1. 1
Dr. Mohammed Alruby
Dynamics of smile
and
its orthodontic implications
Prepared by:
Dr Mohammed Alruby
Smile: is the most pleasant and wanted expression by each one of us.

2. 2
Dr. Mohammed Alruby
Smile: is amused facial expression with the corner of mouth turned up and exposed front teeth
Facial expression, postures of lips, occlusion and arrangement of teeth, buccal corridor, shape of
teeth, gingival color, texture, contour and other several aspects constitute component of smile
Most of patients come to us to improve their smiles, the orthodontic studies stress on skeletal
structure than soft tissue structure, and the smile still receives relatively little attention
Nature of smile:
1- Posed smile: voluntary, static, sustained, social smile not elicited by an emotion
2- Un-posed smile: spontaneous, involuntary, dynamic, natural, and not sustained
characterized by greater lip elevation
Smile types: smile styles:
1- Commissures smile: the corner of the mouth turned upward called Monalisa smile
2- Cuspid smile: the upper lip is elevated, the entire lip rises like a window shade
3- Complex smile: the upper lip moves superiorly as in cuspid smile and lower lip moves
inferiorly
Evaluation of posed smile:
variables Normal smile Not good smile
Smile arc Consonant Non consonant
Smile index Average Increased / decreased
Morley’s ratio 75 – 100% (normal) Disturbed
Buccal corridor Average Obliterated / excessive
Smile line Average High / low
Occlusal plane No canting Canting occlusal plane
Important definitions:
Smile arc:
the curvature formed by an imaginary line tangent to the incisal edges of the teeth, modified in
varying degree of curvature in relationship to the lower lip
Range: from no curvature to an accentuated curvature was in relation to the lower lip, so
quantification differed for each model
Buccal corridor:
the amount of dark space displayed between the facial surfaces of the posterior teeth and the corner
of the mouth, calculated as the total dark space on both sides of the mouth as a percentage of the
total smile width
Range: from 6% to 26.5 in approximately 0.5% increments
Maxillary gingival display or gummy smile:
The amount of gingival show above the central incisor crown and below the center of the upper
lip. Negative number indicate gingival exposure. Positive number indicate tooth overlap by the lip
Range: from 1mm of gingival display (-1) to almost 7mm of tooth coverage for the female models,
and approximately 2mm of gingival display (-2) to 6mm tooth coverage for male models
The variation between the models was due to differences in sizes and coordinating the images for
different faces
Maxillary midline to face:

3. 3
Dr. Mohammed Alruby
The relationship of maxillary dental midline (measured between the central incisors) to the midline
of the face, defined by the center of the philtrum and the facial midline
Range: the maxillary midline was moved to the left of the face in approximately 0.25 mm
increments. The right and left buccal corridor was maintained throughout the movement of the
dentition. The maximum deviation show is 6mm
Maxillary to mandibular midline:
The relationship of maxillary dental midline to the mandibular dental midline, the ideal was
considered to be 0
Range: maintaining the maxillary dental midline the lower dentition was moved to the left in
approximately 0.25mm increments. The right and left buccal corridor were maintained throughout
the movement of lower dentition. The maximum deviation shown is 5.5mm
Overbite:
The vertical overlap of the central incisors measured by mm or percentage of coverage
Range: the range from 0 – 9mm (100%) coverage
Central incisors gingival margin discrepancy:
The vertical gingival margin difference between the central incisors, the ideal was considered to
be 0
Range: the gingival margin of the left maxillary central incisors was altered in approximately
0.25mm
The incisal edges were maintained at their original height
The maximum deviation was 3mm
Maxillary anterior gingival height discrepancy from central to lateral:
The difference in the vertical height in the gingival zenith of the central incisor to the lateral incisor
Average value: indicated that the lateral incisor gingival margin was incisal to the central incisor
gingival margin
A positive value: indicated that the lateral incisor gingival margin was apical to the central incisor
Range: variation from increased to decreased height were presented in approximately 0.25mm.
the range was -2.6 to almost 1mm
Incisal edge discrepancy or lateral step:
The vertical difference between the incisal edges of central and lateral incisors
Range: variation was assessed by moving both lateral incisors up or down together in
approximately 0.25mm. the range was 0.4 – to 2.4mm
Cant:
The divergence of the occlusal plane from the horizontal axis, as seen when smiling
Altered by gradual rotating the plane through a point between the central incisor
The ideal was considered to be 0
Range: the rotation of the plane occurred in 0.25 degree increment, the range was 0 to 6 degree
Smile component:

4. 4
Dr. Mohammed Alruby
- Lip line
- Smile arc
- Upper lip curvature
- Lateral negative space
- Smile symmetry
- Frontal occlusal plane
- Dental component
- Gingival component
1- Lip line:
The amount of vertical tooth exposure in smile
a- optimal: the upper lip reaches the gingival margin, displaying the total length of maxillary
central incisors
b- high: expose all the clinical crowns plus continuous band of gingival tissue
c- low: displays less than 75% of the maxillary anterior teeth
with age, there is a gradual decrease in exposure of maxillary incisors at rest and increase
mandibular incisors display
the amount of vertical exposure in smiling depends on the following factors:
1- Upper lip length:
the average lip length as measured from the subnasal to the most inferior point of upper lip at
midline and should equal the two commissures heights
short lip length relative to commissure height results in unaesthetic (reverse resting upper lip)
Male female
23.8 -+1.5 Burston 20.1 -+1.9
21.8 -+2.2 Farkas et al 19.6 -+2.4
23.8 -+1.5 Powel 20.1 -+1
22 -+2 Wolford 20-+2
23.4 -+2.5 Peck et al 21.2 -+2.4
19--22 Bergman, Arnett 19 -- 22
2- Lip elevation:
In smiling the upper lip is elevated by about 80% of its original length, displaying 10mm of
maxillary incisors. Women have 3.5% more lip elevation than men
Actually there is a considerable individual variability in upper lip elevation from rest position to
the full mouth smile ranging from 2 –12mm, with an average 7 -8mm
If gingival smile is caused by hypermobile lip, it would be a mistake to correct it with aggressive
incisor intrusion or maxillary impaction surgery. Because that would result in little or no incisors
display
If a low lip is due to hypo-mobile lip, extensive incisors extrusion would result in an overbite with
excessive incisors display at rest
3- Vertical maxillary height:
when upper lip length and mobility are normal, a gingival smile with extensive incisor display at
rest (vertical maxillary excess)
low lip line and no incisor display at rest – skeletal due to a vertical deficient maxilla
4- Crown height:

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Dr. Mohammed Alruby
The average vertical height of maxillary central incisors is 10.6mm in males and 9.8mm in females
Short crown can be due to attrition or excessive gingival height
If there is little or no incisors display at rest, but the lip is normal in smiling, the crown height can
be increased incisally with cosmetic dentistry
A Gingivectomy when short clinical crowns with a gingival smile and a normal incisor display at
rest
5- Vertical dental height:
In deep bite: should be corrected by maxillary incisors intrusion in patient with excessive incisor
display at rest. But with posterior extrusion and /or lower incisor intrusion in patient with normal
lip line at rets
In Openbite: should be corrected by maxillary incisor extrusion if there is inadequate incisor
display at rest. But with posterior intrusion and /or lower incisor extrusion if lip line is normal at
rest
= proclined maxillary incisors as in class II div 1 or in class III compensation tend to reduce
incisor display at rest and at smiling
= uprighted or retroclined maxillary incisors as in class II div2 or after orthodontic retroclination
without torque tend to increase the incisor display
2- Smile arc:
The relationship between a hypothetical curve drown along the edges of maxillary anterior teeth
and the inner contour of the lower lip in posed smile
Optimal (consonant) smile arc: the curvature of maxillary incisal edge coincides with parallel to
the border of lower lip in smiling
In some treated orthodontic case, have flatter smile arc than in normal occlusion group that
resulting in denture mouth.
Causes of denture mouth:
A- Over intrusion of maxillary incisors: if the maxillary incisors are over-intruded to correct
an overbite or gingival smile without considering the incisor lip position at rest
Indiscriminate use of utility arches can not only flatten the smile arc but also result in lower
lip line at rest and smile which ages the patient
B- Bracket positioning: during bracket position must take in consideration the curvature of
smile arc in each individual patient
As in patient with reversed arc, bracket should be positioned in higher than usual on the
maxillary incisors to correct the smile arc during treatment
C- Cant of occlusal plane: extra-oral forces, inter-maxillary elastics and orthognathic surgery
can affect the occlusal plane, if the maxillary occlusal plane is canted upward anteriorly
resulting in a non-consonant smile arc
If the occlusal plane has an excessive clockwise tilt, the upper incisal edges will be covered
by the lower lip making smile arc less attractive
3- Upper lip curvature:
Is assessed from the central position to the corner of the mouth in smiling
Upward: when the corner of mouth is higher than the central position
Straight: when the corner of mouth in the same level to the central position
Downward: when the corner of mouth is lower than the central position
4- Lateral negative space:

6. 6
Dr. Mohammed Alruby
Buccal corridor; space between the posterior teeth and the corner of the mouth in smiling
Orthodontic refer buccal corridor as negative space that can be eliminated by transverse maxillary
expansion. Broad arch form is more likely to fill the buccal corridor than the narrow arch
Moving the maxilla forward will reduce the negative space because a wider portion of the arch
will come forward to fill the inter-commissure space
5- Smile symmetry:
The relative positioning of the corner of the mouth in the vertical plane can be assessed by the
parallelism of the commissural and pupillary lines
A large differential elevation of the upper lip in a symmetrical smile may be due to deficiency of
muscular tonus on one side of the face
6- Frontal occlusal plane:
Is represented by a line running from the tip of right canine to the left canine
A transverse cant can be caused by differential eruption of maxillary anterior teeth or skeletal a
symmetry of the mandible.
Having patient to bite on tongue blade in premolar area is a good way to diagnosis the cant
7- Dental component:
A pleasant smile also depends on the quality and beauty of the dental element
Dental component includes: size, shape, color, alignment, crown angulation, midline, arch
symmetry.
 The dental midline is an important focal point in an esthetic smile
= a practical and reliable method to locate the facial midline: use two anatomical landmarks,
Nasion and base of philtrum, known as the cuspid bow in the center of upper lip. A line drawn
between the two points not only locate the facial midline but also dental midline is important
than coincident
= in fact: 4mm maxillary midline deviation was not detected by dentist or Lay persons whereas
2mm deviation of incisors angulation was more obvious
 Arch symmetry is also important in achievement of balancing smile so peg shaped lateral
or missing lateral incisor can affect symmetry of arch, also midline diastema and lack of
inter-proximal contact can affect dental components
8- Gingival component:
The gingival component of the smile are; color, texture, contour, open gingival embrasure,
height of gingiva, inflammation even gingival margin, blunted papilla {affect the quality of smile}
The space created by missing papilla above the central incisors contact point. Referred as black
triangle, may be caused by root divergence or advanced periodontal disease
== orthodontic root paralleling and flattening of the mesial surface of the central incisors,
followed by space closure will lengthen this contact area and move it apically toward the papilla
== the gingival margin of the central incisors is normally at the same level or slightly lower than
those of canine. While gingival margin of lateral incisors is lower than those for central
== gingival margin discrepancy may be due to: attrition of teeth, ankylosis due to trauma
== gingival margin can be levelled by orthodontic intrusion or extrusion or by periodontal surgery
depending on: lip line, crown height, gingival level of adjacent teeth.
Characteristic of optimal smile:

7. 7
Dr. Mohammed Alruby
1- Upper lip reaches the gingival margin
2- Upward or straight curvature between the philtrum and commissures
3- Upper incisal line coincident to the lower border of lower lip
4- No lateral negative space
5- Commissural line and occlusal frontal plane parallel to pupillary line
6- Harmonize dental and gingival component
N: B:
 The eight component of smile not rigid boundaries but as artistic guide line to help
orthodontist to treat individual patient that no more aware about smile and esthetics
 Smile attractiveness is important because most lay people use a smile as a parameter to
judge whether treatment is successful or not
 2mm midline deviation was acceptable
Smile index:
Was given by Proffit and Ackerman, it describes the area within the vermilion borders of the upper
and lower lip during the social smile.
It determined by dividing the inter-commissures width by the inter-labial gap during smile
It is increased in clinical situations where decreased incisor show is present and decreased where
increased incisal show is present
Morley’s index:
It describes the percentage of incisal show on posed smile with respect to clinical crown height
Average ratio 75 -100%
A greater ratio would necessitate appropriate measures to decrease the incisor show
Smaller ratio less than normal incisor shows due to vertically deficient maxilla, increased length
of upper lip or short clinical crown height
Incisal show can increase by:
- Vertical maxillary excess
- Palatal plane tipping downwards in anterior region
- Short upper lip or greater crown height