004 articulo estetica nishimura

Reconstruction of coronal anatomy in ceramicrestorations of the anterior teeth

Yoshimi Nishimura*

Very tooth in a natural dentition has its ownnatomy, which, at first glance, seems to havelO connection with that of the other teeth,"he reality is that although every tooth is spe-ifically designed for a certain job at a certaintte in the mouth, it also fits in harmoniously/ith the dentition as a whole. This is becauseiie design of each row of teeth follows a spe-ific set of norms and rules that takes into ac-uunt each tooth's individual anatomy. Pros-leses can likewise be fabricated to blend inarmoniously with existing dentition by fol-iwing these same guidelines.Key elements when fabricating the restora-on of an anterior crown are design and toothantour. It is critical to take note of the rela-onship between the expanse and direction ofle ridges and grooves and to consider the an-tomic variations of the teeth that will be ad-icent to the restoration.In this article, the anatomic variations of theiterior teeth (central incisor, lateral incisor,mine), which are vital for esthetic considera-3ns, are examined from the point of view ofle dental technician.

Anterior Teeth Viewed From theLabial Aspect

When examining the individual teeth in theanterior region, the external anatomy of theteeth can be divided roughly into five areas(Figs 1 and 2):

The incisai edgeThe mesioincisal and distoincisal anglesThe contact areasThe contour lineThe cervical line

11-607, M2JD, Ibargi-stii, Osaka 567, apar.

The Incisai Edge

The incisai edge is the straightcst in the cen-tral incisor, because its mesial, central, and dis-tal ridges all lie on almost the same level.Pronounced tapering begins and progresses inthe lateral incisors and the canines as the dis-tal and mesial ridges of the incisai edge appearin increasingly lower positions in these teeth,and a clearly distinguishable arrow-headshape results (Figs 2 and 3).

Compared to the central incisor, the positionof the highest incisai elevation moves increas-ingly toward the mesial part of the tooth inthe lateral incisor and canine. The horizontaldistance between the transition from the mes-

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Nishimura Reconstruction of coronal anatomy in ceramic restorations of the anterior teeth

Fig 1 Anterior teeth: {a) labial view, {b) incisai view, (L) palatal view, (li) cervical view.

contact surfaceincisai edge

angular region

proximalcontour line

cuniatute ofthe cervical line

Fig 2 Variations in anatomy of central incisor, lateral incisor, and canine. Note differences in incisaiedge, angular region, contact surface, cervical tapering, and cervical line.

Fig 3 Tapering of indsal shapeand enlargement of angular re-gion.

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Fig 4 Contact surfaces; note shift in positionfrom incisai area to middle of crown. Surfacesdecrease in size so that a > b > c .

iolabial ridge to the incisai edge and betweenthe transition from the distolabial ridge to theincisai edge is longest in the central incisorand becomes progressively shorter in the lat-eral incisor and the canine. This is because theratio of the mesial and distal thicknesses tothe palatal and vestibular thicknesses grows,leading to an increasingly tapered androunded shape.

Mesioincisal and Distoincisal Angles

The angular region grows progressively largerfrom the central incisor to the canine, assumesan increasingly rounder form proximally, andincreasingly tapers incisally (Figs 2 and 3). Themesial angle in all teeth is smaller and sharperthan the distal angle, while the distal angle ischaracteristically rounder and larger, in addi-tion, the angles become absolutely rounderand larger as one moves from the mesial anglejf the anterior incisor to distal angle of the ca-line. The mesial angle of the central incisor issharpest and smallest, the distal angle of therentrai incisor is slightly rounder and larger,md the mesial angle of the lateral incisor is?ven rounder and larger; this pattern contin-les to the canines.

"Contact Areas

^he contact areas in the central incisor lienesially near the incisai edge and shift in-reasingly to the middle of the crown in the

lateral incisor and canine. The shape of theseareas, which is initially elongated, graduallyshortens, following the same progression (Figs2 and 4).

Contour Lines

The labial silhouettes of the teeth show an in-creasing cervical taper in the same pattern, be-coming sharper from the central incisor to thelateral incisor and then to the canine. In addi-tion, the mesial and distal sides of the teethbecome increasingly asymmetric; specifically,the labial concave contour becomes lower anddeeper distally. The resultant shape is doublycurved (Fig 2).

Curvature of the Cervical LineThe cervical line is almost horizontal in thecentral incisor and gradually arches downwardin the lateral incisor and canine.

The incisai embrasure exhibits a very sharpangle in the center of the row of anterior teethand is smallest there. The angle becomeslarger distally, both incisovertically and mesio-distally. The incisai embrasure between the ca-nine and first premolar is the largest androundest. This is caused by the tapering of theteeth, by the difference in angle characteris-tics, and by the transposition of the contactsurface cervically. The cervical embrasure be-tween these teeth is large incisocervically andnarrow mesiodistally. Laterally, the embrasure

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Nishlmura Reconstruction of coronal anatomy in ceramic restorations of the anterior teeth

labial surface

transition surface

prxima i surface

Fig 5 Tootb outhne viewed from the incisai aspect. Compare labial, labioproximal transition, proximal,palatoproximal transition, and palatal surfaces.

Fig 6 Progression of width:strength ratio (ratio between themesiodistal and labiopalatai ex-tensions of tooth); compared iviththe central incisor, the labiopalataiextension (thickness) increasesand the mesiodistal extension(width) decreases in the lateral in-cisor and canine.

becomes smaller incisovertically and widensmesiodistally. This is caused by the displace-ment of the contact zone to the middle of thecrown and by the increasing cervical tapering.

Incisai View of the Contour Lines

When the teeth are examined from the incisaiaspect (Fig 5), a change in the ratio betweenthe mesiodistal width and the labiopalataithickness is apparent; from the centra! incisorto the canine, the labiopalatal thickness in-creases as the mesiodistal width decreases pro-portionately (Fig 6),

The Labial External Anatomy

As a result of the changed ratio of width tothickness and the differing shapes of the mes-ial, central, and distal labial ridges, the labialoutline of the lateral incisor and canine gradu-

ally becomes more clearly curved labially thandoes that of the central incisor. At the sametime, the curvature becomes less pronounced(Fig 7) because of the curve characteristic andthe tooth anatomy, which is similar in the ad-jacent zones surrounding the contact surfaces.

The degree of tapering is slight and the pala-tal surface broad in the central incisor, so thatthe tooth's cross section is asymmetric labio-palatally. This cross section becomes increas-ingly symmetric in the lateral incisor andcanine (Fig 8a). Conversely, the central incisoris more symmetric mesially and distally, andthe other anterior teeth become increasinglyasymmetric in this aspect as the twisting ofthe teeth becomes visible (Fig 8b).

Lnterdental Embrasures

In addition to the anatomy of the anteriorteeth, the spaces created by this anatomy,known as interdental embrasures, are also im-

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Fig 7 Progression of the curvature characteris-tic; compared with the central incisor, the curva-ture increases in the lateral incisor and canine.

Figs 8a and 8b (Left) Incisai view of central incisor, lateral incisor, and canine; labial and palatal surfaces become in-creasingly symmetric. (Right) Mesiodistal view of central incisor, lateral indsor, and canine; labial and palatal surfacesbecome increasingly asymmetric.

Fig 9 Upper and lower interdental embra-sures; angles of upper spaces enlarge so thatA

Nishimura Reconstruction of coronai anatomy in ceramic restorations of the anterior teeth

Fig 11 Proximal view of anatomic variations'angles formed hy the labial and palatal surfacesof the incisai region grow larger so thatC


ig 13 Cervical view of anatomic variations in theicisal region; the incisai edge is smooth in the centralidsor, the mesial and distal sides slope down, and theliddle part of the crown becomes increasingly promi-ent in the lateral incisor and canine.

I A / \-,~->H~^^ L\

Fig 14 Cervical view of embrasures; their size increasesso that A


Fig 15 Photomontage of the contour image o!the labial surfaces.

Fig 16 Cervical and labial surface ridges.

Fig 17 Variations in the proximally directiprogression of the labial surface ridges.

The Progression of the ContourImage of the Labial Surface

The Ridges of the Labial SurfaceThe mesial, central, and distal ridges in the la-bial surface of the central incisor are virtuallythe same height. In the lateral incisor and ca-nine, the initial positions of the ridges become

progressively lower both from tooth to toothand from ridge to ridge, in the sequence cen-tral, mesial, distal (Fig 15). In the labial surfaceof the central incisor, the three ridges areabout equally thick, but the central ridge be-comes increasingly thicker than the other twoin the lateral incisor and canine (Fig 16),

The external cervical taper becomes sharperfrom the central incisor to the canine, whichcauses the grooves in the labial surface to be-come more slanted in the same way.

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Fig 18 Peaks of the survey line; note incisaishift in the lateral incisor and canine. Sharp ta-pering changes the U shape of the line to a Vshape, and the slope increases mesially anddistally.

Fig 19 Grooves of the labial surface andV-shaped groove. Paralleling the relative de-crease in the incisai region in the lateral incisorand canine, the grooves in the labial surface be-come smaller incisaliy. Also, the V-shapedgroove shifts incisaliy because of the incisai dis-placement of the survey line and the decreasein size of the incisai region. Compared to thecentral incisor, the cervical end of the mesio-distal V-shaped groove in the lateral incisorand canine exhibits an increasing slope.

The initial positions of the mesial and distalridges on the labial surface of the central inci-sor illustrate the tendency to originate from alower position and run to the contact surfacein comparison with the lateral incisor and ca-nine (Fig 17). These ridges in the teeth ofyoung people are concentrated toward themiddle tip of the incisai edge, that is, towardthe tapering. In addition, the more asymmetricthe tooth is (progressing from the central inci-sor to the canine), the more the confluence ofridges moves mesially.

The Survey Eine, V-Shaped Groove, andGrooves in the Labial SurfaceThe survey line runs in the direction of thecervical ridge (Fig 18). In the central incisor, itis more or less horizontal and located far tothe cervical portion of the tooth. In the lateralincisor and canine, the survey line is increas-ingly sloped from the mesial to the distal por-tion and shifts incisaliy.

The grooves in the labial surface become less

and less visible as a result of the change inshape of the incisai edges and the increasingprominence of the cervical ridge (Fig 19).

In the central incisor, the V-shaped grooves(Fig 19) have mesially and distally similarshapes and are greatly extended incisaliy. Inthe lateral incisor and canine these groovesbecome gradually more different. This is be-cause of the development of the three-partform that accompanies the change in shape ofthe incisai edges, the growing prominence ofthe cervical ridge, and the change in the sur-vey line.

The initial position of the V-shaped grooveshifts incisaliy in the lateral incisor and caninebecause, as a result of the change in the three-sided form, the incisai region becomes nar-rower in these teeth. The end points of theV-shaped groove change along with the sur-vey line. These points are located at practicallythe same height mesially and distally, while inthe canine a steep slope is apparent betweenthe position of the mesial and distal V-shapedgrooves. Specifically, the end of the mesialV-shaped groove shifts cervically.

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Fig 20 Compared to the central incisor, theconcave line in the lateral incisor and caninebecomes more clearly visible.

Fig 21 Labial triangular area formed by a lineconnecting the ridge positions dlstally and theconcave lines distally. The labial triangular areanarrows distally around the contact surfaces.Note that the ridges in the labial surface be-come constricted proximally.

Fig 22 Contour image of the anteriorteeth.

The Concave Line

The concave line is more clearly visible in thelateral incisor and canine than in the centralincisor. It is high and flat mesially and lowand deep distally, and this difference is in-creased toward the posterior teeth. The twist-ing of the teeth gradually becomes morevisible because of this configuration (Fig 20).

The Triangular Area of the LabialSurfaceFrom the central incisor, the mesial and distalridges shift downward and move increasinglytoward the contact surfaces in the central ind-sor and canine. The triangular area of the la-bial surface is described by a line connectingthe place where the ridge in the labial surface

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Fig 23 Mesial view of contour image of anterior teeth. Fig 24 Proximal view of lines of the contact and cervi-cal areas; note progression of positions at which theridges in the labial surface cross. Contact areas shift tothe middle of the crown, and the cervical areas thatstand out maximally on the proximal surface becomelower from A to B to C and produce a flatter line.

bends toward the contact surface and a lineconnecting the posterior distal concave line,with the contact surface as its center. This areabecomes increasingly smaller in the lateral in-cisor and canine (Fig 21 and 22).

The Contour Image of the ProximalSurface

The Contact SurfaceCompared to the central incisor, the extensionof the contact surfaces becomes smaller verti-cally in the lateral incisor and canine becausethe contact area shifts to the center and simul-taneously becomes larger labiopalatally as aresult of the change in the width-thicknessratio described above (Fig 23).

The Cervical Line

From the central incisor, the cervical line runsprogressively more horizontally in the lateralincisor and canine, because the ratio of the ex-tension labiopalatally to the extension mesio-distally (width-thickness ratio) becomes larger(Fig 24).

The Grooves in the Proximal SurfaceThe external shape of the proximal surface inthe lateral incisor and canine develops an in-creasingly rounded shape compared to that inthe central incisor. Also, the width-thicknessratio changes as mentioned above. For thisreason, the groove in the proximal surface be-comes steadily broader and flatter posteriorly,until it is nearly invisible in the canine.

The Ridges in the Labial and PalatalSurfacesWhen examining the slope between the posi-tion of the central ridge and the position atwhich the ridge of the labial and palatal sur-faces meet, it appears that this slope becomesprogressively greater in the lateral incisor andcanine as compared to that in the central inci-sor (Figs 25a and 25b). This is true mesially aswell as distally, but is especially pronounceddistally.

From the proximal aspect, the ridges in thelabial surface mesially, centrally, and distallyare almost in the same position. From the cen-tral incisor to the canine, the central ridge inthe labial surface protrudes more labially, and

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Fig 25a Proximal view of incisal edge, cervicalline, and tubercle; the slope of incisal edge in-creases in the lateral incisor and canine as thecervical line and tubercle shift to the middle olthe tooth.

Fig 25b Compared to the central incisor, thedistance between the point of taper and the in-tersection of the grooves in the labial surface othe lateral incisor and canine progressivelyincreases.

Fig 26 Palatal view of contour image of ante-rior teeth.

Fig 27 Palatal view of variations in the mesial and distal ricof tbe anterior teeth.

Fig 28 Palatal view of incisal edges; note grad-ual assumption of a shape approximating out-spread wings whose angles become more obtusein the sequence A


Fig 29 Palatal view of incisai region and tuhercle; theincisai region becomes smaller posteriorly, and the tu-bercle expands upward.

the mesial and distal ridges increasingly be-come constricted inward as the central ridgedevelops better labially in the lateral incisorand canine. As a result, more and more of thelahial surface becomes visible when the teethare examined from the direction of the mesialor distal contact surface.

The configuration of the ridges in the palatalsurface appears similar. While in the centia!incisor the middle of the palatal surface showsa concave shape and the mesial as well as thedistal incisai ridges protrude palatally, the cen-tral ridge steadily protrudes more palatally inthe lateral incisor and canine, and the mesialand distal incisai ridges retrude in the sameprogression. In addition, the tubercle expandspalatally, and the secondary ridge becomesclearly visible. For this reason, more of thepalatal surface becomes visible in the lateralincisor and canine.

The Contour Image of the PalatalSurface

The Incisai Ridge

An examination of the outline of the palatalsurface shows that the central incisor has awell-developed indsal ridge and poorly devel-

oped central and secondary ridges. The centraland secondary ridges become increasingly bet-ter developed and more cleariy visible in thelateral incisor and canine (Figs 26 and 27). Theorigination of the incisai ridge shifts distallyfrom the center in the central incisor to an in-creasingly downward position in the lateral in-cisor and canine. The ridge also takes on theshape of a pair of wings spreading out distallyfrom the mesial region. Further, embracing thesecondary ridge of the palatal surface, theridge becomes constricted proximally (Fig 28).

The Cervical Region

The cervical region is shaped in such a waythat, with the concave line as a boundary, itexpands upward labially (Fig 29).

The V-Shaped Groove

As is the case with the labial surface, aV-shaped groove forms between the centralgroove of the palatal surface and the incisaigroove. This V-shaped groove shifts incisallyfrom the centra! incisor to the canine, and, asa result of the change in the tubercle, the ter-minal point of the groove also shifts upward.In addition, the shape and depth of the groovebecome increasingly visible because of the de-velopment of the central ridge in the palatalsurface and the secondary groove (Figs 26 and29).

The Incisal Ridge and the Concave Line

When the anterior teeth are examined fromthe palatal aspect, it appears that the distancebetween the line connecting the initial posi-tions of the respective incisal ridges with eachother and the line connecting the respectiveconcavities with each other decreases in thesame manner as the labial surface (Fig 30).The area that is created inside this pair of linesis called the palatal triangular area.

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Fig 30 Palatal triangular area in the anteriorteeth, which is formed by a line connecting theplace where the incisai ridges become con-stricted proximally and a line connecting thedistal concavities. This area narrows in the lat-eral incisor and canine.

Fig 31 Incisai view of contour image of anterior teeth. Fig 32 Incisai view of progressive anatomic variation olmesial, central, and distal ridges in the labial and palatalsurfaces.

The Contour Image Viewed Fromthe Incisai Aspect

The Ridges of the Labial Palatal SurfacesWhen the outlines of the anterior teeth are ex-amined from the incisai aspect, either themesial and distal ridges in the labial surfaceappear to be protruding outward, or all threeridges appear to be approximately the same(Fig 31). This is because the mesial and distalridges in the lahial surface of the central inci-sor are strongly developed and the centralridge is weakly developed.

The central ridges in both the labial and pal-atal surfaces are increasingly strongly devel-oped and stand out more distinctively in the

lateral incisor and canine than in the centralincisor.

Compared to those in the central incisor, themesial and distal ridges in the labial surfaceincreasingly exhibit a shape that enfolds thesecondary ridge and bends off proximally inthe lateral incisor and canine (Fig 32).

The Concave Line

The concave line in the cervical area assumesan increasingly gentle curve toward the centerand becomes narrower and more clearly rec-ognizable as a groove posteriorly in the ante-rior teeth further from the midline. Also, thedistal concave line is located deeper and far-ther down than the mesial one in the samepattern.

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Fig 33 Labiocervical view of contour image ofanterior teeth.

Fig 34 Labiocervical view of labial surfaceridges; note area between the cervical andinrisal regions becomes thicker in the lateral in-dsor and canine.

Fig 35 Labial view of contours of the incisaiedges cf anterior teeth viewed from the labialaspect; note external shape of the incisai edges,V-shaped groove, and groove in the labialsurface.

The Contour Image Viewed Fromthe Cervical Aspect

the outside, and the mesial and distal ridgeswiden incisally (Fig 34).

The Ridges in the Labial SurfaceWhen examining the central incisor from thecervical aspect, the cenhral, mesial, and distalridges stand out about equally strongly, andthe mesial and distal ridges are parallel (Fig33). In the lateral incisor and canine, on theother hand, ihe mesial and distal ridges in thelabial surface bend to the outside and widenproximally. As a result, the central ridge in thelabial surface exhibits a shape that projects to

The Cervical Ridge

Compared to its position in the central incisor,the cervical ridge develops incisally in the lat-eral incisor and canine. For this reason, theincisai region becomes proportionately smaller,and the grooves in the labial surface and theV-shaped groove in the central incisor becomeless visible in the lateral incisor and canine.Also, the V-shaped groove shifts incisally, re-suiting in an incisai contour (Fig 35).

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The Three-Dimensional Nature ofCrown Anatomy

Relationship of the DevelopmentalAngles and Cuspation of the Incisai EdgeThere is greater variation in the anatomy ofmaxillary teeth than in those in the mandible,as is shown by the larger variations in theincisai embrasures of the maxillary dentition(Fig 36). The reasons for these greater varia-tions include the wider differences in thethickness of the teeth and the developmentalangles formed by the mesial, central, and dis-tal ridges of the labial and lingual surfaces.

The greater the difference in the develop-mental angle when viewed in cross section

Fig 36 Intraoral view of maxilia and mandiblein a young person. Note iarge variations in theincisai anatomy and embrasures in o the maxil-lary dentition as compared with that of themandible.

nmFigs 37a to 37j Labial, linguai, mesial, distal, and incisai views of natural mandibular central incisor {a,b,c,d,e) arnatural maxillary canine {f,g,h,i,j). Note the small differences in the developmental angles in the mandibular central in-cisor when the mesial, central, and distal ridges of the labial and lingual surfaces are viewed from the proximal direc-tion. In contrast, there are large differences in the developmental angles of the maxillary canine, These differencesaffect the irtercuspation of the teeth.

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Fig 38 Illustration of process by which an in-crease in developmental angles causes cusp for-mation to become more pronounced. Notehow, as the angle between the compass legsgrows, the top of the compass is lowered.

mesially, centrally, and distally, the strongerthe cusp formation. This is true in both maxil-lary and mandibular teeth. The smallest dif-ferences in the developmental angles arefound in the mandibular central incisors, sothat the incisal edges of these teeth appear tobe in a straight line. The extent of cusp forma-tion increases in the lateral incisor and canine,and the teeth gradually take on an arrow-headshape. The differences in developmental an-gles are much larger in the maxillary canines,where cusp formation is stronger (Fig 37).

To illustrate this principle, consider the com-pass shown in Fig 38. As the angle formed byopening both compass legs equally increases,the height of the compass decreases. Likewise,the cusp formation in the anterior teeth de-pends on the size of the developmental angle(Figs 39a to 39c). The developmental anglesare smallest in the central incisor, which alsohas the least conspicuous cusp formation. Thelateral incisor and canine, with larger develop-mental angles, have increasingly noticeablecusp formation. The outline of the incisal edgeof the teeth also changes with the variation inthe developmental angles.

Differences in the formation of the mesial,central, and distal surfaces of the tooth be-come more pronounced in teeth further awayfrom the midline. As a result, the pattern ofmovement for the abrasives used during actualanatomic modifications is such that it does notimpart much difference in the central incisor.When working with the lateral incisor and ca-nine, it is therefore better to impart this differ-ence in the preparation of the three surfaces.

Ten Check Points for Integrating theAnatomic Variations of the AnteriorTeeth

The pattern of anatomic changes in the ante-rior teeth, gradually changing from the centralincisor to the lateral incisor to the canine,should be apparent. An understanding of thispattern allows one to carry out anatomic mod-ifications on particular points on the centralincisor so that it will blend in with the otheranterior teeth. This tooth is the key to a har-monious restoration.

There are, in fact, 10 such check points, sixon the labial surfaces and four on the lingualsurfaces (Figs 40a to 40f). Points 1 through 4and 7 through 10 in Figs 40a to 40f markwhere carving of the cuspation of the incisaledge occurs when teeth are viewed labialiy.Points 1 through 4 show the anatomic varia-tions of the incisal edge outline viewed fromthe cervical direction, while points 5 and 6 il-lustrate the constriction and torsion visible inthe cervical outline when viewed incisally.

Essentials of Carving

Points 1 through 4 mark the positions of theV-shaped grooves on the labial surface of thetooth, and points 5 and 6 correspond to themesial and distal concave lines (Fig 40a). Onthe central incisor, points 1 through 4 shouldbe carved to follow the prescribed form. For

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A B C A

Figs 39a lo 39c Diagrams of maxillary central incisor (top), lateral incisor (middle), and canine (bottom). Di-agrams on left show the locations of the vertical sections through the lahial surface of each tooth: A = mesialregion; B = central region; C = distal region. Also shown are the cross sections of each of these regionsviewed from the proximal direction. Diagrams on right show the relationship of the cusp formation of thetooth and the developmental angle of the ridge in the labiolingual section. The triangle formed hy the in-clined surfaces shows the inclination of the ridges on the labial and lingual suifaces. The horizontal line con-nects the highest points (central mamelon or cusp) of the incisal edge of each tooth. The greater the spacebetween this line and the peak of the triangle in the mesial and distal regions, the greater the cusp forma-tion. Note also the distance between the upper line and the triangle (developmental angle) formed by the re-spective labial and lingual surface ridges of each tooth. For the central incisor there is virtually no differencebetween the developmental angles in the central, mesial, and distal regions, and the space between this lineand the peak of the triangle is small. However, in the lateral incisor and canine the difference in the develop-mental angles becomes larger, and the space between the upper line and the triangle peaks also becomesgreater. As the difference in the developmental angles increases, there is a stronger tendency for cuspation.

the lateral incisor and canine, these pointsshould be carved so that they fan out mesiallyand distally, so that they greatly lower theincisal edge mesially and lingually while curv-

ing around in the proximal direction. Points 1through 4 should be carved deeper in the an-terior teeth farther from the midline.

In addition, the terminal position of points 3

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igs 40a to 40f The 10 carving points; there are six checkpoints on the labial surface and four on the lingual surface.

-ig 40a Direct view of the labial surface. Fig 40b Direct view of the lingual surface.

Fig 40c View of the mesial proximal surface. Fig 40d View of the distal proximal surface.

le View of the incisai edge. Fig 40f View from the cervical direction.

and 4, and 1 and 2 cervically, should becarved more sharply. Points 1 and 4 should becarved to define the line of the labial trianglearea toward the incisai edge. This allows for asmooth transition, from the mesial to the dis-tal sections, in the lahial surface ridges of thecentral incisor, lateral incisor, and canine. Har-

mony is preserved in variations of the labialoutline of each tooth, and a smooth anatomictransition is created in the associated teeth.

The vertical separation between points 5 and6 becomes more pronounced and the areaaround point 6 becomes more clearly definedin the teeth further away from the midline.

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The degree of constriction in the cervical re-gion and the torsion on the mesial and distalregions are expressed by incorporating points5 and 6. To express asymmetry and torsion incrown anatomy, more emphasis is placed oncarving points 3 through 5 in teeth furtherfrom the midline.

Points 7 through 10 show the position of theV-shaped grooves on the lingual surfaces ofthe teeth (Fig 40b), They are all about thesame level incisally on the central incisor. Inthe teeth further from the midline these pointsare carved more strongly and cut to curvemore significantly proximally. This creates agreater slope cervically in the lateral incisorand canine. In addition, the difference in thedevelopmental angles, which are formed bythe mesial, central, and distal labial surfaceridges defined by points 1, 2, 3, 4 and 7, 8, 9,10, becomes larger in these same teeth. Con-currently, cuspation arises in the incisai anat-omy and a slight unevenness appears in theincisai edge.

In the lateral incisor and canine, points 1, 7,4, and 10, in this order, are carved deeper inthe labiolingual direction (Figs 40c and 40d).When this is done, the difference in the devel-opmental angle as defined by the central la-bial and lingual ridges becomes greater, andthe distance between the intersection of points1 and 7 and 4 and 10 with the central tuberclebecomes greater. A line separating points 1and 7, 2 and 8, 3 and 9, and 4 and 10 crossesthe tooth in the incisai region (Fig 40e).

Points 5 and 6 are carved primarily to ex-press the constriction in the cervical region,the torsion of the tooth, and asymmetry be-tween the mesial and distal halves of thetooth. The carving of point 5 is carried out pri-marily on the transitional surfaces, proximally,so as not to section the labial surface ridges. Incontrast, point 6 is carved bolder in teeth fur-ther from the midline. This is done not onlyon the transitional surfaces, but also on por-tions of the labial surface proper. Carving inthese areas naturally constricts the proximaloutline and expresses torsion in the tooth. Inaddition, the characteristic double curve is ex-pressed in the distal region. By carving points3 and 4 in the cervical direction in the lateral

incisor and canines, these points connect withpoint 6, the mesial region appears to bulgeout, and the distal region become constricted.This expresses the asymmetry of the mesialand distal halves of these teeth.

Figure 40f shows points 1, 2, 3, and 4 fromthe cervical direction. In the teeth further fromthe midline, points 1 and 4 should be carvedmore boldly to curve in sharply in the proxi-mal direction. After reaching the incisai edge,points 2 and 3 are carved so that the centralridge projects outward, and the V-shapedgroove seems to appear on the incisai edge. Asmentioned earlier, the V-shaped grooves canbe made to appear toward the incisai edge bycarving points 1 through 4 deeper in the lat-eral incisor and canine.

The Actual CarvingAs an example of the effect these points haveon teeth, they were carved into three identicalcasts which were formed by flowing resin intuan impression of a central incisor (Figs 41a to43e).

In Figs 41a to 41c, the widthidepth ratioof the teeth on the right side changes to pro-duce a good balance in the anatomic varia-tions of the teeth adjacent to the centralincisor; the transitional surfaces have alsobeen correctly incorporated. Comparing theseteeth with those on the left side, it is apparentthat anatomic variations have been achievedhere by solely carving the 10 points similarlyin each central incisor, without taking into ac-count the anatomic variations in the adjacentteeth. The teeth have a certain amount of har-mony, but they are flat and lacking in fullness.

An impression was taken of a central incisor,three resin models were made (Fig 42a), andthe 10 points mentioned here were carved(Figs 42b to 42g). Note that because only onetype of central incisor was used as the basisfor fabricating the examples in Figs 42a to42g, the width:depth ratio needed to incorpo-rate the anatomic variations of the associatedteeth has not been realized. In particular, thefullness of the cervical and the central regions

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Figs 41a lo 41c Example of how anatomic variations established by incorporating the proper width depth ra-StioTof'aSerior e t " ' " " ' ^""' ' " ' ^"^"'^ "^"^' checkpoints'comhi^ to r^ea'te harmontos r-

Fig 41b Lateral view of a lateral incisor andcanine (the teeth on the left m Fig 41a} thatwere fabricated and arranged from identicalcentral incisors. Anatomic variations weremade according to the 10 carving points.

Fig 41a Frontal view of six anterior teeth carvedto compare restorations fabricated using only the10 carving points {left) with those fabricated whileaiso taking into consideration the anatomic varia-tions and the widthidepth ratio of the associ-ated teeth (right). The six anterior teeth shown allhave the same mesiodistal dimension. Comparethe labial surfaces of the three teeth on the ieft,which lack fullness because their width;depth ra-tios are all the same, with those on the right,which have the proper ratios.

Fig 41c Lateral view of crowns (the teeth onthe right in Fig 41a) with porcelain extendingto the root that were fabricated and arrangedbased en the left centrai incisor as the keytooth. Anatomic variations were carried out onthe associated teeth while incorporating theproper width:depth ratio.

uf the crown appears deficient both labiallyand lingually in the teeth farther from themidline. This shows the importance of incor-porating such variations during the actual clin-ical modifications by properly carving the 10check points after first considering thewidthidepth ratio of the teeth. Furthermore,depending on the patient, there may well berestrictions on the width:deptb ratio.

The teeth were arranged in Figs 43a to 43eso that they can be seen as a set. The figuresand their legends explain the actual carving ofthe 10 checkpoints.

Expression of the Labial Triangular AreaWhen fabricating anterior restorations, avoid-ing too strong an appearance in any individualtooth is important. It is also essential that thearrangement of the teeth is as near as possibleto normal, so close attention must be paid tothe labial triangular area when fabricating thecrowns. If, for example, only a lateral incisor ismissing and other anterior teeth are in theirnormal positions, the form of the restorationmay be harmonized by keeping the labial tri-angle in mind during fabrication.

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Fig 42a to 42g Central incisor, lateral incisor,and canine fabricated and arranged from resinmodels of the same central indsor as In Fig 41.Anatomic variations were added using the 10carving points. Although the width:depth ratioand mesiodistal dimension were the same for allthree of the teeth, it was possible to incorporateconsiderable anatomic variation simply by carv-ing the six labial and the four lingual points.

Fig 42a Resin models of the central incisorsfabricated from impressions of the same tooth.

Fig 42b Direct view of the labial surface.Cusp formation of the incisal edge is expressedby carving points 1, 2, 3, 4, 7, 8, 9, 10 in theincisal region. A constricted, twisted appear-ance is expressed in the cervical region by carv-ing points 5 and 6.

Fig 42c Direct view of the lingual surface. Adecline in the height where the marginalridge begins is achieved by carving points 7and 10, and the accessory ridges at the incisalregion are brought out by carving points 7, 8,9, and 10.

rmrmFig 42d and 42e Views of the mesial and distal surfaces. The slope where the labial and lingual sur-face ridges cross the incisal edge on the mesial, central, and distal regions is expressed by the extentto which points 1 and 7 and 4 and 10 are carved.

Fig 42f Incisal view. The cervical region be-comes more constricted in the teeth furtherfrom the midline depending on the extent towhich points 5 and 6 are carved, resulting in aprotruding appearance. Also, the constriction ofthe tooth and the asymmetry of the mesial anddistal halves can be expressed by the extent iowhich points 1,2,5 and 3,4,6 are carved.

Fig 42g Cervical view. Points 1 and 4 affect theprojection of the central region. Also, theV-shaped grooves are brought out in the vicinityof the indsal edge by carving points 1,2,3, and 4.The asymmetry of the mesial and distal V-shaped grooves in tho teeth farther from the mid-line can be expressed by lengthening the connec-tions between points 3 and 6 and 4 and 6.

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Figs 43a 10 43d The same teeth as in Figs 42a to 42g after modifications

mrmFig 43a Labial surface view. The smooth tran-sitions in the inclined surfaces of the mesialand dista) areas near the incisal edges of thelateral incisor and canine are prepared by carv-ing points 1 and 2 and 3 and 4. The gap in themesial line angle region is created by carvingpoint 7. The labial triangular area is'properlybalanced by establishing points 1, 4, and 6 onthe labial triangle line.

Fig 43b Lmgual surface view. The transitionof the marginal ridge for the teelh that are far-ther from the midhne is expressed by establish-ing points 7 and 10 on the lingual triangle line.

Fig 43c Incisal view. Note that all of the teethlook the same because the transitional surfacetowards the proximal region is not carved. Con-sequently, there is no difference in the labialembrasure, which would result from the natu-ral anatomic variation in the original associatedteeth. It is necessary to incorporate the labialembrasures separately from the 10 carvingpoints when making the anatomicmodifications.

The Three Basic Tooth Forms and theLabial Triangular Area

The labial triangular area is not always thesame shape in each tooth, and also differs ac-cording to the specific characteristics such astooth alignment, facial features, and sex of thepatient The three basic tooth shapes (square.

Fig 43d Cervical view. The incisal embrasuresare expressed by carving points 1, 2, 3, and 4.The orientation of the prescribed form of themesial and distal ridses is also established.

round, and tapered) have different effects onthe labial triangle area.

The upper and lower triangle lines are al-most parallel in the square tooth, in which thearea of the triangle region is also the greatest(Fig 44a). In the round tooth, the upper andlower lines are essentially parallel, but, com-pared to the square tooth, they are more cen-

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A, square

B, round

C, tapered

A, young

B, middle-aged

C, elderly

Figs 44a to 44c Drawings of the three basic crownshapes of the surface of the anterior teeth showing thelabial triangle area (upper line = incisai edge, lower line= labial triangle area).

Figs 45a to 45c Examples of labial surface and triangleareas in the young, middle-aged, and elderly.

trally located. The area of the region is alsosmalier (Fig 44b). Although the incisai line ofthe tapered tooth is nearer the incisai edgethan in the square or round teeth, it has a

strong tendency to rise up in teeth away fromthe midline. For this reason the triangular areaof this type has the strongest tendency to con-strict in these teeth (Fig 44c). In addition, it is

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Fig 46 Illustration of use of disk to create the anatomy of the connecting region. Note that the toothcontact point become shorter vertically in the associated teeth farther from the midline, and its positionalso moves towards the center of the crown.

necessary to keep in mind that the shape ofthe labial triangular area also differs in long orshort teeth independently of their shape.

shorter vertically in the lateral incisor andcanine.

Variations in the Triangular Area With

Even in the same dentition, the triangular areachanges with age. Although the anatomic fea-tures of a younger person's dentition is notmuch changed from that which existed whentheir teeth first erupted, attrition of the incisaiedge is pronounced in middle-aged and eld-edy persons. Attrition normally starts in thecanine and progresses to the central and lat-eral incisors. Furthermore, recession of theperiodontal tissues increases with age. For thisreason, the labial triangular area appears tomove incisally with age (Figs 45a to 45c),

The Importance of the Contact Area ofthe Connector

The connecting region, corresponding to thecontact areas of independent teeth, is oftenoverlooked when doing anatomic modifica-tions on a restoration. It is necessary toshorten this area vertically in teeth fartherfrom the midline and manipulate the polish-ing material of the disc, which determines theanatomy of the connecting region (Figs 46aand 46b), so that the contact has a long verti-cal shape at the central incisors and becomes

Actual Restoration of AnteriorCrowns

Three clinical cases and a model case wereused to illustrate actual restorations of crowns.

In all clinical cases (Figs 47a to 47f), the pa-tients' oral cavities were first observed to sug-gest an ideal basic anatomy for the restora-tions based on the condition of adjacent teeth,and attempts were made to harmonize thedentition. Prostheses were prepared followingthe rules guiding basic tooth anatomy for cre-ating a balanced dentition and for varying theanatomy of anterior teeth as outlined earlier.

Clinical Case 1

Porcelain-fused-to-metal crowns were fabri-cated for both maxillary central incisors andthe maxillary left lateral incisor of this patient.Almost no attrition of the incisa! regions orabrasion of the labial surface were present.The basic tooth shape was flat and rounded,with a certain amount of rotation. Inspectionof the oral cavity revealed crowns that hadbeen fabricated on standard forms, giving theappearance of teeth that had just erupted.

The left lateral incisor was matched to theanatomy of the root cross section at its mar-

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Figs 47a to 47f Three clinical cases in which all of the patients' oral cavities were observed, imageswere established for the basic anatomy of the teeth to be restored based on the condition of tbe adjacentteeth, and attempts were made to establish harmony in the dentitions. The prostheses were prepared asper the principles discussed earlier and before treatment photographs (a,c,e) and posttreatment photo-graphs (b,d,fl are shown.

gin, the adjacent canine, and the contralateralincisor. The central incisors were fabricated byinferring their anatomy from the lateral inci-sors and canines.

Clinical Case 2

A prosthesis was fabricated for both maxillarycentral incisors and the maxillary left lateral

incisor of this patient, who desired a restora-tion in harmony with existing teeth.

Special anatomic characteristics included at-trition of the incisai edge and a certain amountof abrasion on the labial and lingual surfaces,as is typical in a middle-aged person. The res-toration was harmonized with the adjacentteeth and incorporated the anatomic variationsof the adjacent teeth while expressing thesespecial characteristics.

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Figs 48a to 48h Samples of anterior teeth formed by fabricating a central indsor based on the basic an-atoniic type and the age of tbe patient. Note changes in crowns representing those for older patients. La-bial surface abrasion becomes more pronounced and marked attrition appears in the incisal edge.

Fig 48a Square-shaped tooth of a younger Fig 48b Round-shaped tooth of a youngerpatient. patient.

Fig 48c Tapered tooth of a younger patient. Fig 48d Ovoid tooth of a younger patient.

Fig 48e Mixed tooth of a younger patient. Fig 48f Teeth of middle-aged pahent.

Fig 48g and 48h Teeth of elderly patients.

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Clinical Case 3

A prosthesis was fabricated for the right andleft maxillary canines, right and left maxillarylateral incisors, and right and left maxillarycentral incisors. The patient was a youngwoman who expressed a desire for younglooking, bright, feminine teeth.

The teeth were of the round type and had ayouthful appearance. The round shape waspreserved in the maxillary central incisors,which were used as a basis for establishing theanatomic variations in the maxillary lateral in-cisors and canines.

Model Restoration

The central incisor was fabricated based on astandard anatomic type as described earlierThis tooth was then used as the basis for amodel of the anterior dentition that wouldpreserve the anatomic variations of the associ-ated teeth.

Figures 48a to 48e show model dentitionsfor a young person. Fig 48f shows a modeldentition for a middle-aged person, and Figs48g and 48h show model dentitions for anolder person.

Note that the anatomy of each toothchanges with age. Marked attrition appears inthe incisal edges of the teeth, and a strong,carved-out abrasion appears on the labial sur-faces. Attrition in the incisal regions cause thelabial triangle areas and embrasures of theincisal line angles to appear different in theteeth of older persons. As abrasion fromtoothbrushes and the lips lead to acquired an-atomic changes on the labial surfaces, it isnecessary to consider such variation whenfabricating crowns for older patients.

ConclusionAs the statistical and scientific elucidation ofthe expression of the shade and anatomic res-

toration of anterior crowns has moved forwardin such aspects as coloration and constructionof natural teeth, the technology of materialshas also progressed. The point has now beenreached where theoretically based technicalexpression can be carried out. On the otherhand, even though a person might learn thefundamentals of dental anatomy, the anatomicexpression of the final product may be want-ing if one does not understand how to carryout the technique. In the past, the technician'sinstincts took precedence over theoretic con-siderations. For this reason, it took beginners avery long time and considerable experience tomaster anatomy.

The development of a basic theory and crite-ria for the fabrication of a restoration hastensthis process. The ability to fabricate clinicallyacceptable restorations of all anatomic typesmay then be acquired easily and in a mini-mum amount of time by anyone who has acertain degree of practice and has learnedthese theoretic foundations.

Fabricating a restoration that is in harmonywith the remaining dentition and that ex-presses the coronal anatomy of anterior teethrequires an understanding of both the anat-omy of the teeth and the means necessary forachieving this harmony with the adjacentteeth. This article was structured to simplifythe guiding principles needed to accomplishsuch restorations and set them forth from adental technician's viewpoint.

A cknowledgm en Is

The author would like to express gratitude to his em-ployer, Dr Ryuji Fujii, head of the Fujii Dental Clinic, forcontributing his time and assistance in preparation ofthis manuscript and his cimical examples; to Drs ShigeoKataoka, Mitsuru Morihiro, and Hiroto Yamamoto fortheir advice and checking of the manuscript; to Mr YujiOkubo, who was in charge of the illustrations for themanuscript; and to the staff at the Misshin Companywho provided material for the skull photographs.

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