*Article* **Effects of Boric Acid Pretreatment on the Properties of Four Selected Malaysian Bamboo Strips**

**Norwahyuni Mohd Yusof 1 , Lee Seng Hua 2, \* , Paridah Md Tahir 1,3, \* , Redzuan Mohammad Suffian James 1 , Syeed Saifulazry Osman Al-Edrus 1 , Rasdianah Dahali 1 , Adlin Sabrina Muhammad Roseley 3 , Widya Fatriasari 4 , Lubos Kristak 5, \* , Muhammad Adly Rahandi Lubis 4 and Roman Reh 5**

**Abstract:** Bamboo requires treatment to extend its service life. However, as bamboo strips could serve as a suitable candidate for lamination, the treatment may affect its bendability. The current study investigated the effects of boric acid treatment on the physical, mechanical, adhesion, and morphological properties of bamboo strips. Owing to their availability and popularity in local industries, four Malaysian bamboo species were used in this study, namely *Gigantochloa scortechinii*, *Gigantochloa levis*, *Dendrocalamus asper*, and *Bambusa vulgaris*. These four species' bamboo strips were treated with 5% boric acid and their properties were evaluated. The findings revealed that the boric acid treatment had varying degrees of effect on the properties of the bamboo. Despite having lower treatability and stability, both *G. scortechinii* and *G. levis* have greatly superior mechanical properties that justify their use in the production of laminated products. The boric acid treatment was found to provide several benefits to bamboo strips intended for lamination, including increased wettability, dimensional stability, and mechanical strength.

**Keywords:** bamboo; boric acid; physical properties; mechanical properties; adhesion properties; morphological properties

#### **1. Introduction**

Bamboo is regarded as an eco-friendly plant that grows and matures quickly, has a versatile use, a unique appearance, is efficient at photosynthesis, and has great potential as a substitute material for wood with the various fibre products that can be produced [1–3]. Because of its higher physical and mechanical properties, in comparison to some commercial wood species, it has also been used for engineered products, offering higher value addition and market potential [4–6]. Due to its high strength and rapid growth, bamboo is the best alternative for replacing timber [7]. Bamboo is no longer restricted to round forms, but has been extended to splits or strips, which have been encouraged to form in engineered products such as composites, laminated bamboo boards, and plybamboo, which can be used in structural applications [8–12].

In Malaysia, at least 70 bamboo species from 10 genera have been identified, with 59 of them found in Peninsular Malaysia. The top three most studied bamboo species in Malaysia are *Gigantochloa scortechinii* (buluh semantan), *Bambusa vulgaris* (buluh minyak), and *Dendrocalamus asper* (buluh betong), with *G. scortechinii* dominating the list. The basic

**Citation:** Yusof, N.M.; Hua, L.S.; Tahir, P.M.; James, R.M.S.; Al-Edrus, S.S.O.; Dahali, R.; Roseley, A.S.M.; Fatriasari, W.; Kristak, L.; Lubis, M.A.R.; et al. Effects of Boric Acid Pretreatment on the Properties of Four Selected Malaysian Bamboo Strips. *Forests* **2023**, *14*, 196. https://doi.org/10.3390/f14020196

Academic Editor: Diego Elustondo

Received: 12 December 2022 Revised: 14 January 2023 Accepted: 17 January 2023 Published: 19 January 2023

**Copyright:** © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

properties of these bamboos, particularly *G. scortechinii*, have been extensively researched. Local researchers have extensively studied the anatomical, physical and mechanical properties, machining properties, and chemical content of *G. scortechinii* [13–15]. Several researchers [16,17] have also reported on the chemical composition, morphology, physical and mechanical strength of *B. vulgaris*. In the meantime, there are few reports on the basic properties of *D. asper* in comparison to the previous two bamboo species. *D. asper*, on the other hand, is a favorite bamboo species among local researchers for the production of wood-based products such as particleboard [18,19]. *G. levis* (buluh beting), on the other hand, has received very little attention in the country. However, Siam et al. [20] found *G. levis* to be a very promising bamboo species for laminated bamboo production. *G. levis* has a culm wall thickness of 12 mm, a high density of 750 kg/m3 , and superior mechanical strength, making it a suitable candidate for laminated products. These four bamboo species have been found in abundance in the surrounding forest. Furthermore, these are the bamboo species most commonly used in the local industry and community for the production of various bamboo-based household products.

Bamboo culms, on the other hand, are easily impacted by fungus and insects due to their high carbohydrate, including starch content. Improving bamboo's mechanical properties and fungi resistance is critical for increasing its outdoor use. Bamboo, like most lignocellulosic materials, is vulnerable to biological degradation agents [21]. As a result, treating the bamboo is required to extend the product's service life. Chemical treatments are the best option, because they ensure that the bamboo products have a longer service life while also maintaining their quality [22]. The preservatives used determine the success of the bamboo treatment. As many wood preservatives have already been banned due to arsenic and/or chromium content, boron-based preservatives with lower toxicity, such as boric acid, have become a popular alternative [23]. Boric acid is a water-based preservative that is much less toxic than arsenic or chromium compounds. Boric acid is well-known in wood preservation for its insecticide and fungicide properties [24].

However, while boric acid treatment improves biological durability, it may also change the physical and mechanical properties of the bamboo. According to some studies, wood treated with boric acid has lower mechanical strength than untreated wood [25,26]. Simsek and Baysal [27], on the other hand, discovered that boric acid treatment increased the surface roughness, density, and modulus of elasticity (MOE) of the treated wood. Because bamboo has the potential to be used in lamination, it is necessary to investigate the effects of boric acid treatment on the adhesion and bonding characteristics of bamboo, as well as its buffering capacity [28,29], which measures the resistance of wood to changing pH levels in acid or alkaline liquid. Density, moisture content, anatomical structure, buffering capacity of the bamboo surface, and species, are all factors that influence bonding quality. Therefore, the purpose of this study was to look into the effects of boric acid treatment on the physical, mechanical, and adhesion properties of bamboo strips that will be used to make laminated bamboo boards. This study used four Malaysian bamboo species based on their abundance and importance in the local industry: *G. scortechinii*, *G. levis*, *D. asper* and *B. vulgaris*.

#### **2. Materials and Methods**

#### *2.1. Materials Preparation*

Selected culms from a matured (3–5 years old) bamboo stand were harvested in a forest area near Sik, Kedah. Four bamboo species, namely *B. vulgaris* (buluh minyak), *D. asper* (buluh betong), *G. levis* (buluh beting), and *G. scortechinii* (buluh semantan) were used in this study for the production of bamboo strips (Figure 1). These bamboos were chosen due to their extensive use in the local bamboo industry and widespread distribution in Malaysia.

To obtain shorter and more workable pieces, the harvested culms were cut to lengths of 2 meters using a cross-cutting machine (CYM-001, Chang-hua Hsien, Taiwan). Before being ripped into splits, the culms were further cut to 1 meter lengths. The hollow bamboo culms were longitudinally split into 22 mm width segments with a thickness of 7–9 mm. The splitting of cylindrical bamboo stems resulted in slightly curved strips as shown in Figure 1. The bamboo strips were flattened and shaped using a thicknesser machine before being planed with a 2-side removal machine (PBM-TSP-001, Nagpur, Maharashtra, India). The process removed the bamboo green and bamboo yellow to ensure the middle part of the splits, called the bamboo timber, were extracted [30]. The strips had to be rectangular, flat on each side, and without an inner or outer layer to ensure proper bonding on all four sides. To ensure better bonding and no voids in the laminated bamboo sample, the bamboo S4S machine (MBXD-10B, Hangzhou, Zhejiang, China) was used to shape the strips into a fixed width and thickness (20 mm width × 5 mm thickness).

#### *2.2. Treatment of Bamboo Strips*

**–** A 5% boric acid solution was prepared for the treatment of the bamboo strips. The treatment's goal was to provide bamboo strips with short-term protection against biodegrading agents, such as borers, termites, and fungi, before they were laminated. For 24 h, the bamboo strips were immersed in a 1 m × 1 m tank containing a boric acid solution. The strips were removed from the treatment tank after treatment, and the excess water was drained. The strips were then kiln dried for three days at 60 ◦C and 40% RH until the moisture content reached around 12%. After that, the strips were conditioned at 20 ± 2 ◦C and 65 ± 5% RH before testing

#### *2.3. Evaluation of Physical Properties*

**on**

The conditioned bamboo strips were then cut into samples with dimensions suitable for the different properties' evaluations. Physical properties, such as moisture content, specific gravity, moisture excluding efficiency, water absorption, thickness swelling, dry salt retention, and weight percent gain, were determined according to the formula listed in Table 1.

#### ' *2.4. Surface Morphology Due to Boric Acid Treatment*

 The presence of boric acid in the bamboo strips was observed by using a Scanning Electron Microscope (SEM, Leo 1455VP, Thornwood, NY, USA). The samples were taken from both the treated and untreated bamboo strips. Cubes of 10 × 10 × 5 mm were prepared using a sharp knife. Morphological investigations were performed on the untreated and treated bamboo (boric acid) with a Scanning Electron Microscope (SEM, Leo 1455VP, Thornwood, NY, USA) machine. The SEM instrument was used at an emission current of

−

'

58 µA and an acceleration voltage of 5.0 kV; the working distance was set at 6.2 mm. Before the SEM analysis, the samples were coated with gold.

**Table 1.** Experimental test methods of bamboo strips for the determination of physical properties.

#### *2.5. Evaluation of Adhesion Properties*

#### 2.5.1. Evaluation of Surface Wettability by Contact Angle

The contact angle measurements were performed on bamboo green (previously removed during planing) samples measuring 60 mm in length, 20 mm in width, and 4 mm in thickness. A Theta Lite (TL100 and TL101, Västra Frölunda, Sweden) surface wettability tester was used to measure the contact angle of the specimens. A microscope with an attached camera was used to observe the contact angle. The specimens were conditioned at 20 ◦C and 65% RH for 24 h. Distilled water was dropped onto the surface at room temperature. To calculate the contact angle, the height and diameter of each droplet was recorded, and the contact angle was observed and measured. Thirty replicated surfaces for each species were tested.

#### 2.5.2. Buffering Capacity

Samples of untreated bamboo strips were ground and dried. After that, fifteen grams of dry bamboo particles were boiled in a 200 mL flask for 30 min. The mixture was filtered using a glass crucible with a filter porosity (40–100 µm) (Carl Roth E562.1, Karlsruhe, Baden-Wuerttemberg, Germany) equipped with an aspirator vacuum (A-1000S, Jalan Bukit Merah, Singapore) and the filtrates were diluted with distilled water to a final volume of 200 mL each. After that, the dilute extract was cooled at 20 ◦C for 24 h. A digital Mettler Toledo Delta 320 pH Meter (MPN: 320, Columbus, Ohio, USA) was used to measure the actual pH of the diluted sample before proceeding to the aqueous extraction. The aqueous extract was manually titrated with 0.1 N sodium hydroxide (NaOH) and 0.1 N hydrochloride (HCl) solution until pH 10.0 and pH 3.0, respectively. The pH value was recorded after the addition of every 0.2 mL of titrant. After that, a graph of the pH vs. titrant volume (mL) was plotted to examine the change in pH [31].

#### *2.6. Mechanical Properties*

The samples were stacked in a conditioning chamber at 20 ± 2 ◦C and a relative humidity of 65 ± 3% (EMC 12%) for a week prior to testing. The samples for static bending and compression parallel to the grain were prepared in accordance with BS EN373:1957 [32]. A total of 240 specimens (30 samples × 4 species × 2 treatments) were tested. The test was performed on an Instron Universal Testing Machine (UTM, Instron-3366, Norwood, MA, USA) with a capacity of 100 kN. The loading rate and formula used to calculate the MOR, MOE, and compressive strength parallel to the grain, are given in Table 2. Bamboo strips were placed on the supporting span for the static bending test, with the bamboo green surface facing the load of the testing machine.

**Table 2.** Testing parameters of bamboo strips for the static bending and compression parallel to the grain tests.

#### *2.7. Experimental Design and Statistical Analysis*

The collected data were analyzed using an Analysis of Variance (ANOVA). Meanwhile, the mean separation was carried out using the Least Significant Difference (LSD) method.

#### **3. Results and Discussion**

#### *3.1. Treatability of Bamboo*

#### 3.1.1. Weight Percent Gain (WPG)

Weight percent gain (WPG) represents the extent of chemical penetration into a material and indicates its treatability. The WPG of bamboo strips is tabulated in Table 3. The variation of WPG values is expected as it is highly dependent on the wood species. In this study, *G. levis* has a higher treatability with a WPG of 3.61% or 25.34 kg/m3 compared to *D. asper*, which has a WPG of only 1.47% or 8.97 kg/m3 . Meanwhile, both *B. vulgaris* and *G. scortechinii* have moderate treatability, as evidenced by their WPG values, which were 2.89% or 19.06 kg/m3 and 1.98% or 13.51 kg/m3 , respectively. The gain in weight is due to the precipitation of boric acid. Boric acid dissolves in water primarily in the chemical form of B(OH)3, with only a trace of boric acid dissociating into H+ and B(OH)4 [33]. Yamauchi [34] discovered that B(OH)3 is the dominant form of boric acid. According to their research, B(OH)3 localization occurs during the air-drying process. The analysis of the

≤ 0.05

–

Fourier-transform (FT)-Raman spectra revealed that a portion of microcrystalline B(OH)3 precipitated in the lumen, while another portion of the B(OH)3 units penetrated the cell wall of the samples [34].

**Table 3.** Weight percent gain of untreated and treated bamboo strips of four selected species.

Means followed with the same letters A,B,C,D in the same column were not significantly different at *p* ≤ 0.05.

#### 3.1.2. Dry Salt Retention (DSR)

The mean dry salt retention (DSR) of bamboo with different species of bamboo are tabulated in Figure 2. Overall, the DSR of bamboo strips after boric acid treatment ranged from 13–14 kg/m3 . The highest DSR was recorded on the bamboo strips from *D. asper* followed by *B. vulgaris*, *G. levis* and *G. scortechinii*, respectively. Comparing the WPG and DSR, there are some discrepancies that occurred in terms of ranking treatability of the four bamboo species. In WPG, the rank (descending order) was *G. levis*, *B. vulgaris*, *G. scortechinii* and *D. asper* whereas in DSR, the rank was *D. asper*, *B. vulgaris*, *G. levis*, and *G. scortechinii*.

#### *3.2. Surface Morphological Due to Boric Acid Treatment*

' Figures 3 and 4 show the SEM images of untreated and treated bamboo strips. The bamboo strips' fibre lumen and parenchyma cells appear to have been filled with boric acid (Figure 4). Gigantochloa genus has a complete vascular bundle structure that comprises of three parts: a central, vascular strand, and two fibre strands, on each side of the central strand [35]. Dendrocalamus genus contained two parts, a central vascular strand and one fibre strand inside the central strand, while *Bambusa vulgaris* contained two parts, one fibre strand at the bottom of the main vascular bundle and two fibre strands located above and below the main vascular bundle [36]. This explained the reason why semantan and beting generally behave similarly (in almost all of the properties mentioned above) as compared to minyak and betong. Boric acid can remove the starch found in parenchyma, and improve the bonding properties of bamboo strips.

**Figure 3.** SEM for untreated bamboo strips of (**a**) *Dendrocalamus asper*, (**b**) *Bambusa vulgaris*, (**c**) *Gigantochloa scortechinii,* and (**d**) *Gigantochloa levis* (350×).

**Figure 4.** SEM for treated bamboo strips of (**a**) *Dendrocalamus asper*, (**b**) *Bambusa vulgaris*, (**c**) *Gigantochloa scortechinii*, and (**d**) *Gigantochloa levis* (350×).

#### *3.3. Physical Properties of Untreated and Treated Bamboo Strips*

After a week of conditioning, the moisture content of the bamboo strips was within the range of 7%–9.5%. The density and specific gravity (SG) for the treated and untreated bamboo strips are shown in Table 4. The density of the strips varied between the four species, ranging from 623.17 to 701.7 kg/m3 for treated and 604.63 to 689.91 kg/m3 for untreated. The culms' specific gravity ranged from 0.62 to 0.70 for treated and 0.60 to 0.69 for untreated. The moisture content of the bamboo strips ranged from 6.9 to 9.5% for treated and 7.2 to 8.0% for untreated bamboo strips. The density of *G. scortechinii* was higher than the others, with an average density of 713.35 kg/m3 , closely followed

by *G. levis* (696.28 kg/m3 ) and *B. vulgaris* (672.24 kg/m3 ), while *D. asper* had the lowest density at 625.68 kg/m3 . The density result was close to previous research performed by Siam et al. [20]. In general, the boric acid treatment increased both the density and specific gravity, slightly. The increment in density and SG is mainly contributed to by the increment in WPG mentioned above. The treatment, however, had the greatest impact on *D. asper*.

**Table 4.** Density and specific gravity of treated and untreated bamboo strips of four selected species.

Note: Values in ( ) are the standard deviation. Means followed with the same letters A,B,C in the same column were not significantly different at *p* ≤ 0.05.

The moisture excluding efficiency (MEE) was calculated from the EMC to evaluate the hydrophobic or hydrophilic properties of the material at high humidity [37]. Figure 5 depicts the effects of boric acid treatment on the MEE values. According to Figure 5, the MEE for treated bamboo strips was higher than for untreated strips. For *D. asper*, *B. vulgaris*, *G. scortechinii* and *G. levis*, the results were 7.98%, 4.34%, 5.62%, and 3.15% for untreated strips and 9.52%, 7.08%, 5.60%, and 3.64% for treated strips. The results show that there was no significant difference between the untreated and treated strips of *G. scortechinii* and *G. levis* when compared to *D. asper* and *B. vulgaris*. However, bamboo strips treated with boric acid become more hydrophobic when compared to untreated strips by an average of 12%–20%. *D. asper* had the highest MEE in this study, indicating that it is more resistant to moisture uptake than the other species. All of the MEE values of the bamboo strips increased after being treated with boric acid, regardless of species. Although *D. asper* maintained its superiority, *B. vulgaris* improved significantly in resisting moisture uptake. This characteristic may have a significant impact on bamboo bonding and coating.

The water absorption and thickness swelling of the bamboo strips for the four bamboo species are shown in Table 5. A different pattern was observed for both water absorption and thickness swelling, with the treated strips having the lowest values. After soaking in water for 24 h, the untreated strips absorbed 2%–5% more water and swelled 1%–2% more than the treated strips. Meanwhile, treated bamboo strips from *D. asper*, *G. scortechinii*, *B. vulgaris*, and *G. levis* outperformed the untreated bamboo strips by 5.52%, 4.13%, 3.31% and 2.04%, respectively. The bamboo strips with a higher density had a lower WA value and a higher TS value. Biswas et al. [38] found similar trends in both WA and TS for bamboo strips, which supported this finding. A study by Borthakur and Gogoi [39] stated that the bulking of the cell wall confers better dimension stabilization in bamboo. *D. asper* had the least swelling, which could be attributed to its lower density. As evidenced by the high WA of *D. asper*, low density bamboo has more void volume and, thus, can accommodate

more water. The reduction in WA could be attributed to the precipitation of boric acid on the bamboo and the reduced availability of voids for water absorption [40]. The reduction of thickness swelling and water absorption of the treated bamboo strips could confer better dimensional stability to the laminated products.

–

**Figure 5.** Moisture Excluding Efficiency (MEE) of untreated and treated bamboo strips for four selected species. Note: Bars of mean followed with the same letters A,B,C,D were not significantly different at *p* ≤ 0.05.

**Table 5.** Water absorption and thickness swelling of untreated and treated bamboo strips for four selected species.

Note: Means followed with the same letters A,B,C in the same column were not significantly different at *p* ≤ 0.05.

#### *3.4. Adhesion Properties of Untreated and Treated Bamboo Strips*

#### 3.4.1. Wettability

The contact angle is formed between the surface and a liquid, and this provides useful information about how well an adhesive wets, spreads, and penetrates into wood samples, according to Paridah et al. [41]. In this study, all of the contact angles reached less than 30 ◦ after 60 s (Figure 6). Based on the smaller contact angle after 60 s, treated bamboo strips appear to have better wettability than untreated bamboo strips, implying that the surface of treated bamboo strips is more wettable and hydrophilic [42]. Boric acid treatment increased the surface roughness of the bamboo, most likely due to raised fibres on the bamboo surface. Higher roughness causes increased wettability [31], which explains the increased wettability in treated bamboo. Lesar et al. [43] discovered that wood treated with

boric acid is more hygroscopic than untreated wood. When compared to other bamboo species, *G. levis* appears to be the least wettable, while *B. vulgaris* appears to be the most wettable. It took more than 40 s for *D. asper* to reach the contact angle obtained for other species. The increased wettability of the bamboo strips after boric acid treatment may benefit the bonding quality of laminated bamboo boards by allowing the adhesive to spread more easily.

**Figure 6.** Changes in the contact angle of untreated and treated bamboo strips for four selected species.

#### 3.4.2. Buffering Capacity of Bamboo Strips

– – – – Buffering capacity is the resistance of wood and non-wood materials to changes in pH. Understanding the pH value and buffering capacity is critical because they influence the curing behavior of resin [31,41,42]. The pH and buffering capacity values of untreated and treated strips from the four bamboo species are shown in Table 6. As shown in Table 6 and Figures 7 and 8, all of the untreated bamboo appeared to be more stable in acidic conditions than in alkaline conditions because this required more HCl (20–40 mL) to reach pH 3.0 rather than NaOH (12–27 mL) to reach pH 10.0. In contrast, treated bamboo is more stable in alkaline conditions than in acidic conditions because a greater amount of NaOH (43–61 mL) was used compared to HCl (15–25 mL) to achieve a pH 10.0 and 3.0, respectively.

#### *3.5. Mechanical Properties of Untreated and Treated Bamboo Strips*

Table 7 shows the mechanical properties of the treated and untreated bamboo strips of four bamboo species. Treated strips appears to be much stronger compared to untreated strips. Treatment with boric acid increased the MOR, MOE, and maximum load in bending, as well as the compressive strength and the maximum load parallel to the grain. *G. scortechinii* showed superior bending properties, while *D. asper* was the least strong irrespective of the treatment. Similarly, concerning compression parallel to the grain, *G. scortechinii* tops other species in both compressive strength and maximum load. *D. asper* remained the weakest among the four species. The strength values for *G. scortechinii* and *G. levis* were rather close, which may be due to being in the same genus and having a similar structure of wall thickness among the bamboo species, and the internode lengths were longer than those for *D. asper* and *B. vulgaris*, even though the wall thickness for both bamboo species, from the bottom to the top portions, were the greatest [35]. The increased strength value can be correlated with the formation of boric acid (salt crystals) within the bamboo's microstructure, which may aid in accommodating the applied force during loading [44]. Nevertheless, some studies did report the negative effects of boric acid treatment towards the mechanical strength of bamboo [25,26]. It could be because water-based preservative formulations undergo hydrolytic reduction when they come into contact with wood sugars, causing a reaction with the cell wall components. Wood strength may be diminished due to fixation, a process that oxidizes the components of wood cell walls [45]. However, the goal of the boric acid treatment in this study is only to provide the bamboo with short-term protection against biodegradation agents. The concentration of boric acid used was relatively low, at 5%, and the WPG recorded was also low, ranging from 1.47 to 3.61% (Table 3). Therefore, the increase in MOR and MOE could be attributed, primarily, to an increase in the density of the treated bamboo strips.

**Table 6.** The pH and buffering capacity values of untreated and treated strips from four bamboo species.

Notes: Mean value of 3 samples. \* The amount of acid to reach pH 3.0. \*\* The amount of alkali to reach pH 10.0 Mean followed by the same letters ( A–E ) in the same column were not significantly different at *p* ≤ 0.05. – ≤ 0.05

**Figure 7.** Stability of untreated and treated bamboo strips of four selected species in alkaline conditions.

**Figure 8.** Stability of untreated and treated bamboo strips of four selected species in acidic conditions.

**Table 7.** Mean values for the mechanical properties of untreated and treated bamboo strips from different species.

Note: Means followed with the same letters A,B,C,D in the same column were not significantly different at *p* ≤ 0.05.

#### *3.6. Failure Behavior of Bamboo Strips in Mechanical Testing*

The failure of bamboo strips loaded in static bending, for untreated and treated bamboo, is depicted in Figure 9. The bamboo fails in in two ways: (a) brittle shear tension mode, and (b) splintering tension mode. Brittle shear tension failure was caused primarily by extensive longitudinal shear in the node section and occurred in all portions of the node. Meanwhile, splintering tension failure was caused by splintering failure at the radial

edge of the lower layer of the specimen and was common in the internodes of all portions. This finding is consistent with previous research using *Gigantochloa scortechinii* bamboo strips [46]. The bending failure for both the untreated and treated bamboo strips appeared in the node of the strips and in the lower layer, for which the failure in both the parenchyma and vascular bundles regions was due to the mechanical load applied to the specimens. The parenchyma and vascular bundles were crushed and split extensively in the node, whereas in the internodes, the failure only occurred in the parenchyma without any failure in the vascular bundles.

≤ 0.05

**Figure 9.** Failure mode of strips from four bamboo species loaded in static bending: (**a**) brittle shear tension mode, (**b**) splintering tension mode.

Figure 10 depicts the failure in compression of the bamboo strips, with various failure behaviors observed in both the untreated and treated strips. The failure is illustrated in Figure 10a, showing crushing from the bottom end and shear splitting in the middle and upwards; the shear splitting propagated above the crushed area and upwards, due to a weakness in compression. Figure 10b shows, on the other hand, that the crack tended to form from the bottom end and from the middle, upwards, and sheared perpendicularly to the maximum shear plane along 45 ◦ but terminated below the nodal area. At the node, the crack occurred from the bottom end and sheared perpendicularly, while for the internode, the crushing started from the bottom end and the shear splitting occurred in the middle, upwards. After about 80% of the stress load, creases appeared on the compression side of the bamboo. This could be attributed to the vascular bundle's thick polylamellated layer of fibre and the high percentage of parenchyma found in stress-resistant bamboo complements. The frequency of occurrence of these failures in bending and compression was nearly identical for both treated and untreated bamboo strips, indicating that the boric acid treatment had no effect on bamboo strip failure behavior. Table 7 shows that, despite the increased bending and compression of the treated bamboo strips, the values are not statistically different from the untreated bamboo strips, with the exception of compression in treated *G. scortechinii*.

'

#### **4. Conclusions**

The present study determines the effect of boric acid treatment on the physical, mechanical, adhesion and morphological properties of strips from four bamboo species *(Dendrocalamus asper*, *Bambusa vulgaris*, *Gigantochloa scortechinii* and *Gigantochloa levis)*. All four species of bamboo can be treated easily with boric acid, with a reasonable DSR and WPG. Based on the DSR and WPG values, the treatability of these bamboo species ranked (in descending order) as follows: *B. vulgaris*, *D. asper*, *G. levis* and *G. scortechinii*. In general, treatment with boric acid increased both the density and specific gravity slightly. *D. asper* was the most affected by the treatment. Treatment with boric acid reduced the WA and TS of the bamboo strips significantly. Based on the WA and TS results, *D. asper* was the most stable (high WA, low TS) while the most unstable was *B. vulgaris* (high WA, high TS). *G. scortechinii* showed superior bending properties, while *D. asper* was the least strong, irrespective of treatment. Similarly, concerning compression parallel to the grain, *G. scortechinii* tops other species in both compressive strength and maximum load. *D. asper* remained the weakest among the four species. Compared to *B. vulgaris* and *D. asper*, *G. levis* possessed acceptable strength next to *G. scortechinii*. Based on the overall properties, and despite having relatively poorer treatability and stability, both *G. scortechinii* and *G. levis* had greatly superior mechanical properties, which warrants these species being considered for the production of laminated products. Boric acid treatment was found to provide several benefits to bamboo strips intended for lamination, including increased wettability, dimensional stability, and mechanical strength.

**Author Contributions:** Conceptualization, L.S.H. and P.M.T.; methodology, P.M.T.; software, S.S.O.A.- E.; validation, A.S.M.R., L.K. and R.R.; formal analysis, M.A.R.L. and W.F.; investigation, N.M.Y., R.M.S.J. and R.D.; resources, P.M.T.; data curation, N.M.Y., R.M.S.J. and R.D.; writing—original draft preparation, N.M.Y.; writing—review and editing, L.S.H., L.K., M.A.R.L., W.F. and R.R.; visualization, S.S.O.A.-E.; supervision, L.S.H. and P.M.T.; project administration, L.S.H. and P.M.T.; funding acquisition, L.S.H. and P.M.T. All authors have read and agreed to the published version of the manuscript.

**Funding:** The presented work is supported by the Fundamental Research Grant Scheme (FRGS 2019-1), Reference code: FRGS/1/2019/WAB07/UPM/02/3; by the Ministry of Higher Education, Malaysia; a Higher Institution Centre of Excellence (HICoE) grant; and an RMK11 collaboration with the Malaysian Timber Industry Board (MTIB).

**Data Availability Statement:** Not applicable.

**Acknowledgments:** The authors also wish to express gratitude to the Faculty of Forestry and Environment, Universiti Putra Malaysia, for providing the mechanical testing facilities. This work was also supported by the Slovak Research and Development Agency under contracts No. APVV-19-0269 and No. SK-CZ-RD-21-0100.

**Conflicts of Interest:** The authors declare no conflict of interest.

#### **References**

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Dental Implants: Immediate Placement and Loading in the Esthetic Zone

*Nachum Samet*

#### **Abstract**

Extraction of an anterior tooth is always a traumatic event for patients, regardless of their age. In the past, patients were required to wait long months for bone healing and for implant integration, using an uncomfortable removable denture. In the last decade or so, dentists came to the understanding that when done correctly and in the right cases, immediate placement and loading techniques can result in aesthetically pleasing temporary and long-term results, while maintaining supporting bone and soft tissues. In fact, it was found, that placing an immediate implant rather than waiting can in fact prevent some of the bone resorption which happens after extractions.

**Keywords:** dental implants, immediate placement, immediate loading, aesthetic zone, temporary/provisional crown, ovate pontic

#### **1. Introduction**

Anterior teeth function in eating and speaking, of course, but also have a role in shaping facial aesthetics. In fact, many people see them as part of their personal identity. For these reasons, loss of an anterior tooth is always a traumatic event for patients, regardless of their age. To relieve their physical and emotional pain, patients seek a fixed restorative solution as fast as possible.

Patients who suffered severe trauma and lost multiple teeth are usually aware of the fact that it is almost impossible to restore their teeth to their original look. With a good explanation from a dentist, their expectation level can be adjusted so that it is realistic and so that they can accept a non-ideal restoration, which is both aesthetic and functional but not identical to the way their original teeth and gums looked before the trauma.

Patient expectation level is completely different when only one anterior tooth is lost. In these cases, it is clear to patients, regardless of their condition, that it is possible to restore both the "white" and the "pink" to their original state so that both the restoration and the gum-line look exactly like the homologous existing tooth.

The problem is that when a tooth is lost, two known phenomena happen: flattening and loss of proximal papillae as well as horizontal and vertical bone loss.

Although there are techniques to restore lost soft and hard tissues, these techniques are complex, require extremely high skills and experience, require long healing periods and are expensive. And on top of this, even in the best hands, these techniques are not 100% predictable [1–3].

Two advancements opened the way to preserve both bone and soft tissue architecture in the anterior upper segment. One is the understanding that placing an implant immediately after extraction can reduce bone loss at the site, maintaining the buccal aspect above the restored tooth as close as possible to the way it looked prior to the trauma [4–6]. Another way to preserve buccal bone and gingival architecture is the "Socket-Sheild" technique. In this technique, the root is cut mesiodistally leaving its buccal aspect attached to the buccal bone, and the implant is placed behind it. Although found effective [7–9], this technique is extremely difficult to perform and requires conditions that do not always exist, therefore, it will not be discussed in this chapter.

Prior to treatment, and as in any medical and dental procedure, it is critical to start with a correct diagnosis. The entire site and its surroundings with a focus on the remaining root, the integrity of the buccal bone, the architecture of the gums around the site and any evidence of infection at the gum level or around the root must be evaluated. Taking photographs of the anterior region before treatment is highly recommended, both for further analysis and evaluation of the healing phase and medico-legal reasons.

The second most important phase is to carefully evaluate all possible treatment options and discuss them with the patient, who should be notified about the pros and cons of each option, including restoring the missing dentition with a fixed bridge, a removable device, or an implant. If an implant-based solution is chosen, the different treatment sequences: immediate placement, immediate placement and loading or late placement with or without immediate loading must also be discussed with the patient, presenting again the pros and cons of each option. And lastly, the patient expectations must be discussed, ensuring that he/she understands that no one can achieve 100% success rates in any medical or dental procedure.

Short and long-term success requires mastering both the "white stuff" (the crown) and the "pink stuff" (the gingiva surrounding the site). The control over the "white stuff" is almost always in the hands of a master dental technician. And indeed, dental technicians who are also artists can achieve amazingly wonderful aesthetic results when it comes to mimicking the natural shade, translucency, transparency and anatomical characteristics of the adjacent teeth. It is not always easy, but undoubtedly possible. In contrast, the control over the 3D position of the implant and the recreation of correct emergence profile and gingival architecture is completely in the hands of the operating dentist or the dental team. The correct positioning of the implant at the site, its angulation, depth and especially the position of its opening is critical to enable achievement of the desired aesthetic and functional result. Next, a temporary crown with a unique gingival design, which ensures proper support for the gums and papillae, must be placed [10–15]. Following a period of healing and gingival maturation, it is mandatory to transfer the exact achieved gingival architecture to the dental laboratory so that the final crown is made with the desired gingival shape to ensure long-term stability of the gumline.

This chapter aims to present the different stages of immediate placement and loading in the anterior aesthetic zone, focusing on critical influencing parameters that affect short- and long-term success.

#### **2. Stages of immediate implant placement and loading in the aesthetic zone**

The long-term aesthetic success of a restoration in the anterior zone and its gingival architecture requires a thorough analysis of the condition of the injured area. Patients need to be informed and must understand their condition so that they develop realistic expectations related to the possible final outcome.

#### **2.1 Evaluation of the site**

Bone condition and height around the socket, especially in the buccal aspect and near adjacent teeth, are critical. Loss of bone in any direction, especially in the buccal area, severely affects the ability to simply restore site's aesthetics. Loss of bone due to infection, periodontal disease, root fracture or crack or iatrogenic accidental damage to the delicate buccal bone during extraction may contra-indicate immediate placement and loading of implants in such sites. In these cases, a staged approach, including bone and/or gingival augmentation, may be required prior to implant placement. The type of gingiva is also important since it is easier to control thick biotype gingiva than thin biotype gingiva, although, with careful management, it is possible to achieve good results in any gingival type.

#### **2.2 Implant design and drilling protocol alterations**

Immediate implant placement and loading is an accepted and predictable dental procedure, with high success rates. As in other implant placement procedures, high initial stability is one of the most important factors related to their short- and longsuccess rates.

There is a critical difference between the way immediate implants and standard implants gain their primary stability. While standard implants gain stability throughout their length, immediate implants gain stability through the threads of their apical section. This is a result of the fact that the diameter of the extraction socket is almost always wider than the diameter of the implant (**Figure 1**). Because of this, it is highly recommended that the dentist chooses an implant with deep and sharp apical threads, (**Figure 2**), that can cut through bone to ensure high initial stability. In addition, the dentist MUST alter the standard drilling protocol, taking into account the diameter of the apical core of the implant used, so that the osteotomy is not wider than this core. In other words, high initial stability is gained through these apical threads, and mild compression of bone at the apical section of the placed implant, utilizing the accepted concept of "Under Drilling" techniques [16, 17]. Since each implant system has different diameters at the apical section and different drill diameters, the dentist must study these parameters of the system used, to ensure that the osteotomy is small enough to ensure high implant stability while being large enough to allow the core of the implant to penetrate in.

Correct planning considering these parameters will ensure high initial stability (above 35NCM) to support immediate placement of a temporary restoration that enables aesthetics without being exposed to functional occlusal loads.

#### **2.3 Drilling depth and implant position**

The specific 3D position of the implant's head is critical for an ideal restoration [18–20]. A depth of 3–4 mm is usually sufficient to allow the creation of a correct

**Figure 1.** *Areas of support for an anterior implant.*

**Figure 2.** *An implant with wide apical screw design.*

#### *Dental Implants: Immediate Placement and Loading in the Esthetic Zone DOI: http://dx.doi.org/10.5772/intechopen.109458*

emergence profile, without creating a deep gingival pocket that is too hard to maintain. It should be clear that screw-retained restorations are by far better than cementretained restorations as temporary restorations on immediate implants. One reason is that there is no cement involved in screw-retained restorations, so no cement may accidentally be pushed into the fresh socket. The second reason is the ease of manipulation of screw-retained restorations and the fact that no vertical force needs to be placed on the newly placed implant while preparing and while trying-in the temporary crown. This means, while placing the implant, effort must be put to place the opening of the implant at the cingular area of the restored tooth and at an angle that would enable easy access to the retaining screw from the palatal side of the crown (**Figure 3**).

Regarding implant's depth, many dentists are not aware of the difference between platform-stitching implants and standard internal hex ones when it comes to the position of the restorative platform. While in standard internal hex implants, the crown may emerge from the implant's platform or very close to it, in platform-stitching implants, there is a 1–2 mm gap between the implant's platform and the base of the restoration (**Figure 4**). This means that when using platform-switching implants, the head of the implant must be placed deeper than when using standard internal hex ones.

#### **2.4 Creating a temporary crown with an emergence profile that supports the gingiva**

The alveolar bone is critical to support the gingiva. Lack of bone at the buccal aspect of the socket, at the proximal aspect/s or even at the palatal aspect may lead to gum recession and the creation of "black holes" and flattening of the gingival architecture [20, 21]. Therefore, it is critical to ensure that the socket is intact after extraction, and that bone surrounds it all around. When this is the situation, it is beneficial to support the gum tissue immediately after extraction with a correctly

**Figure 3.** *Screw hole at the cingulum area.*

**Figure 4.** *Platform switching implant type.*

made temporary crown, which will maintain the shape of the gums and papillae. The best and easiest way to do it is by using a screw-retained temporary crown, made with an "ovate pontic" emergence profile design at its base facing the implant (**Figure 5**) [22–25]. A standard and round-shaped healing abutment is not ideal since it creates a round opening in the gingiva that does not have the required gingival architecture (**Figure 6**). This means that when standard healing abutments are used, an additional surgical procedure may be required to achieve the desired gingival contour.

The design of a correct emergence profile requires an analysis of the 3D position of the head of the implant, its depth, and the level of support needed by the gingival tissues. 3–4 mm of depth is sufficient to create correct ovate-pontic shape that will support the gums (**Figure 7**). The gingival aspect of the temporary crown must be polished to prevent gum irritation and plaque accumulation, and the patient must be taught how to clean it. Since gingival tissues tend to shrink and change during the healing phase, some mild adjustments of the emergence profile may be required once osseointegrate is completed, to ensure aesthetically pleasing outcome.

*Dental Implants: Immediate Placement and Loading in the Esthetic Zone DOI: http://dx.doi.org/10.5772/intechopen.109458*

**Figure 5.** *Ovate pontic design.*

**Figure 6.** *Tissue around a standard healing cap.*

Once the temporary crown is completed, it should be firmly attached to the implant, and the access hole must be sealed. Occlusal adjustment must ensure that minimal (if any) occlusal loads are placed on the crown during the healing phase. It is also recommended that proximal contacts are minimal and sufficient to prevent

**Figure 7.** *Ovate pontic emergance profile.*

food impaction between the temporary crown and the adjacent teeth. It is mandatory to explain to patients that the temporary crown is made for supporting the gums and for aesthetic reasons only and that biting, chewing or any other application of forces (such as during smoking, parafunction, nail-biting etc.) may cause implant failure.

The temporary crown must not be removed during the healing and osteointegration period and sufficient time must be given to allow gingival maturation. When done correctly, the gingival architecture is preserved, as seen when removing the temporary crowns (**Figure 8a** and **b**).

#### **2.5 Transferring gingival data to the dental laboratory**

To ensure that the lab technician fabricates a crown that is identical to the temporary one, the internal shape of the healed gingival architecture must be transferred to the laboratory. There are several published methods to do that. Both silicone-based impressions and intra-oral scanning are acceptable [26, 27]. In addition, it is recommended to transfer a physical impression of the emergence profile and the shape of the temporary crown (**Figure 9**), as well as photographs from a few angles. This allows the technician to better visualize the required shape and its actual environment.

*Dental Implants: Immediate Placement and Loading in the Esthetic Zone DOI: http://dx.doi.org/10.5772/intechopen.109458*

#### **Figure 8.**

*a. Tissue of 28 year old patient after crown removal. b. Tissue of 80 year old patient after crown removal.*

**Figure 9.** *A technique to transfer crown shape to the dental lab.*

#### **2.6 Long-term maintenance**

Like any tooth, the tissues around an implant are dynamic and constantly change and are impacted by the accumulation of plaque, calculus and food particles and time, of course. Daily cleaning must include soft brushing, the use of floss, or a super-floss underneath the ovate-pontic shaped crown. In addition, patients need to understand the need to have periodic check-up visits and treatment by a hygienist to ensure shortand long-term success of any tooth and restoration.

#### **3. Conclusion**

The restoration of a single anterior tooth is one of the most demanding procedures in dentistry. Each aspect of the treatment influences the end result: from a correct

#### **Figure 10.**

*Ten years follow up of an immediate loaded implant with final crown.*

diagnosis to case selection, from the choice of a specific implant design to alteration of the drilling protocol, and from the clinical decision of where to three-dimensionally place the head of the implant to the shape of the gingival aspect of the temporary and final crown. Thorough understanding and correct implementation of these principles, coupled with the help of an artist dental technician can lead to long-term solutions for the benefit of our patients (**Figure 10**).

#### **Acknowledgements**

Crown 21, shown in Fig 10 was fabricated by Mr. Tamir Heker from Tamir Heker Dent. Tel-Aviv, Israel.

*Dental Implants: Immediate Placement and Loading in the Esthetic Zone DOI: http://dx.doi.org/10.5772/intechopen.109458*

#### **Author details**

Nachum Samet1,2,3,4,5

1 Kyung Hee University, South Korea

2 Titu Maiorescu University, Romania

3 Taishan Medical University, China

4 Universidad Católica San Antonio de Murcia, Spain

5 Harvard School of Dental Medicine, Boston, USA

\*Address all correspondence to<EMAIL_ADDRESS>
© 2023 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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#### **Chapter 13**