Introduction

Amelogenesis imperfecta (AI) describes a heterogeneous group of clinical and genetic conditions that affect tooth enamel and causes damage to function, due to modified dental structure, affects quality of the enamel, adhesion, and aesthetic, causes hypersensitivity, and also loss of vertical dimension and orthodontic deviations^1-3.

To improve function and esthetics, new treatment options are emerging and digital flow with 3D printing has been widely used^4-6 in the production of crowns and it uses an additive manufacturing method, stereolithography, that doesn't waste material, has lower cost, optimized resolution, accuracy and smooth surface finish^7-10.

3D-printed composite resin crowns showed high fracture resistance and can be suggested as a viable solution in conservative dentistry¹¹. New load- increasing microfilled resins for 3D printing of crowns have benefits such as increased mechanical properties which offers time saving, higher precision, accuracy and fitting, lower risk of distortions, manufacturing of complex shapes (as of crowns with no tooth preparation) and almost no waste of material.

Another new technology is the S-PRG Filler which is a combination of ‘glass ionomer cement’ and ‘resin composite’¹². These materials have high fluoride release, excellent adhesion and aesthetics. Digital flow and 3D prints have enabled minimal intervention oral rehabilitation for pediatric dentistry and cases of developmental enamel defects¹³. The objective of this article is to report an oral rehabilitation case of amelogenesis imperfecta using 3D-printed composite resin crowns with minimal intervention principles.

Case report

This case report was conducted in compliance with the Helsinki Declaration and was prepared according to CARE guideline¹⁴. A 13-year-old male presented to the clinic with pain, sensitivity, and aesthetics complaints. The patient's main complaint was difficulty eating and brushing his teeth due to high hypersensitivity, also as he entered adolescence, the patient reported being bullied at school because of the aesthetics of his teeth. Medical history showed no systemic conditions. Dental history showed that the patient has been diagnosed with Amelogenesis Imperfecta (AI) Hypomaturation-Hypoplastic, Type IV (AIHHT - OMIM: 104510) (Figure 1) and has and an anterior dental crossbite (tooth 12).

AI is a genetic condition resulting from a mutation in genes present in the mineralization process of tooth enamel. Because of this genetic characteristic, people with this condition have enamel malformation in both deciduous and permanent teeth. Treatment began at the age of 13, as this was when the patient arrived at the Enamel Defects Clinic at the School of Dentistry of the University of São Paulo. The family reported that they had been looking for treatment for years, but due to their low socio-economic status they had not been able to find treatment solutions that they could afford and in many public treatment centers they were informed that they did not provide the type of treatment needed due to its cost and complexity.

The treatment plan was conducted according to the timeline below (Table 1 and 2 ), the initial consultation included a clinical examination, intraoral and extraoral

photographs, and complementary tests such as panoramic radiography and intraoral scans. One week after the initial consultation, phase 1 of the treatment began, which consisted of preparing the oral environment for rehabilitation, with two sessions of supra- and subgingival scraping, with a week in between, for hygiene and dental tartar removal. Next, a sensitivity management protocol was carried out using an infrared laser associated with fluoride varnish (Table 1). Four sessions of the protocol were carried out once a week.

The minimally invasive rehabilitation was performed with the use of an intraoral scanner, digital planning software and

3D printing (Table 2, Figures 2 and 3). The planning software was used to plan all functional characteristics such as thickness and orientation of the printed layer, printing orientation and position, build angle, vertical dimension, crown sizes and occlusal dimension. The patient’s waxed-up models were printed, and a bis- acryl mock-up was made to try on the characteristics planned on the software (Figures 1 and 2).

The printing process and parameters are explained in Tables 1 and 3, after printing the crowns were placed in ultrasound (Table 2) with 99,5% alcohol for 5 minutes and then post-curing process (Table 1) in the curing oven (Table 2 and Figure 3) for 10 minutes, polishing and final glaze. Crowns installations were performed one tooth at a time. ResiCem Universal Resin Cement (Table 2) has the highest reported bond strengths of any resin cement, has excellent adhesion and aesthetics, customized to be universal for all materials, high fluoride release and very low film thickness (9µm)¹⁵.

Operatory phase and crown placement followed the steps: 1) Prophylaxis; 2) Try in crowns; 3) Selective surface etching - ortho-phosphoric acid 37% ; 4) Wash and dry; 5) 2 step adhesives (Table 2); 6) Cement injection and crown placement; 7) Photoactivation 20 seconds (Table 2); 8) Flossing and cleaning all excesses (diamond burs and abrasive discs/stripes); 9) Occlusal adjustment (carbon paper and finishing burs); 10) Photographs were taken during the whole process (Figure 4). The printed crowns were cemented directly onto the tooth structure without any tooth preparation.

The whole treatment process took approximately 3 months and 10 dental appointments with one week interval between the first 6 appointments (Phase 1) and two-week intervals between the next 4 appointments (Phase 2). In phase 1, we opted for weekly appointments so that the sensitivity protocol would be more successful. In the second phase, appointments were made every 15 days, due to the need to plan and produce the crowns and also so that the patient would have a longer period to adapt to the new crowns, as there were major aesthetic changes and also in relation to the occlusal vertical dimension.

appointments were made every 15 days, due to the need to plan and produce the crowns and also so that the patient would have a longer period to adapt to the new crowns, as there were major aesthetic changes and also in relation to the occlusal vertical dimension.

This rehabilitation process allowed the continuity of the patient's treatment, with the adhesion of orthodontic fixed appliance parts. Follow-up appointments were conducted weekly during the first month after crown installation. In the subsequent two months, appointments were held every 15 days, and after this initial period, the patient attended monthly appointments for monitoring. After 1 year of follow up it was possible to install fixed orthodontic appliances and there was no damage to crowns and adhesion in this period, the crowns were stable in the oral cavity (Figure 5).

Discussion

This case report describes the use of new technology combined with well-defined dentistry principles like the use of minimally invasive treatments for pediatric dentistry. The main complaints of the patient were hypersensitivity, aesthetics and function, also the high rehabilitation cost. The traditional methods for oral rehabilitation in pediatric dentistry for amelogenesis imperfecta in permanent teeth are composite restorations, composite, ceramic, and zirconia crowns, which present great aesthetic improvement but all of those need tooth preparation, ware of dental surface and has higher cost^4,5. As far as we are aware, there are no other case reports that have used 3D-printed crowns for the oral rehabilitation of patients with amelogenesis imperfecta following the principles of minimal intervention. Most cases reported have undertaken conventional rehabilitative procedures, including dental preparation and the use of laboratory-fabricated crowns^4,5.

When the patient arrived for treatment, we realized it was a complex oral rehabilitation case, and the family could not afford the costs of conventional rehabilitation (crowns produced by dental laboratories). Therefore, we had to consider a treatment option that was affordable, did not rely on third-party work (laboratories), and could be performed using the materials and equipment available at the university clinic.

3D printing is already well used in prosthetic rehabilitation, it has successfully established function and aesthetics and it can also be used, as shown in this article, as a minimally invasive technique¹³, because digital planning allows the cementation of crowns/veneers without wear of dental tissue and has an accessible cost.

Regarding the cost of resin-printed crowns, after the initial investment in a 3D printer, resin, curing oven, and ultrasonic washer, the approximate cost of a printed crown is $2.00 (R$10.00 - Brazilian currency). When compared to metal-free crowns produced in a laboratory, despite the initial investment in the necessary equipment, since it is third-party work, it is not possible to pay the cost price. Therefore, the final price of a metal-free crown made by a laboratory is approximately $70.00 (R$400) in Brazil, which is significantly higher.

A major difficulty in AI cases is adhesion. Success rates for adhesively bonded single-tooth restorations in AI patients compared with patients without AI presented by Klink, Groten & Huettig (2018)³ were high, giving us encouragement regarding the case report presented and the long-term durability of cement-retained crowns. Shofu’s resin cement was a success, with no adhesion failures after one year of follow up.

Conclusion

It is possible to conclude that digital workflow and 3D printing have many benefits for dentistry such as treatment predictability, lower cost, less material waste, shorter working time, independence in the production of prosthetic parts and better communication with the patient, this case shows that digital dentistry made possible to perform oral rehabilitation following minimally invasive principles and reestablishing not only function but also aesthetic ^7-10.

We concluded that the case was a success, greatly improving the patient's aesthetics and function, with an improvement in quality of life, diet and hygiene due to the improvement in sensitivity.