ORIGINAL ARTICLE

Mandibular arch form: The relationshipbetween dental and basal anatomyValerie Ronay,a R. Matthew Miner,b Leslie A. Will,c and Kazuhito Araid

Vienna, Austria, Boston, Mass, and Tokyo, Japan

Introduction: We investigated mandibular dental arch form at the levels of both the clinically relevantapplication points of the orthodontic bracket and the underlying anatomic structure of the apical base. Thecorrelation of both forms was evaluated and examined to determine whether the basal arch could be usedto derive a standardized clinical arch form. Methods: Thirty-five mandibular dental casts (skeletal and dentalClass I) were laser scanned, and a 3-dimensional virtual model was created. Two reference points (FA, themost prominent part of the central lobe on each crown’s facial surface, and WALA, a point at the height ofthe mucogingival junction) were selected for each tooth from the right to the left first molars. The FA andWALA arch forms were compared, and the distances between corresponding points and intercanine andintermolar widths were analyzed. Results: Both arch forms were highly individual and the tooth valuesscattered. Nevertheless, a highly significant relationship between the FA and WALA curves was found,especially in the canine (0.75) and molar (0.87) areas. Conclusions: Both FA and WALA point-derived archforms were individual and therefore could not be defined by a generalized shape. WALA points proved to bea useful representation of the apical base and helpful in the predetermination of an individualized dental arch

form. (Am J Orthod Dentofacial Orthop 2008;134:430-8)

The size and shape of the dental arches haveconsiderable implications for orthodontic diagno-sis and treatment planning. These factors have an

effect on space available, stability of the dentition, anddental esthetics. Furthermore, the definition of arch formwould improve the understanding of malocclusion andassist clinicians in producing orthodontic results that areconsistent with the natural laws of biologic variation.Although most arch form studies have looked at similarpatient samples—subjects with orthodontically untreatedideal occlusions—few come even close to agreementabout the natural shape of the dental arch. It is commonlybelieved that the dental arch form is initially shaped by theconfiguration of its supporting bone.1 Nevertheless, 2opposing theories about modifying the dental arch formhave coexisted for 100 years.2,3

The bone-growing theory is that the supportingbone grows in response to normal stimulation, such as

aStudent, Clinic of Dentistry, Vienna University, Vienna, Austria.bAssistant clinical professor, Department of Developmental Biology, HarvardSchool of Dental Medicine, Boston, Mass.cProfessor and graduate program director, Department of Orthodontics, TuftsUniversity School of Dental Medicine, Boston, Mass.dAssistant professor, Department of Orthodontics, Nippon Dental University,Tokyo, Japan; visiting professor, Department of Developmental Biology,Harvard School of Dental Medicine, Boston, Mass.Reprint requests to: R. Matthew Miner, One Lyons St, Dedham, MA 02026;e-mail, r_miner@hsdm.harvard.edu.Submitted, April 2006; revised and accepted, October 2006.0889-5406/$34.00Copyright © 2008 by the American Association of Orthodontists.

doi:10.1016/j.ajodo.2006.10.040

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mastication, if the teeth are aligned in the ideal position.Angle4 reported stable orthodontic treatment results ofhis expanded crowding patients and first advocated thebone-growing theory. In the latter part of the 19thcentury a basic biologic principle was introduced calledWolff’s law in which the bone structure changes inresponse to external force. According to this theory,tooth size is controlled by heredity, but size and shapeof the supporting bones depend largely on environmen-tal stimuli including eruption of the teeth, pressure fromtongue and cheek, and mastication. For example, asmall mandible can result from the lack of healthy jawfunction and indicates degeneration.5 This approachresulted in fewer extractions and is often called thenonextraction theory.

According to the “apical base” theory, the size andshape of the supporting bone are largely under geneticcontrol, and there is a limit to expansion of a dental arch.In 1925, Lundström6 proposed a new term—apicalbase—to describe the limits of expansion of the dentalarch and wrote extensively on this topic. He stated that theapical base (1) is not changed after loss of teeth, (2) is notinfluenced by orthodontic tooth movement or masticatoryfunction, and (3) limits the size of dental arch. If the teethare orthodontically moved beyond this limit, labial orbuccal tipping of the teeth,6 periodontal problems,7 or anunstable treatment result8 could be expected.2 One ofAngle’s students, Tweed,9 also observed unstable results

after nonextraction treatment with Angle’s mechanics

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during the 1930s. He established his diagnostic analysis infavor of extraction and refined the mechanics for extrac-tion treatment. Simultaneously, another Angle student,Begg,10 also changed to the extraction technique andsought anthropologic evidence for extraction treatmentbecause of less mastication required in modern diets.Since then, this theory was confirmed by case reports, andmost orthodontists are now convinced of the validity ofthis theory.11,12 However, an objective limit for buccal orlabial tooth movement in any patient, especially thosewith mild crowding, is still not available today.2

As the frequency of extraction orthodontic treatmenthas decreased over the last 30 years, a new bone-growingtheory has emerged. Esthetic preference for fuller profiles,temporomandibular disorder problems,2 and the emer-gence of functional appliance therapy13 were contributingfactors, but, most significantly, it was found that extrac-tion did not insure stability.14 With stability not guaran-teed, extraction treatment lost much of its perceivedadvantage. Recently, the clinical results of a new orth-odontic appliance were reported.15 Its developer claimedthat buccal tooth movements without tipping could beachieved with his biocompatible appliance with extremelylight forces. Computed tomography images of expandedteeth from severely crowded dental arches were shown,and apparently healthy alveolar bone was demonstrated asevidence for this bone-growing theory. Most clinicians,however, still explain to their patients that there might bea limit for expansion of the dental arch with any appliance.Furthermore, we still do not know exactly the limit foreach patient.

The purpose of this study was to investigate therelationship between the dental arch form and thesupporting bone. We hypothesized that there is aquantifiable relationship between basal and dental archforms, and that basal-bone landmarks can be used asreliable references for determining biologic arch formin clinical orthodontics.

MATERIAL AND METHODS

The mandibular dental casts of 35 patients (13male, 22 female) were randomly selected from asample of 750. The mandible was studied becausetherapeutic possibilities are more limited than in themaxilla, and the maxillary arch form is strongly asso-ciated with the mandibular form.2,16 The subjects’pretreatment casts were identified as skeletal Class I(ANB angle, 0°-4°) and dental Class I (canine andmolar relationship according to Angle classification)with fully developed permanent dentitions from firstmolar to first molar. The second molars were excludedfrom analysis because the age of most patients pre-

cluded ascertainment of complete eruption of this tooth.

The patients had only minimal restorations with noprosthetic crowns and were excluded if they hadocclusal wear or gingival defects, or if the mucogingi-val junction was not identifiable on the model. Mildcrowding or spacing (�2 mm) was acceptable, but nosubjects requiring extractions for arch-length defi-ciency were included in the sample. The average age ofthese patients was 17 years 11 months.

The dental casts were laser scanned with a computer-assisted noncontact high-definition 3-dimensional (3D)scanning system. This system consisted of a laser-scanning unit (Dental Plaster Model Shape ScanningSystem,17 Surflacer model VMS-100F, UNISN, Osaka,Japan), a computer-aided-design software program(Dent-Merge, version 5.0; UNISN), and dental castanalyzing software (Surfacer, version 9.0, Imageware,Ann Arbor, Mich). This setup was used for imageproduction and refinement, and landmark identification.A detailed description of the performance characteris-tics, including measurement accuracy of this data-recording system, was reported elsewhere.18 The mea-suring device of the laser-scanning unit consisted of aslit-ray laser projector and 2 sets of charged-coupleddevice video cameras to capture the reflected images.X, y, and z coordinate data and data to measure thecircumference of the object was produced as a result.The scanner was connected to the computer for imageprocessing. The dental casts were projected andscanned by a revolving polygon mirror with a slit-raylaser beam of 670 nm wavelength at 3 mW output.Triangulation was used to determine the location ofeach point with a measurement error of less than 0.05mm.The generation of 3D graphics of each dental casttook approximately 80 minutes. About 90,000 sets ofcoordinates (x, y, z) per model were stored in thecomputer.

Each mandibular dental cast was scanned at 3angles in the frontal and sagittal planes (Fig 1, a). Theimage processor converted the raster coordinates andbrightness data of the analog video signals’ input fromthe video cameras into digital data. The computerimported the digital data and converted the picturecoordinates to 3D spatial coordinates. The data wassynthesized, manually corrected for scanning errors, andmerged into a single data set for each model with theDent-Merge software. With cast analyzing software, a 3Dmodel of the entire mandibular dentition and its adjacentstructures was constructed (Fig 1, b and c).

By using the cast analyzing software, 2 referencepoints (1 on the crown, and 1 at the mucogingivaljunction) were selected for each tooth from the right to theleft first molar for a total of 24 points for each model.

The FA point is defined as the midpoint of the facial

on wir

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432 Ronay et al

axis of the clinical crown, which is the most prominentpart of the central lobe on each crown’s facial surfaceexcept for the molars.19 For the first molars, the facialaxis of the clinical crown is represented by the mesio-buccal groove that separates the 2 large facial cusps.

The WALA ridge is defined as the most prominentpoint on the soft-tissue ridge immediately occlusal to themucogingival junction. It is located at or nearly at thesame vertical level as the horizontal center of rotation ofeach tooth.20 WALA was measured directly below FA ofeach tooth perpendicular to the occlusal plane. This pointvaried in its occlusogingival position from tooth to tooth.

Both points were digitized as coordinates (x, y, z)and exported in an ASCII format from the Surfacersoftware into Excel 2002 software (Microsoft, Red-

Fig 1. a, Original model scanning; b, polyg

Fig 2. Sample FA and

mond, Wash). A standard graph format was created to

enable comparisons of the patients. The data was firsttranslated, shifting the midpoint between the WALAand FA points of the central incisors to the origin of thegraph (x-y intersection). Then it was rotated, relocatingthe midpoint of the first molars to the y-axis. Thepositions of the rotated reference points and the curvewere confirmed on the graphic display of the softwareprogram. This method was applied to the data of eachset of FA and WALA points, and average FA andWALA curves were created (Fig 2).

Statistical analysis

Descriptive statistics including the average andstandard deviation of the relative distances between FAand WALA points of corresponding teeth were com-

e-frame image; c, Gouraud-shaded image.

curves superimposed.

WALA

puted and shown graphically. The average values and

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Ronay et al 433

standard deviations of the intercanine and intermolarwidths at FA and WALA including their ratios werecalculated. The Pearson correlation coefficients be-tween the width at the bilateral FA points and theWALA points at the canine and molar levels werecalculated and statistically analyzed at the 0.01 and0.05 levels of significance. Furthermore, the Pearsoncorrelation coefficients between the ratios at the FA andWALA point widths were calculated and also statisti-cally analyzed at the 0.01 and 0.05 levels. Theseevaluations were made to investigate the relationshipbetween points representing the dental arch and those

Fig 3. Digitized FA and WALA points were impFirst, the distances between the 12 pairs were dthe data was “translated” with the midline at theto relocate the first molars as bilateral referewould permit comparison between subjects. Cmolar ratios, were determined. This methotooth-numbering system; R, right; L, left.

constituting the basal arch.

RESULTS

A data table was created for each patient (Fig 3).All 3 coordinates (x, y, z) of the FA and the WALApoints were described for each tooth, starting at theright first molar and ending with the left first molar. Thethird dimension (z, vertical) was omitted in furtheranalysis to facilitate comparison in arch width andlength. To compare patients, the data was standardizedas described above. The patient tables also show theabsolute distance between FA and WALA of thecorresponding teeth in millimeters. The FA and WALA

into Excel 2002 (Microsoft, Redmond, Wash).y calculated to create the “original” data. Thenof the x-y axis. Finally, the data was “rotated”

oints for standardized y-axis positioning thatand molar widths and depths, and canine toapplied to each FA-WALA data set. FDI

ortedigitallorigin

nce panine

d was

curves were superimposed to evaluate their relationship

ar inte

ar inte

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434 Ronay et al

(Fig 2). Male and female data were combined becauseinitial analysis showed them to be indistinguishable.

The distribution of FA and WALA points on themandibular cast is shown in Figures 4 and 5, respec-tively, with the FA and WALA curves producedthrough connection of their single values by linearinterpolation. Those curves are individual and thevalues describing the same teeth are scattered, espe-

Fig 4. FA curves created through line

Fig 5. WALA curves created through line

cially in the premolar and molar areas.

The average relative distances between correspond-ing FA and WALA points were created by summing thevalues of the right and left sides. This data (Table I) isshown in Figure 6, illustrating which FA points arelocated more lingually (positive values) and which arelocated more labially (negative values) in relation tocorresponding WALA points.

Table II gives the intercanine and intermolar widths

rpolation of the individual FA values.

rpolation of the individual WALA values.

for the FA and WALA points in millimeters and the FA

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Ronay et al 435

and WALA ratios of the canines and molars to eachother, including averages and standard deviations. Inthe canine area, increasing distances between FA pointswere accompanied by increasing distances betweenWALA points. However, the corresponding increase indistances between FA points was always larger. With acanine correlation coefficient of 0.75, this data washighly statistically significant (Table III). Similarly, inthe molar region where the proportional increase indistances between the WALA points was even larger,the correlation was also highly significant (0.87). Acomparison of the x- and y-coordinates shows that inthe canine area there was greater variation in FA than inWALA distances. To a lesser degree, this tendency wasalso observed in the molar region.

DISCUSSION

Retention is still a major issue in orthodontics.Theories have been proposed to minimize posttreat-ment relapse, such as creating a proper occlusion4 andmuscular balance,21 uprighting mandibular incisors,22

and maintaining the pretreatment apical base6 andintercanine and intermolar widths.14 The purpose of ouranalysis was to estimate arch dimensions that permitstable treatment goals.2 Orthodontists generally acceptthe importance of respecting basal bone when planningtreatment. Treatment decisions regarding arch form inparticular should be related to the patient’s underlyingbasal anatomy.

The definition of apical base is not completely clearin the literature. These words—apical base, basal bone,basal arch, and supporting bone—are not anatomicterminology and are used only in orthodontics. Defini-tions of the vertical position of the basal area of thealveolar process vary. For example, in 1925, Lund-ström6 defined it as follows: “in normal cases the apicalbase will in the horizontal plane coincide with theregion in which the apices of the roots are located.”Howes23 stated that the basal arch refers to the apicalthird of the alveolus and the bone that supports thealveolar processes below the mandibular teeth. He alsoexplained that it is the most constricted area of thealveolus and is generally about 8 mm below the

Table I. Average distances (mm) of WALA pointsrelative to corresponding FA points and their standarddeviations (n � 70) (FDI tooth-numbering system)

Tooth 1 2 3 4 5 6

Average �1.21 �0.88 �0.32 0.59 1.78 2.77SD 1.24 1.07 1.63 1.28 1.10 0.89

gingival margin.

Clinicians generally assess basal anatomy by eithersubjective palpation or analyzing lateral cephalograms.The latter uses Points A and B to define the anteriorlimit of the apical bases, but it obviously does not takeinto account actual width and overall size. With dentalcasts, the method of recording the most concave con-tour of the sulci in relation to the apices of the teeth hasbeen reported.24

Various studies have looked at the position of theteeth in the basal bone, and several methods fordetermining this relationship have been used. In 1945,Tweed25 described a method of sectioning dental castsin the midline to determine the relationship of theincisors to the alveolar and basal bone. Sergl et al24

measured the maxillary and mandibular apical basearea using a gnathograph specially designed for thispurpose. Oda et al26 presented a technique to record andevaluate mandibular apical base form and tooth posi-tion with computed tomography scans.

The use of 3D scanning devices has been reportedrecently.27 The area of interest is most likely betweenthe bottom of a periodontal pocket and the apex of atooth. A reason for this variation in definition is thedifficulty in estimating the height of the root apex oftooth without x-ray evaluation. However, there is notenough data about the limit of buccal or labial toothmovements, and it is not clear how much the bones canbe changed. In 2000, Andrews and Andrews20 pro-posed a new term, WALA ridge, to indicate a surfacestructure at the same level as basal bone. The WALAridge is the ridge of tissue at the mucogingival junction,and they suggested that the horizontal arch shape of thisridge of an initial mandibular basal arch in an orthodon-tic patient is similar to the archwire form of the dentalarch. The WALA ridge is easy to identify and might bemore clinically reliable than estimation of the rootapex. However, that hypothesis has not been widelydiscussed and confirmed. This is the first report thatexamines the usefulness of WALA points to representthe basal arch and their relevance in determining dentalarch form, but further research is required.

The use of different points in different reports couldhave caused confusion regarding arch form. Somestudies used the arch form based on points where theorthodontic bracket is placed, and others used the archform connecting the incisal edges and cusp tips of theteeth. Different results are obtained with these measure-ment methods on the same dental cast.28 This is the firststudy to investigate the mandibular dental arch formwhile considering both the clinically relevant workingpoint of the orthodontic bracket and wire and theunderlying anatomic-biologic structure of the basal

bone to correlate these structures. Most other arch-form

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436 Ronay et al

studies attempted to fit generalized mathematic orgeometric functions to the dentition but did not look foran anatomic reference for deriving an “ideal” form foreach patient.

Arch form has been analyzed on plaster reproduc-tions of the dentition for years. By using digital models(3D virtual images), point identification takes on newmeaning, particularly for basal arch form. Each identi-fied point has 3 known Cartesian coordinates thatpermit precise analysis of its position. Relationshipsbetween some points can be determined on digitalmodels regardless of interfering structures. Virtualpoints within the model can also be created andcomparisons made between internal and external orsurface landmarks.

Relatively large individual variations of dental archform were found with both FA and WALA points asshown in Figures 4 and 5, in spite of excluding dentalcasts with significant crowding or irregularities. Thiscan be seen as a naturally occurring variation of toothposition and bone anatomy in Class I occlusion. Thesewide variations in dental and basal arches can beexplained by genetic background and environmentalfactors influencing the patient’s growth and develop-ment. These observations suggest that the quantifiedarch forms are highly individual and should not beviewed as variations of a general arch form as had beendone in the past.

On the other hand, a statistically significant positivecorrelation was found between the dental and basalarches in untreated patients. Comparisons of canine and

Fig 6. Average distances (mm) of WALA postandard deviations (n � 70).

molar values in Tables II and III show a constant

relationship between dental and basal arch forms. Astatistically significant positive correlation of canineand molar widths to corresponding FA and WALApoints was found. This suggests that the dental archform is affiliated with the basal arch form (defined bythe WALA points) in each patient, supporting theabove-mentioned apical base theory. If the dental archform is altered without considering the basal arch form,it might result in unhealthy periodontal conditions orunstable treatment results. Additionally, by determin-ing WALA values, one can estimate their correspond-ing FA values and then determine clinical arch form,which can produce an archwire form. A statisticallysignificant positive correlation also was found for theWALA and FA canine-to-molar width ratio. This rela-tionship was observed for both dental arch size andshape.

These findings have considerable relevance fortreatment outcomes. An implant study in the 1980sreported significant lateral expansion of the maxillarybasal bone by a functional appliance.13 A recent articlereported thinned or dehisced buccal plates after maxil-lary palatal expansion therapy with computed tomog-raphy.29 Ultimately, the new bone-growing theory isstill at odds the apical base theory.15 The new bone-growing theorists claim that crowded posterior teethcan be moved laterally, and buccal bones can bedeveloped without tipping and bone loss with ex-tremely light forces. However, most orthodontists be-lieve that the dental arch cannot usually be expanded ina short time without a heavier force, such as with

lative to corresponding FA points and their

ints re

palatal expansion. Thus, a classic controversy in orth-

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Ronay et al 437

odontics has been reignited. Research on the morphol-ogy of the supporting bone after conventional andnewly developed orthodontic mechanics and stabilityof the treatment results is therefore critical, and theWALA and FA points used in this study might beuseful references for this purpose.

Our results demonstrate the ability to look at theapical base and predict a patient’s dental arch form. Itwill be of future interest to study whether other ana-tomic landmarks could serve as an even more accurate

Table II. FA and WALA point distances between ca-nines and molars and their ratios

Patient

Distances (mm)Ratios (%)

FA points WALA pointsFA

ratio(3-3/6-6)

WALAratio

(3-3/6-6)3-3

width6-6

width3-3

width6-6

width

1 28.00 54.50 29.27 60.27 51.37 48.572 27.05 50.26 26.50 54.54 53.81 48.593 29.80 52.50 28.50 57.76 56.77 49.334 28.29 55.28 30.85 59.25 51.17 52.075 26.81 48.34 29.37 56.10 55.45 52.346 28.26 53.35 30.82 58.15 52.97 53.007 30.01 48.77 31.50 54.75 61.53 57.538 27.07 52.29 28.01 55.78 51.77 50.239 26.00 50.29 28.26 56.33 51.70 50.17

10 26.50 50.75 28.00 53.78 52.21 52.0511 28.95 56.48 29.42 57.58 51.25 51.1012 27.02 53.11 27.01 59.26 50.86 45.5713 26.05 50.10 28.29 56.78 52.00 49.8214 26.36 48.93 26.53 53.41 53.87 49.6715 26.05 53.14 24.34 57.35 49.02 42.4516 28.53 51.59 30.76 59.55 55.31 51.6517 28.00 48.75 30.75 53.25 57.43 57.7618 29.54 51.05 30.04 54.06 57.87 55.5819 24.27 45.50 23.75 49.75 53.35 47.7320 30.25 59.30 29.75 66.51 51.02 44.7321 26.50 49.00 27.75 53.75 54.08 51.6222 29.50 50.74 31.75 57.00 58.12 55.7123 25.76 47.83 27.81 52.80 53.87 52.6824 23.52 51.00 24.50 55.50 46.11 44.1425 27.54 50.01 27.00 52.76 55.06 51.1726 27.01 49.77 30.00 55.01 54.26 54.5327 25.67 46.34 27.25 53.05 55.40 51.3728 28.75 50.50 31.01 58.50 56.92 53.0129 29.95 54.35 30.29 60.59 55.11 49.9930 27.00 50.99 30.50 54.75 52.94 55.7131 27.50 53.00 29.75 58.75 51.88 50.6332 27.25 54.00 29.99 59.77 50.46 50.1833 27.07 46.40 29.55 52.81 58.35 55.9634 29.26 49.31 29.51 55.79 59.34 52.9035 27.77 50.33 30.04 56.30 55.17 53.36Average 27.51 51.08 28.81 56.32 53.94 51.22SD 1.60 2.92 2.02 3.14 0.03 0.04

3-3, Canine to canine; 6-6, first molar to first molar.

representations of basal bone. Additionally, it should be

determined whether the buccolingual relationships be-tween the FA and WALA points are related to archwiretorque. Further research should also include the thirddimension when assessing patient data to give clini-cians more information about the curve of Spee. How-ever, the vertical distribution of WALA points mightdepend on not only tooth inclination but also periodon-tal conditions, such as the attachment level or the rootlength of the patient. We expect that the WALA-FArelationships will be different in patients with Class IIand Class III dental and skeletal relationships, as wellas in adults relative to growing patients. These are thesubjects of continuing investigations.

This study shows that distal to the mandibularcanines, the average distance between FA and WALApoints describing the same tooth changes buccolin-gually. In this posterior area, the FA points are morelingually located than the WALA points. This factmight be linked to the clinically observed gradient ofcrown torque along the dental arch but also to thedifferences in basal vs dental arch shape. Andrews andAndrews20 obtained different results. They reportedonly positive values between FA and WALA points andprojected that the points at the mucogingival junctionwere always more buccally positioned than the mostprominent part of the tooth crown. The difference inresults can be explained by their method or sampleselection. Nonetheless, our findings support their hy-pothesis that WALA points can be used to describe thebasal arch and to draw conclusions regarding thedimensions of the dental arch form. Additionally,individual variations of the distance between theWALA and FA points for each tooth were observed.This might reflect the buccolingual inclination of theteeth.

As a result of our research, we cannot confirm pastresearch postulating the existence of an ideal arch formtemplate. On the contrary, this study suggests that allbasal and dental arches should be individually derived.Furthermore, the basal arch, represented by WALA

Table III. Correlation coefficients between FA andWALA points at 3-3 width, 6-6 width, and (3-3/6-6)ratio

3-3width

6-6width

(3-3/6-6)ratio (%)

Correlation coefficient 0.750 0.869 0.750t value (degree of freedom n-2 � 33) 6.520 10.105 6.5165% significance level 1.69 1.69 1.691% significance level 2.45 2.45 2.45

3-3, Canine to canine; 6-6, first molar to first molar.

points, can be used as a clinical guide in fabricating

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438 Ronay et al

individualized archwire templates. Consideration of theanatomy of each mandibular base also ensures thatoptimal function of the occlusion, periodontal health,desired esthetic appearance, and, of course, stability ofthe dental arch form can be achieved. With increasingaccess to 3D patient data, this important informationwill be available to practitioners and must be consid-ered in orthodontic treatment planning and archwiredesign.

CONCLUSIONS

1. Arch forms derived from both FA and WALA areindividual and cannot be defined by 1 generalizedshape. These results show that form, degree ofcurvature, and other parameters of the alveolarridge and dental arch are subject to much variation.

2. WALA points can be useful in the predeterminationof a dental arch form. The highly significant corre-lation of WALA and FA point width in the canineand molar areas proves that assessments of WALApoints enable prediction of corresponding FA val-ues and the clinical arch form.

We thank Mutsuji Muramoto, UNISN, Osaka, Ja-pan, for generously providing the VMS Dental PlasterModel Shape Scanning System for this study.

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