A composite approach to the management of worn maxillary first molar teeth

Case report

A 29-year-old lady with toothwear was referred to the restorative department at Bristol Dental Hospital by her GDP for restoration of her maxillary first molars. Her presenting complaint was a nine month history of dentine hypersensitivity from these teeth. Her GDP had attempted direct adhesive resin composite restoration conforming to the patient's pre-existing occlusion. These failed twice due to restoration fracture and debond of the composite material. There was no relevant medical history.

On examination, the teeth missing were UR8, UR7, LR8 and LL8. Her oral hygiene was good and the BPE scores were:

There was generalized moderate toothwear which had the pattern of erosion from an extrinsic dietary source and she also exhibited signs of bruxism. The maxillary first molar teeth were the worst affected with exposure of occlusal dentine (Figures 1 and 2). The UR6 was partially restored with an occlusal amalgam filling and a superficial dentine crack was noted. There were two remnants of occlusal composite UL6.

There was also dento-alveolar compensation of the opposing first molar teeth which were in contact in a half unit Class II buccal relationship (Figures 3 and 4). There was therefore not enough space for placing composite resin to conform to the patient's current ICP (Figure 5). The maxillary first molars were otherwise caries free and indicated a healthy nerve supply in response to an electric pulp test. Generalized mild wear facets were visible.

Prevention

This was tailor-made for the patient using the Department of Health's Evidence-Based Toolkit for Prevention6 and UK National Clinical Guidelines in Paediatric Dentistry: diagnosis, prevention and management of dental erosion.7 Dietary analysis was in the form of a three-day diet consecutive diary, including one weekend day. The completed analysis showed evidence of acid in the diet from daily orange and tomato intake.

Dietary advice to help prevent erosion was given. The nature of acid erosion and its timing was discussed, including issues about frequency and quantities of erosive foodstuffs, along with consuming fewer erosive alternatives. Sugar-free chewing gum was recommended to increase salivary flow and to aid remineralization. The patient was advised to take drinks quickly or, if consumed slowly, to place a wide bore straw towards the back of the mouth in order to reduce contact time of acidic fluid with the teeth. The habit of frothing or swishing drinks around the mouth is likely to increase the risk of dental erosion and the patient was discouraged from doing this.

The patient was advised not to brush for 45 minutes after acid intake. The natural history of the slow progression of acid erosion was discussed with her. She was informed to seek medical advice if gastric reflux or vomiting occurred in the future as intrinsic acid would expedite her dental erosion.

Baseline study models were cast to help monitor toothwear progression and casts are to be repeated at one-yearly intervals. Clinical photographs were taken with the patient's valid informed consent. She was prescribed a 2800ppm sodium fluoride toothpaste and 0.05% ppm sodium fluoride mouthwash for home use. It was planned for her to have professionally applied fluoride, 22600ppm sodium fluoride (Duraphat) at 6-monthly intervals till her erosion status stabilized.

Planning

If posterior teeth are in contact in intercuspal position and restorations are planned, the traditional view is that interocclusal space is required for these. General options to create space are summarized as follows:^2,5,8

It was decided to attempt to restore the maxillary first molar teeth, with direct composite resin restorations acting as orthodontic devices to produce a stable occlusal contact over time on these teeth and their counterparts in intercuspal occlusion.

The rationale for this approach was that it was simple, conservative, aesthetic, requires no lab work or between-visits provisional restorations and no tooth reduction of the already reduced eroded tooth tissue. The procedure for direct composite restoration was forecast to be largely reversible. There was good residual enamel to bond to which made this the treatment of choice in this case. There was an excellent fallback position if the composites failed as no sound residual tooth structure had been removed.

The concern, however, was the predictability as a long-term restoration as, although there are results available for this approach on anterior teeth,^9,10,11 there are no studies specifically detailing the longevity of posterior composites which are cemented high. Median survival rates for composites conforming to the existing intercuspal occlusion of 7.8 years have been quoted.12 It might be assumed that, once the occlusion has compensated for the high restoration, the composite might behave as a routine posterior filling in the planning of this case. Conventional cast restorations were disregarded owing to the destruction of healthy tooth structure and the associated risk of damage to the pulp.13 Cast gold restorations could also have been placed high with resin cement, which would require less tooth reduction than a conventional cast restoration,2 but the patient declined these for aesthetic reasons.

Informed consent for the procedure was given by the patient, which was to be performed under local anaesthetic. The benefits to the patient and the reasons to provide the teeth with composite restorations were to eliminate dentine hypersensitivity, prevent further toothwear of the occlusal surfaces of the upper first molars, and restore the anatomy and shape of the teeth.

The potential risks other than those involved with local anaesthetic use included pain, sensitivity, an altered bite with reduced masticatory efficiency for a number of weeks and an anterior open bite. She was informed that composite restorations could also lead to post-operative sensitivity, could wear over time and chip, thereby requiring repair or replacement.

The patient understood these risks and was happy to give consent for the treatment as it was a relatively short procedure.

Clinical procedure

Enamel and dentine were acid-etched with 37.5% phosphoric acid gel (Kerr UK Ltd, Peterborough, Cambs) for 15 seconds and then washed and dried with a 3-in-1 syringe. The exposed dentine was not desiccated in order to maintain tubule patency for tag formation.

A single stage bonding agent (Optibond Solo Plus, Kerr UK Ltd) was applied and light-cured for 20 seconds.

Point 4 Unidose composite (Kerr UK Ltd) was placed incrementally and light-cured for 40 seconds. It was placed on dentine first followed by enamel. In this case, the composite was placed first on the occlusal surface only and then on to the buccal and palatal surfaces. Sufficient composite was placed to restore the missing tooth structure occlusally. The composite restorations were overbuilt and then polished with Enhance discs (Dentsply Limited, Addlestone, Surrey UK).

The occlusion was checked with the teeth coated with Lösungsmittel Biflurid amalgam liner (VOCO, Cuxhaven, Germany) using Double Check articulating paper (65 microns, Swedish Dental Supplies AB, Åkarp, Sweden). Stable and even bilateral contacts on the first molar teeth were created. Figure 6 shows the incisal relationship after composite placement.

Outcome

On review at two weeks, there was no dentinal hypersensitivity from the maxillary first molar teeth. Though the patient was still aware of an altered occlusion, she said she had got used to her new posterior contacts within two days. A small composite fracture of the mesial marginal ridge on the upper right first molar was reported by the patient, which was repaired.

She was reviewed again at six weeks after placement and stated she was still aware of an altered bite.

On review at 4 months after placement, the patient was happy with her occlusion. On examination it was apparent that the composite had worn in areas of heavy contact but, since the teeth were now asymptomatic, she declined repair or addition (Figures 7, 8, 9 and 10).

Literature review

Anderson investigated the occlusal effects of placing a 0.5 mm metal casting on one lower first molar in five patients.1 Only these lower molar teeth and the opposing teeth were in contact in maximum intercuspation, with separation of the remaining teeth with occlusal forces directed in an axial angulation. These castings were worn continuously by the patients for a range of 23–41 days. The subjects were able to make contact on the initially separated teeth within 24 hours of placing the casting by clenching their teeth hard, though this contact became easier to achieve over the next few days. Anderson stated that the movement which ensues after placement of the castings which led to re-establishment of the occlusion could be due to intrusion of the treated tooth and its opposing tooth, eruption of the separated teeth or a combination of both. A substantial amount of the cumulative tooth movements observed occurred within 24 hours after placement of the castings. This was then followed by a slower phase of tooth movement which Anderson suggested could include bony changes, which were not present in the faster tooth movement stage. This experiment showed that, despite a major alteration to the occlusion on a first molar tooth, the affected and separated teeth move and re-establish occlusal contacts. However, in some cases, the new occlusal contacts differed in location and angulation compared to the pre-existing occlusion.

A series of papers by Dahl investigated the occlusal effects of placing a removable cobalt chromium splint on the palatal surfaces of worn upper anterior teeth in order to create space for restoration after tooth movement had occurred.^14,15,16 These showed that patients adapt to occlusal changes well and that, by a combination of eruption or extrusion and intrusion, teeth move to contact again.

The experiments conducted by Dahl were on patients with worn anterior teeth with insufficient space to place conventional restorations. Metallic implants were inserted into the maxilla and mandible to monitor face height radiographically and patients were provided with maxillary removable cobalt chromium splints to be worn as long as possible.

The results showed that, in 16 patients who completed treatment with an age range of 18–50 and an increase in 1.8 mm to 4.6 mm in face height, all patients adapted to their new occlusions comfortably. Conscientious splint-wear influenced the speed at which space was created to restore the worn teeth and age or sex did not seem to influence this. In all patients, the adequate amount of tooth movement was achieved in order to place conventional restorations on the worn teeth. This occurred due to a combination of eruption/extrusion and intrusion. Dahl initially predicted that the ‘outward’ tooth movement was due to eruption, but later said an element of extrusion must also have been at play as some of these teeth intruded after loading.16 The majority of the movement was extrusion/eruption, which occurred 40% more than intrusion, and there was a tendency for more extrusion/eruption in younger age groups of patients. Most of the tooth movements had occurred by two months, at which point an equal amount of eruption/extrusion and intrusion had occurred. When the cephalogram radiographs were analysed, there was a very small amount of inclination of the upper anterior teeth and retroclination of the lower anterior teeth produced by this splint-wear, but the net movement was that of intrusion of the teeth occluding on the splints.15

Dahl's original removable approach to create localized space has since been modified for an approach where the worn anterior teeth are restored directly with composite. A prospective single-study trial by Poyser et al showed that 15 patients with worn anterior teeth treated with direct composite placed ‘high’, adapted without any significant problems to occlusal changes ranging from 0.5 mm to 5 mm.10 The posterior occlusal contacts re-established after an average of 6.2 months in 14 of the 15 patients. The one patient (7% of the total) in which the posterior contacts did not re-establish initially already had reduced posterior support and a Class III incisal pattern. Poyser et al state that this may be explained by a lack of eruptive potential. The restorations placed ‘high’ performed as well as those which conformed to the current occlusion, despite the high restorations being at risk of a theoretically higher loading until establishment of posterior contacts.

Redman et al found a mean time of seven months for posterior occlusion to establish in a retrospective single-centre study of 225 direct composites placed ‘high’ and that the required tooth movement occurred in 100% of patients.11 Hemmings et al performed a retrospective study of 102 direct composite restorations cemented ‘high’ on worn anterior teeth with a mean establishment of the posterior occlusion of 4.2 months and the occlusion re-established in 94%.9

Chana et al retrospectively evaluated the multi-centre survival of 158 cast gold veneers with little amounts of preparation cemented with Panavia Ex resin (Kuraray, Osaka, Japan).2 Of these veneers 12% were placed high, there were no failures and there was no statistical difference between this approach and others to create space for restoration including: orthodontic treatment, tooth preparation, crown lengthening surgery (followed by tooth preparation), use of retruded contact position and using a removable cast metal maxillary anterior occlusal platform. This showed that posterior metal veneers may be the ideal restoration for replacing worn molars in those patients who do not have an aesthetic concern for their appearance, as their success rates are the same as other methods to intrude teeth and longevity is the same as veneers that conform to the occlusion.

Gough and Setchell conducted a retrospective single-centre study of 50 treatments in 45 patients provided with an appliance used to produce localized occlusal space by relative axial tooth movement and the success in achieving this movement was 96%.3 Only one appliance did not succeed in producing the required movement and it was found that patient compliance was good in 94% of cases, satisfactory in 4% and poor in only 2%. The patients with poor compliance requested removal of their fixed appliances.

The occlusion is generally quoted as re-establishing on average after 6 months but this can take up to 18 months.8

Discussion

In the case described the maxillary first molar teeth were successfully restored with ‘high’ direct composites that cured the presenting sensitivity and have lasted two years so far. The patient adapted easily to the occlusal changes caused by the ‘high’ restorations and the surrounding occlusion successfully re-established within 4 months. This is longer than the mean time quoted by Anderson of 24 hours and may be because the bulk of composite was at least 2 mm thickness compared to the 0.5mm thickness castings placed by Anderson. Similar mean times have been quoted by Hemmings, Redman and Poyser.^9,10,11 The success rates for re-establishing occlusion range from 94–100%. The tooth movement observed in this case may have been due to intrusion of the teeth in contact, eruption/extrusion of the separated teeth, or a combination of both. In this situation, eruption may be defined as the outward movement of a tooth along with its supporting gingival-dento-alveolar complex, whereas extrusion is the outward movement of the tooth alone in its socket. This concept of extrusion means that these teeth may be intruded easily and quickly when put under an axial force. An assumption that the separated teeth moved predominantly by eruption, and not extrusion, can be made as these teeth did not intrude, as far as the patient was aware and on clinical observation, once they came into contact again. Dahl initially suggested the outward tooth movement which occurred in his experiments was due to eruption only.4 However, he later found that some extrusion was also at play.16

There are no studies examining the tooth movement that occurs once posterior composites have been placed ‘high’. In anterior ‘high’ restoration cases, the majority of tooth movement that ensues is outward of separated teeth and more eruptive potential exists in younger patients.

Only two of the studies presented in the literature review provided ‘high’ posterior restorations and appliances, and the others investigated ‘high’ anterior appliances and restorations. In the study by Gough and Setchell, these were placed as provisionals to create interocclusal space for a new definitive restoration after the occlusion had re-established.3 The advantage offered by placing high cast or composite restorations is that they can function as a conventional restoration after re-establishment of the occlusion and, theoretically, no removal and replacement is required unless the restoration fails, eg bulk fracture. In the studies performed by Poyser et al10 and Redman et al,11 it was observed that, in the cases in which the posterior occlusion had re-established, in 39% and 33% of these, respectively, only partial contact was achieved. However, these patients remained comfortable and able to function and so did not request any more posterior contacts to be provided. This shows that, when placing ‘high’ anterior composite restorations, the posterior occlusion may re-establish, either partially or completely. However, it is unclear in the case we describe above how the anterior contacts differed after re-establishment. Flowable or hybrid composites have been proposed for small to large posterior restorations.17 The previous restorations in this case failed as they were placed too thinly to provide sufficient strength in compression by conforming to the patient's occlusion. Other reasons cited for failure of composites include: variations in dentine structure, lack of enamel and polymerization shrinkage.5

The ideal characteristics of posterior composites for intrusion restorations are summarized as follows:18

A slight shade mismatch between the composite and tooth can be an advantage as finishing and monitoring are facilitated. Currently, a wear rate of less than 50 microns over 18 months is the standard required for posterior composites, but most modern products wear at a rate of 10–30 microns per annum.19

Resin composites are stronger in compression compared to their shear or tensile strength. The method in which composite resin was bonded in this case created opposing occlusal contacts which put the composite restorations under compression forces and thus reduced the likelihood of composite fracture.

The strength of resin composites is directly related to the filler content and, where the filler content is greater than 65% by volume, the fracture resistance is high. Larger filler particles accompany higher filler contents and this leads to higher abrasion and attrition resistance. The filler content of Point 4 composite is 57.2% by volume, which may account for the level of wear seen in Figures 9 and 10. These figures showed that most of the wear occurred on the palatal surface of the occlusal tables and this is probably because these areas were involved in tooth contacts.

Conclusion

Direct composite resin restorations are a conservative, predictable and an effective method to help generate occlusal space for restoration of teeth. They offer a range of applications in restorative dentistry and orthodontics. Other than its uses as a material for fillings and bonding, composite resin may be used on posterior teeth to produce relative intrusion movement. This application is varied in its use, depending on the clinical presentation of the patient, the number of teeth involved and the clinical management goals.

Composite resins can be bonded to posterior teeth and can remain in situ if placed in sufficient bulk to provide strength in compression for function. Composite restorations placed ‘high’, greater than or equal to 2 mm in depth, which act as intrusion appliances, put the material in compression, which optimizes its mechanical properties. If the composite remains in place as the predicted intrusion movement occurs, the occlusion will re-establish.

This process can take between 6–18 months, but in this case took only 4 months, which is similar to that in anterior toothwear direct composite cases. The composite may then act as a long-term restoration requiring repair or replacement only when necessary.

Patients should be fore-warned that composite restorations may chip and may therefore require occasional repair. However, this is a small price to pay and a negligible nuisance compared to using destructive irreversible methods to restore worn teeth that have adequate enamel still available for bonding.

Good success rates have been shown for direct anterior composites placed ‘high’ but research is required into long-term success and survival rates of fixed intrusion composite devices on posterior teeth. Double-blind randomized controlled trials investigating the longevity of different posterior composites used as fixed intrusion restorations are also required. The disadvantage that the composite wears is minimal compared to using cast restorations which require tooth preparation, because preparing teeth for traditionally prepared crown and bridgework has a risk of developing periapical pathology. An alternative to this is to bond gold veneers ‘high’ with resin cement on minimally prepared posterior teeth with chamfers for seating and location only. However, the composite solution is totally reversible and the fact that the composite can simply be replaced or repaired if worn once the occlusal compensation has occurred provides an excellent fallback position. The new composite will wear less quickly as sufficient space will have been created through previous intrusion movement to conform to the patient's occlusion. The amount of composite that wears could also be reduced by placing composites on multiple other worn teeth, which will distribute occlusal forces through more teeth. This is particularly relevant in generalized toothwear cases.

Placement of direct posterior composites is not complex or particularly demanding. However, it requires an accurate technique to optimize results and to meet patients' demands.