Using a matrix during restorative work contributes to case outcomes in multiple ways. We examine how matrices help with restorative work, why they increase success, what makes a system helpful, and what options are available for different cases.
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How a Dental Matrix System Can Help with Restorative Dentistry
Jason Goodchild, DMD, Vice President of Clinical Affairs at Premier Dental Products Company, says the most common direct posterior restoration is Class II per the American Dental Association (ADA). And that proper restoration of interproximal areas via an efficient matrix system is critical to restorative success.
Along with the proper materials and techniques, understanding the mouth’s form and function is essential to avoid poor outcomes for restorative cases. The matrix system helps shape and contour dental restorations by maintaining their form during placement and setting.1
A flexible band that wraps around a natural tooth, the dental matrix conforms to the tooth's surface, recreating the natural curves and walls possibly missing in the interproximal area. This band holds the restorative dental material in place, ensuring the completed restoration takes the right shape and fits well between adjacent teeth.2 Matrices also allow clinicians to create a non-retentive surface finish for plaque or food debris, reducing the chances of secondary caries. Additionally, using a dental matrix for your restorative work increases the longevity of composite restorations and protects the adjacent teeth during cavitary prep.2
Before everyone was using composite for these restorative procedures, clinicians used amalgam. The Tofflemire-type systems worked well with that material, Dr Goodchild explains. However, dentists needed a new solution since the migration to dental composite materials, which clinicians cannot pack into the system the same way they could when using amalgam. Hence, the sectional matrix systems came into play around 20 years ago.
“Those sectional matrices had 3 pieces: a ring, a matrix, and a wedge. The wedge is supposed to push the matrix against the tooth, but the ring is designed to separate the tooth to account for the thickness of the matrix and to help achieve proper contact,” Dr Goodchild says. “The matrices are usually pretty contoured, designed primarily for composite.”
Why Does Proper Recreation of the Interproximal Area Matter?
Restoring the interproximal area is critical. The contact area, the interproximal niche, and the triangular-shaped interdental papilla are crucial in protecting the gums. However, having proper contact between teeth also contributes to the stability of the dental arches by providing combined support.2
Proper interproximal contact also avoids future oral health problems. Improper contact or having open spaces between teeth can cause misalignment in the arch. It also contributes to oral health issues like food getting stuck in gaps, bad breath, cavities, and gum disease.3
What Characteristics Make a Dental Matrix Helpful?
A few qualities of a dental matrix system can help improve your treatment workflow. Per DentalTix, a dental supplies distributor in Spain, there are a few characteristics of a helpful dental matrix2:
The Types of Matrices
DentalTix also explains that dental matrix systems have different types. Some differ in material, with metal options like steel or titanium and plastic choices such as acetate or celluloid, which may be less durable but permit the passage of photopolymerization light. Also, some matrices are universal and standardized, like Tofflemire-type matrices, while others are custom-made by dentists for specific cases. Additionally, some matrices have fixed shapes due to their elastic memory, while others, like laminated matrices, can be modified to enhance contour and contact points. Finally, adaptation systems differ, meaning some matrices remain stable without a holder, while others require one for proper adaptation.2
Two types of dental matrix systems are circumferential and sectional:
Circumferential matrices are already shaped in 3 dimensions and, when combined with wedges and separators, create tight contacts between teeth. They are comfortable and provide good visibility for quick work on a section of teeth.
Sectional matrices are shaped like natural teeth, and have a long lifespan. Dentists use sectional matrices when they want to achieve the best tooth shape and function and save as much of the natural tooth structure as possible.3
A British Dental Journal study suggests sectional matrices can be challenging. First, they require specific techniques, which could lead inexperienced clinicians to use circumferential matrices even if sectional matrices might lead to better clinical outcomes. Second, sectional matrices have numerous options. For dentists with limited experience in this area, choosing the optimal sectional matrix system can feel overwhelming. Additionally, sectional matrix techniques with separating rings establish predictable contact areas but could lead to a concavity in the restored surface there. This concavity is hard to clean, allowing the buildup of biofilm that could go unnoticed clinically, leading to caries on the neighboring surface of an untreated tooth.4
That same study says that circumferential matrices have some drawbacks, too. Recreating a natural emergence is challenging, making achieving a proper contact area difficult. Also, contact might exist as a single point rather than a broad area and in a non-natural position. This situation results in a ridge more prone to fracture and a flatter emergence form that can catch and shred floss, leading to patient complaints. Combining a higher or non-existent contact point and a flatter, non-natural cervical emergence increases the chances of incomplete papilla infill, creating spaces below the contact point where food can get stuck. Additionally, the design of the circumferential matrix holder can also limit access for wedge placement, impacting their effectiveness.4
A study looked at the performance of each of these types with respect to pediatric patients. The researchers determined that the circumferential matrices were more time-efficient, but the sectional matrices produced more restorations with ideal contacts. Overall, the preference favored the circumferential matrix band system for its efficiency, except when clinicians were aiming for ideal contacts in pediatric cases.3
A paper suggests the specific matrix system significantly influenced tooth anatomy and treatment success. The paper also looked at the evidence for the advantages and disadvantages of the various dental matrix types, which include the following5:
Thin, Sectional Matrices:
Pros:
Provide tight interproximal contacts.
Show fewer problems with marginal overhangs.
Cons:
May result in concave contours.
Less effective in avoiding overhangs.
Circumferential Bands (Tofflemire-type):
Pros:
Produce flat contours.
Decrease the occurrence of marginal overhangs.
Cons:
COTISEN supply professional and honest service.
Interproximal contacts may not be as tight.
Traditional bands may have more problems with fitting.5
Dr Goodchild says that like most dental materials and systems, clinician develop a feel for a given system and tend to stick to it. Some of the common Matrix Systems that clinicians choose are the Garrison’s Strata-G,Palodent Plus, Premier X5 Sectional Matrix System, andUltradent’s Halo Sectional Matrix System. Each have their distinguishing characteristics that may appeal to a clinician.
For example, the Premier X5 Sectional Matrix System comes with 10 Universal Matrix Rings made of their proprietary resin. This feature makes it possible to have more rings in the practice without being concerned about accidentally throwing one away. By contrast, the rings in other systems can be expensive to replace.
“We came up with this idea of having a resin that will hold its shape and create the separating force, but it's less than $4 per ring. So, you can buy a bag of 30 rings and have enough rings around the office. Or they could be used in a school where they can become disposable after single-patient use,” Dr Goodchild explains. “It’s just a different approach, and all of it will work. Do you like to have 1 ring that you protect with your life and don't throw that thing away, or do you have 30 rings lying around that you can throw away and pick up a brand new one each time?”
So, When Do You Use Either Type?
Brett Richins, DMD, Clinical Advisor for Ultradent Products, Inc., writes on the Ultradent Blog that his preferred choice for regular Class II restorations with well-aligned adjacent teeth and no major damage is a sectional matrix system.6 Sectional matrix systems offer a fast and reliable way to achieve good results. However, having circumferential bands as part of the tools is crucial. In specific situations, like when there's no adjacent tooth or restoring the buccal or lingual surface, Dr Richins prefers circumferential bands. In the past, when he was focused solely on sectional bands, he would sometimes try to rebuild these teeth without any matrix system. Now, he realizes that circumferential bands help him quickly and easily place a restoration in the intended area, avoiding frustrating situations.6
In Dr Richins's Salt Lake City practice, circumferential bands prove helpful when dealing with patients who have missing cusps, a situation where sectional matrices may result in under-contoured restorations due to insufficient tooth structure support. Additionally, circumferential bands are particularly advantageous in pediatric cases, where placing sectional bands on primary teeth can be challenging, and achieving critical contours is less straightforward. For restoring MOD in primary teeth, circumferential bands are often more stable and efficient in Dr Richins' approach.6
Dr Goodchild says that many clinicians have likely adopted a sectional matrix system. However, sectional matrices require more technique to place than a Tofflemire-type, and the case's complexity (e.g., the morphology or existence of misalignment makes it difficult to seat the ring) can steepen the technique’s difficulty. Likewise, multiple restorations in a quadrant increases the technical difficulty of using a sectional matrix. Dr Goodchild says he might use a Tofflemire-type, or both systems in some of those more complicated cases.
“When I have a Class II on my schedule, I plan to use a sectional, but sometimes it doesn't work, or I can't get it seated. So, I still need a Tofflemire-type matrix system in my office,” Dr Goodchild says. “There is always the right tool for the right job.”
Posterior composite restorations generally perform less well than amalgam restorations,1,2 especially in primary care.3 Clinicians are much less confident in placing posterior composite restorations, especially in difficult situations due to their increased technique sensitivity.4 Techniques classically taught at undergraduate level to rebuild the lost interproximal portion of a tooth involve the use of a circumferential matrix band with a matrix holder (for example, Toffelmire and Siqveland) and a wooden wedge.5 This is by far the most commonly used technique in UK primary care for the placement of both amalgam and composite restorations.6 Amalgam is actively placed, in that it must be firmly packed and compacted into the cavity to form the restoration. This packing, alongside the firm placement of a wooden wedge,7 puts pressure on a pre-burnished matrix, which favours the formation of a contact point (or more accurately, contact area). Creating a contact area between the restored tooth and adjacent tooth is important to prevent food impaction in the area, often being uncomfortable for patients and a common cause for complaint.6,8 It can also potentially increase the risk of further caries and periodontal disease, though evidence commonly cited to support this contention is cross-sectional and therefore not robust.9,10
Composite on the other hand is passively placed, in that there is limited force imparted and maintained during placement before curing (most commonly) with a light. It also shrinks when undergoing polymerisation.11 This explains the tendency of composites to perform less well than amalgam in terms of contact point creation and prevention of food impaction,6,7 even with so-called 'packable composites'.11 The consistency of the composite material can have an effect on contact point formation, however, with paste-like formulations performing better than flowable formulations.12 When restoring proximal cavities where only one surface is lost, the circumferential matrix band also has to pass through the intact contact point at the other side of the tooth, which will result in tooth displacement, further reducing the chances of achieving a contact area between the resulting restoration and adjacent tooth.13
Sectional, pre-contoured (more anatomically shaped) matrices were developed to overcome these problems. They are classically used in combination with a separating ring, which provides separation of the teeth and stabilises the matrix coronally, favouring the formation of a contact area.13,14,15 Circumferential matrices are tightened around the tooth and are therefore described as being placed actively. This active placement does potentially confer an advantage over sectional matrices, which are passively placed (not tightened), in that it stabilises the matrix, both cervically and coronally, resulting in reduced formation of overhangs, especially bucco-palatally.16 This is also very useful for teeth which are heavily broken down.11 Circumferential matrices have many relative disadvantages however, in that it is very difficult to recreate an anatomical emergence12,15 which makes achieving a contact area difficult.14,17 They also result in an inferior morphological contact with reduced contact tightness.15,17 Even if a contact is achieved, it is more akin to a single point of contact rather than a broad area and is positioned in a non-anatomical, more coronal position.18 This then often results in a laterally positioned, unsupported marginal ridge form which is more susceptible to fracture19 and a flatter emergence form from the embrasure with the potential to catch and shred floss, resulting in a patient complaint. The combination of a higher or non-existent contact point and a flatter, non-anatomical cervical emergence lead to an increased chance of incomplete papilla infill.20 This leads to dead space (seen as black triangles) below the contact point which can predispose to food impaction, as evidenced by the increased reported food packing when using circumferential compared with sectional matrices for posterior composites in primary care (Fig. 1).6 The matrix holder also often limits access for wedge placement, which can have an impact on their efficacy (see later).
Recent research suggests that the use of sectional matrices for placing posterior composites where an interproximal surface has been lost is low in the UK,6 despite the advantages previously described and their use being referred to as a gold standard of care.5 There is a fairly steep learning curve involved in using sectional matrices however, and they are quite technique-sensitive to place, such that inexperienced operators preferred to use circumferential matrices even when obtaining better clinical outcomes.14 Sectional matrices are available in different material constructions, opacities, heights, widths, rigidities and emergence profiles (Fig. 2), with a bewildering array of associated equipment, which can make selection difficult for any dentist with limited experience in this area.
While sectional matrix techniques using separating rings can result in the predictable establishment of contact areas,13,14,15 they have been shown to result in surface concavity in the restoration at the contact area, which is much less of a problem with circumferential matrices.21 A concavity in the restored surface at the contact area will be inaccessible to cleaning and tend to harbour biofilm and is often not identifiable clinically21 (Fig. 3). Given that composite materials favour growth of a cariogenic biofilm on their surface,22 this could potentially result in the initiation and progression of caries in the proximal surface of an unrestored adjacent tooth.
This paper will explore why this, along with the increased propensity for overhangs occurs and potential solutions to these problems.
The aim of a sectional matrix is to produce a cleansable, anatomical restoration with a smooth convex surface, which is continuous with the remaining tooth structure and has a contact area at the level of the maximum convexity of the intact adjacent tooth.
This is achieved by fulfilling the objectives related to sectional matrices summarised in Table 1. These will be explained in turn, before discussing matrix distortion, its possible sequelae and how available materials and techniques can influence this.
There are a wide variety of sectional matrices available (Fig. 2) and selection of the most appropriate one can influence the resulting marginal overhang, with flexible types performing better than malleable, soft types.16 Matrix choice will primarily be governed by the shape of the tooth, the shape and depth of the cavity and its proximity to the adjacent tooth (Fig. 2). A matrix should be selected such that it extends beyond the extent of the cavity and can be engaged and stabilised. The maximum convexity of the matrix should be positioned against and in contact with the maximum convexity of the intact adjacent tooth to create an appropriate contact area (Fig. 4). The matrix should be able to be placed passively, unimpeded by contact with the adjacent tooth.
The mesio-distal matrix curvature and curvature occlusal to the contact area will also affect the marginal adaptation and therefore potential ledge formation in the resulting restoration, which will impact on the need for finishing of the restoration (Fig. 4). Matrices may need to be modified; for example, by trimming them cervically, to optimise adaptation.
The matrix has to be stabilised and sealed at the base of the cavity. These elements optimise the adhesive bonding process and prevent ledge formation in the resultant restoration. Once formed, ledges in this area can be difficult to remove. If left, ledges can be difficult to clean, resulting in biofilm accumulation, potentially resulting in secondary caries and periodontal disease.23 Composite resin and resin adhesives have been shown to support and favour the development of a cariogenic biofilm on their surfaces,22,24 which could exacerbate the potential for secondary caries in ledged composite restorations.
Wedges are most commonly used for cervical stabilisation of a matrix, though mechanical separators (for example, Elliott) or the 'Teflon-floss' technique may be used as alternatives (Fig. 5).17,25 Insertion of the wedge from the buccal or palatal can have varying effects on the cervical stability and seal achieved (Fig. 5). Plastic wedges are available in multiple designs, though the majority are contoured and flexible with the aim of engaging around the interproximal curvature (Fig. 5) in an attempt to seal the whole base of the cavity. They also generally have concavities on their undersides, which allow them to sit over the papilla with a low profile26 and facilitates their insertion from each side of a cavity to further obtain a better cervical seal (Fig. 5). Polytetrafluoroethylene (PTFE) tape can also be applied in conjunction with a wedge to stabilise and seal any open area at the base of a cavity (Fig. 5). The Teflon-floss technique involves winding PTFE tape around two pieces of knotted floss and simultaneously drawing them in from both sides of the matrix, adapting the matrix to the base of the cavity25 (Fig. 5). This is purported to result in a reduced tendency to break the dental dam seal than when using wedges, which can pick up and drag the dam, opening up gaps. The Elliott Separator is suggested to have a similar advantage, but can be difficult to position and stabilise. Likewise, there is reduced control over the positioning of the Teflon-floss due to its lack of rigidity, which could potentially move the matrix and it may therefore be better used after a separating ring has been placed,25 which can result in its own issues (discussed later).
Following this process, the matrix should be in contact with the adjacent tooth. If it isn't, a different matrix should be selected with more cervico-occlusal curvature (Fig. 4).
When placing an interproximal composite with the aim of creating an interproximal contact between the restored and adjacent teeth, the thickness of the matrix is critical to consider. The matrix is removed after placement of the restoration and would therefore result in a gap between the restored tooth and the adjacent tooth, if these teeth aren't separated before placement of the restoration. The teeth can be transitorily moved apart by virtue of the compressibility of their periodontal ligaments before placement, thus allowing the formation of a contact when the matrix is removed.7 This can be achieved by using wooden wedges, separating rings, or Elliott Separators,7,13,17 though whether this is the case for the different designs of plastic wedges or the Teflon-floss technique is currently uncertain. Wooden wedges can predictably provide lasting separation of 50 microns,7 which is sufficient to accommodate most metal matrices available, but some clear matrices are 75 microns thick, therefore separation with a wooden wedge alone would not be recommended.
The matrix has to be stabilised coronally. Lack of coronal stabilisation can lead to distortion of the matrix during composite placement.21 Coronal stabilisation is also important to minimise ledge formation, though this is also affected by the adaptation of the matrix. Coronally located overhangs are much more accessible for finishing than those at the base of the cavity when the cavity is appropriately designed (see later), so they aren't as critical to avoid. Coronal stabilisation can be active, where a force is applied to the matrix using a separating ring, or passive, where the stabilisation is provided without an applied force, through the use of unbonded flowable composite. More rigid matrices have a tendency to self-stabilise to a degree, whereas more flexible ones do not.
When a force is applied to a sectional matrix, distortions can occur. They can arise during placement, separation and (cervical and coronal) stabilisation of the matrix and when placing the restorative material.
Sectional matrix distortions can occur peripherally and/or centrally, with different potential sequelae. Peripheral gaps or distortions commonly result in ledged restorations, or failure to seal the base of the cavity, whereas central distortions often lead to concavities at the contact area (Fig. 3). Distortions can also result in the loss of a contact.
A cavity design where the proximal contacts are cleared both cervically and bucco-palatally is critical to facilitate passive matrix placement (Fig. 3). This helps to avoid distortion of the matrix during placement (Fig. 6). It also has the added benefits of placing the tooth-restoration interface away from a contact area, allowing access to the margin for optimal finishing of the restoration and subsequent cleaning of the restored tooth, thereby potentially reducing the risk of future caries development. Distortion can also occur around the critical contact area during placement of the matrix, as this is the most bulbous part of the pre-contoured matrix and therefore the part most likely to be distorted by contact with the adjacent tooth during placement (Fig. 7). Distortion of metal matrices during placement is more likely to be permanent than with clear matrices. More curved matrices are also more susceptible to this distortion. This results in an altered matrix shape. Clear matrix distortions are more able to be resolved once positioned, due to their increased elasticity (Fig. 7).
As the sectional matrix is passively placed and often not stabilised before placing the wedge, it can have a tendency to move. This potentially results in distortion of the matrix peripherally and/or centrally, or moving the matrix to an incorrect position. Stabilising the matrix from the occlusal with a finger or thumb while placing the wedge can generally overcome this tendency.
It is important to ensure that the wedge is inserted below and subsequently lies below the base of the cavity.26 Fulfilling these objectives help to obtain a seal and prevent both peripheral and central matrix distortion. Appropriate management of the papillae to achieve this is important where the cavity margin lies sub-gingivally.26 Wooden wedges may require modification to prevent their protrusion coronally above the base of the cavity (Fig. 8). This process can be performed with a bur and has previously been pictorially demonstrated.26 When inadequately performed, the wedge can impinge on the matrix, which in turn can prevent the recreation of an anatomical emergence and subsequent formation of a contact area in the resulting restoration (Fig. 8). The Teflon-floss technique is also prone to this distortion because of its own propensity to distort, which offers an advantage in adapting the matrix to the base of the cavity, but a lack of control over positioning (Fig. 5e). Ideally, the wedge would engage the tooth at the level of the cavity margin, preventing the potential for gaps to open up when subsequently applying forces to the matrix, but this is unrealistic and other solutions should be sought to minimise peripheral stabilisation distortion (see later). Wedges are therefore ideally tried in to check their adherence to the achievable goals before insertion of the matrix.
Active coronal stabilisation and separation with a separating ring can result in loss of a contact (Fig. 9) and/or peripheral and/or central distortion, which depends on the type of ring and placement technique, though the rings assessed in these studies are mostly outdated (Fig. 9).16,21,27 This potential exists with all designs of ring, in the author's experience (Fig. 10). The rings often create persistently tighter contacts than those occurring naturally, quite likely due to this distortion, suggesting the separation obtained is more than required.13,28 The peripheral and central distortion often results from a tendency of rings to tent the matrix, opening up gaps peripherally and forcing the contacting area against the adjacent tooth causing it to dimple in (Figures 9 and 10). Ultimately, different rings affect different matrices in different situations in different ways (Fig. 10), but then even the same ring, with the same matrix in the same situation, will result in different distortions even when placed by the same operator (Fig. 11). Therefore the technique, though it can be effective, has a level of unpredictability. These issues have led to the exploration of other methods to coronally stabilise sectional matrices in a more passive way, such as the use of unbonded flowable composite resin (Fig. 12), which reduces coronal stabilisation distortion.
Distortion can also occur when a matrix is insufficiently stabilised (coronally or cervically), during placement of uncured composite resin which is then able to extrude beyond the confines of a cavity. Pressure is therefore exerted on the moveable periphery of the matrix, potentially changing its shape, leading to peripheral and central distortion (Fig. 9).21 Anecdotally, flexible matrices are more susceptible to this distortion than rigid designs.
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