Dental esthetic principles

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Content:

              1. Dental Morphology

                            A. Central Incisors

                            B. Lateral Incisors

                            C. Canines

                            D. Premolars

              2. The Incisal Edge

              3. Gingival Esthetics

              4. Width/Length Ratio

              5. Recurring aesthetic Dental (RED) proportions

              6. Shade and characteristics

1. Dental Morphology:

              A. Central incisors:

This is the most important and dominant tooth because of its location and size. The two incisors are ideally symmetrical. Together, they form the dental midline that should be completely vertical and ideally corresponds with the facial midline [1].

Buccal Aspect. The buccal surface is convex in both mesiodistal and incisogingival directions, the convexity is greater at the cervical third than at incisal third. The three mamolons and lobes form the macro texture of the tooth, consiting of alternating convexities and concavities in the mesiodistal direction [2].

Transition lines are located at the transition between light reflective and deflective zones on the buccal surface, they are esthetically important, manipulating their location changes the perceived tooth width [1, 3].

Mesial and Distal Outline. Both outlines are convex, but the distal is more so. The contact points move gingivally towards the distal, making the incisal embrasures wider towards the distal as well [2].

The incisal outline. The incisal edge is almost flat. The incisal plane should be parallel to the inter-papillary line. And the distal incisal angle is more rounded than the mesial [1].

              B. Lateral Incisors:

The lateral incisors resemble a smaller and rounder version of the central incisors. They have rounder mesial, distal outlines. The incisal edge is also rounder and 0.5 - 1 mm shorter. The tooth has a lower width/height ratio in comparison (Fuller et al, 2001). It is less important that the laterals are symmetrical. In fact, it is asymmetrical in 70% of the patients [1].

              C. Canines:

The crown of the upper canine is seen mainly from its mesial side. Canines are bulky and greatly convex in the mesiodistal direction and they have a smaller Width/Length ratio [2].

The mesial outline (between the contact point and gingiva) is convex and longer than its concave distal outline. Canines have an incisal cusp with two incisal slopes: the shorter mesial slope and the longer distal slope, this usually changes after natural attrition [2].

              D. Premolars:

Premolars are similar to the outline of canines from the buccal perspective, they are shorter and appear smaller because of their posterior location. Depending on the smile width, the second premolar and first molars may also appear in the smile [2,3].

Note: due to the word limit, this section discussed the upper anterior teeth only. Lower anterior teeth morphology are out of the scope of this article.

       2. The Incisal edge:

Esthetic treatment planning should start from determining the location of the incisal edge of the central incisor. And from there, the optimum length of the tooth can be calculated, which ranges between 10.4 to 11.2 mm. This assists in determining the incisal edge location and width/height ratio of the remaining teeth [3].

The location of the incisal edge is influenced by age. Less upper and more lower incisal visibility is seen as we advance in age, this is caused by the effect of aging on lips and normal dental wear. At the age of 20, around 3.5 mm of the upper incisors is shown when at rest position. Furthermore, the amount of teeth visibility during speech and smiling is additionally dictated by patient’s desired self image. In addition, the smile line should correspond to the curve of the lower lip when smiling [3,1].

Furthermore, the letter F places the incisal edge buccolingually between the mucosal and cutaneous parts of the lower lip. Additionally, the letter S brings the mandible forward to correctly pronounce the letter S [1].

      3. Gingival Esthetics:

Healthy gingiva has a stippled appearance, it is a pale pink and does not bleed on probing. On the other hand, inflamed gingiva has a shiny red appearance that bleeds on probing. Before any esthetic treatment is started, the gingival health has to be established to prevent common complications [4].

The gingival margins on the centrals and canines are on the same horizontal level, the lateral is slightly below that by 0.5 - 1 mm. Symmetry between the right and left sides is important especially on the easily compared central incisors [3,4].

The zenith points are the most apical point on the gingival margins, their location is influenced by the root curvature. They influence the perceived long axis of the tooth. As a general rule, they are located slightly distally, with the exception of the centrally positioned zenith point on the lateral incisor [3,1].

The gingival papilla fills the spaces between the teeth. Its partial resorption causes an unpleasant appearance known as the black triangles. The distance between the contact point and crestal bone dictates the presence or absence of the papilla. When this space is 5 mm or less, the papilla was present in 100% of the patients. When it was 6 mm, the papilla was present in 56% of the patients. And when the distance was 7mm, it was present in only 27% of the patients [5].

The need for management of gingival esthetics depends on the level of the upper lips, low lip level conceals the gingiva making its management less important. Gingivectomy or gingivoplasy can be used to correct excessive gingival display or to modify the location of the zenith points, accounting for the biologic width in the process. Additionally, periodontal surgeries like apically positioned flap can restore gingival recession when indicated [3,4].

             

       4. Width/length ratio

This is one of the most important elements to consider. Changing the width or length of a tooth without considering the width/length ratio can cause excessively wide or long teeth. An example of this would be closing anterior spaces of normally proportioned anterior teeth, leading to wide square-shaped teeth [3].

Pascal studied 146 extracted anterior teeth to analyze their average width, length and width/length ratio, he included worn teeth as well. The study’s results are displayed in table 1 [6].

	Centrals		Laterals		Canines		Premolars
	Unworn	Worn	Unworn	Worn	Unworn	Worn	Unworn	Worn
Width	9.10 - 9.24		7.07 - 7.38		7.90 - 8.06		7.84
Length*	11.69	10.67	9.55	9.34	10.83	9.90	9.33
W/L ratio	78%		73%		73%

Table 1: Mean measurements of anterior teeth by mm. *: Length was measured from the cementoenamel junction. This can result in longer teeth than what is clinically observed, as CEJ is often covered by gingiva.

       5. Recurring Esthetic Dental (RED) Proportions:

I will write briefly about this to avoid re-using materials from the previous assessment.

At the beginning, Levin [8] theorized that the golden proportions (0.628) is found in nature. And that esthetically pleasing smiles have this ratio between the teeth. Meaning that each tooth is %628 of its preceding tooth.

However, subsequent studies have shown that the golden proportions is not a requirement of pleasant smiles. On the contrary, it was found that utilizing this proportion for unsuitable cases can cause an overly dominant central incisors and excessively narrow canines [7].

Instead, it was suggested that pleasant smiles have a Recurring Esthetic Dental (RED) proportion that is constant for each successive tooth. [14]. The RED proportions influences the buccal corridor as well. The buccal corridor is the amount of empty space between the posterior teeth (premolars and molars) and the inner cheek when smiling. In addition to soft tissue influence, higher RED proportions cause more visible posterior teeth which is associated with a wider buccal corridor [1].

       6. Shade and characteristics:

Shade matching is one of the most important and challenging aspects of the esthetic treatment, failure in shade or characteristics hampers otherwise well executed treatments.

Dental clinics should be equipped with color corrected lights (Daylight - 6500K) and a neutrally colored environment for accurate shade matching. It is useful to confirm the selected shade with different lighting conditions. Electronic devices used for shade reading are yet to gain more popularity and reliability [10].

Shade matching is done on a wet tooth at the beginning of the appointment to avoid eye strain and subsequent increased value after tooth dehydration [9].

Shade communication with the lab should be detailed. A high quality close up image with optimum lighting of the tooth and shade tab provides the technician with valuable information. Furthermore, it is possible to accentuate the tooth’s special characterizations by digitally decreasing the value (Brightness) and increasing the contrast of the close up image [11].

Traditional methods for shade matching rely mainly on chroma and value. This has proven to be insufficient. Vanini’s work offers more predicable and detailed approach for shade matching [10].

Vanini’s introduced the 5 dimensional color concept:

•  Chromaticity: This is the hue and chroma. 80% of teeth hue are close to the shade A (Vita classic shade guide) which has a red-orange hue.

•  Value: Also known as brightness or luminosity. It is noteworthy that young enamel teeth incorporate perikimatas that increase surface light reflection, and subsequently increases value in comparison with older smooth enamel.

•  Intensities: they are the milky white opaque spots, Categorized as Stains, Small clouds, Snowflakes or Horizontal.

•  Opalescence: it is caused by the translucent enamel at the edges of the tooth. It is categorized as: mamelon-like, split-mamelons, comb-like, window-like and stain-like.

•  Characterizations: they are described as: mamelons, bands, margins, stains or cracks. [10]

An illustration demonstrates the esthetic principles combined:

1: Dental midline ideally corresponds to the facial midline and mandibular dental midline.

2: Gingival line: notice the location of the zenith points. The lateral incisor zenith point is located centrally and 0.5 - 1 mm below the line.

3: Incisal plane: notice the location of the incisal edges. The lateral incisor is 0.5 - 1 mm shorter. Notice the corresponding curvature of this line with the lower lip during smiling.

4: Contact points: notice how their gingival location towards distal. Also notice the incisal embrasures increase in size towards distal.

5: Shade and characteristics: In addition to shade value and hue and chroma, teeth have variety of special features that contribute to its appearance, such as the location of the transitions lines, surface macro and micro texture, opalescence or intensities.

6: Width/length ratio: it is around 78% for central incisors and 73% for laterals and canines. Also notice the RED proportions

7: Buccal corridor contributes to the fullness of the smile.

References:

1.    MacKenzie, L. Tooth Morphology. [Lecture]. Smile-On Education Support Platform. 2015.

2.     James L Fuller, Gerald E. Denehy, Thomas M. Schulein. Concise dental anatomy and morphology 4th edition. Year Book Medical Pub. 2001.

3.    Gürel, G. The Science and Art of Porcelain Laminate Veneers. Quintessence publishing. 2003.

4.    Kakar, A. Interdisciplinary Treatment- Periodontics [Lecture], Smile-on Education Support Platform. 2016.

5.    Yu-Jen Wu, Yu-Kang, Shay-Min. The Influence of the Distance from the Contact Point to the Crest of Bone on the Presence of the Interproximal Dental Papilla. 2003.

6.    Pascal Magne, PD, Dr Med Dent, German O. Gallucci, DMD and Urs C. Belser,.Anatomic crown width/length ratios of unworn and worn maxillary teeth in white subjects، 2003.

7.    PRESTON, J. The Golden Proportion Revisited. Esthet Restor Dent, 5(6), pp. 247-251. 1993.

8.     Levin,E. Dental Esthetics And The Golden Proportion. The journal of prosthetic dentistry 40 (3), St Louis, Mosby: Academy of Denture Prosthetics and other prosthetic dentistry societies. 1978. pp.244-252

9.    Hilton, T., Ferracane, J. and Broome, J. Summitt's fundamentals of operative dentistry. 2014. Ch 6, 16.

10. Vanini, L. Determination and communication of color using the five color dimensions of teeth. Practical Procedures and Aesthetic Dentistry. 2001

11. Brambilla, G. Advanced Anterior Composite Techniques. [Webinar] Smile-on Education Support Platform. 2015.