Recording the severity of malocclusion: Orthodontic indices

Introduction

An index of malocclusion measures the deformity by assigning a numerical weight value to different malocclusion traits and summing up to give a value which denotes the severity of the problem and/or complexity of the treatment and possible difficulties in attaining the outcome.

The qualitative assessment of the deformity has evolved since the first formal classification of malocclusion was proposed by EH Angle (1899, 1904 and 1907), grouping all malocclusions into three distinct classes. Although Angle classification has received many modifications and is used in population surveys, it was soon realised that qualitative categorisation methods were not suited for measuring the severity of the malocclusion and complexity of treatment, hence providing insufficient information on the treatment need.

World Health Organisation/Federation Dentaire Internationale (WHO/FDI)’s basic methods for recording malocclusion (1979) followed the recording of symptoms of malocclusion with carefully defined criteria. This method of recording malocclusion was primarily derived from the principle developed by Bjork et al. (1964) to identify and record individual malocclusion traits.

Efforts to quantify malocclusion by assigning each trait a ‘score’ and assigning ‘weightage’ to the attributes/traits of occlusion (malocclusion) detrimental to oral health or aesthetics have been proposed and researched. A significant issue with recording a malocclusion lies in ambiguity in the perception of the problem. The ‘objective of treatment’ and the ‘severity of the problem’ are greatly influenced by the social norms of aesthetics and the value system of orthodontists. The traits of occlusion/malocclusion are in a state of transition and difficult to ascertain during the mixed dentition period because the occlusion changes from mixed to permanent dentition over the years. The mixed dentition occlusion/malocclusion may improve with growth and not necessarily worsen in all circumstances.

It is necessary to record the occurrence of malocclusion and its severity among different population groups for several reasons.

1.
It helps to document the prevalence of different malocclusion types and traits in different population groups.
2.
It allows us to establish the severity of traits of malocclusions.
3.
Scientific studies require information on occlusion development according to age.
4.
Quantifying the severity of malocclusion can help prioritise the treatment provided in society. This information is especially significant in public health care settings where orthodontic treatment is provided at little or no cost.
5.
Data on the prevalence and severity of malocclusion are fundamental to developing a mechanism for training human resources, building capacity and allocating resources for health care services.
6.
Measuring pre-treatment malocclusion and traits of occlusion can help objectively quantify the outcome of orthodontic treatment and, therefore, establish a self or peer-review process.

Requirements of an index for orthodontic purposes

The index of recording malocclusion should be valid with time and exclude symptoms of developmental changes in occlusion, which are normal for the age.

The index should be ‘sensitive’ to record primary malocclusion defects, that is variation beyond the range of normal occlusion.

Therefore, an index of scoring the malocclusion and its traits should exhibit either an increase in a score (worsening of malocclusion) or remain constant (malocclusion does not worsen), presuming that self-correction of the primary defect of malocclusion does not occur from the transitional stage to permanent dentition stage. The fundamental requirements for an index for orthodontic purposes are summarised in Table 6.1 .

TABLE 6.1

Requirements for an index of occlusion

Source: Reproduced with permission: Tang EL, Wei SH. Recording and measuring malocclusion: a review of the literature. Am J Orthod Dentofacial Orthop. 1993 Apr;103(4):344–51. doi:10.1016/0889-5406(93)70015-G . PMID: 8480700.

1.
The status of the group is expressed by a single number, which corresponds to a relative position on a finite scale with definite upper and lower limits, running by progressive gradation from zero, that is absence of disease, to the ultimate point, that is disease in its terminal stage.
2.
The index should be equally sensitive throughout the scale.
3.
Index value should correspond closely with the clinical importance of the disease stage it represents.
4.
Index value should be amenable to statistical analysis.
5.
Reproducible.
6.
Requisite equipment and instruments should be practicable in an actual field situation.
7.
The examination procedure should require a minimum of judgement.
8.
The index should be facile enough to permit the study of a large population without undue cost in time or energy.
9.
The index would enable the prompt detection of a shift in group conditions, for better or for worse.
10.
The index should be valid during the time.

Several malocclusion indices were developed to fulfil different purposes. Significant attributes of indices were epidemiological recording, grading the severity of malocclusion and differentiating between the types of malocclusion that require urgent treatment or priority over others.

Commonly used indexes are broadly categorised into three groups:

1.
Qualitative diagnostic classification index.
2.
Quantitative methods of scoring classification.
3.
Index to record outcome after treatment. A change in the scores from pre-treatment to post-treatment measures treatment outcomes and categorises the quality of the outcome.

Diagnostic classification index

1.
Occlusal index (OI) of Summers (1966) ^,
2.
Grainger’s Treatment Priority Index (TPI) (1967)
3.
Handicapping malocclusion assessment record (HMAR) of Salzmann (1968)

Occlusal index

Occlusal index (OI) was created to conduct epidemiological research on occlusion or malocclusion. A scoring system was designed for each stage to effectively evaluate dental development, including deciduous, mixed and permanent dentition stages. Each stage required a distinct scoring form, and the system comprised nine unique characteristics.

1.
Dental age
2.
Molar relation
3.
Overbite
4.
Overjet
5.
Posterior crossbite
6.
Posterior open bite
7.
Tooth displacement (actual and potential)
8.
Midline relations
9.
Missing permanent maxillary incisors

OI categorises malocclusion into two broad categories and seven syndromes ( Table 6.2 ):

- a.
  Division I normal and Division II distal molar relation
- b.
  Division III mesial molar relations
- c.
  Seven malocclusion syndromes

TABLE 6.2

Summers Occlusal Index (OI)

Source: Based on Summers CJ. The occlusal index: a system for identifying and scoring occlusal disorders. Am J Orthod. 1971 Jun;59(6):552–67. doi:10.1016/0002-9416(71)90002-9 . PMID: 5280423.

Division I (normal) and Division II (distal molar relation)	Division III (mesial molar relation)
Syndrome A: overjet and anterior open bite	Syndrome F: mesial molar relation, negative overjet, overbite, posterior crossbite, midline diastema and midline deviation
Syndrome B: distal-molar relationship, positive overjet, overbite, posterior crossbite, midline diastema and midline deviation	Syndrome G: Mixed dentition analysis and tooth displacement
Syndrome C: congenitally missing incisors
Syndrome D: Potential tooth displacement and tooth displacement
Syndrome E: posterior open bite

The OI scoring system has undergone the process of testing validity, validity during time and intra-examiner reliability. The OI score is highly valid (r _s = 0.920) compared to the clinical standard and valid over time. The OI score displays high intra-examiner reliability (r _s = 0.963). The OI score is determined by combining the scores of seven syndromes. The highest scoring syndrome is identified, and half of the sum of the remaining scores is added to it. If there is no occlusal disorder, the score is zero.

Treatment priority index

The treatment priority index (TPI) was developed by Grainger (1967) to assess the severity of common malocclusions. Based on the severity of malocclusion, patients could be ranked for the degree of handicap or considered a priority for the provision of orthodontic treatment ( Table 6.3 ).

TABLE 6.3

Treatment priority index by Grainger (1967)

Source: Based on Grainger JW. Orthodontic treatment priority index. National Center for Health Service. Series II. No. 25. Washington: United States Department of Health, Education, and Welfare. Washington DC; 1967.

S no.	Weighted and defined measurements	Malocclusion syndromes
1.	Upper anterior segment overjet	Maxillary expansion syndromes
2.	Lower anterior segment overjet	Overbite
3.	Overbite of upper anterior over lower anterior teeth	Retrognathism
4.	Anterior open bite	Open bite
5.	Congenital absence of incisors	Prognathism
6.	Distal molar relation	Maxillary collapse syndrome
7.	Mesial molar relation	Congenitally missing incisors
8.	Posterior crossbite (maxillary teeth buccal to normal)
9.	Posterior crossbite (maxillary teeth lingual to normal)
10.	Tooth displacement
11.	Gross anomalies

The handicap malocclusion defined by Grainger included the following:

1.
Unacceptable aesthetics
2.
Traumatic conditions predisposing to tissue destruction
3.
Significant reduction in masticatory function
4.
Speech impairment due to malocclusion
5.
Unstable occlusion
6.
Gross or traumatic defects in occlusion

Exclusion: Grainger considered midline diastema and slight asymmetries of little public health significance, and therefore, they were rejected.

TPI is a valid epidemiologic indicator of malocclusion similar to OI. However, it differs in ignoring the possibility of tooth movement and the assessment of mixed dentition. Therefore, TPI is deemed unsuitable for assessing deciduous or mixed dentition occlusion. The values recorded in transitional dentition are not predictive of severity in permanent dentition.

Handicapping malocclusion assessment record

In 1968, Salzmann developed Handicapping malocclusion assessment record (HMAR) to devise a framework for ranking the treatment of malocclusion that results in handicaps.

Malocclusion and dentofacial abnormalities that lead to handicaps were categorised as conditions that can interfere with oral health maintenance and impede the patient’s overall well-being by impacting their mandibular function, speech or appearance ( Table 6.4 ).

TABLE 6.4

Handicapping malocclusion assessment record by Salzmann (1968)

Source: Based on Salzmann JA. Handicapping malocclusion assessment to establish treatment priority. Am J Orthod 1968 Oct; 54 (10): 749–65. PubMed PMID: 5245740. doi:10.1016/0002-9416(68)90065-1

WEIGHTED MEASUREMENTS
Intra-arch deviation	Inter-arch deviation	Handicapping dentofacial deformities
Missing teeth	Overjet	Facial and oral clefts
Crowding	Overbite	Lower lip palatal to maxillary incisors
Rotation	Crossbite	Occlusal interference
Spacing	Open bite	Functional jaw limitation
	Mesiodistal deviation	Facial asymmetry
		Speech impairment

The HMAR allocates scores for dental irregularities and arch mal relationships, multiplied by a weighting factor before the total score is assigned. The scoring and weighting were based on relative point values by orthodontists across the United States based on clinical experience. HMAR also records and weighs functional problems, unlike any other index. A specially designed form records the evaluation of orthodontic models in a clinical setting. Additional scores are assigned for dentofacial deviations such as cleft lip and palate, facial asymmetry and functional disabilities. The evaluation is rapid and does not require special instruments.

The usefulness of any of the indices is judged by the ‘reliability’ to produce the same measurement score when one or more examiners assess a case of malocclusion at any given time or interval. Research has shown that Summer OI has the most negligible bias, correlates best with clinical standards and has the highest validity during a ‘time’.

Quantitative methods of scoring malocclusion and treatment outcome

1.
Dental aesthetic index (DAI)
2.
Index of orthodontic treatment needs (IOTN) and peer assessment rating (PAR)
3.
Index of complexity outcome and need (ICON)
4.
American Board of Orthodontics (ABO) grading system and discrepancy index (DI)
5.
European Board of Orthodontics (EBO)
6.
Discrepancy index of Indian Board of Orthodontics (IBO)

Dental aesthetic index

The DAI index was developed by Cons et al. and represents a relatively simple index that can be obtained intraorally without the need for radiographs. This index has been recognised by the World Health Organization (WHO) as a cross-cultural index, and it was integrated into the items of the international collaborative study of oral health outcomes by the WHO in 1989. ^,

The DAI index comprises 10 components, each carrying its respective weighting, as outlined in Table 6.5 .

TABLE 6.5

Components of and weight used in DAI (1986)

Dental aesthetic index (DAI) components	Weight
No. of missing incisor, canine or premolar teeth in maxillary and mandibular arches	6
Crowding in the incisal segments (no. of segments crowded)	1
Spacing in the incisal segments (no. of segments spaced)	1
Midline diastema in millimetres	3
Largest anterior irregularity on the maxilla in millimetres	1
Largest anterior irregularity on the mandible in millimetres	1
Anterior maxillary overjet in millimetres	2
Anterior mandibular overjet in millimetres	4
Vertical anterior open bite in millimetres	4
Anteroposterior molar relation: largest deviation from normal either left or right, 0 = normal, 1 = 1/2 cusp either mesial or distal	3
Constant	13
Total	DAI score

The cut-off point for malocclusion treatment need index is a value determining whether or not treatment is necessary. When the severity of malocclusion falls below this value, treatment is not considered necessary. Conversely, when the severity of malocclusion exceeds this value, treatment is deemed mandatory. According to Table 6.6 , the recommended cut-off point for the DAI is 31.

TABLE 6.6

Cut-off point of DAI scores

Source: Tables 6.5 and 6.6 are based on: Cons NC, Jenny J, Kohout FJ. DAI: The dental aesthetic index. Iowa City: College of Dentistry, University of Iowa; 1986.

DAI scores	Severity levels
<25	Minor or no anomaly (no or slight treatment needed)
26–30	Definite malocclusion (treatment elective)
31–35	Severe malocclusion (treatment highly desirable)
≥36	Handicapping malocclusion (treatment mandatory)

Limitations of DAI . DAI is a user-friendly tool with limitations. One notable limitation is the failure to consider dental conditions such as buccal crossbite, open bite, centerline discrepancy and deep bite. While these conditions may not be significant from an aesthetic perspective, they could be substantial considerations in outlining the requirements for orthodontic treatment for functional adequacy. ^, It is therefore advisable to carefully examine the limitations of the DAI tool before relying on it to make informed decisions regarding orthodontic treatment.

Index of orthodontic treatment needs and peer assessment rating

IOTN was developed in the United Kingdom by William C Shaw and colleagues to prioritise and group malocclusions according to the severity of the condition and the patient’s treatment needs. This index is particularly advantageous in circumstances where resources for treatment are limited, such as in publicly funded health care services. The IOTN system ranks malocclusions based on the significance of various occlusal traits for the person’s dental health component (DHC) and perceived aesthetic impairment component (AC)). Its primary purpose is to identify individuals who would most benefit from orthodontic treatment.

The index consists of two major components to be evaluated.

A.
Aesthetic component (AC).

DHC ( Table 6.7 )

TABLE 6.7

IOTN and its Dental Health Components (1991)

Source: Shaw WC, Richmond S, O’Brien KD, Brook P, Stephens CD. Quality control in orthodontics: indices of treatment need and treatment standards. Br Dent J 1991 Feb 9; 170 (3): 107–12. PubMed PMID: 2007067. doi:10.1038/sj.bdj.4807429

Grade 1 (no treatment required)
1
Extremely minor malocclusions, including displacements less than 1 mm
Grade 2 (little)
2a
Increased overjet greater than 3.5 mm but less than or equal to 6 mm with competent lips
2b
Reverse overjet greater than 0 mm but less than or equal to 1 mm
2c
Anterior or posterior crossbite with less than or equal to 1 mm discrepancy between retruded contact position and intercuspal position
2d
Displacement of teeth greater than 1 mm but less than or equal to 2 mm
2e
Anterior or posterior open bite greater than 1 mm but less than or equal to 2 mm
2f
Increased overbite greater than or equal to 3.5 mm without gingival contact
2g
pre-normal or post-normal occlusion with no other anomalies. Includes up to half a unit discrepancy
Grade 3 (moderate) or borderline need
3a
Increased overjet greater than 3.5 mm but less than or equal to 6 mm with incompetent lips
3b
Reverse overjet greater than 1 mm but less than or equal to 3.5 mm
3c
Anterior or posterior crossbite with greater than 1 mm but less than or equal to 2 mm discrepancy between retruded contact position and intercuspal position
3d
Displacement of teeth greater than 2 mm but less than or equal to 4 mm
3e
Lateral or anterior open bite greater than 2 mm but less than or equal to 4 mm
3f
Increased and complete overbite without gingival or palatal trauma
Grade 4 (great) or treatment required
4a
Increased overjet greater than 6 mm but less than or equal to 9 mm
4b
Reverse overjet greater than 3.5 mm with no masticatory or speech difficulties
4c
Anterior or posterior crossbite with greater than 2 mm discrepancy between retruded contact position and intercuspal position
4d
Severe displacements of teeth greater than 4 mm
4e
Extreme lateral or anterior open bite greater than 4 mm
4f
Increased and complete overbite with gingival or palatal trauma
4h
Less-extensive hypodontia requiring pre-restorative orthodontics or orthodontic space closure to obviate the need for a prosthesis
4l
Posterior lingual crossbite with no functional occlusal contact in one or both buccal segments
4m
Reverse overjet greater than 1 mm but less than 3.5 mm with recorded masticatory and speech difficulties
4t
Partially erupted teeth, tipped and impacted against adjacent teeth
4x
Presence of supernumerary teeth
Grade 5 (very great) treatment required
5a
Increased overjet greater than 9 mm
5h
Extensive hypodontia with restorative implications (more than one tooth missing in any quadrant) requiring pre-restorative orthodontics
5i
Impeded eruption of teeth (except third molars) due to crowding, displacement, presence of supernumerary teeth, retained deciduous teeth and any pathological cause
5m
Reverse overjet greater than 3.5 mm with reported masticatory and speech difficulties
5p
Defects of cleft lip and palate
5s
Submerged deciduous teeth

Of the two parts of the IOTN, DHC is in the most frequent use. The index synthesises the current evidence for the deleterious effects of malocclusion and the potential benefits of orthodontic treatment. Each occlusal trait is thought to contribute to the longevity and satisfactory functioning of the dentition. Each occlusal attribute is defined and placed into five grades, with clear cut-off points between the grades.

DHC has five grades, categorising cases from grade 1 (no need for treatment) to grade 5 (great need). The DHC may be applied clinically and to study casts. When used on study casts, there are minor differences in the definition of some traits ( Table 6.7 ).

The evaluation protocol on dental study models considers the worst-case scenario of the trait. However, some assumptions may fulfil the worst health component (HC) criteria. An excellent example of the assumption is recording the crossbite. The presence of crossbite assumes a discrepancy of more than 2 mm between the retruded contact position and the intercuspal position of occlusion. Therefore, the DHC in cross bite will always fall under 4a. Various malocclusion features are noted and measured with a specially designed ruler ( Fig. 6.1 ). DHC recognises the recording of the most severe defect/deformity. Other deviations less than the most severe are ignored for grading purposes.

Aesthetic component

The AC consists of a 10-point scale illustrated by a series of numbered photographs. This scale was developed based on attractiveness as rated by lay persons and selected as equidistantly spaced through the range of scores. A rating is given for overall dental attractiveness rather than the specific morphologic similarity to the photographs ( Fig. 6.2 ).

The dental attractiveness (unattractiveness) score indicates the need for orthodontic intervention based on aesthetic impairments. The AC rating reflects and includes the malocclusion’s social and psychological association, leading to the need for treatment.

Peer assessment rating

PAR ^, was developed in 1987 by the British Orthodontic Standards Working Party, which consisted of 10 experienced orthodontists. Following a series of meetings where over 200 study models were analysed, the specialists concluded that evaluating the individual characteristics of occlusion and traits is crucial in determining the alignment and occlusion before and after orthodontic treatment. The objective was to measure the changes that occur after orthodontic treatment and thereby determine the efficacy of the treatment based on the initial severity of the malocclusion.

The occlusion traits are assigned a weighting score based on the evaluation of the study models. However, no consideration is made for improved profile, underlying skeletal base or functional aspects of occlusion. A specially designed ruler ( Fig. 6.3 ) is used to assess the dental casts. The ruler is engraved with each index component to prompt the evaluator to evaluate each element quickly. The PAR index has been tested for its reliability and validity.

The PAR index consists of 11 components:

1.
Upper right segment.
2.
Upper anterior segment.
3.
Upper left segment.
4.
Lower right segment.
5.
Lower anterior segment.
6.
Lower left segment.
7.
Right buccal occlusion.
8.
Overjet.
9.
Overbite.
10.
Centre line.
11.
Left buccal occlusion.

The scoring method involves recording occlusion features of alignment, crowding, spacing and impacted teeth.

The PAR index ruler is used to measure contact point displacement between adjacent teeth parallel to the occlusal plane. The score severity increases as the contact point displacement increases. However, the scoring process does not include contact point displacement between the first, second and third molars. A tooth is considered impacted if the space for its eruption between the two adjacent teeth is 4 mm or less. By convention, impacted canines are recorded in the anterior segment. In case of potential crowding in the mixed dentition, the space deficiency is calculated using the average mesiodistal widths of the permanent successors ( Tables 6.8.1 and 6.8.2 ).

7, 11.

Right buccal occlusion and left buccal occlusion.

Buccal occlusion on both sides is evaluated in all three space planes, that is, anteroposterior, vertical and transverse. The buccal segment relationship is assessed on both sides of the dentition from the canine to the last molar, excluding temporary developmental stages and submerged deciduous teeth. The buccal segment score is the sum of the anteroposterior, vertical and transverse scores ( Table 6.8.3 ).

TABLE 6.8.3

Buccal occlusion assessments

Score	Discrepancy
Anteroposterior
0	Good interdigitation, class I, II and III
1	Less than half unit discrepancy
2	Half a unit discrepancy (cusp-to-cusp)
Vertical
0	No discrepancy in intercuspation
1	Lateral open bite on at least two teeth greater than 2 mm
Transverse
0	No crossbite
1	Crossbite tendency
2	Single tooth in crossbite
3	More than one tooth in crossbite
4	More than one tooth in a scissors bite

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Recording the severity of malocclusion: Orthodontic indices

Introduction

Requirements of an index for orthodontic purposes