Successfully restoring a heavily broken tooth with Amalgam depends upon a specific
preparation design for the tooth; considering the remaining tooth structure, anatomy,
occlusion and the required resistance and retentive form, adequate to keep the future restored
amalgam mechanically in place.
We can categorise the methods we employ by “pin” and “non pin” retention and resistance
features, and the “Bonded” amalgam.
Pins
Silver, Gold, Steel and Titanium and used in their production.
Self threading pin is most commonly used and most retentive. The cemented pin is the least
retentive.(6)
Cemented – pin is 0,002’ smaller than the channel
Friction-locked – pin is 0.001’ larger than the channel
Self-threading (TMS) – pin is 0.001-0.004’ larger than the channel
Avoiding furcations/depressions on roots, pins are placed in area of greatest bulk of dentin,
0.5-1.0mm from dentinoenamel junction (dej) to prevent crazing and halfway between pulp
and external surface of root, if gingival margin is in cementum.
Tips of pins should be covered with at least 2mm of amalgam. Pins should clear matrix brand
laterally, and be is surrounded by 0.5mm-1.0mm of dentin. (Larger pins or non-vital teeth
require 1.0mm)
Friction-locked and self-threading pins retention is lessened when the pin exceeds 2.0 mm
into dentine and 4mm for cemented pins. (18)
Pins provide retention and a conservative technique but do not offer any mechanical
advantage over other “non pin” methods (1)(5)(7) and may craze dentine (3), fracture enamel or
create pulp or periodontal membrane perforation (2). This subsequently leads to microleakage.
Since pins are metal, they conduct heat and transmit thermal changes close to the pulp (4).
Photo. Crazing A, and pin not engaging channel fully B (35)
Voids around pins due to inadequate condensation or weakness in amalgam, can occur. As
amalgam is placed too thin over the pin, it fractures in thin section.
Other risks include pins not fitting, or breaking while bending.
Failure of pins occur in 5 areas (14)
1. Fracture within dentine
2. At pin-dentine interface (pin pulls out)
3. Pin fracture
4. At pin-amalgam interface (pin pulls out of
restorative material)
5. Fracture within amalgam.
Non-Pin Resistance & Retention Features
Generally non-pin resistance & retention in teeth come in the way of parallelism in all walls
of preparation, proximal box forms, retention grooves in proximal line angles, box form in
buccal & lingual groove areas of molars, dovetails. However there are 3 main methods used.
Dentine slots, amalgapins, and peripheral shelves.
They all have similar benefits of increased retention and resistance, but with less chance of
causing damage to the tooth than pins. They require tooth loss in preparation and are varied
in their amount of retention and resistance.
Slots
Slots are retentive grooves in dentine whose length is in a horizontal plane. Length depends
on the extent of tooth preparation. Slots are usually placed on facial/lingual/mesial/distal
aspects of preparation. Slots are continuous or segmented and 0.5mm axial of DEJ.
33 ½ bur
Depth of usually 0.5-1.0 mm
2.0 – 4.0 mm long.
Resistance from slots is comparable to 4 pins, but is more sensitive to displacement during
matrix removal(8).
Slot failure causes the whole restoration to fail, while pin failure usually leads to a fracture in
the amalgam, first which is hard to detect and then over time catastrophic full failure. (8)
Slots tend to not have the same detrimental effect on the pulp as pins(4) and less likely to
cause dentine fractures. They are effective in short clinical crowns (12).
Amalgapins
Placement location is similar to conventional pins. Resistance has been noted equal or greater
than in pins (9). In other studies amalgapins have performed less well in comparison to dentine
slots and amalgam bonding techniques. (10)(11)(12)
Depth 1.5-2.0 mm (19)(20)
Diameter 0.8 mm
Place with 330 bur (0.8mm dia.)
Peripheral Shelves
Common use is segmental than circumferential.
Preparation is 2.0 mm wide
1.0 mm height (13)
This technique provides resistance and retention, but not comparable to pins, amalgapins and
slots (15)(16) (17).
Bonded Amalgam Restorations
Bonding to amalgam has been mentioned for some time with the Baldwin Technique (36),
resin adhesives are now able to bond tooth to amalgam.
Some amalgam bonding agents:
Imperva Dual
superbond c&b
Panavia
All Bond 2
Bond Plus
Amalgam
They contain active ingredients such as 4 META, HEMA, MDP.
Different types of bonds have different bond strengths (27)(29).Filled resin bonding agents
provided stronger bonds than unfilled (33).
Studies show when properly placed these agents can enhance bond strength (30) so retention
and resistance form can be reduced (22)(25), or show no difference in
performance(24)(26).Bonding has shown to inhibit marginal caries(23), decrease microleakage
and sensitivity(28)(31). However, mechanical retention should be provided where possible with
the addition of bonding.(32)(34).
The disadvantage of resin adhesives is they require a multi-stage technique (etch, prime and
bond). Time and effort ensuring no contamination, such as moisture, will destroy the bond is
needed.
Whichever method is chosen, a good sturdy matrixband should be placed with good contour
and contacts. Wedges are recommended for good gingival adaptation and emergence. Then
the amalgam should be placed and condensed with small tools at first to prevent voids, while
larger tools can be utilised while condensing more occlusally. Over pack amalgam, burnish
and remove excess. Initially carve the anatomy with matrix band in place for 5 minutes.
Remove matrix band with wedges and finish carving. Smooth with cotton wool/burnisher.
References
1 JB Summit Op Dent 2004
2 Pickards manual operative dentistry 7th edition
3 Segović S J Prosthet Dent. 2002 Changes in dentin after insertion of self-threading titanium
pins with 3 methods: a scanning electron microscope pilot study
4 D A Felton The Journal of prosthetic dentistry. 01/12/1991Pulpal response to threaded pin
and retentive slot techniques: a pilot investigation
5 T A Garman Journal of the American Dental Association (1939). A clinical comparison of
dentinal slot retention with metallic pin retention
6 S I Vitsentzos The Journal of prosthetic dentistry. 01/11/1988 Study of the retention of
pins
7 Randall L. Vaught J Dent Educ. 71(10): 1356-1362 2007 Mechanical Versus Chemical
Retention for Restoring Complex Restorations: What Is the Evidence?
8 W C Outwaite fixed prosthodontics operative dentistry. Pin vs Slot retention in extensive
amalgam restorations
9 T A Imbery Retention of complex amalgam restorations using self-threading pins,
amalgapins, and Amalgambond American journal of dentistry
10 Axial compressive strength of amalgam fillings in correlation with cavity
preparationAuthors: S Mangklabruks, D Heidemann
11 A clinical evaluation of dentinal slot, amalgapin & T.M.S. retention in amalgam
restorations Authors: S Tewari, C P Govila, Y N Paharia
12 Retention and resistance features for complex amalgam restorations Authors: J W
Robbins, J O Burgess, J B Summitt
13 Fracture resistance of complex amalgam restorations with peripheral shelves used as
resistance features Authors: S E Reagan, S E Gray, T J Hilton
14 J P Moffa Pins- Comparison of their retentive properties. J Of American Dent Assoc 1969
15 Summitt JB Comparison of resistance features for complex amalgam restorations Am J
Dent. 1991 Dec;
16 Kane JJ Modification of the resistance form of amalgam coronal-radicular restorations J
Prosthet Dent. 1991 Apr
17 Compressive shear strength of core materials and restoring techniques Sahmali SM Int J
Periodontics Restorative Dent. 2000 Jun
18 Moffa JP Pins-A comparison of their properties J Am Dent Assoc 1969
19 A review of the amalgapin technique for complex amalgam restorations Authors: J J
Eberting General dentistry. 48
20 A second look at the Amalgapin technique Authors: C D Leach, J T Martinoff, C V Lee
CDA journal California Dental Association. 05/1983
21 The amalgapin technique for complex amalgam restorations. H M Shavell
22 The development of resin-bonding for amalgam restorations Authors: J C Setcos British
dental journal. 01/05/1999
23 Inhibition in vitro of caries around amalgam restorations by bonding amalgam to tooth
structure Authors: Y Torii, M Staninec Operative dentistry. 01/02/19
24 JB Summit 6 yr Clinical evaluation of bonded and pin retained complex amalgam
restorations. Operative Dentistry 2004
25 Effect of bonding amalgam on the reinforcement of teeth Authors: Ammar A Journal of
prosthetic dentistry. 01/02/2005
26 Longevity of conventional and bonded (sealed) amalgam restorations in a private general
dental practice. Bonsor SJ BDJ 2009 January
27 In vitro comparison of filled and unfilled universal bonding agents of amalgam to dentin
A Bagley Operative dentistry. 19
28 The Journal of the Dental Faculty of Ankara University. 01/06/1989 Experimental use of
dentin bonding agents and a cavity varnish to reduce marginal microleakage in high copper
amalgam restorationsAuthors: S Aras
29 Bonding of amalgam to dentine: microleakage and shear bond strength evaluation
Authors: P J van der Vyver, The Journal of the Dental Association of South Africa
30 The performance of bonded vs. pin-retained complex amalgam restorations: a five-year
clinical evaluation. J Am Dent Assoc. 2001 Dec Summitt JB,
31 Estafan, Gen Dent, March-April 2000
32 "...amalgam bonding is an adjunct to and not a substitute for mechanical
retentive form. The main advantage of conventional amalgam adhesives seems
to be their ability to seal the tooth restorative interface, preventing
microleakage into the dental tubules and pulp and reducing post-operative
sensitivity." Cobb, et al, Am J Dent, Oct 1999
33 In vitro comparison of filled and unfilled universal bonding agents of amalgam to dentin.
Oper Dent. 1994 May-Jun Bagley A
34 Until clinical research data are available to support the efficacy of bonding as the sole
provider of resistance and retention, bonding agents should be used only in conjunction with
proven mechanical forms of resistance and retention." (Swartz, Summitt & Robbins,
Fundamentals of Operative Dentistry1996)
35 British Dental Journal 11 May 2002 Crowns and other extra-coronal restorations: Cores
for teeth with vital pulps R W Wassell1
36 Baldwin H. Cement and amalgam fillings. Br J Dent Sci. 1897; vol. XL
Cement bonding (Baldwin technique)
The Baldwin technique uses amalgam to be condensed on a thin layer of unset cement (eg
zinc phosphate). It is not advocated as the cement could extrude out from the margins and
lead to breakdown. Also unset cement could cause displacement in amalgam when being
condensed.
GIC is now being used as bonding dentine and amalgam but until more trials and studies are
produced we cannot rely on this method in restoring heavily broken down teeth.
37 G C van Beek Dental Morphology 2nd Edition