Complex Esthetic and Functional Rehabilitation with an Additive, Minimally Invasive Restorative Approach

Treatment of extensive tooth wear can pose particularly complex challenges to the clinician. This is primarily due to the difficulty in determining the source of what is often a multifactorial etiology, as well as determining the diagnosis of tooth wear and the definitive management of the patient. Patients may seek initial dental care in an attempt to improve the esthetic appearance of their smile without fully comprehending the source, complexity, or problems associated with tooth wear. Typical symptoms that present with tooth wear include: poor esthetics; chipping/thinning and/or fracture of teeth, particularly incisal edges; dentinal hypersensitivity; reduced occlusal vertical dimension (OVD); and minimal tooth height. Other signs of tooth wear are: classic cupped erosive defects on occlusal surfaces and incisal grooving; broad concavities within smooth surface enamel; loss of enamel and dentinal exposure; and restorations “raised” from tooth structures. Additionally, the patient may have concerns regarding the financial affordability of treatment because of the potentially complex nature of the problems.

The pathologic loss of tooth structures may be caused by a single factor or, more commonly, from multiple etiologies, including the following:

Erosion: the progressive loss of tooth substance by chemical processes that does not involve bacterial action. This may be from an extrinsic source such as unbalanced dietary habits with high consumption of acidic food and drinks as well as abnormal intrinsic acid production from bulimia nervosa, gastroesophageal reflux disease (GERD), and hiatus hernia. Other adjunctive factors may include insufficient saliva flow rate or buffer capacity and saliva composition changes induced by various diseases, medications, and aging.

Abrasion: an abnormal wearing away of the tooth substance by causes other than mastication, eg, toothbrushing.

Attrition: the wear resulting from mastication or parafunction, limited to occlusal surfaces of the teeth.

Abfraction: the loss of tooth structure owing to biomechanical forces (flexion, compression, or tension) or chemical degradation; it is most visible as V-shaped notches in the cervical area of a tooth.

Historically, the management of patients presenting with extensive tooth wear was with the use of conventional fixed prosthodontics. This approach often involved preparation with crowns on the teeth where tooth structures were already compromised. This would increase the biomechanical risk to the dentition due to the reduction of tooth structures, which negatively impacts the structural rigidity of the teeth. Edelhoff and Sorenssen¹ found that 62% to 73% of tooth structure could be removed while undertaking the preparation to receive either a full-coverage all-ceramic crown or porcelain-fused-to-metal crown. The minimal height of teeth present and after preparation would yield insufficient retention or resistance form for conventional crowns. An axial height of 4 mm is required for sufficient retention form, and in order to obtain the required axial height and adequate retention form it may be necessary to carry out osseous crown-lengthening procedures or perform subgingival preparation.²

Furthermore, a conventional approach could result in a loss of pulpal vitality of the teeth. Teeth requiring fixed prostheses have a 6% to 11% requirement for endodontic treatment. This approach is more invasive and is irreversible.^3,4

With the development of adhesive bonding, clinicians have the means of restoring a patient’s dentition in a much more conservative manner using an additive approach. Advantages of adhesive restorations include the following: retention form and resistance form are irrelevant; enamel bonding is predictable; there is decreased endodontic risk; remaining tooth structure is maximized; and the approach is conservative and minimally invasive.

This case will describe the concepts involved in a complex rehabilitation using both direct and indirect restorations with minimal biological risk to the patient.

Clinical Case Overview

The patient, a 41-year-old woman, presented with her chief complaint being the short nature of her teeth and resultant poor esthetics. She was particularly concerned about the extensive loss of tooth structure and the chipping of her teeth (Figure 1).

A comprehensive history and examination was performed. The patient had a history of bulimia nervosa, a condition that consists of recurrent episodes of compulsive binges (ie, consumption of large amounts of food) with or without self-induced vomiting or purgation. Due to the exposure of the oral environment to stomach acid, this resulted in erosion of all maxillary teeth and the mandibular anterior teeth.

The patient reported occasional bilateral masseter muscle tenderness. She realized her teeth had been wearing and her bite had been changing over the past several years. It appeared that the attrition was primarily due to chemical erosion rather than functional forces. The functional symptoms of clenching and muscle tenderness were secondary to the unstable occlusion that resulted from the erosion.

There was no decay found at the time of the clinical examination, but a number of fillings were defective; no periodontal problems were noted. Intraorally, the tooth surface loss was generalized, involving all teeth in both arches and extending into dentin anteriorly, where there was thinning and chipping of the incisal edge resulting in reduced clinical crown height.

Diagnosis

The diagnosis of tooth wear requires a need to identify the factor(s) contributing to the condition, which may be difficult due to what is often a multifactorial etiology.⁵ Identifying these factors is important in order to preserve the remaining dentition and improve the long-term prognosis of any restorative treatment completed.

The patient was diagnosed to have tooth wear due to tooth erosion that had occurred when she was bulimic, with a secondary etiology of bruxism. Chronic exposure to acidic substrates had led to exposure of the dentin and chipping of the teeth, and the condition was exacerbated by the patient’s parafunctional habits.

Patients that present with generalized tooth wear often do not display a loss of OVD because the loss of tooth surfaces occurs at a slow rate, which allows time for alveolar compensation. However, in cases where the surface loss is active and rapidly progressing this may lead to loss of OVD, as alveolar compensation may not be keeping up at the same rate.⁶ In occlusion, the patient in the present case appeared to have a decreased lower face height due to a loss in OVD, which had not been fully counteracted by alveolar compensation (Figure 2).

Following an evaluation of the existing OVD and freeway space, patients presenting with generalized wear may be assigned to three categories, according to Turner and Missirlian7:

Category 1: excessive wear with loss of OVD

Category 2: excessive wear without loss of OVD, but with space available for restoration

Category 3: excessive wear without loss of OVD, but with limited space for restoration due to encroachment on freeway space

The patient presented with Category 1 generalized tooth wear. The objectives of treatment were to:

- improve dentofacial esthetics

- restore OVD and improve occlusal function, establishing a stable position of maximum intercuspation with bilateral simultaneous occlusal contacts

- restore and protect structurally compromised and exposed dentinal teeth structures with minimal- or no-preparation designs prevent further tooth erosion

Treatment

The extent of the damage to the patient’s dentition necessitated a rehabilitative approach. However, in areas where tooth wear is minimal and where the patient has no concerns, management of the situation should consist of a preventative approach that includes patient education and advice. Monitoring can be carried out using silicone indices, photographs, and study models. Tooth wear prevention depends on the compliance of the patient with dietary modification, use of topical fluorides, use of occlusal splint, medical assistance, and other treatment considerations that extend beyond the scope of this article. The key to success is to determine the primary etiological factor and institute an appropriate preventive program to deter further deterioration. This is also important when restoring the dentition, as treatment can fail if the causes of tooth wear are not addressed.

The extraoral examination allowed assessment of the amount of incisal display while the upper lip was relaxed (Figure 3) and while the patient was talking and smiling (Figure 4). This revealed that there was insufficient display of the teeth and that there was potential to lengthen the incisal edges of the maxillary teeth.

Following a comprehensive intraoral clinical assessment, including diagnostic photographs, study casts were taken and mounted on a semi-adjustable articulator. A diagnostic wax-up was undertaken (Figure 5 and Figure 6), with the requested esthetic changes communicated to the dental ceramist. The occlusal prescription included contouring the wax build-ups to provide bilateral, even contacts in retruded contact position. Furthermore, the plan included providing anterior guidance, a canine-guided occlusion in lateral excursive, and protrusive mandibular movements with posterior tooth separation on dynamic mandibular movements.

Upon completing the work-up, the treatment plan that was decided upon in consultation with the patient included the following:

Mandibular: direct resin composite build-ups on teeth Nos. 22 through 28 and coverage of dentinal-exposed areas on teeth Nos. 19, 30, and 31

Maxillary: no-preparation restorations on teeth Nos. 2 and 5 through 12; minimally invasive onlay preparations on previously restored teeth Nos. 3, 14, and 15

Mandibular Direct Composite Resin Build-Ups

Teeth Nos. 22 through 28 were prepared by abrading with 27-micron aluminum oxide, and a total-etch adhesive technique (OptiBond™ Solo Plus, Kerr Dental, www.kerrdental.com) was used. Placement of resin composite (Herculite^® Ultra, Kerr Dental) was accomplished with the aid of a silicone matrix formed from the palatal anatomy established from the diagnostic wax-up (Figure 7). Resin composite was carefully adapted in layered increments, no greater than 1.5 mm per increment. The use of the matrix allowed the placement of composite to form the palatal contour and incisal length of the teeth as planned from the diagnostic wax-up (Figure 8). This would enable minimal adjustment at completion of the restorations.

Hemmings et al⁸ used direct composite to restore anterior worn teeth with a success rate of 89.4% over a mean 30-month follow-up period. Poyser et al⁹ also found only a 6% complete failure rate of composite restorations on worn lower anterior teeth over a 2.5-year follow-up period. The main causes of failure were due to the composite wearing away over time and marginal discoloration. The evidence to support the use of direct resin for tooth wear is promising. The conservative nature, cost-effectiveness, and reparability make direct composite resin an attractive material for treatment of tooth wear.

Maxillary Indirect Restorations

Prep-less or additive restorations were planned for the majority of the maxillary teeth, as these were in a lingualized axial position and, furthermore, needed to be lengthened for ideal esthetics. Hence, there would be no need to prepare the teeth to achieve the desired outcome. Additionally, by not preparing the teeth, the restorations would be bonded mainly to enamel, away from areas that had dentin exposure on the incisal/occlusal surfaces.

The success and predictability of bonding to enamel are major factors in terms of longevity and durability of the restorations.¹⁰ In a 12-year study by Gurel et al of 583 veneers, 42 (7.2%) veneers failed, with those bonded to dentin and teeth with preparation margins in dentin approximately 10 times more likely to fail than those bonded to enamel.¹¹

In the present case, for teeth that were previously restored, the restorations were removed and the preparations completed to allow a path of insertion for onlays (Figure 9). An impression was taken of the preparations and bite registration at the planned occlusal vertical dimension. A bonded functional esthetic prototype (BFEP) was spot-etched and bonded into position utilizing putty indexes made from the diagnostic wax-ups (Figure 10). This allowed the patient to assess a “trial smile” prior to completion of the final restorations (Figure 11). This transitional stage provides the patient time to accept the proposed new smile and also to assess the occlusal changes from the increase in OVD and occlusal stability over a period of weeks or even months.

The patient had initial reservations about the length of the provisional prototypes, which is often the case for patients who undergo a major transformation. Hence, patients should be given a period of time to get accustomed to their new look before a decision is made on the final length of the teeth.

The provisional restorations were removed with careful attention given when removing areas that had been spot-etched and bonded with a bur. The remaining tooth structures were air-abraded with 27-micron aluminum oxide.

The final restorations were fabricated with pressed lithium-disilicate materials (e.max^®, Ivoclar Vivadent, www.ivoclarvivadent.com) using a B1 LT ingot (Figure 12). The lithium-disilicate restorations were individually placed to assess marginal fit and contact points. The restorations were then placed with a clear try-in gel to display for approval prior to permanent cementation.

Each restoration was etched with 4.5% hydrofluoric acid for 20 seconds, followed by cleaning of the chemical salts by rinsing and insertion into an ultrasonic bath with distilled water. After air-drying, each restoration was then silanated for more than 60 seconds.

Because the ceramic restorations were thin, and had minimal retention due to minimal or no preparation, the cementation process required that the restorations be adhesively bonded with resin cement. A strong, durable resin bond provides high retention,¹² improves marginal adaptation reducing microleakage,¹³ and increases fracture resistance of the restored tooth and restoration.¹⁴

The teeth were adhesively bonded with a total-etch technique (OptiBond Solo Plus), and the restorations bonded with a light-cure resin cement (NX3 Nexus^®, Kerr Dental) for the anterior teeth, and a dual-cure resin cement (NX3 Nexus) for the posterior onlays, which were thicker in cross-section. The author prefers to initiate veneer cementation using the central incisors as a starting point, which allows correct orientation, symmetry, and balance. After the central incisor veneers were placed, the subsequent left- and right-side veneers were then placed using the same technique.

The restorations were then adjusted and finished with ceramic polishing and finishing techniques. The margins were finished into an “infinity margin” (Figure 13). Once the margins were no longer detectable with an explorer, they were polished with rubbers and diamond polishing pastes. The occlusion was evaluated and adjusted in centric occlusion, lateral and protrusive movements, and, finally, in the chewing envelope. Due to the patient’s nocturnal bruxism habit, a full maxillary occlusal splint was fabricated and careful instructions on its use were given.

Figure 14 provides a retracted view of both the maxillary and mandibular final restorations, and Figure 15 shows the patient’s smile with the completed restorations.

Conclusion

The aim of managing a worn dentition should be to determine the etiological factors and institute an appropriate preventive program to protect the remaining tooth structures while restoring function, occlusal stability, and esthetics. Treatment planning entails understanding the etiological factors and includes the planning of the steps involved with the reconstruction of the dentition to meet both functional and esthetic requirements. A minimally invasive or prep-less approach is preferred, and the use of direct and/or indirect restorations can be utilized in reconstructing the lost tooth structures in an additive approach.

ACKNOWLEDGMENT

The author thanks Mr. Brad Grobler (dental ceramist) for the technical and artistic expertise of restorations included in this article.

REFERENCES

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ABOUT THE AUTHOR

Christopher CK Ho, BDS (Hon), Grad Dip Clin Dent, M Clin Dent
Private Practice, Sydney, NSW, Australia