Dental caries remains a widely prevalent disease despite tremendous advances in prevention and treatment . The interplay of multiple factors was found to influence caries development and progression. Several in vitro studies have discussed the biological plausibility that changes in salivary parameters can contribute to the development of dental caries [5, 18]. However, controversy exists about the incidence of dental caries and its associated salivary risk factors in children with CP . Identification of individuals at high risk of caries as children with special health care needs would be of considerable importance in allocating resources for caries prevention.
The relatively wide age range in the present study allows the evaluation of different risk factors for dental caries affecting primary and mixed dentitions. The results of the current research accept the proposed hypothesis as intra-oral examination revealed that SG had higher caries experience in their primary and permanent teeth than CG. However, this difference was only statistically significant in the primary teeth (dmft). Similar findings were found by Jaber et al. . Ruiz et al. also reported no significant difference in caries experience in permanent teeth (DMF) between both groups among elder children . On the other hand, Grzic et al. reported no significant difference in a tooth morbidity (DMTF/dft) between the SG and CG .
Multivariable linear regression in our results clearly shows that the presence of CP was significantly associated with great variation in caries experience in both primary and permanent teeth. Additionally, children with CP have significantly more decayed primary teeth than healthy children, representing the major contribution of the dmft score. This was in line with former studies reporting higher treatment needs and less dental services provided for CP children [20, 22].
On the other hand, lower caries experience that was observed in the permanent than primary teeth among both CP and healthy children, might probably be due to the fewer number of erupted permanent teeth, and less exposure time to the cariogenic oral environment than primary teeth . Moreover, the physical abilities of CP children could change with time , that may result in more self-dependence in their daily activities, as well as changing the dietary consistency to a more solid food, and hence better oral hygiene as they grow up .
The level of oral hygiene status reflects the efficiency and frequency of brushing and possibly of dietary habits. In line with previous reports, the current research reported unsatisfactory oral hygiene in SG . This could be attributed to impaired natural cleansing by the oral musculature, reduced manual dexterity, some degree of cognitive impairment, which further hinders the adoption of adequate oral hygiene practices and result in partial or total reliance on the caregiver . Quritum et al. reported poorer oral hygiene within children with CP who have dental caries compared to caries free CP children when studying the impact of oral hygiene practices and dietary habits on their caries experience .
It has been long recognized that saliva acts as a mirror for body's health and can be used as a non-invasive diagnostic tool for monitoring general or oral conditions in children and non-cooperative subjects . Alteration of salivary parameters encountered in children with CP compared to their healthy counterparts, could play a pivotal role in caries incidence and progression .
Unfortunately, few studies have been published on the salivary composition of children with CP. Unstimulated whole saliva was considered in the present study as it correlates to clinical conditions more accurately than stimulated saliva . Children with CP had demonstrated about 40% reduction in their salivary flow rate, which may explain the higher caries experience observed among them. Parallel findings were observed by Diniz et al. . This may be due to their complete dependence on their caregivers to offer them liquids, their persistent pathological oral reflexes can also interfere with the normal oral function and result in impaired level of hydration . On the other hand, Tahmassebi and Curzon found no difference in the flow rate between SG and CG. However, their study was based on a small number of participants and used different methods of salivary collection .
In line with the literature, a high prevalence of drooling was observed among children with CP, despite the lower values of salivary flow rates recorded among them . Tahmassebi reported that drooling among these children is not due to hyper salivation, but it usually results from incontinency secondary to impaired cerebral control of orofacial musculature. Other predisposing factors could also include quadriplegic topographical pattern, absence of cervical control, epilepsy, intellectual disability, lack of speech, open anterior bite, as well as dysphasia .
The consistency of the saliva can affect its capacity to flush microorganisms and substrates, as well as maintaining the oral cleanliness. In the present study, it was observed that greater proportion of SG have thick and sticky saliva than CG but this difference was not found to be statistically significant. This could be referred to reduced water content and increase protein content in the saliva of CP children .
Salivary pH and the buffering capacity are essential parameters in controlling the ion exchanges during re-mineralization and demineralization of enamel. They are determined by the hydrogen bicarbonate balance in saliva. It was noticeable that SG had statistically significant lower salivary pH and buffering capacity than CG (P < 0.0001 for both). These findings were in synchronous with previous research on CP children done by Subramaniam et al. . This can result in an increased susceptibility to demineralization and caries intiation. On the other hand, Tahmassebi reported no significant difference . Linear regression showed that an increase in the salivary buffering capacity was significantly associated with lower caries experience in both primary and permanent teeth. However, this association was not evident with salivary pH, as it is a labile parameter highly influenced by the type and timing of food intake as well as the individual’s oral hygiene habits. Whereas, buffering capacity represents innate resistance to neutralize acids, thus it is more efficient in predicting caries experience.
Total antioxidant capacity (TAC) was estimated in the present study, as it was suggested that free radical/ reactive oxygen species and antioxidant systems appear to act in concert rather than alone. Furthermore, not all the compounds with antioxidant properties are believed to be identified . Comparing the level of salivary TAC among CP and healthy children demonstrated a statistically significant lower level among SG. The efficacy of total antioxidant system may be related to many factors such as antioxidants potency and level, amount of free radical production, individual genetic basis, dietary intake, physical activity, hormones, and stress.
It was reported that children with CP suffer from high levels of oxidative stress throughout their lifespan, consequent to vitamin deficiency, malnutrition, environmental factors as well as epileptic seizures. That is why the radical-scavenging antioxidants get consumed by the increased free radical activity associated with this condition . These finding is partially in agreement to a previous study done by Subramaniam et al. , where an inverse relation between TAC and dental caries was reported. This could be attributed to difference in dmft values, dietary pattern, oral hygiene practice and genetics. Additionally, linear regression models clearly represented that salivary level of TAC was significantly associated with the number of affected primary and permanent teeth.
Bacteria produce free radicals during dental decay progression and their number appears to vary directly with caries activity . Thus, increased level of salivary TAC can be a compensatory mechanism, to neutralize the effect of the high oxidant level. This could also be verified by the statistically significant positive moderate correlation observed between the level of TAC and S. mutans in the current study.
Perhaps in the near future, through longitudinal studies, a TAC index will be introduced as a marker of caries susceptibility in children.
Microbiological examination of the saliva was done through anaerobic culturing of S. mutans, the main organism responsible for caries initiation . its presence was confirmed using MALDI-TOF MS, as it represents a rapid and accurate proteomic approach for identification of bacteria, compared to the conventional biochemical and metabolic techniques .
Significantly, higher level of S. mutans was found in the saliva of children in SG. Parallel finding was reported by Santos et al. . This could be attributed to poorer oral hygiene and faulty dietary habits and reduced self-cleansing mechanism by the impaired oro-motor function, resulting in more food debris. Such practices promotes the growth of these cariogenic microorganisms.
Brain damage associated with CP can be responsible for the alteration in the salivary parameters, which could explain the higher caries experience encountered in this group . The management of children with CP should be done through a multi-disciplinary team approach, involving the cooperation of a wide array of specialties including pediatric dentistry. The presence of multiple risk factors for dental caries in children with CP necessitates vigorous preventive advice and high quality of dental care. Preventive measures must be introduced for children with CP as soon as their condition is diagnosed to improve the general and oral health status.