Arrangement of artificial teeth in abnormal jaw relations Maxillary protrusion and wider upper arch Dr.Mohammad Al Sayed 25/3/2008

Ridge relationship Definition of normal ridge relationship: The maxillary and mandibular ridges are considered to be in normal relation when, in centric relation, the upper ridge in the anterior region is slightly labial to the lower ridge and when, in the posterior region the crest of the lower ridge is slightly buccal to that of the upper ridge

Definition of abnormal ridge relationship: Any deviation in the anterior and /or posterior region from the normal ridge relationship is considered abnormal. In the anterior region. The ridge relationship is abnormal: a- when the upper ridge is located much further anteriorly than the lower ridge i.e. maxillary protrusion. b- when the upper ridge is located in the same line or lingual to the lower ridge i.e. mandibular protrusion or prognathism. In the posterior region. Abnormality is considered to exist: a- when the crest of the lower ridge is placed lingual to that of the upper ridge i.e. a wider upper arch. b- When the crest of the lower ridge is placed much further buccally than normal in relation to the upper arch i.e. a wider lower than upper arch.

Arrangement of teeth in abnormal ridge relations: Arrangement of anterior teeth in maxillary protrusion: Problem 1: As the upper arch in these situation is further forward in the anterior region, the first problem is that of an excessive amount of overjet (horizontal overlap) which results in an abnormal upper and lower canine tooth relationship. No attempt should be made to reduce this horizontal overlap by moving the upper anterior teeth palatally or the lower anterior teeth labially.

Problem 2: In situations where there is a normal upper and lower canine relationship mesiodistally, the distal surface of the lower canine tooth is located at the tip of the cusp of the upper canine. However when the upper anterior teeth have been arranged, it may be that this relation will not be obtained when the lower anterior teeth are arranged. This discrepancy in canine relationship is the result of the upper arch being forward in relation to the lower arch so the lower anterior teeth have to be set further lingually in relation to the upper anterior teeth This results in the lower canine tooth finishing anywhere from the tip to the distal surface of the upper canine tooth

When the maxillary protrusion is excessive, the distal incline of the cusp of the lower canine will sometimes be posterior to the distal surface of the upper canine tooth. This canine relationship also influences the subsequent posterior arrangement of teeth.

Management: 1. If protrusion is not too extreme, the simplest way is to select the lower anterior teeth of a narrower mesiodistal width and try to achieve the normal canine relationship. 2. If esthetics permit, a little crowding of the lower anterior teeth by overlapping may solve the problem well. 3. Another solution which is effective is leaving slight spaces between the upper anterior teeth to attain normal canine relations. However, such a procedure is esthetically limited.

4. In situations where the discrepancy is not too great, grinding of the distal surface of the lower canine is sufficient to restore the normal canine relationship. This procedure can be extended to all of the lower anterior teeth by grinding their mesial and distal surfaces to narrow their total mesiodistal width. 5. In situations where the discrepancy is excessive and cannot be managed by manipulation and modification of the lower anterior teeth, the lower anterior teeth must be left as they are, and the lower first premolars must be eliminated from the dental arch.

If the distal incline of the lower canine is entirely posterior to the distal surface of the upper canine tooth, the situation is ideally suited for such a procedure, and a satisfactory posterior setup can be developed. If however the entire distal incline of the cusp of the lower canine tooth is not free for articulation with the mesial incline of the buccal cusp of the upper first premolar, it is well to move the lower canine slightly to achieve the proper relation with the upper premolar. The slight space created in the lower anterior arch is taken up by the other anterior teeth without affecting the esthetics.

Sometimes slight grinding of the mesial surface of the upper first premolar will bring it into the correct relation with the lower canine. It is sometimes recommended that one of the four lower incisors be eliminated but the problem here is esthetic and we can instead eliminate one of the least important teeth such as the lower first premolar from the lower arch.

Once the anterior teeth are satisfactorily arranged, the posterior teeth are arranged. If the posterior ridge relation is normal , a normal arrangement of teeth is used after the lower first premolars have been removed from the dental arch. In these situations, if the palatal cusp of the upper first premolar interferes with the lower canine, it is ground off to remove this interference.

Arrangement of posterior teeth when the upper arch is wider: The problem in this situation that the lower crest of the ridge in the posterior region is lingual to the upper residual ridge. This will cause difficulty in the placement of the upper and lower teeth in their correct occlusal relationship. In such instances the upper arch is wider than the lower , and if the upper teeth are placed on the crest of the ridge, they will make inadequate occlusal contact with the correctly placed lower teeth.

At the same time if an attempt is made to occlude the lower teeth with the correctly placed upper teeth, the lower teeth will place too far buccaly, leading to an instability of the lower denture.

Management: 1. If the discrepancy is very slight, the upper teeth are moved slightly in a palatal direction to provide a working occlusal contact with the lower teeth. However such a procedure has a very limited application as the upper posterior teeth cannot be moved inside (palatally) to any great extent without affecting phonetics and cheek support.

2. If the upper arch is much wider than the lower one, any of the following method can be followed successfully: a. The lower posterior teeth are correctly placed on the crest of the ridge. The upper teeth are then set so that they occlude well with the lower teeth. Then the buccal contours are built on the upper teeth in wax which is later replaced by tooth colored acrylic resin to fulfill the esthetic requirements and to provide support for the cheeks. b. The upper posterior teeth are arranged first to meet the requirements of esthetics. The lower teeth are kept on the crest of the ridge. This will result in unfavorable occlusal relationship of the upper and lower posterior teeth, so wax is added on the palatal aspect of the upper posterior teeth which will be replaced by tooth colored acrylic resin later.

This gives a functionally effective occlusal contact as well as an esthetically acceptable buccal surface contour of the upper posterior teeth. * Nonanatomic posterior teeth are best for these procedures as they allow more latitude in their buccolingual placement

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