Key findings:

This article emphasizes the essential relationship between malocclusion and classification systems within orthodontics. It underscores the significance of Angle's classification system as a foundational milestone, followed by numerous other classifications that incorporate all three spatial planes, facilitating effective orthodontic treatment. The key findings underscore the pivotal role of classification in delineating malocclusion characteristics, aiding diagnosis, and guiding treatment planning for orthodontic interventions. 

What is known and what is new?

The existing knowledge underscores the integral connection between malocclusion and classification systems, particularly Angle's seminal contribution. What's new lies in the exploration of subsequent classifications that incorporate multidimensional spatial considerations, enhancing diagnostic precision and treatment efficacy in orthodontics. This evolving understanding highlights the dynamic nature of classification frameworks in addressing malocclusion complexities 

What is the implication, and what should change now?

The implication is a call for orthodontic practitioners to embrace advanced classification systems that encompass multidimensional spatial considerations for diagnosing and treating malocclusion effectively. This necessitates updating educational curricula and clinical practices to integrate newer classification methodologies, ensuring optimal patient care and treatment outcomes in modern orthodontics.

Classification forms an important role in diagnosis and treatment planning in various fields and even in the field of orthodontics. It forms the root of the treatment planning and hence being one of the major contents of treatment protocol in orthodontic treatment. It can be defined as grouping of clinical cases of similar appearance for ease in handling and discussion. In order to study the need of classification in orthodontics, we should first know about occlusion, ideal occlusion, normal occlusion and malocclusion [1]

Definition

Occlusion 

It can be defined as the relationship of maxillary and mandibular teeth when the jaws are closed in centric relation without strain of musculature or displacement of condyles in the fossae [2].

Ideal Occlusion 

It is a pre-convinced theoretical concept of occlusal structures and functional relationships that idealized principles and characteristics that an occlusion should have [2].

Malocclusion 

• It can be defined as a condition in which there is departure from the normal relation of teeth to other teeth in the same arch and to the teeth in opposite arch [3].

• An occlusion which is deviated from normal occlusion can be defined as malocclusion [4].

• Malocclusion is an appreciable deviation from the ideal occlusion that may be considered aesthetically unsatisfactory [5].

Therefore, on the basis of normal occlusion and malocclusion, the major criteria to correctly plan a treatment lies in the need of classification. Classification of malocclusion aids in grouping of malocclusion, diagnosis, comparison, treatment planning etc.

Historical aspect of classification of malocclusion [6]

VARIOUS SYSTEMS OF CLASSIFICATION OF MALOCCLUSION

• Angle’s System of classification of malocclusion

• Dewey’s modification in Angle’s Classification

• Lischer’s modification of Angle’s classification

• Simon’s Classification

• Bennett’s classification

• Ackermann and Profitt’s classification

• Ballard’s Classification

• Katz Premolar Classification

• Newly Proposed Classification Systems of Malocclusion.

ANGLE’S SYSTEM OF CLASSIFICATION

This system of classification formed the basic line of index in order to attain a specific system to distinguish malocclusion. The Angle’s classification is the most widely accepted system and most widely used [7] . This system was introduced in the year 1899 by Edward H. Angle which was mainly based on the mesio-distal relation of the teeth, dental arches and the jaws [4]

Basis of Angle’s Classification: [8].

• Most indicative irregularity of teeth found in antero-posterior relationship of the teeth and the jaws.

• There is a normal mesiodistal or antero-posterior position for the body of the mandible with its superimposed mandibular dental arch to occupy in the anatomy of the skull.

• The maxillary dental arch being built upon a base that is a fixed section of the skull anatomy, is more or less stable in its relationship to various landmarks on the head and consequently the first molar teeth in this arch may be quite safely selected as a key tooth from which to judge the relationship of mandibular dental arch and intern to the body of the mandible upon which it is located.

• Curvature and line of occlusion is unique to each individual.

• If there is shifting of maxillary molars in their relationship to the skull anatomy, this variation can be detected by changes in the axial inclination of teeth in the maxillary arch. The axial changes are especially manifested by canine teeth.

Angle used the Roman numerals I,II and III to designate the three main classes of mesiodistal arch relationship which is, Class I or normal, Class II or distal and Class III or mesial relationship of the cusps of the mandibular Ist molar to maxillary Ist molar [9].

He employed the Arabic numerals 1 and 2 to denote division of classification. Unilateral deviations which occurred in malocclusion were referred to as subdivision.

Further, Dr. Angle classified malocclusion on the basis of these numerals and their characteristic features into various types which are [3]

• Class I malocclusion [9]

• Class II malocclusion [10]

• Class II div 1 malocclusion

• Class II div 2 malocclusion

• Class II subdivision

• Class III malocclusion [7]

• True Class III malocclusion

• Pseudo Class III malocclusion

• Class III subdivision

Angle’s Class I malocclusion

It can be defined as the normal relation of the mandibular dental arch and the body of the mandible to the maxillary arch. The relation can be further indicated as the mesiobuccal cusp of the maxillary 1^st permanent molar occludes in the buccal groove of the mandibular 1^st permanent molar [8]. In relation to mesiolingual cusp it can be defined as the mesiolingual cusp of the maxillary 1^st permanent molar occludes in the occlusal fossa of the mandibular first permanent molar when the jaws are in centric relation.

Therefore, malocclusion with respect to Angle’s Class I can be crowding, rotations, abnormal spacing etc. [10]. Another reference taken from the cases involves Class I bimaxillary protrusion and bimaxillary retrusion in which the maxillary and mandibular arch are in normal relation whereas the both upper and lower dentition are in forward relation to facial plane.

Angle’s Class II malocclusion

In Class II malocclusion, the mandibular dental arch and the body of the mandible lies in distal relation to the maxillary arch. Further, in Class II malocclusion the distobuccal cusp of the maxillary permanent 1^st molar lies within the buccal groove of mandibular permanent 1^st molar. In relation to mesiobuccal cusp of the maxillary 1^st permanent molar, it is said that it falls between the space of mandibular 1st permanent molar and the mandibular second premolar

Class II div 1: In this malocclusion, the upper incisors are proclined.

Class II div 2: In this case, the upper laterals overlap the central incisors and the central incisors are retroclined.⁽¹⁰⁾

Salient features of Class II div 1 [11]

• Hypotonic upper lip and fails to form lip seal

• Lower lip cushions the palatal aspect of upper lip

• Unstrained buccinator activity resulting in narrowing of upper arch at premolar and canine region resulting in V shaped arch

• Hyperactive mentalis muscle activity.

Salient features of Class II div 2 [11]

• Lingually inclined central incisors with lateral incisors and canines labially tipped.

• Gives arch a ‘squarish’ appearance.

• Presence of abnormal perioral muscle activity.

• Have an abnormal path of closure due to tipped incisors.

Angle’s Class II Subdivision

When one side of the archhas class I relation whereas the other side of the arch has class II relation, it is referred as Class II Subdivision. The class II subdivision is divided further into 2 types i.e., Angle Class II div 1 subdivision and Class II div 2 subdivision [12].

Angle’s Class III malocclusion

In this type of malocclusion, the mandibular dental arch and the body of the mandible are in mesial relationship to the maxillary arch. It further states that the mesiobuccal cusp of the maxillary permanent 1^st molar occludes in the interdental space between the mandibular 1^st and 2^nd permanent molar. It can be further classified as:

• True Class III (skeletal)

• Pseudo Class III (false or postural) [13]

Salient features of True Class III

• Mainly genetic in origin and is due to:

• Excessively large mandible 

• Forwardly placed mandible

• Smaller than normal maxilla

• Retro positioned maxilla

• Combination of above causes

• Lower incisors tend to be lingually inclined [13]

Salient features of Pseudo class III [13]

• Produced by forward movement of the mandible during jaw closure.

• Can be due to occlusal abnormalities, premature loss of deciduous teeth causing the child to move mandible forward in order to attain contacts and enlarged adenoids.

• Adenoid fasces will be the characteristic feature in cases of enlarged adenoids

Class III Subdivision

The malocclusion is said to be in class III subdivision, if there is class I on one side of the dentition and class III on the other side of the dentition [13].

DRAWBACKS OF ANGLE’s CLASSIFICATION [9]

Angle’s classification involved malocclusion in only anteroposterior direction.

1. The classification wasn’t able to explain malocclusion if molars were absent.

2. It didn’t classify malocclusion related to skeletal relationship.

3. The classification was not applied to the deciduous dentition

4. Severity of malocclusion was not explained.

5. The classification was not able to differentiate between skeletal and dental malrelation and even it was not able to consider various points such as soft tissues, gonial angle, cranial base relations etc.

DEWEY’S MODIFICATION [14]

The modification of Angle’s classification was mainly proposed by Dr. Martin Dewey in 1935 [14]. The modification was introduced in class I and class III relation of Angle’s classification. The modification was as such:

1. MODIFICATION RELATED TO CLASS I MALOCCLUSION

• Type 1: Class I molar relation with crowding of anterior teeth

• Type 2: Class I molar relation with proclined upper incisors

• Type 3: Class I molar relation with anterior crossbite

• Type 4: Class I molar relation with posterior cross bite

• Type 5: Class I molar relation with mesial migration of molars due to early loss of teeth mesial to them

1. MODIFICATION RELATED TO CLASS III MALOCCLUSION

• Type 1: Class III molar relation with edge to edge-- incisor relationship.

• Type 2: Class III molar relation with mandibular incisor crowding.

• Type 3: Class III molar relation with incisors in cross bite.

LISCHER’S MODIFICATION OF ANGLE’S CLASSIFICATION [15]

This modification of Angle’s classification was done in the year 1933 and provided various terminologies for various kinds of molar relationships:

Neutro-occlusion: Synonymous to Angle’s class I malocclusion

Disto-occlusion: Synonymous to Angle’s Class II malocclusion

Mesio-occlusion: Synonymous to Angle’s Class III malocclusion

Bucco-occlusion: Buccal placement of a tooth or a group of teeth

Linguo-occlusion: Lingual placement of a tooth or a group of teeth

Supra-occlusion: When a tooth or a group of teeth have erupted beyond normal level

Infra-occlusion: When a tooth or a group of teeth have not erupted beyond normal level

Mesioversion: Mesial to normal position of tooth

Distoversion: Distal to the normal position of tooth

Transversion: Transposition of two teeth

Axiversion: Abnormal axial inclination of the teeth

Torsiversion: Rotation of a tooth around its long axis.

The nomenclature proposed by Lischer described individual tooth malposition. Therefore, -version was added to each direction of the tooth in order to present its deviation from normal tooth position.

SIMON’s CLASSIFICATION [15-16]

The classification was presented in 1930 and was mainly considered as “craniometric classification”. The classification was mainly related to the vertical orientation of the jaw with respect to the cranial base. The classification mainly involved various planes which were mainly considered in relation to the position of tooth. The planes considered for the classification were:

1. Frankfort Horizontal plane

2. Orbital Plane

3. Mid-Sagittal Plane

Frankfort Horizontal Plane

The plane mainly explained the vertical relationship of the teeth to the plane which included:

1. Attraction: close to the plane 

2. Abstraction: away from the plane

Orbital Plane

It can be defined as a plane dropped perpendicular at a right angle to the F-H plane from the lowermost border of the bony orbit. The plane is mainly associated with anteroposterior relationship

1. Protraction: Teeth are forwardly placed

2. Retraction: Teeth are backwardly placed

Simon’s law of canine: This canine law mainly explains the position of the plane as the plane should pass through the distal third of the canine.

Mid Sagittal Plane

The plane is mainly associated with the transverse relationship of the teeth.

1. Contraction: Teeth are placed closer to the plane

2. Distraction: Teeth are placed away from the plane

The principal contribution of this classification is its emphasis on the orientation of the dental arches to the facial skeleton. This system got the breakthrough in classification as it was able to relate the teeth or dental arches in all the three planes respectively.

However, the classification is a bit confusing and cumbersome and hence makes it difficult to use very often.

BENNETT’s CLASSIFICATION [17]

The classification was proposed in 1912. The classification basically holds the relationship of etiology and its contribution towards malocclusion. 

Class I: It is defined as malposition of tooth or teeth due to any local cause.

Class II: Abnormal formation of the part or whole of the either arch due to the developmental defects of bone.

Class III: Abnormal relationship between upper and lower arch due to abnormal formation of either of the two arches.

ACKERMANN AND PROFFIT CLASSIFICATION [18]

The classification was developed by J.L. Ackermann and W.R. Proffitin [18] the year 1960 which was mainly based on Venn's symbolic diagram. The classification mainly explained the following features which are:

1. Consideration of transverse and vertical discrepancies.

2. Evaluation of arch symmetry and crowding in an arch

3. Incisor protrusion

4. Influence of the dentition on the facial profile

Five main characteristics involved in the classification were

1. Group 1: Intra-arch alignment

The possibilities involved in this group are ideal, crowding, spacing and malpositioned teeth.

1. Group 2: Profile

The profile of a person is most commonly affected due to malocclusion and hence becomes the major set for the classification. This may include anteriorly divergent or posteriorly divergent with lips being concave, straight or convex.

1. Group 3: Transverse skeletal and dental relationships were evaluated

2. Group 4: Assessment of sagittal relationships were evaluated (class of the malocclusion)

3. Group 5: Included malocclusion in the vertical plane (referred as bite depth).

This classification mainly helped further with 2 important aspects that were:

1. Esthetic line of occlusion ^[19]:

This line of occlusion follows the facial edges of the maxillary anterior teeth and posterior teeth and hence becomes a necessary point of view for the occlusion of the arches.

1. Rotational axis ^[19]:

The classification proposed the 3D analysis and became useful in order to evaluate the rotations around the axes perpendicular to all the 3 planes. The 3 points considered were:

1. Pitch

It refers to the vertical relationship of the teeth to the lips and cheeks which can be conventionally described as up-down deviations around anteroposterior axes.

1. Roll

It can be defined as up and down deviations around the transverse axes i.e., the vertical position of the teeth when they are supposed to be different on the right and left sides.

1. Yaw:

It can be defined as right and left deviations around the vertical axes. Therefore, it can be defined as the rotation of the jaw or dentition to one side or the other around the vertical axes.

BALLARD’s CLASSIFICATION[20]

The classification was proposed in the year 1964 and was the main basis for the skeletal classification of malocclusion. The system was developed on the basis of skeletal malformation of the maxilla and the mandible.

Skeletal Class I:

The upward projection of the axis of the lower incisors would pass through the crowns of upper incisors. Therefore, the bases are considered normal

Skeletal Class II

The lower incisors axis would pass palatal to the upper incisor crown and hence shows that the lower apical base is relatively too far backwards.

Skeletal Class III

The projection of lower incisor axis would pass labial to the upper incisor crown and hence shows that the lower apical base is relatively forward.

KATZ PREMOLAR CLASSIFICATION [21-22]

This system of classification was introduced in the year 1992 in which Katz considered the premolar as the major milestone for the classification. The classification involved 3 main classes on the basis of premolar relationships which were:

Premolar Class I

Most anterior upper premolar fits exactly into the embrasure created by the contact of the lower premolars.

Represented as perfect interdigitations and hence regarded as the value 0 mm

Premolar Class II

The most anterior upper premolar is occluding mesial to the embrasure as created by the contacts of the lower anterior premolars. Therefore, these are regarded with positive (+) signs.

Premolar Class III

The most anterior upper premolar is occluding distal to the embrasure created by the contacts of the lower anterior premolars. Therefore, these are regarded with negative (-) signs.

Advantages:

• It provides a quantitative treatment objective that is needed or required to attain excellent buccal occlusion.

• Provides flexibility in terms of finishing a case in functional class II or class III buccal occlusion

• In deciduous and mixed dentition, emphasis is mainly shifted from the permanent 1^st molar to the region of current importance and to the region of space related areas. Hence the classification provides the proper space importance and importance related to the deciduous molar region.

NEWLY PROPOSED SYSTEMS OF CLASSIFICATION

1. WHO CLASSIFICATION

The system of classification was introduced in the year 1995. The system was mainly derived into 6 main groups which are: [23]

1. K07.0: Major anomalies of the jaw size 

      Excludes Acromegaly, hemifacial atrophy or hypertrophy, Robin’s syndrome, unilateral condylar hyperplasia and hypoplasia.

K07.00: Maxillary prognathism.

K07.01: Mandibular prognathism

K07.02: Micrognathia of both jaws

K07.03: Maxillary micrognathia

K07.04: Mandibular micrognathia

K07.05: Micrognathism of both jaws

K07.08: other specified jaw anomalies

K07.09: Anomalies of jaw size unspecified.

1. K07.1: Anomalies of jaw cranial base relationships

K07.10: Asymmetries except hemifacial hypertrophy etc.

K07.11: Mandibular prognathism

K07.12: Maxillary prognathism

K07.13: Mandibular retrognathism

K07.14: Maxillary retrognathism

K07.18: Other specified jaw anomalies

K07.19: Unspecified jaw anomalies

1. K07.2: Anomalies of dental arch relationships

K07.20: Disto-occlusion

K07.21: Mesio-occlusion

K07.22: Excessive overjet

K07.23: Excessive overbite

K07.24: Open Bite

K07.25: Crossbite

K07.26: midline deviation

K07.27: Posterior lingual occlusion of the mandibular teeth 

K07.28: Other specified anomalies

K07.29: Unspecified dental anomalies

1. K07.3: Anomalies of tooth position

K07.30: Crowding

K07.31: Displacement

K07.32: Rotation

K07.33: Spacing

K07.34: Transposition

K07.35: Embedded or impacted tooth in abnormal position excludes embedded or impacted tooth in normal position

K07.38: Other specified anomalies

K07.39: unspecified anatomy of tooth position

1. K07.4: Malocclusion Unspecified

2. K07.5: Dentofacial functional abnormalities

K07.50: abnormal jaw closure

K07.51: Malocclusion due to abnormal swallowing.

K07.54: Malocclusion due to mouth breathing

K07.55: Malocclusion due to tongue, lip or finger habits

K07.58: Malocclusion related to specific abnormalities

K07.59: Malocclusion related to unspecified abnormalities

1. K07.6: Temporomandibular joint disorders

1. NEWLY PROPOSED CLASSIFICATION SYSTEM

Malocclusion classification given by MIGUEL-NETO AND MUCHA in the year 2010 which was based on the Angle’s classification and Katz classification. The above-mentioned classification was compared with the newly proposed classification and yielded a milestone in order to attain suitable results. The newly proposed classification advocated the classification system in anteroposterior orientation, based on the relationship of the distobuccal cusp of the upper 1^st permanent molar and the occlusal embrasure located between the first and second molars.

Therefore, the upper 1^st permanent molar was considered as the reference. So, the classification attained the ultimate goal as to stable the orthodontic treatment by stabilizing the distobuccal cusp between lower 1^st and 2^nd permanent molar embrasure space [24]

1. The Viazis Classification of Malocclusion [25]

This classification system was mainly based on the morphology of the alveolar bone and can be divided into 2 main categories of bone discrepancy. The 2 main categories involved are:

1, HYPOPLASIA

A, ANTERIOR HYPOPLASIA

1. Dental crossbite     =    One-two anterior teeth are in crossbite

2. Dental underbite   =     Two-three anterior teeth are in crossbite

B, GENERALIZED HYPOPLASIA

1. Minor = Has almost negligible hypoplasia

2. Moderate = The doctor can put the brackets exactly where they need to be on the tooth.

3. Severe = The doctor can’t put the bracket exactly where they need to be on the tooth because of the tooth's lingual position.

4. Excess Dental Overjet = In addition to the alveolar bone defect the overjet is more than 3 mm.

5. Excess Dental Overbite = In addition to the alveolar bone defect, the overbite is such that no brackets can be placed on the mandibular anterior teeth   without bite blocks.

6. Dental Open Bite = Inappropriate arch size -tooth discrepancy. 

2, HYPERPLASIA:

1. Hyperplasia with horizontal spacing.

2. Hyperplasia with vertical spacing.

a.    Minor 

b.    Moderate 

c.    Severe 

The classification was further able to understand the proper treatment protocols required to correct the malocclusion. The treatment procedures involved mechanotherapy with interproximal tooth reduction, use of bite blocks, power chains, elastics, cosmetic dentistry etc.

The orthodontic treatment planning has a major milestone of classification of malocclusion. This milestone can be considered as the foundation of the entire treatment planning. Therefore, in orthodontics, a good knowledge of different systems of classification of malocclusion and their merits and demerits becomes an important consideration in treatment protocols.

As Angle’s system of classification was the main system and an effective one when the system is included in tooth arch discrepancies. Simon's classification was the first attempt to provide the most appropriate description of the abnormalities or malrelations in various occlusal considerations.

The Ackermann and Profitt classification were the main aspect that covered malocclusion in all the three planes of space and even came to know about the severity of malocclusion.

The crux of the entire topic is considered as the classification of malocclusion in each and every patient should be done and checked thoroughly by various effective and suitable systems in order to lay down the proper beginning of diagnosis and treatment planning.

Ethical approval: The study was approved by the Institutional Ethics Committee of Genesis Institute of Dental Sciences and Research, Ferozepur, Punjab, India.

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