A New in vitro Model to Study the Relationship of Gap Size and Secondary Caries

Abstract

Objectives: To investigate the relationship of gap size and secondary caries in a newly developed secondary caries microbial model that permits adjustment of the gap between the tooth and a restoration. Methods: Tooth-resin-matrix composite specimens were mounted on gap-model stages with a gap size of 50 or 500 µm in experiment 1, and 0, 25, 250, or 1,000 µm in experiment 2. They were attached to plastic Petri plates, gas-sterilized and then incubated in a microbial caries model (with Streptococcus mutans TH16 in 1% sucrose tryptic soy broth for 1 h, 4 times/day, and with a buffer solution for the rest of the day). After 8 days of incubation, tooth specimens were sectioned and stained overnight with a rhodamine B solution. Digital images taken under a confocal microscope were analyzed for lesion size at the outer surface lesion and wall lesion (WL). Results: Gap size was found to affect the development of dentin WL area in experiment 1 and enamel and dentin WL areas in experiment 2, with bigger lesions being observed in the wider gap group (p < 0.05). Conclusion: The findings of this study suggest that the size of the gap between tooth and restoration affects the development of secondary caries along the cavity wall.

Isolated development of inner (wall) caries like lesions in a bacterial-based in vitro model

“…Both aspects deliver the rationale for the hypothesis that wider gaps allow the development of larger secondary wall lesions. However, the influence of the gap width is still a matter of debate, and conflicting results can be found in the literature [14,16,[21][22][23]. Also, recent investigations in vivo and on extracted teeth were often criticised because the diagnosed caries in the tooth restoration interface was not supposed to be a secondary caries lesion but either an inner part of the outer lesion or a residual caries [12,21,24,25].…”

“…Studies on effects of different gap widths on the extent of caries lesion have been conducted in vivo [13,21], on extracted teeth [15], and in vitro with different bacterialbased caries models [14,16]. Each of these experimental designs has its advantages and disadvantages.…”

“…For the production of defined microspaces, a vice-like appliance was constructed at the Medical Research Department of the Charité based on the construction described by Totiam et al [16]. Our vice-like appliance was made of polyoxymethylene and consists of a static part and a movable part.…”

“…García-Godoy et al [5] also measured gap sizes less than 2 μm next to secondary carious lesions. A recently published study by Totiam et al [16] used a microbialbased in vitro caries model with adjustable gap widths and found that the width of the gab between the tooth and the restoration affects the development of secondary caries. However, also in this study, primary lesions and wall lesions were not considered independently.…”

Secondary caries and microleakage

“…This geometric setup was replicated in an improved mechanical device several years later against a block of resin composite [140]. The authors concluded that there were clear correlations between gap size and demineralized lesions in the contact zone, which they regrettably named "wall lesion".…”