ERRORS IN THE PARTIAL DENTURES FABRICATION PROCESS DURING PPDM LESSONS

Aim: The aim of the research is to make an analysis of the most often FDM-Sofia students’ errors in the partial dentures fabrication process. Materials and methods: A number of 155 partial dentures were analysed after practical exam of the 2nd year FDM-Sofia students. Some of the basic fabrication errors were analysed such as; proper resin polymerization, finishing and polishing process, denture borders shaping, interdental spaces, teeth setup, clasps and major connector profile. Results: The results from the research revealed significant theoretic and practical errors, due to inadequate training process of the students. We found a necessity to introduce a problem-based education in the PPDM training process. Conclusion: The contemporary education in prosthetic dental medicine, should lead the students into understanding the frames of problem based education.

The partial dentures treatment is studied during the lessons and lectures of Prosthetic dental medicine department [1].The errors in fabrication process, could cause trauma to oral mucosa, periodontium, teeth and TMJ [2].These errors are two basic types; in denture planning and fabrication process or clinical mistakes [3].Also another group of errors, could be described -aesthetic errors [3,4].According to another classification of errors, they could be divided to two groups -errors made by dental technicians and errors based on dental work [5,6,7].The successive dental treatment require patients' satisfaction, faster denture adaptation and reduced disadvantageous effects from the treatment [8].
There are researches in the PPDM department about the wax modelling technique, student's theoretical and practical knowledge and there is no studies about the partial dentures fabrication process [2,9,10,11,12].
The aim of the research is to make an analysis of the most often FDM-Sofia students' errors in the partial dentures fabrication process.

MATERIAL AND METHODS
155 partial dentures were examined and analysed during the practical exam of the 2nd year FDM-Sofia students.The partial dentures evaluation was focused on the following criteria, based on the standards created by us about this research.The following criteria were observed: resin polymerization, finishing and polishing process, denture borders shaping, interdental spaces, teeth setup, clasps and major connector profile.A statistical sample is based on the Pearson nonparametric analysis, Phi correlation criterion, and normal alignment criterions.About the statistical sample production we used SPSS for Windows, 21.

Fig. 6. Correlation between polymerization and interdental space criterions
The next special correlation is between polymerization process and the modelled interdental spaces.38.1% (59 dentures) have shaped interdental spaces, and 61.9% (96 dentures) have no good-shaped interdental space.There is correlation between thicker denture plate and not good shaped interdental spaces.
44.5% from the dentures are with sharp, thin, badshaped margins.This is traumatic for the oral mucosa and the denture is not functional.(Fig. 8).The teeth setup is a major factor in the denture stability and retention.32.3% of the dentures were with incorrect teeth setup, away from the centre of the alveolar ridge.
We found errors and in the clasps setting up -47.1% with a sharp tip, 31.67%curved or sliced by the grinders.74% of the maxillary dentures are with errors in the palatal part of the double arm clasp (shortened, sliced or covered with resin).74.8% by the dentures have errors in the retentive part of the clasp included in the denture.This part is shortened and non-functional.The major connector of the mandible denture is correctly possessed in 43.2% by the dentures.3.9% by the dentures are with shortened, 17.4% with elongated and 35.5% with incorrect possessed major connector.
The denture repair was evaluated by 2 factors -selfcuring resin polymerization process and resin possession.We found a high correlation between the repair self-curing resin polymerization and the dentures resin polymerization /χ 2 =26.77,P<0.001/.The well-done denture resin polymerization correlates with well-done self-curing resin polymerization, and the statistical significance is very high / ϕ=0.43,P<0.001/.

DISCUSSION
The analysis of the students' dentures and their errors must be taken into serious consideration.The accumulation of errors is a serious problem about students' theoretical and practical skills in the PPDM lectures and lessons.
Our aim is to show and eliminate these errors of the students in lectures and lessons.The multiplication of those errors in the future clinical exercise will lead to fabrication of non-functional and non-preventive dentures.We look for the students' manual skills development in the practical lessons along with their theoretical knowledge in the lectures.The students must find the correlation between both of them.
Our general aim in the PPDM teaching process is to interpret the correlation between the preclinical and clinical parts of the prosthetic dental medicine and to introduce the main question 'WHY'.'WHY the dentures must be polished?','WHY the teeth must be correctly arranged?',etc.

CONCLUSION:
The contemporary dental medicine studying process includes problem based on students' education.We must create a logical students' thinking process and it to be the base for manual skills and good practice.