Dental Tribune Indian Edition

21Dental Tribune Indian Edition - April 2013 Trends & Applications Aesthetic guidelines for dentures that are natural-looking Björn Maier Germany Natural­looking dentures have always been a great challenge for the den­ tal technician or prosthetist. With so many different brands of acrylic tooth systems on the market, it can be easy to overlook the basics of tooth shape and its relation to the physiology of the face. In this article, I consider the morphology of the anterior teeth in particular. Tooth shapes vary enor­ mously between individuals and to the untrained eye, a system of de­ fining these shapes probably seems remote. However, if you look at the face as a whole, you will very quickly understand how nature con­ stitutes the relationship between tooth shape and facial physiology through human genetic development (Figs. 1–3). This article will help you to identify the corresponding characteristics of tooth shape throu­ gh a systematic approach suitable for each case. First of all, it may help to peruse the illustrations in order to under­ stand the system and the connections between the illustrations. Consider general anterior tooth morphology and you will recognise, in addition to the obvious characteristics, further specific individual features, like the difference between a central incisor and a canine. Although the variety of different shapes of the anterior te­ eth appears to be immense, this can be quiet deceiving. If one leaves asi­ de the tooth positions and the colour of the tooth, the general morphology consists of two factors (Figs. 4–6): 1. the basic shape of the tooth, i.e. de­ finitive width; and 2. the marginal ridges or line angles of the tooth, which defines the optical width. This correlation of optical width and definitive width leads to the different shapes of teeth. This morphological variety can be subdivi­ ded into three basic principles. These three fundamental archetype shapes are square (athletic), tapering (lepto­ some) or ovoid (pyknic). All other to­ oth shapes are considered to be hybrid shapes. In 1914, Leon Williams suggested a now famous classification system of tooth shape, theorising that these three fundamental shape types are reflected in the “Kretschmeric Con­ struction Types” (facial outline types). The shape of the tooth is equal to the horizontally flipped shape of the face (Figs. 7–18). For example, an athle­ tically built person with an angular face would have square­shaped teeth (Figs. 7, 8, 13, & 16). A thin person with a peaked chin (leptosome) would have triangular­shaped teeth (Figs. 9, 10, 14, & 17). Today, this classification of the to­ oth shapes based on the shape of the face is considered to be antiquated. Hence, it only serves as a very rough general guide when selecting a set of anterior acrylic teeth for a patient case. In the fifties, the “dentogenic concept” by Frush and Fisher spread across the US and then to other parts of the world. According to this con­ cept, a “personality spectrum” can also be added to help obtain the shape of the tooth. Next to clinical, intra­ oral and facial relation considerations, the age, sex, and other characteristics of the patient are also considered. To­ day, taking all of these factors into account, one will most likely derive some sort of hybrid shape based on one of the three original basic shapes. The concept of the three basic sha­ pes with regard to the labial effect of Fig. 19: Twelve-year-old patient with nicely indented incisal edges.—Fig. 20: Comparison of a 30-year-old patient with abraded incisal edges ...—Fig. 21: ... and a 50-year-old patient with strongly worn incisal edges.— Fig. 22: Mandibulary anteriors of a 12-year-old patient with strong mamelons.—Fig. 23: Mandibulary anteriors of a 30-year-old patient.—Fig. 24: A set of lower anteriors with strong occlusal wear facets. Fig 19 Fig 22 Fig 21 Fig 24 Fig 20 Fig 23 Fig. 1: The triangular tooth shape.—Fig. 2: The rectangular tooth shape.—Fig. 3: The oval tooth shape.—Fig. 4: When looking at the marginal ridges or line angles, the square tooth shape is recognisable.—Fig. 5: When looking at the marginal ridges or line angles, the triangular tooth shape is recognisable.—Fig. 6: When looking at the marginal ridges or line angles, the oval tooth shape is reco- gnisable. Fig 1 Fig 4 Fig 2 Fig 5 Fig 3 Fig 6 Fig. 7 & 8: An athletically built person with an angular face (square). The labial tooth shape resembles the reversed shape of the face.—Fig.9 & 10: The leptosome tooth shape of a thin or skinny person with the individual characteristics of the marginal ridges.— Fig. 11 & 12: Person with a rounded (ovoid) form of the face (pyknic) and the ovoid tooth shape with the individual characteristics of the marginal ridges.—Fig. 13: Even from the incisal aspect, the respective shape characteristics are visible.—Fig. 14: The triangular type (leptosome) with an introverted labial surface.—Fig. 15: The ovoid type (pyknic) with an extroverted labial surface.—Fig. 16: Detailed characteristics when viewed from the approximal.—Fig. 17: Detailed characteristics of the triangular tooth shape.—Fig. 18: Detailed characteristics of the ovoid tooth shape. Fig 7 Fig 9 Fig 11 Fig 8 Fig 10 Fig 12 Fig 13 Fig 14 Fig 15 Fig 16 Fig 17 Fig 18 → DT page 22