ARCH FORM
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INDIAN DENTAL ACADEMY Leader in continuing dental education www.indiandentalacademy.com
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INTRODUCTION ď Ž
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The achievement of a stable, functional and esthetic arch form has long been one of the prime objectives of orthodontics Despite numerous investigations, there is little agreement as to the best size and shape for an ideal orthodontic arch form. www.indiandentalacademy.com
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Various authors have used different curved mathemetical models,but stability of these arch forms has not been established The mandibular dental arch is considered as a reference element of diagnosis and therapy in dentofacial orthopedics. www.indiandentalacademy.com
DEFINITION ď Ž
ARCH FORM-position and relationship the teeth have with each other in all 3 dimensions
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-It is the collective response of all teeth to all of the environment forces and their resultant positions in the oral cavity (Brader-1974)
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-dental arch form is made up of teeth which assumes unique positions along a compound curve representing an equilibrium at all points and delimited by the counterbalancing force fields of the tongue and of the circumoral tissues(Brader) www.indiandentalacademy.com
DETERMINATION OF ARCH FORM
Determined by -skeletal pattern -muscular forces “ neutral zone” ( Mills 1968)
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TYPES OF ARCH FORM
BONWILL HAWLEY ELLIPSE PARABOLA CHUCKS –ARCH FORM CANTENARY CURVE BRADER PENTAMORPHIC COMPUTER PRIDICTION VARI-SIMPLEX DESIGN ROTH TRUE ARCH STRAIGHT WIRE M.B.T BEGG ARCH FORM LINGUAL ARCH FORM www.indiandentalacademy.com
BONWILL ď Ž
In 1885, he noted the tripod shape of the lower jaw and declared that it formed an equilateral triangle with the base extending from condyle to condyle and the sides extending from each condyle to the midline of the central incisors. www.indiandentalacademy.com
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He stated that this triangle existed for the proper functioning of the teeth. Importantly, he noted that the bicuspids and molars formed a straight line from the cuspids to the condyles.
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HAWLEY
In 1905, Hawley employed some of Bonwill’s principles in proposing a geometric method for constructing the ideal arch form. Hawley suggested that the six anterior teeth be made to lie along a circle whose radius equaled their combined widths. From this circle he created an equilateral Triangle, the base of which represented the intercondylar width. www.indiandentalacademy.com
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It was proposed that the bicuspids and molars should be aligned along these extended straight lines. Hawley did, however, advised against the strict use of this method for determining arch form, and that it be used only as a guide in establishing arch form. www.indiandentalacademy.com
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Arch form is constant for all induviduals The radius of the arch varied depending on the size of the anterior teeth This arch form is no longer recommended www.indiandentalacademy.com
CONSTRUCTION
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PARABOLA
Angle , 1907, - Defined “line of occlusion”, as being “the line with which, in form and position according to type, the teeth must be in harmony If in normal occlusion”. The form Of this line was said to resemble a Parabolic curve but one that varied greatly due to race, type, temperament, etc. of the individual. www.indiandentalacademy.com
PARABOLA ď Ž
By E.H.Angle in 1906
Fits as well as any ideal arch Ignors narrowing of arch form over the second molars
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In describing the First order bends, Angle objected particularly to the straight line proposed from cuspid to third molar. Angle stated that a straight line existed from the cuspid to the mesiobuccal cusp of the first molar, however, there was a natural curvature needed in the molar region. www.indiandentalacademy.com
Landmarks A,D,D’,E,E’
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GRAY
In 1942, Gray’s Anatomy stated :
“The maxillary dental arch forms an elliptical curve...The mandibular dental arch forms a parabolic curve”
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CHUCK ď Ž
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Chuck -In 1934, noted the variation in human arch form and pointed out that arch forms had been referred to as square, round, oval, tapering. He stated that while the BonwillHawley arch form was not suitable for use in each patient, it could serve as a template for the construction of individualized arch forms. www.indiandentalacademy.com
Chuck superimposed this arch form on a millimeter grid and used this template for archwire construction according to Angle’s method. Chuck suggested that the bicuspid regions should be wider than the cuspids to prevent excessive expansion of the cuspids.
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DRAWBACKS OF PARABOLAELLIPSE ARCH FORM ď Ž
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MacConaill -1949, stated that, in considering the line of occlusion, it would be impossible for an ellipse and a parabola to meet one another at every point. He concluded that the ellipseparabola description of the two dental arches, although elegant, had no immediate relation to function. www.indiandentalacademy.com
BLACK ď Ž
In 1902, he stated that the upper teeth are arranged in a semiellipse and that the lower teeth were arranged similarly on a smaller curve.
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CATENARY CURVE
Mcconnail and scher -1949 He stated that the catenary curve, fit so many cases with exactness that it could be taken as the “ideal curve” of common occlusions.
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Shape formed by a length of chain held at each end and allowed to drop Catenary curve could be described as a central core or central perimeter around which teeth arrange themselves
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Ignores narrowing of archform over the second molar The length of the chain and the distance between the supports determine the precise shape of the curve
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Catenary curve fits the dental arch form of the premolar-canine-incisor segment of a arch very nicely for most individuals The curve doesn’t fit accurately if it is extended posteriorly, because the dental arch normally curves lingually in the second and third molar region www.indiandentalacademy.com
Catenary curve a better representation of mandibular dental arch Ellipse or parabola represents maxillary arch (Neilans-1968) Catenary curve is a good fit in 27%of the samples studied (White LW-1977) www.indiandentalacademy.com
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In 1957, Scott also supported the concept of the catenary curve as the shape of the human arch based on the developmental anatomy of the dental arches and surrounding anatomic structures.
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He pointed out that the basal bone of the maxilla and mandible remains much more constant in form in all mammals and forms a foundation on which a great deal of variation in form of alveolar processes are constructed
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Burdi and Lillie in 1966 stated that the basic bony arch is established as early as 9.5 weeks in utero and that this form was that of the catenary curve.
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Musich, in 1973, supported the concept of the catenary curve as the ideal arch form and suggested the use of the catenometer as a reliable device for construction of arch perimeter. The catenary curve creates a rather tapered arch form and many of the tapered arch forms provided by orthodontic manufacturers today are based on the catenary curve. www.indiandentalacademy.com
BRADER ARCH FORM ď Ž
By Brader-1972
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He stated that dental arch form was made up of teeth which assume unique positions along a compound curve representing an equilibrium at all points and delimited by the counterbalancing forces of the tongue and circumoral tissues. www.indiandentalacademy.com
Also called as trifocal-ellipse Arch form is similar to cantenary curve but tapers over the second molar Several manufacturers use Brader arch form
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The geometry of the curve of the dental arch form was said to be best approximated by a closed curve with the curvilinear properties inherent in the trifocal ellipse, with the teeth occupying only the portion at the constricted end of the curve. www.indiandentalacademy.com
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Brader recommended an arch guide with five arch forms. The selection of the proper arch form was based on arch width at the second molars as measured at the facial, gingival surface. The maxillary archform was selected one size larger than the mandibular arch form.
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They differ in size as dictated by width of second molar
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The maxillary arch form is always one size larger than the mandibular arch form
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It differs from a cantenary curve in producing greater width across premolar
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The Brader arch form will more closely approximate the normal position of the second and third molars www.indiandentalacademy.com
SELECTION OF ARCH WIRE ď Ž
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Measure the greatest intermolar diameter in millimeter This measurement gives the optimum arch curve on guide chart
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The unique geometry of the Brader arch is that it forms a superior dental arch form
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The primary determinants of arch form morphology are the tissue force in resting state www.indiandentalacademy.com
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The geometry of the dental arch form is so related with the resting forces of the tongue
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PR=C
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The lips and cheek exert inward counterbalancing tension against the teeth
PI=Pe+t{1/R+1/R’}
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Arch form characteristics are such that the form is stabilized and dental equilibrium is attained whenever C=T
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DRAWBACK OF BRADER ARCH FORM ď Ž
Many clinicians found that this arch form created excessive narrowing in the cuspid region of many patients and led to excessive wear of the incisal portion of the cuspids.
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VARI-SIMPLEX ARCH FORM
By Dr Garland McEvain-baylor university He studied 102 treated cases of Dr Alexander and found 2 arch form which fits to all his cases “u” form and”v” form
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The anterior section of Vari-simplex arch forms is flatter than PAR arch forms and more pointed compared to roth arch forms
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TYPES OF ARCH FORM
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Vari simplex arch form serves merely as treatment guide, they never intended to be final arch wire
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Final mandibular arch wire is always fitted to the original study model
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Care is taken to determine that cuspids are not expanded
Mandibular expansion occures in molar and premolar region
The maxillary arch form is built to fit the mandibular arch form www.indiandentalacademy.com
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Dr Alexander does not correlate arch form to the facial type to keep the cuspid stable.
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He does not use Tweeds concept of co-relating upper and lower arch wires since similar arch wires are not placed in upper and lower arch at the same time www.indiandentalacademy.com
PENTAMORPHIC ARCHES
By Ricketts Atleast 10 factors needed to be taken into account in the research of arch form
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This includes -Arch correlation -Arch size -Arch length -where the arch to be measured -contact details -final determination of the bracket location www.indiandentalacademy.com
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Twelve arch forms were originally identified, these were narrowed down to 5 by ricketts and are called as pentamorphic arches
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They are -narrow ovoid -ovoid -normal ideal -tapered -narrow tapered
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NARROW OVOID
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OVOID
NORMAL IDEAL
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TAPERED
NARROW TAPERED
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ROTH TRU-ARCH FORMS ď Ž
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The Roth Tru-Arch form was derived from his extensive clinical testing and recording of jaw-movement pattern in treated patients who were out of retention and had stable results Comparison with arch form derived by Andrews from measurement of his 120 normal cases shows that the Roth arch form is wider by few millimeter in the bicuspid region www.indiandentalacademy.com
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Roth notes that superimposition of his Tru-Arch form on Ricketts normal form shows that they coincides almost exactley The Roth Tru-Arch form actually overcorrects the arch width slightly;over correction is part of roths goal www.indiandentalacademy.com
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Arch width varies with facial type the brachyprosopic arch is seldom more than 2-3mm wider than the dolichoprosopic arch, but the individual jaw width may wary more and the arch wire should be adjusted to harmonize
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The widest point in the entire arch is at the 1st molars, but in the front part of the arch, the widest part is in the bicuspids and not cuspids
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There are actually 5 arcs in the arch -1) the arc acros front -2,3) another arc in each cuspid , bicuspid region -4,5)a uniform curve in the buccal segment
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TYPES
TAPERED OVOID SQUARE
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STRAIGHT WIRE TECHNIQUE ď Ž
The arch wire used in this technique is slightly expanded in the bicuspid region to allow proper functional movements and it is close to roth arch forms
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M.B.T ARCH FORM
M.B.T technique uses arch form used by chuck(1932) Classified by chuck in 1932 Tapered (narrow) Ovoid (normal) Square (broad)
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TAPERED ď Ž
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Ovoid arch form has the narrowest inter canine width Used in -gingival recession in canine and premolar region -single arch treatment cases
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OVOID
Preferred arch form Has resulted in good stability When superimposed with tapered arch form there is 6mm difference in canine region
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SQUARE
Used in cases with broad arch forms, Useful atleast in part of the treatment in cases requiring expansion of upper arch, buccal uprighting of lower posteriors
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ANDREIKO THEORY OF ARCH FORM
By Andreiko et al -1994 Shape of the mandible should dectate arch form,with the teeth aligned and contained with in the limits of the mandibular bone
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ADVANTAGES -The arch form are derived from the skeletal and dental anatomy and are therefore designed to be closer to an anatomic ideal than mathemetical ideal -Individualized treatment is simplified www.indiandentalacademy.com
ARCH FORM CONSIDERATIONS IN BEGG TREATMENT
Dr BEGG –each patient is an entity unto himself, as far as the most favorable arch form should bear in relation to rest of the face and skull
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MOLLENHAUER-There has not been the rigorous teaching of arch form in begg technique as in edgewise. Neglect-due to the belief that use of light wires could not alter the patients original arch form ( but this is not true)
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An arch wire as light as 0.016� can alter the arch form if kept in the brackets for few months
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METHOD TO DRAW INDIVIDUAL ARCH FORM
The arch form consists of 3 segments – an anterior segment between the two canine teeth, and 2 posterior segments from canine to molars on either side
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The dimensions and curvetures of these segments depends on 1)-anterior tooth materialdetermines the anterior segment length from one canine cusp to the other canine cusp
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2)-width across the cusp tips of 33,43, mesio buccal cusp of 36,46 and disto buccal cusp of 37,47 determines the transverse dimension of the arch
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3)-arch length measured as perpendicular distance from the mid point between 31,41 to the line joining the tips of disto buccal cusps of 37-47,determines the sagittal dimension of the arch
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DRAWING A ARCH FORM
Obtain the above said measurements from patient Draw a midline on a graph paper Transfer the canine locations on the graph paper on either side of the arch midline
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Take a 4” long 0.016” s.S wire.Mark on it the length of the anterior segment,the wire is flexed such thar these pointslie on the canine location in graph,the wire gives the anterior curvature
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Location of mesio buccal cusps of first molars are marked exactely and the canine marking is extended to it using a straight or curved line The upper arch form is drawn parallel to and outside the lower arch form keeping a distance of 2-3 mm
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COMPUTER PREDICTION
Schulof-1975 Various other arch form have been constructed using algebraic equations
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Arch form are produced from measurements of intermolar width, intercanine width and arch depth from labial surface of incisors to last standing molars
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OTHER ARCH FORMS ď Ž
Williams -1917 described anterior teeth as lying on the arc of a circle with its centre midway between the buccal grooves of 1st molar
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Sicher-1952-upper arch-elliptical, lower arch-parabolic Baz -1958 determined normal arch size by a geometric construction based on measurements taken from patient’s face
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Kato-1964 no great disparity between arches, same arch form may be classified differently by different workers Lu 1964 dental arch could be described by a polynomial equation of the 4th degree
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THE RELAPSE TENDENCY INHERENT IN ARCH FORM CHANGES ď Ž
MCCAULEY,STRANG,GRABER,AND ERSON,HUGGINS,MILLS,LUDWIG --numerous authors who had reported that when inter-cuspid and inter-molar width had been changed during orthodontic treatment, there was a strong tendency for these teeth to return to their pre-treatment position. www.indiandentalacademy.com
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Walter- reported the maintenance of slight increase in mandibular inter-cuspid width after all retention had been removed for what was termed an adequate period. .
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Steadman also reported similar results. Arnold later pointed out that at least five years must elapse before an apparent maintenance of increase in inter-cuspid width could be accepted
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In 1976 Gardner studied intercuspid, inter-first bicuspid, intersecond bicuspid and inter-molar widths, as well as arch length changes in 103 cases, 74 of which were treated nonextraction, and 29 of which were treated with extraction of four first bicuspids. His conclusions were as follows: www.indiandentalacademy.com
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1. Inter-cuspid width was expanded during treatment but had a strong tendency to return to or close to its original pre-treatment width in both non-extraction and extraction cases. 2. It would appear that the inter-first bicuspid width showed the greatest treatment increase in width with only a minimal amount of post-treatment width decrease. www.indiandentalacademy.com
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3. Second bicuspid width for nonextraction cases showed a significant amount of increase with a slight tendency for postretention decrease. 4. Second bicuspid width for extraction cases showed a decrease with treatment and a slight continued decrease postretention. www.indiandentalacademy.com
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5. The inter-molar width of nonextraction cases showed signifi- cant increase in width with treatment and the extraction cases showed a significant decrease with treatment, However there were no changes in either extraction or non-extraction cases postretention. www.indiandentalacademy.com
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6. The incisor to inter-molar distance decreased with treatment and had a slight tendency to continue to decrease post-retention.
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In 1995 De La Cruz, et al., studied the long term changes in arch form of 45 Class I and 42 Class II Division 1 cases after orthodontic treatment and a minimum of 10 years post retention.
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They concluded that arch form tended to return toward the pretreatment shape after retention and that the greater the treatment change, the greater the tendency for post-retention change. They suggested that the patient’s pre-treatment arch form appeared to be the best guide for future arch form stability, www.indiandentalacademy.com
NORMAL GROWTH AND DEVELOPMENT ď Ž
Arch dimensions changes with growth, it is therefore necessary to distinguish changes induced by appliance therapy from those that occur from natural growth
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MOORREES-has pointed out that considerable individual variations in arch form will occur with normal growth, with a general tendency towards an increase in the intermolar width during the change over from the decidous to permanent dentition.
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It is difficult to predict the growth potential in induvidual patients, but information is available on the average changes in arch dimension in centered samples
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The average changes reported by Moyers et al shows changes in arch width vary between males and females and that more growth in width occurs in upper than the lower arch, this growth occurs mainly between 7 to 12 years of age, after 12years growth in width is seen only in males www.indiandentalacademy.com
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SINCLAIR et al have confirmed that the increase in molar width after age 12 is statistically different in males and females. -Male arches grow wider than female arches -Lower intercanine width increases significantly in the change over dentition but does not increase in permanent dentiton after 12 years of age
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-upper and lower inter molar width increase spontaneously to a considerable extent between ages of 7 and 18 in males -little changes in arch width occurs in the premolar region after age of 12
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-changes in arch width may not be accompanied by changes in arch length,there is a tendrncy towards a decrease in arch depth in third and forth decades
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APPLIANCE INDUCED GROWTH ď Ž
It is difficult to determine the contribution of appliance, as a normal growth change would be expected for each individual
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McNAMARA and BURDON-it seems logical to consider increasing arch size at a young age so that skeletal ,dentoalveolar, and muscular adoptations can occur before the eruption of permanent dentition.
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An appliance inserted in an actively growing patients, shows a favorable response,however this response may have occurred in the absence of treatment,the relative contribution of appliance being difficult to determine
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SPILLANCE and McNAMARA -Examined the records of PATIENTS IN THE Michigan study who presented with narrow arch forms and compared them with the average sample. result show that those with initially narrow arch forms tend to become more average, and ppliance therapy is therefore more likely to achieve a stable change www.indiandentalacademy.com
INTER CANINE WIDTH ď Ž
LEWIS & LEHMAN & BAUME have shown that the inter canine width increases during eruption of permanent incisors and again during eruption permanent canines
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DUTERLOO and BIERMAN show that the alveolar crest is relatively inactive after the deciduous teeth erupt, but it is most active during eruption of permanent teeth and then becomes relatively inactive again after the permanent teeth have erupted. Therefore if mandibular lateral expansion is ever to be considered, the optimal time is prior to and during eruption of permanent teeth www.indiandentalacademy.com
FACIAL FORM VS ARCH FORM ď Ž
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dolicocephalic form --longer but narrower and deeper maxillary arch and palate. Brachy cephalic type --wider but shorter and more shallow palate and maxillary arch.
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ROLE OF SOFT TISSUE MATRIX IN MAINTAINING ARCH FORM; ď Ž
Frankel postulates that the increase in crowding is the result of hypertonic muscles in the buccinator mechanism restricting the lateral growth of teeth and their supporting tissues.
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The equilibrium theory states that the positions of the teeth are determined by the balance between the intrinsic forces of tongue, lips, dental occlusion, and periodontal ligament Supported by Tomes-1873 Opposed by Scott-1967 www.indiandentalacademy.com
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ORAL RESPIRATION- Ricketts has shown that mouth breathing tends to lead to narrow arches, cross bites and increased crowding Linder-Aronson and backstrom report that children scheduled for adenoidectomy generally have longer, more narrow faces than control children www.indiandentalacademy.com
AJO 1980 January ď Ž Anoop Sondhi, John F. Cleall and Ellar A. Be Gole ď Ž Distal movements of canines during treatment does not ensure stable increase in mandiular inter canine width. www.indiandentalacademy.com
Analysis of change in arch form with premolar expansion ď Ž
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Ellen A.BeGole, Cyril Sadowsky (Ajo1998) The arch forms of 38 cases in which expansion, while maintaining arch form, were analyzed before treatment, after treatment, and an average of 6 to 8 years after retention. www.indiandentalacademy.com
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Significant stable expansion of the premolar and molar widths may be possible in both the maxillary and mandibular arches in nonextraction cases.
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Upper dental arch morphology of adult unoperated complete bilateral cleft lip and palate ď Ž Omar Gabriel, daSilva Filho.(Ajo 1999) ď Ž Cast model analysis of the maxillary dental casts of 31 adult persons with unoperated complete BCLP and those of a matched sample of 31 noncleft patients indicate the following:
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¡ Gender has a differential effect on the maxillary arches of cleft and noncleft patients; significant differences are present in the noncleft group (wider and longer arches in males), but not in the unoperated cleft group.
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· BCLP results in an anteriorly progressive constriction of the upper dental arch in both genders. · The BCLP group has a significantly longer maxillary dental arch, which is attributed to the premaxillary anterior projection.
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CONCLUSION ď Ž
Clinicians should be cautious when treating to mathematically derived arches, since studies have not determined conclusively what that shape might be
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