|Year : 2005 | Volume
| Issue : 4 | Page : 185-186
The macboyle retainer
Vivek V Nair, KN Velayudhan Nair
Government Dental College, Trivandrum - 695011, Kerala, India
Vivek V Nair
Sivabhavan, Valiasalai, TC 23/558, Trivandrum - 695036, Kerala
Source of Support: None, Conflict of Interest: None
The Mac Boyle retainer should be employed only under the most favourable conditions and when workmanship is of the highest order. When a Mac Boyle retainer is constructed by one who understands its limitations and does not exceed its potentialities, the prosthesis will have a surprisingly long life. When its use can be justified, minimal tooth surface is covered by metal. It is akin to the partial veneer crown, but the preparation is not so deep and the retention is derived from grooves at the labial line angles instead of on the proximal surfaces.
Keywords: Retainer, minimal tooth reduction, esthetics
|How to cite this article:|
Nair VV, Velayudhan Nair K N. The macboyle retainer. J Indian Prosthodont Soc 2005;5:185-6
| Introduction|| |
In the field of anterior fixed partial dentures, stability and esthetic quality deserve equal consideration. Stability can be obtained with partial veneer and veneered crowns and the Mac Boyle retainer, even though constructed without finesse. However, to achieve a wholly satisfactory appearance with the partial veneer crown, alterations that might lessen both retention and stability may have to be made in the standard preparation. ,,, The Mac Boyle retainer usually leaves much to be desired esthetically. It should be considered primarily as a retainer for temporary bridges.
1. The Mac Boyle retainer,, may be used on mandibular central and lateral and maxillary lateral incisors, even though these teeth have proximal caries or large pulps.
2. It is indicated particularly for adolescents, but will be satisfactory for any patient who does not object to a display of metal.
The steps in the preparation are as follows:
1. reduction of the mesial and distal surfaces
2. reduction of the lingual surface from the crest of the cingulum to the incisal edge
3. reduction of the incisal edge
4. beveling the mesiolabial and distolabial line angles
5. grooving the mesiolabial and disto labial bevels
6. reduction of the cingulum and establishing the cervical finish line,
7. placing a pinhole in the cingulum.
The mesial and distal cuts, made with a disk in a straight handpiece, should be parallel to the path of insertion. Labially they can extend beyond the line angles, but should converge lingually less than the proximal cuts for the anterior partial veneer crown [Figure - 1].
A. Top to bottom
Uncut tooth: proximal slices; lingual reduction; incisal bevel.
B. Top to bottom
Labial line angles beveled; labial chamfer; finishing line, lingual pinhole and rounded angles at labioincisal.
The lingual surface may be prepared 0.5 mm deep, with a round-edge wheel stone of appropriate size. This cut, starting on the cingulum, must include the incisal edge. Here the reduction is made at an angle similiar to abrasion, or indicated abrasion, on this surface. Using a disk or stone, the labial line angles can be beveled from 0.3 to 0.5 mm. Onto the labial surface and as far cervically as the contour of the tooth will permit, which usually is three fifths or two thirds of the length of the surface. A small cylindrical or tapered stone is used to make the bevels concave, but not so deep that their axial margins are at right angles to the labial enamel surface [Figure - 2].
Schematic explanation of Mac Boyle preparation showing retentive grasp on labial. Lines A-A designate the direction of the proximal cuts; lines B-B show the labial convergence of the labial bevels, which provides resistance to lingual displacement.
The cingulum is shaped the same as for a partial veneer crown. The cervical finishing line is continued onto the proximal surface and may go into the gingival crevice, although this is not a requisite.
A No. 700 or 701 tapered fissure bur is used to make a pinhole in the cingulum, 1 mm deep and parallel to the path of insertion. The labial margin at the incisal edge is beveled only enough to protect the enamel rods. When accelerated speeds are used for this preparation, the proximal surfaces should be reduced with a disk to avoid an exaggerated display of metal at labial line angles. Direct wax patterns may be carved and casting executed in the usual manner as for other partial veneer crowns.
| Discussion|| |
Preservation of unblemished labial enamel is always an asset to appearance., A correctly designed and well made pinledge displays minimal metal, requires the least cutting of tooth structure of any of the anterior retainers, and has the expectancy of long life. It is unexcelled if used in mouths in which the caries index is low or in which it has been controlled, if used on caries- free teeth or those that have been restored, and if used on teeth some bulk in the incisal one -third. With meticulous application, when the occlusion is favourable, it can be placed on thin teeth and if the patient and operator will co-operate in observing the mouth closely in the future, it can be placed over proximal caries or large pulps. New techniques in preparation of the abutment tooth,, and methods of obtaining the die and casting have given the profession a retainer with esthetics equal to that produced by the direct technique heretofore used, and with retention or stability seemingly equal to the partial veneer crown and many of the veneered crowns that are built over the omnipresent tapered preparation.
| Conclusion|| |
The Mac Boyle retainer will be a serviceable retainer if meticulously designed and constructed. Its application is limited, but in a few instances it supersedes all other retainers.
| References|| |
Grubb HD. Fixed bridge work. J Prosthet Dent 1953;3:121-5.
Willey RE. Preparation of abutments for veneer retainers. JADA 1956;53:141-7.
Barker BC. The crowning of vital anterior teeth. Aust Dent J 1965;10:449-55.
Pruden KC. Abutments and attachments in fixed partial dentures. J Prosthet Dent 1957;7:502.
[Figure - 1], [Figure - 2]