The wholly impacted maxillary 3rd molars are difficult to extract, due to the limited surgical view and the risk of increased adjacent tooth movements and oroantral communications [1,2,3,4,5]. With the soft tissue surrounded and the adjacent teeth erupted distally, the surgical field is usually narrow and should be carefully widened with small retracts. The risk of adjacent tooth injury is related to two factors impaction depth and the angle towards the adjacent tooth. The deeper the tooth impacted, the larger amount of bone is needed to be removed. Thus, it leads to the loss of distal support to the adjacent tooth1. The traditional method uses the occlusal approach, which means the distal bone support would be removed to the level of the impacted crown. Therefore, it calls for a novel method to remove bone in another approach, especially when deep impacted teeth are needed to be extracted. The bigger the angle between the axes of the impacted tooth and the adjacent tooth is, the larger crown resistance is existed during extraction [11]. Although the remove of the distal bone of the impacted tooth crown is relatively not hard due to the low bone density of the maxilla, the buccal approach could avoid almost all crown resistance, which reduces the adjacent tooth injury risk. The oroantral communication is associated with the proximity of the tooth and maxillary sinus. In literary, the impacted maxillary 3rd molars could be divided into several types based on the orthopantomography (OPG) image features between the tooth root and the sinus bottom white line [12, 13]. However, it could only indicate the possible relationship of the tooth and sinus. To show the detailed relationship, CBCT should be taken [14]. In this study, the focus is not located on this topic, but the surgeons could recognize the oroantral communication risks because all included cases had taken CBCT examinations. The oroantral communication risk is related to the impaction depth and the surgical approach. The proximity is closer between the teeth and sinuses when the teeth impact in deeper positions. For the teeth in close proximity to the sinus, the extraction approach could make passage into the oral environment and the sinus [3]. And without a tight and perfect closure and adequate postoperative care, the oroantral communication could be occurred after surgery. Because the surgical incision is on or near the alveolar crest, the occlusal approach is easier to make this communication due to the close location between the suture and the tooth dislocation passage [15, 16]. In the buccal approach, the tooth dislocation passage is on the buccal side, which is away from the suture. Thus, this novel approach could help decrease this risk. Considering all risk factors above, a novel method to extract impacted maxillary third molars in a buccal approach was introduced and implemented in this study.

For maxillary 3rd molars, OPG could be used to evaluate the surgical difficulty. But for the impacted ones, CBCT could show more details, which valued in guiding the surgery [17,18,19]. Besides, the CBCT data could be transferred for surgical simulation, which has been a hot topic in bone surgery in recent years [20, 21]. In our study, it has been proven valid in evaluation of the 3D reconstruction of CBCT and surgical simulation. The limitations of this computer technique are time-consuming, but it will benefit in pre-surgery patient communication and helping surgical design. With artificial intelligence widely applied in surgical design, it might help to lighten the workload of surgeons in the future.

The surgical procedures of the novel method include the following steps:(1)make incisions near the distal alveolar crest of the maxillary second molar; (2)remove the buccal bone to expose the crown of the impacted tooth based on the surgical design; (3)rotate the impacted crown disto-buccally and extract the whole tooth in buccal approach; (4) embolize gelfoam and make tight sutures. The key step of the surgery was the crown rotation with adequate bone removal. The bone removal side was chosen according to the impaction depth shown in CBCT and its reconstruction. A guiding the pad made before the surgery would contribute to make a more precise location of bone removal [22]. However, it will increase the presurgical work and the surgical cost. It could be a research direction in the future when a low-cost and fast manufacturing guiding pad is introduced.

In this study, deeper impacted maxillary 3rd molars were more likely to use the novel extraction method. It was shown in the study that 82.00% of teeth in position I and 50.00% of teeth in position II were designed using the traditional method, while 83.33% teeth in position III were designed using the novel method (p < 0.05).The possible explanations are listed as follows:(1) there was larger bone resistance of the occlusal side of the impacted crown than the buccal side in the deep impacted tooth; (2) the deeper impacted tooth usually has a closer relationship with the sinus [12], the novel method could decrease the oroantral communication risk as it has been discussed. This study found the teeth which had larger angles with the adjacent teeth were more likely to be extracted using the novel method. The teeth impacted with large angles to the adjacent teeth had large resistances from the adjacent teeth [11]. Therefore, it could be suggested that the novel method was applicable and could reduce even avoid the crown resistance of the adjacent teeth.

The complications happened in this study were mild and acceptable. And all patients recovered no longer than 3 months. In total, 4 cases had complications. Among them, two cases suffered with increased adjacent tooth movements, while two cases got oroantral communication. They were all deep impacted (positions II and III) and had large impacted angles towards the adjacent teeth (angulations B and C). Three of them were extracted using the traditional method, while one was removed using the novel method, indicating that the novel method might help to reduce the risk of complications. The limitation of this study is the observational character. A multi-center with a large sample trial is needed to lead to more meaningful conclusions.