Simple Way of Recording Dental Arch Forms

Like finger prints each individual has a unique dental arch form design. Recording patient’s dental arch form may be required in various fields in dentistry be it longitudinal studies for evaluating growth, forensic dentistry and most importantly in orthodontic practice for fabricating arch wires for individual patients. An easy and practical method to obtain individual arch form for each patient is explained.

For long term stability and retention in orthodontics the importance of individualizing archwires according to patient’s original (pre-treatment) arch forms is well known [1,2]. According to Riedel’s theorems of retention [3]- “Arch form, particularly in the mandibular arch, cannot be permanently altered by appliance therapy.” Altering the original arch form increases the risk of relapse.

As a general guideline the mandibular arch form should be used as a basic guide to record arch forms. An excellent description of the natural dental arch form is provided by a catenary curve which passes along the buccal and incisal edges of lower teeth [4,5]. Conventional methods suggested include making impression of the dental arch on a wax sheet [6] which is prone to distort overtime, taking photocopy [7] of the dental cast on a Xerox machine which demand additional expenses and space for the Xerox machine in the clinical setup, and taking photographs [8] of the model in 1:1 magnification and getting a print out of it which is also a cumbersome alternative. Of lately, engineers and computer specialists have tried to work out arch forms with mathematical equations. According to Braun [9] the human arch form could be represented by a complex mathematical formula known as the beta function. Begole’s [10]Cubic Interpolatory Spline consists of separate cubic polynomial segments connecting a series of points generates different curve configurations of arch forms with minimal error. Similarly, Currier [11] presented with a computerized geometric analysis of human dental arch forms utilizing radiographs of plaster casts. Looking at the phenomenal use of computer and technology it is expected, laser mapping of dental arches and arch wire fabrication through CAD-CAM technology will be the next step in simplifying clinical procedures. However, despite numerous investigations in this regard these systems have not yet been absorbed in the routine dental/orthodontic practice. One of the basic reasons being these techniques seem complicated, expensive, impractical and time consuming in the clinical scenario. Therefore, it is obvious to look out for a more practical, simplified and economical solutions for the same. It has been an accepted fact [2] that the patient’s pre-treatment arch form is the best guide for custom designing the arch forms. Therefore, we propose an easy and practical approach to record and obtain arch form for individual patient utilizing the patient’s pre-treatment lower dental cast.

Step 1: Buccal and incisal edges of lower teeth on the plaster model are marked with a HB pencil [Table/Fig-1].

[Table/Fig-1]:

Buccal and incisal edges of lower teeth are marked with a HB pencil

Step2: A plain sheet of paper (6 cm x 10 cm) is kept over the occlusal surface of lower cast and stabilized from posterior region with thumb and index finger [Table/Fig-2].

[Table/Fig-2]:

A plain sheet of paper (6 cm x 10 cm) is kept over the occlusal surface of lower cast and stabilized from posterior region with fingers

Step 3: Index finger of other hand is moved over the sheet of paper to facilitate transfer of the pencil marks on the sheet [Table/Fig-3].

[Table/Fig-3]:

Index finger of other hand is moved over the sheet of paper to facilitate transfer of the pencil marks on the sheet

Step 4: Pencil marks get transferred on the under surface of sheet of paper and arch form is obtained. Mark the midline. This paper with tooth impressions can be laminated and kept as a record after mentioning the patient name, age, date of record and other details [Table/Fig-4].

[Table/Fig-4]:

Pencil marks get transferred on the under surface of sheet of paper and arch form is obtained. Mark the midline. This paper with tooth impressions can be laminated and kept as a record after mentioning the patient name, age, date of record and other details

Step 5: Pencil marks on the dental cast can be cleaned easily by rubbing a spirit swab over the markings on the dental cast [Table/Fig-5].

[Table/Fig-5]:

Pencil marks on the dental cast can be cleaned easily by rubbing a spirit swab over the markings on the dental cast

The arch form obtained can be transferred to graph paper. Place this paper on tracing table and get the markings on graph paper. Draw a curve out of the markings. It can be laminated with plastic sheet for future reference. Patient’s name and other details can be mentioned with a marker pen [Table/Fig-6].

[Table/Fig-6]:

The arch form obtained can be transferred to graph paper. Place this paper on tracing table and get the markings on graph paper. Draw a curve out of the markings. It can be laminated with plastic sheet for future reference. Patient’s name and other details can be mentioned with a marker pen.

This article introduces a simple, cost effective and convenient solution for accurately obtaining dental arch configuration for individual patients. The arch form thus obtained can be utilized as a template for orthodontic patient’s arch wire fabrication all throughout the treatment, as well as can also be utilized for longitudinal or cross-sectional anthropological, anatomical, dental and prosthodontic research studies on related subjects.

[1]. Felton MJ, Sinclair PM, Jones DL, Alexander RG, A computerized analysis of the shape and stability of mandibular arch form Am J Orthod 1987 92:478-83.  [Google Scholar]

[2]. De La Cruz AR, Sampson P, Little RM, Artun J, Shapiro PA, Long term changes in arch form after orthodontic treatment and retention Am J Orthod 1995 107:518-30.  [Google Scholar]

[3]. Riedel RA, A review of the retention problem Angle Orthod 1960 30:179-94.  [Google Scholar]

[4]. McConaill MA, Scher EA, Ideal Form of the Human Dental Arcade with Some Prosthetic Applications Dent Rec 1949 69:285-302.  [Google Scholar]

[5]. Pepe SH, Polynomial and Catenary Curve Fits to Human Dental Arches J DENT RES 1975 54:1124  [Google Scholar]

[6]. Swennen GR, Mommaerts MY, The use of a wax bite wafer and a double computed tomography scan procedure to obtain a three-dimensional augmented virtual skull model J Craniofac Surg 2007 18(3):533-39.  [Google Scholar]

[7]. BeGole EA, Lyew RC, A new method for analyzing change in dental arch form Am J Orthod Dentofacial Orthop 1998 113:394-401.  [Google Scholar]

[8]. Dostalova T, Racek J, Average Arch Widths and Associated Changes between Initial, Post-treatment and Post-retention Measurements Braz Dent J 2004 15(3):204-08.  [Google Scholar]

[9]. Braun S, Hnat WP, Fender DE, Legan HL, The form of the human dental arch Angle Orthod 1998 68:29-36.  [Google Scholar]

[10]. Begole EA, Application of the cubic spline function in the description of dental arch form J Dent Res 1980 59:1542-56.  [Google Scholar]

[11]. Currier JH, A computerized geometric analysis of human arch form Am J Orthod 1969 56:164-79.  [Google Scholar]