The efficacy of sodium hypochlorite can be simply and practically enhanced by increasing its temperature. This improves its immediate tissue-dissolution capacity (Zehnder M, 2006 Some studies also support that heated sodium hypochlorite removes organic matter from dentine more efficiently than its unheated counterpart (Kamburis JJ et al, 2003).
Heating composite can increase its pliability and aid in better manipulation of material to surfaces.
As a result the physical properties of the material are more favorable for restorations,without having an adverse effect on the chemical composition and therefore not compromising aesthetics or function.
The inevitable removal of sound tooth in a Crown preparation, and therefore weakening of tooth structure, must be justified by the provision of a Crown that will serve to protect the tooth from further loss of tooth structure, and gain of function.Studies have shown that 1-15% of vital teeth become devitalized after Crown preparation, due to exposure of thousands of dentinal tubules, and this needs to be kept in mind when considering Crown preparation, as this can lead to periapical pathology later on.
It is the dentist’s responsibility to communicate the importance of good oral hygiene and the direct influence on the Crown’s success. This information should be followed by oral hygiene instruction including, tooth brushing advice, flossing techniques, mouthwash advice etc. A tell-show-do method has proven to be successful in teaching patients how to brush and floss.
-Ideally, all Crown margins should be placed supra gingivally, to avoid the problems associated with gingival recession, however, in cases where subgingival preparations are indicated, it is important the margins are as smooth as possible.
Subgingival preparations should lie within the depth of the gingival sulcus, and should never encroach onto the biologic width of the periodontium. The biologic width is an approximately 2mm of distance established by the supracrestal connective tissue and the junctional epithelium. If a Crown margin encroaches on the biologic width, it causes inflammation, which may lead to attachment loss, apical gingival migration and pocket formation.
-In a vital tooth with no pulpal involvement, a Crown can be planned without endodontic treatment, but a note kept in mind that there is a risk of devitalization after tooth preparation.
-In a Non-vital tooth, or pulpally involved tooth, endodontic treatment should be carried, to remove infection, prior to Crown placement.
Frequently, the tooth to be crowned has an existing restoration. All previously placed materials should be removed, unless it has been recently placed and you are sure it is retained to sound tooth. If >50% of coronal tooth structure remains after caries and restoration removal, and no more increase in strength is required, then a bonded compomer or resin ionomer base may be used to restore the tooth to the required preparation form. If <50% of coronal tooth structure remains, and there is not a minimum of 2mm sound tooth circumferentially and gingivally to the preparation, a high-strength core build-up is needed to increase tooth strength and provide retention and resistance form.
Sufficient occlusal space is required for the provision of a Crown, and this is deficient in cases of moderate to severe tooth wear. In such cases, a Dahl appliance or grinding of an opposed tooth may be required to create such space, however neither are to be taken lightly and will require a full occlusal assessment.
When you are doing an access cavity, you will notice that the roof of the pulp chamber is a dull, yellow color that is similar to the dentine in your normal cavities. Once you get to the floor of the chamber, it becomes glossy and white. Look for this difference when you are cutting your cavities to avoid drilling too far.
The floor of the pulp chamber usually has a grey/black ‘road map’ – these are developmental grooves where the pulp tissue rested. The significance of this ‘road map’ is that it may help to guide you when looking for canals. Follow the road maps and they will give you clues to the location of canals. Therefore, it is important when removing the roof of your pulp chamber not to damage the floor of the pulp chamber, as you will damage this very useful biological map.
When you access the tooth, use your straight probe around the CEJ of the tooth to determine its angulation, especially under a crown. This will help to angulate your bur to make sure you are drilling in the direction of the pulp chamber rather than through the side of the tooth.
Look for symmetry in the location of the canals, for example, if you find a distal canal that is off to the buccal side in a lower 6, look for a separate canal further towards the lingual. If, on the other hand, the canal is bang in the middle, you can stop there knowing that you have all the canals of the distal root.
To further open the root canal, you can use gates gliddens drill sequentially. Some practitioners start with smaller GG heads and progressively increase the size. Alternatively, you can start big, and create more space for smaller heads to go further along the canal.
You want to get at least a size 15 to the estimated working length, this is because a size 10 may not be picked up on the check X-ray. In teeth with several root canals, you can use different sizes of K files, OR you can use different types of files like a Hedstrom file, just so you can differentiate between the two on the radiograph.
When taking the working length of the canals, take a check x-ray. Check that you are in the right canals, and how close/far you are from the apex. After you’ve taken your x-rays with the file in situ, move the rubber stop to your reference point, take the file out and measure it again. If you are long on the x-ray by 2mm, take 2mm of this measurement, if you are short, add to it. This is your final working length.
The aim of shaping in the final third is to create a 6-8% taper with a size 25 at the apex which you can obturate against. Remember that standard K-files have a 2% taper, which is why you use a step-back technique to create the intended 6-8%. Some hand files, like Pro-Taper, or rotary endo systems have files that create the 6% taper for us, which makes things easier.
At the end of canal obturation, remember to cut the GuttaPercharight back into the canal system. GP has no place in the pulp chamber and just interferes with the final restoration.
Alvogyl; a dry socket treatment which, when placed provides rapid pain relief. It is self-eliminating and has three active ingredients:Butamben: Anaesthetic, Iodoform: Antimicrobial, and Eugenol: Analgesic.
Electric pulp testing involves sending an electric current through the patient's tissues to assess the pulp vitality. The sensation will quickly disappear when the stimulus is removed. When the sensation lingers, it signifies stimulation of C fibres, and irreversible pulpitis. No response means that the nerve is non-vital.
To produce well defined impressions, metal trays are preferable, because they are rigid and reduce the risk of distortions. Recoil is a problem that occurs more commonly in plastic stock trays, whereby the walls of the tray flex outward during occlusal pressure, followed by an inward flexion, producing impressions that are undersized bucco-lingually.
When making an impression after crown preparation, you should retract the gingivae around the Crown preparation, so that the finish line can be recorded accurately. The most common method is the “two cord technique”, where a thin cord is wrapped around the tooth and placed into the sulcus followed by a thick cord, which is removed just before the impression is taken. Sometimes, the cords are impregnated with solutions to prevent haemorrhage i.e. adrenaline and ferric sulphate.
The crown should be tried in without forcing it onto its preparation. You have to make sure that there is no residual temporary cement left underneath the crown, and then you should check and adjust proximal contacts as they prevent seating sometimes. If the crown is not fully seated, burnish marks on the internal wall of the metal might give an indication where it is binding, these marks might be lightly ground with a bur or stone before retrying the crown. Light body silicon can be used to identify these marks.
Once a crown fully seated onto its preparation inside the patient’s mouth, a systematic approach is followed to evaluate it: Proximal contacts, marginal fit and then occlusion.
The tightness of proximal contacts of a fully seated crown can be tested with dental floss and should offer some resistance but not make its passage too difficult. If these are too tight they can be ground a little at a time and polished. Prior to adjustment it may be helpful to mark the proximal contact by sandwiching a small piece of articulating paper between crown and tooth either on the cast or in the mouth.
If open contacts occurred when assessing a fully seated crown inside the patient's mouth,it can only be modified by returning the crown to the laboratory for addition of porcelain.
Marginal fit (the gap between the Crown margin and tooth preparation margin): A poor marginal fit could render a tooth more susceptible to cement dissolution, plaque retention and secondary caries. Data suggests that a marginal gap of 100µm is at the borderline of acceptability for long term success.
Poor fit margins of a crown can present as a gap or an overhanging margin (positive ledge) or deficient margin (negative ledge). Overextended margins and positive ledges may be corrected by adjusting the crown from its axial surface until it is possible to pass a probe from tooth to crown without it catching. A larger problem, necessitating that the crown be remade if it is unacceptable, occurs when a margin remains deficient or has a negative ledge.
Occlusion is the last assessment to make for a fully seated crown. Articulating foils and shim stock are needed to check for occlusion. Both crown and adjacent teeth should hold shim stock firmly in the intercuspal position (ICP).A large flame shaped diamond bur is used to reduce high areas. Once ICP has been re-established the excursions can be checked preferably with a different coloured foil. Occasionally, it may be necessary to adjust the tooth opposing a restoration to avoid crown perforation or exposure of rough opaque porcelain.