Edited by [UK] Subir Bannerji, [UK] Shamir Mehta, [Netherlands] Niek Opdam, [Netherlands] Bas Loomans
Indirect Composite Resin Restoration
Numerous literature sources describe various protocols for treating tooth wear with indirect composite resin restorations, with varying extents of restorations and tooth preparation levels.
Satterthwaite combined direct and indirect techniques, creating several contiguous palatal composite veneers (palatal contours fabricated in the laboratory) on upper anterior teeth, with the labial side treated with direct resin composite material to address upper anterior tooth wear. The long-term treatment plan involved subsequent crown restoration. Mehta et al. used resin onlays made indirectly for treating anterior tooth wear.
Tooth preparation was limited to removing any sharp line angles (to reduce stress concentration after bonding) and preparing beveled/lightly scooped margins to help the technician determine the end line. For the affected teeth, as suggested by Patel, the prepared teeth were sandblasted with 20μm aluminum oxide. After bonding, the margins of the indirect resin restoration could be further strengthened by adding composite resin, enhancing the bond strength between the indirect restoration and the remaining tooth hard tissue. Acevedo et al. initially restored the worn anterior dentition with direct composite material, then replaced it with indirect resin veneers.
Precise tooth preparation was achieved using a PVS silicone guide as a reference (following Magne’s recommendation); depth grooves were prepared on the labial surface, and the preparation depth was marked with a pencil. Finally, the indirect resin veneers were bonded using traditional methods, with the restoration being sandblasted and silanized to ensure marginal fit. A recent clinical trial comparing indirect and direct composite resin restorations for severe tooth wear in first molars showed a higher incidence of fractures with indirect restorations compared to direct ones. However, indirect restorations had a lower wear rate.
When using combined palatal and labial veneers to restore anterior tooth wear, there is a problem with the contact surface between the palatal and labial veneers. This can be avoided if the entire defect on both sides is restored directly. It has been reported that using layered restoration techniques directly can lead to more bonding issues when sandblasting and silanizing are applied.
With advancements in material technology, better results may be achieved using indirect resin composites. Indeed, case reports have documented the use of CAD/CAM to create high-density composite restorations for minimally invasive treatment of severe tooth wear.
Cast Metal Restoration
The use of cast metal restorations for anterior tooth wear is not a recent concept. In fact, in 1975, Dahl et al. used cobalt-chromium alloy to create fixed palatal appliances for removable anterior patients, which were then replaced with traditional cast restorations after reconstructing the posterior occlusion. However, the use of this technique should consider the following factors: 1) Removing metal in some anterior tooth wear cases, using metal palatal veneers can be a long-term restorative treatment method. Type III gold alloy and nickel-chromium (Ni-Cr) alloys are the most commonly used alloys for fixed metal bonded restorations.
For anterior teeth, when preparing for metal palatal veneers (also known as palatal backs), the preparation should remove undercuts and cover all remaining palatal tooth tissue, extending to the incisal edge to enhance retention, aid seating, and increase resistance to shear loads. Depending on the metal material, the occlusal clearance should be 0.5-1.5mm. For cases requiring occlusal elevation, a very conservative approach can be used to reduce the amount of tooth tissue preparation, and some cases may require some preparation of the palatal side to obtain occlusal clearance. In the former case, given the higher fracture resistance of cast metal restorations (compared to composite resin materials or dental ceramics), one can more confidently place the restoration on the palatal side of anterior teeth, especially for patients with high occlusal loads. The shoulder margin of the affected tooth can be polished with a chamfer or shallow scoop bur, or the cingulum can be prepared, but the incisal edge should be avoided. Selecting an appropriate (rigid and accurate) impression tray and high-quality impression material, and achieving accurate impressions through proper gingival retraction, is crucial. Occlusal records should be taken when necessary to facilitate the working model.
Type III gold restorations (Figure 1) require heat treatment of the tissue surface, which can be sintered at 400°C for 4 minutes in an air furnace to form an active oxide layer, or the surface needs to be tin-plated to increase surface activity and enhance the bond with resin adhesives. Wada proposed combining sandblasting and tin plating to maximize the bond strength of resin to gold alloy. Tin plating not only roughens the surface, improving micromechanical retention, but also enhances chemical bonding by forming hydrogen bonds between the resin cement and tin oxide. All metal restorations should be sandblasted with 50μm aluminum oxide on the tissue surface (for Type III gold alloy restorations, oxidation must be completed before sandblasting).
After obtaining the metal veneers, they can be tried in with a calcium hydroxide paste, such as Dycal (Dentsply Ltd, Surrey, UK). Creating auxiliary bonding metal posts helps with the try-in/bonding of metal palatal veneer restorations; the metal posts can be easily removed with a diamond bur and polished with a set of discs after bonding.
Before bonding, effective isolation should be performed, ideally using a rubber dam. The bonding surface of the restoration should be cleaned with air abrasion or non-oil pumice and re-sandblasted if necessary. Veneers should be bonded one by one, with interproximal matrices protecting adjacent teeth during pre-treatment of the tooth for bonding. Using an appropriate metal primer is crucial for achieving effective resin bonding. The passivation effect of metal restorations, often mentioned in the literature as the restoration showing through the tooth tissue, can cause the tooth color to appear “gray” or “metallic,” which is a common problem with such restorations. To some extent, this can be mitigated by using opaque resin cement or applying a shade-matching veneer on the labial side. Bonded onlays can also have aesthetic issues with metal exposure, and in-mouth sandblasting techniques after bonding may help reduce the restoration’s gloss and improve aesthetics.
Eliyas and Martin reported two cases using gold alloy palatal veneers to restore canine guidance (upper canines treated with metal palatal veneers, remaining upper anterior teeth treated with direct composite resin restoration). This case applied Dahl’s concept for restoration, with the canines’ incisal edges also being restored. In this situation, a long and shallow beveled chamfer should be prepared on the incisal edge before bonding the veneer, using dry gingival retraction cord. After bonding the metal veneer, the part of the veneer to be covered with composite resin for shade matching and incisal edge restoration should be sandblasted, coated with a metal conditioner, and then filled with shade-matching resin material and/or resin cement (such as Panavia 2.0F, Kuraray, Japan), finally restoring the incisal edge with appropriate composite resin. This method is also applicable to restoring worn posterior teeth.
Bonded All-Ceramic Restoration
Dental ceramics can be classified according to their microstructure, from veneer ceramics to polycrystalline ceramics. Polycrystalline ceramics include:
1) Glass ceramics/veneer ceramics (feldspathic porcelain and leucite);
2) Filled glass ceramics (lithium disilicate and alumina);
3) Crystalline ceramics infiltrated with glass particles (alumina-magnesia and alumina-zirconia);
4) Polycrystalline ceramics (polycrystalline alumina).
Although veneer porcelain has excellent aesthetics and can be bonded to enamel and dentin using micro-mechanical forces through acid etching, they have lower flexural strength, fracture toughness, and fracture strength.
Therefore, they need to be combined with metal or high-strength ceramics to ensure the necessary strength of the final restoration (especially when applied to high occlusal load areas). Vailati et al. reported a “sandwich” technique using labial porcelain veneers combined with palatal direct resin filling for upper anterior tooth wear restoration. According to the authors’ description, the tooth preparation included preparing a scooped shoulder margin along the gingival curve, rounding off all line angles, immediately sealing any exposed dentin, and preparing the interface for the palatal resin veneer. For bonding the restoration, feldspathic veneer porcelain veneers must be etched with hydrofluoric acid, placed in ethanol for ultrasonic cleaning, dried, coated with three layers of silane, dried in an oven at 100°C for about 1 minute, and finally coated with resin cement.
The tooth should be air-abraded and bonded with preheated composite resin cement under rubber dam isolation. If the patient has a tendency for parafunctional movements, a post-operative night guard with minimal trauma should be made for them. The dentin-bonded crown technique is also a good method for treating lower anterior tooth wear. The dentin-bonded crown is an all-ceramic crown bonded with resin cement to dentin (and available enamel) and is retained by adhesives and micro-mechanical forces.
In fact, a dentin-bonded crown can be understood as a special type of porcelain veneer that completely covers the entire tooth surface and is retained by bonding to the tooth tissue. Burke published a case report describing the use of a dentin-bonded crown made of feldspathic porcelain (treated with hydrofluoric acid) for a patient with severe tooth wear due to bulimia. The case required minimal tooth preparation, obtaining about 1.0mm of occlusal clearance on the labial side, and preparing a chamfer shoulder at the cervical margin.
Dentin-bonded crowns have excellent aesthetic advantages (because they do not have a metal base or opaque porcelain layer) and can achieve good bond strength to tooth tissue, resulting in good marginal seal of the restoration, even when there is a significant loss of tooth hard tissue, especially when the remaining tooth structure is excessively tapered. It has been reported that the fracture resistance of dentin-bonded crowns is also satisfactory. However, for patients with bruxism or significant parafunctional movements, the fracture of dentin-bonded crowns remains a problem. This restoration method is costly and time-consuming and is not suitable for cases where tooth preparation needs to extend below the gingiva.
It has been suggested that the presence of an enamel cervical ring at the gingival margin is key to increasing the relative strength of such restorations.
In some tooth wear patients, high-strength zirconia core all-ceramic crowns have also been reported. The authors prepared the affected teeth with a 360° shallow scoop shoulder at the gingival or supragingival level, opened the contact surfaces, and prepared axially to achieve a 5°-10° taper, without reducing the occlusion.
The inner crown was milled using CAD/CAM to ensure a porcelain layer thickness of >1mm, followed by layering with LAVATM porcelain powder. The crown design should aim to minimize tensile and non-axial loads, with shallow, uniform anterior guidance (mandibular protrusion) and a thick incisal edge. During semi-adjustable try-in, the inner surface of the restoration was roughened by sandblasting, and finally bonded with composite resin cement. Given that zirconia is not etchable with hydrofluoric acid, the bond with bisphenol A dimethacrylate (BisGMA) resin cement may be less reliable. Using resin cement containing 10-methacryloyloxydecyl dihydrogen phosphate (10-MDP) as the functional monomer can improve the bond strength.
Traditionally Retained Restorations
Dental ceramics can be classified according to their microstructure, from veneer ceramics to polycrystalline ceramics.
Polycrystalline ceramics include:
1) Glass ceramics/veneer ceramics (feldspathic porcelain and leucite);
2) Filled glass ceramics (lithium disilicate and alumina);
3) Crystalline ceramics infiltrated with glass particles (alumina-magnesia and alumina-zirconia);
4) Polycrystalline ceramics (polycrystalline alumina).
For treating anterior tooth wear, traditionally retained indirect restorations are generally not the first choice. However, for some patients who have initially achieved good mid-term results with direct bonded composite resin materials, or when the patient agrees to this type of treatment, traditional restoration methods can be considered for tooth wear.
When using traditional full-crown restoration to treat tooth wear, it is important to consider how to achieve a high success rate through correct clinical procedures.
Although detailed information on traditional restoration options such as crowns, inlays, and fixed bridges can be found in any reputable textbook on fixed and removable prosthodontics, we still emphasize the importance of focusing on precision, including preparing accurate diagnostic wax-ups, making precise silicone rubber/acrylic resin guides to assist with tooth preparation, with the aim of ensuring the best aesthetic and functional results from the restoration material while preserving as much tooth tissue as possible.
Generally, noble and non-noble metal alloy restorations have a thickness of 0.7-1.5mm, while metal-ceramic restorations require 1.5mm of preparation on the labial side and 2.0-2.5mm on the incisal edge to ensure the necessary aesthetics, function, and mechanical strength.
For tooth wear patients, additional considerations when using gold-ceramic crowns include:
1) The occlusal contact point in the intercuspal position (ICP) (if possible) should be on the metal, as metal causes less wear on natural teeth compared to porcelain;
2) The gold-ceramic junction should be kept away from the occlusal contact point to avoid porcelain fracture under bending and shear stresses;
3) Using a metal cervical margin to increase the strength of the metal base.
The tooth neck should be prepared with a 0.7mm shallow scoop shoulder, which can reduce the cutting of hard tissue at the cervical margin compared to a 1.2-1.5mm cervical shoulder.
To achieve a successful treatment plan, it is crucial for clinicians to have a thorough understanding of the scope of all treatment methods before starting local anterior tooth wear restoration, so that they can choose the most suitable method.
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