Effect of occlusal loading on secondary caries development in situ’

Rationale:
Secondary caries is tooth decay next to an existing restoration and one of the main reasons to replace restoration in general dental practice. Previous research has shown that secondary caries lesions can develop when a small gap is present between the tooth and restorative material. Gaps as small as 30 µm have been shown to develop secondary caries lesions in vitro and in situ [Kuper et al., 2014; Maske et al., 2019; Maske et al., 2017].
Presence of a gap allows the formation of a wall and surface lesion next to a dental restoration. An in vitro study by Kuper et al. [2013] showed that an increased hydrodynamic flow in the gap between composite and tooth material leads to an increase in wall lesion development.
A more recent study by Askar et al. [2017] found that loading a tooth-restoration sample containing a gap of 100 µm width led to increased caries lesion formation compared to unloaded samples. They theorized that the loading on the sample containing a gap could lead to compression of the gap area. When the force is released, the compression ends, and the gap returns to normal. This cyclic deformation of the gap area could possibly lead to an increased hydrodynamic flow, which explains the increase in lesion formation in loaded samples.
Since only in vitro data is available on this topic, the clinical relevance is so far unclear. Whether the effect of loading of restorations still influences the secondary caries process in a more variable clinical environment, is unknown.

Objective:
The aim of this in situ study is to investigate whether occlusal loading leads to increased secondary caries formation in loaded compared to unloaded samples in a near-clinical environment.

Study design:
A mono-center, single blind in situ study, with split-mouth design.
Edentulous subjects will receive a duplicate of their lower denture containing sterilized tooth samples in slots. Half the samples will be placed in occlusal contact with the upper denture. The other half will be placed slightly lower, out of contact. The appliance has to be dipped in 20% sucrose solution 4 times a day for 10 minutes. The appliance containing samples needs to be worn for 6 weeks, 24 hours a day.

Study population:
Healthy edentulous volunteers (>18 years old) who wear a full denture in the lower jaw. A sample size of n=14 will be aimed for.

Main study parameters/endpoints:
The main study parameters are lesion depth (µm) and integrated mineral loss (µm.vol%) in the tooth sample close to the restoration margin. These will be measured through the microradiographic technique T-WIM.

Compressive occlusal loading of a space between composite and tooth material will lead to an increase in lesion depth and mineral loss in these samples.

Start of wearing denture containing samples = t0
Samples are worn for 6 weeks. Samples are measured afterwards = t42

Lower dental prosthesis is copied and equipped with samples. No direct intervention on subjects. Samples are dipped in sucrose solution 4 times a day.