M. Hevinga

Can Caries Fissures be Sealed as Adequately as Sound Fissures

Sealing caries fissures is considered an appropriate treatment option for arresting the caries process. However, little information is available regarding the sealing of occlusal cavitated dentin lesions. The hypothesis tested in this in vitro study was that no difference in microleakage and sealant penetration depth exists between cavitated and sound sealed fissures when a resin is used. Eighty molars, each with an occlusal cavitated dentin lesion, were treated according to 5 experimental protocols and compared with a control group of sealed sound molars. In the experimental groups, fissure sealants were placed with and without an adhesive, and in various ways. All teeth were sectioned, and microleakage and sealant penetration into the fissure were evaluated. Sealed caries fissures showed significantly more microleakage and insufficient sealant penetration depth than sound fissures. Neither the use of an adhesive nor its intermediate curing influenced the microleakage score and the penetration ability of sealants.

Long-term performance of resin based fissure sealants placed in a general dental practice

OBJECTIVES The aim of the present retrospective study was to evaluate the long-term performance of resin based fissure sealants applied in a general dental practice. METHODS Regularly attending patients visiting the practice between July 2006 until November 2007 and who had received sealants before 1st of January 2000 were included in the study. Date of placement of a sealant in posterior non-discoloured permanent teeth and replacement by a restoration was recorded. In a clinical examination occlusal surfaces were scored for (partial) sealant loss and fissure discolouration. The restoration profile of the patient was assessed as low or high, based on the number of restorations placed per year since the first sealant. Sealants had been applied by four dentists and a dental hygienist. RESULTS 1204 sealants were placed in 148 patients. After a mean follow-up time of 11.6 years, 41.3% of placed sealants were still fully retained and 11.4% were replaced by a restoration. Failure rates were significantly higher in high than in low restoration profile patients and in molars compared to premolars. In those fissures with lost or partially lost sealants, discolouration frequently occurred (40% of all surfaces) irrespective of restoration profile of the patient. CONCLUSIONS In this retrospective practice based study, long-term performance of sealants depended on restoration profile of the individual patient and the tooth type (molar versus premolar).

Trigger-less readout electronics for the PANDA Electromagnetic Calorimeter

The PANDA experiment at the future FAIR facility at Darmstadt, Germany, will employ a novel electronics-readout concept: the trigger-less readout. This concept implies an event selection based on the physics properties of detected particles, such as reconstructed invariant mass or a detected secondary vertex. Such an approach requires a completely new design of the readout chain from the front-end to the data acquisition. This paper describes a fully-functional prototype of the readout chain for one of the PANDA subdetectors - the Electromagnetic Calorimeter. The prototype consists of digitizer and data-multiplexer modules. The crucial component of the prototype is the synchronous optical-link connection, which allows to transfer clock signal and time-synchronisation commands in an unambiguous way. The implementation and performance tests of the synchronous optical-link connection are described in the paper.

Trigger-less readout of the PANDA electromagnetic calorimeter

The PANDA collaboration at the future FAIR facility at Darmstadt, Germany, will employ antiproton annihilations to investigate resonances in the charmonium mass region. In order to gain high flexibility for physics event selection, a readout system without hardware trigger, i.e. a trigger-less data-acquisition system will be employed and is currently being developed. The event-selection is based on high-level reconstructed information, e.g. invariant mass, secondary vertices, and time correlations, which may be contributed from all sub-detector systems. Prototypes of the PANDA Electromagnetic Calorimeter have been exploited to verify the desired event-selection approach. The prototype readout system includes a dedicated Sampling ADC (SADC), data concentrator (DCON) and compute-node (CN) modules. An optical link connects several SADC digitizers to a DCON module from where the data are streamed to the CN network. Data, collected by the SADCs are processed online in FPGAs by a feature-extraction algorithm. This processing technique guarantees a dead-time free operation and allows including an on-line pile-up recovery process for single detector counting rates up to 1 MHz. The prototype of the readout-chain has been evaluated using pulse generators and high-energy photon beams; the proper event correlation could be verified. The applied FPGA has been irradiated with protons to demonstrate its applicability in the radiation environment of the PANDA experiment.

Response: Does Incomplete Caries Removal Reduce Strength of Restored Teeth?

We would like to respond to the comments made by Dr. Maltz to our paper (Hevinga et al., 2010). First, regarding the study by Mertz-Fairhurst et al. (1998), it was pointed out that we had ignored the failure rate of conventional amalgam restorations being just as high as that of ‘composite restorations over caries’. However, in that study, caries was the only reason why conventional amalgams failed, whereas the ‘restorations over caries’ failed for various reasons, including restoration loss and fracture, suggesting that fatigue may have played a role in failure behavior. Dr. Maltz’ statement that similar failure rates show that the failures cannot be attributed to the carious tissues ignores this difference in failure behavior. Second, regarding the clinical study by van Nieuwenhuysen et al. (2003), where fracture was the main reason for failure of composite restorations, it must be noted that a base-lining cement was used. Composite restorations with a GIC lining showed significantly more fracture than those placed with only an adhesive (Opdam et al., 2007). With carious tissue being an even softer base than GIC, it may well be that restorations over caries also show increased fracture. Dr. Maltz considers our carefully worded recommendation a step beyond the data. However, we feel that, in the absence of evidence, it is better to err on the side of caution. If more evidence emerges that substantial volumes of carious tissue can be retained without compromising tooth/restoration prognosis, we will be most happy to change our recommendation.