological stage in the early mixed dentition when the fraenal attachment passes between the upper central incisors. ### 8.4 Early Loss of First Permanent Molars - Decisions about the best options for the management of first permanent molars of poor prognosis in the developing dentition can be a challenging and frequent dilemma in general dental practice. - MIH has been reported to be 14.2% globally, and the aetiology is unknown. - Management of first permanent molars of poor prognosis will be determined by many factors, including age, associated malocclusion, suitability for future restorative and orthodontic treatment, and need for a general anaesthetic. ### 8.5 Displaced Teeth - Canines and second premolars are the most commonly affected teeth. - Management depends upon the degree of displacement. - If displacement is mild: consider extraction of the associated primary tooth plus space maintenance. - If displacement is mild: consider exposure and the application of orthodontic traction. - If displacement is severe: extraction of the affected tooth may be necessary. ### 8.6 Vertical Discrepancies - Variations in the vertical dimension can occur in association with any anteroposterior skeletal relationship. - Increased vertical skeletal proportions are discussed in Chapter 9 in relation to Class II division 1, in Chapter 11 in relation to Class III, and in Chapter 12 with respect to anterior open bites. ### 8.7 Transverse Discrepancies - A transverse discrepancy between the arches results in a cross-bite and can occur in association with Class I, Class II, and Class III malocclusions. ### 8.8 Bimaxillary Proclination - Both upper and lower incisors are proclined. - Seen more commonly in some racial groups (e.g. Afro-Caribbean), and this needs to be borne in mind during assessment and treatment planning. - Management is difficult because both upper and lower incisors need to be retroclined to reduce the overjet. ### 8.9 Trauma - Dental trauma is a common event, with approximately 11% of patients being affected prior to the commencement of any orthodontic treatment at 12 years of age. - Boys are affected to a greater extent than girls and the incidence of incisor trauma almost doubles in individuals with overjets in excess of 9 mm, especially if the lips are incompetent. - The evidence regarding the benefits of early treatment is conflicting. - A recent systematic review suggested that early treatment with a functional appliance reduced the incidence of new trauma from 29% to 20%, but that ten patients had to be treated to prevent one episode of trauma. ### 8.9.1 Management following Traumatic Loss of an Incisor - It is important that these cases are managed in close conjunction with all the specialties involved and that prior to the removal of the orthodontic appliances, the patient should be seen by the restorative/surgical specialist, to ensure that the final tooth positions are optimal for any restorative treatment which is planned. - Following traumatic loss of an incisor, a number of options may be considered, including orthodontic space closure; autotransplantation, along with restorative camouflage; or restorative replacement involving the provision of a removable prosthesis, fixed prosthesis, or implant-retained prosthesis. - The various options can be simulated with a diagnostic (Kesling) set-up which allows the feasibility of different treatment options to be assessed in advance of any active treatment.