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Journal of Peking University (Health Sciences) ›› 2025, Vol. 57 ›› Issue (3): 604-609. doi: 10.19723/j.issn.1671-167X.2025.03.027

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Fitness of onlays fabricated with direct and indirect CAD/CAM technology in vitro

Kun QIAN, Yihong LIU*()   

  1. Department of General Dentistry, Peking University School and Hospital of Stomatology & National Center for Stomatology & National Clinical Research Center for Oral Diseases & National Engineering Research Center of Oral Biomaterials and Digital Medical Devices & Beijing Key Laboratory of Digital Stomatology & NHC Research Center of Engineering and Technology for Computerized Dentistry & NMPA Key Laboratory for Dental Materials, Beijing 100081, China
  • Received:2022-10-06 Online:2025-06-18 Published:2025-06-13
  • Contact: Yihong LIU
  • Supported by:
    National Natural Science Foundation of China(52111530189)

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Abstract:

Objective: To analyze the fitness of zirconia and lithium disilicate glass-ceramic onlays fabricated with direct and indirect computer-aided design and computer-aided manufacturing (CAD/CAM) technology in vitro. Methods: In the study, 48 standardised typodont left mandibular first molars received standardised onlay preparation. Then, all the specimens were randomly divided into 4 groups. There were 12 specimens in each group. The preparation quality was checked under the stereomicroscope. All the specimens were fixed in typodonts. Subsequently, the typodonts were fixed in the dental simulators to simulate the oral conditions. In groups A and B, the digital impressions were obtained by using the intraoral scanner. In groups C and D, conventional impressions of polyether impression material were obtained according to the instructions of the manufacturer using individual trays. The stone casts were made with type Ⅳ gypsum later. Then, all casts were digitized with the model scanner. Based on the data obtained from the scan, onlay restorations of all the groups were designed using the corresponding software, the simulated cement thickness was set to 50 μm. Then, the final onlays restorations of all the groups were machined with the milling machines in lab. The fabrication materials were different in groups. The specimens of groups A and C were fabricated with zirconia. While, the specimens of groups B and D were fabricated with lithium disilicate glass-ceramic. The marginal gap and internal gap of all restorations were analyzed by 3D replica technique, for each measurement, the specimen was digitised using the model scanner. Results: The marginal gap of the onlays fabricated with indirect digital impressions were smaller than that with direct digital impressions (P < 0.05). At the same time, the internal gap of the onlays fabricated with indirect digital impressions were smaller than that with direct digi-tal impressions (P < 0.05). The marginal gap was larger in distal gingival than that in the other regions in all the groups (P < 0.05). Different fabrication materials, zirconia or lithium disilicate reinforced glass-ceramic, had no effect on onlay marginal and internal fit (P>0.05). Conclusion: The marginal and internal adaptation of the onlays fabricated with indirect digital impressions was better than with direct digital impressions. Zirconia and lithium disilicate reinforced glass-ceramic had no effect on the onlay adaptation.

Key words: Dental impression technique, Dental porcelain, Zirconia, Lithium disilicate, Onlay

CLC Number: 

  • R783.3

Figure 1

Schematic diagram showing the designed parameters of the onlay"

Figure 2

Workflow for 3D analysis"

Figure 3

Location of the part where the gaps were measured M, mesial margin; D, distal margin; B, buccal margin; L, lingual margin; I, internal."

Table 1

Internal and marginal gap values for each group"

Group Method Material Internal gap values/μm Marginal gap values/μm
A (n=12) Direct Zirconia 135.54±14.69 144.30±20.44
B (n=12) Direct Ceramic 124.16±22.04 135.53±23.44
C (n=12) Indirect Zirconia 103.77±13.61 104.55±19.02
D (n=12) Indirect Ceramic 108.49±17.83 122.78±23.36

Table 2

Two-way ANOVA analysis of internal gap"

Source Type Ⅲ sum of squares df Mean square F P
Corrected model 5 251.241a 2 2 625.621 8.717 0.001
Intercept 515 841.350 1 515 841.350 1 712.556 < 0.001
Method 5 211.009 1 5 211.009 17.300 < 0.001
Material 40.232 1 40.232 0.134 0.717

Table 3

Three-way ANOVA analysis of marginal gap"

Source Type Ⅲ sum of squares df Mean square F P
Corrected model 150 406.021a 15 10 027.068 9.374 < 0.001
Intercept 2 532 324.909 1 2 532 324.909 2 367.339 < 0.001
Method 13 937.982 1 13 937.982 13.030 < 0.001
Position 84 163.215 3 28 054.405 26.227 < 0.001
Material 3 819.499 1 3 819.499 3.571 0.061
Method×Position 12 588.477 3 4 196.159 3.923 0.010
Method×Material 3 140.300 1 3 140.300 2.936 0.089
Position×Material 14 902.929 3 4 967.643 4.644 0.004
Method×Position×Material 9 945.476 3 3 315.159 3.099 0.029

Figure 4

Different regions' marginal gaps of each group The description of the four groups are shown in the notes of Table 1."

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