Clinical
strong bond Creating a
Olivier Etienne looks at mock-up and tooth tissue preservation techniques in minimally invasive dentistry
D
uring the past 20 years, bonding has no doubt represented a major revolution in dentistry. Constant
improvements in terms of bonding to dental tissue, together with technical improvements in ceramic materials, have made it possible to develop aesthetic dentistry with less risk of fracture. This adhesive revolution has
quickly become part of the concept of tissue conservation by providing new types of preparations, mixtures of traditional techniques and new ideas related to bonding. Especially, one crucial clinical factor has become apparent: the difference in bonding quality between dentine and enamel. In fact, due to the nature of these two substrates, enamel bonding is always superior to dentine bonding. The practitioner must always
systematically find the best compromise between sufficient thickness, to ensure strength and aesthetics (Table ı), and maximum conservation of the enamel on the prepared surface. However, when taking into consideration the variations in ceramic translu- cency and the original shade of the substructure, a more ‘aggressive’ approach may be necessary in order to better conceal a discolouration. Similarly, pressed-ceramic veneers require more overall thickness than feldspathic ones. Whenever clinically possible,
it is recommended to favour a minimally-invasive enamel prepara-
60 Scottish Dental magazine
tion that will enhance the longevity of the restoration and prevent post-operative sensitivity. When preparing for this, the varying degree of enamel thickness must be taken into account first. This thickness depends on the patient’s age, dental history and, most of all, on possible wear of the enamel. This loss of thickness can be
aggravated, either by abrasive compounds (toothpaste with high concentrations of bicarbonate) or acids (acidic drinks, citrus fruits, etc). In order to optimise the aesthetic result and to get a better preview via the wax-up, detailed clinical observations of the initial wear should be undertaken right from the start. Normally the natural thickness of
the labial enamel of anterior teeth will measure on average between: • 0.3 to 0.5 mm in the gingival area, • 0.6 to ı.0 mm in the middle part • ı.0 to 2.ı mm in the incisal area. These average values represent
a wide range of variations for each patient and for each individual tooth.
Evolution of
preparation concepts Taking these basic requirements into account, several clinical propositions have been suggested to minimise the preparation of dental tissue. Mainly, these propositions are based on the idea of progressive reduction or the idea of controlled penetration.
1. Progressive reduction methods In progressive reduction methods, a reference point such as an adjacent
tooth, the dimension of the cutting tool or a pre-op silicone index are used in order to visually enhance and mechanically control the amount of tooth structure that is to be removed.
ABOUT THE AUTHOR
Olivier Etienne is an assistant professor at the prosthodontics department of the Louis Pasteur Univer- sity, School of Dentistry in Strasbourg. He also works in private practice in Strasbourg. He is an interna- tional lecturer on the various aspects of
prosthodontics and has written more than 30 articles in the French dental journals during the last decade. He has also
The depth cut technique During preparation of the teeth, the simplest method is to estimate the volume removed by comparison with neighbouring teeth. This three- dimensional visualisation has great operator variability and makes the results not very efficient in terms of tissue conservation. In order to improve this procedure,
vertical grooves can be cut in the tooth at the beginning of the prepara- tion while visually making sure not to penetrate more than the diameter of the bur. As in the previous method, it relies on the contour of the tooth to be restored and therefore has the great advantage of controlling the preparation. If the shape of the tooth can be reproduced in the same proportions, then this is the method of choice (Figure ı).
given more than 80 national and international lectures during the same time.
The index technique Development of this approach involves using the final morphology of the reconstruction as a reference. This is performed before prepara- tion with an aesthetic wax-up built on the initial plaster cast. Using this model as a guide, it is possible to prepare either a thermoformed transparent matrix (ensuring both control of the preparation and, later, fabrication of the temporary veneers by using it as a mould) or to make one or more silicone indexes
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84 |
Page 85 |
Page 86 |
Page 87 |
Page 88 |
Page 89 |
Page 90 |
Page 91 |
Page 92