In-Jae Won; Kung-Rock Kwon; Ahran Pae; Dae-Gyun Choi

doi:10.4047/jkap.2011.49.1.38

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Won, Kwon, Pae, and Choi: An influence of operator’s posture on the shape of prepared tooth surfaces for fixed partial denture

ORIGINAL ARTICLE

J Korean Acad Prosthodont 2011;49(1):38-48.

Published online: 18 December 2011

DOI: https://doi.org/10.4047/jkap.2011.49.1.38

An influence of operator’s posture on the shape of prepared tooth surfaces for fixed partial denture

In-Jae Won, DMD, MSD, Kung-Rock Kwon, DMD, PhD, Ahran Pae, DMD, PhD, Dae-Gyun Choi, DMD, DSc^∗

Department of Prosthodontics, Division of Dentistry, Graduate School, Kyung-Hee University, Seoul, Korea

∗Corresponding Author: Dae-Gyun Choi Department of Prosthodontics, School of Dentistry, Kyung-Hee University #1, Hoegi-Dong, Dongdaemun-Gu, Seoul, 130-701, Korea +82 2 958 9340: e-mail, choi@khu.ac.kr

Received 9 December 201015 December 2010 Accepted 8 January 2011

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Purpose

Dentists suffer back, neck and shoulder pain during their careers due to bad operating posture. If dentists have a good operating posture ergonomically, there would be less pain and discomfort in the shoulder and back. Therefore, dentists should learn the Home position which enables dentists to approach a stable posture ergonomically. This study was to compare tooth preparation in the Home position and the Random position, and evaluate the clinical efficacy of the Home position.

Materials and methods

Tooth preparation for fixed partial denture was performed on the maxillary left 2nd premolar and maxillary left 2nd molar at the two different operating positions were compared. The amount of occlusal reduction, marginal width, subgingival margin depth, and convergence angle were measured. A T-test was performed separately to compare the results of the Random position and the Home position.

Results

1. The amounts of average thickness of occlusal reduction on fossa were deficient to the ordered ones in the Random position and the Home position (P > .05). 2. The average subgingival margin depth of prepared margin on maxillary left 2nd premolar, maxillary left 2nd molar were excessive in the Random position than in the Home position. On the maxillary left 2nd premolar, there was no statistical difference in the Random position and the Home position except Distal midline, DL line angle, Lingual midline, ML line angle (P < .05). On the maxillary left 2nd molar, there was no statistical difference in the Random position and the Home position (P < .05). 3. Average convergence angle in the Random position and the Home position were excessive compared to the ordered angle. There was no statistical difference in the Random position and the Home position (P > .05). 4. Analysis of pearson correlation : In the Random position, the amounts of average thickness of occlusal reduction, the average subgingival margin depth of prepared margin, convergence angle were significantly associated with each other (P < .05). But in the Home position, they were not significantly associated with each other (P < .05). 5. The time needed for preparation in the Home position was faster or equal than that of the Random position as time went on.

Conclusion

In conclusion, there were no significant differences between Home postion and Random position in measures of occlusal reduction, marginal width, marginal depth, convergence angle. However, preparation time and incidence of damaging adjacent teeth were less in Home position than in Random position. Therefore, if trained properly, Home position which is more ergonomically stable can be adopted for clinical use. (J Korean Acad Prosthodont 2011;49:38-48)

Keywords: Home position, Random position, Tooth Preparation, Operator's Posture

REFERENCES

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Fig. 1.

Measuring method for occlusal reduction, width & depth of margine, convergence angle. A: Measuring point of margin width, B: Artificial gingiva position, C: Margin position, a: Thickness of occlusal surface reduction (Cusp tip), b: Thickness of Occlusal surface reduction (Fossa), c: Measuring point of convergence angle (Upper part of margin: 1.5 - 3 mm), d: Upper part of measuring point of margin width (0.5 mm), e: Upper part of artificial gingiva position (0.5 mm), f: Lower part of artificial gingiva position (0.5 mm).

Fig. 2.

Preparation time of 8 operators in Home position/Random position.

Table 1.

Guideline of tooth reduction for Home position (Max. left 2nd premolar)

Procedure	Reduction surface	Operator's position	Bur	Head position (R-L)	Head position (A-P)	Degree of mouth open	Grip n	Rest F surface	Finger surface for rest	e View
Occlusal	Guide groove	11:00	462	R20°	-20°	2	1	#23 cusp	T-C	D.V.
reduction	Buccal occlusal surface	11:00	102R	R20°	-20°	1 - 2	1	#23 cusp	T-C	1
	Lingual occlusal surface	12:00	102R	L20°	-20°	2	1	#23 cingulum	C	4
Axial	Buccal surface	11:00	102R	R20°	-10°	2	1	#23 cusp	M-C	D.V.
reduction	Lingualsurface	11:30	102R	L20°	-10°	3	1	rugae	C	3 - 4
	(occlusal 1/2)
	Lingualsurface	11:30	102R	L20°	-10°	3	1	rugae	C	3 - 4
	(gingival 1/2)
Proximal	Distal surface	11:00	102R	R20°	-10°	3	1	#13 cusp	T-M	2
reduction	Proximal reduction	12:00	204	R20°	-10°	2	1	#13 cusp, #12 Incisal edge	C	1
	Mesial surface	11:30	102R	R20°	-10°	3	1	#24,25 lingual cusp	T-M	1
Subgingival	DB lineangle-	11:00	SF102R	R20°	-10°	2	1	#23 cusp	M-C	D.V.
margin	MB lineangle
	MB lineangle-	11:30	SF102R	R20°	-10°	3	1	#24,25 lingual cusp	T-M	1
	ML lineangle
	DB lineangle-	11:00	SF102R	R20°	-10°	3	1	#13 cusp	T-M	2
	DL lineangle
	DL lineangle-	11:30	SE102R	L20°	-10°	3	1	rugae	C	3 - 4
	ML lineangle
Finishing & Polishing	Same as the above

D.V.: Direct view.

Table 2.

Guideline of tooth reduction for Home position (Max. left 2nd molar)

Procedure	Reduction surface	Operator's position	Bur	Head position (R-L)	Head position (A-P)	Degree of mouth open	Grip	Rest surface	Finger surface for rest	View
Occlusal reduction	Guide groove	11:00	462	R20°	-20°	2	1	#24 buccal cusp	T-C	D.V.
	Buccal occlusal surface	11:00	102R	R20°	-20°	1 - 2	1	#24 buccal cusp	T-C	1
	Lingual occlusal surface	12:00	102R	L20°	-20°	2	1	#24,25 lingual surface	e C	4
Axial reduction	Buccal surface	11:00	102R	R20°	-10°	3	1	#24,25 lingual surface	e M-C	1 - 2
	Lingualsurface	11:30	102R	L20°	-10°	3	1	#25,26 palatal area	M-C	3 - 4
	(occlusal 1/2)
	Lingualsurface	11:30	102R	L20°	-10°	3	1	#25,26 palatal area	C	3 - 4
	(gingival 1/2)
Proximal reduction Subgingival margin	Distal surface	11:00	102R	R20°	-10°	3	1	#24,25 lingual cusp	T-M	2
	Mesial surface	11:30	102R	R20°	-10°	3	1	#24,25 lingual cusp	T-M	D.V.
	DB lineangle-	11:00	SF102R	R20°	-10°	3	1	#24,25 lingual cusp	M-C	1 - 2
	MB lineangle
	MB lineangle-	11:30	SF102R	R20°	-10°	3	1	#24,25 lingual cusp	T-M	D.V.
	ML lineangle
	DB lineangle-	11:00	SF102R	R20°	-10°	3	1	#24,25 lingual cusp	T-M	2
	DL lineangle
	DL lineangle-	11:30	SE102R	L20°	-10°	3	1	#25,26 palatal area	M-C	3 - 4
	ML lineangle
Finishing & Polishing	Same as the above

D.V.: Direct view.

Table 3.

Average thickness of occlusal surface reduction on maxillary left 2nd premolar (Unit: mm)

Measuring point	Operator's position	Average thickness of occlusal reduction (SD)	Significance
1. Buccal cusp tip	Random P.	2.27 (0.38)	0.45
1. Buccal cusp tip	Home P.	2.18 (0.49)
2. Palatal cusp tip	Random P.	1.97 (0.42)	0.20
2. Palatal cusp tip	Home P.	1.82 (0.35)
3. Mesial fossa	Random P.	1.17 (0.26)	0.99
3. Mesial fossa	Home P.	1.17 (0.30)
4. Distal fossa	Random P.	0.77 (0.36)	0.84
4. Distal fossa	Home P.	0.76 (0.29)

Table 4.

Average thickness of occlusal surface reduction on maxillary left 2nd molar (Unit: mm)

Measuring point	Operator's position	Average thickness of occlusal reduction (SD)	Significance
1. Mesiobuccal cusp tip	Random P.	1.69 (0.50)	0.95
	Home P.	1.68 (0.43)
2. Distobuccal cusp tip	Random P.	1.61 (0.43)	0.01∗
	Home P.	1.93 (0.43)
3. Palatal cusp tip	Random P.	2.05 (0.53)	0.24
	Home P.	2.00 (0.44)
4. Distolingual cusp tip	Random P.	1.74 (1.02)	0.63
	Home P.	1.63 (0.35)
5. Mesial fossa	Random P.	1.02 (0.34)	0.09
	Home P.	0.85 (0.30)
6. Central fossa	Random P.	0.92 (0.39)	0.39
	Home P.	0.84 (0.33)
7. Distal fossa	Random P.	0.85 (0.38)	0.27
	Home P.	0.94 (0.27)

^∗ A P value < .05 level was considered significant.

Table 5.

Average width of prepared margin on maxillary left 2nd premolar (Unit: mm)

Measuring point	Operator's position	Average width of prepared margin (SD)	Significance
1. MB Lineangle	Random P.	1.53 (0.33)	0.55
1. MB Lineangle	Home P.	1.48 (0.26)	0.55
2. Buccal midline	Random P.	1.12 (0.11)	0.32
2. Buccal midline	Home P.	1.44 (1.51)	0.32
3. DB lineangle	Random P.	1.77 (0.89)	0.13
3. DB lineangle	Home P.	1.45 (0.41)	0.13
4. Distal midline	Random P.	1.53 (0.26)	0.85
4. Distal midline	Home P.	1.52 (0.41)	0.85
5. DL lineangle	Random P.	1.20 (0.16)	0.83
5. DL lineangle	Home P.	1.20 (0.11)	0.83
6. Lingual midline	Random P.	1.24 (0.22)	0.28
6. Lingual midline	Home P.	1.39 (0.62)	0.28
7. ML lineangle	Random P.	1.24 (0.18)	0.10
7. ML lineangle	Home P.	1.60 (1.11)	0.10
8. Mesial midline	Random P.	1.65 (0.48)	0.84
8. Mesial midline	Home P.	1.63 (0.28)	0.84

Table 6.

Average width of prepared margin on maxillary left 2nd molar (Unit: mm)

Measuring point	Operator's position	Average width of prepared margin (SD)	Significance
1. MB Lineangle	Random P.	1.55 (0.54)	0.44
1. MB Lineangle	Home P.	1.84 (1.65)	0.44
2. Buccal midline	Random P.	1.74 (0.39)	0.62
2. Buccal midline	Home P.	1.86 (1.02)	0.62
3. DB lineangle	Random P.	1.54 (0.35)	0.08
3. DB lineangle	Home P.	1.33 (0.39)	0.08
4. Distal midline	Random P.	2.51 (0.80)	0.25
4. Distal midline	Home P.	2.29 (0.40)	0.25
5. DL lineangle	Random P.	1.91 (0.45)	0.67
5. DL lineangle	Home P.	1.98 (0.50)	0.67
6. Lingual midline	Random P.	1.44 (0.39)	0.07
6. Lingual midline	Home P.	1.25 (0.26)	0.07
7. ML lineangle	Random P.	1.44 (0.29)	0.82
7. ML lineangle	Home P.	1.46 (0.33)	0.82
8. Mesial midline	Random P.	1.66 (0.46)	0.01∗
8. Mesial midline	Home P.	2.00 (0.34)	0.01∗

^∗ A P value < .05 level was considered significant.

Table 7.

Average depth of prepared margin on maxillary left 2nd premolar (Unit: mm)

Measuring point	Operator's position	Average depth of prepared margin (SD)	Significance
1. MB Lineangle	Random P.	0.74 (0.76)	0.26
1. MB Lineangle	Home P.	0.59 (0.39)	0.26
2. Buccal midline	Random P.	0.18 (0.64)	0.90
2. Buccal midline	Home P.	0.20 (0.43)	0.90
3. DB lineangle	Random P.	0.80 (0.88)	0.77
3. DB lineangle	Home P.	0.74 (0.58)	0.77
4. Distal midline	Random P.	1.00 (0.81)	0.04∗
4. Distal midline	Home P.	0.65 (0.42)	0.04∗
5. DL lineangle	Random P.	0.88 (0.79)	0.05∗
5. DL lineangle	Home P.	0.54 (0.31)	0.05∗
6. Lingual midline	Random P.	1.86 (0.79)	0.03∗
6. Lingual midline	Home P.	1.43 (0.33)	0.03∗
7. ML lineangle	Random P.	0.99 (0.59)	0.02∗
7. ML lineangle	Home P.	0.57 (0.58)	0.02∗
8. Mesial midline	Random P.	0.09 (0.75)	0.08
8. Mesial midline	Home P.	-0.15 (0.39)	0.08

^∗ A P value < .05 level was considered significant.

Table 8.

Average depth of prepared margin on maxillary left 2nd molar (Unit: mm)

Measuring point	Operator's position	Average depth of prepared margin (SD)	Significance
1. MB Lineangle	Random P.	0.55 (0.82)	0.03∗
1. MB Lineangle	Home P.	0.17 (0.43)	0.03∗
2. Buccal midline	Random P.	1.03 (0.77)	0.01∗
2. Buccal midline	Home P.	0.54 (0.41)	0.01∗
3. DB lineangle	Random P.	1.78 (0.63)	0.01∗
3. DB lineangle	Home P.	1.34 (0.53)	0.01∗
4. Distal midline	Random P.	1.44 (0.68)	0.01∗
4. Distal midline	Home P.	1.02 (0.40)	0.01∗
5. DL lineangle	Random P.	1.38 (0.75)	0.01∗
5. DL lineangle	Home P.	0.90 (0.42)	0.01∗
6. Lingual midline	Random P.	0.99 (0.66)	0.02∗
6. Lingual midline	Home P.	0.58 (0.39)	0.02∗
7. ML lineangle	Random P.	0.81 (0.63)	0.04∗
7. ML lineangle	Home P.	0.46 (0.33)	0.04∗
8. Mesial midline	Random P.	1.39 (0.83)	0.03∗
8. Mesial midline	Home P.	0.97 (0.46)	0.03∗

^∗ A P value < .05 level was considered significant.

Table 9.

Average convergence angle on maxillary left 2nd premolar (Unit: °)

Measuring point	Operator's position	Average convergence angle (SD)	Significance
1. Mesiodistal axial wall	Random P.	14.11 (7.94)	0.31
1. Mesiodistal axial wall	Home P.	12.21 (6.17)	0.31
2. Buccolingual axial wall	Random P.	11.95 (7.41)	0.83
2. Buccolingual axial wall	Home P.	11.55 (4.39)	0.83

Table 10.

Average convergence angle on maxillary left 2nd molar (Unit: °)

Measuring point	Operator's position	Average convergence angle (SD)	Significance
1. Mesiodistal axial wall	Random P.	19.08 (13.53)	0.23
1. Mesiodistal axial wall	Home P.	14.98 (6.92)	0.23
2. Buccolingual axial wall	Random P.	13.66 (9.84)	0.17
2. Buccolingual axial wall	Home P.	10.39 (5.73)	0.17

Table 11.

Pearson correlation of random position on maxillary left 2nd premolar

		Occlusal reduction	Margin depth	Margin width	Mesiodistal convergence angle	Buccolingual convergence angle
Occlusal reduction	P.C.C.	1
	Significance
Margin depth	P.C.C.	-0.080	1
	Significance	0.436
Margin width	P.C.C.	0.518∗∗	-0.084	1
	Significance	0.000	0.247
Mesiodistal convergence angle	P.C.C.	-0.090	0.557∗∗	0.160	1
	Significance	0.674	0.005	0.457
Buccolingual convergence angle	P.C.C.	-0.154	0.510∗	0.206	0.570∗∗	1
	Significance	0.472	0.11	0.333	0.004

^∗∗ A P value < .01 level was considered significant

^∗ A P value < .05 level was considered significant, P.C.C.: Pearson correlation coefficient.

Table 12.

Pearson correlation of random position on maxillary left 2nd molar

		Occlusal reduction	Margin depth	Margin width	Mesiodistal convergence angle	Buccolingual convergence angle
Occlusal reduction	P.C.C.	1
	Significance
Margin depth	P.C.C.	-0.326∗∗	1
	Significance	0.000
Margin width	P.C.C.	-0.154∗	0.169∗	1
	Significance	0.046	0.019
Mesiodistal convergence angle	P.C.C.	-0.330	0.694∗∗	-0.080	1
	Significance	0.877	0.000	0.711
Buccolingual convergence angle	P.C.C.	0.235	0.382	-0.363	0.444∗	1
	Significance	0.269	0.065	0.081	0.030

^∗∗ A P value < .01 level was considered significant

^∗ A P value < .05 level was considered significant, P.C.C.: Pearson correlation coefficient.

Table 13.

Pearson correlation of home position on maxillary left 2nd premolar

		Occlusal reduction	Margin depth	Margin width	Mesiodistal convergence angle	Buccolingual convergence angle
Occlusal reduction	P.C.C.	1
	Significance
Margin depth	P.C.C.	-0.209∗	1
	Significance	0.041
Margin width	P.C.C.	0.043	-0.092	1
	Significance	0.675	0.204
Mesiodistal convergence angle	P.C.C.	0.010	0.260	0.192	1
	Significance	0.962	0.220	0.368
Buccolingual convergence angle	P.C.C.	0.217	0.126	0.115	0.214	1
	Significance	0.309	0.556	0.594	0.314

^∗∗ A P value < .01 level was considered significant

^∗ A P value < .05 level was considered significant, P.C.C.:Pearson correlation coefficient.

Table 14.

Pearson correlation of home position on maxillary left 2nd molar

		Occlusal reduction	Margin depth	Margin width	Mesiodistal convergence angle	Buccolingual convergence angle
Occlusal reduction	P.C.C.	1
	Significance
Margin depth	P.C.C.	-0.423∗∗	1
	Significance	0.000
Margin width	P.C.C.	0.059	0.014	1
	Significance	0.450	0.848
Mesiodistal convergence angle	P.C.C.	0.224	0.172	-0.059	1
	Significance	0.293	0.421	0.784
Buccolingual convergence angle	P.C.C.	0.126	0.217	-0.130	0.800∗∗	1
	Significance	0.558	0.310	0.545	0.000

^∗∗ A P value < .01 level was considered significant

^∗ A P value < .05 level was considered significant, P.C.C.: Pearson correlation coefficient.

Table 15.

Average time of crown-prepared (Unit: sec)

Measuring tooth	Operator's position	Average time (SD)
1. Maxillary left 2nd premolar	Random P.	465.0 (188.3)
	Home P.	387.2 (108.8)
2. Maxillary left 2nd molar	Random P.	509.6 (192.8)
	Home P.	382.0 (64.9)

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