Reconstruction of dental roots for implant planning purposes: a retrospective computational and radiographic assessment of single-implant cases

Abstract

Purpose: The aim of the study was to assess the deviation between clinical implant axes (CIA) determined by a surgeon during preoperative planning and reconstructed tooth axes (RTA) of missing teeth which were automatically computed by a previously introduced anatomical SSM.

Methods: For this purpose all available planning datasets of single-implant cases of our clinic, which were planned with coDiagnostix Version 9.9 between 2018 and 2021, were collected for retrospective investigation. Informed consent was obtained. First, the intraoral scans of implant patients were annotated and subsequently analyzed using the SSM. The RTA, computed by the SSM, was then projected into the preoperative planning dataset. The amount and direction of spatial deviation between RTA and CIA were then measured.

Results: Thirty-five patients were implemented. The mean distance between the occlusal entry point of anterior and posterior implants and the RTA was 0.99 mm ± 0.78 mm and 1.19 mm ± 0.55, respectively. The mean angular deviation between the CIA of anterior and posterior implants and the RTA was 12.4° ± 3.85° and 5.27° ± 2.97° respectively. The deviations in anterior implant cases were systematic and could be corrected by computing a modified RTA (mRTA) with decreased deviations (0.99 mm ± 0.84 and 4.62° ± 1.95°). The safety distances of implants set along the (m)RTA to neighboring teeth were maintained in 30 of 35 cases.

Conclusion: The RTA estimated by the SSM revealed to be a viable implant axis for most of the posterior implant cases. As there are natural differences between the anatomical tooth axis and a desirable implant axis, modifications were necessary to correct the deviations which occurred in anterior implant cases. However, the presented approach is not applicable for clinical use and always requires manual optimization by the planning surgeon.

Keywords: Dental implant; Implant planning; Statistical shape model; Virtual surgery.

Fig. 1

Annotated intraoral scan of patient #23

Fig. 2

Dataset with missing tooth 11. The tooth-crown landmarks of the missing tooth were estimated by the SSM (black dots). A straight line passing through the occlusal and apical center point of the conventionally planned implant (green line) depicts the CIA with the corresponding occlusal entry point (green dot). The RTA (blue line) and the estimated cemento-enamel-junction line (CEJL, blue dot) deviate from the CIA

Fig. 3

Scheme of measured errors. The distance d was measured as the shortest connection line between the occlusal entry point (green dot) of the implant (black) and the RTA (blue line). The angular deviation α was measured between the RTA and the CIA (green line)

Fig. 4

Determination of an oro-vestibular reference plane perpendicular to the incisal edges of the missing tooth (black dots) for further evaluation of the angular deviation. Left: The CIA (green line) with the occlusal entry point of the implant (green dot), the RTA (blue line) with the estimated height of the CEJL (blue dot) and the mRTA (red line) with the calculated pivotal-point (red dot) are depicted in a dataset with missing tooth 11. The reference plane is depicted as a gray rectangle, which is perpendicular to the estimated incisal edge (connection line of black dots) Right: Projection of the CIA (green), RTA (blue) and mRTA (red) onto the reference plane (yellow) for further analyses

Fig. 5

Example of a comparable accurate reconstruction result (patient #29) with an implant in region 15. The original implant is depicted in green. The implant placed along the mRTA is depicted in yellow

Fig. 6

Example of a comparable poor reconstruction result (patient #34) with an implant in region 21. The original implant is depicted in green. The implant placed along the mRTA is depicted in yellow and appears to be shifted into a palatal-left direction leading to undercut safety distances to the neighboring tooth 23 (0.73 mm, see left image)