Craniofacial growth, diagnosis and treatment planning

• The cranial base

• The nasomaxillary complex

• The mandible

• The dentition/occlusion

Cranial base

The cranial base is essentially a midline structure in which the bones are formed initially in a cartilage and later transformed to bone by endochondral ossification. The changes in the cranial base take place primarily as a result of endochondral growth, mainly at various synchondrosis (Figs 1.1 and 1.2). As ossification proceeds, bands of cartilage called synchondroses remain between the centres of ossification, which subsequently get converted into bone. The midline cranial base contains four primary cartilaginous sutures or synchondroses: the intersphenoidal sutures close by birth, the intraoccipital synchondrosis closes around 5 years of age, the sphenoethmoidal synchondrosis closes around 6–7 years of age and the sphenooccipital synchondrosis closes by 13–15 years of age.

As the sphenoethmoidal synchondrosis closes by 6–7 years of life, the segment of the anterior cranial base – designated as the planum sphenoidale – becomes relatively stable, early in life.¹ Therefore, this area is usually used for cephalometric superimpositions to evaluate the changes in the face due to either growth or treatment. The sellanasion (SN) plane is frequently used as a reference plane in order to more accurately determine the changes occurring in the facial structures. The distance between sella and nasion normally increases by approximately 1 mm per year from 6 to 16 years of age. Another frequently used reference plane is nasion–basion plane. The distance between nasion and basion increases by approximately 1.7 mm per year between 6 and 16 years of age. After the closure of the sphenooccipital synchondrosis, any changes occurring either in the length or in the flexure of the cranial base are as a result of remodelling or surface deposition or resorption.²

Though there are minor opening and closing movements in the cranial base angle, this angle is relatively stable for most part. The average cranial base angle is approximately 130°. Obtuse or open cranial base angles are usually associated with a more backward position of the mandible and hence a Class II type of facial pattern. A more acute or closed cranial base angle is normally associated with a more forward position of the mandible and hence a Class III type of facial pattern. The sagittal growth centre – the sphenooccipital synchondrosis – is located in the region of the posterior cranial base, and the growth changes in this area determine the position of the fossa. A large angle between the anterior and posterior cranial base, measured cephalometrically as N-S-articulare (Ar), indicates a posterior position, and a small angle indicates an anterior position of the fossa. The mean value is 123° ± 5° (Fig 1.3). This deviation in the position of the fossa is often compensated by the length of the ascending ramus. If there is no compensatory growth of the ascending ramus, this leads to either retrognathic or prognathic facial profile. Because the glenoid fossa determines the posterior/superior limit of the mandible, it holds important implications for mandibular displacement. Björk³ indicated that the distance between the fossa and the nasion increases by 7.5 mm between 12 and 20 years of age when the landmark Ar is used. As a result of the elongation of the posterior cranial base, the fossa and the temporal bone are displaced inferiorly and posteriorly.⁴ It was observed that the glenoid fossa was displaced between 1.8 and 2.1 mm posteriorly and between 1.0 and 1.8 mm inferiorly, and it demonstrated greater posterior and inferior displacement during adolescence than during childhood.⁵ Therefore, during the treatment planning process for skeletal correction, the clinician should consider posterior fossa displacements to be added to any existing anterior discrepancies and future growth deficiencies. Another important growth change that occurs in the cranial base is the remodelling that takes place in the anterior cranial fossa. This brings about a forward displacement of the frontal bone and the nasal area.⁶

Maxilla

The maxillary complex is surrounded by a system of sutures such as zygomaticomaxillary, frontozygomatic, sphenopalatine and pterygomaxillary. The maxilla mainly grows by bone apposition at the sutures that connect the maxilla to the cranium and the cranial base and by surface remodelling (Fig 1.4). Björk⁷ in his implant study carried out to evaluate the changes in the growth direction of the nasomaxillary complex between 7 and 19 years of age and observed that the maxilla grew in a downward and forward direction at an angle of approximately 51° to the anterior cranial base (SN plane) with a very large range of 0–82° (Fig 1.5). This variation explains the fact that the maxilla would grow primarily in a horizontal direction in some patients, while it would grow primarily in a vertical direction in others. It has been observed that during the first decade of life, the maxillary growth proceeds normally in a horizontal direction, while during the second decade of life, it proceeds in a more vertical direction.⁷

The displacement and remodelling changes play an important role in the growth of the maxilla.⁶ The horizontal displacement of the maxilla is primarily due to remodelling expansion within the middle cranial fossa. Also, deposition of bone on the posterior aspect of the maxilla, in the area of tuberosity, allows it to keep pace with the forward displacement of the frontal and nasal bones (as a result of expansion of the anterior cranial base) and to accommodate for the eruption of the permanent molars. The maxillary length changes are shown in Table 1.1. The vertical displacement of the maxilla occurs primarily by growth and expansion of the eyeballs and the nasal septum. The growth of the cartilaginous nasal septum, especially the vomer and the perpendicular plate of the ethmoid, carries the nasomaxillary complex downward and forward.¹ At birth, the nasal septum is made up entirely of cartilage and extends down to lie within the U-shaped vomer in the vomerine groove. During the first year of life, ossification begins in the perpendicular plate of the ethmoid. By 3 years of age, ethmoid reaches the vomer, and by 10 years of age, it is in contact. After this period, the downward growth of the upper face occurs primarily by the process of apposition. On an average, the amount of this vertical displacement measured from the SN plane to the palatal plane is just over 1 mm per year.

The maxilla, as a result of remodelling changes, takes on periosteal deposits of bone on all of its surfaces. The most significant amount of bone deposition occurs on the posterior aspect of the maxilla. This, in addition to the lateral deposits, allows for lengthening of the dental arch and eruption of the upper teeth. The palate receives periosteal deposits on its oral surface and is resorbed on its nasal surface. In addition to these horizontal and vertical growth changes, the maxilla can undergo rotational change (Fig 1.6). The maxilla can rotate in a downward and forward direction anteriorly, as occurs in the anterior deep bite case, or it can rotate in an upward and forward direction, as occurs in anterior open bite case. The amount and the direction of these rotational changes can be determined by the angle between the SN plane and the palatal plane or by the angle of inclination (AM Schwarz) between the Pn line (perpendicular from N') and the palatal plane. The posterior end of the hard palate does not seem to be subjected to influence by Class III elastics.⁸ However, the maxillary molars may be encouraged to grow downward away from the palatal plane. Anterior end of the hard palate is easily influenced by Class II elastics and extraoral anchorage.⁹ Growth at the intermaxillary and interpalatine sutures, contributing mainly to the maxillary width, occurs during the first 5 years of life.

Mandible

Compared with the growth of the maxilla, both endochondral and periosteal activity play an important role in growth of the mandible. For years, the condylar cartilage was considered a primary growth centre, acting in a manner similar to the epiphyseal growth plate of a long bone. However, histologically, the condylar cartilage is quite different from the cartilage of the epiphyseal growth plate. The mandible is a unique bone that grows in many different ways. It should not be considered a single growth entity but rather different entities, mainly at condyle and ramus, corpus, posterior alveolar process and anterior alveolar process. Other than condyle, all other areas of the mandible are formed and grow by direct surface apposition and remodelling.⁶ (Fig 1.7).

Björk¹⁰ provided an excellent information on the growth of the mandible with his implant studies. These studies revealed that average direction of condylar growth was 6° anterior to a line drawn tangent to the posterior border of the ramus (Fig 1.8). This emphasized the distinct curvature in the direction of condylar growth. He observed condylar growth of 3 mm per year during the childhood period, a slight decrease to prepubertal minimum, followed by an adolescent spurt peaking at 5.5 mm per year at approximately 14.5 years of age. Baumrind et al¹¹ observed that condylar growth remains relatively constant between 8.5 and 15.5 years for both treated and untreated patients. The results of another study showed that the condyle grew between 0.8 and 1.3 mm posteriorly and between 9.0 and 10.7 mm superiorly over the 4-year period.⁵ The vertical condylar growth was approximately nine times greater than the posterior condylar growth. Boys showed significantly greater superior condylar growth during adolescence than during childhood.

The average individual experiences resorption below the ramus and deposition of bone below the symphysis. These two changes by themselves would tend to increase the gonial angle. The anterior aspect of the chin is generally unaffected and chin prominence occurred by horizontal growth and some resorption at point B. Due to extensive and variable remodelling changes on the inferior border of the mandible, it is considered unsuitable to be used as a reference plane. Björk stated that the four areas in the mandible that are most suitable for the purpose of superimposition are the tip of chin, the inner cortical surface of the inferior border of symphysis, the mandibular canal and the lower contour of the third molar germ from mineralization to root formation.

The posterior growth of the condyle and the posterior border of the ramus contribute to the elongation of the mandibular corpus and the primary displacement of the mandible. Table 1.2 shows growth changes in the mandibular length. The mandible also undergoes secondary displacement as a result of the enlargement of the middle cranial fossa. However, this is not as pronounced as that of the maxilla since the middle cranial fossa growth is mostly localized anterior to the condyles. On the average, ramus height increases by 1–2 mm per year and body length increases by 2–3 mm per year.¹²

The mandible also undergoes rotational change due to the rotation that occurs in the core of the jaw, called internal rotation, and due to surface bone remodelling and alterations in the rate of tooth eruption leading to external rotation¹³ (Fig 1.9). The internal rotation essentially consists of rotation around the condyle (matrix rotation, 25%; Fig 1.9A) and rotation centred within the body of the mandible (intramatrix rotation, 75%; Fig 1.9B). The combination of internal and external rotation results into the overall change in the orientation of the jaw. In majority of the individuals, the core of the mandible, the bone that surrounds the inferior alveolar nerve, rotates during growth in a manner that tends to decrease the mandibular plane (MP) angle (up anteriorly and down posteriorly).

The compensatory surface changes (external rotation) do not allow proportionate decrease in the MP angle as a result of the forward rotation of the core of the mandible. In the average individual during childhood and adolescence, approximately 15° of internal rotation (forward rotation), as observed normally, results into just 3°–4° of decrease in MP angle due to compensatory 11°–12° of external rotation (backward rotation). This compensatory external rotational change is considered to be due to resorption at the posterior part of the lower border of the mandible and due to the apposition at the anterior part of the lower border.

Dental arches

The growth of the maxillary and mandibular alveolar bone is significantly influenced by the presence and eruption of the teeth. Alveolar processes undergo selective remodelling changes through bone deposition and resorption. The facial height is increased primarily due to the vertical growth of the maxillary and the mandibular alveolar processes, which in turn is determined by the eruption of the teeth.

As mentioned earlier, the growth of the alveolar processes is influenced by the presence and the eruption of the teeth. After the eruption of teeth, the progression of the primary dentition to the permanent dentition has an impact on dental arch length, circumference and intercanine and intermolar widths¹⁴ (Fig 1.10). In the maxillary arch, there is an increase in the intercanine width by an average of 6 mm between 3 and 13 years of age and by an average of 1.7 mm between 13 and 45 years of age.¹⁴ The intermolar width in the primary dentition increases by 2 mm between 3 and 5 years of age. The inter-first-molar width increases by 2.2 mm between 8 and 13 years of age, and by 45 years of age, it decreases by 1 mm.

In the mandibular arch, the intercanine width increases by approximately 3.7 mm and then decreases by 1.2 mm between 13 and 45 years of age.¹⁴ There is an increase in intermolar width of 1.5 mm between 3 and 5 years of age. An increase in inter-first-molar width of 1 mm between 8 and 13 years of age is followed by a decrease of 1 mm by 45 years of age.¹⁴ Certain changes in the mixed and permanent dentition like uprighting of the incisors and the loss of the leeway space result in decrease in the arch length.

Horizontal and vertical growth interrelationship

It has been recognized that the growth at the mandibular condyles brings the chin forward, not downward, nor downward and forward. Then, how does the chin move downward and forward or downward and backward? It is only when the vertical growth increments of facial growth begin to influence the condylar growth through occlusal contact that a downward and forward/backward direction of the chin is produced. Therefore, the final vector of growth of the chin is a resultant of the interaction between horizontal growth (condylar growth) and vertical growth (vertical growth of molars). If the condylar growth is greater than the vertical growth in the molar region, there is counterclockwise rotation of the mandible with a resultant horizontal change in the chin position and a less increase in anterior facial height. The greater change in this relationship leads to deep bite. However, if the vertical growth in the molar region is greater than the growth at the condyles, the mandible rotates clockwise with a resultant vertical change in the chin position (less horizontal change) and an increased anterior facial height. The greater change in this relationship causes open bite.

Fred Schudy¹⁵ pointed out that the following vertical growth increments contribute to an increase in facial height:

It should be remembered that, in a patient with clockwise rotation of the mandible, an excessive vertical growth would not help to reduce the ANB angle and also the correction of Class II molar relationship. However, it does facilitate the correction and retention of overbite.¹⁵ On the other hand, counterclockwise rotation of the mandible associated with excessive condylar growth moves the pogonion forward, increases the facial angle, flattens the MP and tends to increase the overbite. In patients showing this type of growth pattern, it is difficult to correct the overbite and retain it. Therefore, molar height plays an important role in controlling the vertical position and, to some extent, the anteroposterior position of the chin.

It is evident from the above discussion that the clinician must have deep understanding of these five principal growth increments – condylar growth, anteroposterior growth at nasion, the vertical growth of the corpus of the maxilla, vertical growth of the maxillary alveolar process and the vertical growth of the mandibular alveolar process –and the impact of their interaction on the chin position and outcome of the treatment. For the normal expression of the growth and the behaviour of the mandible, the condylar growth should equal the total of other four growth increments¹⁵ (Fig 1.11). The vertical growth of the anterior alveolar processes does not have a significant effect on facial height. However, it results in varying degrees of overbite. The vertical growth of the posterior alveolar process of the maxilla exceeds that of the mandible from age 8 to 14.¹⁶ Average growth (in millimetres) of maxilla, maxillary first molar, maxillary incisor, mandibular condyle, mandibular first molar and mandibular incisor in a 3-year period is shown in Figure 1.12.

Overbite changes

The growth of the jaws plays an important role in establishing varying degrees of overbite. The relationship between the condylar growth and the vertical growth of the posterior and anterior alveolar processes controls the amount of overbite. Therefore, to control deep bite or open bite, the clinician should control growth increments that determine this vertical relationship. Fred Schudy¹⁷ has called attention to the following growth increments that are relevant to the overbite relationship.

As mentioned earlier, the vertical growth of the body of the maxilla and maxillary molars has the effect of pushing the mandible downward and backward through occlusal contact, influencing the overbite. The downward growth of the maxillary molars significantly exceeds the downward growth of maxillary incisors (by almost 2:1). Of all the six growth increments, the movement of maxillary incisors downward and away from the palatal pane is the smallest, while the mandibular incisor growth is perhaps the greatest and most variable.¹⁷ The vertical growth of the mandibular molars plays a minor role among these factors.

Facial soft tissue growth

Establishing optimal facial aesthetics is the primary goal of orthodontic treatment. As the position of the underlying hard tissues influences the morphology of the overlying facial soft tissues, it is essential for the clinician to have adequate knowledge of the soft tissue components of the face. In addition to this, the soft tissues of the face undergo significant changes throughout life due to growth, maturation and ageing; this information plays an important role in orthodontic diagnosis and treatment planning.

Posttreatment craniofacial growth

In this chapter, the discussion on craniofacial growth so far has been related to actively growing individuals who constitute a large portion of the average orthodontic patient population. However, a portion of growth that usually occurs after orthodontic treatment can influence the long-term stability of a treated case. Therefore, for comprehensive and successful treatment of the growing child, every clinician should have knowledge about this ‘terminal growth’ of the craniofacial complex. George Schudy²⁵ studied 74 orthodontically treated Caucasians to analyse the effects of post-treatment terminal growth on dentition and deeper basal structures (Fig 1.14). He suggested that the typical terminal growth is characterized by a decrease in SN-MP, SN-occlusal plane and the gonial angle. The mandible moves forward more than the maxilla, and the condylar growth proceeds in a predominantly vertical direction. The maxillary first molar moves forward more than the mandibular first molar. The upper incisors usually tip forward during the terminal phase of jaw growth. Posttreatment mandibular rotation, expressed by decreased SN-MP angle and lingual movement of lower incisor teeth, contribute to the overbite relapse and arch length reduction. The facial profile becomes progressively less convex primarily due to nasal growth and forward movement of the chin.

Ageing: skeletal and soft tissue changes

Knowledge on changes in the dentofacial complex as a result of ageing process is crucial to modern orthodontic diagnosis and treatment planning and should be of significant value to all orthodontists. The study by Behrents²⁶ involving 113 untreated individuals from 17 to 83 years of age provided comprehensive data on the subject. In his study, the subjects from the age of 17–41 years (young adulthood) maintained their craniofacial patterns – Class II individuals grew as Class II individuals, and Class III individuals grew as Class III individuals. The subjects in the age group of 41–83 years showed vertical dimensional changes and became less protrusive. The males showed counterclockwise rotation of the mandible, and females tended to be more vertically growing. The percentage of change in the females was less than that in the males.

The soft tissue changes from age 17 to 83 included increased nasal projection and inferior movement of the nasal tip. The lips became less prominent and positioned inferiorly. Due to decreased lip prominence and lowering of the nasal tip, the nasolabial angle tended to become more acute. Dental changes included uprighting of the maxillary incisors and protrusion of the mandibular incisors in female group only. The mandibular molars uprighted in the males, and it moved forward in the females. The maxillary molars tipped mesially in the males, and it uprighted in the females.

1. To identify various elements of malocclusion and their contribution to the development of a problem

2. To define the nature of the abnormality with an emphasis on exploring the possible aetiological factor

3. To formulate a treatment plan based on the specific needs and desires of the patient

Patient interview (Questionnaire)

The patient interview is often the first formal interaction between the patient and the orthodontist. Patient's general personal information and demographic data should be recorded to facilitate efficient communication between the patient and the office. The patient interview essentially consists of family history and patient history. The goal is to understand the development of the problem to institute appropriate therapeutic procedures and eliminate early causative factors. The author considers the patient's chief complaint or concern as the most important ingredient of patient interview process, as it provides valuable information on whether the patient is seeking functional improvement, aesthetic improvement or both. It also helps in designing a treatment strategy that should ideally incorporate the specific needs and desires of the patient.

A family (genetic) history is aimed at gathering some valuable information about certain malocclusions and other abnormalities present in members of the same family. A data pertaining to the history of orthodontic treatment for any siblings of the patient and either or both parents and the nature of their problems should be recorded. It should be noted that relatively a large number of craniofacial abnormalities are inherited and transmitted through a dominant gene, while in cases of cleft lip and palate, it is mostly through a recessive gene. During the course of interaction, it is common to have a patient or a parent respond that a close relative had a severe problem that required surgery.

Patient's history should include any postnatal trauma, the manner of feeding and nutritional disturbances. Inquiries should be made with respect to the child's general development like the initiation of walking and talking and the eruption of the first deciduous tooth. It is important to explore the possibility of having any abnormal habits like digit sucking and mouth breathing. Relevant information regarding allergies, medications, previous hospitalizations or traumatic injuries should be carefully recorded. While taking patient history, psychological aspects of orthodontic treatment should be discussed with the patient to determine motivation and attitude towards treatment, treatment result expectations, patient compliance etc. Such information is extremely useful to estimate future cooperation during treatment. Medical history of the patient forms an important part of the diagnostic information as it can indicate compromising factors that need special attention during treatment.

In patients with diabetes mellitus, it is essential to get blood glucose level under control prior to orthodontic treatment.²⁷ Plaque control is critical in such patients as they are more prone to develop tooth decay and periodontal breakdown. Diabetes-related microangiopathy can occasionally occur in the periapical vascular supply, resulting in unexplained odontalgia, sensitivity on percussion, pulpitis or even a loss of vitality in sound teeth.^28,29 The clinician should be alert to this phenomenon and should regularly check the vitality of teeth involved, especially when treatment is carried out for a prolonged duration. In adult patients with diabetes, it is important, prior to orthodontic treatment, to obtain a full-mouth periodontal examination including probing depth, plaque and gingivitis scores to determine the need for specific periodontal treatment. Deviations from appropriate diet and the scheduled insulin injections will result in distinct changes in the serum glucose level.³⁰ Hypoglycemic reactions might occur more often in these patients. Type I diabetes mellitus is more often encountered in younger patients who frequently come for orthodontic treatment. For such patients, it is advisable to schedule long duration appointments in the morning hours, and the patient is advised to eat a usual meal and take required medication.

Orthodontic patients with bleeding disorders present two main challenges to the orthodontist: risk of viral infection (hepatitis and HIV) and risk of excessive bleeding. Treatment planning in such patients should incorporate reduction in the duration of treatment and nonextraction treatment whenever possible. Any gingival or mucosal irritation should be avoided; therefore, bonding of molar tubes is preferred over placing bands on the molars. In painful situations, it is better to prescribe acetaminophen with codeine if required and avoid aspirin. In case of gingival bleeding, 25% zinc chloride should be applied.

Patients with HIV infection are in an immunodeficient state and are more susceptible to infections. Therefore, necessary precautions should be taken to avoid cross-infections. Case history pertaining to the past and current medications should be obtained, and its relevance to the orthodontic treatment should be assessed. Low dosage of corticosteroids (1 mg/kg body wt) decreases tooth movement by suppressing osteoclastic activity.³¹ However, high dosage of corticosteroids (15 mg/kg body wt) increases osteoclastic activity, producing more rapid tooth movement and subsequent relapse.³² Therefore, it is advisable to avoid use of corticosteroids during orthodontic treatment.

As there are more and more adults seeking orthodontic treatment, it is important to know the impact of use of bisphosphonates, used in the treatment of osteoporosis and malignancies, on orthodontic treatment. Certain procedures like extractions and placement of miniscrews for skeletal anchorage should be avoided.³³

Clinical examination

Orthodontic complications almost always arise from errors in diagnosis and not from failures in implementation of the proposed treatment plan. The clinical findings, therefore, become the basis of diagnostic procedures to establish accurate diagnosis. The goals of clinical examination are as follows:

Functional examination

Clinical examination of various components of the craniofacial complex in static relationship should be followed by the analysis of functional units of the masticatory system. The goals of this examination are directed towards the aeti-ologic evaluation of abnormality and the determination of type of orthodontic therapy. Modern orthodontic diagnosis and treatment planning should include three most important areas of functional analysis.⁴²

Diagnostic records and their analysis

It is essential to obtain high-quality, uncompromised diagnostic records for further evaluation of teeth and oral structures, occlusion and facial and jaw proportions. These records consist of study models and occlusal records, facial and intraoral photographs and radiographic records. The diagnostic records document the patient's pretreatment condition and provide additional information required to establish accurate diagnosis.

Cephalometric analysis

An analysis of the lateral cephalometric radiograph is one of the valuable tools used in orthodontic diagnosis and cranio-facial research. With the help of various linear and angular measurements, both sagittaly and vertically, it is possible to localize the malocclusion, assess the configuration of the facial skeleton, ascertain the extent of jaw bases and their interrelationship, assess the soft tissue morphology, identify the growth pattern and direction, evaluate the axial inclination of incisors, analyze the posttreatment changes and define the treatment possibilities and limitations. As a clinician, it is important not to establish the diagnosis solely based on the lateral cephalometric analysis as it lacks information on certain important criteria like transverse discrepancies, functional relationships and soft tissue dynamics.

Clinical examination is useful in assessing the facial proportions and jaw relations along with the soft tissue drape in all three planes of space. However, accurate quantification of size, position and orientation of the jaws, teeth and the soft tissues is possible only with cephalometric assessment. The information generated from cephalometric analysis helps in pinpointing the problem areas, which is essential in arriving at accurate diagnosis and establishing a detailed treatment plan. In fact, the data, on numerous occasions, also helps predict the prognosis for a case.

The basic cephalometric points required to analyze various components of the craniofacial complex are shown in Figure 1.33.

Systematic approach to cephalometric analysis should include assessment of

Diagnostic process

The entire process of orthodontic diagnosis and treatment planning involves recognition of the various characteristics of malocclusion, defining the nature of the problem and its aetiology and designing a treatment strategy based on the needs and desires of the individual patient. The diagnostic procedure begins with the patient interview and the initial examination; however, the diagnostic process is focused on the synthesis of relevant diagnostic information and its proper interpretation to establish an accurate diagnosis. The patient interview and the initial examination quickly capture the attention of the clinician to formulate an initial diagnosis, which then guides the practitioner to carry out relevant detailed examination and analysis of records to establish a final diagnosis (Fig 1.42).

The goal of the diagnostic process is to synthesize the relevant diagnostic information and its proper interpretation to produce a comprehensive but concise list of patient's problems. This should ultimately help the clinician to design a rational treatment plan that maximizes benefit to the patient. It is important to derive a problem list from the diagnostic information and prioritize it according to the patient's needs and desires. The patient's concern and the chief complaint are essential components of this process.

1. Static occlusal relationships

2. Dynamic occlusal relationships – functional occlusion goals

3. Optimal dentofacial aesthetics

4. Normal periodontal health

5. Posttreatment stability

Static occlusal goals

Achieving proper occlusal relationship of maxillary and mandibular teeth at the conclusion of orthodontic treatment has been a fundamental goal of any treatment plan. Angle⁵⁰ proposed his most famous key to occlusion as a guide to orthodontic diagnosis and treatment planning. It was based on the sagittal relationship of the maxillary permanent first molar to the mandibular permanent first molar. Since the occlusal problems exist in all three planes of space – sagittal, transverse and vertical – the contemporary orthodontic diagnosis must include a three-dimensional assessment of these abnormalities and establishment of goals accordingly. Andrew's⁵¹ six keys to occlusion, which he developed by studying untreated ideal occlusions, constitute a well-defined goals for static dental alignment. It is important to establish treatment goals for each individual tooth with respect to its best-fit, both anatomically and functionally, and achieve them with appropriate treatment mechanics. Proper alignment of maxillary and mandibular teeth, a well-coordinated archforms, levelled marginal ridges, proper position of contact points, three-dimensional position of individual teeth and the maximum intercuspation of posterior teeth are some of the important static occlusal goals.

Dynamic occlusal relationships

In addition to the above-mentioned static occlusal relationships that at least partially contribute to the stability of a treated case, the clinician should expand the scope of these goals to include the neuromuscular and bony structures of the temporomandibular joint (TMJ). This requires a careful consideration of mainly three areas of functional occlusion: centric relation (CR), anterior guidance and stability of posterior tooth arrangement. CR of the mandible is a superior limit position of the condyles in the fossae, with the mandible centred and at its most closed position.⁴⁸ The essence of optimal TMJ form and function is considered the ‘seated condylar position’, which is defined as superior, anterior and midsagittal (centred transversely).⁵² This should represent an idealized treatment goal. It is important to achieve stable CR of the mandible with maximum intercuspation of the teeth at this position. In the intercuspal position and retruded contact position, the mandible should be situated in the same sagittal plane; the distance between the two positions being less than 1 mm. When the mandible is in CR, all the teeth must occlude in maximum intercuspation. The occlusal scheme that is most successful in preventing occlusal problems in patients over a long period of time is the mutually protected occlusion.⁵³ In the absence of other problems, mere presence of centric occlusion – centric relation (CO-CR) discrepancy by itself is not an indication for treatment. However, if there is sufficient cause to treat, the treatment goal should be to achieve the physiologic position of the condyles as determined by the musculature in a superior-anterior fossa position, with the maximum inter-cuspation of the teeth taking place in this position.

As soon as the mandible moves out of centric closure, the maxillary and mandibular anterior teeth should work against each other to separate or disclude the posterior teeth. This anterior guidance is determined by the position of the maxillary and mandibular anterior teeth and their relationship to each other. The lingual surfaces of the upper anteriors should provide harmonious glide path to disclude posteriors during the protrusive excursion of the mandible.

During the mandibular lateral excursions, the maxillary and mandibular canines work against each other and form the main gliding inclines to provide gentle lateral lift, with no lateral interferences on the balancing side. Under certain situations when maxillary cuspid is missing, the mandibular cuspid can be made to work satisfactorily with a maxillary bicuspid. If more teeth than the cuspids on working side are allowed to contact in lateral excursions, uneven wear is likely to occur because each tooth is at a different distance from the rotating condyle and therefore moves on a different arc.⁵⁴ Therefore, in order to achieve the optimal functional occlusion, the following criteria should be carefully observed.

Acceptable goals for centric occlusion (CO)–CR discrepancy for orthodontic cases are as follows:

Occlusal disharmonies cannot be studied in the functioning mouth because the muscles and nerve reflexes, often called neuromuscular avoidance mechanism, protect the teeth by overriding the joint's guidance.⁵⁵ Records taken in the seated condylar position and mounted on the articulator allow the joint and tooth relationships to be evaluated without interferences from the neuromuscular avoidance mechanism. In the process of diagnosis, in order for the clinician to recognize the potential or existing problem cases, it is necessary to know the signs and symptoms of occlusal disharmony. Some of the signs and symptoms of occlusal interferences include⁴⁸ the following:

Orofacial functional goals

The traditional approach to orthodontic treatment planning has been directed towards the achievement of hard tissue goals, while contemporary principles of treatment planning place an emphasis on the soft tissue assessment and management. However, when it comes to defining orthodontic treatment goals, the focus has been on planning tooth movements to achieve ideal occlusal relationships and aesthetics, almost ignoring the goals for stomatognathic function. It is important to understand a relationship between anatomic form and physiologic function and the effects of abnormal functional influences on dentofacial structures and growth.

The clinician should define goals related to the functional criteria that exist in the soft tissue relationships to the teeth. This includes the ability of the patient to achieve adequate lip closure after orthodontic treatment.⁵⁶ The assessment of lip dysfunctions should be done in relation to the configuration and functioning of the lips, and if present, appropriate measures should be taken to eliminate nonnutritive sucking habits, including the visual evidence of mentalis muscle hyperactivity.

The abnormal pressure habit like thumb sucking generally interferes with normal eruption of incisors and promotes excessive eruption of posterior teeth. This habit should be corrected prior to the initiation of orthodontic therapy to make sure that there are no abnormal influences that bring about displacement of teeth. Restoration of normal tongue function and teeth-together swallowing pattern should be the integral parts of treatment goals. As the chronically impeded nasal breathing represents a dysfunction of the orofacial musculature, the patient should be examined carefully to identify the mode of respiration. If abnormal function is detected, a suitable plan should be instituted to encourage nasal breathing to promote normal development of the dentition and efficient orthodontic treatment.

Optimal facial aesthetics

Achievement of optimal facial aesthetics is the primary goal of orthodontic treatment. The aesthetic benefits of orthodontic treatment are the most universally recognized by both patients and practitioners.^57,58 Orthodontic diagnosis and treatment planning have become more sophisticated and scientific, and the emphasis should be placed on soft tissue analysis and its influence on treatment planning. This information should help the clinician to define treatment goals for a well-proportioned, balanced and harmonious soft tissue profile at the conclusion of treatment. The relationships of nose, lips, chin and facial soft tissue dynamics are important considerations. A comprehensive soft tissue evaluation of the patient's facial frontal and profile view should provide valuable information for better understanding of the patient's aesthetic characteristics. This ensures that the patients are treated to their soft tissue/facial aesthetic goals and not just to the cephalometric norms. It should be emphasized that the facial aesthetic goals are not compromised for a good occlusion. The patient's facial aesthetic is determined by the interrelationships and proportions of nose, upper and lower lips and the chin. Those goals can be outlined as follows:

One of the most important aesthetic goals of orthodontic treatment pertaining to the soft tissue dynamics of face is to achieve a ‘balanced smile’. There is no universal ideal smile. The orthodontic treatment should be aimed at achieving the perfect smile that is characterized by the maxillary anterior dentition following the curvature of the lower lip, the corners of the lips that are elevated to the same height (symmetrical), the bilateral negative spaces that separate the teeth from the corners of the lips and displaying appropriate position of the teeth and normal gingival architecture.^59,60

The ideal facial aesthetics require the following:

Other desirable features include the following:

For attractive faces, a range for facial profile analysis (Powell) is as follows:

Periodontal health

One of the prime goals of orthodontic treatment is to achieve optimal periodontal health. This includes the preservation and minimum treatment–induced deterioration of hard and soft tissues of the periodontal apparatus. In postorthodontic treatment, the patient should not show signs of gingival recession, fenestration, dehiscence, periodontal pockets, root resorption or unusual pattern of attrition or crown wear facets. The orthodontist should make a careful assessment of patient's existing periodontal condition and the potential for bone loss or gingival recession during orthodontic tooth movement. An evaluation of the periodontal soft tissues should include an assessment of oral hygiene, areas of mucogingival tension, frenum pulls, amount of attached gingiva etc. Of paramount importance is the amount of attached gingiva – both height and labiolingual thickness.

The following procedures, directly or indirectly, promote better periodontal health:

Posttreatment long-term stability

Long-term stability of tooth positions achieved after orthodontic treatment should be the primary goal of every orthodontic treatment plan. It is an area of great concern to the orthodontic profession and greatly influences the treatment plan. Many of the posttreatment changes in the dentition like deepening of overbite, increased overjet, relapse of treated Class II relationship and crowding of the maxillary and the mandibular incisors are being considered mainly due to posttreatment growth changes. The posttreatment growth significantly contributes to the lingual movement of mandibular incisors leading to deepening of overbite, loss of arch length and lower incisor crowding.²⁵ Other post-treatment changes like anterior open bite and interdental spacing and changes in a single rotated tooth are considered primarily due to local factors such as persistent habits, inability of the periodontal fibres to reorganize and lack of adaptability of the soft tissues.

As mentioned earlier, achievement of static and dynamic occlusal goals, optimal periodontal health and bone support as guidelines to finish orthodontic cases to the highest standards at least partially contribute to the stability. In addition to this, the clinician should consider anticipated posttreatment growth and local factors in the planning of active treatment and retention protocol to enhance long-term stability.

Factors influencing treatment planning

Growth prediction

The ability to forecast or predict dentofacial growth is perhaps the most essential and integral part of contemporary clinical orthodontics. There are several elements the clinician has to deal with in the prediction of craniofacial changes: the direction, the magnitude, the timing, the rate of change and the effects of treatment.⁹ The growth changes in the face are complex and demonstrate a great degree of individual variations, but how predictable are these variations that are considered to be normal, in the growth of the face?

In a broader perspective, the growth prediction can be accomplished by three basic methods: longitudinal, metric and structural.¹⁰

Treatment options

In designing a treatment plan, it is an important step to select the appropriate treatment strategy to resolve the discrepancy. There are several general treatment options available, which need to be carefully explored and evaluated before finalising on the modality of choice. As stated earlier, the treatment plan should be individualized – tailored to individual patient needs. This guides the clinician to make sure that the potential treatment option is carefully assessed and fits with the general treatment goals. One of the common mistakes made by the orthodontist is to design a treatment strategy instinctively based on a quick impression of whether the patient needs extractions or not. It requires a great deal of flexibility on part of the clinician to examine all the rational possibilities to formulate the successful treatment plan.

Treatment sequencing

Establishing a ‘sequenced-treatment mechanics plan’ based on the specific tooth movement goals is essential for a smooth and efficient treatment progress. After the formulation of final treatment plan, the practitioners must be precise in outlining the steps of treatment and the rationale for these steps. In most patients, the treatment mechanics used to achieve a particular goal will also help in the correction of another problem.¹⁰⁰

In a routine orthodontic treatment, the posterior cross-bites should be corrected first prior to addressing other problems. The gross correction of asymmetries may be accomplished easily before the complete bonding is done. However, in some cases, it is mandatory to achieve intra-arch alignment of teeth to facilitate correction in both the maxillary and mandibular arches, especially if elastics are going to be used. Typical treatment sequencing in patients with deep overbite involves initial alignment of teeth followed by intrusion of incisors. Overbite correction usually precedes the closure of extraction spaces; however, in some cases, simultaneous intrusion and retraction of incisors can be accomplished. In nonextraction treatment approach, the maxillary molars can be distalized using fixed distalizing modules to gain adequate space and accomplish molar correction. This will be followed by the stabilization of molars in their new positions, intrusion of incisors, distal drifting of bicuspids, bonding of mandibular arch and progressing to finishing and detailing (Fig 1.44). The above-mentioned couple of examples demonstrate the fact that the treatment sequencing should be individualized, should not follow a set pattern and should be based on the specific tooth movement goals.

The concept of treatment sequencing in the management of patients with interdisciplinary treatment approach is little different and more complex. An interdisciplinary dentofacial therapy is the ultimate utilization of the expertise and skills in the various disciplines of dentistry.¹⁰¹ It involves a team of various specialists like orthodontist, prosthodontist and periodontist with active communication among themselves throughout treatment, from the diagnosis and treatment planning stages through to the completion of active treatment and into the retention phase. The primary goal of treatment sequencing here is to organize the sequence of various treatment procedures provided by different specialists into a logical order so that each intervention performed by one of the specialists from the interdisciplinary team facilitates the next in order.¹⁰² Interdisciplinary treatment typically involves a sequence of disease control (periodontal, periapical infections), correction of structural malrelationships, correction of periodontal defects, restorative therapy and maintenance of optimal oral health.

Evaluation of treatment progress

After the execution of final treatment plan, it is an important step to closely monitor the treatment progress. Active orthodontic treatment phase, the duration of which is estimated and defined at the beginning of treatment and the same is communicated to the patient, involves a series of procedures and events; the goal of every practitioner is to make sure that it proceeds smoothly and efficiently. This is often influenced by many factors like efficiency of orthodontic appliances and their clinical management by the doctor, keeping regular appointments by the patient and reinforcement of oral hygiene protocol by the orthodontic office. It is a good practise to continue to focus on certain specific treatment goals like planned tooth movements or skeletal movements and roughly estimate the time frame by which these goals are expected to be met in order to have total control of progress throughout treatment.

If, for example, maxillary molar distalization therapy with fixed distalizing module has been implemented to gain space in the maxillary arch, its progress should be monitored to check if the molar is being moved distally in a predetermined direction. Certain associated untoward movements like palatal movement of molars should be detected early and the force direction should be altered promptly to avoid unnecessary delays. Quite often, in spite of careful formulation of treatment plan, treatment does not always proceed as planned, especially for patients in whom growth or cooperation is expected. Decalcification of the enamel surface mainly due to poor patient compliance is associated with fixed orthodontic appliance therapy.^103,104 Therefore, appropriate measures should be instituted to prevent the development of white spot lesions and ensure proper treatment progress. An initial inaccurate diagnosis may sometimes lead to the changes in treatment direction. These unexpected revisions of treatment plan are generally expected by the patient if the possibilities are defined and explained at the beginning of treatment. The goal of any good orthodontic treatment plan is to make sure that the decision-making process is complete before the treatment is executed. Progressive evaluation and reevaluation of treatment progress will only help the clinician intercept and reverse untoward events, if any, as they appear rather than allowing them to become big problems leading to a significant extension of overall treatment time. This will also ensure good patient experience and higher levels of patient satisfaction.

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