Procedurespecific Analyses Rhinoplasty

The aesthetic proportion-based measurements include the following (Figs. 2-4):

From the basal view, columellar length twice the length of the lobule.

A transverse line across mid-nostril on basal view should be equidistant from the nasal tip and alar crease.

From the lateral view, 2-4 mm of columellar show (the amount of columella visualized on lateral view)

A nasolabial angle of approximately 90° in men and 110° in the women.

The presence of a supratip depression in women (an area cephalic to the point where the lobule meets the dorsum).

The presence of a double break: this describes the aesthetic phenomenon of the division of the lobule-dorsum angle into two angles defined by lines following the columella, dorsum, and lobule at the nasal tip.

From the frontal view, a gentle curve from the supraorbital rim to the tip (6).

Although tip projection and the perceived size of the nose depend on other facial fea- §

tures and the person's height and weight (7), two methods of measurement for tip @

Mentolabial Sulcus
Figure 1 Common soft tissue cephalometric points: G - glabella; N - nasion; R - rhinion; T - tip; CM - columella; Sn - subnasale; LS - labrale superius; Vs - superior vermilion; Vi -inferior vermilion; LI - labrale inferius; SI - mentolabial sulcus; PG - pagonion; ME - menton; C - cervical point.

projection are commonly used: the Upper Vermilion-subnasale Sn) distance should equal the Sn-nasal tip distance (8); and Crumley's method of superimposing a right-angled triangle based at the alar groove with vertices at the nasion and nasal tip whose sides have 3:4:5 proportions (9) (Fig. 5).

Mentolabial SulcusNose Alar Groove

Important relationships exist with the rest of the face and chin. The width of the nose (ala-to-ala) should equal the distance between the medial canthi (a neoclassical canon that accurately reflects the aesthetic ideal). Also, the aesthetic triangle of Powell and Humphries (10) (the base of the triangle is a line connecting the nasion and pogonion and its apex is at the nasal tip) (Fig. 6). The ideal values are: nasofrontal angle = 120°; nasofacial angle = 36°; nasomental angle = 130°; mento-cervical angle = 85°.

Nasion Height Measurement

Figure 4 Normative values for nasal prominence and the nasomaxillary angle.

Nasomaxillary angle 102-110.

Figure 4 Normative values for nasal prominence and the nasomaxillary angle.

Genioplasty

The visual relationship between the nose and the chin is so intimate that to change the size and shape of one influences the apparent size and shape of the other. Prior to evaluation of the position of the chin, the dental occlusion should be documented. Angle's classification (1899) is widely used and is based on the anteroposter-ior relationship of the maxillary and mandibular first permanent molars:

Figure 6 The aesthetic triangle of Powell and Humphries characterized by the nasofrontal angle, nasomental angle, and nasofacial angle.

Class I (neutroclusion). The first molars contact normally.

Class II (distoclusion). The mandibular first molar is displaced posteriorly with respect to the maxillary first molar.

Division 1. In addition to distoclusion, the upper maxillary arch is narrow and the incisors incline in a buccal direction.

Division 2. Distoclusion and the upper incisors incline in a lingual direction.

Class III (mesioclusion). The mandibular first molar is displaced anteriorly with respect to the maxillary first molar.

Patients with malocclusion usually have an abnormal profile and chin position irregularities. A class II malocclusion may result in a receding chin, and a class III deformity may result in a protruding chin. Surgical repair of malocclusions will affect the profile; therefore, patients with malocclusion should be offered orthognathic surgery prior to consideration of genioplasty. Angle's classification system is inadequate to describe chin position completely since malocclusion is only an indirect measure of the potential position of the chin.

Inadequate chin protrusion is usually the clinical finding in potential genio-plasty candidates; it may be due to micrognathia, retrognathia, or microgenia. Micrognathia refers to a hypoplastic mandible in which both the ramus and body are underdeveloped, usually associated with neutroclusion or a class II malocclusion. Retrognathia refers to a mandible with an underdeveloped ramus, a normal body, and usually a class II malocclusion. Microgenia refers to a mandible with an isolated underdeveloped chin (normal body and ramus). Microgenia results in a chin that is both retruded and deficient by palpation, unlike micrognathic and retrognathic chins that are retruded but normal by palpation. Micrognathia or retrognathia associated with malocclusion requires more extensive surgical intervention than pure genio-plasty, including sagittal osteotomies and mandibular advancements that are beyond the scope of a purely cosmetic procedure. Patients not desiring orthognathic work or those with microgenia are candidates for genioplasty involving augmentation (or retrusion in the case of chin overprotrusion or macrognathia) of the mandibular symphysis.

There are essentially three anatomical abnormalities often associated with a recessive chin: a recessive and procumbent lower lip, a deep labiomental fold, and diminished to normal lower facial height. Therefore, preoperative analysis must include an assessment of these components in both the anteroposterior and vertical planes (Fig. 7). A perpendicular line is dropped from the Frankfort Horizontal (soft tissue cephalometric radiograph) or from the true horizontal line with the patient in the natural head position (photograph) through the subnasale (reference point). Measurements are taken from the vertical line to the lip vermilion and pogonion: Sn-vermilion (Vu) = 0 ± 2 mm, Sn-lower vermilion (Vl) = —2 ± 2 mm, g and Sn-Pogonion (Pg) = (—4 ± 2 mm). The vertical chin position is determined e by comparing the glabella-Sn distance to the Sn-menton distance: these should m be equal (11). Two other methods for determining chin position are also widely ^

used:

A line through superior vermilion and Vi should be tangent to the pogonion.

A line dropped perpendicular to Frankfort's line from the nasion should be tangent to the pogonion (12). @

Mentolabial Sulcus
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  • ilta
    How to measure nasolabial angle?
    8 years ago

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