A Comparative Assessment Of manual Versus Digital Analysis of Quality of Tooth Preparations for Single Crowns in Nairobi, Kenya

Abstract

Introduction: Tooth preparation refers to the process of removal of diseased and/or healthy enamel and dentin to shape a tooth to receive a crown. The quality of tooth preparation is an important clinician variable as it determines the retention and resistance form of the indirect restoration. Different analogue and digital methods have been used in research to assess the quality of tooth preparations. There is a need to determine which method has greater precision. Objective: To conduct a comparative assessment of manual versus digital analysis of quality of tooth preparations for single crowns in Nairobi, Kenya Study design: A laboratory based cross sectional study based in a dental laboratory in Nairobi, Kenya. Materials and methods: The study was conducted in a dental laboratory in Nairobi Kenya. The laboratory was identified through purposive sampling. One hundred and twenty-five dies for single teeth preparations made from elastomeric material were included in the study. These were conveniently sampled from elastomeric impressions delivered to the laboratory for full coverage crowns fabrications. The buccal-lingual convergence, occlusal cervical height, margin design and the presence/absence of auxiliary retentive features were analyzed using an analogue method by direct measurement on the die and a digital method on scanned dies on a metrology software (GOM Inspect Suite, 2020). Data analysis and results presentation: The collected data was analyzed using the Statistical Packages for Social Sciences (SPSS) 20.0 for Windows. Descriptive summaries (frequencies, means and standard deviations) and inferential statistics (independent sample ttest, Fischer’s test) were used. A 95% confidence level was considered for the study Results: The overall mean Buccal-Lingual convergence angle assessed using manual method for maxillary anterior, premolars and molars were 21.9, 17.3 and 30 degrees respectively. While using the digital method, maxillary anterior, premolars and molars had mean buccal lingual convergence angles of 23.3, 18.6 and 30.9 degrees respectively xvi From the manual assessment, the maxillary anterior, premolars, and molars had a mean occlusal cervical height of 4.47mm, 3.22mm, and 3.62mm. In the mandibular arch, anterior teeth, premolars, and molars had a mean of 3.05mm, 3.69mm, and 3.16mm respectively. In both measurement methods, mandibular molars had the highest number of non-ideal preparation height (86.36%/ 90.91% manual/digital). Maxillary anterior teeth and premolars had most preparations having an ideal occlusal cervical height. The results for the presence/absence of auxiliary retentive were the same for manual and digital method. Majority of the dies (97.6%) did not have any auxiliary retentive feature. Majority (77.6%) of these preparations had been made for All- ceramic crowns while 22.4% were for Metal-ceramic crowns. The results for visual assessment of margin design were the same for manual and digital methods. In most of the cases, the all-ceramic crowns had a shoulder margin on the facial aspect (97.9%). A chamfer margin was used on the facial aspect for all ceramic crowns in 2.1% of the cases. For metal ceramic crowns, a shoulder facial margin was consistently used in 100% of cases. On the lingual aspect, all ceramic crowns had a shoulder margin in 95.9% of cases. The chamfer margin for all ceramic crowns was used in 4.1% of cases. For metal-ceramic crowns, the shoulder margin was used lingually in 82.1% of preparations made for PFM while the chamfer was used in 17.9%. There was no statistically significant difference between the mean of the buccal lingual convergence angle as assessed using manual and digital method (t = -0.8941, p-value = 0.3722). No statistically significant difference was found between the mean of occlusal cervical height as assessed using manual and digital methods (t= 1.4138 p-value = 0.1587). There were no significant differences between digital and manual methods when evaluating for both margin design and presence/absence of auxiliary retentive features (Fisher’s exact score = 0.00) Conclusions: Differences in output between manual and digital methods of analyzing the geometry of tooth preparations exist. However, these are not statistically significant for linear and angular measurements. No differences exist between the two methods for visually assessed variables of presence of auxiliary retentive features and the marginal design. xvii There is a high proportion of non-ideal preparation geometry in Kenya since only 42.2% on manual and 37.8% on digital analysis had the ideal buccal lingual convergence and 38.9% on manual and 35.6% on digital analysis had the ideal occlusal cervical height. Recommendations: Poor geometry of teeth preparations warrants needs for continuous education among practicing clinicians. Further studies can be done using different metrology software to evaluate differences among systems.