Trevisi Arch Form Article

TREVISI INDIVIDUALIZED ORTHODONTIC ARCH FORM DIAGRAMS

Hugo Trevisi**

Renata Trevisi***

ABSTRACT:

Research on dental arch form since the early 20th century has shown that a successful stability after orthodontic treatment can be achieved if the orthodontist refrains from significantly altering the patient's mandibular arch form, intercanine width and intermolar width.

Thus, this research aimed to devise an ideal archwire form for the patient prior to orthodontic treatment. An archwire form that could prove ideal for the patient based on his/her original dental arch form, while determining whether or not changes are required in light of the form, anterior diameter and posterior diameter of the mandibular dental arch. The authors' recommendation is that the patient's original dental arch form be preserved, unless it has undergone significant changes.

The proposed methodology is straightforward. It consists in superimposing the templates buccally over the patient's mandibular cast, from canine to canine, and in the molar region in the cervical third, precisely on the gingival sulcus.

Once an arch form suitable for the patient has been found, the orthodontist can then proceed to produce - guided by the appropriate diagram - the steel archwires that will be used at the end of the alignment phase, in the biomechanics phase (space closure) and in the detailing and finishing phase.

INTRODUCTION:

Given the development of preadjusted appliances it became possible to design an orthodontic diagram suitable for each patient by defining dental arch forms. In-and-out - now built into preadjusted brackets - enables the design of dental arch forms without the need to place first-order bends in orthodontic treatment.6

The system proposed by the authors of this article consists in defining an orthodontic diagram that preserves the individual characteristics of each patient's arch form, be it tapered, ovoid or square, and then determining the anterior curvature from canine to canine, the intercanine width, intermolar width and arch perimeter.6

With the aid of this system professionals can use tapered, ovoid or square preformed memory archwires in the alignment phase, design a diagram suitable for the patient, and then fabricate the steel archwires for use in the final leveling phase, working phase (space closure), and detailing and finishing phase.3

The research disclosed 48 dental arch forms with which the professional can easily design, in orderly fashion, a diagram ideally suited for the patient.

METHODS:

This investigation entailed a survey of 120 dental casts of the lower arches of patients prior to orthodontic treatment who, in the authors' assessment, showed no significant changes in the incisor, canine, premolar and molar segments (Figure 1).

Figure 1
Occlusal view photograph of a dental cast selected for the study, exhibiting an adequate arch form, minimal anterior crowding, and adequate intercanine, interpremolar and intermolar widths. The relationship between dental arch line and Wala edge is adequate, and the Wilson curve is flat.

The first study examined the curvature of the dental arch buccally, from canine to canine, in continuation of which curvature a circumference might be drawn (Figure 2).

Figure 2
Photograph of dental cast selected for the study displaying adequate anterior curvature from canine to canine.

In investigating the curvatures of arches formed by anterior teeth, the radii of the circumferences were obtained and the casts separated into groups.

Eight canine-to-canine curvatures were found, with radii ranging from 18 mm to 26 mm, graded as follows:

  • Curvature with 18 mm radius: Diagram #1
  • Curvature with 19 mm radius: Diagram #2
  • Curvature with 20 mm radius: Diagram #3
  • Curvature with 21 mm radius: Diagram #4
  • Curvature with 22 mm radius: Diagram #5
  • Curvature with 23 mm radius: Diagram #6
  • Curvature with 24 mm radius: Diagram #7
  • Curvature with 26 mm radius: Diagram #8 (Figure 3)

These casts were divided according to their number, yielding eight discrete groups:

Figure 3
Study of anterior canine-to-canine curvatures. Eight curvatures were found, with radii ranging from 18 mm to 25 mm, which were numbered from 1 to 8.

The second study measured individually the diameter (width) of the mandibular arch in the region of first and second molars of each group. Measurements were made from the first molar on the right side to the first molar on the left side in the cervical region, with the procedure being repeated on the second molars.

This study obtained various distances, but for the purpose of designing each diagram the maximum and minimum distances found for each group were taken into account (Figures 4 and 5).

Figures 4 and 5
The figures show the widths between first molars and between second molars via the buccal surfaces in the gingival third of the clinical crowns.

The third study found a geometrical point which, by means of a curvature, joined the curvatures of the anterior teeth in the region of the canines as far as the minimum and maximum widths obtained from the molars. Four additional intermediate curvatures were created between the minimum and maximum intermolar widths.

This curvature, which connects the distal surface of the canines to the molar region, automatically determines the widths between first and second premolars (Figure 6).

Figure 6
Geometric points (X point) were created which joined the distal surface of the canines to the maximum and minimum intermolar widths of the individualized groups. By means of this geometric point the curvatures and arch forms were designed. Four additional intermediate lines were traced between maximum and minimum, totaling six posterior openings for each diagram number.

The fourth study defined the perimeter (length) of the upper and lower dental arches from the labial of the central incisors to the distal of the second molars. A lateral vertical scale was created in the diagrams so as to enable the professional to fabricate archwires with a length as close as possible to the length of the patient's dental arch (Figure 7).

Figure 7
A vertical scale was drawn on the sides of the arches with the purpose of ensuring enough arch perimeter (length) to facilitate diagram definition and allow the professional to work comfortably in the patient's mouth.

HOW TO USE THE DIAGRAM AND HOW TO FABRICATE INDIVIDUALIZED PATIENT ARCHWIRES

The first phase in designing diagrams best suited for the patient consists in carrying out a detailed analysis of the patient's dental arch using a cast of the lower dental arch.3,5 In this evaluation the professional should verify that there are no significant changes in arch form, intercanine width, interpremolar width and intermolar width.11 This assessment may also encompass the distance between the midpoint of the clinical crowns and the Wala edge (Figure 1).

In the event that the patient's dental arch form does not present with any anterior or posterior transverse sagittal changes, the professional should follow the sequence5 using templates (individualized patient diagrams), thus:

1°- Find in the patient's mandibular cast the best suited template buccally from canine to canine, represented by numbers 1 to 8 (Figure 8).

Figure 8
The photograph shows the selection of an individualized patient diagram by superimposing the template over the mandibular cast. Firstly, one should select the template number that provides the best fit buccally from canine to canine. Once the number has been found, one should find the letter best suited for the posterior intermolar opening, which should be in the gingival thirds of the labial surfaces.

2°- After selecting the corresponding number that represents the anterior curvature from canine to canine, one should check the posterior diameter which is represented by the letters A, B, C, D, E and F. The posterior diameter should match the cervical third of the buccal surfaces of the first and second molars (Figure 8).

3°- Find the best suited diagram for the patient from among the set of individual arch forms (Figure 9).

Figure 9
The photograph shows the individualized diagram best suited for the patient, which was selected with the aid of templates.

4° - Check the perimeter (length) of the lower arch with the aid of the vertical scale, increasing it by 3 mm from the distal surface to the first or second molar, and placing the letter I on the left and right sides of the patient's best suited diagram (Figure 10).

Figure 10
The photograph shows the diagram best suited for the patient. The letter I was placed on the right and left sides to indicate the perimeter (length) of the patient's lower (inferior) arch, increasing it by 3 mm from the distal surface to the first or second molar.

4° - Check the perimeter (length) of the upper (superior) arch using the same diagram with the aid of the vertical scale, increasing it by 3 mm from the first or second molar, and placing the letter S on the left and right sides of the patient's best suited diagram. (Figures 10 and 11)

Note: The individualized diagram will not fit the mandibular cast. This procedure should be carried out in order to check the arch length to ensure that the archwire is fabricated without causing discomfort to the patient.

Figure 11
The photo shows the template superimposed over the patient's mandibular cast with the sole purpose of checking the length of the upper arch. Figure 10 shows the letter S stamped on left and right sides, representing the ideal length of the upper (superior) arch.

5° - Fabricate the lower archwire based on the selected diagram and fabricate the upper archwire 2 mm larger than the maxillary archwire (Figure 12).

Note: In cases of premolar extractions, it is recommended to use the highest diagram number relative to the corresponding letter.

Figure 12
The photo shows the fabrication of the mandibular steel archwire based on the diagram line, and fabrication of the maxillary archwire 2 mm larger than the mandibular arch over its entire extension.


DIAGRAM SELECTION IN INDIVIDUALIZED ORTHODONTIC CASES CONSIDERED ATYPICAL

In cases with severe anterior crowding:

In cases where there is severe mandibular crowding with misaligned buccal surfaces of the teeth it is recommended to select the diagram via the lower alveolar ridge.6 If there are no significant changes, the alveolar ridge will preserve the patient's mandibular arch form (tapered, ovoid or square) and posterior diameter (width) of the molars in the cervical region (Figure 13).

Figure 13
The photo shows a dental cast with severe crowding in the anterior region. It is advisable to choose the diagram considering the anterior contour of the alveolar ridge.

In cases of mandibular atresia:

In cases of dental arch atresia, it is recommended to select a larger size diagram to fabricate individualized archwires for the patient. Five points are important in selecting the diagram: a) Dental arch form, b) Intercanine width, c) Intermolar width, d) Curve of Wilson, and e) Relationship between arch form and Wala edge.

In cases where canines do not allow expansion, one should select a diagram that enables expansion only in the posterior region (Figure 14).

Figure 14
Dental cast of a patient with adequate intercanine width, intermolar width atresia, lingually inclined curve of Wilson and inadequate relationship between arch form and Wala edge. In this case it is recommended to devise a diagram to define intermolar widths and maintain intercanine width.

In cases where canines allow expansion, one should select a diagram that enables expansion in both the anterior and posterior regions (Figure 15).

Figure 15
The photo shows a cast with canine and molar lingual inclination, exhibiting an inadequate relationship between arch line and Wala edge in the molar region. In this case expansion is recommended to be performed in the canine and molar regions.

Cases with posterior crossbites:

It is recommended that patients presenting with posterior crossbites, or those who will undergo rapid maxillary expansion utilize a larger upper diagram in order to prevent crossbites in posterior teeth during corrective treatment. The mandibular dental arch should be outlined according to the selected diagram and the upper arch should be expanded. In the phase where rectangular steel archwires are used it is recommended that after expanding the maxillary arch buccal torque be gradually applied from the distal of the canines to the last molar (Figure 16).

Figure 16
Diagramming and coordination between the upper and lower dental arches in a case that presents with crossbite, or underwent maxillary expansion or palate splitting.

DISCUSSION:

In seeking stability after orthodontic treatment, the authors surveyed in this study aimed to establish an ideal arch form for all patients prior to orthodontic treatment. The study results showed that all authors tried to finish orthodontic treatment with an arch form resembling as closely as possible the arch form present at the beginning of treatment.

In light of scientific advances in orthodontics and the widespread use of preadjusted appliances, these authors defined minimum arch form patterns without worrying about individualized arch forms.

Based on the research, the authors of this study recommend the use of preadjusted appliances combined with archwires with good elasticity in the alignment and leveling phase, as well as in the working phase and finishing (detailing) phase. Also recommended is the use of diagrams on the steel archwires to restore form patterns and anterior and posterior sagittal diameters that resemble as closely as possible the patients' original arch forms.

CLINICAL CONSIDERATIONS

To be successful, an orthodontic treatment should take into account the following factors:9,10

  • Proper diagnosis and treatment planning
  • Restoring functional dynamics by achieving occlusion in centric relation and functional movements by means of incisor and canine guidances
  • Ensuring an ideal anteroposterior positioning of lower incisors with proper muscle balance
  • Determining an ideal dental arch form for the orthodontic treatment

The authors' many years clinical experience has shown that long-term stability in orthodontic treatment is closely related to the above factors.

Disorderly changes in the patient's dental arch forms may compromise treatment, causing relapse in intermolar, interpremolar and intercanine widths, in addition to incisor crowding.

Since 1979 one of the authors7,8 has strived to carefully select the form and diameter of patient arches as he considers this procedure to be a primary factor for a successful treatment.

Therefore, the purpose of the Individualized Diagrams described in this article is to contribute evidence-based criteria to help ensure long-term stability of orthodontic treatment.

REFERENCES:

  1. Interlandi S. 1986. Ortodontia ‐ Mecânica do Arco de Canto Introdução à Técnica. Sarvier Editora de Livros Médicos Ltda;
  2. Trevisi H 2007 SmartClip™: tratamento ortodôntico com sistema de aparelho autoligado ‐ conceito e biomecânica. Elsevier, Rio de Janeiro;
  3. McLaughlin R P, Bennett J C, Trevisi H 2004 Mecânica sistematizada de tratamento ortodôntico. Artes Médicas, São Paulo;
  4. Hawley C A 1905 Determination of the normal arch and its application to orthodontics. Dental Cosmos 47:541‐552;
  5. McLaughlin R P, Bennett J C 1999 Arch form considerations for stability and esthetics. Revista Española de Ortodoncia 29:46‐63;
  6. Andrews L F 1976 The Straight Wire Appliance explained and compared. Journal of Clinical Orthodontics 10:174‐195;
  7. Trevisi H, Zanelato R T, Satat‐Of‐The‐Art Orthodontics. Mosby Elsevier;
  8. Bennett J C, McLaughlin R P 1998 O tratamento ortodôntico da dentição com aparelho pré‐ajustado. Artes Médicas, São Paulo;
  9. Little R, M Stability and relapse of dental arch alignment British Journal of Orthodontics, Vol. 17, 235‐241, Copyright © 1990 by British Orthodontic Society;
  10. Tecco, S. et al Maxillary Arch Width Changes During Orthodontic Treatment With Fixed Self-Ligating And Traditional Straight‐Wire Appliances World Journal of Orthodontics Winter 2009, Volume 10, Issue 4;
  11. Douglas C, W Comparative Changes In Mandibular Canine And First Molar Widths The Angle Orthodontist Volume 32, Issue 4 (October 1962) pp. 232‐241.

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