Quantifying Workflow-Induced Vertical Measurement Variability Between Pre- and Post-Preparation Intraoral Scans on Typodont Models: A Primescan–Exocad Study

Abstract

Aim: Preoperative intraoral scans are routinely used as baseline references for CAD/CAM restoration design by superimposing them with post-preparation scans. This study quantified the workflow-induced apparent vertical discrepancy between pre- and post-preparation intraoral scan datasets after a clinically common registration approach. Method: Twelve maxillary typodont models were scanned at baseline (T0) with an intraoral scanner. A standardized full-crown preparation was performed on a preselected tooth (FDI 14; maxillary right first premolar), followed by post-preparation scanning (T1). T0 and T1 meshes were aligned in dental CAD software using rigid 3-point registration. Apparent vertical (tooth long-axis) differences (|ΔL|, mm) were measured on non-prepared reference teeth (maxillary central incisor, canine, and first molar) to isolate scan–registration variability. Descriptive statistics and empirical cumulative distribution functions were reported. Tooth-type differences were tested using the Friedman test with Holm-adjusted post hoc comparisons (α=0.05). Results: Across 36 measurements, median (IQR) |ΔL| was 0.039 (0.020–0.049) mm for the central incisor, 0.051 (0.037–0.176) mm for the canine, and 0.021 (0.012–0.102) mm for the first molar. The 95th percentiles were 0.311, 0.382, and 0.164 mm, respectively; maximum values approached 0.4–0.5 mm. Overall differences among tooth types were significant (P=0.039), whereas pairwise comparisons were not significant after adjustment. Conclusion: Pre/post intraoral scan superimposition using rigid 3-point alignment can generate non-zero apparent vertical discrepancies on unchanged teeth, occasionally reaching several tenths of a millimeter. Small pre/post differences—used to guide CAD/CAM design—should therefore be interpreted cautiously as they may reflect workflow variability rather than true morphologic change.

Keywords

• computer-aided design
• Intraoral scanners
• measurement reproducibility
• superimposition
• three-dimensional imaging
• tooth preparation

Supporting Institution

None.

Ethical Statement

Non applicable.

Thanks

The authors would like to thank the specialist (residency) students of Inonu University, Faculty of Dentistry, Department of Prosthodontics, for their support during the study.

Tipodont Modellerde Preparasyon Öncesi ve Sonrası Ağız İçi Taramalar Arasında İş Akışına Bağlı Dikey Ölçüm Değişkenliğinin Nicelendirilmesi: Primescan–Exocad Çalışması

Abstract

Amaç: Preoperatif ağız içi taramalar, CAD/CAM restorasyon tasarımında sıklıkla başlangıç (baseline) referansı olarak kullanılır ve post-preparasyon taramalar ile üst üste bindirilerek (süperpozisyon) değerlendirilir. Bu çalışma, klinikte yaygın kullanılan bir eşleştirme (registrasyon) yaklaşımı sonrasında preparasyon öncesi ve sonrası ağız içi tarama veri setleri arasında iş akışının (workflow) oluşturduğu görünen dikey uyumsuzluğu nicelendirmiştir. Yöntem: On iki maksiller tipodont model, başlangıçta (T0) bir ağız içi tarayıcı ile tarandı. Önceden seçilen bir dişte (FDI 14; maksiller sağ birinci premolar) standardize tam kron preparasyonu yapıldı ve ardından post-preparasyon tarama (T1) alındı. T0 ve T1 ağ (mesh) verileri, dental CAD yazılımında rijit 3-nokta registrasyonu ile hizalandı. Taramaya/registrasyona bağlı değişkenliği izole etmek için, preparasyon yapılmayan referans dişlerde (maksiller santral kesici, kanin ve birinci molar) görünen dikey (dişin uzun ekseni) farklar (|ΔL|, mm) ölçüldü. Tanımlayıcı istatistikler ve ampirik kümülatif dağılım fonksiyonları raporlandı. Diş tipleri arasındaki farklar Friedman testi ile değerlendirildi ve Holm düzeltmeli post hoc karşılaştırmalar uygulandı (α=0,05). Bulgular: Toplam 36 ölçümde medyan (IQR) |ΔL|; santral kesicide 0,039 (0,020–0,049) mm, kaninde 0,051 (0,037–0,176) mm ve birinci molarda 0,021 (0,012–0,102) mm bulundu. %95 persentil değerleri sırasıyla 0,311; 0,382 ve 0,164 mm olarak hesaplandı; maksimum değerler ise yaklaşık 0,4–0,5 mm’ye ulaşmıştır. Diş tipleri arasındaki genel fark anlamlıydı (P=0,039); ancak ikili karşılaştırmalar düzeltme sonrası anlamlı değildi. Sonuç: Rijit 3-nokta hizalama kullanılarak yapılan preparasyon öncesi/sonrası ağız içi tarama süperpozisyonu, değişmemiş dişlerde sıfırdan farklı görünen dikey uyumsuzluklar oluşturabilir ve bu farklar zaman zaman milimetrenin birkaç onda birine ulaşabilir. Bu nedenle CAD/CAM tasarımını yönlendirmek için kullanılan küçük pre/post farklar, gerçek morfolojik değişim yerine iş akışı değişkenliğini yansıtıyor olabileceğinden dikkatle yorumlanmalıdır.

Keywords

• bilgisayar destekli tasarım
• Ağız içi tarayıcılar
• ölçüm tekrarlanabilirliği
• süperpozisyon
• üç boyutlu görüntüleme
• diş preparasyonu

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