Preliminary Resin Infiltration of Hypomineralised Enamel for Posterior Indirect Adhesive Restoration: An Innovative Approach

ABSTRACT

Hypomineralised enamel presents a significant challenge for resin bonding due to its altered mechanical and structural properties. Our innovative clinical approach of resin infiltration prior to the bonding of a posterior indirect adhesive restoration aims to preserve dental tissues, reduce post‐operative sensitivity, and strengthen the supporting enamel. A 14‐year‐old male experienced cold‐induced pain from his maxillary left first permanent molar (26) affected by molar incisor hypomineralisation (MIH). Resin infiltration (Icon, DMG) of the remnant hypomineralised enamel after tooth preparation was performed before the bonding of a lithium disilicate glass–ceramic restoration, which avoided extending the margin sub‐gingivally. The six‐month follow‐up confirmed satisfactory results: an optimal marginal adaptation without visible leakage, an absence of dental sensitivity, and satisfactory aesthetic appearance.

Summary.

• The resin infiltration of hypomineralised enamel prior to the bonding of a posterior indirect adhesive restoration is an innovative approach aimed at preserving dental tissues, reducing post‐operative sensitivity and strengthening the areas of hypomineralised enamel supporting the restoration.

1. Introduction

Molar‐incisor hypomineralisation (MIH) presents as demarcated opaque enamel lesions with decreased mineral density affecting at least one first permanent molar (FPM), often the permanent incisors, and less commonly, other primary and permanent teeth can be affected by similar lesions [1]. The European Academy of Paediatric Dentistry (EAPD) agreed on MIH diagnostic criteria characterised by at least one of these factors affecting one or more FPMs: demarcated enamel opacity, post‐eruptive enamel breakdown, atypical restoration (an opacity can be frequently noticed at the margins of the restoration), or atypical extraction due to MIH [2]. The worldwide MIH prevalence, varying according to location, is 12.8% (11.5%–14.1%) [3]. Histologically, mineral density in normal enamel increases from the dento‐enamel junction to the enamel surface, contrary to a reverse gradient in hypomineralised (MIH) enamel lesions [4]. Yellow brown lesions have lower mineral density compared to white lesions, with or without post‐eruptive enamel breakdown [5]. Clinically, numerous difficulties are involved in managing MIH‐affected teeth due to hypersensitivity, anxiety, potential difficulties with local anaesthesia, poor aesthetics, development of carious lesions with fast progression and failure of restorations [6, 7]. Posterior indirect adhesive restorations (PIAR) are recommended by the EAPD to treat severe hypomineralisation on FPMs [8]. Concerning preparation design/outline, it is recommended that all hypomineralised enamel should be removed before bonding in order to maximise the success of the restoration [8]. Adhesion to MIH‐affected enamel has reduced bond strength [9], further complicated in some cases when molars are not fully erupted, where the opacity extends sub‐gingivally, making isolation of a sound enamel margin for bonding difficult. Moreover, the practitioner cannot be sure that all hypomineralised enamel has been removed, as there is a transitional region between sound and hypomineralised enamel which may not be visible [4]. Resin infiltration and oxidative pre‐treatment increase microshear bond strength of resin composite to hypomineralised enamel [10]. We proposed, prior to cementing a PIAR, to infiltrate the marginal hypomineralised enamel with a low viscosity resin in order to reinforce the mechanical properties and increase the enamel bond strength. Resin infiltration will also reduce dentinal sensitivity [11]. Deep infiltration has been shown to be effective in the treatment of anterior MIH opacities [12, 13] but to the authors' knowledge, it is the first time that this protocol has been applied prior to a PIAR.

2. Case Description and Results

The patient was a 14‐year‐old male who suffered from cold‐induced pain from his maxillary left FPM (26). The Schiff Cold Air Sensitivity Scale (SCASS) was used to assess the subject's response to air stimuli [14]. The scale includes the following scores: 0. The subject does not respond to the air stimulus; 1. The subject responds to the air stimulus but does not request it to be stopped; 2. The subject responds to the air stimulus and requests it to be stopped or moves away; 3. The subject responds to the air stimulus, considers it painful, and requests it to be stopped. This tooth scored 3, affected by severe hypomineralisation with post‐eruptive enamel breakdown, had an atypical, non‐sealed resin composite restoration with marginal leakage and staining (Figure 1). Taking into consideration the severity and extent of the defect and following the therapeutic gradient, we chose to restore this tooth with a PIAR. The patient, a minor, and their legal guardians were informed and consented to the taking of dental photographs and the secondary use of the relevant healthcare data for educational purposes and scientific publication (use of the ‘One‐Shot’ form from the Bordeaux University Hospital).

FIGURE 1.

Initial occlusal view showing the hypomineralised lesion with an atypical resin restoration on tooth 16.

2.1. First Step

1. Local analgesia was given via buccal infiltration. Under rubber dam isolation, the pre‐existing restoration was removed and the marginal hypomineralised enamel was partially removed (Figures 2, 3, 4). The total removal of the marginal hypomineralised enamel would have created a sub‐gingival margin which was not possible to isolate completely. A margin with as little residual hypomineralised enamel as possible was prepared (Figure 5).

2. Treatment and optimisation of hypomineralised enamel. Before carrying out this infiltration protocol, the entire surface to be treated was deproteinised by applying a 5.25% NaOCl solution for 60 s and rinsing thoroughly with triplex water.

FIGURE 2.

Isolation of tooth 16.

FIGURE 3.

Removal of the atypical restoration.

FIGURE 4.

Removal of the altered tissues and shaping according to the principles of overlay preparation.

FIGURE 5.

Occlusal view of the prepared tooth; a hypomineralised lesion is observable in the mesio‐proximal band of enamel.

The resin infiltration protocol followed three steps:

• –Etching: 15% hydrochloric acid gel (Icon Etch, DMG, Hamburg, Germany) was mechanically agitated on the enamel for 2 min, rinsed for 30 s and dried slowly with triplex air (Figures 6 and 7);
• –Dehydration: ethanol (Icon Dry, DMG) was applied to desiccate the lesion (Figure 8);
• –Infiltration: the resin (Icon Infiltrant, DMG) was applied actively for 3 min and then light cured for 40 s. A second application was made for 1 min and then light cured again for at least 40 s (Figure 9). The hypomineralised lesion became translucent after infiltration (Figure 10).

• 3
  Immediately, Dentine Sealing Was Performed by Mean of Vigorous Application of the Resin Adhesive Before Light Curing

  • ○
    Impression and Temporisation: The shade for the PIAR was chosen (shade 3 M2). After the impression, a temporary restoration (Cimavit, Acteon Pierre Rolland, Merignac, France) was placed on the prepared tooth to protect it until the permanent restoration was fabricated in a dental laboratory (Figure 11).

FIGURE 6.

Etching with hydrochloric acid (Icon Etch, DMG) on the enamel is applied with a microbrush.

FIGURE 7.

The entire band of enamel is etched for 2 min.

FIGURE 8.

Dehydration of the enamel with ethanol (Icon dry, DMG).

FIGURE 9.

Resin infiltration (Icon infiltrant, DMG) for 2 min, photopolymerization for 40 s, followed by a new resin application for 1 min, then photopolymerization for 40 s.

FIGURE 10.

Occlusal view of the infiltrated tooth; the hypomineralisation is no longer visible.

FIGURE 11.

A temporary restoration (Cimavit, Acteon Pierre Roland) is placed on the preparation.

2.2. Second Step

The lithium disilicate glass–ceramic restoration (Figure 12) was carefully positioned on the prepared tooth. The fit and colour match were assessed positively. The dental surface was sandblasted with 30 μm alumina particles before applying 37% phosphoric acid for 15 s, then rinsed and dried (Figure 13). At the same time, the fitting surface of the ceramic PIAR was prepared:

• –Sandblasting with alumina (50 μm, Mini Sandblaster Airsonic, Hager&Wergen),
• –Hydrofluoric acid 5% (Porcelain Etch, Ultradent, Cologne, Germany) application for 20 s, then rinsing and drying (Figure 14),
• –Phosphoric acid application for 15 s (Figure 15),
• –Silane application for 1 min,
• –Adhesive placement (Scotchbond universal, 3MEspe)

FIGURE 12.

The lithium disilicate glass–ceramic restoration fabricated by the laboratory.

FIGURE 13.

The temporary restoration is removed and the tooth is isolated.

FIGURE 14.

Hydrofluoric acid 5% is applied on the PIAR for 20 s, then rinsed and dried.

FIGURE 15.

Phosphoric acid is applied on the PIAR for 15 s.

A resin bonding agent (NX3, Kerr, California, United States) was used, and the marginal excess was removed before photopolymerization under glycerine gel (Gradia Air Barrier, GC Tokyo, Japan) to ensure that the bonding resin composite polymerized without exposure to air (Figure 16). A polishing and finishing step of the dento‐prosthetic junction and a check of the occlusion finalized the procedure (Figure 17). A review appointment 1 week after the restoration was placed validated the aesthetic outcome and the score SCASS is 0. Six months later, the restoration showed satisfactory clinical characteristics (Figure 18).

FIGURE 16.

The tooth is photopolymerized under glycerin gel on each surface for 20 s, repeated three times.

FIGURE 17.

Final situation of the restored tooth.

FIGURE 18.

Control of the restoration 6 months later.

Two years later, the onlay was evaluated (Figure 19). The patient is currently undergoing orthodontic treatment. The evaluation was based on a clinical assessment [15] using the following criteria:

• –Aesthetic (surface lustre, surface staining, colour stability and translucency, anatomic form).
• –Functional properties (fractures and retention, marginal adaptation, wear, contact point/food impact, radiographic examination, patient's view).
• –Biological properties postoperative hypersensitivity and tooth vitality, recurrence of caries, erosion, abfraction, tooth integrity (enamel cracks, periodontal response, adjacent mucosa, oral and general health).

FIGURE 19.

Control of the restoration 2 years later.

Regarding this case, these criteria are clinically very good and the score SCASS is 0.

3. Discussion

Hypomineralised enamel poses significant challenges for dental bonding due to its altered mechanical and structural properties. A systematic review established that hypomineralised enamel in MIH‐affected teeth has reduced mineral quantity and quality (reduced mineral density), a reduction of hardness and modulus of elasticity (also in the clinically sound‐appearing enamel bordering the MIH lesion), and increased porosity, carbon/carbonate concentrations and protein content compared to unaffected enamel [16]. These enamel characteristics make it less favourable for bonding, especially due to the protein level in MIH enamel that is 8–21 times higher than in sound enamel [17], limiting acid contact with the hydroxyapatite. Therefore clinical investigations have explored pretreatment of hypomineralised enamel with the proteolytic sodium hypochlorite (5.25%) and the use of self‐etch or total‐etch techniques [9]. An in vitro study highlighted that oxidative pretreatment increased the microshear bond strength of resin composite to hypomineralised enamel [10]. However, current clinical evidence suggests that none of these techniques substantially improve the success of resin composite restorations [8, 18]. The resin infiltration of hypomineralised enamel is an interesting proposal for optimising bonding; in white spot lesions (WSL) this treatment increases the bond strength by 89% in vitro [18]. In the erosion‐infiltration protocol, the potential deproteinising action of hydrochloric acid has been hypothesised but requires further investigation, particularly regarding whether it influences the extent of diffusion into the lesion [19]. Icon resin has extremely low viscosity and contains low molecular weight TEGDMA monomers, enabling deep resin penetration. Resin infiltration into this weakened enamel not only increases its micro‐hardness, but also enhances its bond to overlying restorations [20]. Preparation of the restoration implies access to the full thickness of enamel, ensuring that the full extent of the lesion is reached.

Icon was initially created for the treatment of white spot lesions (WSL) and its indications have subsequently been extended to hypomineralised enamel. A systematic review demonstrates that infiltrative resins effectively change the properties of both sound enamel and demineralised enamel [21]. In sound enamel, infiltrative resins reduced surface roughness, microhardness and shear bond strength. Regarding WSLs, infiltrative resins reduced enamel surface roughness, but increased its microhardness and resin shear bond strength. Furthermore, estimates point to an average penetration depth capacity of 65% into the WSL by this type of resin [21]. In hypomineralised lesions, microhardness increased in areas of resin penetration by 1.0 ± 0.7 GPa representing a proportional increase of 2.2 ± 2.5 times [12]. However, there is no certainty that full infiltration of the hypomineralised lesion will occur. It should be noted that the depth of resin infiltration in hypomineralised enamel can be heterogeneous, presenting challenges in achieving consistent and complete infiltration throughout the lesion [12]. Furthermore, the authors demonstrated that the penetration depth of resin into MIH enamel was greater than for WSL [12].

The porosity of hypomineralised enamel contributes to tooth sensitivity; in addition, bacterial infiltration through the hypomineralised enamel into the dentine may exacerbate hypersensitivity in MIH‐affected teeth [11]. One study reported a reduction of hypersensitivity after infiltration, and it can be hypothesised that porosity obliteration by resin reduces sensitivity [22]. Nogueira and colleagues infiltrated MIH‐affected molars and demonstrated that resin infiltration positively influenced the maintenance of structural integrity of these teeth by decreasing the prevalence of enamel breakdown over an 18‐month follow‐up period. Resin infiltration proved to be a more efficacious intervention to maintain the structural integrity of MIH‐affected teeth than fluoride varnish therapies [23].

A new infiltrating resin named IBMA, a synthetic bio‐derived monomer of bis‐methacrylate isosorbide and a zwitterionic compound 2‐methacryloyloxyethyl, has been developed [24]. It has the advantage of not containing TEGDMA, a substance that may be restricted in dental products in the future. According to various comparative tests, the final outcome is that the infiltration depth of IBMA resin is not statistically different from that of Icon, indicating that IBMA can penetrate micropores and form a similar resin‐enamel complex [24]. Additionally, the IBMA resin resulted in higher enamel microhardness compared to Icon, which can be attributed to the higher microhardness of the IBMA resin itself. These results suggest that the new infiltration resin may be more resistant to masticatory pressure in the oral environment [24].

It is also important to consider the potential toxicity of resin infiltration on the dental pulp, although specific studies investigating this aspect are lacking. Resin infiltration of in vitro produced WSL adversely influenced the metabolic activity of pulp cells [25]. The detrimental effects were related to the use of HCl; however, after more than 10 years of commercial availability, no adverse outcomes for pulp health have been reported [25].

To conclude, infiltrating hypomineralised enamel with low viscosity resin before bonding posterior indirect adhesive restorations may be an innovative approach to preserve dental tissues, reduce post‐operative sensitivity and strengthen the enamel margin supporting and sealing the restoration. However, controlled trials are required in order to confirm the benefit of using this technique compared to a more invasive conventional approach. Studies have shown that resin infiltration positively influences the structural integrity of MIH‐affected teeth, reducing the risk of enamel breakdown over an extended follow‐up period. Further research is needed to optimise resin infiltration techniques for MIH lesions, addressing the issue of heterogeneous infiltration patterns, and investigating the potential of additional pre‐treatments, such as sodium hypochlorite, to enhance infiltration of and bonding to hypomineralised enamel. Future research should focus on optimising the clinical techniques and address concerns regarding sensitivity and pulp toxicity, ultimately advancing the clinical outcomes for patients with MIH‐affected teeth.

Author Contributions

David J. Manton, Patrick Rouas, Ana Ribeiro, Julia Estivals: writing – original draft; writing – review and editing. Elsa Garot: conceptualization; writing – original draft; writing – review and editing.

Consent

The ‘one‐shot’ questionnaire was completed on the Dxscare software (Dedalus, France) regarding the use of photographic data for publication purposes.

Conflicts of Interest

The authors declare no conflicts of interest.

Data Availability Statement

The data that support the findings of this study are available from the corresponding author upon reasonable request.