An automated artificial mouth to produce secondary caries like lesions

Objective: To design an automated artificial mouth in order to simulate secondary caries at resin composite margins in vitro.

Methods: 48 caries-free human third molars received standardized Class-V restorations. Six groups with three materials (Ceram X with Prime & Bond NT [CX], Dentsply DeTrey; Ketac Molar [KM], 3M ESPE and an experimental hydroxyapatite cement [HC], Heraeus Kulzer) were used with two different protocols. After storage in water for four weeks at 37°C, teeth were subjected to 10,000 thermocycles (±5°C and ±55°C). Streptococcus mutans 10449 (SM) was used in a nutrition medium to initiate a secondary caries process. The teeth were automatically incubated for 4 or 22 hours in SM containing nutrition medium followed by 22 or 4 hours incubation in artificial saliva for a total period of 10 days (protocol 1 or 2). After thermocycling and biological load cycling, precision polysiloxane impressions were taken and replicas were investigated under a light microscope for gap widths at enamel and dentin margins. Demineralization was evaluated by fluorescence microscopy using a special FITC filter. The demineralization depths at the cavity margin were calculated using a pixel distance of 5 µm.

Results: After SM incubation, gap widths and demineralization depths were significantly dependent both on SM incubation time and material (p<0.05). The resulting data were: gap width enamel margin (GE) in µm (SD) after 4 h/22h; dentin margin (GD) after 4 h/22h in µm (SD); dentin demineralization depths (DD) in µm (SD) ; CX: GE 37.2(11.6)/41.5(26.3); GD 19.2(7.5)/34.4(17.9); DD 95.0(42.4)/98.(37.3) KM: GE 19.2(8.4)/41.8(35.4); GD 31.2(8.8)/35.49(7.4); DD 50.0(19.4)/84.3(25.5) HC: GE 60.2(14.6)/66.7(47.7); GD 50.2(24.8)/67.0(28.2); DD 82.5(25.6)/97.5(26.8).

Conclusions: After 4 h/day incubation with SM, the resulting secondary caries like lesions are comparable to the clinical situation. Supported by Heraeus-Kulzer, Germany.