MIH is usually an esthetic problem in affected anterior teeth due to the lower degree of hypomineralization.1 In the molar region, however, posteruptive enamel breakdowns with subsequent exposure of the dentin (especially in the area of the cusp tips)2 may occur due to the masticatory functional stress. This situation may require immediate intervention.
Several options are available for the restoration of hypomineralized teeth, depending on various factors: the age of the patient, their compliance, the extent and quality (hardness) of the tooth structure, the severity, the extent of sensitivity, and the localization of the affected teeth. They all influence the choice of material to be used for the restoration.1
In particular, special attention must be paid to the compliance of children for the choice of treatment option. Compliance is often reduced in children with severe MIH.3 If there are also pain symptoms, solutions for quick and easy temporary restoration of the teeth must be found. Direct restorations are preferred compared with indirect restorations due to their wide range of applications, their protection of tooth structure, their reparability, and the fact that they are more time- and cost-efficient. In the Würzburg concept4 presented in Chapter 8, the following options for direct restorative techniques are noted among the restorative variants: temporary restoration (short-term) with glass-ionomer cement (with or without orthoband) (Therapy C) and permanent restoration using composite (Therapy E) (Fig 12-1).
These two options of direct restorative procedures are explained in detail next.
As already described in detail, MIH is a qualitative enamel defect. Consequently, affected enamel areas exhibit special features that must be considered in the context of restorative therapy. Hypomineralized enamel shows a lower mineral and a higher protein content as well as higher porosities and a significantly reduced microhardness of the hard tissue. The prismatic structures are less dense and their interfaces broadened.5
This is reflected in a deterioration of the mechanical properties of the tooth – its surface hardness, wear behavior, and fracture toughness are reduced – and in the bonding properties of dental materials,6 ie, stable micromechanical interlocking is not possible. This results in the risk of marginal fractures in composite fillings if the preparation margins are not extended into sound enamel areas (Fig 12-2). This becomes particularly evident as soon as masticatory forces stress the vulnerable area. In most cases, the tooth fractures around a more or less intact filling (which is extremely rare in conventional adhesive dentistry), or chipping fractures occur on cusps carrying the masticatory force7,8 (Fig 12-3).
Glass-ionomer cements (GICs have traditionally been widely used in pediatric dentistry due to their ease of handling.9 They consist of a mixture of glass powder and polyalkenoic acids and harden in an acid-base reaction. The ionic bonds of the carboxylate groups create an independent adhesion to the tooth structure. Conventional, highly viscous, and resin-modified glass-ionomer cements are available.
The relatively simple pretreatment of the cavity compared with composites is advantageous. No complex adhesive technique is required. In addition, extensive conditioning and drying steps can mostly be omitted and the cement can be applied in bulk-fill technique. The often-described fluoride release, whose clinical efficacy, however, is discussed quite controversially, seems to play a minor role. The main disadvantage of conventional GICs is their high sensitivity to drying out and moisture supply during the setting phase.10,11 This problem can be avoided by covering the restoration with a surface coating or varnish after application. Other shortcomings are the low abrasion resistance and the low flexural strength,12,13 which can lead to marginal defects and isthmus fractures (especially in Class II fillings).
In the case of resin-modified or light-curing GICs, methacrylate groups are added to the polyacrylic acids of the conventional GICs.14 This extends the working time. These cements have the advantage of controllable curing and also exhibit improved mechanical properties. These include higher fracture strength and lower sensitivity to moisture.
High-viscosity GICs, as a further development of conventional GICs, can be plugged. Their higher viscosity compared to conventional GICs is attributed to the addition of polyacrylic acid into the powder, in addition to the finer grain size. The setting mode is not changed compared with the conventional GICs.14
The generally described disadvantage of the less satisfactory esthetic appearance of GICs (due to the usually high opacity) is negligible and of minor importance when restoring MIH molars. In fact, shaded materials tend to be favored because they can be easily distinguished from the enamel (Fig 12-4).
Glass-ionomer cements are ideally suitable as an initial and temporary restoration of MIH molars that have not yet erupted completely into the oral cavity, as moisture control is not possible in these cases3 (Fig 12-5). In addition, this material is used when the child shows insufficient compliance and a filling therapy is indicated, but pain symptoms are present and make it advisable to take a step back from the indicated permanent restoration (complex adhesive treatment) to a temporary restoration. The sometimes very rapid destruction cycle of such teeth can be stopped, further loss of tooth structure can be prevented, and the hypersensitivity can be reduced to a tolerable level.15 Thus, at this point valuable time can be obtained for the patient. If even a glass-ionomer cement restoration is not possible due to lack of compliance and pain symptoms are present, a resin-modified glass-ionomer cement sealing varnish can also be used temporarily (Clinpro XT Varnish, Fa. 3M, Seefeld, Germany), which is easy to apply15 (Fig 12-6).
In the long term, however, fillings with glass-ionomer cement should then be replaced by definitive fillings, as the replacement of large, masticatory-loaded areas with these materials cannot be successfully realized due to their low flexural strength and low abrasion stability. After complete eruption of the teeth, composites are a good therapeutic option for small to medium defects.16
Glass-ionomer cement fillings that have already been placed can then be reduced for a filling beneath the further adhesive restoration.7
Before applying the cement, the tooth should be cleaned – as much as possible. The material can then be applied to soft but non-carious dentin without further preparation. Only a short time window of isolation is required for this (Fig 12-7).
Restorations made of glass-ionomer cement can be supported by orthodontic bands if required, which can be used to protect the teeth from fractures and chemical and physical influences.17
Often, an orthodontic separator must be inserted in advance to loosen the contact point to the neigboring second primary molar and to open up the required space for the exact positioning of the band. The upper part of the rubber remains above the contact point, while the lower part is not visible between the teeth. The separating effect may cause local discomfort. Hard as well as sticky foods should be avoided during this short phase in order to avoid an increase in pressure and to prevent possible food-related removal of the gum. The separator should be placed at least 24 hours before application of the orthodontic band and subsequent placement of the filling. Figure 12-8 shows the step-by-step procedure for a patient.