Caries Developments in Recent Decades

Dental caries reached a climax in the 19th and 20th centuries due to the increased availability of sugar for the general population of developed countries [1]. Only with the extensive use of fluorides in the 1970s was the rapid rise of the disease of dental hard tissue diminished [2]. Nevertheless, dental caries is one of the most common intraoral diseases, with serious consequences for both the individual patient and for the public in terms of medical, social, and economic concerns. The individual patient suffers from pain, dysfunction of the oral system, and reduced quality of life [3], while the general public must bear the cost of treatment and possible lost productivity of those affected.

Recent reports have confirmed an increase in caries on a worldwide scale, confirming its status as an important global oral health burden [4–7]. Unfortunately, caries predominantly attack the occlusal surfaces of premolars and molars during their eruption [8]. On the other hand, smooth surface caries have shown a significant decline, likely a result of increased worldwide access to fluoride [9,10]. In previous reports, an incomplete post-eruptive maturation [11–13] and the presence of narrow and deep fissures were blamed for the increased caries susceptibility of occlusal surfaces [14]. However, this theory has been questioned [8].

A more obvious explanation seems to be that dental plaque can mature undisturbed in the pits and fissures of teeth in eruption; as a result, enamel will be dissolved by the unimpeded repeated acid attacks [15]. This also explains why fluorides are not as effective in pits and in the fissure system as on smooth surfaces. Fluorides can effectively inhibit demineralization, promote remineralization, and also prevent acid formation by bacteria. However, they must act on a local level, which is not always possible with pit and fissures. A recently published Cochrane review reported a decrease of Dent. J. 2018, 6, 18; doi:10.3390/dj6020018 www.mdpi.com/journal/dentistry Dent. J. 2018, 6, 18 2 of 8 caries in 3.7% and 29% of children after two and nine years, respectively, when a resin-based sealant was placed in comparison to fluoride varnish applications [16]. This could be seen as an indirect suggestion for favoring resin-based sealing materials.

During tooth eruption, natural cleaning mechanisms through the tongue, lips, and cheeks during chewing and swallowing are absent [8]. The occlusal surfaces of erupting teeth are especially affected by the reduced ability of cleaning [17]. As a result, bacteria and food residues can accumulate in the pits and fissures, produce a biofilm, and lead to demineralization and caries [15]. An epidemiological study investigating data from 2011–2012 observed that the decrease in occlusal surface caries had not kept pace with the decrease in smooth surface caries [10]. The authors assumed that preventive interventions, such as the addition of fluoride to water and toothpastes as well as topical fluoride application, more effectively reduced caries on smooth surfaces than in pits and fissures [10].

Caries Prophylaxis

Indisputable approaches to preventing caries are regular oral hygiene with fluoride-containing toothpaste, a reduction in the intake of cariogenic food, as well as local and systemic fluoridation. For anatomically sensitive areas such as pits and fissures, additional approaches exist. The idea of sealing pits and fissures of occlusal surfaces had already been developed by the 1960s [18–20]. Sealing the surface creates a physical barrier that blocks the biofilm’s nutrition and, as a result, inhibits biofilm growth [21,22]. Hence the use of sealing materials is a simple physical problem solution as fluorides inhibit demineralization, promote remineralization, and prevent acid formation by plaque bacteria [23,24]. Nevertheless, numerous investigations have reported on the significant benefits for resin-based sealants in comparison with fluoride varnishes [25–27]. The efficacy of resin-based sealing materials is beyond question, having been proven in many studies [28,29]. One study even showed that a time-delayed application of the fissure sealant of about one year already led to a substantial increase in caries frequency [30]. However, its efficacy is dependent on a tight closure [21].

A conference paper of the American Academy of Pediatric Dentistry, Pediatric Restorative Dentistry Consensus Conference in 2002 strictly recommends the use of sealing materials in permanent molars in children and adolescents [10]. This advocacy is based on an analysis of nine randomized controlled trials on permanent molars with a follow-up period of two to three years. The incidence of caries showed a reduction of about 76% in occlusal caries [31–37]. Furthermore, a comparison of the efficacy of sealing materials and of fluoride varnishes was conducted with reference to three randomized controlled trials [32,34,38]. In addition, a reduction of about 73% of the incidence of occlusal caries in permanent molars after two to three years in the sealing groups was found in comparison to the fluoride varnish group.

Another study by Bravo et al. [27], which placed sealing materials on sound occlusal surfaces, reported on a caries incidence of only 27% in sealed surfaces compared to a caries incidence of about 77% in the unsealed control group, and about 56% in another control group using fluoride varnishes after nine years. A clinical study with 360 children and an observation period of 15 years showed a reduction in caries of 36% when all first molars were sealed and a reduction in caries of 54% when all posterior teeth were sealed [39]. Positive reports on the use of sealing materials were also confirmed by a systematic review of the Cochrane library [20]. The exploration of randomized and quasi-randomized controlled trials with a minimum period of 12 months, which compared the efficacy of sealing materials on occlusal and approximal surfaces with no sealing, resulted in an unambiguous recommendation: “the application of sealants is a recommended procedure to prevent or control caries” [20].