Accurate positioning and proper angulation of a dental implant determine successful treatment outcomes and contribute to the durability of an implant prosthesis. In Russia, the freehand approach has become a gold standard in implant dentistry [1]. The decision about implant positioning is guided by a surgeon’s professional expertise. A misangled implant poses a serious problem for further treatment. According to the official guidelines, the maximum acceptable divergence between the implants is 7° [1]. A few researchers report that in some cases the freehand technique can result in a substantial divergence of up to 35° [2].
Angulation can be significantly improved by using surgical navigation systems that guide the placement of a dental implant [3, 4]. Such systems minimize angular deviation from an implant’s axis, bringing it to the acceptable 7° [5–7]. However, these platforms are not widely applied in clinical routine because they are too costly and can be only used by specially trained surgeons [8–11]. In light of this, freehand surgery still remains one of the most popular methods of implant placement that, unfortunately, can negatively affect treatment outcome if performed unskillfully [12–15].
Stability of dental implants can be evaluated by measuring osseointegration of the installed implant using such systems as Periotest or Osstell ISQ [16, 17].
The aim of this study was to compare divergence between the insertion axes of dental implants installed using a classic freehand technique.

METHODS

The study was carried out at the facilities of the Maxillofacial Surgery Unit of Samara State Medical University between 2015 and 2018. All patients underwent clinical examination. Their medical histories were also taken; complaints, unhealthy habits and comorbidities that could cause postoperative complications or be regarded as contraindications for dental implantation were noted down. The study included 32 partially edentulous patients of both sexes, aged 18 to 65 years, with no comorbidities. The majority of the participants (53.1%) were females aged 26 to 66 years (tab. 1). Dental implantation was performed using a classic freehand technique. Postoperatively, the patients underwent a CT scan (Vatech Pax Duo scanner; Vatech; Korea).

RESULTS

A follow-up clinical examination was conducted in the postoperative period. The patients’ complaints (including those of pain) and body temperature were taken; facial configuration, tissue condition at the site of surgery, implant excursion, sutures and gingiva formers were evaluated.
The MISS and DENTIUM dental implants (Israel) were installed following a conventional two-step protocol. The procedure was carried out by a dental surgeon specialized in implant dentistry. The number and size the installed implants are given in tab. 2.
Ten patients were randomly selected for a CT scan (Vitech Pax Duo) in order to estimate the average divergence between the axes of the installed implants. The angles were calculated using the following algorithm (software patent 2018661716):

formula

A total of 22 implants were analyzed in 10 patients.
Briefly, Cartesian coordinates of necks of the compared implants were determined on the CT image in the XOY (horizontal) plane (fig. 1A) followed by the coordinates of apices (fig. 1B). The obtained data were fed to the software developed by the authors of this study (patent 2018661716 issued September 12, 2018); the software computed the angle between the axes of the installed implants.
Then, the data were structured and analyzed, and the dynamics of angular deviations were determined.
In 100% of the studied cases, the implants were not parallel. In sector 4, the implants were minimally divergent. On average, the angle between the insertion axes ranged from 2° 58ˈ to 5° 4ˈ, falling into the accepted range of deviations. In sectors 2 and 3, the angles between the insertion axes of the installed implants varied from 3° 4ˈ and 17° 96ˈ (sector 3) and from 1° 83ˈ to 17° 75ˈ (sector 2), suggesting an unsatisfactory implantation result. In sector 1, the deviation reached 27° 4ˈ, which might have resulted from difficult anatomy. Summing up, the most significant divergence was observed in sector 1.

DISCUSSION

The divergence between the insertion axes of the installed dental implants was significant (27° 4ˈ) in 87% of cases, falling outside of the acceptable values (fig. 2). In this study, the axis was defined as a geometric center of an implant shaped as a regular cylinder.
The most significant divergence was observed in the projection of sector 1, which is consistent with the findings of other researchers [6, 12, 15]. The lowest statistically significant values were ± 0.5°. In the present study, the teeth were assigned to 4 sectors, according to the WHO classification: sector 1, teeth 1.1 to 1.8; sector 2, teeth 2.1 to 2.8; sector 3, teeth 3.1 до 3.8; sector 4, teeth 4.1 to 4.8.
Understanding the effects of divergence between the installed implants on treatment outcomes and the importance of accurate implant placement is critical for the health of the entire dentofacial system.

CONCLUSIONS

In this work we studied the angles between the axes of the implants installed during a freehand surgical procedure. The freehand approach should be further improved by using mechanical devices and semi- or fully automatic systems for guiding dental implant placement. We recommend our mathematical model as a tool for measuring divergence between the axes of dental implants.