Anterior dental aesthetics: Dental perspective - Nature

BRITISH DENTAL JOURNAL VOLUME 199 NO. 3 AUGUST 13 2005 135

Anterior dental aesthetics: Dental perspectiveI. Ahmad1

The purpose of this series is to convey the principles governing our aesthetic senses. Usually meaning visual perception,aesthetics is not merely limited to the ocular apparatus. The concept of aesthetics encompasses both the time-arts such asmusic, theatre, literature and film, as well as space-arts such as paintings, sculpture and architecture.

1BDS, The Ridgeway Dental Surgery, 173The Ridgeway, North Harrow, Middlesex,HA2 7DF, United Kingdom.Tel: +44 (0)20 8861 3535, Fax: +44 (0)208861 6181, www.IrfanAhmadTRDS.co.ukEmail: [email protected]

Refereed Paperdoi: 10.1038/sj.bdj.4812569© British Dental Journal 2005; 199:135–141

• The shape, length and width of maxillary anterior teeth are open to interpretation, includingmathematical, physiological and psychological.

• Tooth alignment, in three dimensions, creates a pleasing tooth-to-tooth progression.• The position of the teeth in the dental arches also ensures correct phonetics and occlusion.

I N B R I E F

INTRODUCTIONThe dental perspective concerns the teeth,their shape, size, intra- and inter-arch rela-tionships. The fourth paper in this series onanterior maxillary dental aesthetics discussesnovel and redundant concepts for these dentalelements. Numerous hypotheses have beenpostulated and dismissed emphasising, as withgeneral principles of aesthetics, that empiricalknowledge takes precedence over dogmaticscientific laws.

SHAPEThe morphology of maxillary anterior teeth is afusion of the three basic shapes: circle, square

and triangle (Fig. 1). These shapes are analo-gous to the primary colours (red, green andblue), from which any colour can be created.Similarly, any shape can be created from a circle,square or triangle. The unique composite mor-phology of the teeth allows diversity and indi-viduality. Essentially, no two teeth are everalike, but all share the same geometric buildingblocks. This configuration has allowed naturecarte blanche to produce inimitable shapesbased on only three variables. Emphasising oneshape and suppressing the others, has promotedmanufacturers of artificial teeth for dentalprostheses to classify teeth as circular, rectan-gular or triangular.

4

ANTERIOR DENTALAESTHETICS1. Historical perspective2. Facial perspective3. Dento-facial perspective4. Dental perspective5. Gingival perspective6. Psychological perspective*

* Part 6 available in the BDJ book of this series

Fig. 1 The three basicshapes circle, square(rectangle) andtriangle

VERIFIABLE CPD PAPER

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136 BRITISH DENTAL JOURNAL VOLUME 199 NO. 3 AUGUST 13 2005

The shape of the maxillary anterior teeth hasbeen the subject of numerous studies. The most prominent are by Williams1 and Frushand Fisher.2-4 Williams proposed that the shape

of the central incisor was the inverted frontalview of the face, while Frush and Fisher sug-gested that sex, age and personality related tothe contour of the anterior dental segment.Williams’ theory was invalidated by subse-quent studies.

The Frush and Fisher concept is concernedwith the dominance of the central incisors andtheir wear in advancing years. It is worth not-ing that the chronological age of a patientmight not coincide with the dental age. In caseswhere a patient has pronounced wear, either bylocal or systemic causes, the dental age may begreater than the chronological age (Fig. 2). Theopposite is evident for older individuals withsharp incisal edges and pronounced incisalembrasures, conveying a youthful dentalappearance (Fig. 3). Other theories have proposed correlating tooth shape with skeletaland soft tissue landmarks, but these ideas haveproved inconclusive. The shape of teeth isgenetically determined and the prosthodontistshould, if possible, obtain pictures of a patient’srelatives before determining the shape of thedefinitive prosthesis.

If no records are available, the points to con-sider are age, sex, race, and personality. Forexample, youthful teeth are sharp, havingunworn incisal edges; with the central incisorsdominating the composition, and in harmonywith the laterals and canines. The reverse istrue for an older dentition, ie blunt incisaledges and wear and attrition without conclu-sive dominance of the maxillary central inci-sors. Sociologically, stereotypes are readilyrecognised and associated with specific indi-viduals. These divisions are culturally specificand relevant to a particular country or demo-graphic locality. For example, it is generallyrecognised that females display curvaceousfeatures (both facially and bodily), devoid ofsharp line angles. On the other hand, masculin-ity is associated with ruggedness and sharp lineangles. The process of transposing these gendervariations onto the shape of the teeth (Figs 4and 5) is a concept termed morphopsychology(see part 2: Facial perspectives).

Finally, personality is significant for per-ception of an individual in society. A gregari-ous, vivacious persona is linked to an efferves-cent personality, while a sombre, reclusivecharacter is perceived as bland and unsociable.Once again, these stereotypes are influencedby upbringing, intellect, culture, and theology.Linking these traits to dental morphology isconforming purely to society’s perception ofan individual. Making teeth, which are bright,bulbous, and prominent, are appropriate for anoutgoing person. Conversely, teeth that con-vey subtlety with a lower value, and hence areless conspicuous, may be more suited to anintrovert.2 Personality traits are discussed fur-ther in the sixth and final article entitled Psy-chological perspective, which looks at the psy-chological influence of our cerebral perceptionto the dentition.

Fig. 2 Maxillarycentral incisors withworn incisal edges,conveying an ageddentition

Fig. 3 Virgin maxillarycentral incisors withpristine unworn incisaledges anddevelopmental lobes

Fig. 4 Feminine teeth:Curvaceous outlines,devoid of shape lineangles. Also, notice themesial inclination ofthe lateral incisors

Fig. 5 Masculineteeth: Rugged outline,dominance of thecentral incisor anddistal inclination of thelateral incisors(compare with Fig. 4)

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SIZETooth size is determined by mesio-distal widthdivided by the inciso-gingival length, whichyields the width/length (w/l) ratio (Figs 6 and 7):

No definitive value for the w/l ratio exists andexperts dispute its value. The mesio-distal width ismore important than the inciso-gingival length3

and the former measurement has attracted muchdebate. Research has focused on measurements ofextracted teeth, racial and gender differences,together with facial landmarks such as the bizygo-matic width. House and Loop4 postulated that themesio-distal measurement of the central incisorwas 1/16 of the bizygomatic width. Other studieshave also sought to assign geometric values forthe mesio-distal width of the centrals, eg 1/16 ofthe face height or the width of the iris.5

There are two schools of thought regardingthe size of the maxillary central incisors. Thefirst is by Rufenacht6 who proposed mor-phopsychological determination of an idealproportion, and suggested that the width andlength of the central incisor should be con-stant throughout life. This view relies on thephilosophical notion of eternal youth asdescribed by French writer Robert Brasillachwho said, ‘in life only one youth exists and wepass the rest of our days regretting it’. Whilethis statement may seem romantic, manyregard it as sacrosanct and seek a myriadoptions to stave off our ‘final destination’.Bearing this in mind the clinician’s role is notto act as judge, but as a conduit for patients’desires. If a person seeks such an option, thedental team should try not to deny a patient’swishes.

The second theory states that our bodies arein perpetual change throughout life. We areborn small, become taller, and eventually loseheight in advancing years. Our skin has toneand suppleness in youth but becomes flaccidand dull as we grow older. The dentition is noexception to this transformation. When thecentral incisors erupt, they are pristine withdefined incisal lobes, a textured surface rough-ness, bright enamel, with a smaller w/l ratio(Fig. 8). During normal functioning, excludingthe effects of disease, the incisal edges wear(resulting in a larger w/l ratio), surface texturebecomes smooth, and the enamel dulls due toincreased translucency (Fig. 9). These processesare congruous with the ageing of the rest of thebody. Creating teeth with a youthful appear-ance is discordant in an older person and createsa sense of artificiality.

The evidence behind each theory is incon-clusive and each concept is still open to discus-sion. Furthermore, the overriding factor in anycase is a patient’s wish including their percep-tion of themselves in society. Nevertheless,general guidelines are useful for creating apleasing result.

Firstly, the w/l ratio of the central incisorshould range from 0.75 to 0.8, a value less than0.6 creates a long narrow tooth, and beyondthis number results in a short wide tooth

Fig. 6 Measuring themesio-distal width ofthe central incisorswith callipers

Fig. 7 Measuring theinciso-gingival lengthof the central incisorswith callipers

Fig. 8 Youthful teeth:Textured surfaceroughness, visibleperikymata and brightenamel

Fig. 9 Aged teeth:Smooth surfaceroughness, stainedfracture lines and a lowvalue, dull enameloverlay

width/length (w/l) ratio of a tooth =width

length

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(Fig. 10). Secondly, the central incisor should bethe dominant element in the anterior dental com-position (Fig. 11). Lastly, the vertical overbite inrelation to speech and anterior guidance needsaddressing (Fig. 12). Besides these fundamentalprinciples, subtle variations can be introducedwhich account for gender, race, facial, mor-phopsychological, and psychological factors.

The buccolingual thickness shows wide vari-ance, ranging from 2.5 mm to 3.3 mm for the max-illary central incisors.7 The thickness is measured

with a width gauge, at the junction of the middlethird and incisal third of a tooth (Fig. 13). For acrown, if a reading of more than 3.5 mm is appar-ent, then over-contouring of the prosthesis is sus-pected, usually because of under-preparation bythe clinician leaving the ceramist inadequateroom for the porcelain layer build-up, resulting ina bulbous crown. If the thickness of a tooth is lessthan 2.5 mm, elective endodontic therapy may benecessary to achieve the desired aesthetics. Incases where a tooth is inclined facially or lingual-ly, and the proposed prosthetic treatment is tosimulate its location beyond 2 mm, interceptiveorthodontic therapy may be mandatory.8

INTRA-ARCH RELATIONSHIPHaving established guidelines for shape anddimensions of the maxillary anterior segment,and in particular that of the central incisor, thenext point to consider is the relationshipbetween incisors and canines. The tooth-to-tooth relationship frequently relies on the Divine(or Golden) proportion and dynamic symmetry,initially proposed by the ancient Greeks.

In 530BC Pythagoras suggested beauty couldbe defined as an exact mathematical concept,which led to the Divine or Golden proportion(1/1.618=0.618). Similarly, Plato proposed theBeautiful proportion (1/1.733=0.577) as thequintessential ratio for beauty. Both ideas statedthat an object with these proportions had innatebeauty. The most widely used concept in den-tistry is the Golden proportion — where S is thesmaller and L the larger part:

The uniqueness of this ratio is that whenapplied by three different methods of calcula-tions, linear, geometric and arithmetic, the pro-portional progression from the smaller to thelarger to the whole part always produces thesame results. Lombardi9 and Levin10 have trans-posed this ratio to the maxillary anterior sextant(Fig 14). Other researchers11 have indicated thatclinically the Golden proportion is not always

Fig. 10 Width/length ratio (w/l): theblue tooth has a w/l ratio of 0.8, thered (‘ideal’) 0.75, and the green 0.6

Fig. 11 The dominance of thecentral incisor is paramount forpleasing anterior maxillaryaesthetics

Fig. 12 Overbite assessment of twocrowns on the maxillary centralincisors

Fig. 13 The Bucco-lingual thickness ismeasured at thejunction of the middlethird and incisal thirdof a tooth (depicted bythe green line)

Fig. 14 The Golden proportion relates to the mesio-distalwidths of the central and lateral incisors and the mesialaspect of the canine

= L

S + L= 2

1 + √5

S

L= 0.618

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evident and variations are often apparent. In onestudy, measurements of plaster casts of naturalteeth revealed that only 17% conformed to theGolden proportion.12 This begs the question thatif only some teeth conform to this rule, whichratio is prevalent for the rest of the population?Although the Golden proportion is invaluable asa starting point for aesthetic appraisal, the reali-ty is that any ratio from 0.6 to 0.8 is aestheticallyacceptable. The salient points to consider areharmony, balance, morphopsychology, and psy-chology.

Firstly, to create harmony the chosen ratioshould be repeated moving distally from the cen-tral, to lateral incisors, to the canines. Harmony relies on similar repeated proportions,rather than the actual size of the elements (Figs15-17). For example, if an individual has a largenose, small eyes and thin lips, the face will lackharmony because the nose will predominate.However, large eyes, full lips, and a large nosewill blend harmoniously with the rest of the face.

Secondly, the right and left sides of the max-illary sextant should be balanced. If the right lat-eral incisor is lingually inclined or rotated inrelation to the arch, the contralateral lateralshould show a similar misalignment to create abalanced look (Figs 18-20). An example of thelatter scenario is evident in patients with Angle’sClass II, division II occlusion (Fig. 21).

Lastly, morphopsychological and psychologi-cal factors can influence the chosen ratio for thetooth-to-tooth relationship. For example, if theintention is to convey masculinity by choosing alarger recurring ratio in a small arch, a disto-facialimbrication of one or more teeth in the maxillaryanterior segment resolves the predicament. Con-versely, a mesio-facial imbrication conveys

Fig. 15 Harmony: narrow repeated proportions ofanterior maxillary sextant (0.6 w/l ratio – small)

Fig. 16 Harmony: ‘ideal’ repeated proportions ofanterior maxillary sextant (0.75 w/l ratio)

Fig. 17 Harmony: wide repeated proportions of anteriormaxillary sextant (> 0.8 w/l ratio)

Fig. 18 Balance: lingually inclined rightlateral incisor with a similarcontralateral misalignment (facial view)

Fig. 19 Balance: lingually inclined rightlateral incisor with a similarcontralateral misalignment (occlusalview)

Fig. 20 Balance: mesio-buccalrotations of the right and left lateralincisors

Fig. 21 In an Angle’s Class II, division IIocclusion, the mesial aspect of thelateral incisor facially overlaps thedistal aspect of the central incisor

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femininity with a narrow maxillary arch form. Tosummarise, the paramount issue for gaining aesthetic approval in a composition is ensuringharmony and balance, irrespective of size or ratio.

Another aesthetic marker is the axial inclina-tion of the upper anterior teeth. Ideally, a mesialaxial inclination seems to attract aestheticapproval, while a distal one conveys visual ten-sion. One explanation why a mesial inclination,as opposed to distal one, invokes a sense of aes-thetic approval (Fig. 22) is that the curvature ofan object (convex or concave) is important tothe way it is perceived. Concavity conveysreceptiveness and belonging, while convexitythe opposite, eg pushiness and aggression. Anexample is a relaxed smile when the concavityof the maxillary incisal plane is parallel to theconcavity of the mandibular lip. Both theseconcavities are perceived as welcoming andreceptive, which after all, is the purpose of asmile. In a similar manner, mesial axial inclina-tion forms a concave curvature, also conveyingreceptiveness and belonging. Further enrich-ment of the anterior dental segment is createdby ensuring that the interproximal contactpoints coincide with the incisal edges, and thecurvature of the mandibular lip, enhancing thecohesiveness of the dentofacial composition.

Incisal embrasures have a distinct appear-ance depending on age and sex. For virginteeth, soon after eruption, the embrasure angleincreases anterior-posteriorly from the maxil-lary incisors to the canines (Fig. 23). As a gen-

erality, pronounced embrasures convey youth-fulness and femininity, while shortened, wornedges convey ageing and masculinity (Fig. 24).The clinician should be guided by patient pref-erences, age and gender before prescribingprecise incisal embrasure angles for artificialrestorations.

INTER-ARCH RELATIONSHIPHorizontal and vertical overbite depends on theinciso-gingival length of the anterior teeth(both maxillary and mandibular), the shape ofthe arches, and angulations of the teeth in thesagittal plane. In ideal circumstances, the max-illary central incisors are 12 mm long, perfectlyaligned and the arch form is within the norm,with the mandibular central incisor 10 mmlong. In this case, the vertical overlap and hori-zontal overlap are 4 mm and 2 mm, respectively.Furthermore, with this ideal overbite and over-jet, the occlusal vertical dimension (OVD) is 18mm, measured from the gingival zeniths of themaxillary and mandibular central incisor.

Once again, these utopian clinical presenta-tions are rare. To establish a correct inter-archrelationship, the starting point is the location ofthe maxillary central incisor edge position withthe lips at rest, and during a relaxed smile (Figs25 and 26).

During these two soft tissue positions, theincisal edges are assessed, and influenced bythree variables. The first is aesthetics. Ideally,the maxillary incisal edges should be parallel tothe curvature of the mandibular lip. The secondissue is to ensure that phonetics are not com-promised. In the sagittal plane, when the ‘f’ and‘v’ sounds are spoken, the buccal surfaces of themaxillary incisors should contact the inner ormucosal surface of the mandibular lip (Fig. 27).If these teeth encroach on the cutaneous part ofthe mandibular lip, this indicates either an over-contoured, or bulbous restoration or incorrecttooth angulations. Lack of contact with thelower lip indicates shortened or incorrectlyaligned maxillary incisors. The ‘s’ sound deter-mines the vertical dimension of speech, charac-terised by an unimpeded edge-to-edge positionof the maxillary and mandibular incisors. Finally,during a ‘th’ sound, the tongue should makecontact with the palatal surfaces of the maxil-lary incisors.

Fig. 22 A mesial axial convergenceof the anterior teeth is conducive foraesthetic approval

Fig. 23 Sharp, well-defined incisalembrasures, with increasing anterio-posterior angles

Fig. 24 Blunt, worn incisal embrasures, with constantanterio-posterior angles

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The third determinant of the incisal edgeposition is the anterior guidance, often ignoredat the expense of aesthetics, resulting in ultimatefailure of restorations due to unwanted protru-sive interferences.

CONCLUSIONThe teeth, as with the other perspectives of den-tal aesthetics, display variance and nuances,showing individuality in a given dentition. Thisarticle has tried to present old and new con-cepts on tooth morphology, size and their rela-tion to each other. In conclusion, no singleaspect can be accredited with successfullyarriving at the final shape and dimensions ofthe maxillary anterior teeth. The clinician and

ceramist ultimately rely on their experienceand observations, combined with patients’desires, for creating functioning and aestheti-cally pleasing prostheses.

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3. MacArthur D R. Are anterior replacement teeth too small? JProsthet Dent, 1987; 57: 462–465.

4. Housemm, Loop J L. Forum and colour harmony in DentalArt. Whittier, Calf: mm House, 1939.

5. Marquad S. Esthetic facial analysis. 30th Annual USCPeriodontal and Implant Symposium, Los Angeles, California,January 21-23, 2005.

6. Rufenacht C R. Fundamental of esthetics QuintessencePublishing Co. Inc., Chicago, II, 1990; 4: 114.

7. Chiche, G J and Pinault A E Fundamental of esthetics ofanterior fixed prosthodontics. Quintessence Pub Co.Inc.,1994; 3: 59.

8. Sulikowski A, Yoshida A. Three dimensional management ofdental proportion: A new esthetic principle – ‘The Frame ofReference’ . QDT 2002; 25: 8-20.

9. Lombardi R E. The principles of visual perception and theirclinica; application to dental esethetics. J Prosthet Dent,1973; 29: 358–381.

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11 Woelfel J B. Dental Anatomy: Its relevance to Dentistry, ed 4.Philadelphia: Lea and Febiger, 1990.

12. Ward D H. Proportional smile design using the recurringesthetic (RED) proportion. Dent Clin North Am, 2001; 45:143–154.

Fig. 25 Assessment of incisal tooth exposure with thelips at rest

Fig. 26 Assessment of incisal tooth exposure during arelaxed smile

Fig. 27 Correct phonetics and incisal inclination: during‘f’ and ‘v’ sounds of speech, the buccal surfaces of themaxillary central incisors touch the inner, or mucosal,surface of the mandibular lip

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