The aim of the study was to establish a live/dead qPCR with propidium monoazide (PMA) that can quantitatively differentiate between viable/non-viable microorganisms in dental hard tissues. Human premolars (n = 88) were prepared with nickel–titanium instruments and incubated with E. faecalis (21 d). Subsequently, the bacteria in half of the teeth were devitalized by heat inactivation (100 °C, 2 h). The following parameters were tested: PMA concentrations at 0 µmol (control), 50 µmol, 100 µmol, and 200 µmol; PMA incubation times of 30 min and 60 min, and blue light treatment for 30 min and 60 min. The teeth were ground using a cryomill and the bacterial DNA was quantified using qPCR, ANOVA, and p = 0.05. The qPCR of the control group detected a similar number of avital 9.94 × 10⁶ and vital 1.61 × 10⁷ bacterial cells. The use of PMA inhibited the amplification of DNA from non-viable cells during qPCR. As a result, the best detection of avital bacteria was achieved with the following PMA parameters: (concentration, incubation time, blue light treatment) 200-30-30; 5.53 × 10⁴ (avital) and 1.21 × 10^0.7 (vital). The live/dead qPCR method using PMA treatment is suitable for the differentiation and quantification of viable/non-viable microorganisms in dentin, as well as to evaluate the effectiveness of different preparation procedures and antimicrobial irrigants in other biological hard substances.

Extensive biofilm formation on materials used in restorative dentistry is a common reason for their failure and the development of oral diseases like peri-implantitis or secondary caries. Therefore, novel materials and strategies that result in reduced biofouling capacities are urgently sought. Previous research suggests that surface structures in the range of bacterial cell sizes seem to be a promising approach to modulate bacterial adhesion and biofilm formation. Here we investigated bioadhesion within the oral cavity on a low surface energy material (perfluorpolyether) with different texture types (line-, hole-, pillar-like), feature sizes in a range from 0.7–4.5 µm and graded distances (0.7–130.5 µm). As a model system, the materials were fixed on splints and exposed to the oral cavity. We analyzed the enzymatic activity of amylase and lysozyme, pellicle formation, and bacterial colonization after 8 h intraoral exposure. In opposite to in vitro experiments, these in situ experiments revealed no clear signs of altered bacterial surface colonization regarding structure dimensions and texture types compared to unstructured substrates or natural enamel. In part, there seemed to be a decreasing trend of adherent cells with increasing periodicities and structure sizes, but this pattern was weak and irregular. Pellicle formation took place on all substrates in an unaltered manner. However, pellicle formation was most pronounced within recessed areas thereby partially masking the three-dimensional character of the surfaces. As the natural pellicle layer is obviously the most dominant prerequisite for bacterial adhesion, colonization in the oral environment cannot be easily controlled by structural means.

Common antibiotic therapies to treat bacterial infections are associated with systemic side effects and the development of resistance, directly connected to duration and dosage. Local drug delivery systems (DDSs) offer an alternative by localising antibiotics and thereby limiting their side effects while reducing the dosage necessary. A biodegradable polyester polycaprolactone (PCL)-based DDS was thus produced, containing various clinically relevant drugs. It was shown that the incorporation of four distinct antibiotic classes (amoxicillin, doxycycline, metronidazole and rifampicin), with very high mass fractions ranging up to 20 wt%, was feasible within the PCL matrix. This DDS showed the capacity for effective and sustained release. The release kinetics over 14 days were proven, showing a significant decrease in cytotoxicity with smooth muscle cells as well as an antibacterial effect on (1) aerobic, (2) anaerobic, (3) Gram-positive and (4) Gram-negative pathogens in vitro. The DDS demonstrated a markedly diminished cytotoxic impact owing to sustained release in comparison to pure antibiotics, while simultaneously maintaining their antibacterial efficacy. In conclusion, DDSs are a more tolerable form of antibiotics administration due to the hydrophobic PCL matrix causing a slower diffusion-controlled release, proven as a release mechanism via the Peppa–Sahlin model.