Enamel defect

RE: Enamel defect

Peter Southerden — Sun, 06 Mar 2016 23:45:10 GMT

I think that a lot of the principles for crown preparation taught in vet dentistry has been taken from human prosthodontics and applied directly to our patients. I don't think that this the best approach in many cases.

In human dentistry the aim is to get a conversion angle of around 6 degrees (so near parallel). Human teeth are cubic and this is achievable. In our patients we can't achieve this in some cases, for example on a maxillary fourth premolar but can in others (mandibular first molar). The lingual and buccal aspects of a canine tooth are near parallel which gives excellent retention. However if you try and get this with the mesial and distal surfaces it involves removing a lot of healthy tooth and you end up with a peg like preparation which is nothing like the original tooth shape.

So I maintain the tooth shape and don't worry about trying to get a parallel preparation between the mesial and distal surfaces.

You may have been taught to produce a chamfer finish to your crown preparation which involves removing between 0.5-1mm tooth (enamel and dentine) at the margin which will remove 1-2mm of the tooth diameter. I aim for a feather margin and remove less than 0.5mm at the margin (more likely to be around 0.1-0.2mm) thus conserving more healthy tooth. The crowns are 0.4mm in thickness.

Retention in our patients is produced by achieving a near parallel preparation where possible. However tooth surface area is also important in retention and our patients benefit from a large tooth surface area which helps. This compensates for the difficulty in achieving a near parallel preparation. As do modern highly effective cements.

RE: Enamel defect

Evelyn Barbour-Hill — Sat, 05 Mar 2016 15:47:14 GMT

[quote user="Rob Davis"]I have only ever done this on a cadaver in a wet lab session, but I was under the impression that the crown prep should have near parallel sides. Is this not really necessary?[/quote]

Fairly sure that's not quite right nowadays.

Mr. Southerden will tell you more.

RE: Enamel defect

Rob Davis — Sat, 05 Mar 2016 08:36:41 GMT

[quote user="Peter Southerden"]Crown preparation wouldn't involve removing any dentine. Normally I would remove very little tooth in crown preparation - most of the prep would be in enamel and the crown would have a feather margin. However in this case I might remove all of the enamel down to just above the gum margin as I wouldn't want to bond the crown to weak enamel.[/quote]

I have only ever done this on a cadaver in a wet lab session, but I was under the impression that the crown prep should have near parallel sides. Is this not really necessary?

RE: Enamel defect

Evelyn Barbour-Hill — Fri, 04 Mar 2016 20:16:35 GMT

OK, fair enough.

RE: Enamel defect

Peter Southerden — Fri, 04 Mar 2016 20:04:35 GMT

Ionoseal is only a base liner/small restoration material. It wouldn't be strong enough. I agree that a nano-hybrid flowable composite would be a good second best. My concern would be very long term durability and loss of enamel at the margin of the restoration.

Crown preparation wouldn't involve removing any dentine. Normally I would remove very little tooth in crown preparation - most of the prep would be in enamel and the crown would have a feather margin. However in this case I might remove all of the enamel down to just above the gum margin as I wouldn't want to bond the crown to weak enamel.

RE: Enamel defect

Rob Davis — Fri, 04 Mar 2016 19:54:16 GMT

[quote user="Evelyn Barbour-Hill"]If finances or preferences rule out a metal crown, "restoration" with a flowable composite would not be such a bad second-best.[/quote]

Could you use a flowable glass ionomer such as ionoseal, or do you think that wouldn't be strong enough?

RE: Enamel defect

Evelyn Barbour-Hill — Fri, 04 Mar 2016 19:34:13 GMT

[quote user="Peter Southerden"]The surface of the canine tooth is plaque retentive and it will be weaker than the contralateral canine and so I would recommend a full jacket cast metal crown - this would certainly be better than a composite restoration. [/quote]

Not disagreeing but I'm not quite sure why the tooth would be weaker – weak enough to justify removing more tooth substance in a crown prep. Dentine is the substance that contributes most to the strength of a tooth, isn't it? It's only enamel that's missing.

If finances or preferences rule out a metal crown, "restoration" with a flowable composite would not be such a bad second-best.

RE: Enamel defect

Rob Davis — Fri, 04 Mar 2016 19:29:10 GMT

Interesting... Given that this tooth is going to have a massive pulp chamber at this age, would crown preparation not be very difficult to achieve without entering the pulp or further weakening the tooth? Would you prefer to wait for the tooth to mature a little and build up more dentine, or do you feel that it is currently too vulnerable to leave for a while?

RE: Enamel defect

Peter Southerden — Fri, 04 Mar 2016 19:16:29 GMT

I agree with Rob. Certainly radiographs are important to assess the development of the canine tooth and to see what's happening with the incisors and other missing teeth. There may be some benefit from sealing the exposed dentine with an unfilled resin.

The surface of the canine tooth is plaque retentive and it will be weaker than the contralateral canine and so I would recommend a full jacket cast metal crown - this would certainly be better than a composite restoration.

RE: Enamel defect

Rob Davis — Fri, 04 Mar 2016 18:44:27 GMT

Given the localised nature of the problem, I suspect this pup had and injury during amelogenesis (approx 2-12 weeks old). Radiography would be sensible to see what's there. Teeth with enamel dysplasia/hypoplasia are at increased risk of developing pulpitis and subsequent periapical pathology. I believe that some people advocate fluoride treatment, though I'm not aware of any evidence that it helps (the enamel will never be replaced). You could try to seal the dentine tubules with a bonding agent or possibly flowable composite, but it probably won't last very long.

Be careful if scaling these teeth - use hand scaler only - ultrasonic is likely to strip off further enamel. Strict oral hygiene and periodical radiography to check for periapical lesions would be my approach.

I will await the experts to chip in...

PS It looks as though 305 and 306 are missing too (although they may be hiding behind 304 in the photo). If they are missing, then I would definitely be radiographing this area too to check for any embedded teeth.