This doctoral thesis highlights epidemiological, anatomical, diagnostic, clinical and broad biomedical aspects of the permanent maxillary molars (PMMs) with a supernumerary palatal root (SPR). In the first study, we examined the external morphology of 44 PMM (18 second and 26 third PMMs) with SPR and a reference sample of 44 PMMs with one palatal root from the collection of extracted teeth. The same teeth were also analysed for the internal morphology after they were scanned using the cone-beam computed tomography (CBCT). In the second study, we performed a retrospective clinical study on the CBCT scans of the upper jaws belonging to 1173 patients. In the third study, we retrospectively analysed 15 clinical cases of patients who had a total of 17 PMMs with a SPR.
The results of our studies contradict a widespread belief that the SPRs, as well as other supernumerary roots (SNRs) on PMMs, are very rare. Based on our results from the retrospectively analysed clinical CBCT scans, we can expect that on average every 19th patient visiting the dental office has at least one PMM with a SNR (5.29% of patients). Our study on extracted teeth and CBCT scans confirmed the literature data that SPR only rarely develops on the first PMM (0.2% of teeth); however, with increasing frequency on the second (1.3% of teeth) and the third (2.7% of teeth) PMM. We can, therefore, expect to find PMMs with SPR more often on the second PMM during endodontic treatment, and more often on the third PMM during the tooth extraction. The similarity of our results with previously reported frequencies ascertains that the prevalence of SPR is similar among different ethnic groups. The absence of gender differences established in our study is also in agreement with the previous findings.
Clinically, the early identification of SPR is crucial for successful endodontic, periodontal, and surgical treatment. However, the SPR can be difficult to identify from periapical radiographs as palatal and buccal roots often overlap. During the routine dental examination, this root constellation might be predicted mainly by observing the external tooth morphology during the clinical examination; however, until now this has not been empirically tested. We demonstrated that it is possible to differentiate PMMs with SPR from those with one palatal root by observing specific morphological traits on the palatal aspect of the tooth. These distinguishing morphological traits include crown wider on the palatal half, double Carabelli cusp, pronounced palatal indentation of the crown, thick palatal enamel extension, palato-radicular groove, and palatal enamel pearl. The clinical part of our study indicates that the enlarged palatal half of the crown can also result in omega-shaped maxillary dental arch, which may indeed represent the first clue observed by clinician while performing the oral examination. The results from all three studies showed that at least one distinguishing trait is commonly observed on PMMs with SPR (63% to 94% of teeth). These findings could be the key to improve the currently poor clinical identification of the SPR: in none of the 15 retrospectively analysed clinical cases, the SPR was detected prior to referral.
The root morphology of PMMs with SPR varies considerably and cannot be classified according to the existing classifications of Christie et al. (1991) and Baratto-Filho et al. (2002) in over two-thirds of cases. We analysed the data with two multivariate ordination methods. Based on these results, we propose that it is better to describe the roots of these teeth with the type and level of root fusion, and the level of divergence of palatal roots.
We developed a new system for classifying the external root morphology of the teeth of the upper jaw. The new classification codes the number of roots, the type of root fusion, and the level of fusion. We used this classification system to classify permanent maxillary premolars (PMPs) and PMMs from the CBCT scans. Our results indicate that the external root morphology exhibits a high level of left-right symmetry (P > 0.05). The only observed asymmetry was a higher prevalence of right PMMs with SPR (P < 0.01). It is also clinically relevant to note that if one of the teeth is diagnosed with an SPR that there is a 27% probability of finding the SPR on a contralateral or ipsilateral teeth.
Our analysis of CBCT scans of extracted teeth revealed very complex root canal morphology in molars with SPR. In around half of the PMMs with SPR, we can expect challenging endodontic treatment. The complex root canal morphology was most commonly observed in the fused roots. Our results are therefore in contrast with the results from one previous study where simple root canal morphology was described on a relatively small sample of PMMs with SPR. However, our results are comparable to the internal morphology previously observed on second PMMs with fused roots. We also observed other significant deviations from the normal root canal morphology. The distance between the palatal orifices was significantly greater than the distance between the buccal orifices (P < 0.05). The orifice of the distobuccal root canal was positioned more buccally than in PMMs with one palatal root. There was also a pronounced divergence of the mesiopalatal and distopalatal root canal which was also present in the middle third of the root canals, making the palatal root canals significantly more divergent in the middle third compared to the buccal root canals (P < 0.05).
Considering the three different methodological approaches used, we have reason to believe our data on the frequency, external and internal morphology of the PMMs with SPR in the Slovenian population are reliable and will undoubtedly contribute to the identification and more effective treatment of these teeth in the future.
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