Accuracy assessment of digital impressions with varied scanning paths in partially edentulous ridges with mobile abutment teeth: An in vitro comparative study

Abstract

Background: Periodontal prosthesis or removable partial dentures are essential treatments for partially edentulous dentition with periodontal issues. This study aimed to assess the accuracy of digital impressions obtained through an intra-oral scanner, employing different scanning paths versus conventional impressions in partially edentulous ridges with mobile abutment teeth.

Methods: Eight lower Kennedy class I and class III models were employed as test models. The abutment teeth in these models were subjected to various mobility grades, according to the Miller classification. Reference data was generated by scanning the test models using an extra-oral laboratory scanner. An intra-oral scanner (TRIOS 4; V21; 3Shape A/S) was used to obtain ten digital impressions following two different scanning paths (Scan path A and Scan path B). For conventional impressions, two impression materials (Monophase polyether and Polyvinyl siloxane) were used to create ten impressions with a one-step technique. Working stone casts were produced and converted to digital data. Accuracy was assessed by analyzing the deviation between test data (digital and conventional data) and the reference data using 3D software (Geomagic Control X). The data was analysis using sequential tests, including two-way and one-way ANOVA, and paired t-tests (p < 0.05).

Results: Digital impressions obtained through an intra-oral scanner exhibited significantly higher accuracy. Within the digital impression category, those recommended by the manufacturer obtained using scan path A showed lower deviations than those acquired through scan path B. Considering the degree of tooth mobility, models with GII and GIII mobile RPD abutment teeth displayed significantly higher deviations (p < 0.001) than those with G0, GI across all impression techniques. The accuracy of conventional impressions with GII and GIII mobility was clinically unacceptable (deviation >200µm).

Conclusion: For partially edentulous cases with mobile abutment teeth, digital impressions exhibited superior accuracy for G0, GI. Following the manufacturer-recommended scanning protocol in scan path A can improve the accuracy of impressions. Furthermore, if there is persistent mobility, particularly in GII and GIII, the use of final conventional impressions is forbidden.

Fig 1. (A) Mandibular model of Kennedy class I, (B) Mandibular model of Kennedy class III modification 1.

Fig 2. (A) Digital designing of premolar to decrease 1 mm of root surface, (B) 3D printed tooth compared to artificial tooth of model.

Fig 3. Schematic diagram of study procedures, n = number of impressions per model.

Fig 4. Scanning paths.

(A) Scan path A, (B) Scan path B.

Fig 5. (A) and (B) Digital design of custom tray in posterior view and overhead view, (C) and (D) internal and side view of stop points fabricated in the external surface of the custom tray.

Fig 6. (A) Digital segment of mobile abutment teeth.

(B) Data selection of mobile abutment teeth for the best-fit alignment. (C) Data selection of mobile abutment teeth to make a 3D comparison. (D) Color map image of mobile abutment teeth accuracy.

Fig 7. Color images of differences between overall surface of test and reference scanners of digital and conventional impressions for Kennedy class I of the mandibular edentulous ridges.

The color difference map is adjusted from −0.5 mm to +0.5 mm. Positive deviations are indicated by yellow to red color, negative deviations by blue color, and nearly no error between two superimposed models by green color. (A) Color images of deviation from digital impressions (Scan path A) and reference models; (B) Color images of deviation from digital impressions (Scan path B) and reference models; (C) Color images of deviation from Conventional impressions (Monophase polyether) and reference models; (D) Color images of deviation from Conventional impressions(Polyvinyl siloxane) and reference models; 0- Indicates mobility grade 0; 1- Indicates mobility grade I; 2- Indicates mobility grade II; and 3- Indicates mobility grade III.

Fig 8. Color images of differences between mobile abutment teeth of test and reference scanners of digital and conventional impressions for Kennedy class I of the mandibular edentulous ridges.

The color difference map is adjusted from −0.5 mm to +0.5 mm. Positive deviations are indicated by yellow to red color, negative deviations by blue color, and nearly no error between two superimposed models by green color. (A) Color images of deviation from digital impressions(Scan path A) and reference models; (B) Color images of deviation from digital impressions(Scan path B) and reference models; (C) Color images of deviation from Conventional impressions(Monophase polyether) and reference models; (D) Color images of deviation from Conventional impressions (Polyvinyl siloxane) and reference models; 0- Indicates mobility grade 0; 1- Indicates mobility grade I; 2- Indicates mobility grade II; and 3- Indicates mobility grade III.

Fig 9. Box plot diagrams of the significant interaction between impressions techniques and abutment teeth mobility in Kennedy class I models.

(A) The overall surface, (B) Mobile abutment teeth.

Fig 10. Color images of differences between overall surface of test and reference scanners of digital and conventional impressions for Kennedy class III modification one of the mandibular edentulous ridges.

The color difference map is adjusted from −0.5 mm to +0.5 mm. Positive deviations are indicated by yellow to red color, negative deviations by blue color, and nearly no error between two superimposed models by green color. (A) Color images of deviation from digital impressions(Scan path A) and reference models; (B) Color images of deviation from digital impressions(Scan path B) and reference models; (C) Color images of deviation from Conventional impressions(Monophase polyether) and reference models; (D) Color images of deviation from Conventional impressions (Polyvinyl siloxane) and reference models; 0- Indicates mobility grade 0; 1- Indicates mobility grade I; 2- Indicates mobility grade II; and 3- Indicates mobility grade III.

Fig 11. Color images of differences between mobile abutment teeth of test and reference scanners of digital and conventional impressions for Kennedy class III modification one of the mandibular edentulous ridges.

The color difference map is adjusted from −0.5 mm to +0.5 mm. Positive deviations are indicated by yellow to red color, negative deviations by blue color, and nearly no error between two superimposed models by green color. (A) Color images of deviation from digital impressions (Scan path A) and reference models; (B) Color images of deviation from digital impressions (Scan path B) and reference models; (C) Color images of deviation from Conventional impressions (Monophase polyether) and reference models; (D) Color images of deviation from Conventional impressions (Polyvinyl siloxane) and reference models; 0- Indicates mobility grade 0; 1- Indicates mobility grade I; 2- Indicates mobility grade II; and 3- Indicates mobility grade III.

Fig 12. Box plot diagrams of the significant interaction between impressions techniques and abutment teeth mobility in Kennedy class III models.

(A) The overall surface, (B) Mobile abutment teeth.