Many studies have found that 3D model is helpful to reduce surgical trauma and achieve a good prognosis 14–22. For the model material, PLA has the advantages of good toughness, well stability, excellent water tightness and high durability. It will not produce toxicity or side effects during manufacturing and finally degrade into harmless lactic acid. In addition, compared with other model materials, the manufacturing method of PLA is simpler than cobalt-chromium alloy 20,23, the environmental protection is better than light-cured UDMA material 22 and acrylic resin 19 material, and the manufacturing cost is the lowest.
However, most literature only focus on the intraoperative application of 3D model instead of exploring its preoperative application and function in donor tooth extraction 14–22. In order to understand the effect of 3D model on ATT donor tooth extraction, questionnaires and clinical studies were explored in the present study.
The results of the questionnaire showed that more than half of the general practitioners considered that it was difficult to extract the donor teeth completely, but 65.2% of the surgeons thought that it was less difficult, which may be caused by the insufficient skills and experience of general practitioner on tooth extraction. The results further represented that the model is more helpful for general practitioners on the complete extraction of donor teeth (Question 3), especially in terms of the number of root (Question 5) and the evaluation of root curvature (Question 6), which indicated that general practitioners were inexperienced in the three-dimensional morphology of the root as surgeons. Therefore, it is suggested that oral general practitioners and beginners routinely use three-dimensional printing models pre-operation to obtain more help for complete tooth extraction.
Clinical study results indicate that 3D model can provide information beyond what was traditionally gathered in clinical and imaging examinations, so as to improve the consistency rate between predicted results and actual results.
Furthermore, if the donor tooth is a highly impacted maxillary single rooted tooth, the consistency rate between the predicted results and the actual results is relatively high regardless of the model prediction. On the contrary, if the donor tooth is a median or low impacted mandibular tooth with two or more roots, the consistency rate is relatively low. The corresponding reasons are as follows: (1) The maxillary bone is more osteoporotic. The impaction state of maxillary impacted teeth is simpler than that of mandibular impacted teeth. Most of them have fully erupted teeth, so it is easy to predict. (2) The single rooted teeth are usually conical, due to numerous roots of multiple rooted teeth and big bifurcation in most of them, it is not uncommon to see malformed micro-roots that are difficult to be recognized by CT, so the former is easy to predict. (3) The elimination of resistance of mucous membranes mainly focused on high impacted donor extraction, which is an easy process of toto extraction; whereas, the elimination of resistance of bone and adjacent teeth is a difficult surgeon process in low impacted donor tooth extraction, leading to the incomplete tooth extraction. Both of them are easy to predict pre-surgeon with high consistency rate. However, the situation of middle impacted donor teeth is complex, and the consistency rate between prediction and actual results is the lowest.
Table 4 shows that with the help of the 3D model, we can intuitively observe the shapes and integrities of the various surfaces of the tooth crown, the number, shape, length and developmental status of the tooth root, the angle of the root bifurcation as well as the excessively curved and slender root tip in the donor tooth. We can also find adjacent caries, weak part of tooth tissue, and malformed micro-roots that are missed or incompletely demonstrated on CT, so as to supplement the insufficient imaging examination. At the same time, it also reminds both general practitioners and oral surgeons that once it is expected that the donor teeth cannot be extracted in toto, the surgical plan should be designed after root fracture, and prepare retrograde root canal filling instruments before operation, and avoid improper force and blind operation during the operation. For the actual failure to extract the donor tooth in toto, it is necessary to summarize the reasons in time and make later improvement.
Further comparative study resulted that the prediction coincidence rate of donor tooth extraction in the model group is statistically significant higher than that in another group. This is a new function that we discover and summarize in ATT besides the 3D model of donor teeth. This also suggests that we can continue to look for the role of the model in postoperative fixation and root canal therapy, and further explore the role of the model in preparing alveolar fossa during operation.
In the present study, the strengths of using 3D model provide dentists with further evidence for tooth extraction prediction and help general practitioners to improve pre-operative preparation of tooth extraction, so as to facilitate the subsequent transplantation surgery. However, there are also some limitations, such as the need for professionals to make the 3D model, the necessity for additional time to make model, and the increase in patient medical expenses.