Authors’ reply

Dear Editor,

This letter is written in response to the letter to the editor dated 16^th February 2012.[1]

In our study an optical spectroscopy based method was used to measure/monitor the bacterial-mediated acidogenic-profile of saliva. Additional correlations with a standard pH meter and past caries experience of the patients were made. The experiments showed a strong correlation between the pH reading measured using a pH meter and the absorbance reading measured (from a photosensitive pH indicator) using the optical spectroscopic sensor. It is important to note that the optical spectroscopic system was calibrated, before any test is carried out using standard pH solutions (at pH 4 and 7). Previous publications have described similar optical spectroscopy based principles to monitor clinically relevant variables for quick diagnostic applications (References: 13-18 in the manuscript). The sensitivity, specificity and the predictive values have been clearly discussed in the manuscript (Page 399). Author AA is an experienced clinical epidemiologist. In addition, the sample size was chosen based on the power calculation carried out at statistics unit, at the National University of Singapore.[2]

The basic mechanism of optical sensor is based on the absorbance of a sample. Using the Beer Lambert's law, the variation in the absorbance could be related to the concentration of any specific parameter in a sample. Different biomedical equipments such as UV-visible spectrophotometers and ELISA plate readers work on the same basic principle of absorbance. Although optical spectroscopy could be a relatively newer technology compared to a pH meter for a practicing dentist, these are established systems/approaches in biotechnology. By applying this approach to determine pH changes, we are looking at a photometric resolution in the range of 0.001 absorbance unit and a photometric accuracy in the range of +/-1% +/- 0.0010 Abs from 0 to 2.000 Abs

Cost effectiveness is a relative feature. The caries detection systems such as Diagnodent (http://kabdental.com/dental-equipment/high-tech-equipment/kavo-diagno-dent-pen.htm) could cost around $4000-5000 per unit. Another caries detection kit, Dentocult SM costs approximately $10 for one patient. The OSS can be assembled using a LED (light source), optical fiber and a detector, which might not be an expensive option at all, especially when compared to many of the current caries detection systems. Further, with rapid advances in instrumentation, these schemes can be easily developed to be a cost-effective, miniature system.

Thus we believe that an optical spectroscopy based approach will provide information with high resolution and sensitivity, and can be used to monitor clinically important variables such as salivary pH. We did not imply that this single measurement can be used for caries risk assessment. Dental caries is a multifactorial disease, and we believe that rapid cost effective sensors that can measure different (multiple) risk factors from saliva may be a potential system for caries risk assessment. In that line, optical spectroscopic sensor is a worthwhile strategy.

Thank you for this opportunity to explain further on this article.