Clinical Evaluation and Laboratory Wear- Testing Methods - Dental Biotribology - page 38

quantitative, accurate, and provides storable 3D databases that can be compared to
other 3D databases. However, considering that it needs expensive equipment, few
clinical studies have used 3D scanning technology to measure wear although it has
been available since the mid-1980s.

2.3.2 In Situ Testing

No matter which in vitro method is employed, it is diffi cult to extrapolate fi ndings
into clinical meaning, particularly since the wear of teeth is multifactorial and phys-
ical and chemical processes interact. Indeed, it is this multifactorial etiology of
tooth wear that has hampered the development of in vivo methods to study the tri-
bological properties of dental materials. During in situ testing, specimens are
mounted in devices worn in the mouth and later removed for ex vivo measurements.
Therefore, specimens can be exposed to the real oral environment. In short, in situ
testing provides a partial compromise between in vivo and in vitro conditions.
For most in situ methods, the conditions of any experiment can be carefully con-
trolled so that the effects noted can be ascribed to the agent under test. In situ studies
can use sensitive equipment, such as a profi lometer and scanning force microscopy,
to measure the loss of a material surface due to various factors, so that experiments
could be conducted over comparatively short time periods. Initially, in situ methods
were used mainly to measure the erosion of dentin and enamel by soft drinks, and
then they were gradually used to study a variety of phenomena in the mouth, includ-
ing abrasion of dental materials by toothpastes.

2.3.3 In Vitro Laboratory Simulation

Clinical studies on dental wear are limited by diffi culties in the accurate quantifi ca-
tion of intraoral wear and by a lack of control over the oral environment. The quest
for a wear-testing machine in vitro that would simulate the masticatory process as
well as the oral environment and predict the clinical performance has been the
dream of many materials scientists. Therefore, laboratory simulation methods were
widely developed to mimic wear conditions in the mouth, such as a clinical mastica-
tory cycle and oral environment, and then used for in vitro evaluation of dental
materials after the 1940s. According to the literature, a multitude of artifi cial wear-
testing methods and machines have been developed, varying in force applications
and motion patterns. The simplest type consists of a mechanism whereby vertical
impact stresses of different magnitudes can be applied to a prepared specimen; this
type was used by Sarkar [ 22 ]. However, according to examinations of the literature,
two fundamental modes can be classifi ed in wear tests of dental materials: unidirec-
tional and reciprocating sliding wear tests [ 23 , 24 ]. For the fi rst mode, several kinds
of test rigs, such as pin-on-disk, ball-and-crater, twin-disk, and one-way slide