Archform

Abbreviations

CBCT: Cone Beam Computed Tomography; CCD: Charged Couple Device.

Introduction

The basic principle of arch form in orthodontic treatment is that within reason, the patients original arch form should be preserved. Arch form at start is established by the configuration of the bony ridge and then by tooth eruption, perioral muscles, and intraoral functional forces to diminish some of these factors, specialists have explored the most effective approach for the proper repositioning of teeth to provide esthetics, function, and stability, and to define the size and configuration of the dental arch. It is well defined that increase in dental arch length and width during orthodontic treatment tend to return toward preliminary values after retention. This lack of stability of the post treatment dental arches is a difficult problem for the orthodontist. Relapse has long been recognized as being partly due to neglect in maintenance of arch form during orthodontic treatment [1].

Importance of Archform

Arch form is important mainly to obtain proper:

• Esthetics
• Function
• Stability

MBT Archform

Mclaughlin RP, et al. [2] have classified arch forms as tapered, square and ovoid when enveloped, the three Arch forms mainly in inter-canine and inter-first premolar width, giving a range of approximately 6 mm in this area [3].

Recent Developments

The era of 3D radiographic imaging with Cone Beam Computed Tomography (CBCT) has led to aggregation of clinical application across all dental disciplines. Frontal views of dental arches aid in the assessment of vertical and transverse dimensions to evaluate inter arch discrepancies (Figure 4).

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Occlusal views of arches reveal relative tooth positions and shape of alveolar bone support. Arch form tracings are made at the height of the alveolus. The arch forms can then be posed to reveal the similarities (Figure 5).

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Arch Form in Lingual Orthodontics

Due to the lingual morphology of the teeth, a straight wire cannot be engaged lingually. The arch form is altered accordingly. The wires used here are “Mushroom Shaped”, with an offset present between canine and premolar. The arch forms are derived from the skeletal and dental anatomy and are therefore designed to be closer to an anatomic ideal than a mathematical ideal. Previous arch wire shapes had their in the concept of an ideal arch form; anatomy probably was not given enough consideration in design [4].

Laser P Mapping

Another interesting concept being developed by Syrinx Technologies, Texas (1976) is to place brackets on teeth, followed by laser mapping to establish the arch form. and transfer those 3 dimensional data to a computer for storage and usage. After the clinician decides the direction the teeth are to go on “arch wire bending robot” can fabricate an individually designed arch wire to achieve the desired movements [5].

Wire Bending Robots

If the effort to fabricate a complex archwire were eliminated, “plain vanilla” brackets without all the straight wire compensations could be used instead of going to the trouble of producing custom brackets with elaborate prescriptions.

In lingual orthodontics, the laser-scanned casts needed for fabrication of custom bracket pads also can provide the data needed to generate computer-fabricated archwires. For labial archwires the data can be accomplished via an intraoral scan that is done using a charged couple device (CCD) video camera connected to a projector [6].

Variation in Arch Form

Over the years the great majority of authors on the subject of arch form have recognized that there is variability in the size and shape of human arch form.

Arch Form Differences Based on Facial Type

Kageyama T, et al. [11] in their study to evaluate dental arch forms associated with various facial types in adolescence with class II div. 1 malocclusion came to the conclusion that dental arch depth of the brachyfacial subjects was significantly greater than that of the mesofacial subjects in the maxillary arch [11].

Even Williams PM [12] recommended that the shape of the head and the face should be considered in order to determine the shape of dental arch. Grabber describes dolichocephalic individuals have long, narrow face and relatively narrow dental arches. Brachycephalic facial type individuals have very broad and relatively short faces and broad round dental arches. Mesocephalic individuals fit somewhere in between these two [12].

Narrow arch forms with V shaped arches and vaulted palates result in many of the intra oral occlusal signs of wear, facets, crowding of teeth, lingual inclination of lower teeth, teeth chipping and cusp breakage with accompanying dry mouth syndrome and a asymmetric faces. These problems if unrecognized and untreated will lead to unstable bites and lack of long term retention after orthodontic therapy. Thus orthodontic or orthopaedic concepts are changing with the dental profession due to numerous clinical results and long term treatment outcomes that many general orthodontic practitioners and orthodontic specialist are experiencing in their clinical care.

Conclusion

The search for a universal ideal arch form has been one of the most persistent but elusive tasks that orthodontic researchers have pursued. Current literature illustrates many divergent views on the shape of arch form it is now generally believed that the arch shape is determined by an interplay between genetic and many varied environmental factors such as pressure from soft tissues; shape and position of jaws; alteration in eruptive mechanism and morphology of teeth.

The basic principle of arch form in orthodontic treatment is that within reason, the patients original arch from should be preserved. These variations in arch form, however, are not reflected in the preformed arch wires presently available and it is important to keep in mind during orthodontic treatment that if they are used, their shape should be considered a starting point for the adjustments necessary for proper individualization Clinicians should therefore be cautious when treating Individuals to a mathematically derived ideal.

The common consensus though seems to be that individualization and coordination of arch forms for each patient is a must to obtain optimum long term stability. A study of any aspect of orthodontics immediately involves the problem of variation in the size of structure variation in the form of parts and variation in function and dental arch from is no exception to this. The form and size of dental arches is Influence by at least 4 factors. Firstly, skeletal parts may not be harmonious or in proportion and this will mean appropriate compromises are indicated from otherwise ideal relations. Secondly, functional problems may alter the oral environment when muscle structure itself may be Inadequate Thirdly psychologic factors may be present causing prolonged habits and fourthly, discrepancies in tooth size and tooth form may alter an otherwise harmonious situation. Because of these complex problems and relatively low knowledge of dental arches as of today. There is no universally accepted ideal arch form. The irony of wisdom is that the more we know about a particular subject, the more our ignorance unfolds and the goal seems far ahead.

Hence, we know that presently there is no generalized, universal, ideal arch form and It is great challenge for an orthodontist to treat the patient we should follow what Dr. Angle suggested nearly a century ago, and which still holds true, that is, “The best the orthodontist can do is to secure normal relations of the teeth and correct general form of arch leaving the finer adjustments to individual type and form to be worked out by Nature through her forces, which must in any event, finally triumph”.