Procedures in Operative Dentistry
The aim of this chapter is to describe the operative procedures that restore the function and appearance of teeth which have lost tooth structure through various processes. Enamel and dentine can be lost because of:
- Dental caries.
- Tooth wear.
- Root resorption.
- Developmental disturbances in enamel/dentine formation.
- Iatrogenic causes.
Prior to carrying out any operative treatment on a patient, a full history and examination should be taken. This should include determining what the expectations of the patient are, a full medical and dental history and extra/intraoral examination. The periodontal tissues should be examined, the teeth and the patient’s static and dynamic occlusions. A restoration may have fractured and a careful examination of the patient’s occlusion may detect an interference or overerupted tooth.
Special tests should then be carried out. These might include sensibility testing and radiographs. Bitewings and long cone periapical radiographs can show more detail then a dental panoramic tomogram. Percussion tests may also be indicated.
A diagnosis should be made and possible treatment options presented to the patient along with their respective cost. The patient should be given enough information so that they can make an informed decision. The clinician should be able to communicate effectively with the patient and any accompanying person and be able to discuss the advantages and disadvantages of each treatment option in lay terminology.
It is important to develop a painless technique to deliver effective local anaesthesia as this will help the patient have a positive experience. Proficiency in placing a rubber dam will also instill confidence in the patient towards the operator.
The following topics will be discussed in this chapter:
- Management of dental caries.
- Correct use of dental adhesives.
- Composite resin.
- Glass ionomer cement.
- Operative management of tooth wear.
- Repairing fractured restorations.
- Restoring the endodontically treated tooth.
|The following questions should be considered:|
||Caries can be detected using:
||How does dental caries appear?
Caries has many appearances.
||Early carious lesions may present as white lesions in enamel, which may not have cavitated, whereas lesions that have been present for some time may have caused significant destruction of enamel and dentine.|
||It should be remembered that a ‘white spot’ enamel carious lesion that has not cavitated may have in fact progressed into dentine as the Figures 11.1 and 11.2 show.|
||Assessing caries risk is important.
If the patient is assessed as being at ‘low risk’ of caries, then a decision might be made not to intervene operatively.
If the patient is assessed as being ‘high risk’ and if the caries process has entered the dentine, operative intervention might be instigated sooner.
The patient’s medical history will reveal any medications with side effects or medical conditions that may cause a dry mouth. Saliva is an important buffer and lack of saliva will render the patient at a high risk of developing carious lesions. The patient should be asked about their diet to determine the frequency of any acidic or sugary intakes of food or drink. Their level of plaque control should be assessed and how often they use a fluoride toothpaste and mouthwash.
Non‐Operative Management of Caries
|If caries is detected in a tooth, then this should be recorded in the clinical notes and a decision made whether to treat non‐operatively or operatively.|
|We have entered the era of minimal intervention in medicine and dentistry. With respect to caries management this may involve non‐operative as opposed to operative intervention.|
|Nonoperative treatment may consist of:
Operative Management of Caries
Once the lesion of caries has cavitated and is a ‘plaque trap’, or the caries has been observed on a bitewing to progress beyond the enamel–dentine junction (EDJ) into dentine, operative intervention has to be considered. The important question to consider is if caries is to be removed, where should it be removed from and how much should be removed whilst still preserving as much enamel and dentine as possible. Teeth which become grossly carious may remain asymptomatic and vital (Figure 11.3).
What Does the Evidence Tell Us About Managing Caries Operatively?
To date, there has only been one significant clinical trial in which caries was sealed in using composite restorations bonded to enamel around the lesions.
Mertz‐Fairhurst et al. (1998) treated frank cavitated caries extending no deeper than halfway into dentine between the EDJ and the pulp chamber, or between the EDJ and the nearest pulp horn by placing a 45–60° bevel in the enamel surrounding the frank cavitated lesion. The deep soft portions of the caries remained untouched. The bevel and the adjacent enamel were etched for 60 s followed by application of the bonding agent. Using hand instruments, a self‐curing resin‐based composite was placed. Then all the occlusal, buccal and lingual pits and fissures were etched for 60 s, washed thoroughly and covered with a pit and fissure sealant. Surprisingly, in the majority of cases, the caries beneath the sealed resin‐bonded composite restorations ceased to progress. No pulps became non‐vital in the 10‐year study. This study is now proving to be a pivotal study in the modern‐day management of dental caries.
To date, despite the results of this study, it is not deemed acceptable practice among clinicians to leave soft dentinal caries untouched in the cavity. However, this may change in future years.
What is Current Thinking Regarding Removal of Carious Dentine?
The decision when to remove carious tooth tissue is complicated by the fact that it is an irreversible procedure. It is common practice that surgical intervention is delayed until the caries is clearly visible in dentine. Once the lesion has involved the outer third of dentine, shown by radiographs, then it should be removed. When removing carious dentine, it is important to consider in what way the dentine has been altered by the carious process as this will dictate what should be removed and what should be left. This necessitates an understanding of the histological changes that have taken place in the carious dentine.
Figure 11.4 illustrates that the carious lesion gradually undergoes a series of colour changes from the EDJ towards the pulp. At the EDJ, the lesion appears dark brown in colour, amber in the deeper aspects and then more translucent nearer the pulp. These colour changes reflect the histological changes that the dentine has undergone as a result of the carious process.
Dentine caries proceeds through three changes: demineralisation by dissolution of the inorganic component, calcium hydroxyapatite; degeneration of the organic substance; and bacterial invasion (Deery, 2013).
The lesion is cavitated at the EDJ and in the outer aspect of the lesion, the intermolecular crosslinks of the collagen are broken and the collagen fibres lose the crossbanded structure, which exists as a base to which the calcium hydroxyapatite crystals become attached. As a result, the apatite crystals become dislodged and are scattered around as small granules. Within the dentinal tubules, the odontoblast processes are replaced by bacteria. This region cannot be remineralised and is insensitive with regards to pain. This region has been given the name ‘caries‐infected dentine’ (Fusayama, 1979; Ogawa et al., 1983).
Within the inner aspect of the carious dentine, the initial acid attack on the collagen fibres is reversible. The acid dissolves the hydroxyapatite from the crystal peripheries in the peritubular and intertubular dentine. The dissolved calcium phosphate diffuses into the dentinal tubules and begins to precipitate new whitlockite crystals. Under the optical microscope, this layer looks ‘transparent’ due to its refractive index. This inner aspect is not infected with bacteria and is remineralisable and therefore should be preserved. This region has been given the name ‘caries‐affected dentine’ (Fusayama, 1979).
When a decision has been made to remove the carious dentine, the aim must be to remove the ‘caries‐infected’ dentine and leave the ‘caries‐affected’ dentine. This requires much thought as a subjective judgement must be made in the clinical situation through colour observations and an assessment of the softness/hardness of the dentine. The hardness of carious dentine has been measured using the diamond indenter of a Knoop Hardness Detector and has shown to change across the carious lesion (Ogawa et al., 1983).
In Figure 11.5, the ‘y’ axis represents the Knoop hardness of the dentine surface and the ‘x’ axis represents the distance from the EDJ (left) to the pulp (left). Near the EDJ, where the bacteria have invaded the lesion, the lesion is very soft because of the dissolution of the hydroxyapatite crystals and the denatured collagen fibrils (Mattos et al., 2013). This soft, ‘caries‐infected’ dentine should be removed. However, caries removal should stop when the ‘caries‐affected’ dentine is reached. There is no clear demarcation between these two regions and it is only through a subjective assessment of the increased hardness in the region of the ‘caries‐affected’ dentine that a clinical decision can be made. It can be seen in Figure 11.5 that there is an increase in surface hardness in the deeper ‘caries‐affected’ region (Figure 11.6). Below the graph is a diagram of a dentinal tubule showing how the tubule is filled with mineral deposits.
If a decision has been made to intervene operatively, sensibility testing should be carried out prior to administering local anesthetic. The results should then be documented. The radiograph should be consulted to give a ‘rough guide’ to the extent of the caries lesion. Placement of a rubber dam prior to cutting the tooth is advisable, if acceptable to the patient, as the cavity will be protected from ingress of saliva.
A systematic approach should be undertaken when removing caries‐infected dentine. This can be considered to consist of four steps:
- Gain access to the caries‐infected dentine.
- Removal of peripheral caries.
- Management of deeper caries overlying the pulp.
- Modification of cavity design according to which restorative material will be used.
Gaining Access to the Caries‐Infected Dentine
Access to the caries must be gained. This may entail access through the sound enamel of an occlusal surface or removal of an existing restoration. Cutting is best achieved using a diamond or tungsten carbide bur in a high‐speed handpiece under copious water spray. Demineralised and grossly unsupported enamel should be removed but sound enamel and dentine should be preserved as much as possible (Figure 11.7).
Removal of Peripheral Caries
Once access to the dentinal caries has been achieved, removal of any soft, caries‐infected dentine should commence at the periphery of the lesion adjacent to the EDJ. All the soft ‘caries‐infected’ dentine should be removed (Figure 11.8). In recent years, there has been a debate among cariologists as to how clean or free from caries the EDJ should be. Laboratory research has shown that adhesives have a stronger bond to sound caries‐free dentine than they do to caries‐affected dentine. Therefore, the dentine adjacent to the periphery of the cavity must be free of any caries so that optimal bonding can be achieved. Ideally this would consist of an enamel margin and sound dentine adjacent to the EDJ. This would allow optimum bonding of the dental adhesive to enamel and dentine. Optimum bonding would create a hybrid layer in dentine and penetration of adhesive into enamel that would be resistant to bacterial penetration.
Management of Deeper Caries Overlying the Pulp
After a decision has been made on the management of the carious dentine close to the EDJ, operative treatment of the floor of the lesion can commence. To ensure that caries removal from the floor of the cavity is not overdone, it is important to be aware that a careful approach should be undertaken taking into consideration when the caries‐infected dentine is likely to have been removed and the caries‐affected dentine reached. This can be only achieved using instruments that offer tactile feedback, such as excavators. If the caries has not spread too deep into the dentine, it will be possible to stop excavating the carious dentine when it stops feeling soft and feels harder and scratchy (Figure 11.9).
The Dentine–Pulp Complex
Any teeth requiring operative treatment should have their vitality assessed prior to administering local anesthetic, using sensibility tests such as response to electric pulp testing and ethyl chloride. A positive response to ethyl chloride or the electric pulp test does not indicate vitality but the condition of the nerve fibres within the pulp. Vitality testing would involve assessment of blood flow into the pulp using Doppler assessment, which at present is not clinically practical.
If the tooth gives a positive sensibility test prior to operative treatment and has not caused the patient discomfort, then all efforts should be made not to damage the pulp. As previously discussed, dentinal caries was sealed in one clinical trial and the teeth did not lose vitality over a 10‐year period. Therefore, after the EDJ and peripheral caries have been managed, the temptation to chase the caries removal towards the pulp should be resisted. Indirect pulp capping involves leaving deep caries when it is thought that further removal of the caries will result in pulpal exposure. The results of the Mertz‐Fairhurst et al. (1998) study support leaving deep caries as long as a well‐bonded adhesive restoration can be placed on top.
Step‐wise caries removal has been proposed whereby a calcium hydroxide liner is placed over the residual caries and the cavity restored. The restoration is then removed along with the deep caries several months later. In practice, re‐entering the lesion is not widely practiced. Again, the evidence of the Mertz‐Fairhurst study would indicate that re‐entry is not necessary.
If the pulp is inadvertently exposed, then it is possible to place a direct pulp cap. The response of the pulp tissue will depend on whether the tooth has a good blood supply. When permanent teeth in young patients suffer trauma and complex enamel–dentine fractures then it is possible to carry out a pulpotomy and place calcium hydroxide powder on the pulpal tissue once it has stopped bleeding. A layer of glass‐ionomer cement is placed over the non‐setting calcium hydroxide powder and then composite resin used to replace the missing enamel and dentine. Once root formation is complete then pulpotomy is less likely to be successful. Mineral trioxide aggregate (MTA) is an alternative material to calcium hydroxide powder. MTA is a promising material to use as a direct pulp capping material but it can take up to 20 min to set and has been reported to discolour the tooth. White MTA is now available and this may cause less discolouration. If the pulp exposure is ‘pin‐point’ in size, then protection from microorganisms in saliva through the placement of a rubber dam is essential, and direct capping with a setting calcium hydroxide‐based material carried out. Alternatively, a new bioactive cement based on tricalcium and dicalcium silicate and calcium chloride, which forms calcium hydroxide when setting is available.
Procedures to be Undertaken when Managing Deep Caries
- Ensure rubber dam isolation is in place and the tooth has been anaesthetised.
- After removing soft ‘caries‐infected’ dentine at the EDJ, a decision should be made on the harder ‘caries‐affected’ dentine at the EDJ. If enamel is present and aesthetics are not a concern then hard, stained dentine at the EDJ can be left and removed if aesthetics will be affected.
- If no peripheral enamel is present, then achieving a good seal on dentine will be more challenging as good dentine bonding is more reliably achieved to sound dentine unaffected by caries.
- Consideration should be given to leaving soft deep caries if pulpal exposure is likely. In young patients, pulp horns will be more readily exposed. The adhesive can then be placed and the cavity restored with a definitive material such as composite resin.
- If a pulp exposure has occurred and it is ‘pin‐point’ in size, disinfect the pulp by gently blotting a cotton wool pledget soaked in chlorhexidine and then place a setting calcium hydroxide liner or Biodentine™.
- If the pulp exposure is larger, a ‘Cvek’ pulpotomy is possible if the root is likely to have a reasonable blood supply such as would be found in an immature single‐rooted tooth.
- In older patients and multirooted teeth, consideration must be given to pulpectomy and endodontic treatment as the blood supply may not be sufficient.
Once the caries has been removed, which material to be used in the resultant cavity should be decided. Ideally, the patient must be adequately informed of the possible materials along with their advantages and disadvantages so that they can make an informed decision. However, various factors may need to be considered and this can make selection of the appropriate material quite complicated. The most durable restoration that preserves as much tooth as possible should be chosen. If it is in the ‘aesthetic zone’ it should have a good appearance.
Factors to consider are:
- Patient wishes after having been informed of the possible options.
- Remaining enamel and dentine.
- Ability to achieve adequate moisture control.
- Location of cavity in the mouth. Is it in an area where good aesthetics is important or is it in a posterior tooth, which could be subjected to loading or parafunctional activities?
- Operator skill and knowledge of how to use materials correctly and control the occlusion.