CHAPTER 3

DENTOLABIAL ANALYSIS

In Tthis chapter we will focus our attention on the lower third of the face.: tThis is in fact the area where the lips and teeth are to be found, the subject of this specific part of ourthe investigation. The face and lips together are a dynamic frame thatwhich, constantly changesing during speakingech and smilinge, givinge a different tooth exposure each time. The systematic approach presented here, which is based on the evaluation of precise parameters, allows a complete dentolabial analysis to be made and, helpsing to achieve correct esthetic integration of the prosthetic rehabilitation to be achieved.

OBJECTIVE: To guide the clinician in re--establishing a correct position of the incisal edge, re-creating appropriate incisal and tooth lengths and adequate harmony between the occlusal plane and the commissural line.

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The patient’s natural head position, a determining factor in an overall evaluation of the face, is equally also important in dentolabial evaluation.^{1, 2} This analysis is essential for evaluating the correct ratio between the teeth and lips during the various phases of speakingech and smilinge.

Smiling is one of the most expressive non-verbal forms of communication. It conveys a range of emotions:, from embarrassment through happiness to the most ecstatic joy.^{3, 4}

Smiling is made possible because of the muscular action not only of the lips but also of the periocular muscles.⁵ A natural smile, expressing joy and spontaneity, does in fact brings certain specific faciale muscles into play, such as the zygomaticus and the lower part of the orbicularis, which contract simultaneously to allow maximum elevation of the upper lip.^{6, 7} It should be noted, oin the contrastry, that this combined muscular action would does not take place if we asked the patient was asked to smile non-spontaneouslyon cue.⁸ In thatis case, the orbicularis would does not contract, resulting in an unnatural mimico-facial movement.

I. [A]LIP MOVEMENT

Observation of the lip movements allows us to evaluation ofe the dental exposure during the various phases of speakingech and smiling.

To analyze the natural lip motility, it will be is necessary to interact with the patient induring athe nonpre-operativeonal phase, in an informal and relaxed atmosphere, observing the lip movements during a friendly and spontaneous conversation [(see cChap.ter 1, – page. ..xx.)] (Figs from 1_3/-1a to 1_3/-1d).

In fact, dDuring the clinical phases, if patients were are asked to smile, all that the clinician would in fact be obtained isonly an unnatural smile, due tobecause of the natural state of tension of the situationsion they find themselves in. It is obvious, but important, to remember that this evaluation must be carried out before administering the anaesthesiatic, which would completely distort ourthe observation completely.

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The lips should maintain move consistently in a horizontal plane when moving and therefore be parallel to the interpupillary line, which, it should be remembered, represents the facial reference plane (Fig 1_3/-2). ^9-–11

The lips can undergo substantial alterations to their tonicity, which will affect their movement (Figs 1_3/-3a and 1_3/-3b). It is not uncommon to find patients with labial ptosis due secondary to neurological problems or, sometimes, a compensatory psychological mechanism that allows them to hide unattractive restorations. Regardless of the cause, any differences in muscle tone between the right and the left sides produce a different degree of tooth exposure, which will should be noted on the esthetic checklist. In such cases, the lips cannot therefore provide a reliable reference.

If parallel with the horizontal plane, the interpupillary line will beis, all the more reason, the most useful parameter for determining both the incisal and occlusal planes, as well as the gingival contour.

Considerable variation in dental exposure is can be found between the two arches, even in the same individual.: iIf when during smiling the upper maxillary teeth are in fact more visible, oin the contrastry, in many phases of speech, the lower mandibular teeth are exposed more (Figs from 1_3/-4a to 1_3/-4d).

This latter fact must be duly taken into consideration if the treatment plan involves the lower areas. When speaking of contemplating esthetics, the tendency is to consider just the appearance of the antero-superior sextant, and often overlooking the important role played by the opposing arch is overlooked [(see Cchap.ter 5, – page. ...xxx).]

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II. [X]Prosthetic considerations and applications

Many subjects limit the width of their smile to hide incongruous restorations, discolored teeth, or clinical situations which that are notun pleasing from thean esthetic point of view (Figs from 1_3/-5a to 1_3/-5c). When a pleasing appearance has been given back to the patient, he or she will be able to smile spontaneously again, whichin this way can helping the perioral muscles to resume their lost natural movement (Figs from 1_3/-5d to 1_3/-5h). To this end, assistance can be provided by a few specific exercises devised by Gibson,¹², even if their effects do not seem to be long lasting, but are limited only to the period in during which they are practiced.^{13, 14}

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I. [A]DENTAL EXPOSURE AT REST

When the teeth are at maximum intercuspation, the lips touch lightly and the incisal third of the upper maxillary incisors is covered by the wet surface of the lower lip.^{15, 16}

When the mandible is in the rest position, the teeth do not come into contact, the lips are slightly apart, and a portion of the incisal third of the upper maxillary incisors is visible;, this varyiesng from 1 to 5 mm, depending on the height of the lips and the patient’s age and sex (Figs 1_3-/6a, 1_3/-6b, 1_3/-6d, and 1_3/-6e).^{16, 17}

Vig and Brundo¹⁶ reported that, on average, the upper maxillary incisors are exposed more in women when at rest compared tothan in men (3.40 mm against versus 1.91 mm), and that young patients show them much more than middle-aged patients (3.37 mm against versus 1.26 mm).

As some writers stress,^{16, 18-–20} with age, the portion of upper maxillary incisors that is visible can in fact diminish, as the result of both due to abrasion of the incisal margins and, more commonly, because of the inevitable reduction in perioral muscle tone, which leads to greater and greater exposure of the lower mandibular incisors (Figs 1_3-/6c, 1_3-/6f, and 1_3/-6g).

And so it is then, that the smallest teeth in the mouth, which are already normally visible during speech, take on a decisive role in our patients’ esthetics, especially in older patients.

DENTO-LABIAL ANALYSIS:

ExamineXAMINATION

§TOOTH EXPOSURE AT REST

§INCISAL EDGE

§SMILE LINE

§SMILE WIDTH

§BUCCAL CORRIDOR

§INTERINCISAL LINE VERSUS FACIAL MIDLINE

OCCLUSAL PLANE VERSUS COMMISSURAL LINE

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II. [X]Prosthetic considerations and applications

“Rejuvenationg" of the smile is one of the requests most frequently made by patients who haveing to undergo prosthetic treatment (Figs 1_3/-7a and 1_3/-7b). It is our the clinician’s task to explain to them that, as well asin addition to a lighter and more attractive coloring, one of the fundamental elements for satisfying this request is increased exposure of the upper maxillary teeth, which are often not aso visible in older individuals due tobecause of the biological reasons outlined above. A dDetermination ofing how muchwhat portion of the upper maxillary incisors is visible with the lips at rest constitutes one of the key parameters for evaluating whether any alteration to tooth length is needed [(see Table, Cchap.ter 5, – page . 237xxx)] (Figs from 1_3/-7c to 1_3/-7i).

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I. [A]INCISAL EDGE

Identifying Identification of the position of the incisal edge, in both the apicocoronal (incisal curve), and antero-posterior directions (incisal profile), represents a fundamental aspect of the esthetic diagnosis. Its correct location will affect significantly affects many of the procedural choices that the dentist clinician and the dental technician will make in order to provide a suitable prosthetic restoration.

.[A] INCISAL CURVE VERSUS LOWER LIP

II. [B]CONVEX INCISAL CURVE

As a rule, the incisal plane, when observed from the front, has a convex curve, whichthat follows the natural concavity of the lower lip during smilinge.

This parallelism is seen in a high percentage of individuals, reaching as much as 85% of cases according to a study carried out by Tjan and coworkers²¹, and 75% in an investigation by Owens and associates.^{9, 10, 22} The curvature of the incisal plane may be more or less accentuated. It tends to be slightly evident in dental Cclass I patients and, to flatten out considerably in cClass III subjects., while iIn cClass II patients it can be noticeably convex, where a marked difference in length between the central and lateral incisors can be seen. The latter of these are usually around about 1 mm away from the convex line described by the incisal edges of the canines and of the centrals, giving the incisal plane a typical “gull wing” appearance.

III. [C]Radiating symmetry

The convexity of the incisal curvature, together with the ideal tooth proportions, produces a radiating symmetry²³ which that is more evident the more dominant the central incisors are in relation to the laterals. Radiating symmetry gives a pleasing smile and is normally found in young people.

The relationship between the two curves, ideally drawn by the upper incisal margins and the lower lip, can vary from one patient to another. In many cases a certain separation is found between the incisal edge and the lower lip; this type of relationship is said to be not touching (Figs 1_3-/8a and 1_3/-8b).

In a study carried out on the Asian population, Dong and coworkers⁵ found this situation in the majority of subjects tested (56%). In other cases, a relationship of contiguity between the lips and teeth occurs, termed as touching (Figs 1_3-/9a and 1_3/-9b), and is considered to be particularly pleasing from the an esthetic standpoint. Then there are situations where the lower lip completely covers the incisal third of the upper maxillary teeth (covering) (Figs 1_3/-10a and 1_3/-10b). To create a harmonious smile, the incisal margins should in any all cases maintain a parallel alignment with the lower lip.

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II. [B]FLAT OR REVERSE INCISAL CURVATURE

Sometimes, abrasion of the incisal edges can lead to a flat or even a reverse incisal curvature, producing unpleasing effects from the esthetic point of view. For these reasons,A as well aslong with the decrease in tooth length being decreased, this leads to the reduction, or in some cases even the disappearance, of the interincisal angles, the progression of which is easily seen in the natural dentition, contributing significantly to the pleasing appearance of the smile [(see Cchap.ter 5, - page… xxx)].¹⁰ This situation usually creates leads to a discrepancy between the incisal plane and the curvature of the lower lip, creating a negative anterior space (Figs from 1_3/-11a to and 1_3/-12b).

III. [C]Horizontal symmetry

A flat incisal plane, with uniform tooth length and the reduction or disappearance of the interincisal angles, gives the smile horizontal symmetry. This causes the loss of the so-called “cohesive force” in the dentofacial composition,⁹, creating an unattractive esthetic effect and an inevitable sense of an “aged” smile.

II. [X]Prosthetic considerations and applications

The ideal esthetic treatment involves re-establishing a correct incisal curvature in harmony with the concavity of the lower lip by restoring adequate tooth shape and proportion (Figs 1_3/-13a and 1_3/-13b). An increasing number of patients wish to rejuvenate their appearance²⁴ in order to regain confidence and to reinforce their personality. More and more requests are therefore made for teeth which that are “whiter and more prominent”.” Whenever possible, we the clinician shouldwill try to test out the new tooth lengths on patients, either, by means of a rapid composite mock-up made in the office (Figs 1_3-/13c, 1_3/-13d, and 1_3/-13f) or with an indirect acrylic mock-up [(see Vvolume 2, - cChap.ter 1)] (Fig 1_3-/13e). This will is not only be essential for esthetic previewing, but also in order to evaluate correct phonetiscis and the suitability of the anterior guide (Figs from 1_3/-13g to 1_3/-13jk).

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Nevertheless, some patients prefer to maintain a slightly flat incisal curvature, especially if before treatment the incisal edges were abraded (Figs from 1_3/-14a to 1_3/-14c). In such cases it will be necessary to explain to the patient that the need to create a convex incisal curvature, apart from esthetic considerations, can also have functional purposes, such as re-establishing an anterior guide that allows disclusion of the posterior teeth (Figs from 1_3/-14d to 1_3/-14j).

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The curvature of the lower lip is not always homogeneous. There can in fact be asymmetry between the right and the left sides, which wethe clinician must note each time on the esthetic checklist. Under these circumstances we will havethe clinician must to decide whether in ourthe treatment plan the upper maxillary incisal curvature is to follow the anomalous line of the lower lip, or whether to maintain the parallelism between the incisal plane and the horizontal reference plane should be maintained (Figs from 1_3-/15a to 1_3/-15d). Remember that the curvature and the concavity of the lower lip constitute a variable parameter, thatn cannot being ignoredable to exclude in anticipationdvance of further unforeseen alterations of the lip motility. This makes means that it is all theeven more important to keep a fixed parameter such as the horizontal plane as a stable reference to determine the incisal plane (Figs from 1_3/-15e to 1_3/-15h).

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I. incisal [A]INCISAL PROFILE

The incisal profile is the position of the incisal edge in the antero-posterior direction and, as a rule, is contained within the inner border of the lower lip [(see cChap.ter 4, – page. .. xxx.)]. This allows adequate closure of the lips, so they can come together without any impediment interference from an incorrectly positioned third incisor of the front teeth.^{25, 26}

II. [X]Prosthetic considerations and applications

If the teeth are inclined too far forward, this can generate a feeling of excessive tooth length and, make closing the lips more difficult (Figs from 1_3-/16a to 1_3/-16c and, 1_3/-16g). This situation can make the upper lip too prominent and it can sometimes alter the actual morphology of the lower lip.

Repeated stimuli in the localized area may in addition cause the formation of unwanted labial tubercles (Fig 1_3-/16d).⁹

Prosthetic rehabilitation in such cases should involve modifying the incisal profile so as to allow the anterior teeth to remain inside the vermilion border of the lower lip (Figs 1_3-/16e, 1_3/-16f, and 1_3/-16h).

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I. [A]SMILE LINE

The first step in this analysis is to evaluate the exposure of the anterior teeth during smilinge.^{10, 21, 27-–32} On the basis of the amount of dental and gingival display in the antero-superior area seen in this phase, Tjan and coworkers²¹ has identified three types of smile lines: low, average, and high.

II. [B]LOW SMILE LINE

The motility of the upper lip exposes the anterior teeth by no more than 75% (Figs 1_3-/17a and 1_3/-17b).

II. [B]AVERAGE SMILE LINE

Labial movement reveals 75% to 100% of the anterior teeth, as well as the interproximal gingival papillae (Figs 1_3-/18a and 1_3/-18b).

II. [B]HIGH SMILE LINE

As well as the anterior teeth, which are completely exposed during the smile, a gingival band of varying height is also displayed (Figs 1_3-/19a and 1_3/-19b).

A pleasing smile can be defined as one that exposes the upper maxillary teeth completely, and along with approximately 1 mm of gingival tissue. Gingival exposure that does not exceed 2- to 3 mm is nevertheless considered esthetically pleasing, while an excessive display (>(more than 3 mm) is generally thought considered unattractive by most of our patients.³³

Tjan and coworkers²¹ found in one of his studies that 20.5% of subjects tested showed a low smile line, while 69% had an average smile line and only 10.5% displayed a high smile line. The same authors²¹ stateds that the high smile line wais found in twice as many female subjects compared to male subjects. This fact wais confirmed by Owens and associates,²², who found it repeatedly in each of the six races they examined. A high smile line is often correlated with particularly efficient labial muscles and/or a short upper lip.

Measuring the distance between the base of the nose and the lower border of the upper lip (labial philtrum), Peck and Peck³⁴ verified that the average length is roughly 20- to 22 mm in women and 22- to 24 mm in men. The reduced height of the upper lip found in female subjects gives results in a smile line that is 1.5 mm higher on average by 1.5 mm compared than in to male subjects.³⁵

This accounts for the greater number of high smile lines found in women.^{21, 22} Regardless of the type of smile line the patient may possess (low, average, or high), when moving upward,s the lower edge of the upper lip may take on a convex, flat, or concave shape in at itsthe center. Depending on the length of the upper lip, this gives a different amount of tooth exposure in this area each time.⁵

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The upper lip can sometimes show different levels of exposure between the right and left sides, with resulting in an irregular smile line (Figs 1_3/-20a and 1_3/-20b).

The upper lip, too, just like the lower lip, is a structure that changes with time and so is “unreliable” as a reference parameter. We willClinicians should therefore use the same criteria adopted for the lower lip:, parallelism of the incisal plane with the horizontal reference line (the interpupillary line), regardless of the curvature of the upper lip.²¹

II. [X]Prosthetic considerations and applications

In the presence of a high smile line, a lack of harmony in the gingival levels can induce the clinician to resort to pre-prosthetic surgical or orthodontic treatment to re-establish optimum symmetry and parallelism [(see cChap.ter 6, – pag.e …xxx)] (Figs from 1_3/-20b to 1_3/-20f).

Furthermore, eExposure of the gingival margins during smilinge furthermore often obliges the dentist to hide the restorative margin inside the gingival sulcus (Figs from 1_3/-20g to 1_3/-20k). This choice can compromise the biological integration of the restoration and prove to be in vainunsuccessful if the patient does not completely expose the teeth when smiling.^36-–54

Too often, in fact, the clinician positions the prosthetic margin is positioned subgingivally, without having first analyzed the patient’s smile line.^{55, 56}

If it is true, as Watson and Crispin⁵⁷ has found, that the majority of those interviewed (73.6%) prefer not to expose the marginal limits in the presence of a high smile line, it is also true that 87% of them would be prepared to accept the margin positioned supragingivally if, in the case of a low smile line, the margin would not be visible.

It should also be noted that 63.8% of patients declare a preference for a perfect state of health, even at the cost of esthetic appearance, if its esthetic optimization canwill put the biological integration at risk.⁵⁷

However, tThe habit of many patients of checking the appearance of the restoration by raising the upper lip in front of the mirror should, however, also be made knownemphasized.

It is not unusual for many of them, despite being informed of the biological risks involved, to request in any case that the restorativeon margin be hidden, even though they show a low smile line. ⁵⁸

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I. [A]GUMMY SMILEGummy smile

The exposure of a band of gingival tissue in excess of 3- to 4 mm (gummy smile) is judged by many patients to be esthetically unattractive (Figs 1_3/-21a and 1_3/-21b).

There are various factors whichthat, either individually or combined, can cause this excessive visibility of the soft tissue^59-–62:

§• A Sshort upper lip

§• Labial hypermotility

§• Altered passive tooth eruption

§• Anterior dento-alveolar extrusion

§• Excessive vertical development of the upper maxilla

II. [X]Prosthetic considerations and applications

When facedIn treating with a gummy smile, correct diagnosis will allow the most appropriate choice to be made in relationwith consideration to the etiology of each individual casepatient.^{23, 62} Among the various treatment options that can be considered with the patient, the orthognathic and orthodontic ones treatments prove to beare often especially suitable, particularly where healthy teeth are involved (Figs from 1_3/-22a to 1_3/-22f). [NOTE: Ref #63 is not cited.]

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If the patient needs to be requires prosthetically rehabilitationed, the restorative therapy will often have to be combined with orthodontic or surgical crown lengthening procedures,^64-–68, with the dual aims of both re-establishing ideal tooth length and reducing the amount of visible gingiva (Figs from 1_3/-23a to 1_3/-23g).

The cChoice of the different treatment options must be made while taking into due proper consideration the following esthetic and functional parameters: