Crowns and other extra-coronal restorations: Occlusal considerations and articulator selection (original) (raw)

Abstract

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This article discusses key occlusal considerations for the successful provision of crowns and extra-coronal restorations, emphasizing the importance of clear terminology and understanding of occlusal positions such as intercuspal position (ICP) and retruded contact position (RCP). It outlines the interrelationship between tooth guidance and jaw movements, and offers practical insights into the manipulation of the mandible for accurate restorations, presenting various methods and potential pitfalls in impression-taking and articulator selection.

Figures (11)

chew). The other side, the side the mandible is moving away from, is called the non-working side. So for example, an excursion to the right (as may occur during chewing) will make the right side the working side and the left the non- working side, whilst during an excursion to the left the reverse will be true. During these excur- sions the upper and lower guidance teeth will be in contact and partly dictate the movement of the mandible. Canine guidance is where the upper and lower canines on the working side are the only teeth in contact during a lateral excur- sion, causing all of the posterior teeth to disclude (Figs 1 and 2). When several pairs of teeth, usu- ally premolars or premolars and canines (and sometimes molars) on the working side share the contacts during excursions group function is said to take place (Fig. 3). Other patterns of guid- ance can take place, using almost any combina- tion of teeth.

chew). The other side, the side the mandible is moving away from, is called the non-working side. So for example, an excursion to the right (as may occur during chewing) will make the right side the working side and the left the non- working side, whilst during an excursion to the left the reverse will be true. During these excur- sions the upper and lower guidance teeth will be in contact and partly dictate the movement of the mandible. Canine guidance is where the upper and lower canines on the working side are the only teeth in contact during a lateral excur- sion, causing all of the posterior teeth to disclude (Figs 1 and 2). When several pairs of teeth, usu- ally premolars or premolars and canines (and sometimes molars) on the working side share the contacts during excursions group function is said to take place (Fig. 3). Other patterns of guid- ance can take place, using almost any combina- tion of teeth.

closed with the condyles in this position, there is a contact between a pair of teeth somewhere around the mouth (Fig. 5). The mandible will then close, from this retruded contact, down into ICP, usually sliding forward and _ laterally (Fig. 6). If you want to try to manipulate a patient’s mandible into this position it is impor- tant that they are relaxed (Fig. 7), otherwise it can be very difficult and you will feel resistance to free movement of the mandible. For about 10% of people ICP will be the same as RCP? and in these cases if you hinge the mandible until the teeth are in contact they will go straight into ICP with no deflective contact. Fig. 4 A non-working side interference between the left first molars and the possible consequences of carrying out crown preparation without appreciating its presence (transverse section): a) During a right lateral excursion (see black arrow) the left first molars act as a cross-arch pivot lifting the teeth out of contact on the working side; b) The maxillary first molar has been prepared for a crown. Occlusal reduction has eliminated the pivot, allowing the teeth on the working side to contact during lateral excursion. However, clearance between the preparation and opposing teeth is now inadequate which may cause problems with the provisional restoration. Worse still, the definitive restoration may require gross adjustment resulting in its perforation; c) You can avoid these problems by removing the non-working side contact prior to tooth preparation (blue line represents tooth recontoured in this way)

closed with the condyles in this position, there is a contact between a pair of teeth somewhere around the mouth (Fig. 5). The mandible will then close, from this retruded contact, down into ICP, usually sliding forward and _ laterally (Fig. 6). If you want to try to manipulate a patient’s mandible into this position it is impor- tant that they are relaxed (Fig. 7), otherwise it can be very difficult and you will feel resistance to free movement of the mandible. For about 10% of people ICP will be the same as RCP? and in these cases if you hinge the mandible until the teeth are in contact they will go straight into ICP with no deflective contact. Fig. 4 A non-working side interference between the left first molars and the possible consequences of carrying out crown preparation without appreciating its presence (transverse section): a) During a right lateral excursion (see black arrow) the left first molars act as a cross-arch pivot lifting the teeth out of contact on the working side; b) The maxillary first molar has been prepared for a crown. Occlusal reduction has eliminated the pivot, allowing the teeth on the working side to contact during lateral excursion. However, clearance between the preparation and opposing teeth is now inadequate which may cause problems with the provisional restoration. Worse still, the definitive restoration may require gross adjustment resulting in its perforation; c) You can avoid these problems by removing the non-working side contact prior to tooth preparation (blue line represents tooth recontoured in this way)

Fig. 8 Tools for examining occlusal contacts: foil shimstock held in forceps and high quality ultra-thin articulating tapes held in Millers forceps There is little merit in examining study casts for planning purposes on a simple hinge or other ‘non-anatomical’ articulator because the ability to replicate physiological movements will be, at best, crude, and at worst, wholly misleading. A non-anatomical articulator will allow casts to be put into a reproducible ICP, which may be helpful if there are insufficient contacts to make hand- held casts stable, but that is the limit of what a simple hinge articulator can do.

Fig. 8 Tools for examining occlusal contacts: foil shimstock held in forceps and high quality ultra-thin articulating tapes held in Millers forceps There is little merit in examining study casts for planning purposes on a simple hinge or other ‘non-anatomical’ articulator because the ability to replicate physiological movements will be, at best, crude, and at worst, wholly misleading. A non-anatomical articulator will allow casts to be put into a reproducible ICP, which may be helpful if there are insufficient contacts to make hand- held casts stable, but that is the limit of what a simple hinge articulator can do.

Fig. 9 Impression material has been pulled away from th tray on withdrawal from the mouth. This will equate to at least a 1mm occlusal error

Fig. 9 Impression material has been pulled away from th tray on withdrawal from the mouth. This will equate to at least a 1mm occlusal error

Fig. 10 Large stone blebs on the palatal surfaces of upper anterior teeth as a result of air bubbles in the impression

Fig. 10 Large stone blebs on the palatal surfaces of upper anterior teeth as a result of air bubbles in the impression

with all interproximal tags and undercuts removed is the ideal. It is usually necessary to trim the record to achieve these requirements and silicone materials trim very easily with a scalpel (Fig. 13). One final consideration is that stone casts and dies can easily be abraded by IORs especially those made of acrylic resin and special care is required in the laboratory when these materials are used in combination.

with all interproximal tags and undercuts removed is the ideal. It is usually necessary to trim the record to achieve these requirements and silicone materials trim very easily with a scalpel (Fig. 13). One final consideration is that stone casts and dies can easily be abraded by IORs especially those made of acrylic resin and special care is required in the laboratory when these materials are used in combination.

Fig. 13 A carefully trimmed interocclusal record restricted to the area of tooth preparation. The resulting crowns needed no adjustment

Fig. 13 A carefully trimmed interocclusal record restricted to the area of tooth preparation. The resulting crowns needed no adjustment

Fig. 14 Preparation of the teeth has resulted in loss of all guiding surfaces on the anterior teeth

Fig. 14 Preparation of the teeth has resulted in loss of all guiding surfaces on the anterior teeth

Fig. 15 A custom acrylic guide table for use with a semi-adjustable articulator. This is an excellent method of copying tooth guidance into definitive restorations

Fig. 15 A custom acrylic guide table for use with a semi-adjustable articulator. This is an excellent method of copying tooth guidance into definitive restorations

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References (7)

  1. Okeson J P. Management of temporomandibular disorders and occlusion. 1998. 4th Edition. St Louis: Mosby, pp47-51.
  2. Posselt U. Studies in the mobility of the human mandible. Acta Odontol Scand 1952; 10 : 109.
  3. Wise D. Occlusion and restorative dentistry for the general practitioner. Part 2-Examination of the occlusion and fabrication of study casts. Br Dent J 1982; 152: 160-165.
  4. Howat A P, Capp N J, Barrett N V J. A colour atlas of occlusion and malocclusion. 1991. London: Wolfe Publishing, pp137- 139.
  5. Loos L G. Clinical criteria used to select an articulator. Compend Contin Educ Dent 1993; 14: 80-88.
  6. Walls A W G, Wassell R W, Steele J G. A comparison of two methods for locating the intercuspal position (ICP) whilst mounting casts on an articulator. J Oral Rehabil 1991; 18: 43- 48.
  7. Wise D. Occlusion and restorative dentistry for the general practitioner. Part 9 -Restoration of anterior teeth. Br Dent J 1982; 152: 407-413.