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Tissue surface adaptation of CAD-CAM maxillary and mandibular complete denture bases manufactured by digital light processing: A clinical study
RESEARCH AND EDUCATION
Tissue surface adaptation of CAD-CAM maxillary and mandibular complete denture bases manufactured by digital light processing: A clinical study Se-Na Yoon, DDS,a Kyung Chul Oh, DDS, PhD,b Sang J. Lee, DMD, MMSc,c Jung-Suk Han, DDS, MS, PhD,d and Hyung-In Yoon, DDS, MSD, PhDe Since computer-aided design and computer-aided manufacturing (CAD-CAM) technology was introduced in dentistry in the 1980s, clinical and laboratory procedures have advanced regarding fixed and removable dental prostheses.1-6 A CAD-CAM removable complete denture system can reduce the number of patient visits, treatment time, and expensive laboratory work.2-8 Patients have been reported to prefer CAD-CAM removable dentures to conventionally generated dentures.9-11 Subtractive manufacturing is used to remove unnecessary parts from a prefabricated polymethyl methacrylate (PMMA) block.12,13 Additive manufacturing can simultaneously build multiple complex geometric shapes by continuous layering while reducing the waste of raw material.14-16
ABSTRACT Statement of problem. Clinical studies evaluating the tissue surface adaptation of complete denture bases fabricated by digital light processing (DLP) are lacking. Purpose. The purpose of this clinical study was to assess the tissue surface adaptation of complete denture bases generated by the DLP technique and to compare the adaptation with that of denture bases manufactured by 5-axis milling (MIL) and pack-and-press (PAP) method. Material and methods. A total of 9 participants with 12 edentulous arches (7 maxillary and 5 mandibular) were included in this study. For each edentulous arch, the complete denture bases with occlusion rims were prepared by 3 different techniques (PAP, MIL, and DLP). A virtual denture base with occlusion rim was designed by means of a digital subtraction tool and served to fabricate the DLP and MIL denture bases. The complete denture bases were placed intraorally with an indicator applied to the intaglio surfaces. The thickness of the indicator was measured within the denture-bearing areas and anatomic landmarks of the edentulous arch to obtain the absolute tissue surface adaptation (ATA) value. The relative tissue surface adaptation (RTA) value was calculated from the differences between the ATA values of DLP or MIL techniques and those of the PAP technique. The Kruskal-Wallis test and the McNemar test were used for statistical analysis (a=.05). Results. No statistically significant differences were found among the 3 denture base fabrication techniques with respect to the ATA values of either arch (P>.05). In terms of the RTA values for the maxillary arch, the DLP base was significantly different from the MIL base in the RC and P areas (both P<.05). The DLP base exhibited a higher frequency of negative RTA values than the MIL base. Regarding the RTA values for the mandibular arch, no significant differences were detected between the DLP and MIL denture bases (P>.05). Conclusions. The DLP and MIL denture bases demonstrated clinically acceptable tissue surface adaptation to both edentulous the maxilla and mandible. The DLP denture base was likely to exhibit intimate tissue adaptation in the stress-bearing areas of maxillary arches compared with the PAP denture base. The maxillary MIL denture base was likely to exhibit small gaps between the supporting tissue and denture base. Both DLP and MIL mandibular denture bases were likely to show intimate adaptation on the lingual slope compared with the PAP base. (J Prosthet Dent 2019;-:---)
S.-N.Y. and K.C.O. contributed equally to this work. This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (NRF-2017R1C1B2007369) and also by grant no. 04-2018-0096 from the SNUDH Research Fund. a Graduate student, Department of Prosthodontics, School of Dentistry and Dental Research Institute, Seoul National University, Seoul, Republic of Korea. b Clinical Research Assistant Professor, Department of Prosthodontics, Yonsei University College of Dentistry, Seoul, Republic of Korea. c Assistant Professor, Department of Restorative Dentistry and Biomaterials Sciences, Harvard School of Dental Medicine, Boston, Mass. d Professor and Dean, Department of Prosthodontics, School of Dentistry and Dental Research Institute, Seoul National University, Seoul, Republic of Korea. e Assistant Professor, Department of Prosthodontics, School of Dentistry and Dental Research Institute, Seoul National University, Seoul, Republic of Korea.
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Clinical Implications Compared with the PAP technique, the DLP technique should provide excellent adaptation of complete denture bases in the stress-bearing areas of the maxilla. In the mandible, the denture base fabricated by either DLP or MIL techniques was likely to adapt intimately to the lingual slope.
Digital light processing (DLP), which is increasingly applied in dentistry, uses a digital micromirror device and a digital light projector to build up an object by layering a photopolymerizable material.17 A complete denture base can be digitally manufactured with high accuracy by using a DLPbased system from a printable resin.18,19 Accurate tissue surface adaptation is an essential for the retention, masticatory performance, and stability of removable dentures.20 Steinmassl et al20 compared the tissue surface adaptation of different CAD-CAM milled dentures with conventionally fabricated dentures. Although the milled dentures showed better tissue surface adaptation than the conventional dentures, they had some problems reproducing the anterior and lateral denture-bearing areas with undercut regions beneath the crest of the alveolar ridge.20 Goodacre et al21 reported that CAD-CAM milled denture bases showed better tissue surface adaptation than conventional dentures. However, another study22 concluded that the tissue surface adaptation was better in conventional dentures than in milled dentures. In terms of additive manufacturing, Tasaka et al23 reported that maxillary complete denture bases fabricated by photopolymer jetting were more accurate than denture bases generated by the conventional heat-polymerizing method. Yoon et al18,19 conducted in vitro studies comparing CADCAM complete denture bases (5-axis milled or DLPgenerated) with conventional denture bases with the pack-and-press technique (PAP) to evaluate tissue surface adaptation. In the maxilla, the DLP denture base showed slightly better tissue surface adaptation than the milled or PAP denture bases.19 Unlike the milled denture base, the DLP denture base fully reproduced the morphology of the residual ridge.19 In the mandible, the DLP denture bases exhibited tissue compression similar to that of the milled or PAP denture bases.18 To the best of the authors’ knowledge, however, no study has compared in vivo tissue surface adaptation of complete denture bases fabricated by PAP, 5-axis milling (MIL), and DLP. Therefore, the purpose of this clinical study was to evaluate tissue surface adaptation of complete denture bases fabricated by PAP, MIL, and DLP. The null hypothesis was that the tissue surface adaptation of the THE JOURNAL OF PROSTHETIC DENTISTRY
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complete denture bases for maxillary and mandibular edentulous arches would not differ among the 3 fabrication techniques. MATERIAL AND METHODS This research was approved by the Ethics Committee of Dental Hospital (IRB No. CDE18005). A total of 9 participants (6 women and 3 men; mean age of 73 years) who required complete denture treatments for edentulous maxillary and mandibular arches were recruited for this study. The inclusion and exclusion criteria are shown in Table 1. Each participant was informed about the clinical and laboratory procedures and signed an informed consent form. Twelve edentulous arches (7 maxillary and 5 mandibular arches) were evaluated (Table 2). At the first visit, a preliminary impression of an edentulous arch was obtained by using irreversible hydrocolloid (Aroma Fine Plus; GC Corp) and a stock impression tray to fabricate a diagnostic cast with Type III dental stone (Snow Rock Dental Stone; DK Mungyo). Before the definitive impression, any pathologic soft tissue was conditioned and managed to a healed state. At the second visit, a custom tray fabricated from auto-polymerizing resin (Quicky; Nissin Dental Products Inc) was border molded by using modeling plastic impression compound (Peri Compound; GC Corp). A definitive impression was made with the open mouth technique by using polyvinyl siloxane (Imprint II Garant light body; 3M ESPE) to fabricate a definitive cast with Type IV dental stone (Fujirock; GC Corp). The definitive cast was duplicated with a silicone material (Vivid Image; Pearson Dental) and Type IV dental stone (Fujirock; GC Corp). The original definitive cast was scanned by using a scanner (Identica blue; Medit Corp) at a 10-mm accuracy and exported as a standard tessellation language (STL) file. The original cast was used to fabricate the definitive complete denture for the participant, while the duplicate cast was designated for the study. A record base with occlusion rim was then fabricated on the original definitive cast of each participant. At the third visit, using the prepared record base with the occlusion rim, the vertical dimension of occlusion was determined by measuring the interocclusal distance at the physiologic rest position, swallowing, and phonetics. A horizontal jaw relation was recorded after guiding each participant into the centric relation position. Using this jaw relation record of each participant, the original definitive cast was mounted in a semiadjustable articulator (Hanau Modular Articulator; Whip Mix Corp). For the research, the record base with occlusion rim mounted on each original definitive cast was digitally scanned (Identica blue; Medit Corp) and stored as an STL file. By digitally subtracting the scan data of each original Yoon et al
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Table 1. Inclusion and exclusion criteria Inclusion Criteria Fully edentulous ridge with no severe tissue undercut or exostosis No pathology on temporomandibular joint or muscle with reproducible mandibular position Prosthodontic Diagnostic Index (PDI) I-III (based on Classification of American College of Prosthodontists)
Table 2. Basic information of participants
Fully edentulous ridge with severe tissue undercut or exostosis Pathologic temporomandibular joint or muscle, with or without unstable mandibular position Prosthodontic Diagnostic Index (PDI) IV (based on Classification of American College of Prosthodontists) Congenital or acquired defects in maxillary or mandibular bones Unable to receive ordinary dental treatment because of medically compromised systemic condition
definitive cast, a virtual maxillary or mandibular record base with occlusion rim (STL) was obtained for each edentulous arch by using a CAD software program (3Shape Dental Designer; 3Shape A/S). Each virtual record base with occlusion rim was used to fabricate a DLP-generated (DLP) or 5-axis milled (MIL) complete denture base with an occlusion rim. The DLP denture base with the occlusion rim was fabricated from a printable resin (NextDent Base; NextDent B.V.) and a printer (Bio 3D W11; NextDent B.V.) with a light-emitting diode of 405-nm wavelength. The thickness of each building layer was set as 100 mm. The supports were located at a 100-degree build angle on the labial or buccal flange of the denture. Each printed denture base was ultrasonically cleaned in isopropyl alcohol for 10 minutes and treated by using a postpolymerization device (LC 3DPrint Box; NextDent B.V.) for 15 minutes. The MIL denture base with occlusion rim was fabricated from the PMMA block (VIPI Block GUM; VIPI) by using a 5-axis milling machine (ARUM 5X-200; Doowon). After properly positioning the record base with occlusion rim on the duplicated definitive cast, the PAP denture base with occlusion rim was fabricated by using the pack-and-press technique with a split-mold flask (Hanau Varsity Flasks; Whip Mix Corp) and heatactivated PMMA resin (SR Triplex Hot; Ivoclar Vivadent AG). For each edentulous arch of each participant, 3 different denture bases with occlusion rims were prepared (Fig. 1). All the denture bases were fabricated according to the manufacturers’ recommendation and then stored in water until the next visit. At the fourth visit, each denture base with occlusion rim made with 3 different techniques (PAP, MIL, and DLP) was randomly sequenced by using the random number generator function in a spreadsheet (Excel 2016; Microsoft Corp) and evaluated intraorally. At each evaluation, the participant was instructed to occlude firmly into the predetermined vertical dimension of occlusion and centric relation position. To evaluate the tissue surface adaptation, an indicator (Fit Checker II; GC Corp) was placed on the intaglio surface and occlusion force Yoon et al
Study Arch
Exclusion Criteria Number
Age
Sex
Opposing Arch
PDI Classification
1
68
Male
Mandible (single)
Removable dental prosthesis
II
2
78
Female
Maxilla (single)
Removable dental prosthesis
I
3
62
Male
Maxilla/ mandible (both)
-
II/I
4
65
Female
Maxilla/ mandible (both)
-
I/I
5
71
Female
Maxilla/ mandible (both)
-
I/I
6
82
Female
Maxilla (single)
Removable dental prosthesis
III
7
79
Female
Mandible (single)
Removable dental prosthesis
III
8
81
Female
Maxilla (single)
Fixed dental prosthesis on natural teeth
II
9
61
Male
Maxilla (single)
Fixed dental prosthesis on natural teeth
II
PDI, Prosthodontic Diagnostic Index.
Figure 1. Preparation of 3 different denture bases with occlusion rim. PAP, pack-and-press; MIL, 5-axis milling; DLP, digital light processing.
maintained as instructed until the indicator polymerized. At least 10 minutes were allowed between the denture base trials for tissue recovery. After removing the denture base from the participant’s mouth, a polyvinyl siloxane impression material (Examixfine; GC Corp) was applied to the surface layer of the indicator relining on the intaglio surface of each denture base. To measure the thickness of the indicator, a silicone replica index was made with its base parallel to the plane of the occlusion rim by using polyvinyl siloxane materials (Exaflex Putty and Examixfine; GC Corp). From the fourth visit, the clinical procedures to provide a removable complete denture to each participant were continued in a conventional manner. The definitive prostheses were fabricated by means of PAP by using a split-mold flask THE JOURNAL OF PROSTHETIC DENTISTRY
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Figure 2. Measured points on maxillary arch. Six points on residual ridge crest (RC), 3 points on midpalatal suture area (MP), 18 points hard palate except midpalatal suture (P), and 7 points on posterior palatal seal (PPS). Red dotted circle area is incisive papilla.
(Hanau Varsity Flasks; Whip Mix Corp) and heatactivated PMMA resin (SR Triplex Hot; Ivoclar Vivadent AG) and delivered to the participants. The measuring points of the indicator layer thickness were located on the denture bearing areas and anatomic landmarks of the edentulous arches. A total of 34 measuring points were designated in 4 anatomic landmarks of the maxillary arch (Fig. 2): 6 points on the crest of the residual ridge (RC), 3 points on the area of the midpalatal suture (MP), 18 points on the hard palate except midpalatal suture (P), and 7 points on the posterior palatal seal (PPS). The vestibular sulcus, incisive papilla, anterior flabby ridge, maxillary tuberosity, and hamular notches were excluded from the measurement. For the mandibular arch, a total of 33 points in 3 anatomic landmarks were measured (Fig. 3): 9 points on the crest of the residual ridge and the most anterior point of the retromolar pad (RC), 12 points on the buccal slope and buccal shelf (BS), and 12 points on the lingual slope (LS). The vestibular sulcus, retromylohyoid fossa, and retromolar pad were excluded from the evaluation. The silicone index with the layer of indicator was sectioned perpendicular to the base at the designated points. The layer thickness of the indicator was measured at each designated point under a stereomicroscope (SZX16; Olympus Corp) at ×50 magnification by using an image analysis software program (ToupView; ToupTek). Two different parameters were designed to evaluate the tissue surface adaptation of the complete denture bases fabricated by using the PAP, MIL, and DLP techniques: the absolute tissue surface adaptation (ATA) and the relative tissue surface adaptation (RTA). The layer thickness (mm) of the indicator measured at the designated points in each anatomic landmark (RC, MP, P, and PPS for maxilla; RC, BS, and LS for mandible) was referred to as the ATA value. The RTA value was then THE JOURNAL OF PROSTHETIC DENTISTRY
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Figure 3. Measured points on mandibular arch. Nine points on residual ridge crest and most anterior point of retromolar pad (RC), 12 points on buccal slope and buccal shelf (BS), and 12 points on lingual slope (LS).
calculated from the ATA value. At the designated points of each anatomic landmark, the ATA value of each DLP (or MIL) denture base was subtracted from that of the PAP denture base to calculate the RTA value of the DLP (or MIL) denture base. Assuming the consistency of the indicator was constant and that the underlying alveolar bone was not deformed, the thickness of the indicator layer would depend on the surface deviation of the denture base, as well as the amount of mucosal displacement of the edentulous ridge, at the vertical dimension of occlusion of each participant. The RTA value of each DLP (or MIL) denture base was equal to the difference in the amount of surface deviation between the PAP and DLP (or MIL) denture bases, as the PAP denture base served as a clinical reference for the definitive prosthesis in this study. If the RTA value was negative, the DLP or MIL denture base adapted more intimately to the denture-bearing tissue than the PAP denture base at the designated point. If the RTA value was positive, the DLP or MIL denture base would exhibit loose adaptation to the supporting tissue compared with the PAP denture base. To differentiate the pattern of 3D surface deviation of the intaglio surface of the DLP or MIL denture base from that of the PAP denture base (reference), all the positive and negative RTA values were coded as either 1 (positive) or 2 (negative). By using each complete denture base fabricated by 3 different techniques, each of the 3 different thickness values of the indicator measured in the anatomic landmarks was recorded according to the arch: maxilla or mandible. For each arch, the means, standard deviation, median, and interquartile range of all the measurements (ATA) were statistically analyzed by using a software program (IBM SPSS Statistics, v22.0; IBM Corp). The Kruskal-Wallis analysis of variance was performed to evaluate the statistical significance of the differences in ATA values between each fabrication technique group. Yoon et al
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Table 3. Measured ATA (mm) values of complete denture bases fabricated by 3 different techniques at designated points in each anatomic landmark PAP Arch
Landmark
Maxilla
Mandible
MIL
DLP
Mean ±SD
Median
IQR
Mean ±SD
Median
IQR
Mean ±SD
Median
IQR
RC
376.82 ±200.15
307.23
266.03
548.62 ±268.86
509.90
454.57
306.20 ±195.11
227.71
363.63
P
432.14 ±115.54
394.37
145.50
521.13 ±66.01
522.45
106.61
465.28 ±133.93
431.15
215.60
MP
289.22 ±191.52
207.18
440.09
438.07 ±176.48
446.86
326.00
348.82 ±134.66
338.29
299.97
PPS
613.83 ±472.50
414.87
536.46
701.52 ±281.53
641.77
324.39
589.27 ±267.01
536.25
402.86
RC
356.43 ±185.28
449.33
354.94
285.50 ±175.62
250.92
313.77
308.80 ±176.25
292.38
327.82
BS
309.53 ±128.64
321.42
251.48
346.04 ±284.75
268.36
461.29
320.08 ±233.23
219.35
331.14
LS
266.53 ±170.11
181.00
245.33
158.26 ±85.74
139.19
140.88
173.79 ±73.75
199.13
123.31
ATA, absolute tissue surface adaptation; BS, buccal slope and buccal shelf; DLP, digital light processing; IQR, interquartile range; LS, lingual slope; MIL, 5-axis milling; MP, midpalatal suture; P, hard palate except midpalatal suture; PAP, pack-and-press; PPS, posterior palatal seal; RC, crest of residual ridge (maxilla) or crest of residual ridge and most anterior point of retromolar pad (mandible); SD, standard deviation.
To evaluate the difference in the surface deviation pattern of both DLP and MIL denture bases compared with that of the PAP denture base, the coded RTA values (either 1 or 2) of both DLP and MIL denture bases were statistically analyzed with the McNemar test. The difference in the frequency (%) of coded RTA values between the DLP and MIL denture bases was compared to estimate the likelihood of intimate or loose adaptation to the tissue compared with the PAP denture base for each anatomic landmark of both the maxilla and mandible. The statistical analyses were performed by using a software program (IBM SPSS Statistics, v22.0; IBM Corp) (a=.05). A post hoc power analysis was performed with G*Power (v3.1.9.4).24 RESULTS The measured ATA values of the PAP, MIL, and DLP complete denture bases for each anatomic landmark of each edentulous arch condition are presented in Table 3. In terms of the ATA values of complete denture base fabrication techniques, no statistically significant differences were observed for the anatomic landmarks of the maxillary arch (Fig. 4) (P=.251 for RC; P=.243 for P; P=.340 for MP; and P=.571 for PPS) or for those of the mandibular arch (Fig. 5) (P=.811 for RC; P=.887 for BS; and P=.330 for LS). Regarding the frequency of the coded RTA values of complete denture base fabrication techniques for the maxillary arch, the DLP complete denture base was significantly different from the MIL denture base in the RC area (P=.001, post hoc power=0.99; Table 4). The DLP denture base exhibited a higher frequency of negative RTA values than the MIL denture base. However, the MIL denture base showed a higher frequency of positive RTA values than the DLP denture base. In the P area, the difference between the DLP and MIL denture bases was also statistically significant (P=.005, post hoc power=0.82). The DLP denture base showed a higher frequency of negative RTA values than the MIL denture base, while the MIL denture base presented a higher frequency of positive RTA values than the DLP denture Yoon et al
base. In the PPS and the MP areas, no significant differences were found between the DLP and MIL denture bases (both P=1.000). With regard to the frequency of the coded RTA values for the mandibular arch, no statistically significant differences were found between the DLP and MIL denture bases on all the anatomic landmarks (P=.180 for RC, P=.454 for BS, and P=.388 for LS). DISCUSSION Based on the results of this study, no significant difference was observed with respect to the tissue surface adaptation (ATA) among the complete denture bases fabricated by 3 techniques in either the maxillary or mandibular edentulous arches. Therefore, the null hypothesis was not rejected. This is consistent with in vitro comparative studies on the tissue surface adaptation of CAD-CAM denture bases.18,19 In the present study, the frequency of the coded RTA values was significantly different between the DLP and MIL denture bases in 2 anatomic landmarks (RC and P) of the maxillary arch. On the crest of maxillary residual ridge and hard palate, in comparison with the PAP denture base, the MIL denture base was likely to exhibit small gaps between supporting tissue and the denture base, and the DLP denture base showed a likelihood of intimate adaptation to the tissue. Generally, the complete denture base shows a high degree of adaptation to the residual ridge and palate, whether fabricated by the conventional or CAD-CAM technique.20 However, the current findings suggested that the DLP technique may lead to better adaptation of the maxillary complete denture base in the stress-bearing area than the PAP or even the MIL technique. This finding was consistent with the results of a previous in vitro analysis.19 Compared with the PAP base, the DLP base may adapt more intimately to the crest of the maxillary residual ridge.19 In the MP area, both DLP and MIL denture bases were likely to exhibit loose tissue adaptation compared with the PAP denture base. This finding was also consistent with a previous in vitro analysis.19 The PAP base tended to press the center of the palate, THE JOURNAL OF PROSTHETIC DENTISTRY
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600.00
Absolute Tissue Surface Adaptation Value (μm)
700.00
Absolute Tissue Surface Adaptation Value (μm)
1000.00
600.00 400.00 200.00 0.00
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Issue
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500.00 400.00 300.00 200.00
PAP
MIL Group
DLP
PAP
A
MIL Group
DLP
MIL Group
DLP
B
600.00 Absolute Tissue Surface Adaptation Value (μm)
Absolute Tissue Surface Adaptation Value (μm)
2000.00
400.00
200.00
0.00
1500.00
1000.00
500.00
0.00 PAP
MIL Group
DLP
PAP
C
D
Figure 4. Comparison of absolute tissue surface adaptation (mm) of maxillary complete denture bases fabricated by using 3 different techniques: packand-press (PAP), 5-axis milling (MIL), and digital light processing (DLP). A, Residual ridge crest (RC). B, Hard palate except midpalatal suture (P). C, Midpalatal suture area (MP). D, Posterior palatal seal (PPS).
while the DLP base had some spaces at the midpalatal suture.19 The denture base fabricated by pressure packing may press the center of the palate (up to 150 mm) because of residual stress-induced deformation.23 Uneven pressure to the denture-supporting area may decrease the retention of the complete denture base.23 In the present study, the mean difference in the ATA values in the MP area between the DLP (or MIL) and PAP denture bases was below 150 mm. The current findings suggested that both the DLP and MIL denture bases were less likely to press the center of the palate than the PAP base. In the PPS area, both the DLP and MIL denture bases showed no likelihood of either intimate tissue adaptation or loose fit compared with the PAP denture base. On the crest of mandibular residual ridge, the MIL denture base was likely to adapt more intimately to the tissue than the PAP denture base, whereas the DLP denture base showed no likelihood of either intimate adaptation or loose fit. Yoon et al18 reported that the mandibular MIL denture base showed uniform adaptation to the majority of denture-bearing tissue, THE JOURNAL OF PROSTHETIC DENTISTRY
while the mandibular PAP denture base was likely to compress the crest of the residual ridge. On the lingual slope of the residual ridge, both the DLP and MIL denture bases showed a likelihood of intimate tissue adaptation compared with the PAP denture base. The 5-axis milling technique has been widely used because of its precision; however, its accuracy relies on the diameter and the accessibility of tools.12 In this study, the irregular morphology of the maxillary residual ridge may not be fully reproduced in the milled complete denture base. This could be a major drawback of milled complete denture bases.19 With the DLP technique, the build angle has been reported to affect the quality of DLP-generated objects.16,17 In this study, the build angle for every DLP denture base was consistent at 100 degrees to compare the results of this study with those of previous in vitro studies.18,19 Limitations of this clinical study included that the number of evaluated edentulous arches was small. In addition, the thickness of the indicator could be influenced by the opposing arch condition. The current Yoon et al
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Table 4. Frequency of coded RTA values of complete denture bases fabricated by 3 different techniques at designated points in each anatomic landmark
Absolute Tissue Surface Adaptation Value (μm)
600.00 500.00
Positive RTA (%) Arch
400.00
Maxilla
300.00 200.00
Mandible
100.00 PAP
MIL Group
DLP
A
Absolute Tissue Surface Adaptation Value (μm)
1000.00 800.00
Negative RTA (%)
DLP
MIL
DLP
MIL
P
RC
42.9
76.2
57.1
23.8
.001
P
50.8
64.3
49.2
35.7
.005
MP
61.9
66.7
38.1
33.3 >.999
PPS
53.1
53.1
46.9
46.9 >.999
RC
48.9
37.8
51.1
62.2
.180
BS
50.0
56.7
50.0
43.3
.454
LS
30.0
23.3
70.0
76.7
.388
BS, buccal slope and buccal shelf; DLP, digital light processing; LS, lingual slope; MIL, 5-axis milling; MP, midpalatal suture; P, hard palate except midpalatal suture; PPS, posterior palatal seal; RC, crest of residual ridge (maxilla) or crest of residual ridge and most anterior point of retromolar pad (mandible); RTA, relative tissue surface adaptation.
satisfaction, clinician preference, retention, and masticatory performance.
*
600.00
CONCLUSIONS 400.00
Based on the findings of this clinical study, the following conclusions were drawn:
200.00 0.00 PAP
MIL Group
DLP
B
600.00 *
Absolute Tissue Surface Adaptation Value (μm)
Landmark
500.00 400.00
1. Both DLP and MIL techniques are clinically feasible to fabricate complete denture bases. 2. In comparison with the PAP denture base, the DLP denture base was likely to exhibit intimate adaptation in the stress-bearing areas of the maxillary arch. 3. The maxillary MIL denture base, on the contrary, was likely to display loose adaptation to the tissue. 4. Both DLP and MIL denture bases were likely to show either intimate adaptation or mild impingement on the lingual slope of mandible.
300.00
REFERENCES
200.00 100.00 0.00 PAP
MIL Group
DLP
C
Figure 5. Comparison of absolute tissue surface adaptation (mm) of mandibular complete denture bases fabricated by using 3 different techniques: pack-and-press (PAP), 5-axis milling (MIL), and digital light processing (DLP). A, Residual ridge crest and most anterior point of retromolar pad (RC). B, Buccal slope and buccal shelf (BS). C, Lingual slope (LS).
findings should be applied with caution considering clinical conditions and fabrication parameters. A standard protocol for evaluating the tissue surface adaptation of complete denture bases is needed. Further clinical studies with a larger sample size are required to evaluate the DLP-generated complete denture in terms of patient Yoon et al
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10. Srinivasan M, Schimmel M, Naharro M, O’ Neill C, McKenna G, Muller F. CAD/CAM milled removable complete dentures: time and cost estimation study. J Dent 2019;80:75-9. 11. Pereyra NM, Marano J, Subramanian G, Quek S, Leff D. Comparison of patient satisfaction in the fabrication of conventional dentures vs. DENTCA (CAD/CAM) dentures: a case report. J N J Dent Assoc 2015;86:26-33. 12. Alghazzawi TF. Advancements in CAD/CAM technology: options for practical implementation. J Prosthodont Res 2016;60:72-84. 13. Kattadiyil MT, Goodacre CJ, Baba NZ. CAD/CAM complete dentures: a review of two commercial fabrication systems. J Calif Dent Assoc 2013;41: 407-16. 14. Petrovic V, Vicente Haro Gonzalez J, Jordá Ferrando O, Delgado Gordillo J, Ramón Blasco Puchades J, Portolés Griñan L. Additive layered manufacturing: sectors of industrial application shown through case studies. Int J Prod Res 2011;49:1061-79. 15. Chen H, Yang X, Chen L, Wang Y, Sun Y. Application of FDM threedimensional printing technology in the digital manufacture of custom edentulous mandible trays. Sci Rep 2016;6:19207. 16. Osman RB, Alharbi N, Wismeijer D. Build angle: does it influence the accuracy of 3D-printed dental restorations using digital light-processing technology? Int J Prosthodont 2017;30:182-8. 17. Stansbury JW, Idacavage MJ. 3D printing with polymers: challenges among expanding options and opportunities. Dent Mater 2016;32:54-64. 18. Yoon HI, Hwang HJ, Ohkubo C, Han JS, Park EJ. Evaluation of the trueness and tissue surface adaptation of CAD-CAM mandibular denture bases manufactured using digital light processing. J Prosthet Dent 2018;120:919-26. 19. Hwang HJ, Lee SJ, Park EJ, Yoon HI. Assessment of the trueness and tissue surface adaptation of CAD-CAM maxillary denture bases manufactured using digital light processing. J Prosthet Dent 2019;121:110-7.
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20. Steinmassl O, Dumfahrt H, Grunert I, Steinmassl PA. CAD/CAM produces dentures with improved fit. Clin Oral Investig 2018;22: 2829-35. 21. Goodacre BJ, Goodacre CJ, Baba NZ, Kattadiyil MT. Comparison of denture base adaptation between CAD-CAM and conventional fabrication techniques. J Prosthet Dent 2016;116:249-56. 22. Srinivasan M, Cantin Y, Mehl A, Gjengedal H, Muller F, Schimmel M. CAD/CAM milled removable complete dentures: an in vitro evaluation of trueness. Clin Oral Investig 2017;21:2007-19. 23. Tasaka A, Matsunaga S, Odaka K, Ishizaki K, Ueda T, Abe S, et al. Accuracy and retention of denture base fabricated by heat curing and additive manufacturing. J Prosthodont Res 2019;63:85-9. 24. Faul F, Erdfelder E, Lang AG, Buchner A. G*Power 3: a flexible statistical power analysis program for the social, behavioral, and biomedical sciences. Behav Res Methods 2007;39:175-91. Corresponding author: Dr Hyung-In Yoon Department of Prosthodontics School of Dentistry and Dental Research Institute Seoul National University 03080, 101, Daehak-ro, Jongro-gu Seoul REPUBLIC OF KOREA Email: [email protected] Copyright © 2019 by the Editorial Council for The Journal of Prosthetic Dentistry. https://doi.org/10.1016/j.prosdent.2019.11.007
Yoon et al
Tissue surface adaptation of CAD-CAM maxillary and mandibular complete denture bases manufactured by digital light processing: A clinical study Se-Na Yoon, DDS,a Kyung Chul Oh, DDS, PhD,b Sang J. Lee, DMD, MMSc,c Jung-Suk Han, DDS, MS, PhD,d and Hyung-In Yoon, DDS, MSD, PhDe Since computer-aided design and computer-aided manufacturing (CAD-CAM) technology was introduced in dentistry in the 1980s, clinical and laboratory procedures have advanced regarding fixed and removable dental prostheses.1-6 A CAD-CAM removable complete denture system can reduce the number of patient visits, treatment time, and expensive laboratory work.2-8 Patients have been reported to prefer CAD-CAM removable dentures to conventionally generated dentures.9-11 Subtractive manufacturing is used to remove unnecessary parts from a prefabricated polymethyl methacrylate (PMMA) block.12,13 Additive manufacturing can simultaneously build multiple complex geometric shapes by continuous layering while reducing the waste of raw material.14-16
ABSTRACT Statement of problem. Clinical studies evaluating the tissue surface adaptation of complete denture bases fabricated by digital light processing (DLP) are lacking. Purpose. The purpose of this clinical study was to assess the tissue surface adaptation of complete denture bases generated by the DLP technique and to compare the adaptation with that of denture bases manufactured by 5-axis milling (MIL) and pack-and-press (PAP) method. Material and methods. A total of 9 participants with 12 edentulous arches (7 maxillary and 5 mandibular) were included in this study. For each edentulous arch, the complete denture bases with occlusion rims were prepared by 3 different techniques (PAP, MIL, and DLP). A virtual denture base with occlusion rim was designed by means of a digital subtraction tool and served to fabricate the DLP and MIL denture bases. The complete denture bases were placed intraorally with an indicator applied to the intaglio surfaces. The thickness of the indicator was measured within the denture-bearing areas and anatomic landmarks of the edentulous arch to obtain the absolute tissue surface adaptation (ATA) value. The relative tissue surface adaptation (RTA) value was calculated from the differences between the ATA values of DLP or MIL techniques and those of the PAP technique. The Kruskal-Wallis test and the McNemar test were used for statistical analysis (a=.05). Results. No statistically significant differences were found among the 3 denture base fabrication techniques with respect to the ATA values of either arch (P>.05). In terms of the RTA values for the maxillary arch, the DLP base was significantly different from the MIL base in the RC and P areas (both P<.05). The DLP base exhibited a higher frequency of negative RTA values than the MIL base. Regarding the RTA values for the mandibular arch, no significant differences were detected between the DLP and MIL denture bases (P>.05). Conclusions. The DLP and MIL denture bases demonstrated clinically acceptable tissue surface adaptation to both edentulous the maxilla and mandible. The DLP denture base was likely to exhibit intimate tissue adaptation in the stress-bearing areas of maxillary arches compared with the PAP denture base. The maxillary MIL denture base was likely to exhibit small gaps between the supporting tissue and denture base. Both DLP and MIL mandibular denture bases were likely to show intimate adaptation on the lingual slope compared with the PAP base. (J Prosthet Dent 2019;-:---)
S.-N.Y. and K.C.O. contributed equally to this work. This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (NRF-2017R1C1B2007369) and also by grant no. 04-2018-0096 from the SNUDH Research Fund. a Graduate student, Department of Prosthodontics, School of Dentistry and Dental Research Institute, Seoul National University, Seoul, Republic of Korea. b Clinical Research Assistant Professor, Department of Prosthodontics, Yonsei University College of Dentistry, Seoul, Republic of Korea. c Assistant Professor, Department of Restorative Dentistry and Biomaterials Sciences, Harvard School of Dental Medicine, Boston, Mass. d Professor and Dean, Department of Prosthodontics, School of Dentistry and Dental Research Institute, Seoul National University, Seoul, Republic of Korea. e Assistant Professor, Department of Prosthodontics, School of Dentistry and Dental Research Institute, Seoul National University, Seoul, Republic of Korea.
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Clinical Implications Compared with the PAP technique, the DLP technique should provide excellent adaptation of complete denture bases in the stress-bearing areas of the maxilla. In the mandible, the denture base fabricated by either DLP or MIL techniques was likely to adapt intimately to the lingual slope.
Digital light processing (DLP), which is increasingly applied in dentistry, uses a digital micromirror device and a digital light projector to build up an object by layering a photopolymerizable material.17 A complete denture base can be digitally manufactured with high accuracy by using a DLPbased system from a printable resin.18,19 Accurate tissue surface adaptation is an essential for the retention, masticatory performance, and stability of removable dentures.20 Steinmassl et al20 compared the tissue surface adaptation of different CAD-CAM milled dentures with conventionally fabricated dentures. Although the milled dentures showed better tissue surface adaptation than the conventional dentures, they had some problems reproducing the anterior and lateral denture-bearing areas with undercut regions beneath the crest of the alveolar ridge.20 Goodacre et al21 reported that CAD-CAM milled denture bases showed better tissue surface adaptation than conventional dentures. However, another study22 concluded that the tissue surface adaptation was better in conventional dentures than in milled dentures. In terms of additive manufacturing, Tasaka et al23 reported that maxillary complete denture bases fabricated by photopolymer jetting were more accurate than denture bases generated by the conventional heat-polymerizing method. Yoon et al18,19 conducted in vitro studies comparing CADCAM complete denture bases (5-axis milled or DLPgenerated) with conventional denture bases with the pack-and-press technique (PAP) to evaluate tissue surface adaptation. In the maxilla, the DLP denture base showed slightly better tissue surface adaptation than the milled or PAP denture bases.19 Unlike the milled denture base, the DLP denture base fully reproduced the morphology of the residual ridge.19 In the mandible, the DLP denture bases exhibited tissue compression similar to that of the milled or PAP denture bases.18 To the best of the authors’ knowledge, however, no study has compared in vivo tissue surface adaptation of complete denture bases fabricated by PAP, 5-axis milling (MIL), and DLP. Therefore, the purpose of this clinical study was to evaluate tissue surface adaptation of complete denture bases fabricated by PAP, MIL, and DLP. The null hypothesis was that the tissue surface adaptation of the THE JOURNAL OF PROSTHETIC DENTISTRY
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complete denture bases for maxillary and mandibular edentulous arches would not differ among the 3 fabrication techniques. MATERIAL AND METHODS This research was approved by the Ethics Committee of Dental Hospital (IRB No. CDE18005). A total of 9 participants (6 women and 3 men; mean age of 73 years) who required complete denture treatments for edentulous maxillary and mandibular arches were recruited for this study. The inclusion and exclusion criteria are shown in Table 1. Each participant was informed about the clinical and laboratory procedures and signed an informed consent form. Twelve edentulous arches (7 maxillary and 5 mandibular arches) were evaluated (Table 2). At the first visit, a preliminary impression of an edentulous arch was obtained by using irreversible hydrocolloid (Aroma Fine Plus; GC Corp) and a stock impression tray to fabricate a diagnostic cast with Type III dental stone (Snow Rock Dental Stone; DK Mungyo). Before the definitive impression, any pathologic soft tissue was conditioned and managed to a healed state. At the second visit, a custom tray fabricated from auto-polymerizing resin (Quicky; Nissin Dental Products Inc) was border molded by using modeling plastic impression compound (Peri Compound; GC Corp). A definitive impression was made with the open mouth technique by using polyvinyl siloxane (Imprint II Garant light body; 3M ESPE) to fabricate a definitive cast with Type IV dental stone (Fujirock; GC Corp). The definitive cast was duplicated with a silicone material (Vivid Image; Pearson Dental) and Type IV dental stone (Fujirock; GC Corp). The original definitive cast was scanned by using a scanner (Identica blue; Medit Corp) at a 10-mm accuracy and exported as a standard tessellation language (STL) file. The original cast was used to fabricate the definitive complete denture for the participant, while the duplicate cast was designated for the study. A record base with occlusion rim was then fabricated on the original definitive cast of each participant. At the third visit, using the prepared record base with the occlusion rim, the vertical dimension of occlusion was determined by measuring the interocclusal distance at the physiologic rest position, swallowing, and phonetics. A horizontal jaw relation was recorded after guiding each participant into the centric relation position. Using this jaw relation record of each participant, the original definitive cast was mounted in a semiadjustable articulator (Hanau Modular Articulator; Whip Mix Corp). For the research, the record base with occlusion rim mounted on each original definitive cast was digitally scanned (Identica blue; Medit Corp) and stored as an STL file. By digitally subtracting the scan data of each original Yoon et al
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Table 1. Inclusion and exclusion criteria Inclusion Criteria Fully edentulous ridge with no severe tissue undercut or exostosis No pathology on temporomandibular joint or muscle with reproducible mandibular position Prosthodontic Diagnostic Index (PDI) I-III (based on Classification of American College of Prosthodontists)
Table 2. Basic information of participants
Fully edentulous ridge with severe tissue undercut or exostosis Pathologic temporomandibular joint or muscle, with or without unstable mandibular position Prosthodontic Diagnostic Index (PDI) IV (based on Classification of American College of Prosthodontists) Congenital or acquired defects in maxillary or mandibular bones Unable to receive ordinary dental treatment because of medically compromised systemic condition
definitive cast, a virtual maxillary or mandibular record base with occlusion rim (STL) was obtained for each edentulous arch by using a CAD software program (3Shape Dental Designer; 3Shape A/S). Each virtual record base with occlusion rim was used to fabricate a DLP-generated (DLP) or 5-axis milled (MIL) complete denture base with an occlusion rim. The DLP denture base with the occlusion rim was fabricated from a printable resin (NextDent Base; NextDent B.V.) and a printer (Bio 3D W11; NextDent B.V.) with a light-emitting diode of 405-nm wavelength. The thickness of each building layer was set as 100 mm. The supports were located at a 100-degree build angle on the labial or buccal flange of the denture. Each printed denture base was ultrasonically cleaned in isopropyl alcohol for 10 minutes and treated by using a postpolymerization device (LC 3DPrint Box; NextDent B.V.) for 15 minutes. The MIL denture base with occlusion rim was fabricated from the PMMA block (VIPI Block GUM; VIPI) by using a 5-axis milling machine (ARUM 5X-200; Doowon). After properly positioning the record base with occlusion rim on the duplicated definitive cast, the PAP denture base with occlusion rim was fabricated by using the pack-and-press technique with a split-mold flask (Hanau Varsity Flasks; Whip Mix Corp) and heatactivated PMMA resin (SR Triplex Hot; Ivoclar Vivadent AG). For each edentulous arch of each participant, 3 different denture bases with occlusion rims were prepared (Fig. 1). All the denture bases were fabricated according to the manufacturers’ recommendation and then stored in water until the next visit. At the fourth visit, each denture base with occlusion rim made with 3 different techniques (PAP, MIL, and DLP) was randomly sequenced by using the random number generator function in a spreadsheet (Excel 2016; Microsoft Corp) and evaluated intraorally. At each evaluation, the participant was instructed to occlude firmly into the predetermined vertical dimension of occlusion and centric relation position. To evaluate the tissue surface adaptation, an indicator (Fit Checker II; GC Corp) was placed on the intaglio surface and occlusion force Yoon et al
Study Arch
Exclusion Criteria Number
Age
Sex
Opposing Arch
PDI Classification
1
68
Male
Mandible (single)
Removable dental prosthesis
II
2
78
Female
Maxilla (single)
Removable dental prosthesis
I
3
62
Male
Maxilla/ mandible (both)
-
II/I
4
65
Female
Maxilla/ mandible (both)
-
I/I
5
71
Female
Maxilla/ mandible (both)
-
I/I
6
82
Female
Maxilla (single)
Removable dental prosthesis
III
7
79
Female
Mandible (single)
Removable dental prosthesis
III
8
81
Female
Maxilla (single)
Fixed dental prosthesis on natural teeth
II
9
61
Male
Maxilla (single)
Fixed dental prosthesis on natural teeth
II
PDI, Prosthodontic Diagnostic Index.
Figure 1. Preparation of 3 different denture bases with occlusion rim. PAP, pack-and-press; MIL, 5-axis milling; DLP, digital light processing.
maintained as instructed until the indicator polymerized. At least 10 minutes were allowed between the denture base trials for tissue recovery. After removing the denture base from the participant’s mouth, a polyvinyl siloxane impression material (Examixfine; GC Corp) was applied to the surface layer of the indicator relining on the intaglio surface of each denture base. To measure the thickness of the indicator, a silicone replica index was made with its base parallel to the plane of the occlusion rim by using polyvinyl siloxane materials (Exaflex Putty and Examixfine; GC Corp). From the fourth visit, the clinical procedures to provide a removable complete denture to each participant were continued in a conventional manner. The definitive prostheses were fabricated by means of PAP by using a split-mold flask THE JOURNAL OF PROSTHETIC DENTISTRY
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Figure 2. Measured points on maxillary arch. Six points on residual ridge crest (RC), 3 points on midpalatal suture area (MP), 18 points hard palate except midpalatal suture (P), and 7 points on posterior palatal seal (PPS). Red dotted circle area is incisive papilla.
(Hanau Varsity Flasks; Whip Mix Corp) and heatactivated PMMA resin (SR Triplex Hot; Ivoclar Vivadent AG) and delivered to the participants. The measuring points of the indicator layer thickness were located on the denture bearing areas and anatomic landmarks of the edentulous arches. A total of 34 measuring points were designated in 4 anatomic landmarks of the maxillary arch (Fig. 2): 6 points on the crest of the residual ridge (RC), 3 points on the area of the midpalatal suture (MP), 18 points on the hard palate except midpalatal suture (P), and 7 points on the posterior palatal seal (PPS). The vestibular sulcus, incisive papilla, anterior flabby ridge, maxillary tuberosity, and hamular notches were excluded from the measurement. For the mandibular arch, a total of 33 points in 3 anatomic landmarks were measured (Fig. 3): 9 points on the crest of the residual ridge and the most anterior point of the retromolar pad (RC), 12 points on the buccal slope and buccal shelf (BS), and 12 points on the lingual slope (LS). The vestibular sulcus, retromylohyoid fossa, and retromolar pad were excluded from the evaluation. The silicone index with the layer of indicator was sectioned perpendicular to the base at the designated points. The layer thickness of the indicator was measured at each designated point under a stereomicroscope (SZX16; Olympus Corp) at ×50 magnification by using an image analysis software program (ToupView; ToupTek). Two different parameters were designed to evaluate the tissue surface adaptation of the complete denture bases fabricated by using the PAP, MIL, and DLP techniques: the absolute tissue surface adaptation (ATA) and the relative tissue surface adaptation (RTA). The layer thickness (mm) of the indicator measured at the designated points in each anatomic landmark (RC, MP, P, and PPS for maxilla; RC, BS, and LS for mandible) was referred to as the ATA value. The RTA value was then THE JOURNAL OF PROSTHETIC DENTISTRY
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Figure 3. Measured points on mandibular arch. Nine points on residual ridge crest and most anterior point of retromolar pad (RC), 12 points on buccal slope and buccal shelf (BS), and 12 points on lingual slope (LS).
calculated from the ATA value. At the designated points of each anatomic landmark, the ATA value of each DLP (or MIL) denture base was subtracted from that of the PAP denture base to calculate the RTA value of the DLP (or MIL) denture base. Assuming the consistency of the indicator was constant and that the underlying alveolar bone was not deformed, the thickness of the indicator layer would depend on the surface deviation of the denture base, as well as the amount of mucosal displacement of the edentulous ridge, at the vertical dimension of occlusion of each participant. The RTA value of each DLP (or MIL) denture base was equal to the difference in the amount of surface deviation between the PAP and DLP (or MIL) denture bases, as the PAP denture base served as a clinical reference for the definitive prosthesis in this study. If the RTA value was negative, the DLP or MIL denture base adapted more intimately to the denture-bearing tissue than the PAP denture base at the designated point. If the RTA value was positive, the DLP or MIL denture base would exhibit loose adaptation to the supporting tissue compared with the PAP denture base. To differentiate the pattern of 3D surface deviation of the intaglio surface of the DLP or MIL denture base from that of the PAP denture base (reference), all the positive and negative RTA values were coded as either 1 (positive) or 2 (negative). By using each complete denture base fabricated by 3 different techniques, each of the 3 different thickness values of the indicator measured in the anatomic landmarks was recorded according to the arch: maxilla or mandible. For each arch, the means, standard deviation, median, and interquartile range of all the measurements (ATA) were statistically analyzed by using a software program (IBM SPSS Statistics, v22.0; IBM Corp). The Kruskal-Wallis analysis of variance was performed to evaluate the statistical significance of the differences in ATA values between each fabrication technique group. Yoon et al
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Table 3. Measured ATA (mm) values of complete denture bases fabricated by 3 different techniques at designated points in each anatomic landmark PAP Arch
Landmark
Maxilla
Mandible
MIL
DLP
Mean ±SD
Median
IQR
Mean ±SD
Median
IQR
Mean ±SD
Median
IQR
RC
376.82 ±200.15
307.23
266.03
548.62 ±268.86
509.90
454.57
306.20 ±195.11
227.71
363.63
P
432.14 ±115.54
394.37
145.50
521.13 ±66.01
522.45
106.61
465.28 ±133.93
431.15
215.60
MP
289.22 ±191.52
207.18
440.09
438.07 ±176.48
446.86
326.00
348.82 ±134.66
338.29
299.97
PPS
613.83 ±472.50
414.87
536.46
701.52 ±281.53
641.77
324.39
589.27 ±267.01
536.25
402.86
RC
356.43 ±185.28
449.33
354.94
285.50 ±175.62
250.92
313.77
308.80 ±176.25
292.38
327.82
BS
309.53 ±128.64
321.42
251.48
346.04 ±284.75
268.36
461.29
320.08 ±233.23
219.35
331.14
LS
266.53 ±170.11
181.00
245.33
158.26 ±85.74
139.19
140.88
173.79 ±73.75
199.13
123.31
ATA, absolute tissue surface adaptation; BS, buccal slope and buccal shelf; DLP, digital light processing; IQR, interquartile range; LS, lingual slope; MIL, 5-axis milling; MP, midpalatal suture; P, hard palate except midpalatal suture; PAP, pack-and-press; PPS, posterior palatal seal; RC, crest of residual ridge (maxilla) or crest of residual ridge and most anterior point of retromolar pad (mandible); SD, standard deviation.
To evaluate the difference in the surface deviation pattern of both DLP and MIL denture bases compared with that of the PAP denture base, the coded RTA values (either 1 or 2) of both DLP and MIL denture bases were statistically analyzed with the McNemar test. The difference in the frequency (%) of coded RTA values between the DLP and MIL denture bases was compared to estimate the likelihood of intimate or loose adaptation to the tissue compared with the PAP denture base for each anatomic landmark of both the maxilla and mandible. The statistical analyses were performed by using a software program (IBM SPSS Statistics, v22.0; IBM Corp) (a=.05). A post hoc power analysis was performed with G*Power (v3.1.9.4).24 RESULTS The measured ATA values of the PAP, MIL, and DLP complete denture bases for each anatomic landmark of each edentulous arch condition are presented in Table 3. In terms of the ATA values of complete denture base fabrication techniques, no statistically significant differences were observed for the anatomic landmarks of the maxillary arch (Fig. 4) (P=.251 for RC; P=.243 for P; P=.340 for MP; and P=.571 for PPS) or for those of the mandibular arch (Fig. 5) (P=.811 for RC; P=.887 for BS; and P=.330 for LS). Regarding the frequency of the coded RTA values of complete denture base fabrication techniques for the maxillary arch, the DLP complete denture base was significantly different from the MIL denture base in the RC area (P=.001, post hoc power=0.99; Table 4). The DLP denture base exhibited a higher frequency of negative RTA values than the MIL denture base. However, the MIL denture base showed a higher frequency of positive RTA values than the DLP denture base. In the P area, the difference between the DLP and MIL denture bases was also statistically significant (P=.005, post hoc power=0.82). The DLP denture base showed a higher frequency of negative RTA values than the MIL denture base, while the MIL denture base presented a higher frequency of positive RTA values than the DLP denture Yoon et al
base. In the PPS and the MP areas, no significant differences were found between the DLP and MIL denture bases (both P=1.000). With regard to the frequency of the coded RTA values for the mandibular arch, no statistically significant differences were found between the DLP and MIL denture bases on all the anatomic landmarks (P=.180 for RC, P=.454 for BS, and P=.388 for LS). DISCUSSION Based on the results of this study, no significant difference was observed with respect to the tissue surface adaptation (ATA) among the complete denture bases fabricated by 3 techniques in either the maxillary or mandibular edentulous arches. Therefore, the null hypothesis was not rejected. This is consistent with in vitro comparative studies on the tissue surface adaptation of CAD-CAM denture bases.18,19 In the present study, the frequency of the coded RTA values was significantly different between the DLP and MIL denture bases in 2 anatomic landmarks (RC and P) of the maxillary arch. On the crest of maxillary residual ridge and hard palate, in comparison with the PAP denture base, the MIL denture base was likely to exhibit small gaps between supporting tissue and the denture base, and the DLP denture base showed a likelihood of intimate adaptation to the tissue. Generally, the complete denture base shows a high degree of adaptation to the residual ridge and palate, whether fabricated by the conventional or CAD-CAM technique.20 However, the current findings suggested that the DLP technique may lead to better adaptation of the maxillary complete denture base in the stress-bearing area than the PAP or even the MIL technique. This finding was consistent with the results of a previous in vitro analysis.19 Compared with the PAP base, the DLP base may adapt more intimately to the crest of the maxillary residual ridge.19 In the MP area, both DLP and MIL denture bases were likely to exhibit loose tissue adaptation compared with the PAP denture base. This finding was also consistent with a previous in vitro analysis.19 The PAP base tended to press the center of the palate, THE JOURNAL OF PROSTHETIC DENTISTRY
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800.00
600.00
Absolute Tissue Surface Adaptation Value (μm)
700.00
Absolute Tissue Surface Adaptation Value (μm)
1000.00
600.00 400.00 200.00 0.00
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500.00 400.00 300.00 200.00
PAP
MIL Group
DLP
PAP
A
MIL Group
DLP
MIL Group
DLP
B
600.00 Absolute Tissue Surface Adaptation Value (μm)
Absolute Tissue Surface Adaptation Value (μm)
2000.00
400.00
200.00
0.00
1500.00
1000.00
500.00
0.00 PAP
MIL Group
DLP
PAP
C
D
Figure 4. Comparison of absolute tissue surface adaptation (mm) of maxillary complete denture bases fabricated by using 3 different techniques: packand-press (PAP), 5-axis milling (MIL), and digital light processing (DLP). A, Residual ridge crest (RC). B, Hard palate except midpalatal suture (P). C, Midpalatal suture area (MP). D, Posterior palatal seal (PPS).
while the DLP base had some spaces at the midpalatal suture.19 The denture base fabricated by pressure packing may press the center of the palate (up to 150 mm) because of residual stress-induced deformation.23 Uneven pressure to the denture-supporting area may decrease the retention of the complete denture base.23 In the present study, the mean difference in the ATA values in the MP area between the DLP (or MIL) and PAP denture bases was below 150 mm. The current findings suggested that both the DLP and MIL denture bases were less likely to press the center of the palate than the PAP base. In the PPS area, both the DLP and MIL denture bases showed no likelihood of either intimate tissue adaptation or loose fit compared with the PAP denture base. On the crest of mandibular residual ridge, the MIL denture base was likely to adapt more intimately to the tissue than the PAP denture base, whereas the DLP denture base showed no likelihood of either intimate adaptation or loose fit. Yoon et al18 reported that the mandibular MIL denture base showed uniform adaptation to the majority of denture-bearing tissue, THE JOURNAL OF PROSTHETIC DENTISTRY
while the mandibular PAP denture base was likely to compress the crest of the residual ridge. On the lingual slope of the residual ridge, both the DLP and MIL denture bases showed a likelihood of intimate tissue adaptation compared with the PAP denture base. The 5-axis milling technique has been widely used because of its precision; however, its accuracy relies on the diameter and the accessibility of tools.12 In this study, the irregular morphology of the maxillary residual ridge may not be fully reproduced in the milled complete denture base. This could be a major drawback of milled complete denture bases.19 With the DLP technique, the build angle has been reported to affect the quality of DLP-generated objects.16,17 In this study, the build angle for every DLP denture base was consistent at 100 degrees to compare the results of this study with those of previous in vitro studies.18,19 Limitations of this clinical study included that the number of evaluated edentulous arches was small. In addition, the thickness of the indicator could be influenced by the opposing arch condition. The current Yoon et al
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Table 4. Frequency of coded RTA values of complete denture bases fabricated by 3 different techniques at designated points in each anatomic landmark
Absolute Tissue Surface Adaptation Value (μm)
600.00 500.00
Positive RTA (%) Arch
400.00
Maxilla
300.00 200.00
Mandible
100.00 PAP
MIL Group
DLP
A
Absolute Tissue Surface Adaptation Value (μm)
1000.00 800.00
Negative RTA (%)
DLP
MIL
DLP
MIL
P
RC
42.9
76.2
57.1
23.8
.001
P
50.8
64.3
49.2
35.7
.005
MP
61.9
66.7
38.1
33.3 >.999
PPS
53.1
53.1
46.9
46.9 >.999
RC
48.9
37.8
51.1
62.2
.180
BS
50.0
56.7
50.0
43.3
.454
LS
30.0
23.3
70.0
76.7
.388
BS, buccal slope and buccal shelf; DLP, digital light processing; LS, lingual slope; MIL, 5-axis milling; MP, midpalatal suture; P, hard palate except midpalatal suture; PPS, posterior palatal seal; RC, crest of residual ridge (maxilla) or crest of residual ridge and most anterior point of retromolar pad (mandible); RTA, relative tissue surface adaptation.
satisfaction, clinician preference, retention, and masticatory performance.
*
600.00
CONCLUSIONS 400.00
Based on the findings of this clinical study, the following conclusions were drawn:
200.00 0.00 PAP
MIL Group
DLP
B
600.00 *
Absolute Tissue Surface Adaptation Value (μm)
Landmark
500.00 400.00
1. Both DLP and MIL techniques are clinically feasible to fabricate complete denture bases. 2. In comparison with the PAP denture base, the DLP denture base was likely to exhibit intimate adaptation in the stress-bearing areas of the maxillary arch. 3. The maxillary MIL denture base, on the contrary, was likely to display loose adaptation to the tissue. 4. Both DLP and MIL denture bases were likely to show either intimate adaptation or mild impingement on the lingual slope of mandible.
300.00
REFERENCES
200.00 100.00 0.00 PAP
MIL Group
DLP
C
Figure 5. Comparison of absolute tissue surface adaptation (mm) of mandibular complete denture bases fabricated by using 3 different techniques: pack-and-press (PAP), 5-axis milling (MIL), and digital light processing (DLP). A, Residual ridge crest and most anterior point of retromolar pad (RC). B, Buccal slope and buccal shelf (BS). C, Lingual slope (LS).
findings should be applied with caution considering clinical conditions and fabrication parameters. A standard protocol for evaluating the tissue surface adaptation of complete denture bases is needed. Further clinical studies with a larger sample size are required to evaluate the DLP-generated complete denture in terms of patient Yoon et al
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