The adaptation of noncemented pins

The adaptation

of noncemented

Enrique Perez R., D.D.S.,* German and Hector Yanahara M., D.D.S. Faculdad de Odontologia, University Guadalajara, Jalisco, Mexico

pins

Schoeneck

A., D.D.S.,**

of Guadalajara,

1 o all intents and purposes, pinholes and pins represent cavity preparations and preformed restorations. As such, the techniques and materials used in pin retention should conform to the principles of operative dentistry. This investigation concerned itself with pinholes formed by twist drills and two types of noncemented pins. As restorations, the pins failed to conform to the principle of adaptation of the restoration to the cavity walls. MATERIALS

AND

METHODS

All tests were made with new twist drills and pins on freshly extracted teeth which were maintained in 10 per cent formalin. Two types of twist drills, and the pinholes they made, were measured. The twist drills and pins were presumed to be representative of all such equipment. The twist drills (Fig. 1) were Unitekt (0.022 inch) and Whaledent (0.027 and 0.021 inch). The data are presented as the mean measurement of 5 twist drills. The pinholes were transversely or longitudinally sectioned for measurement and examination. Every effort was made to section the pinholes through the center for longitudinal measurements and at a true cross section for diameter measurements. The data are presented as the mean dimension for 5 pinholes. Both Friction-lock+ and Self-threadingz pins (Fig. 2) were measured and compared with the pinholes. The morphology of the pins as preformed restorations was evaluated. The measurements represent the mean of 5 randomly chosen pins. The adaptation of the pins to the pinholes was observed and measured in 10 trials for each type of pin and corresponding pinhole. The Friction-lock pins were *Professor

and Chairman,

**Professor tUnitek,

of Fixed Partial Monrovia,

SWhaledent,

Department

of Operative

Dentistry.

Prosthesis.

Calif.

Inc., Brooklyn,

N. Y.

631

632

Perez R., Schoeneck

A., and Yanalrara

Fig. 1. Twist drills used in the study: Whaledent. Note the pointed tips. Fig. 2. Pins used in the study: Minim Self-threading.

Top,

Left,

ITnitck;

Friction-lock;

M.

ccnt~r, ~rnter,

Regular Regular

Whaledent.

right,

Self-threading;

Minim bottom.

applied with 25 pounds of force. The Self-threading pins were inserted under torque until the flattened pinhead separated from the pin. Measurements of the adaptation were made on all specimens and presented as mean results. All measurements were made with a manual micrometer or an eyepiece micrometer and reported in microns. RESULTS Twist drills. The mean diameters of the twist drills were: Unitek, 520 microns: Whaledent Regular, 675 microns, and Whaledent Minim, 530 microns. The pointed end of the twist drill was of particular interest. It resembled a slightly twisted bibeveled bur. The pointed end of the Whaledent Regular and Minim twist drills formed approximately a 100 degree angle. The Unitek twist drill formed approximately a 90 degree angle. The length of the bibeveled point from the body of the twist drill was 240 microns for all drills (Fig. 1 i . The pinhole. The preparation made by a twist drill was, in reality, a cylindrical Class I cavity preparation. The vertical walls formed a tube and lacked the conventional line angles. The pulpal wall presented a hollow cone with the apex directed toward the root. The conical pulpal wall corresponded to the bibeveled por-

Volllme 26 Number 6

Adaptation

of noncemented

pins

633

Fig. 3. Hemisected pinholes in dentin: Left, Unitek; center, Minim Whaledent; right, Regular Whaledent. Note the apex formed by the pointed tips of the twist drills. The sections were filled with blue wax to provide photographic contrast.

tion of the twist drill. The vertical tubular portion of the cavity met the conical pulpal wall at an obtuse angle to form a circular line angle. The walls of the cavity were smooth and accurately conformed to the shape of the twist drill (Fig. 3). The pinholes, measured in transverse sections, were remarkably consistent in size. The results testify to the accuracy of a cavity preparation created by a twist drill. The mean diameters of the tubular portion of the pinholes were: Unitek, 525 microns; Whaledent Regular, 692 microns; and Whaledent Minim, 544 microns. The conical fundus measured in longitudinal section was 245 microns from the base to the apex. Pins. Friction-lock pins are made of magnetized stainless steel. They are intended to provide a press fit and are available in 3/s, y!Z, and 3/ls inch lengths. The mean major diameter of the pins was 546 microns. The pin presented a spiral groove approximately 34 microns deep. The mean pitch or distance between the spirals was 1.17 mm. In essence, the Friction-lock pin represents a bolt with wide flat threads. The minor diameter of the pins was 478 microns (Fig. 4). The major diameter of the pin was 21 microns larger than the diameter of the pinhole; the minor diameter was 47 microns less than the diameter of the pinhole. The ends of the Friction-lock pins presented irregularly cut surfaces. Some were slightly rounded; others were oblique, concave, or had sharp angles. None conformed to the shape of the pinhole since they lacked a conical end (Fig. 4) . Regular Self-threading pins are available in 3/8 inch length and are irregularly coated with wax. The pin is made of stainless steel and electroplated with gold. The self-threading pattern simulated a bolt with sharp threads. One end of the pin had been flattened to fit a torque wrench. The Self-threading pin is thus screwed into the dentin (Fig. 5). The mean major diameter of the Regular pin was 784 microns, which is 94 microns larger than the corresponding pinhole. The minor diameter was 595 microns, which is 89 microns less than the mean diameter of the pinhole. The groove

634

Perez R., Schoeneck

A., uzd Yanalrar-a

XI.

between the major and minor diameters \vas 189 microns. The pitch or distance III*tween the threads was 196 microns, ‘1’11~ end to br inserted was slightly narrows’-1. than the minor diameter of the pin and 1xesentc.d ;I txle;In diametrr of 454 mic~~is (Fig. 5). The Minim Self-threading pin is sin~ilar to the Regular but with smaller dimertsions. It has the same flattened head and bolt form. The mean major diameter \v:ti 624 microns, which is 63 microns larger than tht* corresponding pinhole. The n~;111 minor diameter was 425 microns, which is I 18 Ilricrons less than the diameter of III<, corresponding pinhole. Thr groove betwrsen thcx nlajor and minor diameters X\.IK 199 microns deep. The pitch or distance bc>t\vchcn 11~ thrrads was 192 nlicrons. ‘1’1~. end to be inserted was slightly narrow~cr than thfh Irlinor diameter and presented a mean dimension of 406 microns (Fiq. 5 ‘1. The ends of both Self-threading pins tapcrrtl but not t~nouqh to Inrm a (‘o~w (Fig. 5). Aduptation of the pin to the pinhole. it is inconct:i\,able that a pin, cut rnort* ot less at right angles to the long axis. would fit into the conical fundus (of a pinholt~. The difference in morphology between the pin and pinhole would cause :L failure of adaptation at the fundus of the pinhole. However, no pin, regardless of the type. penetrated the pinhole for the entire extent of the tubular portion. Friction-lock pins, forced to place with 25 pounds of pressure, never rpachrtf the pulpal line angle. There was always a space in the tubular portion of the pinhole. The mean distance between the inserted pin and apex of the conical pulpal wall was 1.06 mm. The shortest distance \I as 0.1- I~IIII. and the longest !\;a~ 1.9 m1n. (Fig. 6). The spiral groove, which was approximately 34 microns deep, created voids which averaged 23 microns in depth (Fig. 7 . A similar result occurred with the Self-threading pins. None of these penetrated

Adaptation

of noncemented

pins

635

Fig. 6. Section of a Friction-lock pin (P) forced into a pinhole under 25 pounds of pressure. The pin failed to penetrate the full length of the pinhole. Remaining space (S). (Original magnification x2 1,) Fig. 7. Section of a Friction-lock pin (P) in a pinhole in dentin (D). The arrow caused by groove. Note the voids in Fig. 6. (Original magnification x60.)

points to void

to the conical fundus of the pinhole. The Regular pin left a mean space of 1.3 mm. The shortest distance was 0.8 mm. In this specimen, the tapered end of the pin penetrated 11 microns into the cone. This was a singular occurrence. The longest distance was 1.8 mm. (Fig. 8). Th e voids, caused by the narrow minor diameter, which was 89 of microns less than the diameter of the pinhole, averaged 39 microns in depth (Fig. 9). The outer edge of the threads engaged the dentin to a depth of 26 microns. The Minim Self-threading pin also failed to reach the conical base of the pinhole. The mean space from the pin to the apex of the pinhole was 0.5 mm. The minimal space was 0.26 mm. and the maximum was 0.74 mm. (Fig. 10). The voids, created by the narrow minor diameter of the pin, averaged 24 microns (Fig. 11). The outer edge of the thread engaged the dentin to a depth of 23 microns. Failure of insertion. The failure of the pins to seat in the pinhole at least to the base of the cone led to an hypothesis worthy of testing. It seemed that the pinhole

Fis. Hattl

rht ninu

spacl

Fia.

it

IfI

\-aid:

contained either air or fluid which precluded seatirlg the pin. Also, if the pin o('cupied the entire tub&t, portion of the pinhole. ;I conical end of th(* pin worrld solve the remaining problcnl. ObviousI>-, fluid could riot be mrnpreswcl iu thr pinhole nor cxx~lcl it esc~lw through the tubules into the pulp. Air lends itself to compression but cannot be cornpressed to nothingness. In my rwntJ the S~IIIC lmt bvould serve to detmuine if the entrance of the pin were bioclwd by tither xir or fluid. ‘1%~ test Jvas conducted on 5 specinwns each of Friction-lock and Regular ScxIftllrmding pins. Routine pinholc~s were nladr in estrackd teeth. An additional pinhole \\YIS made at right angles to tlw origirlal pinhole to n~ake a vent at the apex of tll~ fundus. ‘I‘l~e accessory pinholes pcrnlittced either ;tir or fluid, present in the pinholes. to escape. ‘I’he pins were tlwn inserted under the sanw conditions as other parts of rhis study (Figs. 12 and 13 1.

Volume

2fi

Numhrr

6

Adaptation

of noncemented

pins

637

Fig. 10. Section of a Minim Self-threading pin forced into a pinhole until the flattened head separated. The pin failed to penetrate the length of the pinhole. Remaining space (S). (Original magnification X2 1.) Fig. 11. Section of a Minim Self-threading pin (P) in a pinhole in dentin (D). Arrows point to voids caused by the minor diameter. Note the voids in Fig. 10. (Original magnification x60.)

The pins went to place without difficulty. They occupied the entire tubular portion of the pinhole. Since the conical portion was obliterated by the vent, no observation could be made of this area. Nevertheless, this part of the study confirmed the hypothesis that insertion of the pin was blocked by either air or fluid in the long, narrow pinhole. DISCUSSION The measurements reported in this study were made in microns because no similar equipment was available in thousandths of an inch. To acquaint the reader with comparable sizes, a micron equals 0.00003937 of an inch. Tested against each other, the manual and optical devices were fairly accurate. There were slight discrepancies, but the most meaningful evidence of voids was confirmed by photography (Figs. 6 to 11). If the measurements were in error, the photographs were not. To

638

Perez R., Schoeneck

A., and Yanalzara

J, Prosthet. December,

M.

Fig. 12. Pinhole with vent i I’) accepted a Friction-lock at the apex was removed while creating the vent.

pin (P) to the fundus. ‘l’hr hollow

Fig. 13. Pinhole hollow

with vent (L’) accepted a Regular Self-threading cone at the apex was removed while creating the \,ent.

pin (‘Pj to the lundus.

Dent. 197 I

cnne The

section pinholes at right angles is impossible. An oblique section results in a distorted measurement. The data were not intended to produce absolutes but rather 10 establish differences. The margins of error were undoubtedly small. The measurcments were made with great care; we make no claim to perfection. The twist drills prepared cavities which surpassed any made with burs. Examination of the cavities made with twist drills and burs confirmed the acruracy of the twist drill. The diameters of the pinholes were but 5 to 17 microns larger than the twist drill. Similarly, the twist drill produced a near perfect hollow cone about 5 microns

above

ment produced of the pins.

the dimension

distortions,

of the bibeveled

the exaggerated

tip. However,

diameters

if eccentricities

in equip-

did not exceed the diameters

Volume 26 Number G

Adaptation

of noncemented

pins

639

One cannot reconcile the shape of the pinhole with the shape of the pin. Apparently, Self-threading pins were cut so that the minor diameter would enter the conical apex. The Friction-lock pin just appeared to be cut. None of the pins showed any effort toward design. The major diameter of the pin was always larger than the pinhole. Obviously, the elasticity of dentin played a role in accommodating the pin. In no instance did the pin impinge on the wall of the pinhole even when cut obliquely (Fig. 6). However, the elasticity of dentin lacked the resilience to recoil and thus fill the grooves. Adaptation of a restoration to the cavity walls and minimal marginal leakage are major principles of operative dentistry. lM5 Those restorations, which have survived, have also demonstrated better adaptation and less microleakage than the restorations which have been discarded. No restorations ever showed the gross voids seen in pin therapy. The advent of an anchor bolt system of retention has conserved many teeth. This report does not wish to relegate pin retention to obscurity. The purpose of the report is to illuminate the problem of lack of adaptation and call for a solution. CONCLUSIONS The form of noncemented pins does not conform to the shape of the pinhole. The minor diameter of noncemented pins is less than the diameter of the pinholes. The accumulation of air or fluid in the pinhole prevents seating the pin to the pulpal line angle. The authors wish to thank Dr. William Lefkowitz, of the Faculdad de Odontologia, University of Guadalajara, for directing this study. We also wish to thank the Unitek Co. for providing some of the materials.

References 1. McGehee, W. H. O., True, H. A., and Inskipp, E. F.: A Textbook of Operative Dentistry, ed. 4, New York, 1956, Blakiston Division McGraw Hill Book Company, Inc., p. 303. 2. Phillips, R. W., and Ryge, G.: Adhesive Restorative Dental Materials, Spencer, Ind., 1961, Owen Litho Service, p. 56. 3. Gilmore, H. W.: Textbook of Operative Dentistry, St. Louis, 1967, The C. V. Mosby Company, pp. 153-155. 4. Bell, B. H., and Grainger, D. A.: Basic Operative Dentistry Procedures, Philadelphia, 1971, Lea & Febiger, Publishers, p. 2 17. 5. Moffa, J. P., Razano, M. R., and Folio, J.: Influence of Cavity Varnish on Microleakage and Retention of Various Pin-retaining Devices, J. PROSTHET. DENT. 20: 541-551, 1968. FACULDAD DE ODONTOLOGIA UNIVERSIDAD DE GUADALAJARA CENTRO MEDICO GUADALAJARA, JALISCO, MEXICO