Comparative study of dental arch width in plaster models, photocopies and digitized images

ORIGINAL ARTICLES

ORTHODONTICS

Comparative study of dental arch width in plaster models, photocopies and digitized images

Maria Cristina Rosseto^I; Fernanda Maria Cassinelli Palma^I; Rívea Inês Ferreira^II; Arnaldo Pinzan^III; Flávio Vellini-Ferreira^IV

^IResearch Fellow - Department of Pediatric Dentistry and Orthodontics, University of São Paulo City (UNICID), São Paulo, SP, Brazil

^IIAssociate Professor - Department of Pediatric Dentistry and Orthodontics, University of São Paulo City (UNICID), São Paulo, SP, Brazil

^IIIProfessor, Department of Orthodontics, School of Dentistry of Bauru, University of São Paulo, Bauru, SP, Brazil

^IVProfessor and Chairman - Department of Pediatric Dentistry and Orthodontics, University of São Paulo City (UNICID), São Paulo, SP, Brazil

^{Corresponding author}

ABSTRACT

The aim of this study was to comparatively assess dental arch width, in the canine and molar regions, by means of direct measurements from plaster models, photocopies and digitized images of the models. The sample consisted of 130 pairs of plaster models, photocopies and digitized images of the models of white patients (n = 65), both genders, with Class I and Class II Division 1 malocclusions, treated by standard Edgewise mechanics and extraction of the four first premolars. Maxillary and mandibular intercanine and intermolar widths were measured by a calibrated examiner, prior to and after orthodontic treatment, using the three modes of reproduction of the dental arches. Dispersion of the data relative to pre- and posttreatment intra-arch linear measurements (mm) was represented as box plots. The three measuring methods were compared by one-way ANOVA for repeated measurements (α = 0.05). Initial / final mean values varied as follows: 33.94 to 34.29 mm / 34.49 to 34.66 mm (maxillary intercanine width); 26.23 to 26.26 mm / 26.77 to 26.84 mm (mandibular intercanine width); 49.55 to 49.66 mm / 47.28 to 47.45 mm (maxillary intermolar width) and 43.28 to 43.41 mm / 40.29 to 40.46 mm (mandibular intermolar width). There were no statistically significant differences between mean dental arch widths estimated by the three studied methods, prior to and after orthodontic treatment. It may be concluded that photocopies and digitized images of the plaster models provided reliable reproductions of the dental arches for obtaining transversal intra-arch measurements.

Descriptors: Dental arch; Measures; Malocclusion; Orthodontics.

Introduction

Stability is one of the major goals of orthodontic treatment. Nonetheless, it still remains a controversial issue, perhaps because it involves a multitude of intrinsic and extrinsic factors. Intercanine and intermolar widths are widely discussed, and their maintenance is considered an important factor in attaining stability after treatment.^1,2 From a clinical point of view, it is well-known that these measurements undergo changes in cases treated with extraction of the four first premolars.

Technological advances have provided faster measuring methods, which make it easier to obtain the above mentioned parameters.^3-5 Thus, the present study aimed at evaluating the reliability of intercanine and intermolar widths taken on plaster models (gold standard), photocopies and digitized images of the models of orthodontic patients treated with premolar extractions. The null hypothesis stated that there are no differences in performance between the studied measuring methods.

Material and Methods

This study is in agreement with Resolution 196/96 from the National Health Council/Health Department (Brazil).

Sample selection

The sample comprised 130 pairs of orthodontic plaster models obtained at the pretreatment and posttreatment phases. The selected subjects included 65 white patients (41 female and 24 male) with Angle Class I (n = 33) and Angle Class II Division 1 (n = 32) malocclusions, orthodontically treated by standard Edgewise (not preadjusted) technique, with extraction of the four first premolars. The patients began treatment at ages ranging from 10 to 18 years.

Dental arch width measurements

Maxillary and mandibular intercanine and intermolar widths were measured using as references the canine cusp tip and the molar mesiobuccal cusp tip, on the right and left sides. Reference points were identified and marked with ultrafine graphite (0.5 mm in diameter - Pentel Co. Ltd., Tokyo, Japan) on each orthodontic plaster model at the pre- and posttreatment phases. In cases of cusp tip flattening by wear, the reference point (estimated cusp tip) was marked as the central point in the middle of the wear facet, according to Bishara et al.⁶ (1994), Freitas et al.⁷ (1996) and McReynolds, Little⁸ (1991), in previous studies. Measurements were made by a calibrated examiner directly on the plaster models and photocopies of the models using a digital caliper (Mitutoyo^®, Digimatic, Kawasaki, Japan) accurate to 0.01 mm. All photocopies were acquired by means of a Xerox^® X-C865 machine (Stanford, CT, USA) with the models in the most stable position.⁹

In addition, all models were digitized using a scanner (ScanJet 2200C^®; Hewlett Packard Co., Greeley, CO, USA) at a resolution of 300 dpi. The digitized models were then stored as TIFF (Tagged Image File Format) images. Reference landmarks for measuring the intercanine and intermolar widths were identified and marked from a laptop display (Acer^® 350; Acer Inc., Taipei, Taiwan). Maxillary and mandibular intercanine and intermolar widths were calculated using the RadioCef^® 2000 software (Radiomemory Co., Belo Horizonte, MG, Brazil).

Method error

To estimate reproducibility, measurements from the three modes of reproduction of the dental arches were made twice. Following a calibration session, 20 pairs of plaster models were randomly selected, reproduced and assessed by the examiner. A two-week interval was allowed to elapse between the first and the second assessment. For the analyses of systematic and casual errors, Student's-t test and Dahlberg's formula were used, respectively. Systematic errors were not statistically significant (p > 0.05). The casual errors varied from 0.12 mm to 0.35 mm, according to the region measured (canine or molar) and mode of reproduction of the dental arches. Casual errors in this range may be considered clinically acceptable.

Statistical analysis

The descriptive statistics of the intercanine and intermolar width measurements (mm) obtained from the three modes of reproduction of the dental arches, for the pretreatment (initial) and posttreatment (final) phases, were presented as box plots. The box stretches from the lower hinge (defined as the 25^th percentile) to the upper hinge (75^th percentile) and, therefore, contains the middle half of the values in the distribution. The median is shown as a line across the box.

Differences in the performance of the methods were evaluated by one-way ANOVA for repeated measurements, prior to and after treatment (α = 0.05).

Results

Distribution patterns of the initial (pretreatment) measurements are represented in Graph 1. The measurements taken on the plaster models, photocopies and digitized images evidenced a similar distribution for both intercanine and intermolar widths. As shown in Graph 2, the distribution patterns relative to the three studied modes of reproduction of the dental arches remained apparently analogous after treatment. Based on the five-number summaries of the graphs and mean values, it may be suggested that maxillary and mandibular intermolar widths presented a slight decrease in the posttreatment assessments (Graphs 1 and 2, Tables 1 and 2). Median values were very close to the respective mean values, indicating symmetry of the data distribution.

Despite the numerical discrepancies, no significant differences were found between the measuring methods (Tables 1 and 2).

Discussion

Orthodontic plaster models have long been extensively used for diagnosis and in treatment outcomes assessment. While communication technology was advancing, some modes of reproducing the traditional plaster models were developed.¹⁰ Such diagnostic tools could not only address the universal problem of plaster model storage in an orthodontic office, but also shorten the time necessary to perform measurements and analysis of the dental arches.¹¹ In this way, plaster models would be used just once because after acquiring two- or three-dimensional images they could be given to the patients.

Despite some numerical discrepancies, there were no significant differences between the studied measuring methods (Tables 1 and 2). Hence, it may be suggested that orthodontic plaster models, photocopies and digitized images of the models are suitable reproductions for taking measurements of the anterior and posterior dental arch width. The results of the present study were generally consistent with those reported by Champagne¹² (1992). In fact, Simplício et al.¹³ (1995) found more evident distortions in photocopies of the mandibular models. This finding may be related to the curve of Spee, which is reflected to a greater extent in the canine and premolar regions on photocopies.

Overall satisfactory reliability of transversal measurements made on digitized images of plaster models was demonstrated in several investigations.^3,5,14-17 Moreover, measuring patient's dentition and calculating the Bolton ratio with scanned models (emodels) appeared to be just as accurate and faster than using digital calipers with plaster models.¹¹ Vasconcelos et al.⁴ (2006) reported that the Radiocef^® 2.0 software, used in this study, provided good reliability for taking measurements from digitized tracings. Therefore, it would be reasonable to assume that digitized images of orthodontic plaster models may be useful as adjuncts for measuring occlusal parameters in clinical practice. Nevertheless, taking linear interarch measurements like overjet on scanned plaster models is not recommended as a substitute method for manual assessment.¹⁰ Hildebrand et al.¹⁰ (2008) stated that the digital mounting of the scanned plaster models allows the teeth to overlap, creating improper articulation because two objects cannot occupy the same space.

Concerning the behavior of the measurements estimated by the three methods, it was found that the intermolar width was decreased after treatment in patients with Class I and Class II Division 1 malocclusions, both in the maxillary and mandibular arch (Graphs 1 and 2, Tables 1 and 2). These results are in agreement with those reported by other studies.^6,7 Presumably, the reduction in the posterior arch width was due to the loss of anchorage. Some authors² mentioned that the increase of this measurement may be an important factor related to posttreatment relapse. On the other hand, the decrease in posterior arch width seems to have little clinical relevance. The increase in transversal dimensions, i.e. intercanine and intermolar widths, produced during orthodontic treatment has been associated to long-term reduced stability due to a trend towards anterior crowding.^2,18 Conversely, decreased intercanine and intermolar widths should not be considered risk factors for the greater probability of incisors crowding relapse in the mandibular arch.⁷

From a critical perspective of the Brazilian legal guidelines, it is recognized that the mandatory filing of orthodontic documentation for around 20 years increases the demands for physical space, particularly to keep the plaster models. Photocopies would not constitute the method of choice for proper replacement of plaster models, since they depict two-dimensional static images and do not allow the assessment of maxillo-mandibular relationships. Scanning orthodontic plaster models may provide three-dimensional images and, additionally, offers the possibility of computed-manipulation to improve clinical diagnosis.^11,14 Enhancement features of digitized images, as opposed to the limitations of photocopies, would highlight the former reproduction method as an adequate substitute for the traditional orthodontic plaster models. Although there are some drawbacks that still must be overcome, scanned models carry the potential for notably simplifying and improving orthodontic diagnosis.

Orthodontic files could be much smaller if digitized images of plaster models were used. The reproduction method also yields on-line exchange of diagnostic information. However, some care must be taken during the digitization process. An appropriate scanner is needed, a minimum resolution of 300 dpi must be selected and the acquired pictures should be stored as TIFF images. Nowadays, there are commercially available systems specially developed for scanning dental casts, which acquire dynamic three-dimensional images. Based on an overview of the current knowledge, with the increasing applications of cone-beam computed-tomography in Orthodontics, it would perhaps be feasible to take measurements directly from tomographic images of the dental arches. Possibly, in the near future, obtaining alginate impressions will no longer be necessary.

Conclusions

1. Orthodontic plaster models, photocopies and digitized images demonstrated similar performance for measuring maxillary and mandibular intercanine and intermolar widths.

2. Considering the demand for physical space in a dental office, it may be suggested that a digitized image is a suitable alternative to a traditional plaster model for obtaining transversal intra-arch measurements.

Received for publication on Jan 17, 2007

Accepted for publication on Jul 17, 2007

• 1. Loddi PP, Scanavini MA. Estudo da estabilidade do alinhamento dos incisivos inferiores e do desvio da linha média, oito anos pós-contenção, e suas correlações com as assimetrias dentárias ântero-posteriores em pacientes tratados com e sem extrações dos primeiros pré-molares. Ortodontia. 2002;35(2):57-68.
• 2. Martins PP, Freitas MR, Freitas KMS, Canuto LFG, Janson GRP, Henriques JFC et al Apinhamento ântero-superior: revisão e análise crítica da literatura. R Dental Press Ortodon Ortop Facial. 2007;12(2):105-14.
• 3. Dostalova T, Racek J, Tauferova E, Smutny V. Average arch widths and associated changes between initial, post-treatment and post-retention measurements. Braz Dent J. 2004;15(3):204-8.
• 4. Vasconcelos MHF, Janson GRP, Freitas MR, Henriques JFC. Avaliação de um programa de traçado cefalométrico. R Dental Press Ortodon Ortop Facial. 2006;11(2):44-54.
• 5. Zilberman O, Huggare JA, Parikakis KA. Evaluation of the validity of tooth size and arch width measurements using conventional and three-dimensional virtual orthodontic models. Angle Orthod. 2003;73(3):301-6.
• 6. Bishara SE, Bayati P, Zaher AR, Jakobsen JR. Comparisons of the dental arch changes in patients with Class II, division 1 malocclusions: extraction vs nonextraction treatments. Angle Orthod. 1994;64(5):351-8.
• 7. Freitas MR, Henriques JFC, Pinzan A. Estudo em modelos da recidiva do apinhamento ântero-inferior em pacientes tratados ortodonticamente, com extrações dos primeiros pré-molares, 5 e 10 anos após contenção. Ortodontia. 1996;29(1):19-30.
• 8. McReynolds DC, Little RM. Mandibular second premolar extraction - postretention evaluation of stability and relapse. Angle Orthod. 1991;61(2):133-44.
• 9. Machado CR. Orthodontic cast analysis using xerox copy. Ortodontia. 1976;9(2):125-8.
• 10. Hildebrand JC, Palomo JM, Palomo L, Sivik M, Hans M. Evaluation of a software program for applying the American Board of Orthodontics objective grading system to digital casts. Am J Orthod Dentofacial Orthop. 2008;133(2):283-9.
• 11. Mullen SR, Martin CA, Ngan P, Gladwin M. Accuracy of space analysis with emodels and plaster models. Am J Orthod Dentofacial Orthop. 2007;132(3):346-52.
• 12. Champagne M. Reliability of measurements from photocopies of study models. J Clin Orthod. 1992;26(10):648-50.
• 13. Simplício AHM, Souza LA, Sakima MT, Martins JCR, Sakima T. Confiabilidade de xerox de modelos de estudo para o traçado de oclusogramas. Ortodontia. 1995;28(3):62-7.
• 14. Costalos PA, Sarraf K, Cangialosi TJ, Efstratiadis S. Evaluation of the accuracy of digital model analysis for the American Board of Orthodontics objective grading system for dental casts. Am J Orthod Dentofacial Orthop. 2005;128(5):624-9.
• 15. Okunami TR, Kusnoto B, BeGole E, Evans CA, Sadowsky C, Fadavi S. Assessing the American Board of Orthodontics objective grading system digital vs plaster dental casts. Am J Orthod Dentofacial Orthop. 2007;131(1):51-6.
• 16. Santoro M, Galkin S, Teredesai M, Nicolay OF, Cangialosi TJ. Comparison of measurements made on digital and plaster models. Am J Orthod Dentofacial Orthop. 2003;124(1):101-5.
• 17. Stevens DR, Flores-Mir C, Nebbe B, Raboud DW, Heo G, Major PW. Validity, reliability and reproducibility of plaster vs digital study models: comparison of peer assessment rating and Bolton analysis and their constituent measurements. Am J Orthod Dentofacial Orthop. 2006;129(6):794-803.
• 18. Castellanos EC, Vigorito JW. Estudo das modificações nas dimensões transversais dos arcos dentários superior e inferior durante e após o tratamento ortodôntico. Ortodontia. 1977;10(2):92-8.

Publication Dates

• Publication in this collection
  20 Oct 2009
• Date of issue
  June 2009

History

• Accepted
  17 July 2007
• Received
  17 Jan 2007