Dental fluorosis is a growing public health problem. Its manifestation could compromise esthetics and function.

Several treatment modalities have been proposed to manage mild to severe dental fluorosis. Treatment options varied from bleaching to full coverage crowns. This clinical report demonstrates the use of two different ceramic biomaterials for the treatment of two different levels of fluorosis.

Keywords: dental fluorosis, veneer, zirconia, lithium disilicate, CAD-CAM

Dental fluorosis is a chronic condition in which the excess of fluoride intake leads to irreversible biochemical changes within the tooth structure. High levels of fluoride anion could be responsible for disrupting the enamel formation.¹ The widespread use of fluoride based caries preventive strategies helped to decline dental caries prevalence and incidence in developed countries over the last two decades.

However, it has been recognized that fluoride ingestion in excess amounts could be responsible for the hypo mineralization of the enamel. A conducted study in 2017 showed that approximately 25% of the Tunisian population presented a potential dental fluorosis risk.² Dental fluorosis may undergo a continuum of post eruptive changes among the enamel surface. It may manifest with white spots, or fine opaque striations as much as it could present discrete or confluent pitting aspect of the enamel.^1,3 Thylstrup–Fejerskov index classifies theses histopathological changes, in an ordinal scale extending from 0 to 9, in order to simplify diagnostic criteria.

At a grade of 0, the enamel stands on its normal translucency. Scores ranging from 1 to 4 demonstrate several shades of opacities with no loss of the outer layer of the enamel surface. Scores of 5 or more indicate increasing degrees of loss within the enamel structure.^4–6 Treatment modalities for fluorosis depend on its severity. They vary from bleaching, micro/macro abrasion, and resin infiltration to veneers and full coverage crowns.⁷ Contemporary dental rehabilitation relies on finding the balance between the patients’ expectations and the most conservative means of treatments. Although the fact that achieving ideal esthetics may be facilitated by the use of all-ceramic restorations, it still challenging to choose the appropriate restorative material to reach esthetics as well as proper biomechanics.⁶

Improvements in restorative dental materials have made glass ceramic a desirable option for indirect esthetic restorations.⁸ In the last decade, zirconia gained an enormous interest for its exceptional mechanical and biological properties. However, 3Y-TZP zirconia is an opaque material. Therefore, research has turned to developing a more translucent zirconia. Zirconia fifth generation 5Y-TZP associates, nowadays, high levels of translucency while keeping an intersting flexural strenght. Zirconia restorations offer long-term stability thanks to the inertness of its surface.⁹ However, unlike silica-based ceramic, this chemical inertness makes the bond strength with resin composite cement challenging even more so with fluorotic enamel.¹⁰

Owing to the need to improve compromised esthetics and under the light of scientific evidence of the successful use of 5Y-PSZ zirconia, this manuscript reports a serial case describing the treatment of two different levels of dental fluorosis of maxillary incisors using lithium disilicate–reinforced ceramic and zirconia veneers.

A 42-year-old healthy Tunisian woman was referred to the department of fixed prosthodontics in the dental clinic of Monastir for an esthetic restorative consultation. Her chief complaint was about her discolored brown teeth. She complained of severe dental fluorosis with a TF score 5. She was born and raised in Kairouan, an area known to contain high fluoride levels in the groundwater. The extra oral examination showed a symmetrical face with competent lips and proper ratio of the lower face to the middle third heights.

The comprehensive oral examination and sectional radiographic series revealed the absence of active dental caries and signs of periodontal disease. Medical history manifested no contraindication for elective dental treatment. The treatment options were discussed with the patient. She decided to include whitening and micro-abrasion therapy while restoring her maxillary anterior teeth with lithium disilicate veneers.

The whitening and micro-abrasion of the teeth allows to lighten the dental stumps’ shade to better control the final color. At the first appointment, the polishing of all teeth was done. Initial diagnostic impressions were taken with alginate for the treatment planning. After achieving an acceptable shade, we waited two weeks for oxygen free-radical dissipation and color stabilization. A mock-up was completed to enhance the predictability of the final esthetic result.

Once validated, mini-invasive preparation started, threw the mock-up. It included a butt-joint margin, 1.5mm reduction of the incisal edges and 0.7mm on facial surfaces using a round-ended diamond burs. The preparations were then rounded and polished with fine diamond burs.

Digital impressions were taken with a 3 shape TRIOS 4 digital scan after color selection. The provisional veneers were temporarily cemented using the acid-etch point technique and bonded with flowable resin composite.

After receiving the final ceramic restorations, we verfied the marginal adaptation, interproximal contacts and occlusion, individually and then collectively using a translucent try-in paste (VARIOLINK®N).

After the final approval of the patient, the internal surfaces of the laminate veneers were etched with a 10% hydrofluoric acid for 20 seconds and silanated. As for teeth surfaces; they were etched with 35% phosphoric acid for 20 seconds, rinsed and thoroughly dried to then, be treated with an adhesive system. The final restorations were cemented using translucent dual-cured resin cement (VARIOLINK®N). After curing, the excess of the cement was removed with a scalpel blade (Figures 1–8).

Figure 1 Pre-operative view.

Figure 2 Aspect of the teeth after removing the superficial intrinsic enamel discoloration defects with Opalustre®.

Figure 3 (a) Silicone index for mock-up, wax model and (b) diagnostic mock-up with self-cured temporary composite material.

Figure 4 (a) Horizontal and vertical depth grooves marked on the teeth with a pencil (b) Clinical aspect after final preparations of the anterior teeth.

Figure 5 Lithium disilicate restorations.

Figure 6 Dual-cure resin cement (Variolink®).

Figure 7 Completion of cementing of the ceramic veneers.

Figure 8 Final smile view.

A 21 year-old female patient reporting small, discolored upper front teeth as her main complaint. The clinical findings revealed the absence of an obvious pathology among soft-tissues. Irregular chalky white lines manifested along the facial surfaces of all maxillary and mandibular teeth. Clinical assessment revealed severe dental fluorosis (TF =7) with a slight discrepancy in the anterior plane of occlusion. The treatment objectives were discussed with the patient that preferred to restore her smile with ceramic veneers. Diagnostic impression were taken and sent to laboratory to fabricate stone models. After mock-up validation, minimally invasive preparations were performed along the maxillary anterior teeth. A medium round-ended diamond instrument was used on the buccal surface of the teeth to remove a uniform thickness of 0.4 mm. All angles were rounded before final polishing and color selection. Impressions were taken with an addition silicone and sent to laboratory for final conception. Monolithic ceramic veneers were fabricated with translucent zirconia.

At the insertion appointment, we checked the marginal fit and interproximal contacts before selecting the shade of the final resin cement. Teeth surfaces were etched with 35% phosphoric acid for 20 seconds, rinsed in running water, dried and treated with a universal adhesive system. The internal bonding surfaces of the veneers were abraded with particles of aluminum and treated with a zirconia primer.

A dual-cure resin cement PANAVIA V5 was inserted into the ceramic veneers, which were placed on their respective abatements. The additional excess cement was removed with a scalpel blade (Figures 9–15).

Figure 9 Pre-operative view of the teeth.

Figure 10 Pre-operative view of the patient’s smile.

Figure 11 Stone casts and silicone index for mock-up.

Figure 12 Aspect of the teeth with diagnostic mock.

Figure 13 Clinical aspect of the teeth after preparation.

Figure 14 Zirconia primer and dual-cure resin cement (PANAVIA V5®).

Figure 15 Final cementation of zirconia veneers.

Dental fluorosis is a specific growth-related abnormality that could have deleterious effects on permanent tooth structure. High levels of fluoride ingestion, frequency and timing of exposure define the extent and the severity of damages.¹¹ The different features of hypo mineralized enamel are considered to be the main concern for patients with dental fluorosis expecting to correct their smile.¹ Severe fluorosis was reported to have negative impact on the individuals' oral health related quality of life.¹² Microscopically, incorporated fluoride anions increase the width of the inter crystalline space within the enamel apatite, causing pores.^3,13

The depth of the enamel involvement increases with the severity of fluorosis.^1,14 Various treatment approaches have been proposed for the treatment of moderate to severe fluorosis such as bleaching, abrasion, composite restorations, veneering and crowning.¹⁵ Among these alternatives, nonmetallic veneers are preferred for patients with oral disorders due to their lower risk of allergic reactions compared with metal alloys. Ceramics exhibit many desirable material properties such as compressive strength, abrasion resistance, surface smoothness, diminished thermal conductivity, biocompatibility, esthetics, low plaque accumulation and color stability.^16,17 Porcelain veneers are considered to be viable restorations with only 0% to 5% of failure rates over 1 to 5 years.^18,19

This restoration design is highly esthetic and very effective to wear conditions.^17,19,20 However, porcelain veneers have much higher debonding related failure rates when bonded to fluorotic teeth.^21,22 The adhesion to enamel tissue produces more predictable results than bonding to dentin. It is, for this reason, recommended to indicate ceramic veneers when only 30% of the enamel tissue is lost.²³

Physical and morphological changes induced by dental fuorosis makes bonding to this substrate a clinical challenge because of the resistance of fluorapatite to acid etching.^24,25 High fluoride concentration is usually located along the outer surface of the enamel on a 200 μm thikness.^26,27 The mechanical removal of this layer exposes the subsurface enamel that contains lower fluoride concentration which promotes chemical adhesion. Furthermore, the removal of the outer layer of flurotic enamel conserves the micro tensile bond strength of laminate veneers.^27,28 Al-Sugair and Akapta investigated the depths of etching on different levels of dental fluorosis and concluded that the etching patterns of TF=1-3 was similar to that in non fluorosed teeth. In contrast, the typical etching pattern on teeth with TFI =4 was obtained after 75 to 90 seconds. Consequently, Akapta et al., suggested to double etch severely damaged teeth.^27,29

Studies suggested that etch and rinse bonding systems present higher bond strength with fluorosed teeth than that with self-etch adhesives.^27,30 With the increasing implementation of computer-aided design/computer-aided manufacturing technologies, e. Max CAD crowns have shown to be resistant to fracture and suitable for posterior and monolithic restorations.^19,31 They exhibit superior fatigue resistance compared to veneered zirconia that is more prone to shipping while fracture values of monolithic zirconia are higher than those of lithium disilicate particle filled glass material.^19,32,33 Due to its mechanical properties and shear bond strength to resin cement, lithium disilicate veneers can be considered as shield restorations in the presence of unfavorable biomechanical oral environment.^19,34,35 Moreover, lithium disilicate (LS2) is 30% more translucent than conventional zirconia which makes it exceptional regarding esthetics.^19,36

However, theses ceramic systems have lower fracture toughness and low tensile strength.³⁷ The success of veneer restorations relies on the bond durability of composite cement to the internal surface of the restoration. Unlike zirconia, LS2 contains an etchable glass ceramic phase that is hyper sensitive to 5% concentrated hydrofluoric acid.

The acid etching promotes the micromechanical interlocking between resin cement and the intaglio surface of the restoration. Yttria-stabilized tetragonal zirconia poly crystals (Y-TZPs) outperform lithium disilicate ceramics in terms of mechanical properties.

3Y -TZP possesses the highest strength and fracture resistance thanks to high tetragonal particles that lead to transformation toughening preventing crack propagation.³⁸ Nevertheless, theses mechanical properties decrease with veneering and may lead to chipping.^39–42 Over time, monolithic full contour designs of zirconia have gained popularity over porcelain-veneered zirconia as they preserve more dental tissue allowing reduced prosthetic space.^43,44

The increasing of the yttria content (up to 5 mol%) and the replacement of certain tetragonal zirconia grains with cubic ones has led to diminish the light scattering and the birefringence at grain boundaries.³⁸ The 5 mol% cubic phase zirconia is found to be more resistant to aging behavior than 3 mol% yttria-stabilized tetragonal zirconia (3Y-TZP).^44,45 5Y-PSZ can offers ultra-translucency that is similar or even higher than that of (LS2) ceramic.^44,46,47 Other studies have reported that lithium disilicate has higher levels of translucency than that of cubic-phase zirconia.⁴⁴ Unfortunately, 5Y-PSZ lost a part of its toughening mechanism when acquiring translucency.^44,48 A recently developed method combines two generations of zirconia onto a unique blank to benefit from their mechanical and esthetic properties.^38,49

Although considered as resistant to compression, ceramic material behaves differently from metal alloys when putted under oral functional stress. They are brittle and cannot undergo plastic deformation. Excessive masticatory forces may cause irreversible surface damages. Therefore, the type of the permanent luting agent have a significant influence on the clinical success of these restorations.⁵⁰ Consequently, adhesive bonding with composite resin are mainly used to improve retention of ceramic restorations, increase fracture resistance and reduce microleakage.^51,52

Hydrofluoric-acid etching, followed by the application of a silane coupling agent, is recommended for silicate ceramics.⁵⁰ Studies have reported unsustainable results about the bond strength of resin cement to metal-oxide-based ceramics such as Y-TZP and Y-PSZ.^42,53,54

Other studies suggest to improve the micro chemical interlocking, surface wettability and chemical bonding with a suitable surface conditioning such as air abrasion with silica-coated alumina particles,⁴² tribo chemical silica followed by silane coupling agent application or the use of universal adhesives containing functional phosphate monomers.⁵⁵ A recent review have demonstrated the effect of resin bonding on long term success of high-strength ceramics and suggested to use self-adhesive resin cements for zirconia restorations that do not require bonding.⁵⁶

The APC zirconia-bonding approach includes three practical steps: (A) air particle abrasion with 50 to 60 μm alumina particle at a low speed (below 2 bar), (P) specific zirconia primer containing phosphate monomers, and (C) dual or self-cured adhesive composite resin.

Dental fluorosis is a disease that affects esthetics and function. Thanks to the development of biomaterials and processing technologies, translucent zirconia ultrathin veneers provide strength and satisfactory esthetics. However, further clinical investigations are needed to recommend this type of restoration material, especially, in cases of dental fluorosis.

None.

The authors declare that there are no conflicts of interest.

1. Mascarenhas AK. Risk factors for dental fluorosis: a review of the recent literature. Pediatr Dent. 2000;22(4):269–277.
2. Guissouma W, Hakami O, Al–Rajab AJ, et al. Risk assessment of fluoride exposure in drinking water of Tunisia. Chemosphere. 2017;177:102–108.
3. Fejerskov O, Manji F, Baelum V. The nature and mechanisms of dental fluorosis in man. J Dent Res. 1990;69 Spec No:692–700; discussion 721.
4. Rozier RG. Epidemiologic indices for measuring the clinical manifestations of dental fluorosis: overview and critique. Adv Dent Res. 1994;8(1):39–55.
5. Cangussu MCT, Narvai PC, Fernandez RC, et al. A fluorose dentária no Brasil: uma revisão crítica. Cad Saude Publica. 2002;18(1):7–15.
6. Alahmari MA. Treatment of cases with different grades of fluorosis by lithium disilicate glass–ceramic CAD/ CAM materials: a case report of two cases. J Contemp Dent Pract. 2023;24(5):342–348.
7. Akpata ES. Occurrence and management of dental fluorosis. Int Den J. 2001;51(5):325–333.
8. Taskonak B, Sertgöz A. Two–year clinical evaluation of lithia–disilicate–based all–ceramic crowns and fixed partial dentures. Dent Mater. 2006;22(11):1008–1013.
9. Li R, Wang C, Ma SQ, et al. High bonding strength between zirconia and composite resin based on combined surface treatment for dental restorations. J Appl Biomater Funct Mater. 2020;18:2280800020928655.
10. Edelhoff D, Ozcan M. To what extent does the longevity of fixed dental prostheses depend on the function of the cement? Working group 4 materials: cementation. Clin Oral Implants Res. 2007;18(Suppl 3):193–204.
11. Denbesten P, Li W. Chronic fluoride toxicity: dental fluorosis. Monogr Oral Sci. 2011;22:81–96.
12. Chankanka O, Levy SM, Warren JJ, et al. A literature review of aesthetic perceptions of dental fluorosis and relationships with psychosocial aspects/oral health–related quality of life. Community Dent Oral Epidemiol. 2010;38(2):97–109.
13. Thylstrup A, Fejerskov O: Clinical appearance of dental fluorosis in permanent teeth in relation to histological changes. Comm Dent Oral Epidemol. 1978;6(6):315–28.
14. Richards A, Fejerskov O, Baelum V. Enamel fluoride in relation to severity of human dental fluorosis. Adv Dent Res. 1989;3(2):147–153.
15. Shahroom NSB, Mani G, Ramakrishnan M. Interventions in management of dental fluorosis, an endemic disease: a systematic review. J Family Med Prim Care. 2019;8(10):3108–3113.
16. Tinschert J, Natt G, Mautsch W, et al. Fracture resistance of lithium disilicate, alumina, and zirconia–based three–unit fixed partial dentures: a laboratory study. Int J Prosthodont. 2001;;14(3):231–238.
17. Soares PV, Spini PH, Carvalho VF, et al. Esthetic rehabilitation with laminated ceramic veneers reinforced by lithium disilicate. Quintessence Int. 2014;45(2):129–133.
18. Peumans M, Van Meerbeek B, Lambrechts P, et al. Porcelain veneers: a review of the literature. J Dent. 2000;28(3):163–177.
19. Zarone F, Di Mauro MI, Ausiello P, et al. Current status on lithium disilicate and zirconia: a narrative review. BMC Oral Health. 2019;19(1):134.
20. Kelly JR, Nishimura I, Campbell SD. Ceramics in dentistry: historical roots and current perspectives. J Prosthet Dent. 1996;75(1):18–32.
21. Shida K, Kitasako Y, Burrow MF, et al. Micro-shear bond strengths and etching efficacy of a two–step self–etching adhesive system to fluorosed and non–fluorosed enamel. Eur J Oral Sci. 2009;117(2):182–186.
22. Vamsilatha K, Venkata KM, Aileni KR, et al. Efficacy of new adhesion promoters on compromised hypo calcified enamel. J Clin Diagn Res. 2015;9(7):Zc09–Zc011.
23. Akpata ES. Occurrence and management of dental fluorosis. Int Dent J. 2001;51(5):325–333.
24. Christensen GJ. Clinical factors affecting adhesion. J Operative dentistry. 1992:Suppl 5:24–31.
25. Liu S, Zhu Y, Gegen T. Micro morphological analysis and bond strength comparison of two adhesives for different degrees of dental fluorosis. Appl Adhes Sci. 2020;8:6.
26. Richards A, Fejerskov O, Baelum V. Enamel fluoride in relation to severity of human dental fluorosis. Adv Dent Res. 1989;3(2):147–153.
27. Akpata, Enosakhare S. Therapeutic management of dental fluorosis: a critical review of literature. Saudi J Oral Sci. 2014;1(1):3–13.
28. Ratnaweera PM, Fukagawa N, Tsubota Y, et al. Microtensile bond strength of porcelain laminate veneers bonded to fluorosed teeth. J Prosthodont. 2009;18(3):205–210.
29. Al–Sugair MH, Akpata ES. Effect of fluorosis on etching of human enamel. J Oral Rehabil. 1999;26(6):521–528.
30. Weerasinghe DS, Nikado T, Wettasinghe KA, et al. Micro–shear bond strength and morphological analysis of a self–etching primer adhesive system to fluorosed enamel. J Dent. 2005;33(5):419–426.
31. Furtado de Mendonca A, Shahmoradi M, Gouvêa CVD, et al. Microstructural and mechanical characterization of CAD/ CAM materials for monolithic dental restorations. J Prosthodont. 2019;28(2):e587–e594.
32. Guess PC, Zavanelli RA, Silva NR, et al. Monolithic CAD/CAM lithium disilicate versus veneered Y–TZP crowns: comparison of failure modes and reliability after fatigue. Int J Prosthodont. 2010;23(5):434–442.
33. Kashkari A, Yilmaz B, Brantley WA, et al. Fracture analysis of monolithic CAD–CAM crowns. J Esthet Restor Dent. 2019;31(4):346–352.
34. Sorrentino R, Apiucela D, Riccio C, et al. Nonlinear visco–elastic finite element analysis of different porcelain veneers configuration. J Biomed Mater Res B Appl Biomater. 2009;91(2):727–736.
35. Radz GM. Minimum thickness anterior porcelain restorations. Dent Clin N Am. 2011;55(2):353–370.
36. Baldissara P, Llukacej A, Ciocca L, et al. Translucency of zirconia copings made with different CAD/CAM systems. J Prosthet Dent. 2010;104(1):6–12.
37. Manziuc MM, Gasparik C, Negucioiu M, et al. Optical properties of translucent zirconia: a review of the literature. Euro Biotech J. 2019;3(1):45–51.
38. Ali Dahee Malallah, Nadia Hameed Hasan Al Kazaz, Effect of artificial aging on the fracture resistance of different zirconia laminate veneer restorations. J Glob Scien Res. 2021;6(10):1726–1738.
39. Worpenberg C, Stiesch M, Eisenburger M, et al. The effect of surface treatments on the adhesive bond in all-ceramic dental crowns using four-point bending and dynamic loading tests. J Mech Behav Biomed Mater. 2023;139:105686.
40. Swain MV. Unstable cracking (chipping) of veneering porcelain on all-ceramic dental crowns and fixed partial dentures. Acta Biomater. 2009;5(5):1668–1677.
41. Schmitter M, Mueller D, Rues S. Chipping behaviour of all-ceramic crowns with zirconia framework and CAD/CAM manufactured veneer. J Dent. 2012;40(2):154–162.
42. Greuling A, Wiemken M, Kahra C, et al. Fracture resistance of repaired 5Y-PSZ zirconia crowns after endodontic access. Dent J (Basel). 2023;11(3):76.
43. Harada K, Raigrodski AJ, Chung KH, et al. A comparative evaluation of the translucency of zirconias and lithium disilicate for monolithic restorations. J Prosthet Dent. 2016;116:257–263.
44. Min-Zin Ahn, Do-Gwan Ahn, Se-Wook Pyo, et al. A noninvasive esthetic treatment of isolated microdontia using new high-translucent cubic-phase zirconia (5Y-PSZ) laminate veneers: a case report. J Korean Acad Prosthodont. 2019;57(3):263–270.
45. Zhang F, Inokoshi M, Batuk M, et al. Strength, toughness and aging stability of highly-translucent Y-TZP ceramics for dental restorations. Dent Mater. 2016;32(12):e327–e337.
46. Yan J, Kaizer MR, Zhang Y. Load-bearing capacity of lithium disilicate and ultra-translucent zirconias. J Mech Behav Biomed Mater. 2018;88:170–175.
47. Baldissara P, Wandscher VF, Marchionatti AME, et al. Translucency of IPS e.max and cubic zirconia monolithic crowns. J Prosthet Dent. 2018;120(2):269–275.
48. Kwon SJ, Lawson NC, McLaren EE, et al. Comparison of the mechanical properties of translucent zirconia and lithium disilicate. J Prosthet Dent. 2018;120(1):132–137.
49. Michailova M, Elsayed A, Fabel G, et al. Comparison between novel strength-gradient and colorgradient multilayered zirconia using conventional and high-speed sintering. J Mech Behav Biomed Mater. 2020;111(8):103977.
50. Blatz MB, Alvarez M, Sawyer K, et al. How to Bond Zirconia: The APC concept. Compend Contin Educ Dent. 2016;37(9):611–617.
51. Blatz MB, Sadan A, Kern M. Resin-ceramic bonding: a review of the literature. J Prosthet Dent. 2003;89(3):268–274.
52. Blatz MB, Conejo J. Cementation and bonding of zirconia restorations. Compend Contin Educ Dent. 2018;39(Suppl 4):9–13.
53. Wegner SM, Gerdes W, Kern M. Effect of different artificial aging conditions on ceramic-composite bond strength. Int J Prosthodont. 2002;15(3):267–272.
54. Kern M, Wegner SM. Bonding to zirconia ceramic: Adhesion methods and their durability. Dent Mater. 1998;14(1):64–71.
55. Lu ZC, Jia LH, Zheng ZF, et al. 15-Methacryloyloxypentadecyl dihydrogen phosphate improves resin-to-zirconia bonding durability. J Adhes Dent. 2023;25(1):23–30.
56. Blatz MB, Vonderheide M, Conejo J. The effect of resin bonding on long-term success of high-strength ceramics. J Dent Res. 2018;97(2):132–139.