The current study was conducted to investigate the accuracy of the open and closed implant impression techniques in partially edentulous patients with two adjacent implants. The ethical principles were adhered to, and ethical approval to conduct the study was duly obtained from the Ministry of Health, State Khartoum, Khartoum University Teaching Hospital, number: [WK/OS/AETEA/44/1].

Patients who were scheduled to receive two adjacent implants were invited to participate in the study. The sample that would have sufficient power for analysis was calculated based on data from the previous clinical study by Stimmelmayr in 2013 [9]. The sample size was determined using the following formula:

where:

n = the required sample size

Z = is the critical value of the normal distribution

σ = the standard deviation taken from the previous study

d = the margin of error (10% × mean).

The sample size was 31 patients; this was increased to 40 participants to accommodate patient dropouts during the study.

The inclusion criteria were patients over 18 years of age and willing to participate. A prerequisite to participation was a treatment plan that would involve two adjacent implants. The patient should also be category ASA I or ASA II medical history (American Society of Anesthesiologists Classification) [10]. Furthermore, evidence of bone loss or implant mobility at the time of impression making, formed part of the exclusion criteria [11, 12].

Informed consent was made, and participants who agreed to participate signed the consent form. For every patient, a surgical positioning guide was fabricated from a diagnostic wax-up that correlated the anatomic conditions. The implant (Osstem Implant System, Seoul, Korea) installation directions were carried out according to the amount and status of the available bone [13]. A Specialist Oral Surgeon placed the implants using the manufacturer’s standardized technique, and similarly, a Specialist Prosthodontist carried out the related restoration steps. For making the impressions, individual trays were initially checked intraorally, and the final impressions made using Virtual Monophase vinyl polysiloxane impression material (Ivoclar Vivadent AG). Before impression making, the horizontal distance between the two impression copings was measured inside the patient’s mouth using a digital caliper (HSL 246-15, Karl Hammacher GmbH, Germany) and recorded (Fig. 1). This recorded intraoral horizontal distances would later be compared against similar horizontal measurements on the master casts, to evaluate discrepancies or horizontal displacements between the positions intraorally and on the master casts. The same impression evaluation criteria used in our previous study were also used here [8], which was described by Lee and Gallucci as follows [14]: