intro, ideal occlusion, and extraoral evaluation

lecture given 8/28/2026

orthodontics

the field within dentistry concerned wiht the prevention and correction of facial and skeletal disharmony and malocclusion

what are the goals of orthodontics?

diagnosis, prevention, interception, treatment, maintenance

what plane is shown here?

sagittal / AP

what plane is shown here?

frontal / vertical

what plane is shown here?

horizontal / transverse

what are andrew’s 6 keys of occlusion?

correct interarch relationships

correct crown angulation (tip)

correction crown inclination (torque)

no rotations

tight contact points

level curve of spee

correct interarch relationships

the mesio-buccal cusp of the upper first premanent molar falls within the buccal groove of the lower first premanent molar

the mesio-lingual cusp of the upper first molar seats in the central fossa of the lower first

premolars have a cusp to embrasure relationship buccally and cusp to fossa relationship lingually

maxillary canine has a cusp to embrasure relationship with the mandibular canine and first premolar

maxillary incisors overlap mandibular incisors

midlines of arches match

normal occlusion

class I malocclusion

class II malocclusion

class III malocclusion

class I

class II

class III

in a compromised case finish, what angle’s classification should you prioritize?

class I canine

correct crown angulation (tip)

when looking from the facial, the mesio-distal angulation of the tooth

normally occluded teeth demonstrate gingival portion of crown more distal than occlusal portion of crown

correct crown inclination (torque)

crown inclination determined by angle between a line 90 to the occlusal plane and a line tangent to the middle of the labial or buccal clinical crown

torque on incisors

maxillary incisors are flared → crown has buccal inclination → buccal crown torque or lingual root torque

mandibular incisors are either upright or have a lingual crown inclination → lingual crown torque or buccal root torque

torque on posteriors

all have lingual crown inclination → lingual crown torque or buccal root torque

increases as you go more posterior

no rotations

no rotations should be present

a rotated molar occupies more mesiodistal space, creating a situation unreceptive to normal occlusion

why are tight contact points desirable?

to avoid being a food trap

level curve of spee

occlusal plane → flat or slightly concave curve of spee (0 - 2.5mm)

what is the ideal dental arch?

coordinated arches

specific mesial-distal angulation

specific buccal-lingual inclinations

no rotations

tight contact points

flat curve of spee

what makes an ideal composite (photos)?

no eyewear, no headwear, hair out of face/tucked behind ears, no distracting jewlery/makeup

as straight on as possible, include at least first molars on all photos, should be able to see gingival margins (for proof of prior recession)

when looking from AP, what should you you examine?

profile- convex/concave/flat

nasiolabial angle

upper and lower lip protrusion

upper lip length

labiomental angle

when looking from transverse, what should you you examine?

facial symmetry, horizontal 1/5ths, UDML in relation to facial midline, buccal corridors

when looking from vertical, what should you you examine?

vertical 1/3s, lip competence, smile arch, smile line, maxillary incisor display on smiling, mandibular incisor display on smiling

what are the points of reference to determine profile?

most prominent point on forehead

point where the nose meets the lip

most prominent point on chin

convex

straight

concave

nasolabial angle

formed between nose and upper lip

normal: 95 - 110

what affects nasolabial angle?

upturned/drooping nose

protruded/flat upper lip

what determines the position of the upper lip?

maxillary incisiors

lip protrusion, E plane

multiple reference planes, tip of nose to point of chin

both upper and lower lip should be behind

what determines the position of the upper lip?

upper incisors

what determines the position of the lower lip?

upper incisors

what do you need to keep in mind pertaining to E plane?

distance increases with age

important to consider today’s trends and racial norms

what is normal upper lip length?

20 - 24mm

increases with age

labiomental angle

can indicate protruded incisors

potential lip trap

transverse symmetry

evaluate facial structures

soft tissue deviations- nose, muscular pull, eyes

skeletal deviations- chin point, mandible length

horizontal fifths

eyes should be same width as inter-canthal distance

can indicate specific areas of asymmetry

upper dental midline

should be concident with facial midline (assume facial harmony)

soft tissue deviation- treat to average midline

buccal corridors

negative space between buccal surface of posterior teeth and cheeks

should have slight negative space (~8% on each side)

what happens if a patient has vertical maxillary excess?

gummy smile

lip competence

lips should naturally come together at rest

lip incompetence

inability to keep lips together at rest

non-competent lip indicates disharmony

can result in mentalis strain

mentalis strain

lips do not meet at rest

mentalis muscles strain to keep lips sealed

visible dimpling/puckering in chin

can be seen from frontal and profile views

mentalis strain

smile arc

esthetic parameter

curvature of maxillary anterior teeth should follow curvature of lower lip

consonant / flat / exaggerated

low smile line

decreased incisor display

gets lower with age

average smile line

no/slight gingiva display

high smile line

normal in children/adolescents

100% maxillary incisor display

‘gummy smile’

can be due to overactive muscles pull or maxillary skeletal vertical excess

what is the key to facial esthetics?

lower 1/3 of the face