A pilot study investigating the possible relation between inter-subject variation in parameters of whole saliva and differences in susceptibility to erosion

Erosive wear is the loss of enamel due to a chemical process without the
involvement of bacteria. The main cause of erosive wear is the excessive
consumption of acidic drinks. Recently there is an increasing interest for
erosive wear in young people [Truin et al., 2004]. A wide variation between
individuals in susceptibility to developing erosion has been found [O*Sullivan
and Curzon, 2000; Vieira et al, 2007]. Saliva and pellicle composition could be
of importance in explaining this difference. The pellicle, a thin layer of
salivary proteins adsorbed to the tooth surfaces, has an important function in
the protection of the dental hard tissues. From the point of view of erosive
wear it is interesting to know that it acts as a diffusion barrier to H+-ions
and is protective against enamel erosion [Hannig and Balz, 1999; Lendenmann et
al., 2000; Hannig et al., 2005]. Also, the composition (minerals, proteins),
flow, buffercapacity, pH and viscosity of saliva could be of influence
[Johansson et al., 2004; Dawes and Kubieniec, 2004; Tenovuo and Lagerlöf,
1994].

To investigate a possible relation between saliva parameters and susceptibility
to erosive wear and to determine the number of subjects for a larger follow-up
study.

Samples

Thirty hydroxyapatite discs (Himed medical applications Inc, Old Bethpage NY,
USA) with a diameter of 8 mm and a thickness of 2 mm will be used.
Hydroxyapatite is often used in in vitro studies and in in situ studies
[Barbour et al., 2003; Joiner et al., 2003; Shellis and Wilson, 2004; Tanizawa
et al., 2004; Vacca Smith and Bowen, 2000a; Vacca Smith and Bowen, 2000b]. The
advantage of hydroxyapatite is that it is much more homogenous in structure and
composition than to human enamel [Barbour et al., 2005].

Design

It is a single centre, single blind study. Twelve healthy volunteers will
participate in this study. Unstimulated and stimulated saliva will be collected
in the morning (9.00). The volunteers will carry the discs in the buccal sulcus
for 1.5 hours. This place is preferred because of the reduced chance of
swallowing the samples. Eating, drinking, brushing and smoking is not allowed
with the samples in situ. After 1.5h the samples are collected and are exposed
for 2 minutes to an erosive solution (50 mM citric acid (pH = 3)).

Wear measurements

The loss of calcium from the hydroxyapatite after an erosive challenge is
measured using Atomic Absorpion Spectroscopy (AAS). First, baseline
measurements of the eroding solution will be performed. After exposing the
samples to the eroding solution the calcium concentration of the solution is
measured again. The differences in calcium concentration are an indication of
the loss of hydroxyapatite [Dijkman et al., 1983; Vieira et al., 2005].

Saliva measurements

Protein composition of unstimulated and stimulated saliva is measured using
SDS-PAGE (gel-electrophoresis). The pH, buffercapacity, total protein
concentration and the viscosity of the saliva will be determined. Also the
potassium, sodium, chloride, urea, fluoride and bicarbonate concentration will
be measured [Veerman et al., 1996].

The burden for the participants is to carry 2 samples in the buccal sulcus for
1.5 hour and to hand over saliva. Swallowing of the samples is a possible risk.
By placing the samples in the buccal sulcus this risk is reduced. If swallowing
of the samples occurs this will not give a big problem because of the surface
characteristics of the samples.