Effect of milling tool wear on the internal fit of PMMA implant interim prosthesis

밀링 공구의 마모가 PMMA 임플란트 임시보철물 변연 및 내면적합도에 미치는 영향

  • Shin, Mi-sun (Central Dental Laboratory, KyungHee University Medical Center, Seoul, Republic of Korea)
  • 신미선 (경희대학교치과병원 중앙기공실)
  • Received : 2019.04.19
  • Accepted : 2019.06.12
  • Published : 2019.06.30


Purpose: The purpose of this study is to evaluate the effect of CAD/CAM system milling tool wear on the marginal and internal fit of PMMA implant interim prosthesis three-dimensional manner. Methods: A total of 20 crowns were fabricated with CAD/CAM method. Their designs were unified to first molar of the left maxilla. The Customized abutments were prepared and scanned with on optical model scanner. Five crowns were milled by the newly replaced tool (1st milling), and 15 crowns were milled by 2nd, 3rd, 4th milling tool. The marginal and internal fit of 20 interim crowns were measured using the triple-scan protocol. Results: Statistically significant difference was found between the $1^{st}$ milling group ($51.8{\pm}14.6{\mu}m$) and the $3^{rd}$, $4^{th}$ milling group ($128.6{\pm}43.8{\mu}m$, $146.2{\pm}38.1{\mu}m$, respectively) at the distal margins. In the mesial margins, There was a statistically significant difference between the $1^{st}$ milling group ($63.6{\pm}25.9{\mu}m$) and the $3^{rd}$, $4^{th}$ milling group ($137.2{\pm}25.9{\mu}m$, $186.8{\pm}70.6{\mu}m$, respectively). In the distal line angle, significant difference was found between the $1^{st}$, $2^{nd}$, $3^{rd}$ milling groups and the $4^{th}$ milling group. In the mesial axial wall, significant difference was found between the $1^{st}$ milling group ($52.2{\pm}20.3{\mu}m$) and the $3^{rd}$, $4^{th}$ milling groups ($22.8{\pm}8.8{\mu}m$, $7.8{\pm}5.7{\mu}m$). Conclusion: As a result of the experiment, decrease of the marginal and internal fit was statistically significant as the number of machining cycles increased. In order to produce clinically excellent restorations, it is recommandable to consider the condition of the milling tool wear, when designing the restoration with CAD program.


CAD/CAM;triple-scan protocol;milling tool;PMMA implant interim prosthesis

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Figure 1. Customized abutment of titanium used in this study

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Figure 2. PMMA crown fabricated using CAD/CAM system

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Figure 3. The constant seating force

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Figure 4. Scanner three dimensional surface data(A) Titanium master die, (B) PMMA Crown(C) Superimposed crown on the master die

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Figure 5. Measurement points for marginal gap (1,7) and internal gap (2,3,4,5,6,7)

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Fig. 6. Mean of marginal and internal gap of PMMA Crown

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Figure 7. Mesiodistal section of crown superimposed on the master die. (A) 1st milling, (B) 2nd milling, (C) 3rd milling, (D) 4th milling

Table 1. Marginal and internal gap discrepancy of PMMA crown(unit: ㎛)

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