The functions of mastication, speech and esthetics, can suffer varying degrees of disturbance without exerting an unfavorable influence on the development of the dentition and on facial growth. That does not apply to disturbances in other functions in the orofacial region, particularly not in respiration. Further, the behavior of the tongue and the rest of the musculature play an important role. Moreover, sucking habits may have deleterious effects.
Anomalies in the dental arch are numerous, so it is necessary that one has a good knowledge of the optimal and abnormal development of the dentition so that one is able to distinguish between them. (This book is not the place to go into the development of the dentition and the reader is directed to an earlier work by the first author.*)
Other anomalies considered in this chapter are those of the occlusion, and the relationship between the jaws.
Some functional features have a role in the development of the dentition and facial growth, whilst others have little or nothing to contribute (see Chapter 1). Only functional matters of clinical relevance are discussed here.
Long-lasting mouth breathing is often associated with an adaptation in the growth of the face. The lower anterior facial height is increased and the mandibular border runs more steeply. Often there is an anterior open bite and the maxillary dental arch is too narrow. From a general dental and medical standpoint, there are of course other disadvantages.
It is important to recognize if a patient is mouth breathing before a treatment plan is devised. Habitual mouth breathers often need much encouragement to change over to breathing through their noses. Where a restricted nasal passage exists, appliances that may obstruct the airway through the mouth (e.g. activators) may not be worn long enough for treatment to be successful, or may in fact not be worn at all.
There are no indications that motor defects in speech give rise to orthodontic anomalies. It is therefore unrealistic to expect that speech correction will change any dental or skeletal features. Furthermore, it is far from certain if the correction of an orthodontic anomaly—besides, in particular cases, the elimination of diastemata—will actually alleviate a speech defect.
An abnormal tongue position may often be seen in mouth breathers, digit suckers and those whose neuromuscular pattern seem to be predisposed against keeping their tongues within the confines of the dental arches. This latter condition is usually associated with a relatively too small an intra-oral functional space, or too large a tongue.396
Interposition of the tongue between the opposing teeth will impede a good vertical contact from developing. Consequently, the adaptation of the maxillary arch to the mandibular arch will not take place. Depending on the extent of the interposition of the tongue, the dental arches involved will not meet correctly.
It is not realistic to have the same expectations regarding the development of the dentition and facial growth as one might have when there is no interposition of the tongue. It is for this reason that it is essential to diagnose when and where tongue interposition does occur and if possible to find out if the interposition is cause or effect. However, this is not always simple to do because, during transition, gaps exist in the dental arch into which the tongue at rest often extends and at least partly fills. Further, as a consequence of digit sucking, there may be an anterior open bite into which the tip of the tongue is protruded—that is whenever it is not filled by the finger and thumb.
An abnormal form, size, position and activity of the upper and lower lips can have far-reaching effects on the position and inclination of the incisors. This applies also to the mentalis muscle (see 1.7).
However, an initial deficiency in lip material—not infrequently seen after the transition of the incisors—will often change to normal as growth proceeds. “Incompetent lip seals” can change to normal lip closure. Similarly, it is also possible for an initial lip posture, with the lower lip behind the maxillary incisors, to correct itself to a normal position; muscles mature as other parts of the body.
Hypertrophy of the masseter is often associated with limited vertical development of the lower part of the face, and a small gonial angle.
Digit sucking often leads to abnormal tooth position and inclination, and will in certain circumstances influence the growth of the facial skeleton. The effect produced will of course depend on the way in which the digit is sucked, how hard, how often, and for how long.141
Sucking and biting on lips or strange objects (e.g., face flannel, pencil, or the leg of a doll) can result in a typical change in the position of the teeth.
Anomalies within the dental arches are briefly discussed here. The anomalies are compared with the normal adult situation because, in the development of the dentition, a number of phases can be identified in which the position, inclination and angulation of the teeth (particularly the incisors) will differ from the adult picture. Only limited mention is made of some of the characteristics found in the different developmental phases.
It is impossible to make a good orthodontic diagnosis if one is not fully acquainted with the normal picture and the different deviations that may occur within it. However, it is outside the ambit of this book to fully review all the anomalies which can present themselves within the dental arches and only the principal features (and then only very broadly) are discussed. This also applies to occlusal anomalies and jaw relationships, which are dealt with later.
The most prevalent anomaly in a dental arch is the difference between the needed and available arch length. The space available for the teeth in an arch may be too large or too small to accommodate them all harmoniously, and in proper interproximal contact. This deviation is called “Arch Length Discrepancy” (ALD) which manifests itself as “crowding” when teeth have insufficient space, or “spacing” when diastemata are present. (These terms are left open as to whether there is too much or too little of either, and the reader is referred to the footnote in Chapter 1 for an explanation of the way these terms are used here). ALD can be measured in segments of the dental arch.256
As mentioned, crowding is seldom seen in the complete deciduous dentition, but is fairly frequent in the transitional and intertransitional periods. In the adult, crowding is also the rule rather than the exception, especially in the mandibular incisor region.323 Spacing is less often encountered.
In Section 1.5.2 a distinction has been made between primary, secondary and tertiary crowding; they are illustrated and further discussed in Figure 2-1. The three types of crowding can accumulate. Secondary crowding manifests itself earlier in cases of primary crowding than where excess space is present.
Fig. 2-1 Crowding can be divided into primary, secondary, and tertiary crowding.
A Primary crowding in the intertransitional period reveals itself in overlapping and/or rotations of the permanent incisors.
B Primary crowding in the canine region in both arches, which was preceded by early resorption of the root of the mandibular deciduous canine and its loss on emergence of the adjacent permanent lateral incisor.
C Secondary crowding in both arches, which is the sequel to early loss of the second deciduous molars.
D Tertiary crowding of the mandibular incisors, which is attributed to an uprighting of these teeth and continued growth of the mandible. The lack of flat interproximal contacts between the mandibular incisors encourages the development of tertiary crowding.
(Revised from: Van der Linden, F.P.G.M.: Theoretical and practical aspects of crowding in the human dentition. J. Am. Dent. Assoc. 89: 139–153, 1974).
Deciduous teeth very rarely deviate in number. In fact, when a deciduous incisor is absent, the successor is usually also missing. The congenital absence of one or more permanent teeth occurs in about 5% of the population.17 The absence of permanent teeth can give rise to some disturbing complications.
Supernumerary teeth are seen less often than agenesis (about 1%) and give few problems in therapy. They can appear at any place in the arch, though are mostly found in the maxilla and principally in the midline when they are called “mesiodentes”. They can be located in many positions, occasionally they come in pairs.373 An extra deciduous incisor is usually accompanied by a supernumerous successor.
Anomalies in the number of teeth are sometimes not noticed. This is particularly the case with the mandibular incisors and in the molar regions. It is therefore essential to carefully count and properly identify the teeth, and so avoid future embarrassing surprises.
Anomalies in crown size in the permanent incisors, particularly in the maxillary incisors, cause problems.
Too narrow maxillary permanent lateral incisors, but also excessively broad central incisors, can be esthetically disturbing. Very small crowns go with multiple diastemata, very large ones with crowding. The presence of geminated teeth can make treatment rather complex.
The problem of anomalies in tooth form manifests itself mostly in the incisors, though occasionally an abnormally formed molar or premolar will spoil a good occlusion.
In the formation of teeth, disturbances can occur that lead to various anomalies of form of crowns and/or roots, though some abnormal forms, by their typical anatomy (e.g., dens in dentes) are not particularly suitable for preservation. This should be recognized in good time, as early extraction of useless teeth can facilitate treatment considerably.
Peg-shaped crowns of maxillary lateral permanent incisors are frequently ugly, “shovel-shaped” incisors are not. The latter can however make it difficult to obtain a good contact between maxillary and mandibular incisors, and can also increase the tendency to tertiary crowding.94
If one or more teeth in one arch are too wide, or too narrow, this can lead to opposing teeth not fitting well into each other if the other arch has no similar deviation in tooth width; a “Tooth Size Discrepancy” (TSD) exists.
Anomalies in tooth position are very common. Teeth can vary in position, in vestibular, lingual, mesial, distal directions and be similarly tilted. In addition, there can be deviations in relation to the occlusal plane, which concerns vertical dimensions, or in rotation about the long axis of the teeth. A description of these anomalies and the terminology preferred is given below.
The nomenclature of orthodontic anomalies and the Angle Classification are discussed here, as well as abnormalities of occlusion and of jaw relationships, which are considered separately according to whether the components are sagittal, transverse or vertical. The position of maximum occlusion is taken as the starting point in each case. Forced bites and other disturbances affecting the articulation are also considered.
In the naming of tooth positions, occlusions and jaw relationships, there is a sad lack of uniformity. Moreover, the same terms are sometimes interpreted differently. The Orthodontic Department of the University of Groningen, The Netherlands, has constructed a preferred terminology that is systematic and explicit, which is described here.96
The position of an anatomical structure (e.g., the dentition, the nasal floor, the mandible, or the chin), can, with the help of the three planes of orientation be given in relation to the rest of the skull. The planes of orientation are: the Frankfort Horizontal Plane, the Median Plane and the Orbital Plane (Fig. 2-2).
The Frankfort Horizontal Plane runs through both Porion points and the left Orbitale point. The Median Plane runs through the intermaxillary suture and is perpendicular to the Frankfort Horizontal Plane. The Orbital Plane runs through the left Orbitale and is perpendicular to the other two planes. All planes parallel to the Frankfort Horizontal Plane are called “horizontal planes”; all planes parallel to the Median Plane are called “sagittal planes”; and all those parallel to the Orbital Plane are called “frontal planes”.
The position of the teeth is also given in relation to three orientation planes: the occlusal plane, the median plane, and the tuberosity plane (Fig. 2-3). These planes are based on maxillary structures. The occlusal plane is taken to be the imaginary plane through the mesiobuccal cusp tips of the maxillary first permanent molars and the buccal cusp tips of the first premolars. The median plane is found on the plaster model passing through a point on the palatine raphe at the level of the second palatal rugae and the rearmost point on the palatal raphe at the level of the palatine foveola. The median plane is perpendicular to the occlusal plane. The tuberosity plane is the plane tangential to the most dorsal maxillary tuberosity, running perpendicular to the two other planes.
The normal position of a tooth is indicated by the term “orthoposition”; an abnormal position approximately parallel to the normal position with the term position, using a prefix, indicating the direction of the displacement. In sagittal (anteroposterior) directions the prefixes “pro” and “retro” are used; in transverse directions “endo” and “exo”; and in vertical directions “infra” and “supra” (“infra” = at some distance from the occlusal plane; “supra” = passed the occlusal plane). A survey of abnormal positions of teeth and the related terminology is given in Figures 2-4 and 2-5.
In the international literature the position of teeth is frequently given in relation to the dental arches. In such cases the above planes are not used as references, but the prefixes used are “mesio”, “disto”, “labio”, “bucco”, and “vestibulo”, and “palato” and “linguo”.
In a sagittal direction, incisors and canines can be in proposition (labioposition) or retroposition (palatoposition, linguoposition). Premolars and molars can be in proposition or retroposition (mesio or distoposition). Transversely premolars and molars can be in “endo” (palatoposition, linguoposition) or “exo” (buccoposition, vestibuloposition) position.
In a vertical direction all deviating teeth are indicated by infra or supraposition in the way already stated above.
A tooth can also be tipped by rotating about an axis that is perpendicular to its long axis. Tipping is identified by the term “version”. If the tipping axis of anterior teeth is in the direction of the dental arch, then inversion indicates that the crowns of incisors or canines have tipped inwards, and eversion indicates outward tipping. In the case of premolars and molars the term “buccoversion” refers to tipping outwards of the crowns, while “palatoversion” and “linguoversion” apply to inward tipping.
If the axis of tipping is perpendicular to the direction of the dental arch, for all teeth either the terms “mesioversion”, or “distoversion” are used according to whether the crowns tip mesially or distally.
Fig. 2-2 The orientation planes in the skull.
(Duterloo, H.S., De Jager, T.: Terminologie voor orthodontische diagnostiek. Vakgroep Orthodontie, Rijksuniversiteit Groningen, 1978).
Fig. 2-3 The orientation planes of the plaster model. (From: see Fig. 2-2)
Fig. 2-4 Survey of abnormal positions of teeth with the pertinent appellations, illustrating the maxillary right central permanent incisor and right first permanent molar. The normal situation is indicated with a thin outline, the abnormal with a thick one, in both this Figure and Figure 2-5. The same descriptions are used for corresponding maxillary and mandibular teeth. In the maxilla, however, the lingual aspect is frequently called palatal as an alternative.
(Van der Linden: F.P.G.M.: Development of the Dentition. Quintessence Publ. Co., Chicago, 1983).
Fig. 2-5 Schematic representation of some rotations of the maxillary central incisor, first premolar and first molar, all on the right side. In indicating the abnormal positions and their terminology reference is made to the crowns of those teeth.
(From: see Fig. 2-4).
To also describe the direction of the long axis of the tooth, the term “inclination” is often used: labio, linguo, palato inclination, and mesio and disto-inclination. In Anglo-Saxon literat/>