Orthodontics at a Glance

Daljit S. Gill

• Éditeur: Wiley-Blackwell
• Année: 2013
• ISBN:
  9781118697702
• Édition: 1
• Sujet: Medizin
• Sous-sujet: Kieferorthopädie

Orthodontics at a Glance is part ofthe highly popular at a Glance series. It provides a concise and accessible introduction and revision aid. Following the familiar, easy-to-use at a Glance format, each topic is presented as a double-page spread with key facts accompanied by clear diagrams encapsulating essential knowledge.

Structured over four sections, Orthodontics at a Glance covers:

• Craniofacial growth and development
• Diagnosis and treatment planning
• The management of malocclusion
• Treatment techniques

Orthodontics at a Glance is the ideal companion for all students of dentistry, junior clinicians and those working towards orthodontic specialization. In addition the text will provide valuable insight for general dental practitioners wanting to update their orthodontic knowledge, orthodontic nurses, therapists and technicians.

1

Introduction

Figure 1.1 The scope of orthodontic treatment. Orthodontics can be used for (A) the correction of malocclusion, (B) to facilitate restorative treatment, (C) to aid surgical correction of severe skeletal discrepancies, (D) to facilitate the treatment of cleft lip and palate, and (E) for the comprehensive management of craniofacial deformity as in this patient with Sturge—Weber syndrome.

Figure 1.2 A risk–benefit analysis should be undertaken before commencing orthodontic treatment. Only if the benefits outweigh the risks should treatment be undertaken.

Orthodontics is the specialty of dentistry concerned with growth and development of the face and dentition, and the diagnosis, prevention and correction of dental and facial irregularities. The word orthodontics comes from the Greek words ortho meaning straight and odons meaning tooth.

The scope of orthodontic treatment

Orthodontic treatment is commonly undertaken for the management of malocclusion. Malocclusion is any deviation from normal or ideal occlusion. It should not be considered as a disease but a variation of normal. When such a deviation impacts on an individual’s psychological or dental health one should consider orthodontic treatment.

Besides the management of malocclusion, orthodontics is increasingly being undertaken to enhance the results of other forms of dental and surgical treatment (multidisciplinary care, Figure 1.1A–E). For example, orthodontics can be used to facilitate:

• restorative treatment;
• the management of severe skeletal discrepancies in combination with orthognathic surgery;
• management of cleft lip and palate;
• management of severe craniofacial deformity;
• management of obstructive sleep apnoea.

The demand and need for orthodontic treatment

The patient’s perception of the need for treatment does not necessarily always correspond with the professional’s viewpoint. Often patients will request treatment when there is very little need on dental health grounds. In other cases, patients may not want to pursue treatment even when there would be a clear dental health benefit. A risk-benefit analysis is a useful method of determining whether to undertake treatment. This involves weighing up the risks and benefits of treatment and only undertaking care if the risks are clearly outweighed by the benefits (Figure 1.2).

The need for orthodontic treatment, based on professional criteria, is dependent on the population studied. The treatment need in the UK, on the basis of the Index of Orthodontic Treatment Need (IOTN, see Appendix 1), is estimated to be approximately 45% in 12-year-olds and 35% in 15-year-olds (IOTN Dental Health Component 4 and 5). The uptake of treatment among females is greater than among males even though the need is equal. In the USA, the treatment need is estimated to be 42% in white adolescents and 30% in black adolescents aged 12–17 years. These figures assume that patients who had already received treatment at the time of survey had a definite need for treatment.

Where is orthodontic treatment provided?

The majority of orthodontic treatment is undertaken within specialist orthodontic practices by orthodontic specialists or dentists with a special interest in orthodontics. The latter are not specialists but have undergone some training in orthodontics in addition to training at the undergraduate level. Hospital services provide treatment for those patients requiring complex multidisciplinary care and management of those malocclusions that are of value for the purposes of teaching and training. In the UK, the community dental services also provide care for people from disadvantaged groups for whom access to treatment is otherwise difficult.

How is orthodontic treatment provided?

The majority of orthodontic treatment is provided with the use of fixed orthodontic appliances. There has been a steady increase in the number of patients treated with fixed appliances over time (Table 1.1). The proportion of patients treated with removable appliances has reduced. The quality of the final occlusal result is significantly improved when fixed appliances are used instead of removable appliances. Removable appliances (e.g. functional appliances) are a useful adjunct to simplifying later fixed appliance treatment. The use of fixed appliances should not be attempted without undergoing comprehensive training.

Table 1.1 Types of appliance worn by 12-year-olds (15-year-olds) at the time of survey in 1993 and 2003 (data taken from UK Child Dental Health Survey).

	Percentage of 12(15)-year-olds wearing orthodontic appliances
	1993	2003
Fixed	49% (68%)	72% (83%)
Removable	50% (37%)	28% (18%)

Craniofacial growth and development

2

An introduction to facial growth and development

Figure 2.1 (A) The four main processes involved in growth and development of the craniofacial complex. (B) Various cephalometric features can indicate the likely direction of mandibular growth rotation. These features include the lower anterior face height, the shape of the lower border of the mandible, the inclination of the mental symphysis, inclination of the condylar head and curvature of the mandibular canal. (C) The general pattern of skeletal and neural growth is illustrated (Scammons curves). Mandibular growth has some similarity to the general skeletal growth pattern. (D) This figure shows the height curve for males. The average growth curve (50th centile) as well as curves between the 3rd and 97th centile are shown. The pubertal growth spurt is marked as well as the secondary sexual characteristics that may be present at the beginning and end of the spurt. At least three consecutive measurements (red crosses) are required to estimate with reasonable accuracy the growth curve any particular patient maybe following.

Facial growth and development is a complex three-dimensional process occurring until the late teens and then to a small extent in adulthood. Growth refers to an increase in tissue size as a result of cellular hypertrophy, hyperplasia, an increase in extracellular volume or a combination of these factors. Development refers to an increase in tissue organisation and specialisation. It is essential that the reader appreciates that there is tremendous individual variation in the timing, magnitude and direction of facial growth.

The importance of understanding facial growth

An understanding of normal facial growth and development is important to an orthodontist for several reasons:

• understanding the aetiology of malocclusion;
• recognition of abnormal growth patterns;
• treatment timing (e.g. functional appliances, orthognathic surgery);
• understanding factors influencing treatment stability.

Components of the skull

The skull can be divided into two main components:

• Neurocranium (cranial vault and cranial base);
• Viscerocranium (facial skeleton).

The neurocranium has an important role in supporting and protecting the brain, and provides a passageway for nerves and blood vessels. The viscerocranium is particularly important for mastication, respiration and supporting the eyes.

Processes involved in skeletal growth (Figure 2.1A)

Four processes are important during normal growth and development of the craniofacial skeleton:

• endochondral ossification;
• intramembranous ossification and sutural growth;
• surface remodelling;
• primary and secondary displacement.

Endochondral ossification is the process in which bone develops from a cartilaginous precursor. Cartilage is well adapted to undergoing compressive loading because of its avascular nature. Therefore, it is a good precursor in loaded areas such as the long bones, cranial base and mandibular condyle. Intramembranous ossification is a process in which bone is formed by osteoblasts present in mesenchymal tissue. It is an important mechanism of bone formation in non-weight-bearing areas such as the cranial vault, mandible and maxilla. Surface remodelling refers to the deposition and resorption of bone by the periosteum and endosteum. It alters the shape and size of individual bones and is important during growth and development of the entire facial skele...