Trueness of full-arch IO scans estimated based on 3D translational and rotational deviations of single teeth-an in vitro study.

OBJECTIVES: To three-dimensionally evaluate deviations of full-arch intraoral (IO) scans from reference desktop scans in terms of translations and rotations of individual teeth and different types of (mal)occlusion. MATERIALS AND METHODS: Three resin model pairs reflecting different tooth (mal)positions were mounted in the phantom head of a dental simulation unit and scanned by three dentists and three non-graduate investigators using a confocal laser IO scanner (Trios 3®). The tooth-crown surfaces of the IO scans and reference scans were superimposed by means of best-fit alignment. A novel method comprising the measurement of individual tooth positions was used to determine the deviations of each tooth in the six degrees of freedom, i.e., in terms of 3D translation and rotation. Deviations between IO and reference scans, among tooth-(mal)position models, and between dentists and non-graduate investigators were analyzed using linear mixed-effects models. RESULTS: The overall translational deviations of individual teeth on the IO scans were 76, 32, and 58 µm in the lingual, mesial, and intrusive directions, respectively, resulting in a total displacement of 114 µm. Corresponding rotational deviations were 0.58° buccal tipping, 0.04° mesial tipping, and 0.14° distorotation leading to a combined rotation of 0.78°. These deviations were the smallest for the dental arches with anterior crowding, followed by those with spacing and those with good alignment (p < 0.05). Results were independent of the operator's level of education. CONCLUSIONS: Compared to reference desktop scans, individual teeth on full-arch IO scans showed high trueness with total translational and rotational deviations < 115 µm and < 0.80°, respectively. CLINICAL RELEVANCE: Available confocal laser IO scanners appear sufficiently accurate for diagnostic and therapeutic orthodontic applications. Results indicate that full-arch IO scanning can be delegated to non-graduate dental staff members.

Optical 3D scans for orthodontic diagnostics performed on full-arch impressions. Completeness of surface structure representation.

OBJECTIVE: The purpose of this work was to evaluate the completeness of surface structure representation offered by full-arch impression scans in different situations of tooth (mal)alignment and whether this completeness could be improved by performing rescans on the same impressions reduced sequentially to different levels of gingival height and by adding extra single scans to the number of single scans recommended by the manufacturer. METHODS: Three pairs of full-arch resin models were used as reference, characterized either by normal occlusion, by anterior diastematic protrusion (and edentulous spaces in the lower posterior segments), or by anterior crowding. An alginate impression of each arch was taken and digitized with a structured-light scanner, followed by three rescans with the impression cut back to 10, 5, and 1 mm of gingival height. Both the initial scan and the rescans were performed both with 19 basic single scans and with 10 extra single scans. Each impression scan was analyzed for quantitative completeness relative to its homologous direct scan of the original resin model. In addition, the topography of voids in the resultant digital model was assessed by visual inspection. RESULTS: Compared to the homologous reference scans of the original resin models, completeness of the original impression scans--in the absence of both gingival cutback and extra single scans--was 97.23 ± 0.066% in the maxilla or 95.72 ± 0.070% in the mandible with normal occlusion, 91.11 ± 0.132% or 96.07 ± 0.109% in the arches with anterior diastematic protrusion, and 98.24 ± 0.085% or 93.39 ± 0.146% in those with anterior crowding. Gingival cutback and extra single scans were found to improve these values up to 100.35 ± 0.066% or 99.53 ± 0.070% in the arches with normal occlusion, 91.77 ± 0.132% or 97.95 ± 0.109% in those with anterior diastematic protrusion, and 98.59 ± 0.085% or 98.96 ± 0.146% in those with anterior crowding. CONCLUSION: In strictly quantitative terms, the impression scans did capture relatively large percentages of the total surface. However, the topographic examinations revealed that regions essential for orthodontic model analysis were missing. The malocclusion models were particularly affected. Thus, impression scans performed with structured-light scanners cannot replace scans of positive casts for diagnostic use in orthodontics.

Dimensional accuracy of jaw scans performed on alginate impressions or stone models: A practice-oriented study.

OBJECTIVES: Digital jaw models offer more extensive possibilities for analysis than casts and make it easier to share and archive relevant information. The aim of this study was to compare the dimensional accuracy of scans performed on alginate impressions and on stone models to reference scans performed on underlying resin models. METHODS: Precision spheres 5 mm in diameter were occlusally fitted to the sites of the first premolars and first molars on a pair of jaw models fabricated from resin. A structured-light scanner was used for digitization. Once the two reference models had been scanned, alginate impressions were taken and scanned after no later than 1 h. A third series of scans was performed on type III stone models derived from the impressions. All scans were analyzed by performing five repeated measurements to determine the distances between the various sphere centers. RESULTS: Compared to the reference scans, the stone-model scans were larger by a mean of 73.6 µm (maxilla) or 65.2 µm (mandible). The impression scans were only larger by 7.7 µm (maxilla) or smaller by 0.7 µm (mandible). Median standard deviations over the five repeated measurements of 1.0 µm for the reference scans, 2.35 µm for the impression scans, and 2.0 µm for the stone-model scans indicate that the values measured in this study were adequately reproducible. CONCLUSION: Alginate impressions can be suitably digitized by structured-light scanning and offer considerably better dimensional accuracy than stone models. Apparently, however, both impression scans and stone-model scans can offer adequate precision for orthodontic purposes. The main issue of impression scans (which is incomplete representation of model surfaces) is being systematically explored in a follow-up study.